Øyvind Kolås    pippin@gimp·org mastodon twitter github bitcoin patreon  

  Ametameric                    

A 16 color palette for dichromats and trichromats

Ametameric is as a system palette that provides the standard CGA/ANSI colors accomodating various forms of human color blindness/color vision deficiencies. 16 colors (including white, black and two grays) that all provide sufficient contrast for all common types of color vision. When working as intended, TUIs made to work well with the system colors (rather than 256/true color) should become accesible for color vision deficient users without further tweaks needed.

The 8bit sRGB palette values and corrsponding color values in CIE Lab and CIE Lch:

idx	name	hex RGB	dec RGB	CIE Lab	CIE Lch
0	black	#000000	0, 0, 0	0, 0, 0	0, 0, 0
1	red	#a02929	160, 41, 41	37, 49, 31	37, 58, 32
2	green	#4aa08b	74, 160, 139	60, -31, 3	60, 31, 175
3	brown	#878453	135, 132, 83	55, -5, 27	55, 27, 100
4	blue	#2424ed	36, 36, 237	31, 56, -99	31, 114, 300
5	magenta	#ab4adf	171, 74, 223	50, 58, -60	50, 83, 314
6	cyan	#3b6bb1	59, 107, 177	44, 1, -43	44, 43, 272
7	bright-gray	#c3c3c3	195, 195, 195	79, 0, 0	79, 0, 0
8	gray	#6f6f6f	111, 111, 111	47, 0, 0	47, 0, 0
9	bright-red	#edac82	237, 172, 130	76, 21, 32	76, 38, 56
10	bright-green	#99edba	153, 237, 186	87, -35, 16	87, 38, 155
11	yellow	#e9d808	233, 216, 8	86, -7, 84	86, 84, 95
12	bright-blue	#82b4ed	130, 180, 237	71, -6, -34	71, 35, 260
13	bright-magenta	#d66fed	214, 111, 237	63, 55, -47	63, 72, 320
14	bright-cyan	#1de1ed	29, 225, 237	82, -42, -19	82, 46, 204
15	white	#ffffff	255, 255, 255	100, 0, 0	100, 0, 90

Downloads

ametameric.gpl	GIMP Palette
ametameric.esc	initializes ametameric as the 16 system colors, reset foreground/background.
ametameric-reverse.esc	initialize ametameric as the 16 system colors, but with dark on bright text.
ametameric-desaturated.esc	The ametameric palette linearly combined in XYZ space with its corresponding luminance by a factor of 0.85. The internal color relationships remain as in the base ametameric palette. This is also useful with wide gamut displays to avoid super-saturated colors in the part of the gamut that is wider than normal in non-color managed terminal emulators.

The .esc files contains escape sequences compatible with xterm, vte (gnome-terminal and friends), mlterm, kitty and iterm2. By catting these files inside a compatible terminal the system colors are overridden for the session.

user@host:~$ curl https://pippin.gimp.org/ametameric/ametameric.esc
 Ametameric  20200920       
user@host:~$

If it works the colors of the terminal will change, note that most terminal emulators on linux are not color managed; thus with a widegamut display this will yield over-saturated colors.

Change Log

20200423

initial release

20200920

skew all colors away from black and white optimizing contrast with those.

Color Deficiency Preview/Simulation

The following grids show the same grid og all combinations through dichromat simulation, using the tables from Martin Krzywinski's Color Palettes for Color Blindness page. These are different from the color vision deficienct simulator in GIMP as well as different from the Coblis on color-blindness.com, but the differences are large enough to register with all of them; and verification of the approach agrees with discrimination observed by at least deuteranopes.

 

Ametameric internals

The core of ametamerics constraints is puzzling the 16 colors into two 4x4 palettes, that have an unbroken gradient for deuteranopes and tritanopes. As well as acceptable gradients on each row and column, like a multi-dimensional sudoku. For each permutation the colors have been adjusted for improved contrast - as well as maintaining trichromat identification and constraints.

The two 2d gamuts split the colors into three groups, grays, cold and warm colors. For tritanopia the cold shades are blue and warm are red, while in the simulated gamutes for protanopia and deuteronopia the warm patches have a yellow tint.

Full color-blindness, seeing grayscale is rare. But some contrast in grayscale conversions also desirable for printing and other desaturations of screenshots/windows. A final constraint maintained is thus some steps in the grayscale gradient conversion. The gradient has a large gap between black and the grays and white and the grays, this ensures contrast on black as well as white backgrounds.

NOTE:This page relies on background/text color specified in CSS being interpreted as sRGB and correctly converted to display. Otherwise colors will be oversaturated on wide-gamut displays; the desired dichromat discrimination probably still works though.

Exhaustive test of text in all colors on backgrounds with all colors

white
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

black
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

dark-gray.
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

bright gray
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

blue as in midnight commander
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

red
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

green
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

brown
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

magenta
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

cyan
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

bright red
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

bright green
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

yellow
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

bright blue
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

bright magenta
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.

bright cyan
black red green brown blue magenta cyan bright gray dark gray bright red bright green yellow bright blue bright magenta bright cyan white.