Prepress Mod 3-color
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Module 3: Color Theory & Management
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Module 3: Color Theory & Management
Instructor: Doughlas Remy
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Module 3: Color Theory & Management
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Topics Covered in Module 3 Factors Determining Color Characteristics of EM Radiation Spectral Power Distribution Color Temperature Light Sources Visible Light The Newton Color Wheel The Ostwald Color Model The Attributes of Color: HSB Color Output Models Understanding the Three Attributes of Color in the Printing Model Understanding the Three Attributes of Color in the Projection Model Newton's Color Wheel and the Color Output Models More About RGB More About CMYK Comparison of RGB and CMYK Output Comparison of RGB and CMYK Output How CMYK Inks are Layered in Printing How CMYK Inks Combine to Form Composite Colors Exercise: Halftone Screens Color Schemes
Exercise: Understanding Hue, Saturation and Brightness Exercise: Finding Pure Hues on the HSB Slider Exercise: Finding Shades of Gray on the HSB slider Exercise: Using the RGB Slider Exercise: Using RGB Values to Adjust Saturation and Brightness of a Pure Hue Exercise: Finding Pure Hues on the RGB Slider Exercise: Finding Shades of Gray on the RGB Slider Exercise: Using the CMYK Slider Exercise: Using CMYK Values to Adjust Saturation and Brightness of a Pure Hue Exercise: Finding Pure Hues on the CMYK Slider Exercise: Finding Shades of Gray on the CMYK Slider The CIE Color Model CIE Standard Sources The CIE Standard Observer The CIE Chromaticity Diagram CIE Color Gamuts CIEXYZ, CIELAB, and CIELUV The Munsell System
Module 3: Color Theory & Management
Factors Determining Color • The physics of light • Visible light represents one tiny band of the entire electromagnetic (EM) spectrum, which also includes radio waves, microwaves, infrared and ultraviolet rays, X-rays, and Gamma rays. (More about this shortly.)
• The chemistry of matter. • Solids, liquids, and gases reflect light waves differentially. • Solids and liquids heated to approximately 727 degrees Celsius emit light.
• The physiology of human vision • Our receptors and brains vary slightly in the way they gather and interpret color.
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Module 3: Color Theory & Management
Characteristics of EM Radiation Like waves in the ocean, EM waves have a crest and a trough. The speed of the wave is constant (186,000 mps). Wavelength (distance between two crests) and amplitude (distance between crest and trough) are variable.
Wavelength
Crest
Amplitude
Trough
Module 3: Color Theory & Management
EM Radiation (including visible light) is measured by… 1. Wavelength (meters) 2. Amplitude (meters) 3. Frequency (cycles per second, or Hertz) 4. Temperature/Energy (electron volts, measured in Kelvins)
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Wavelength and Amplitude 1. Wavelength (meters) • • • • • • •
Radio waves: 1 cm to 1 km Microwaves: 100 microns* to 1 cm Infrared: 1-100 microns Visible Light: nanometers* Ultraviolet rays (measured in kelvins only) X-rays (measured in kelvins only) Gamma Rays (measured in kelvins only)
1. Amplitude (meters) 2. Frequency 3. Temperature/Energy
*Micron: onemillionth of a meter. *Nanometer: one ten-billionth of a meter
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Module 3: Color Theory & Management
Frequency
1. Wavelength 2. Amplitude
3. Frequency (cycles per second, or Hertz) Example: Radio waves: 1kHz to 1MHz
4. Temperature/Energy
Note The wave’s speed is constant (186,000 mi/sec), so the shorter waves have higher 1 sec frequency, and vice versa. 4 cycles per sec
2 cycles per sec
Module 3: Color Theory & Management
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Temperature / Energy 1. Wavelength 2. Amplitude 3. Frequency
4. Temperature / Energy (electron volts, measured in Kelvins)
Max Planck (German physicist) developed a formula for determining the spectral power distribution of a light source based on its temperature. This is called “Planck’s Law.” Color temperature refers to the heat (or energy) of a light source. As color temperatures vary, so does the makeup of the light in terms of the relative power of its constituent wavelengths.
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Module 3: Color Theory & Management
Temperature / Energy 1. Wavelength 2. Amplitude 3. Frequency
4. Temperature / Energy (electron volts, measured in Kelvins) • •
Longer wavelengths (e.g., radio waves) are lower frequency and lower energy. Shorter wavelengths (e.g., gamma rays) are higher frequency and higher energy.
Lower energy
Higher energy
Module 3: Color Theory & Management
Color Temperature
“Hotter” sources emit shorter wavelengths in larger amounts.
“Cooler” sources emit longer wavelengths in larger amounts.
Note This is somewhat counterintuitive, since we associate red with hot and blue with cold.
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Color Temperature Exercise for home: Find the adjustment buttons on your monitor. Is there one for color? If so, change the color temperature. Do you like it hotter (bluer) or cooler (redder)? This is one example of the difficulties inherent in matching your monitor output to printer or other hardcopy output.
Module 3: Color Theory & Management
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Light Sources • Incandescence: Solids and liquids heated to 1000K or greater emit light. (1000K = 541 degrees Fahrenheit) • The Sun (5800 K on surface) • A candle flame • Tungsten filament light bulb (2854 K)
• Gas discharge: Gases emit light when an electric current passes through them. Variations in the density of the gas produce variations in color. • Sodium lamps • Mercury lamps • Xenon lamps
Module 3: Color Theory & Management
Light Sources (continued) • Photoluminescence: Phosphors are substances that absorb and re-emit light. Florescence: Absorption is concurrent with re-emission. Phosphorescence: Re-emission continues after absorption has stopped.
Note: A florescent tube is really a Mercury light coated on the inside with phosphor.
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Module 3: Color Theory & Management
Visible Light The human eye is only sensitive to EM radiation at wavelengths that range roughly between 780 nanometers and 380 nanometers*. This small segment is called the visible spectrum or visible light. (Note: reptiles and insects)
*Nanometer: one ten-billionth
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More About Visible Light The human eye can distinguish approximately 10,000 colors. We call the most prominent ones, in their order, by the acronym ROY G BIV. (red, orange…) These are the colors as you see them refracted by a prism or in a rainbow. 1666: Isaac Newton experimented with a prism and concluded that “white” light is not homogeneous but rather a composite of myriad-color wavelengths.
Module 3: Color Theory & Management
The Newton Color Wheel Newton shone white light through a prism to produce a spectrum of red, orange, yellow, green, blue, indigo, and violet beams. Then he joined the two ends of the color spectrum together to show the natural progression of colors in the form of a wheel with 360 degrees.
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Module 3: Color Theory & Management
The Newton Color Wheel
Newton’s color wheel was the first truly “scientific” color model because it was an empirical model—i.e., based on observation.
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Module 3: Color Theory & Management
Newton didn’t do saturation or brightness. The Newton Color Wheel describes only hue, not saturation or brightness. The darker core of this illustration is meaningless. So, what do we mean by “saturation” and “brightness”?
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The Ostwald* Color Model—A Useful Tool
Luminance (Brightness)
…characterizes color by • dominant wavelength (hue) • purity (saturation) • luminance (brightness) Dominant Wavelength (Hue)
Purity (Saturation) (a measure of how far the color is from the pure hue) *Proposed by the German scientist Ostwald in 1914, this model is useful as a tool for understanding the properties of color.
Module 3: Color Theory & Management
The Ostwald Color Model—A Useful Tool The color in each cell of the model can be expressed as the percentage of white, black and hue required on a spinning disk to produced the same white perceived color. (brightness)
black no hue
(saturation)
full hue
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The Ostwald Color Model—A Useful Tool However, the illustrative model you’ve just seen does not identify the hue in its coding, so you will not find that model in graphics software. The HSB model, shown to the right (below), identifies the hue by its position on the color wheel (0°-360°), where both 0° and 360° are red. Notice the significance of the numbers.
Illustrative model (from previous slide)
Ostwald’s HSB model. PhotoShop’s color panel
Module 3: Color Theory & Management
Adjusting Hue
Red (hue) in varying degrees of saturation and brightness
Change of Hue
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Module 3: Color Theory & Management
Attributes of Color Hue is determined by wave length.
Brightness
Hue
Brightness is determined by the amplitude of the wave. Saturation refers to the purity of the hue.
Saturation
Module 3: Color Theory & Management
More About Hue… The visible spectrum is composed of pure (fully saturated) hues. The spectral hues may combine to produce… • other pure hues. (E.g., green at 520nm plus red at 66nm equals yellow at 590nm), + = or • less saturated hues. (Pink is a desaturated red insofar as it is basically white light with a greater preponderance of red wavelengths.)
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Module 3: Color Theory & Management
More About Hue… Note that some fully saturated hues, e.g., magenta, are not spectral. They do not occur in the light spectrum, but they may be produced by combining other hues. magenta
Note also that some pure hues are perceived to be less saturated than others. E.g., a fully saturated yellow appears to be less saturated than a fully saturated red or violet.
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Module 3: Color Theory & Management
More About Saturation and Brightness… Saturation refers to the purity of the hue. A fully saturated hue is one that contains no white. Brightness, also known as luminance, is determined by the amplitude of the wave. You may think of the brightness axis as progressing along an achromatic line from white through shades of grey to black. Black is simply the absence of light, whereas white is a complete mix of light.
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Module 3: Color Theory & Management
Attributes of Color HSB describes attributes. Any color may be described in terms of its hue, saturation, and brightness, whether that color is produced by inks, by paints, by projected light, or by the bombardment of electrons against the phosphor coating on the screen of a CRT monitor.
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Color Output Models However, the HSB values don’t tell us how to produce (output) a certain color by using inks, paints, electrons, etc. Notice that the Photoshop HSB color panel only assigns a number (0-360) to a hue without providing any instructions to the printer, to the press, or to the monitor for producing it.
Module 3: Color Theory & Management
Color Output Models So, we need another color model for mixing inks or toners to produce full-color printed output.
And we need yet another color model for mixing wavelengths of light to produce the different hues we see on our monitors.
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Module 3: Color Theory & Management
Understanding the three attributes of color in the printing model: Full-color printing processes use CMYK (cyan, magenta, yellow, and black) inks. CMYK is called a “substractive” color model because it creates white by subtracting (not applying) color. The white is the white of the paper. (No CMY or K inks)
How a press desaturates a magenta (M) for full-color (CMYK) printing on white paper: (1) It adds black ink (K). (desaturating toward black)
Hue
Brightness
(Magenta)
--OR-(2) It adds equal amounts of cyan (C) and yellow (Y). (desaturating toward black) --OR--
Black or CMY combo
(3) It applies less ink to the paper, thereby allowing more white to show. Saturation
(desaturating toward white)
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Module 3: Color Theory & Management
Understanding the three attributes of color in the projection model: A monitor or slide projector works by projecting beams of red, green, and blue light (RGB) in various combinations. RGB is called the “additive” model because it achieves white by adding equal amounts of red, green, and blue. All RGB
How a color monitor desaturates a magenta: It adds white light (which is a mix of spectral hues).
Brightness
No RGB
Saturation
Hue
--OR--
(Magenta)
It lowers the amplitude of the magenta wave(s).
Module 3: Color Theory & Management
Newton’s Color Wheel and the Color Output Models Inscribe an equilateral triangle in Newton’s color wheel, with “red” at the top. Which of the two output models does this triad suggest?
http://www.color-wheel-pro.com/color-theory-basics.html
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Module 3: Color Theory & Management
Newton’s Color Wheel and the Color Output Models Now flip the triangle top to bottom. Which of the two output models does this triad suggest? What’s missing? Answer: Black Black ink (or toner) is used to produce a “blacker” black than a mixture of cyan, magenta, and yellow can produce.
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Module 3: Color Theory & Management
More About RGB • The RGB model is considered additive because it achieves white by mixing red, green, and blue light in equal proportions. • These colors are optically mixed by being placed close together or being presented in very rapid succession. • When the wheel on the right spins, the eye does not distinguish the colors, but sees them as a composite. • A TV screen and a computer monitor produce color pixels (picture elements) by firing red, green, and blue electron guns at phosphors on the screen in very close proximity and in very rapid succession.
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Module 3: Color Theory & Management
More About RGB • The term additive also becomes clearer when you examine this illustration. • Notice what “color” is at the intersection of the red, the green, and the blue circles. • In this model, red, green, and blue are considered primary colors, and they combine to produce the secondary colors cyan, magenta, and yellow. • You can mix red, green, and blue light in varying proportions to produce any other hue. • Again, all hues are produced by adding red, green, and blue together.
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Module 3: Color Theory & Management
A Note About White Light “White” light as we observe it in everyday life—e.g., in a cloud in the sky—is a mixture of all of the colors of the visible electromagnetic spectrum. However, white light can also be produced by combining any three distinct frequencies of light as long as they are widely separated on the spectrum. Such colors are called “primary” colors, and in the RGB model that is used for output to monitors, those colors are red, green, and blue. RGB is simply an arbitrary choice for a triad of primary colors, and it has become a convention in computer video output more for cultural and historical reasons than for scientific ones.* (*The prevalence of words for “red,” “green,” and “blue” throughout world languages indicates that these colors are perceived as being among the most dominant ones.)
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More About CMYK • CMYK is known as the subtractive model because of the way that it produces white. • The three transparent inks used in full-color printing are cyan, magenta and yellow. When these inks are mixed in equal proportions, the result is a sort of muddy black. Black ink (or toner) is added to sharpen the black. (“K” = black) • Remember that by default, the paper is white. So, to produce white in the printing process, we simply “subtract” the CMYK inks or toners. • No ordinary mass printing process produces the color white on paper that is not white. This could theoretically be done, but only by applying a very thick and opaque white ink, and this would not be a costeffective way of achieving white, particularly because press machinery is designed for thin, transparent inks.
Module 3: Color Theory & Management
More About CMYK • Here is the CMY model, where a muddy black results from overlaying the three colored inks. • Notice here that cyan, magenta and yellow--primary colors in this model--combine to produce the secondary colors red, green and blue.
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Module 3: Color Theory & Management
“Super black” The Washington Post reported (2008) that a new paper-thin material has been developed that absorbs 99.955 percent of light that hits it, making it about 30 times as dark as the government’s current standard for blackest black, which absorbs only 98.6 percent of light. This material, made of carbon nanotubes, will be used in solar panels (to absorb more light) and in telescopes (to sop up random bits of reflected light that don’t belong in the telescope’s canister). “Super black” is not yet available in inks or toners, so it will not affect printed images for now.
--The Seattle Times, Feb. 21, 2008
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Module 3: Color Theory & Management
Comparison of RGB and CMYK Output Compare the two models. Notice that the colors don’t look alike. This is because CMY cannot produce the brightness of the RGB colors. (E.g., compare the brightness of an image shown on a computer monitor and on a color print-out.)
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Module 3: Color Theory & Management
A Further Note About White Light You just learned that, in the RGB model of mixing light, you can produce cyan by mixing blue and green together. Logically, then, you should be able to mix red with cyan to get white. And this is in fact the case. Notice that red and cyan are opposite each on the color wheel. They are what we call “complementary” colors. Therefore, any two complementary colors will also produce white light, e.g., magenta and green , yellow and blue , etc.
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How CMYK Inks are Layered in Printing In printing, overlapping layers of varying percentages of transparent C, M and Y inks are used. Light passes through the inks and reflects off the surface below them (the substrate). (Black ink/toner may be added for areas that should not reflect any light.) Each color of ink has chemical properties that allow it to absorb some wavelengths of light while reflecting others. E.g., cyan ink absorbs all the wavelengths except the cyan. So the resulting color in the illustration below is a mixture of reflected wavelengths from the CMY inks as well as the white substrate itself. REFLECTED LIGHT
WHITE LIGHT Magenta 17% Cyan 100% Yellow 87% White substrate, 100% reflectance
Module 3: Color Theory & Management
How CMYK Inks are Layered in Printing
For an in-depth treatment of subtractive color, visit the “Physics Classroom” at http://www.physicsclassroom.com/Class/light/U12L2e.html
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But what do we mean by “percentages” of CMY? In printing, colors are laid down in dots. The centers of these dots are equidistant, so that the dots themselves form a grid, or “screen.” However, the dots do not have to be completely filled with the ink. Figure 1 is an example of a (highly magnified) 50% yellow screen. Figure 2 shows what a printed sample of the 50% yellow might look like. Notice that the yellow is lighter than the individual dots. This is because 50% of the area of each screen cell is white.
Figure 1
Figure 2
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Module 3: Color Theory & Management
A Uniform 50% Yellow Screen Notice, too, that the color in the figure is uniform. (Figure 2) There are no gradations, as you would find in a monotone print of a photograph. (Fig. 3)
Figure 2 Figure 3
For gradations in the saturation of the color, you would need dots of varying sizes. Such variations can be achieved by allowing light to pass through a film negative and then through a screen to a photopolymer plate, where the light will react differentially to form raised and recessed areas for the application of the ink.
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How CMYK Inks Combine to Form Composite Colors This is the dark green that we saw in the earlier diagram showing the layering of inks. Note that the cyan screen at 100% prints as a solid layer and the 87% layer of yellow appears as green dots because in every case the yellow is overlaying the cyan, forming green. The magenta dots, at 17%, appear much darker because they are mostly overlaying both the cyan and yellow. Notice, again, that the resulting color is uniform, not graduated.
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Exercise: “Halftone Screens” (More about these later)
Look carefully at the dots. 1. What colors of inks do you see? 2. Do the magenta dots vary in size? 3. Do the cyan and yellow dots vary in size? 4. Are the centers of the dots equidistant, or are they at varying distances from each other? 5. Are the “lines” (of dots) angled, or are they horizontal and vertical?
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Exercise: “Halftone Screens” (More about these later) Based on the two sectors shown in white, estimate the angle of the halftone screen for magenta. Note that each of the other three screens is at a different angle. The black (K) is usually at 45 degrees.
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Color Schemes
Monochromatic
Analogous
Complementary
Split Complementary
Triadic
Tetradic
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Color Schemes: Monochromatic The monochromatic color scheme uses variations in brightness and saturation of a single color. This scheme looks clean and elegant. Monochromatic colors go well together, producing a soothing effect. The monochromatic scheme is very easy on the eyes, especially with blue or green hues. A disadvantage of this scheme is its lack of contrast and vibrancy, unless blacks or dark grays are used with it. (Note: Brightness and saturation are not shown on the color wheel.) http://www.color-wheel-pro.com/color-theory-basics.html
Module 3: Color Theory & Management
Color Schemes: Analogous The analogous color scheme uses colors that are adjacent to each other on the color wheel. One color is used as a dominant color while others are used to enrich the scheme. This scheme looks richer than the monochromatic scheme, and it offers more contrast.
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Color Schemes: Complementary The complementary color scheme consists of two colors that are opposite each other on the color wheel. This scheme looks best when you place a warm color against a cool color, for example, red versus greenblue. This scheme is intrinsically highcontrast.
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Module 3: Color Theory & Management
Color Schemes: Split Complementary The split complementary scheme is a variation of the standard complementary scheme. It uses a color and the two colors adjacent to its complement. This provides high contrast without the strong tension of the complementary scheme. This scheme is nuanced but difficult to balance.
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Color Schemes: Triadic The triadic color scheme uses three colors equally spaced around the color wheel. This scheme is popular among artists because it offers strong visual contrast while retaining harmony and color richness. The triadic scheme is not as contrastive as the complementary scheme, but it looks more balanced and harmonious.
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Module 3: Color Theory & Management
Color Schemes: Tetradic The tetradic scheme is the most varied because it uses two complementary color pairs. This scheme is hard to harmonize; if all four hues are used in equal amounts, the scheme may look unbalanced, so you should choose a color to be dominant or subdue the colors.
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Module 3: Color Theory & Management
Exercise: Understanding Hue, Saturation, and Brightness 1. Start Photoshop. 2. On the File menu, click New, and then click OK. 3. If the color palette (shown below) is not visible, then click Window on the main menu, and then click Show color. 4. In the top right corner of the color palette, click the small triangle to display the menu. Then click HSB.
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Module 3: Color Theory & Management
Exercise: Understanding Hue, Saturation, and Brightness 1. Notice the symbols to the right of the number fields. 2. What is the highest number in the top field? 3. What is the highest number in the other two fields? Notice the color and the hue number, as expressed in degrees.
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Exercise: Understanding Hue, Saturation, and Brightness Use the values 0, 20, 40, 60, 80 and 100 to fill in the colored cells of the Ostwald chart.
0 0 100
The first number in each sequence is the hue, the second is saturation, and the third is brightness.
0 100 100
Note that the hue, with the number 0, does not change. 0 0 0
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Exercise: Understanding Hue, Saturation, and Brightness
Luminance (Brightness)
0 0 100
Purity (Saturation)
0 20 100
0 60 100
0 0 60 0 40 60 0 40 40 0 0 0
0 100 100
Dominant Wavelength (Hue)
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Module 3: Color Theory & Management
Exercise: Finding Pure Hues on the HSB Slider Using the HSB color sliders, find the values for the following pure hues, plus black and white. Enter “x” where any value will do.
H
S
B
H
Red
Blue
Yellow
Magenta
Green
Black
Cyan
White
S
B
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Exercise: (answers) Finding Pure Hues on the HSB Slider
H
S
B
H
S
B
Red
0
100 100 Blue
240 100 100
Yellow
60 100 100 Magenta
300 100 100
Green
120 100 100 Black
x
x
0
Cyan
180 100 100 White
x
0
100
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Exercise: Finding Shades of Gray on the HSB Slider Now find the values for any three shades of gray.
H Gray 1 Gray 2 Gray 3
S
B
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Exercise: (Sample answers) Finding Shades of Gray on the HSB Slider
Module 3: Color Theory & Management
Exercise: Using the RGB Slider 1. Select the RGB (Red, Green, Blue) slider from the dropdown menu at the arrow.
2. What is the highest number on each slider, and what is the significance of each?
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Why 255? RGB colors are for output from computers, which are digital devices. Digital technology uses binary numbers. A signal may be in an “on” or an “off” state. These two states are represented as 1 and 0 and, together, they are referred to as a “bit” of information. With two bits, we have four possible states: 10, 01, 11, or 00. With three bits, we have eight possible states: 000, 001, 010, 011, 100, 101, 110, and 111.
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Module 3: Color Theory & Management
Why 255? To determine how many possible states can be represented by “N” number of bits, just raise 2 to the power of “N.” Example: 4 bits gives us 16 states (24), and 5 bits gives us 32 states (25). How many states will 8 bits give us? Answer: 28, or 2x2x2x2x2x2x2x2, or 256.
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Why 255? 256? That’s just one more than 255.
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Module 3: Color Theory & Management
Why 255? The software engineers who designed this RGB color palette wanted each slider to begin with a zero, not a “1,” so they shifted the scale back by one.
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Why 255? With the G and B slides at zero, slide the R slider back and forth from 0 to 255. What happens to the color? How many colors do you get?
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Module 3: Color Theory & Management
Why 255? Now set the R and B sliders to 0 and move the G slider back and forth. What happens to the green?
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Why 255? Now set the B slider to 0 and move the other two around. Describe the colors that you see. How many colors can you produce with the R and G sliders? Answer: 64,536 How many colors can you produce all three sliders? Answer: Nearly 17 million.
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Exercise: Using RGB Values to Adjust Saturation and Brightness of a Pure Hue Provide the RGB values for the colored cells, using the numbers 0, 51, 102, 153, 204, and 255.
255 255 255
You may use the Photoshop RGB slider to help in this task.
255 0 0
0 0 0
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Exercise: (Answers) Using RGB Values to Adjust Saturation and Brightness of a Pure Hue
Luminance (Brightness)
100% Red + 100% Blue + 100% Green = White
0% Red + 0% Blue + 0% Green = Black
255 255 255
Purity (Saturation)
255 204 204
255 102 102
153 153 153 153 51 51 102 0 0 0 0 0
255 0 0
100% Red + 0% Blue + 0% Green = Red
Dominant Wavelength (Hue)
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Module 3: Color Theory & Management
Exercise: Finding Pure Hues on the RGB Slider
Find the values for the following pure hues, plus black and white.
R
G
B
R
Black
Blue
White
Yellow
Red
Magenta
Green
Cyan
G
B
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Module 3: Color Theory & Management
Exercise: (answers) Finding Pure Hues on the RGB Slider
Black
R
G
B
R
G
B
0
0
0 Blue
0
0
255
White
255 255 255 Yellow
255 255
Red
255
0
255
0
255
Green
0 Magenta 0 Cyan
0
0
0 255
255 255
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Exercise: Finding Shades of Gray on the RGB Slider Find the RGB values for any three different shades of gray.
R Gray 1 Gray 2 Gray 3
G
B
Module 3: Color Theory & Management
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Exercise: (sample answers) Finding Shades of Gray on the RGB Slider
Any set of equal RGB values (except 0,0,0 and 255,255,255) will produce a shade of gray.
Module 3: Color Theory & Management
Exercise: Using the CMYK Slider 1. Select the RGB (Red, Green, Blue) slider from the dropdown menu at the arrow.
2. What is the highest number on each slider, and what is the significance of each?
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Exercise: Using CMYK Values to Adjust Saturation and Brightness of a Pure Hue Provide the CMYK values for the colored cells, using the numbers 0, 20, 40, 60, 80 and 100.
0 0 0 0
You may use the Photoshop CMYK slider to help in this task.
0 100 80 0
0 0 0 100
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Module 3: Color Theory & Management
Luminance (Brightness)
Cyan: None Magenta: None Yellow: None Black: None
Cyan: None Magenta: None Yellow: None Black: 100%
Exercise: (answers) Using CMYK Values to Adjust Saturation and Brightness of a Pure Hue 0 0 0 0
Purity (Saturation)
0 60 40 0
0 0 0 40 0 40 20 40 0 40 20 60 0 0 0 100
0 100 80 0
Cyan: None Magenta: 100% Yellow: 80% Black: None
Dominant Wavelength (Hue)
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Module 3: Color Theory & Management
Exercise: Finding Pure Hues on the CMYK Slider Find the values for the following pure hues, plus black and white.
C
M
Y
K
C
Black
Yellow
White
Red
Cyan
Green
Magenta
Blue
M
Y
K
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Module 3: Color Theory & Management
Exercise: (Answers) Finding Pure Hues on the CMYK Slider C Black
M
Y
100 100 100
K
C
M
Y
K
0* Yellow
0
0
100
0
0
100 100
0
White
0
0
0
0 Red
Cyan
100
0
0
0 Green
100
0
100
0
0 Blue
100 100* 0
Magenta
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Exercise: Finding Shades of Gray on the CMYK Slider Now find the values for any three shades of gray.
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Exercise: (sample answers) Finding Shades of Gray on the CMYK Slider
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CIE • CIE was devised at Cambridge University in the early 20th century and adopted in 1931. “CIE” stands for “Commission Internationale de l’Eclairage.” • The CIE color models (there was an original and several revisions) are based as closely as possible on how humans perceive color. They are device-independent. • CIE researchers had to define standard (light) sources and standard observers.
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CIE Standard Sources • Source A: A tungsten-filament lamp with a color temperature of 2854K. • Source B: Noon sunlight (in Cambridge, England?), color temperature 4800K. • Source C: Average daylight, color temperature 6500K. These “sources,” also called “illuminants,” are defined by spectral power distribution. They are not actual physical sources of light.
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The CIE Standard Observer • The “standard observer” is actually a composite made from 15 to 20 individuals. The composite represents normal human color vision. • The observer views a pure spectral color alongside one created by three lamps emitting varying amounts of RGB. • When the observer thinks they match, the “tristimulus values” of the RGB lamps are assigned to the pure spectral color.
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The CIE Chromaticity Diagram A
• Why the funny horseshoe shape? • Caveat: Our output devices (monitor, projector) do not show the full range of colors, and the graphic is low-res. • The white point at A is the achromatic point. (No hues) • The numbers around the curve of the diagram are wavelengths (in nanometers) of all spectral hues visible to the human eye.
The CIE Diagram is an extremely precise and widely-used method of producing and identifying color since 1931. The CIE system was created by the Commission Internationale de l’Eclairage.
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CIE: A Highly Mathematical Model B
• Each color inside the curve has a precise mathematical relation to combinations of other colors within the curve. (These combinations may be represented by either straight lines or polygons.) E.g., • The three colors at the vertices of the white triangle combine to form the color indicated by the crosshair at B. • Point B will be in the center of the triangle as long as the three component colors are in equal proportion. • Notice the mint-green bar below the diagram. This shows the color at B. • Shown just below the mint-green bar are the three colors that were combined in equal proportions to produce the color at point B.
http://www.cs.rit.edu/~ncs/color/a_chroma.html
Module 3: Color Theory & Management
The CIE “Center of Gravity” B
• When three colors are mixed in different proportions (see sliders below), notice that point B moves away from the center of the triangle. • Point B is said to represent the “Center of Gravity” of the triad.
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CIE Color Gamuts The chromaticity diagram is also used to define color gamuts, or color ranges. Gamuts are simply polygons placed on the diagram. The CIE diagram is useful in comparing the color gamuts of monitors, printers, slide films and other hardcopy devices. Shown here are the approximate color gamuts for computer monitors (RGB) and printers (CMYK). Actually, the red, green and blue phosphors used in monitors vary from manufacturer to manufacturer. The color gamut of most printers is smaller than that of monitors. Setting your color quality from 24 to 16 bit in the control panel will help you match printer and monitor output more closely.
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CIE Color Gamuts: Points to Remember • Inconsistent color is a problem inherent in all computer-generated color output, whether to a monitor or to print. • Every RGB device (scanner, monitor, digital camera) has its own gamut. • Some RGB colors cannot be reproduced in CMYK, and vice versa. (Open CIE Gamut 2 in PS, change RGB to CMYK and observe the difference. Start to save as TIFF.) • Neither RGB nor CMYK can produce all colors visible to the human eye. • The international standard for color output to print is known as SWOP, or Specifications for Web Offset Publications.
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Where’s Brown? The CIE chromaticity diagram shows only dominant wavelength and saturation. It is independent of the amount of luminous energy (amplitude of the wave). E.g., Brown is not shown on the diagram. It is just a low-luminance orange-red. You could imagine a third axis for this diagram. It would show a range of luminance from 100% (at the surface) to 0% (black). Compare this to the color wheel we studied earlier:
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CIEXYZ, CIELAB, and CIELUV CIEXYZ The scientists who proposed the original CIE model found that, in order to produce certain colors visible to the human eye, some R, G or B values had to be negative. They thought this was unacceptable for an international standard, so they decided to use the letters X, Y, and Z instead. These have values represented solely by positive integers, but they correspond roughly to R, G, and B.
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CIEXYZ, CIELAB, and CIELUV CIELAB is a 1942 revision that defines colors along two polar axes for color (a and b), and a third for lightness (L). CIELAB has become very important for desktop color. Like all CIE models, it is device independent (unlike RGB and CMYK), is the basic color model in Adobe PostScript (level 2 and level 3), and is used for color management as the device independent model of the ICC (International Color Consortium) device profiles.
+a is red -a is green +b is yellow -b is blue 0 is greyscale
Module 3: Color Theory & Management
CIEXYZ, CIELAB, and CIELUV CIELUV A 1960 revision. It uses an altered and elongated form of the original chromaticity diagram.
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Introduction to the Munsell System • • • •
Albert Henry Munsell: an American artist. Wanted a decimal system instead of color names. Published Color Notation in 1905. His system is still a standard for colorimetry (the measurement of color) • To understand this system, first we’ll take you back to the color wheel we saw earlier:
Module 3: Color Theory & Management
How the Munsell System Works Munsell modeled his system as an orb (you have to imagine this) around whose equator there runs a band of pure hues corresponding to those of Newton’s color wheel. The axis of the orb is a scale of neutral grey values with white as the north pole and black as the south pole. Extending horizontally from the axis at each grey value is a gradation of color progressing from neutral gray to full saturation. Munsell used the terms “hue,” “chroma,” and “value,” to describe these aspects of color. However, to avoid confusion, we’re going to stick with “hue,” “saturation,” and “brightness.”
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The Munsell System: Hue (1) •
5 primary hues: • • • • •
•
Red: R Yellow: Y Green: G Blue: B Purple: P
5 intermediate hues: • • • • •
Compare Newton’s wheel. How many “primary colors” are there?
Yellow-red (YR) Green-yellow (GY) Blue-green (BG) Purple-Blue (PB) Red-Purple (RP)
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The Munsell System: Hue (2) • Each primary and intermediate hue is allotted 10 compass degrees and then identified by its place in the segment. • E.g., Primary red is 5R. 2.5R tends towards redpurple, and 7.5R tends towards yellow-red.
http://www.adobe.com/support/techguides/color/colormodels/munsell.html
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The Munsell System: Brightness •
The brightness axis controls the grey level. It runs from black (10) to white (0). E.g., 8 is a dark grey, and 2 is a light grey.
•
So 5PB 6 indicates a middle purple-blue with a brightness level of 6.
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The Munsell System: Saturation (1) Saturation distinguishes between a pure hue and a grey shade. The saturation axis runs at a right angle to the brightness axis. •
Saturation is denoted by a number following the brightness number, separated by a slash (“/”). E.g., 7.5YR 7/12 indicates a yellow/red tending towards Y, with a brightness of 7 and a saturation of 12. It’s a sort of “salmon” color.
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The Munsell System: Saturation (2) • You may have noticed that I did not mention the range of numbers for the saturation value. • This is because full saturation for individual hues occurs at different places. • E.g., 5RP, shown here, reaches full saturation at 5/26, whereas...
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The Munsell System: Saturation (3) • 10YR has a shorter saturation axis, with full saturation achieved at 7/10 and 6/10.
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The Munsell System: Saturation (4) • Munsell originally envisioned his color model as a sphere, but later saw it become radically asymmetrical. • Note that reds, blues and purples tend to reach higher saturation values. • Also note that these same colors reach full saturation at midlevels on the brightness scale, while yellows and greens reach it a higher levels.
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Using the Munsell System • The Munsell system is still internationally accepted. • The Munsell Book of Colors is sold commercially to printers and designers. • There are also digital libraries for the Munsell system. You will find them in Adobe PageMaker and Adobe FrameMaker. • No digital color library, however, will display accurately due to the gamut constraints of RGB. • Printed swatches are the only way to guarantee accuracy. • The Munsell Company is owned by GretagMacbeth and is on the web at www.munsell.com. (Take a look.)
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Module 3: Color Theory & Management
Instructor: Doughlas Remy
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Topics Covered in Module 3 Factors Determining Color Characteristics of EM Radiation Spectral Power Distribution Color Temperature Light Sources Visible Light The Newton Color Wheel The Ostwald Color Model The Attributes of Color: HSB Color Output Models Understanding the Three Attributes of Color in the Printing Model Understanding the Three Attributes of Color in the Projection Model Newton's Color Wheel and the Color Output Models More About RGB More About CMYK Comparison of RGB and CMYK Output Comparison of RGB and CMYK Output How CMYK Inks are Layered in Printing How CMYK Inks Combine to Form Composite Colors Exercise: Halftone Screens Color Schemes
Exercise: Understanding Hue, Saturation and Brightness Exercise: Finding Pure Hues on the HSB Slider Exercise: Finding Shades of Gray on the HSB slider Exercise: Using the RGB Slider Exercise: Using RGB Values to Adjust Saturation and Brightness of a Pure Hue Exercise: Finding Pure Hues on the RGB Slider Exercise: Finding Shades of Gray on the RGB Slider Exercise: Using the CMYK Slider Exercise: Using CMYK Values to Adjust Saturation and Brightness of a Pure Hue Exercise: Finding Pure Hues on the CMYK Slider Exercise: Finding Shades of Gray on the CMYK Slider The CIE Color Model CIE Standard Sources The CIE Standard Observer The CIE Chromaticity Diagram CIE Color Gamuts CIEXYZ, CIELAB, and CIELUV The Munsell System
Module 3: Color Theory & Management
Factors Determining Color • The physics of light • Visible light represents one tiny band of the entire electromagnetic (EM) spectrum, which also includes radio waves, microwaves, infrared and ultraviolet rays, X-rays, and Gamma rays. (More about this shortly.)
• The chemistry of matter. • Solids, liquids, and gases reflect light waves differentially. • Solids and liquids heated to approximately 727 degrees Celsius emit light.
• The physiology of human vision • Our receptors and brains vary slightly in the way they gather and interpret color.
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Characteristics of EM Radiation Like waves in the ocean, EM waves have a crest and a trough. The speed of the wave is constant (186,000 mps). Wavelength (distance between two crests) and amplitude (distance between crest and trough) are variable.
Wavelength
Crest
Amplitude
Trough
Module 3: Color Theory & Management
EM Radiation (including visible light) is measured by… 1. Wavelength (meters) 2. Amplitude (meters) 3. Frequency (cycles per second, or Hertz) 4. Temperature/Energy (electron volts, measured in Kelvins)
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Wavelength and Amplitude 1. Wavelength (meters) • • • • • • •
Radio waves: 1 cm to 1 km Microwaves: 100 microns* to 1 cm Infrared: 1-100 microns Visible Light: nanometers* Ultraviolet rays (measured in kelvins only) X-rays (measured in kelvins only) Gamma Rays (measured in kelvins only)
1. Amplitude (meters) 2. Frequency 3. Temperature/Energy
*Micron: onemillionth of a meter. *Nanometer: one ten-billionth of a meter
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Frequency
1. Wavelength 2. Amplitude
3. Frequency (cycles per second, or Hertz) Example: Radio waves: 1kHz to 1MHz
4. Temperature/Energy
Note The wave’s speed is constant (186,000 mi/sec), so the shorter waves have higher 1 sec frequency, and vice versa. 4 cycles per sec
2 cycles per sec
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Temperature / Energy 1. Wavelength 2. Amplitude 3. Frequency
4. Temperature / Energy (electron volts, measured in Kelvins)
Max Planck (German physicist) developed a formula for determining the spectral power distribution of a light source based on its temperature. This is called “Planck’s Law.” Color temperature refers to the heat (or energy) of a light source. As color temperatures vary, so does the makeup of the light in terms of the relative power of its constituent wavelengths.
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Temperature / Energy 1. Wavelength 2. Amplitude 3. Frequency
4. Temperature / Energy (electron volts, measured in Kelvins) • •
Longer wavelengths (e.g., radio waves) are lower frequency and lower energy. Shorter wavelengths (e.g., gamma rays) are higher frequency and higher energy.
Lower energy
Higher energy
Module 3: Color Theory & Management
Color Temperature
“Hotter” sources emit shorter wavelengths in larger amounts.
“Cooler” sources emit longer wavelengths in larger amounts.
Note This is somewhat counterintuitive, since we associate red with hot and blue with cold.
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Color Temperature Exercise for home: Find the adjustment buttons on your monitor. Is there one for color? If so, change the color temperature. Do you like it hotter (bluer) or cooler (redder)? This is one example of the difficulties inherent in matching your monitor output to printer or other hardcopy output.
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Light Sources • Incandescence: Solids and liquids heated to 1000K or greater emit light. (1000K = 541 degrees Fahrenheit) • The Sun (5800 K on surface) • A candle flame • Tungsten filament light bulb (2854 K)
• Gas discharge: Gases emit light when an electric current passes through them. Variations in the density of the gas produce variations in color. • Sodium lamps • Mercury lamps • Xenon lamps
Module 3: Color Theory & Management
Light Sources (continued) • Photoluminescence: Phosphors are substances that absorb and re-emit light. Florescence: Absorption is concurrent with re-emission. Phosphorescence: Re-emission continues after absorption has stopped.
Note: A florescent tube is really a Mercury light coated on the inside with phosphor.
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Visible Light The human eye is only sensitive to EM radiation at wavelengths that range roughly between 780 nanometers and 380 nanometers*. This small segment is called the visible spectrum or visible light. (Note: reptiles and insects)
*Nanometer: one ten-billionth
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More About Visible Light The human eye can distinguish approximately 10,000 colors. We call the most prominent ones, in their order, by the acronym ROY G BIV. (red, orange…) These are the colors as you see them refracted by a prism or in a rainbow. 1666: Isaac Newton experimented with a prism and concluded that “white” light is not homogeneous but rather a composite of myriad-color wavelengths.
Module 3: Color Theory & Management
The Newton Color Wheel Newton shone white light through a prism to produce a spectrum of red, orange, yellow, green, blue, indigo, and violet beams. Then he joined the two ends of the color spectrum together to show the natural progression of colors in the form of a wheel with 360 degrees.
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The Newton Color Wheel
Newton’s color wheel was the first truly “scientific” color model because it was an empirical model—i.e., based on observation.
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Newton didn’t do saturation or brightness. The Newton Color Wheel describes only hue, not saturation or brightness. The darker core of this illustration is meaningless. So, what do we mean by “saturation” and “brightness”?
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The Ostwald* Color Model—A Useful Tool
Luminance (Brightness)
…characterizes color by • dominant wavelength (hue) • purity (saturation) • luminance (brightness) Dominant Wavelength (Hue)
Purity (Saturation) (a measure of how far the color is from the pure hue) *Proposed by the German scientist Ostwald in 1914, this model is useful as a tool for understanding the properties of color.
Module 3: Color Theory & Management
The Ostwald Color Model—A Useful Tool The color in each cell of the model can be expressed as the percentage of white, black and hue required on a spinning disk to produced the same white perceived color. (brightness)
black no hue
(saturation)
full hue
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The Ostwald Color Model—A Useful Tool However, the illustrative model you’ve just seen does not identify the hue in its coding, so you will not find that model in graphics software. The HSB model, shown to the right (below), identifies the hue by its position on the color wheel (0°-360°), where both 0° and 360° are red. Notice the significance of the numbers.
Illustrative model (from previous slide)
Ostwald’s HSB model. PhotoShop’s color panel
Module 3: Color Theory & Management
Adjusting Hue
Red (hue) in varying degrees of saturation and brightness
Change of Hue
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Attributes of Color Hue is determined by wave length.
Brightness
Hue
Brightness is determined by the amplitude of the wave. Saturation refers to the purity of the hue.
Saturation
Module 3: Color Theory & Management
More About Hue… The visible spectrum is composed of pure (fully saturated) hues. The spectral hues may combine to produce… • other pure hues. (E.g., green at 520nm plus red at 66nm equals yellow at 590nm), + = or • less saturated hues. (Pink is a desaturated red insofar as it is basically white light with a greater preponderance of red wavelengths.)
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More About Hue… Note that some fully saturated hues, e.g., magenta, are not spectral. They do not occur in the light spectrum, but they may be produced by combining other hues. magenta
Note also that some pure hues are perceived to be less saturated than others. E.g., a fully saturated yellow appears to be less saturated than a fully saturated red or violet.
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More About Saturation and Brightness… Saturation refers to the purity of the hue. A fully saturated hue is one that contains no white. Brightness, also known as luminance, is determined by the amplitude of the wave. You may think of the brightness axis as progressing along an achromatic line from white through shades of grey to black. Black is simply the absence of light, whereas white is a complete mix of light.
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Attributes of Color HSB describes attributes. Any color may be described in terms of its hue, saturation, and brightness, whether that color is produced by inks, by paints, by projected light, or by the bombardment of electrons against the phosphor coating on the screen of a CRT monitor.
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Color Output Models However, the HSB values don’t tell us how to produce (output) a certain color by using inks, paints, electrons, etc. Notice that the Photoshop HSB color panel only assigns a number (0-360) to a hue without providing any instructions to the printer, to the press, or to the monitor for producing it.
Module 3: Color Theory & Management
Color Output Models So, we need another color model for mixing inks or toners to produce full-color printed output.
And we need yet another color model for mixing wavelengths of light to produce the different hues we see on our monitors.
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Understanding the three attributes of color in the printing model: Full-color printing processes use CMYK (cyan, magenta, yellow, and black) inks. CMYK is called a “substractive” color model because it creates white by subtracting (not applying) color. The white is the white of the paper. (No CMY or K inks)
How a press desaturates a magenta (M) for full-color (CMYK) printing on white paper: (1) It adds black ink (K). (desaturating toward black)
Hue
Brightness
(Magenta)
--OR-(2) It adds equal amounts of cyan (C) and yellow (Y). (desaturating toward black) --OR--
Black or CMY combo
(3) It applies less ink to the paper, thereby allowing more white to show. Saturation
(desaturating toward white)
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Understanding the three attributes of color in the projection model: A monitor or slide projector works by projecting beams of red, green, and blue light (RGB) in various combinations. RGB is called the “additive” model because it achieves white by adding equal amounts of red, green, and blue. All RGB
How a color monitor desaturates a magenta: It adds white light (which is a mix of spectral hues).
Brightness
No RGB
Saturation
Hue
--OR--
(Magenta)
It lowers the amplitude of the magenta wave(s).
Module 3: Color Theory & Management
Newton’s Color Wheel and the Color Output Models Inscribe an equilateral triangle in Newton’s color wheel, with “red” at the top. Which of the two output models does this triad suggest?
http://www.color-wheel-pro.com/color-theory-basics.html
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Newton’s Color Wheel and the Color Output Models Now flip the triangle top to bottom. Which of the two output models does this triad suggest? What’s missing? Answer: Black Black ink (or toner) is used to produce a “blacker” black than a mixture of cyan, magenta, and yellow can produce.
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More About RGB • The RGB model is considered additive because it achieves white by mixing red, green, and blue light in equal proportions. • These colors are optically mixed by being placed close together or being presented in very rapid succession. • When the wheel on the right spins, the eye does not distinguish the colors, but sees them as a composite. • A TV screen and a computer monitor produce color pixels (picture elements) by firing red, green, and blue electron guns at phosphors on the screen in very close proximity and in very rapid succession.
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More About RGB • The term additive also becomes clearer when you examine this illustration. • Notice what “color” is at the intersection of the red, the green, and the blue circles. • In this model, red, green, and blue are considered primary colors, and they combine to produce the secondary colors cyan, magenta, and yellow. • You can mix red, green, and blue light in varying proportions to produce any other hue. • Again, all hues are produced by adding red, green, and blue together.
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A Note About White Light “White” light as we observe it in everyday life—e.g., in a cloud in the sky—is a mixture of all of the colors of the visible electromagnetic spectrum. However, white light can also be produced by combining any three distinct frequencies of light as long as they are widely separated on the spectrum. Such colors are called “primary” colors, and in the RGB model that is used for output to monitors, those colors are red, green, and blue. RGB is simply an arbitrary choice for a triad of primary colors, and it has become a convention in computer video output more for cultural and historical reasons than for scientific ones.* (*The prevalence of words for “red,” “green,” and “blue” throughout world languages indicates that these colors are perceived as being among the most dominant ones.)
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More About CMYK • CMYK is known as the subtractive model because of the way that it produces white. • The three transparent inks used in full-color printing are cyan, magenta and yellow. When these inks are mixed in equal proportions, the result is a sort of muddy black. Black ink (or toner) is added to sharpen the black. (“K” = black) • Remember that by default, the paper is white. So, to produce white in the printing process, we simply “subtract” the CMYK inks or toners. • No ordinary mass printing process produces the color white on paper that is not white. This could theoretically be done, but only by applying a very thick and opaque white ink, and this would not be a costeffective way of achieving white, particularly because press machinery is designed for thin, transparent inks.
Module 3: Color Theory & Management
More About CMYK • Here is the CMY model, where a muddy black results from overlaying the three colored inks. • Notice here that cyan, magenta and yellow--primary colors in this model--combine to produce the secondary colors red, green and blue.
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“Super black” The Washington Post reported (2008) that a new paper-thin material has been developed that absorbs 99.955 percent of light that hits it, making it about 30 times as dark as the government’s current standard for blackest black, which absorbs only 98.6 percent of light. This material, made of carbon nanotubes, will be used in solar panels (to absorb more light) and in telescopes (to sop up random bits of reflected light that don’t belong in the telescope’s canister). “Super black” is not yet available in inks or toners, so it will not affect printed images for now.
--The Seattle Times, Feb. 21, 2008
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Comparison of RGB and CMYK Output Compare the two models. Notice that the colors don’t look alike. This is because CMY cannot produce the brightness of the RGB colors. (E.g., compare the brightness of an image shown on a computer monitor and on a color print-out.)
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A Further Note About White Light You just learned that, in the RGB model of mixing light, you can produce cyan by mixing blue and green together. Logically, then, you should be able to mix red with cyan to get white. And this is in fact the case. Notice that red and cyan are opposite each on the color wheel. They are what we call “complementary” colors. Therefore, any two complementary colors will also produce white light, e.g., magenta and green , yellow and blue , etc.
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How CMYK Inks are Layered in Printing In printing, overlapping layers of varying percentages of transparent C, M and Y inks are used. Light passes through the inks and reflects off the surface below them (the substrate). (Black ink/toner may be added for areas that should not reflect any light.) Each color of ink has chemical properties that allow it to absorb some wavelengths of light while reflecting others. E.g., cyan ink absorbs all the wavelengths except the cyan. So the resulting color in the illustration below is a mixture of reflected wavelengths from the CMY inks as well as the white substrate itself. REFLECTED LIGHT
WHITE LIGHT Magenta 17% Cyan 100% Yellow 87% White substrate, 100% reflectance
Module 3: Color Theory & Management
How CMYK Inks are Layered in Printing
For an in-depth treatment of subtractive color, visit the “Physics Classroom” at http://www.physicsclassroom.com/Class/light/U12L2e.html
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But what do we mean by “percentages” of CMY? In printing, colors are laid down in dots. The centers of these dots are equidistant, so that the dots themselves form a grid, or “screen.” However, the dots do not have to be completely filled with the ink. Figure 1 is an example of a (highly magnified) 50% yellow screen. Figure 2 shows what a printed sample of the 50% yellow might look like. Notice that the yellow is lighter than the individual dots. This is because 50% of the area of each screen cell is white.
Figure 1
Figure 2
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A Uniform 50% Yellow Screen Notice, too, that the color in the figure is uniform. (Figure 2) There are no gradations, as you would find in a monotone print of a photograph. (Fig. 3)
Figure 2 Figure 3
For gradations in the saturation of the color, you would need dots of varying sizes. Such variations can be achieved by allowing light to pass through a film negative and then through a screen to a photopolymer plate, where the light will react differentially to form raised and recessed areas for the application of the ink.
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How CMYK Inks Combine to Form Composite Colors This is the dark green that we saw in the earlier diagram showing the layering of inks. Note that the cyan screen at 100% prints as a solid layer and the 87% layer of yellow appears as green dots because in every case the yellow is overlaying the cyan, forming green. The magenta dots, at 17%, appear much darker because they are mostly overlaying both the cyan and yellow. Notice, again, that the resulting color is uniform, not graduated.
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Exercise: “Halftone Screens” (More about these later)
Look carefully at the dots. 1. What colors of inks do you see? 2. Do the magenta dots vary in size? 3. Do the cyan and yellow dots vary in size? 4. Are the centers of the dots equidistant, or are they at varying distances from each other? 5. Are the “lines” (of dots) angled, or are they horizontal and vertical?
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Exercise: “Halftone Screens” (More about these later) Based on the two sectors shown in white, estimate the angle of the halftone screen for magenta. Note that each of the other three screens is at a different angle. The black (K) is usually at 45 degrees.
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Color Schemes
Monochromatic
Analogous
Complementary
Split Complementary
Triadic
Tetradic
Module 3: Color Theory & Management
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Color Schemes: Monochromatic The monochromatic color scheme uses variations in brightness and saturation of a single color. This scheme looks clean and elegant. Monochromatic colors go well together, producing a soothing effect. The monochromatic scheme is very easy on the eyes, especially with blue or green hues. A disadvantage of this scheme is its lack of contrast and vibrancy, unless blacks or dark grays are used with it. (Note: Brightness and saturation are not shown on the color wheel.) http://www.color-wheel-pro.com/color-theory-basics.html
Module 3: Color Theory & Management
Color Schemes: Analogous The analogous color scheme uses colors that are adjacent to each other on the color wheel. One color is used as a dominant color while others are used to enrich the scheme. This scheme looks richer than the monochromatic scheme, and it offers more contrast.
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Module 3: Color Theory & Management
Color Schemes: Complementary The complementary color scheme consists of two colors that are opposite each other on the color wheel. This scheme looks best when you place a warm color against a cool color, for example, red versus greenblue. This scheme is intrinsically highcontrast.
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Module 3: Color Theory & Management
Color Schemes: Split Complementary The split complementary scheme is a variation of the standard complementary scheme. It uses a color and the two colors adjacent to its complement. This provides high contrast without the strong tension of the complementary scheme. This scheme is nuanced but difficult to balance.
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Module 3: Color Theory & Management
Color Schemes: Triadic The triadic color scheme uses three colors equally spaced around the color wheel. This scheme is popular among artists because it offers strong visual contrast while retaining harmony and color richness. The triadic scheme is not as contrastive as the complementary scheme, but it looks more balanced and harmonious.
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Module 3: Color Theory & Management
Color Schemes: Tetradic The tetradic scheme is the most varied because it uses two complementary color pairs. This scheme is hard to harmonize; if all four hues are used in equal amounts, the scheme may look unbalanced, so you should choose a color to be dominant or subdue the colors.
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Module 3: Color Theory & Management
Exercise: Understanding Hue, Saturation, and Brightness 1. Start Photoshop. 2. On the File menu, click New, and then click OK. 3. If the color palette (shown below) is not visible, then click Window on the main menu, and then click Show color. 4. In the top right corner of the color palette, click the small triangle to display the menu. Then click HSB.
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Module 3: Color Theory & Management
Exercise: Understanding Hue, Saturation, and Brightness 1. Notice the symbols to the right of the number fields. 2. What is the highest number in the top field? 3. What is the highest number in the other two fields? Notice the color and the hue number, as expressed in degrees.
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Module 3: Color Theory & Management
Exercise: Understanding Hue, Saturation, and Brightness Use the values 0, 20, 40, 60, 80 and 100 to fill in the colored cells of the Ostwald chart.
0 0 100
The first number in each sequence is the hue, the second is saturation, and the third is brightness.
0 100 100
Note that the hue, with the number 0, does not change. 0 0 0
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Module 3: Color Theory & Management
Exercise: Understanding Hue, Saturation, and Brightness
Luminance (Brightness)
0 0 100
Purity (Saturation)
0 20 100
0 60 100
0 0 60 0 40 60 0 40 40 0 0 0
0 100 100
Dominant Wavelength (Hue)
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Module 3: Color Theory & Management
Exercise: Finding Pure Hues on the HSB Slider Using the HSB color sliders, find the values for the following pure hues, plus black and white. Enter “x” where any value will do.
H
S
B
H
Red
Blue
Yellow
Magenta
Green
Black
Cyan
White
S
B
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Module 3: Color Theory & Management
Exercise: (answers) Finding Pure Hues on the HSB Slider
H
S
B
H
S
B
Red
0
100 100 Blue
240 100 100
Yellow
60 100 100 Magenta
300 100 100
Green
120 100 100 Black
x
x
0
Cyan
180 100 100 White
x
0
100
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Module 3: Color Theory & Management
Exercise: Finding Shades of Gray on the HSB Slider Now find the values for any three shades of gray.
H Gray 1 Gray 2 Gray 3
S
B
Module 3: Color Theory & Management
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Exercise: (Sample answers) Finding Shades of Gray on the HSB Slider
Module 3: Color Theory & Management
Exercise: Using the RGB Slider 1. Select the RGB (Red, Green, Blue) slider from the dropdown menu at the arrow.
2. What is the highest number on each slider, and what is the significance of each?
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Module 3: Color Theory & Management
Why 255? RGB colors are for output from computers, which are digital devices. Digital technology uses binary numbers. A signal may be in an “on” or an “off” state. These two states are represented as 1 and 0 and, together, they are referred to as a “bit” of information. With two bits, we have four possible states: 10, 01, 11, or 00. With three bits, we have eight possible states: 000, 001, 010, 011, 100, 101, 110, and 111.
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Module 3: Color Theory & Management
Why 255? To determine how many possible states can be represented by “N” number of bits, just raise 2 to the power of “N.” Example: 4 bits gives us 16 states (24), and 5 bits gives us 32 states (25). How many states will 8 bits give us? Answer: 28, or 2x2x2x2x2x2x2x2, or 256.
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Module 3: Color Theory & Management
Why 255? 256? That’s just one more than 255.
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Module 3: Color Theory & Management
Why 255? The software engineers who designed this RGB color palette wanted each slider to begin with a zero, not a “1,” so they shifted the scale back by one.
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Module 3: Color Theory & Management
Why 255? With the G and B slides at zero, slide the R slider back and forth from 0 to 255. What happens to the color? How many colors do you get?
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Module 3: Color Theory & Management
Why 255? Now set the R and B sliders to 0 and move the G slider back and forth. What happens to the green?
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Module 3: Color Theory & Management
Why 255? Now set the B slider to 0 and move the other two around. Describe the colors that you see. How many colors can you produce with the R and G sliders? Answer: 64,536 How many colors can you produce all three sliders? Answer: Nearly 17 million.
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Module 3: Color Theory & Management
Exercise: Using RGB Values to Adjust Saturation and Brightness of a Pure Hue Provide the RGB values for the colored cells, using the numbers 0, 51, 102, 153, 204, and 255.
255 255 255
You may use the Photoshop RGB slider to help in this task.
255 0 0
0 0 0
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Module 3: Color Theory & Management
Exercise: (Answers) Using RGB Values to Adjust Saturation and Brightness of a Pure Hue
Luminance (Brightness)
100% Red + 100% Blue + 100% Green = White
0% Red + 0% Blue + 0% Green = Black
255 255 255
Purity (Saturation)
255 204 204
255 102 102
153 153 153 153 51 51 102 0 0 0 0 0
255 0 0
100% Red + 0% Blue + 0% Green = Red
Dominant Wavelength (Hue)
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Module 3: Color Theory & Management
Exercise: Finding Pure Hues on the RGB Slider
Find the values for the following pure hues, plus black and white.
R
G
B
R
Black
Blue
White
Yellow
Red
Magenta
Green
Cyan
G
B
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Module 3: Color Theory & Management
Exercise: (answers) Finding Pure Hues on the RGB Slider
Black
R
G
B
R
G
B
0
0
0 Blue
0
0
255
White
255 255 255 Yellow
255 255
Red
255
0
255
0
255
Green
0 Magenta 0 Cyan
0
0
0 255
255 255
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Module 3: Color Theory & Management
Exercise: Finding Shades of Gray on the RGB Slider Find the RGB values for any three different shades of gray.
R Gray 1 Gray 2 Gray 3
G
B
Module 3: Color Theory & Management
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Exercise: (sample answers) Finding Shades of Gray on the RGB Slider
Any set of equal RGB values (except 0,0,0 and 255,255,255) will produce a shade of gray.
Module 3: Color Theory & Management
Exercise: Using the CMYK Slider 1. Select the RGB (Red, Green, Blue) slider from the dropdown menu at the arrow.
2. What is the highest number on each slider, and what is the significance of each?
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Module 3: Color Theory & Management
Exercise: Using CMYK Values to Adjust Saturation and Brightness of a Pure Hue Provide the CMYK values for the colored cells, using the numbers 0, 20, 40, 60, 80 and 100.
0 0 0 0
You may use the Photoshop CMYK slider to help in this task.
0 100 80 0
0 0 0 100
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Module 3: Color Theory & Management
Luminance (Brightness)
Cyan: None Magenta: None Yellow: None Black: None
Cyan: None Magenta: None Yellow: None Black: 100%
Exercise: (answers) Using CMYK Values to Adjust Saturation and Brightness of a Pure Hue 0 0 0 0
Purity (Saturation)
0 60 40 0
0 0 0 40 0 40 20 40 0 40 20 60 0 0 0 100
0 100 80 0
Cyan: None Magenta: 100% Yellow: 80% Black: None
Dominant Wavelength (Hue)
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Module 3: Color Theory & Management
Exercise: Finding Pure Hues on the CMYK Slider Find the values for the following pure hues, plus black and white.
C
M
Y
K
C
Black
Yellow
White
Red
Cyan
Green
Magenta
Blue
M
Y
K
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Module 3: Color Theory & Management
Exercise: (Answers) Finding Pure Hues on the CMYK Slider C Black
M
Y
100 100 100
K
C
M
Y
K
0* Yellow
0
0
100
0
0
100 100
0
White
0
0
0
0 Red
Cyan
100
0
0
0 Green
100
0
100
0
0 Blue
100 100* 0
Magenta
*Black may also have the following values: 0, 0, 0, 100, or 100, 100, 100, 100.
0
100
*50 here makes a better blue.
0 0
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Module 3: Color Theory & Management
Exercise: Finding Shades of Gray on the CMYK Slider Now find the values for any three shades of gray.
C Gray 1 Gray 2 Gray 3
M
Y
K
Module 3: Color Theory & Management
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Exercise: (sample answers) Finding Shades of Gray on the CMYK Slider
Module 3: Color Theory & Management
CIE • CIE was devised at Cambridge University in the early 20th century and adopted in 1931. “CIE” stands for “Commission Internationale de l’Eclairage.” • The CIE color models (there was an original and several revisions) are based as closely as possible on how humans perceive color. They are device-independent. • CIE researchers had to define standard (light) sources and standard observers.
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CIE Standard Sources • Source A: A tungsten-filament lamp with a color temperature of 2854K. • Source B: Noon sunlight (in Cambridge, England?), color temperature 4800K. • Source C: Average daylight, color temperature 6500K. These “sources,” also called “illuminants,” are defined by spectral power distribution. They are not actual physical sources of light.
Module 3: Color Theory & Management
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The CIE Standard Observer • The “standard observer” is actually a composite made from 15 to 20 individuals. The composite represents normal human color vision. • The observer views a pure spectral color alongside one created by three lamps emitting varying amounts of RGB. • When the observer thinks they match, the “tristimulus values” of the RGB lamps are assigned to the pure spectral color.
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The CIE Chromaticity Diagram A
• Why the funny horseshoe shape? • Caveat: Our output devices (monitor, projector) do not show the full range of colors, and the graphic is low-res. • The white point at A is the achromatic point. (No hues) • The numbers around the curve of the diagram are wavelengths (in nanometers) of all spectral hues visible to the human eye.
The CIE Diagram is an extremely precise and widely-used method of producing and identifying color since 1931. The CIE system was created by the Commission Internationale de l’Eclairage.
Module 3: Color Theory & Management
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CIE: A Highly Mathematical Model B
• Each color inside the curve has a precise mathematical relation to combinations of other colors within the curve. (These combinations may be represented by either straight lines or polygons.) E.g., • The three colors at the vertices of the white triangle combine to form the color indicated by the crosshair at B. • Point B will be in the center of the triangle as long as the three component colors are in equal proportion. • Notice the mint-green bar below the diagram. This shows the color at B. • Shown just below the mint-green bar are the three colors that were combined in equal proportions to produce the color at point B.
http://www.cs.rit.edu/~ncs/color/a_chroma.html
Module 3: Color Theory & Management
The CIE “Center of Gravity” B
• When three colors are mixed in different proportions (see sliders below), notice that point B moves away from the center of the triangle. • Point B is said to represent the “Center of Gravity” of the triad.
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Module 3: Color Theory & Management
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CIE Color Gamuts The chromaticity diagram is also used to define color gamuts, or color ranges. Gamuts are simply polygons placed on the diagram. The CIE diagram is useful in comparing the color gamuts of monitors, printers, slide films and other hardcopy devices. Shown here are the approximate color gamuts for computer monitors (RGB) and printers (CMYK). Actually, the red, green and blue phosphors used in monitors vary from manufacturer to manufacturer. The color gamut of most printers is smaller than that of monitors. Setting your color quality from 24 to 16 bit in the control panel will help you match printer and monitor output more closely.
Module 3: Color Theory & Management
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CIE Color Gamuts: Points to Remember • Inconsistent color is a problem inherent in all computer-generated color output, whether to a monitor or to print. • Every RGB device (scanner, monitor, digital camera) has its own gamut. • Some RGB colors cannot be reproduced in CMYK, and vice versa. (Open CIE Gamut 2 in PS, change RGB to CMYK and observe the difference. Start to save as TIFF.) • Neither RGB nor CMYK can produce all colors visible to the human eye. • The international standard for color output to print is known as SWOP, or Specifications for Web Offset Publications.
Module 3: Color Theory & Management
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Where’s Brown? The CIE chromaticity diagram shows only dominant wavelength and saturation. It is independent of the amount of luminous energy (amplitude of the wave). E.g., Brown is not shown on the diagram. It is just a low-luminance orange-red. You could imagine a third axis for this diagram. It would show a range of luminance from 100% (at the surface) to 0% (black). Compare this to the color wheel we studied earlier:
Module 3: Color Theory & Management
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CIEXYZ, CIELAB, and CIELUV CIEXYZ The scientists who proposed the original CIE model found that, in order to produce certain colors visible to the human eye, some R, G or B values had to be negative. They thought this was unacceptable for an international standard, so they decided to use the letters X, Y, and Z instead. These have values represented solely by positive integers, but they correspond roughly to R, G, and B.
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Module 3: Color Theory & Management
CIEXYZ, CIELAB, and CIELUV CIELAB is a 1942 revision that defines colors along two polar axes for color (a and b), and a third for lightness (L). CIELAB has become very important for desktop color. Like all CIE models, it is device independent (unlike RGB and CMYK), is the basic color model in Adobe PostScript (level 2 and level 3), and is used for color management as the device independent model of the ICC (International Color Consortium) device profiles.
+a is red -a is green +b is yellow -b is blue 0 is greyscale
Module 3: Color Theory & Management
CIEXYZ, CIELAB, and CIELUV CIELUV A 1960 revision. It uses an altered and elongated form of the original chromaticity diagram.
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Introduction to the Munsell System • • • •
Albert Henry Munsell: an American artist. Wanted a decimal system instead of color names. Published Color Notation in 1905. His system is still a standard for colorimetry (the measurement of color) • To understand this system, first we’ll take you back to the color wheel we saw earlier:
Module 3: Color Theory & Management
How the Munsell System Works Munsell modeled his system as an orb (you have to imagine this) around whose equator there runs a band of pure hues corresponding to those of Newton’s color wheel. The axis of the orb is a scale of neutral grey values with white as the north pole and black as the south pole. Extending horizontally from the axis at each grey value is a gradation of color progressing from neutral gray to full saturation. Munsell used the terms “hue,” “chroma,” and “value,” to describe these aspects of color. However, to avoid confusion, we’re going to stick with “hue,” “saturation,” and “brightness.”
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Module 3: Color Theory & Management
The Munsell System: Hue (1) •
5 primary hues: • • • • •
•
Red: R Yellow: Y Green: G Blue: B Purple: P
5 intermediate hues: • • • • •
Compare Newton’s wheel. How many “primary colors” are there?
Yellow-red (YR) Green-yellow (GY) Blue-green (BG) Purple-Blue (PB) Red-Purple (RP)
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Module 3: Color Theory & Management
The Munsell System: Hue (2) • Each primary and intermediate hue is allotted 10 compass degrees and then identified by its place in the segment. • E.g., Primary red is 5R. 2.5R tends towards redpurple, and 7.5R tends towards yellow-red.
http://www.adobe.com/support/techguides/color/colormodels/munsell.html
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Module 3: Color Theory & Management
The Munsell System: Brightness •
The brightness axis controls the grey level. It runs from black (10) to white (0). E.g., 8 is a dark grey, and 2 is a light grey.
•
So 5PB 6 indicates a middle purple-blue with a brightness level of 6.
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Module 3: Color Theory & Management
The Munsell System: Saturation (1) Saturation distinguishes between a pure hue and a grey shade. The saturation axis runs at a right angle to the brightness axis. •
Saturation is denoted by a number following the brightness number, separated by a slash (“/”). E.g., 7.5YR 7/12 indicates a yellow/red tending towards Y, with a brightness of 7 and a saturation of 12. It’s a sort of “salmon” color.
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Module 3: Color Theory & Management
The Munsell System: Saturation (2) • You may have noticed that I did not mention the range of numbers for the saturation value. • This is because full saturation for individual hues occurs at different places. • E.g., 5RP, shown here, reaches full saturation at 5/26, whereas...
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Module 3: Color Theory & Management
The Munsell System: Saturation (3) • 10YR has a shorter saturation axis, with full saturation achieved at 7/10 and 6/10.
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Module 3: Color Theory & Management
The Munsell System: Saturation (4) • Munsell originally envisioned his color model as a sphere, but later saw it become radically asymmetrical. • Note that reds, blues and purples tend to reach higher saturation values. • Also note that these same colors reach full saturation at midlevels on the brightness scale, while yellows and greens reach it a higher levels.
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Module 3: Color Theory & Management
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Using the Munsell System • The Munsell system is still internationally accepted. • The Munsell Book of Colors is sold commercially to printers and designers. • There are also digital libraries for the Munsell system. You will find them in Adobe PageMaker and Adobe FrameMaker. • No digital color library, however, will display accurately due to the gamut constraints of RGB. • Printed swatches are the only way to guarantee accuracy. • The Munsell Company is owned by GretagMacbeth and is on the web at www.munsell.com. (Take a look.)
Module 3: Color Theory & Management
End of Module 2
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Module 3: Color Theory & Management
0 0 100
0 100 100
0 0 0
Module 3: Color Theory & Management
Slides to print out at 2 per page for handout
109
110
Module 3: Color Theory & Management
H
S
B
H
Red
Blue
Yellow
Magenta
Green
Black
Cyan
White
H Gray 1 Gray 2 Gray 3
S
B
S
B
111
Module 3: Color Theory & Management
255 255 255
255 0 0
0 0 0
112
Module 3: Color Theory & Management
R
G
B
R
Black
Blue
White
Yellow
Red
Magenta
Green
Cyan
R Gray 1 Gray 2 Gray 3
G
B
G
B
113
Module 3: Color Theory & Management 0 0 0 0
0 100 80 0
0 0 0 100
114
Module 3: Color Theory & Management
C
M
Y
K
C
Black
Yellow
White
Red
Cyan
Green
Magenta
Blue
C Gray 1 Gray 2 Gray 3
M
Y
K
M
Y
K
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