Augmenting Perceived Color Depth

Augmenting perceived color depth with simple hardware logic. “ART001” By Laxer3A

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Why we need more colors ? „P Processing i power, pin i count, t memory… „ Everything increase, even in hobby electronic. „ But most of the FPGA boards out there just

plain sucks to do nice 888 output. „

“low end” (100$~500$) $ $ „

„

“Middl “Middle-end” d” (500$ (500$~1000$) 1000$) „

„

Most of the time RGB111, 323, 333, etc... RGB 555 / 565, some 888 but not the other feature you want. want

“High-end” (>1000$) „

RGB888 10-10-10 RGB888,10 10 10 and DVI DVI, but but… 2500$ ? 2

How do we simply display high colors data on poor color depth displays. MSB

LSB

7 6 5 4 3 2 1 0

MSB

LSB

We simply take the MSB And ignore the LSB.

7 6 5 4 3 2 1 0

555 Bit display

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Ok now what ? Ok, „ Well we could average a color value by

the neighbor pixels (known as “dithering”) 7 6 5 4 3 2 1 0

Use the unused LSB, if “1”, the color can be “averaged”.

555 Bit display

Ex. Value is 37 (100101) for a group of 4 pixels. A B Thus RGB555 : 10010 (A (A=18) 18) (2A+2B)/4 ÆA+B/2 But we can also use A+1 : 10011 (B=19) B A And display them in the following fashion. Basically we physically makes the average color of the surface match the color in higher depth resolution.

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Improvement. Improvement „ What we have done is a called “1 bit” matrix

dithering. „ We could imagine pattern for “2,3… bits”. „ Any imaging software does that AND it is static : the image is processed ONCE. „ But here, we have HARDWARE and can

perform per pixel operation operation… „

Something better ? 5

Ok now what ? Ok, „ Previously, Previously we have always the same pixel lit “up”

and lit “down”. „ Why y not switch at each frame ? A

B

B

A

B

A

A

B

Even Frame

Odd Frame

„ ÆGoing from “spatial” dithering to “temporal”

dithering. (Surface based to time based) „ Do NOT need surface of same color. „ Can work with a single pixel ! The previous method does not.(was not (was using surface to make average value) 6

Physical result result. „ By B switching it hi alternatively lt ti l values l we gett

AVERAGE value. TIME

Average Color.

„ The eye will “integrate” the signal and look

like the two colors are merged. „ Yes, but it may flick… „ „

Correct ! But we still use “closest” colors. Cheap LCD slow latency will help us ! 7

Let’ss get dirty baby : implementation Let implementation. „ Frame 1 0 1

0

1

0

1

1

0

Frame 0 X LSB 0 1

0

1

1

0

0

1

X LSB

Y LSB

Y LSB

(X xor Y) gives “Frame 1” pattern, ((X xor Y)) == Frame)) for all cases. thus,, ((

„ Color Computation (7Æ6 bit). Add For each component

+

B6 B5 B4 B3 B2 B1 B0 To display.

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No problem ? Part 1. 1 Add

+

B6 B5 B4 B3 B2 B1

0 Add

+

B6 B5 B4 B3 B2 B1

1

1 or 0 B6-B1 : Do not change. OK. 1 or 0 B6-B1 : Original or Original + 1. OK. Except…

When B6-B1 Wh B6 B1 iis 111111 already, l d overflow fl occurs, result lt is i 000000 ! Let’s fix it by detecting the overflow case first. Add

+

0 B6 B5 B4 B3 B2 B1 B0

Overflow detector.

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No problem ? Part 2. 2 „ We detect overflow, now fix the value. Add

+

0 B6 B5 B4 B3 B2 B1 B0 S7 S6 S5 S4 S3 S2 S1

OR

S7 S7 S7 S7 S7 S7 S’6 S’5 S’4 S’3 S’2 S’1

If overflow, S t to Set t “max” “ ” legal l l value. l (111111) else do nothing (OR with 000000)

Now one more thing : we do NOT multiply the precision by 2 ! We do increase range from n to (n*2)-1 ! Because original 1111111 does overflow and as no equivalent.

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Cheap isn’t isn t it ? Per component. P t „ Adder of the size of the output component + 2 bit. „

Value to add is only 0 or 1 Æ Logic can be optimized. optimized

„ OR stage of the size of the output component.

Per pixel. „ A ge general e a ADD b bitt co computed puted o once ce pe per coo coordinate. d ate (x xor y) == frame. Globally. „ A frame register bit inversed at each frame. 11

Results fpga ARE fun ! Results, Original RGB 333 : 512 colors 444 : 4,096 4 096 colors 555 : 32,768 colors. 666 : 262,144 colors.

With this basic component post process (15^3) 3,375 colors. (31^3) (31 3) 29,791 29 791 colors. colors (63^3) 250,047 colors. (127^3) 2,048,383 colors.

That is already quite a progress with only a “basic” basic pixel color processing logic. 12

Are we finished ? Not really really… „

We could W ld perform f th the same ttechnique h i and d use 4 4,8,16 8 16 fframes instead of 2 for switching pixels. „ Allowing ¼, 1/8, 1/16 precision. „ At the price of HUGE flickering.(ex : 0001 pattern ?) „

„

Or you must be able to multiply x2,x4,x8 the screen refresh rate.(most likely impossible, we have cheap devices right ?)

Add a “spatial” dithering stage before. „ Take the bit n+1 for temporal. „ Take the bit n+2 n+2..n+m n+m for spatial dithering dithering. „

Spatial dithering as no issue like flickering.

Transform a n+m value into n+1 dithered. Could use more “advanced” dithering technique for spatial dithering. „ Example : Floyd-Steinberg dithering… Æ

„

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Comments „ Any comments are welcome.

p ] hotmail dot com laxer3a [[at-no-spam] „ Please put “[BLOG]” [BLOG] at the beginning of the

mail title.

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References „ Dithering (for further interest)

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