A Study Of Colour Perception

A study of colour perception and its corelation to scientific phenomena

Sumegha Mantri . Semester 5 . Exhibition design National Institute of Design 2008

Index Content 1. Sensation and perception 2. Sense of vision 3. Properties of perception and colour perception 4. Theories of colour perception. 5. Studies in colour perception 5.1 Noughts and crosses 5.2 Tangents 5.3 Brightness contrast 5.4 Volume colour 5.5 Nature of brown 5.6 Scale

6. Bibliography

1. Sensation and perception

Steps in perception [trickle down, siphon up]

To sustain, all forms of life have to survive in their immediate context. The knowledge of this immediate context is acquired by the sensation and perception of the surrounding environment.

Information from the environment trickles down the neural system, is filtered and analysed, till it reaches the ‘inference’ stage, where ‘synthesis’ happens over the substrate of the information. These synthesized ideas are ‘siphoned’ back into the environment as physical actions or manifest themselves as new ideas.

Human sense organs and their sensations.

STIMULUS

Eyes : Vision

Input of raw information

Ears : Hearing

TRANSDUCTION

CHANGE IN ENVIRONMENT

Converting raw information into neural signals.

Tongue : Taste Nose : Olfaction [smell]

Steps in perception

Skin : Touch

PROCESSING

ACTION

Channelizing the neural signals

Fig1.1: Five human senses.

PERCEPTION

COMMAND FOR ACTION

1st level of meaning making

Sensation: The process of intake of information from the environment through the sense organs is called sensation. Perception: the process of converting these ‘sensations’ into the ‘richness of experience’ is known as perception. It is a very quick process that happens in our neural channels.

SYNTHESIS Generation of new ideas, thoughts, physical actions.

Fig 1.2: Steps in perception.

RECOGNITION 2nd level of meaning making. Recording, matching with the brain library. Infering.

2. Sense of vision Light is the external stimulus that activates the visual system [the eyes] and it carries information about the visual world.

Out of the five human senses, our sense of vision has the biggest role to play in the way we perceive our environment.

Incoming optic array light energy, structured pattern of light reflected by the environment.

Optic nerve connects the eye and the brain

SENSATION

TRANSDUCTION Retina A thin layer of light sensitive nerve cells [photoreceptors] at the back of the eye.

PERCEPTION >> INFERENCE Photoreceptors Rods [illumination sensitive] Cones [colour sensitive]

Fig 2.1: The visual system

Colour vision Our sense of vision helps us perceive physical forms, depth and motion in our environment. Colour is an inherent part of normal human vision. Besides aesthetic enhancement, colour vision empowers us to differentiate, associate and to make meanings. It is a tool for ‘perceptual organization.’

Colour is therefore, a sensation created by our visual system. Different wavelenghts of light creating different sensations of colour.

Visible spectrum It is that part of the electromagnetic spectrum that activates our visual system.

However, the colours that we see are not actually physically present in our environments. Neither is the light reaching our eyes coloured. “The rays to speak are not coloured. In them, there is nothing else than a certain power and disposition to stir up a sensation of this or that colour.” - Isaac Newton in his book ‘Optiks’

Fig 2.2: The visible spectrum

3.Properties of perception and colour perception Properties of perception.

Colour primaries

(a) Relativity of perception. We do not perceive absolute values, we perceive differences and relative values. For example, we comprehend how high a building is, by observing it against the height of a man standing beside it.

Those colours, which when combined with each other in different proportions, would effectively yeild all the other colours.

(b) Perceptual constancy. Inspite of the large scale variations in the energy variation reaching our senses, the perceptual world remains fairly constant. For example, a man in the distance appears small, but we perceive him to be of normal height. We don’t perceive the man to be growing as he approaches us from a distance.

Additive primaries [Projected light, spectral colours] Colours of light are additive. Starting from darkness (absence of light), each subsequent addition of these colours produce progressively lighter colours. If the three primaries [Red, Green and Blue] are mixed in equal proportion, then they create white light, as shown in fig.3.1[a].

Our perception of colour also have the above properties (a) Lightness constancy Our perception of whiteness, blackness or grayness of an object remains constant no matter how the illumination changes. This is because, 1. We do not perceive absolute values, we perceive differences. 2. Regardless of the intensity of illumination, the percentage of incident light reflected by a given surface remains constant (b) Colour constancy A colour is perceived as the same, regardless of changing light conditions.For example, a given red colour is perceived as the same red in a well lit and a dimly lit situation, and not as a lighter or a darker red.

Fig.3.1[a]: additive mixing of light.

Fig.3.1[b]: subtractive mixing of pigments.

Subtractive primaries [pigment colours] Starting from white, each addition of these colours subtracts light and produces progressively darker colours. If the three subtractive primaries, Cyan, Magenta and Yellow are mixed equally, then they produce black, that is, an absence of light, as shown in fig.3.1[b].

4. Theories of colour perception. Trichromacy theory [Thomas Young and Helmholtz] The trichromacy theory states that The retina processes colour information separately from luminance information. Physiologically, the retina has two types of photoreceptors, rods for luminance perception and cones for colour perception Colour vision is a result of three different photoreceptors for the three primary colours - red, blue and green. A combination of responses of all three cones enables us to see the ‘colour gamut’* that we see.

The Opponent-process theory

Connecting the trichromacy and opponent-process theories. The trichromacy theory operates at the retinal, receptor level, [sensation] whereas the opponent-process theory operates at a neural, output level [transduction and after] The trichromacy theory explains how we sense colour and our physical ability to sense colour. The opponent-process theory explains how the ‘sensed’ colour information is encoded and processed by the neural channels.

Retina: sensation photoreceptors: rods + cones

Transduction

Optic nerve

[Ewald Hering 1858] The trichromacy theory explained many observations, but left a few areas unaddressed. Ewald Hering pointed out that Yellow, which is supposed to be a combination of red and green was actually perceived as a primary colour, not as a greenish red or a reddish green.

Neural channels opponent-process coding

] ]

Trichromacy theory

Opponent-process theory

He therefore proposed a six colour system of visual perception. Yellow-blue, red-green and black-white pairs of colours, which generate the entire colour gamut by an ‘opponent-process’.

Fig 4.1: connecting the Trichromacy and opponent-process theory.

For each pair, activation of one member inhibits the opposing member.

- Simultaneous brightness contrast [afterimage in complement colours] - Pairwise loss of colour in colour blindness. - The primary ststus of yellow, despite there being no yellow cone.

* colour gamut: The entire range of colours that a device can perceive and reproduce.

The opponent-process theory explains

5. Class studies in colour perception

5.1 Noughts and Crosses Mode: paint and brush technique + coloured paper Given a x x y cm canvas, and three geometrical shapes: a square, a triangle and a circle, compose a ‘colour arrangement’ using these three shapes; where the colour assigned to each shape remains the same, but its position differs (remember playing noughts and crosses?). The colours to be used are red, blue and yellow. Apply stroke and fill separately, against two different backgrounds – white and black. Choose which background to apply in either case. The size of the circle and triangle, are to be dictated by the square, whose sides measure 20cm. Materials: 90 x 90cm canvas board, acrylic paints (R, B, Y), brushes, plastic jar, turpentine Discussion: Luminance, Brightness, Lightness, Hue.

Noughts and Crosses: assigning colours to the shapes

Fig 5.1.1[a]: assigning colours to the shapes

Observations Yellow has a higher luminance value, and therefore, stands out the most on black, due to the high contrast of the pair. Hence, its used in the form of a triangle, which has the least area of all the three shapes. Blue, being of lesser value, almost merges with the black background. In the form of the circle, it stands out relatively more, as compared to the triangle and the square respectively. This is probably because of the continuous smooth shape of the circular form.

Inferences

Selected combination

Colours are never perceived in isolation, but always ‘in relation to’ their context. In this case, the interaction of the background and foreground and the forms of the coloured areas influence the perception of colour. As the light intensity, 'lightness' of the background and the foreground become equal, the perceived boundaries of the forms vanish. This is seen with yellow against a white background and blue against a black background. Therefore, text in a colour of equal lightness as the background becomes difficult to read.

Fig 5.1.1[b]: The assigned colours.

Stroke and fill Observations The perception of the colours and their forms as strokes on the white background is hindered. Especially that of the yellow of the triangle. In comparison to this, strokes are clearly perceived against the black background. Filled colour forms of red and yellow stand out very brightly against the black background. On the white background these filled forms appear more balanced, and easier to perceive.

Inferences The white background reflects more light than the coloured areas. To balance out this effect, the area of colour required on the white background is more. Hence, the colour filled shapes are more visible than the strokes on the white background. The black background reflects the least amount of light as compared to any of the colours. Therefore, strokes on the black [with much less colour area] are easier to perceive than those on white. For the same reason, the red and yellow filled shapes stand out on the black background [the lightness of the coloured area is not balanced by that of the background.]

Stroke on black. Fill on white. Fig 5.1.2: stroke and fill compositions on white and black backgrounds.

Final outcomes

Fig. 5.1.3: The final compositions.

The previously stated observations varied according to the brightness of the hues chosen by the class. For example, a brighter yellow stood out more on the black due to greater contrast, as compared to a less bright yellow.

Terms and their definitions Hue: It is the property of colour defined by the wavelength of light associated with that colour. Brightness: It is the colour intensity of a given colour. Lightness: We see light reflected off an object, or light coming directly from the object [luminous bodies]. ’Lightness’ refers to the intensity of light coming from an object. ‘Luminance' is a measure of this intensity. It is the proportion of incident light that is reflected .

Image from the class display

5.2: Tangents Mode: paint and brush technique You are required to form a composition using once circle and five tangents, where each element (line or circle) is assigned one of the following colours – brown, pink, cyan, purple, orange or grey. You can vary the following parameters: the diameter of the circle, the lengths of the lines, and the weight or thicknesses of the lines. Materials: 60 x 40cm canvas boards, acrylic paints (brown, pink, cyan, purple, orange, Grey), brushes, jars, turpentine Discussion: Cultural naming of

colours, 11 + 1 = 12 colour set

Composition

Fig 5.2.1[a]: Deciding the composition

Fig 5.2.1[b]: Deciding the colours of the composition

Fig 5.2.2: The final compositions of the class.

Observation

Inference

As evident from the pictures above, some of the compositions were more successful than the others. Some of the compositions were balanced and interesting as compared to the others.

Composition and colour are not separate entities, but are inherenlty dependent on each other. The probability of a composition being successful is greater if it has been composed in colour, instead composing first and adding the colours as a second layer.

Tangents: discussions We are able to perceive thousands of different colours. Our visual system is also capable of noticing subtle differences in colours. However, we have only limited number of colour names. Research shows that all the colours that we can distinguish, can be described by using the colours red, yellow, blue, green and their combinations [Abramov & Gordon, 1994; Hurvich, 1981]. Cross-cultural studies [Brent Berlin and Paul Kay, 1969] show that, although cultures vary in the number of terms they use to address colours, the sequence of colours being named in the language follows the sequence shown below.

Purple white

Green

Yellow Pink Blue

Red

Brown Orange

Black

Yellow

Green Gray

Fig 5.2.3: sequence of naming of colours across cultures

All cultures use equivalent names of black and white, followed by red, yellow and green [ or green and yellow], then blue followed by brown. The other colours are added later. These 11 colours [black, white, red, yellow, green, blue, brown, orange, pink, purple and gray] form the basic colour set. When Cyan is added to the above set, the 12 colour set is formed.

Images from the class display

5.3: Brightness Contrast Mode: paint and brush / coloured paper / digital** Given a x x y cm canvas, paint two squares, whose sides measure 20cm each. The squares are to be painted green. One of these squares is to be placed against a black background. Consistency is a key over here, as the hue of both squares needs to be as identical as possible. The use of coloured paper is well suited to this exercise. Repeat the exercise with the colours red, blue, yellow, black and white. Materials: 25 x 30cm canvas boards, green acrylic paint, green, black and white coloured paper sheets

Discussion: Brightness contrast, simultaneous brightness contrast, colour constancy, opponent process theory

Brightness contrast It is the phenomena by which, a given hue is perceived differently, when placed against different backgrounds.

Observations The perceptual green is a hue of green with a little yellow.

100% green

100% red

Perceptual green*

100% blue

Hues appear darker when placed against a light [white] background and brighter when placed against a dark [black] background. For some hues, this perceived difference in brightness is very stark [eg. Red and yellow], for other hues, its relatively less. This difference in brightness is least for green. Hence, it is said that across the visible spectrum, green maintains good brightness contrast. Simultaneous brightness contrast: when we stare at a hue for a very long time, and then shift our focus to a blank area, the complementary hue is seen in the place of the original hue. For example, staring at green shows red as the after-image.

Inferences Perceived pure hues are different from the actual hues. This difference is very subjective. The background subtracts its own light from the foreground. This is why a given hue appears darker on a light background and lighter on a dark background.

*Subject to individual perception

The after-image effect [simultaneous brightness contrast],essentially represents an an instantaneous adjustment of the visual system and produces dramatic effects in colour perception. It is a psycho-physiological phenomena explained by the oppenent-process theory, which says that colour information is encoded as opponent pairs [complementary colours]. If one member of the pair is fatigued, the other automatically fills its place. 100% yellow

Text and colour With text, the concern is legibility. As observed, the white text on the green and the blue backgrounds and the black text on the yellow background are more legible as compared to the other combinations. As inferred earlier, when the foreground and the background are of similar lightness, then their boundaries vanish. This is seen with the yellow text on the white background. In the opposite situation, when the lightness contrast between the text colour and the foreground colour is very high [white text on black], the body of the font seems slimmer, and might also vanish in some cases. Both situations make the text illegible due to colour considerations. This perceptual phenomena is called ‘chromatic aberration’. It is observed in illusion, at the separation boundaries where complimentary colours are juxtapositioned with each other.

Image from the class display

5.4: Gradation Mode: observation, experimentation, workshop This is a group exercise. Cut out 2.5cm wide x 10cm high strips from transparency sheets. Lay 10 strips in arithmetic order i.e. one transparency sheet in row 1, two in row 2, three in row 3, etc. Thus, the layering is sequential i.e. 1, 2, 3, 4…10. Below this row of 10 stripes, create another row. This time, the layering should follow a geometric progression i.e. 1, 2, 4, 8, 16, 32, 64, etc. There will be a distinct difference between the two rows. The steps in the first row are not visually even, whereas the steps in the second row should be perceived as visually even. This phenomena is explained by the Weber-Fechner law. Materials: transparency sheets, mdf board, nuts and bolts Discussion: Weber-Fechner law, logarithm, stimulus

Observations When transparencies are stacked, the decrease in transparency of the stack is directly dependent on the number of elements in the stack. Steps in the first row [Fig 4a] are not even. They are very gradual, and there is no difference perceived in the last three steps. Steps in the second row [Fig 4b] are more even, increasing proportionately with every step. However, towards the end, the grayness increases, but not in the same proportion. The increase becomes progressively less, till a saturation point is reached and there is no change of colour. Fig 5.4a: Strips in arithmetic progression

Weber- Fechner law: The visual perception of an arithmetic progression depends upon a physical geometric progression.

Inference The observed phenomena only apply to transparent solids and fluids. The resultant stack is an additive mixture with regard to colour and a subtractive mixture with regard to light. As the volume of the stack increases, so does the brightness of the hue and the transparency of the stack decreases. This attribute is called ‘volume colour’. The effect is seen commonly in swimming pools, where the water appears ‘more blue’ at the deeper end.

Fig 5.4b: Strips in geometric progression

e curv ion t ra tu a S

Colour Volume

Fig 5.4c: graph showing the observations.

saturation

Inferences

5.5 Nature of brown

The saturation of yellow is brown. Brown is a deep, beep yellow.

The aim was to investigate the nature of brown. Soya sauce, an ebible deep brown pigment was slowly added to a jar of water, till the water was saturated with the colour of the pigment.

The phenomena is similar to the one studied earlier - volume colour. The saturation of yellow follows the same curve as shown in Fig. 5.4c.

Observations Initially, the water was a very light yellow. As more of the pigment was added, the colour of the water moved from light yellow to a deep yellow, and getting deeper, it gradually turned brown and saturated after a deep brown. There was also a gradual loss in the transparency.

The mixture is additive with regard to colour and subtractive with regard to light.

1

2

3

4

5

6

12

11

10

9

8

7

Fig. 5.5a: change in the colour of water as the pigment was mixed.

Explaining the observations

Conclusion

Volume colour is the connecting link between the additive and subtractive colour systems. Volumes of yellow produce brown, and in that process, the transparency of the system is reduced, but not lost.

The colours yielded by mixing pigments [subtractive mixing] of the primaries of light [additive primaries, red, blue and green] are the volume colour saturations of the pigment primaries [subtractive primaries, cyan, magenta and yellow]. Therefore, as observed by mixing the pigment and water, and as explained by fig 5.5b,

Fig 5.5b explains why brown is a deep, deep yellow.

Red + Green = Brown, which is the saturation of yellow. Hence, it can also be stated that, Turquoise is a deep, deep Cyan Green + Blue = Turquoise, which is a saturation of Cyan [fig. 5.5c(i)].

Yellow light Air

Purple is a deep, deep Magenta. Red + Blue =Purple, which is a saturation of Magenta [fig. 5.5c(ii)] Additive mixing of light red + green = yellow light. Additive zone

Filtered light from the coloured water

Dividing surface of water and air

Subtractive zone brown Red + green

The volume of water acts like a colour filter

Fig 5.5c[i]: mixing of copper sulphate crystals in water

Water

Light entering the water

Fig 5.5b: explaining why brown appears yellow

Fig 5.5c: The additive and subtractive colour relationship

Fig 5.5c[ii]: purple potassium permanganate crystals dissolve to give a magenta solution.

5.6 Scale Mode: paint and brush technique, workshop Construct a 3m wide x 2m high wall, at a scale of 1:2. Construct a bench with appropriate dimensions (width, length, depth, height from floor), cantilevered from the wall. Treat the wall as a canvas and the bench as a band of colour. Paint a square patch above the bench. This is a conceptual device. Choose appropriate colours to apply for the wall, the bench and the square. Ideally, all colours must be of a different hue. Materials: timber, canvas, paints Discussion: colour interaction

The process followed

Fig 5.6.1[b]:The selected composition

Fig. 5.6.1[a]: Composing the bench, the square and the wall, so as to attain a balance.

Composing with colour A study of lightness of hues A composition was chosen and 3 different hues of green were applied on it, in six combinations. The aim was to infer the relative lightness values of the hues that would be applied on the elements later. Green was chosen, because, it maintains good brightness contrast. The selected composition has the square in the lightest hue, followed by the bench, which relatively darker than the square and then the wall, which is the darkest [reflects least light].

Fig 5.6.2[b]: The selected composition, with the square as the lightest hue, followed by the bench and the wall.

Fig 5.6.2[a] compositions in green to study the lightness of colours to be assigned to the elements.

Composing with colour Assigning the hues to the elements. Based on the study of lightness overleaf, the following combinations of hues were tried out, as illustrated by fig. 5.6.3

Fig. 5.6.3[a]: different trials of hues for the elements.

Fig. 5.6.3[a]: different trials of hues for the elements.

Bibliography - Albers, Joseph, ‘Interaction of colour’, revised edition, New Haven: Yale University Press, 1975. - Beck, Jacob, ‘Surface color perception’, Ithaca Cornell Uni. Press 1970. - Brian A. Barsky, Todd J. Kosloff, Egon C. Pasztor, Steven D. Upstill, ‘An opponent-process approach to modeling the blue shift of the human colour vision system’, University of California, Berkley, California, 2004. - Forgus, Ronald H. ‘Perception: the basic process in cognitive development’, New York, McGraw-Hill, 1970. - Fraser, Tom and Banks, Adam, ‘The complete guide to colour’, ILEX Press, 2004. - Gibson, James J, ‘The Ecological approach to visual perception’, London Lawrence Erlbaum Associates. - Goldstein, E. Bruce, ‘Sensation and Perception’, Mexico International Thomson Publishing, 2000. - Hering, Ewald, ‘Zur Lehre vom Lichtsinne (Principles of a new theory of the colour sense)’ , translated by Kay Butler, Vienna, 1878.