| | Ghostrider
Administrator
Posts: 45 |
C64 color comparison
<Post edited by Ghostrider on 20/11-2024 15:37>
So, I'm playing around with something that utilizes color differences, and I wanted my code to be as good as I could make it. That led me into a little research, resulting in the below table (and documentation) in my code. I have no idea whether others have done anything like this, I just thought I'd share it in case it could be useful for someone. (Tho I guess there could be someone who doesn't like the Pepto palette). The color-differences range from 0 to 100, as can be seen from the difference between black and white.
/* COLOR-DIFFERENCE TABLE, measuring how alike 2 colors look to the human eye.
*
* Created by translating the correct C64 RGB-palette (as thoroughly researched
* by Philip 'Pepto' Timmermann, and published in the "Commodore VIC-II Color
* Analysis"):
*
* Black White Red Cyan Purple Green Blue
* 00 00 00 ff ff ff 68 37 2b 70 a4 b2 6f 3d 86 58 8d 43 35 28 79
*
* Yellow Orange Brown Lt Red Dark Grey Med Grey Lt green
* b8 c7 6f 6f 4f 25 43 39 00 9a 67 59 44 44 44 6c 6c 6c 9a d2 84
*
* Lt Blue Lt Grey
* 6c 5e b5 95 95 95
*
*
* into the intended perceptually uniform CIE L*a*b* (CIELAB) color space via
* Photoshop CS5:
*
* Black White Red Cyan Purple Green Blue
* 0 0 0 100 0 0 29 21 18 64 -15 -13 35 32 -32 54 -29 33 22 25 -45
*
* Yellow Orange Brown Lt Red Dark Grey Med Grey Lt green
* 78 -15 42 36 10 30 24 0 33 49 20 17 29 0 0 46 0 0 79 -29 33
*
* Lt Blue Lt Grey
* 44 22 -45 62 0 0
*
* and finally, using the above CIE L*a*b* values, computing the
* color-differences between any two C64 colors. This was done using a Matlab
* implementation of the CIEDE2000 color-difference formula, published by
* Gaurav Sharma at the University of Rochester. As of 2016, this should be the
* best visual-color-difference algorithm available.
*/
float colordiff[16][16] = {
{0.00000, 100.00000, 27.29927, 53.26580, 33.36977, 46.54540, 27.91278,
71.32101, 30.91014, 24.36201, 40.40526, 18.97503, 32.86756, 72.80412,
39.20668, 48.53537},
{100.00000, 0.00000, 61.97257, 29.34183, 56.93753, 40.24329, 71.85536,
26.50693, 54.14554, 67.73280, 42.05900, 58.78266, 40.33892, 26.72007,
48.58504, 26.02320},
{27.29927, 61.97257, 0.00000, 53.66487, 28.72115, 44.76018, 33.08048,
56.92023, 14.00707, 21.06269, 17.36067, 19.62648, 24.37162, 61.72667,
35.29397, 37.10740},
{53.26580, 29.34183, 53.66487, 0.00000, 38.60884, 30.82463, 43.73660,
34.43323, 43.05106, 48.64282, 43.62700, 37.61613, 23.58306, 31.63124,
27.79863, 16.38323},
{33.36977, 56.93753, 28.72115, 38.60884, 0.00000, 63.67504, 13.95492,
69.94213, 40.00703, 47.52039, 30.66366, 24.06466, 25.52344, 73.27806,
13.99189, 35.70972},
{46.54540, 40.24329, 44.76018, 30.82463, 63.67504, 0.00000, 55.77398,
21.74555, 31.80033, 31.80176, 38.51345, 32.30988, 24.56106, 20.17950,
49.67790, 24.32458},
{27.91278, 71.85536, 33.08048, 43.73660, 13.95492, 55.77398, 0.00000,
80.90839, 43.71174, 48.31631, 39.23529, 24.73801, 31.07341, 74.86371,
17.74707, 43.54902},
{71.32101, 26.50693, 56.92023, 34.43323, 69.94213, 21.74555, 80.90839,
0.00000, 42.97277, 54.79072, 39.45047, 52.55362, 35.47933, 9.66140,
64.56892, 25.73341},
{30.91014, 54.14554, 14.00707, 43.05106, 40.00703, 31.80033, 43.71174,
42.97277, 0.00000, 12.50487, 17.45413, 19.77869, 20.96770, 47.52027,
42.70317, 32.11929},
{24.36201, 67.73280, 21.06269, 48.64282, 47.52039, 31.80176, 48.31631,
54.79072, 12.50487, 0.00000, 29.37105, 19.29903, 26.19519, 57.58782,
50.39976, 39.71692},
{40.40526, 42.05900, 17.36067, 43.62700, 30.66366, 38.51345, 39.23529,
39.45047, 17.45413, 29.37105, 0.00000, 25.82295, 19.35305, 45.64642,
32.88847, 22.69667},
{18.97503, 58.78266, 19.62648, 37.61613, 24.06466, 32.30988, 24.73801,
52.55362, 19.77869, 19.29903, 25.82295, 0.00000, 14.44913, 53.39135,
26.98485, 31.49222},
{32.86756, 40.33892, 24.37162, 23.58306, 25.52344, 24.56106, 31.07341,
35.47933, 20.96770, 26.19519, 19.35305, 14.44913, 0.00000, 36.41365,
23.94736, 15.38462},
{72.80412, 26.72007, 61.72667, 31.63124, 73.27806, 20.17950, 74.86371,
9.66140, 47.52027, 57.58782, 45.64642, 53.39135, 36.41365, 0.00000,
57.25129, 26.64841},
{39.20668, 48.58504, 35.29397, 27.79863, 13.99189, 49.67790, 17.74707,
64.56892, 42.70317, 50.39976, 32.88847, 26.98485, 23.94736, 57.25129,
0.00000, 29.63502},
{48.53537, 26.02320, 37.10740, 16.38323, 35.70972, 24.32458, 43.54902,
25.73341, 32.11929, 39.71692, 22.69667, 31.49222, 15.38462, 26.64841,
29.63502, 0.00000}
};
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| | Copyfault
Registered: Dec 2001
Posts: 478 |
Quoting OswaldI dont understand half of that german wiki. so rgb to xyz then xyz to lab ? [...]
Die Faktoren 500 bzw. 200 sollen die resultierenden Werte für a* und b* in die gewohnten Größenordnungen bringen, die auch zum maximalen L* von 100 passen.
wat ? :)
These numbers (500, 200) are certain scaling factors to ensure consistency between the values for L*, a* and b*.
As I don't have any experiences with L*a*b*-coordinates as of yet, I can just take those scaling factors as given and assume that they ensure proper calculation results.
Sorry for only posting a German link; unfortunatly, the english wiki did not contain information on how to convert from (some) RGB space to this L*a*b*-thing. At least I did not find anything like that up to now... |
| | Jetboy
Registered: Jul 2006
Posts: 338 |
I'm dabbling in color conversions and color spaces a lot, over a year. I don't know what you use it for, but when converting images to c64, while CEIDE2000 gives the most true representation of colors of original image it does not look too good.
Using XYZ, HSV or even RGB give much more pleasant images (although color shifted). Also trying Manhattan or Minkowsky instead of euclidean distance give interesting results.
As for palette, Pepto is good, but in my experience PALette is better. But it is nuisance, as the results differ depending of way too many factors, including specific c64, monitor, image being processed, lightning in the presentation room, and individual qualities of the observer.
The key to getting nice colors in RGB is to use weight for each color, representing how much it contribute for the human vision. Although if you apply the weights "as the handbook says", you get way too much blue in dark areas, resulting in images looking like they were from old Censor Design demos. If you apply only 80-90 percent of the weights, you avoid this drawback, and get more representative colors.
Also when converting images to c64, when they are too washed out, you can decide not to use dark gray, or dark gray and mid gray. They get much more colorful then, but more bluish. If viewer does not know the original picture, it will be looking good to them in most cases.
All i say here are the generalizations, and individual images may deviate a lot.
Also i do not think doing image processing in kickass is the way to go, as you do not get immediate response and cannot tweak values in real time- which can improve conversion quality greatly. But again, i do not know what you use this color comparisons for :) |
| | Jetboy
Registered: Jul 2006
Posts: 338 |
The more i think about it, the more i think my implementation of CIEDE2000 was somewhat flawed. Will investigate it again when i find some spare time. |
| | Copyfault
Registered: Dec 2001
Posts: 478 |
Quote: <Post censored by CSDb staff>
Hmm, aside from un-necrofying this thread, does this post mean the values have been updated?
If so, did the initial post change along with it? Would be a bit confusing because then nobody has the chance to compare old to new values...
But I guess it's all different and I'm on the wrong path. Still using the values (that used to be here) for looking up substitute colours, but -having read the old posts again- I did not really pick up on writing a proper distance function (in whatever xass).
So, still smth to do I'd say ;) |
| | chatGPZ
Registered: Dec 2001
Posts: 11387 |
These days you should probably use the values Tobias measured (different for odd and even lines) to get optimal results (this is what VICE uses for the CRT emulation/palette generator now) |
| | Copyfault
Registered: Dec 2001
Posts: 478 |
Quote: These days you should probably use the values Tobias measured (different for odd and even lines) to get optimal results (this is what VICE uses for the CRT emulation/palette generator now)
Very good pointer! THX!
Is there a thread or link to a webpage or whatever where I can see these values? Or maybe I should just contact him ;) |
| | chatGPZ
Registered: Dec 2001
Posts: 11387 |
There was some thread on F64, a year ago or so. I usually just contact him directly :) |
| | Ghostrider
Administrator
Posts: 45 |
Hey guys,
just to let you know my account got hacked, so the un-necrofying in post #17 above was not me. You might also notice the PETDel crap that the ill-natured person inserted at the bottom of my original post. (Maybe it will be removed again, I don't know.) I've changed my password.
Had no intention to revive this thread, nevertheless always interesting to see different ideas on the color stuff. |
| | Count Zero
Registered: Jan 2003
Posts: 1933 |
Thanx Ghostrider -removed the post and Admin team is currently looking at further incidents affecting the database. |
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