4.3 KiB
RGB332
RGB332 is a general 256 color palette that encodes one color with 1 byte (i.e. 8 bits): 3 bits for red, 3 bits for green and 2 bits for blue (human eye is least sensitive to blue). RGB332 is an implicit palette -- it doesn't have to be stored in memory because the color index itself determines the color and vice versa. Compared to the classic 24 bit RGB (which assigns 8 bits to each of the RGB components), RGB332 is very "KISS/suckless" and often good enough (especially with dithering) as it saves memory, avoids headaches with endianness and represents each color with just a single number (as opposed to 3), so it is often used in simple and limited computers such as embedded. It is also in the public domain, unlike some other palettes, so it's additionally a legally safe choice. RGB332 also has a "sister palette" called RGB565 which uses two bytes instead of one and so offers many more colors.
A disadvantage of plain 332 palette is the linearity of each component's intensity, i.e. lack of gamma correction, so there are too many almost indistinguishable bright colors while too few darker ones { TODO: does a gamma corrected 332 exist? make it? ~drummyfish }. Another disadvantage is the non-alignment of the blue component with red and green components, i.e. while R/G components have 8 levels of intensity and so step from 0 to 255 by 36.4, the B component only has 4 levels and steps by exactly 85, which makes it impossible to create exact shades of grey (which has to have all R, G and B components equal).
The RGB values of the 332 palette are following:
#000000 #000055 #0000aa #0000ff #002400 #002455 #0024aa #0024ff
#004800 #004855 #0048aa #0048ff #006d00 #006d55 #006daa #006dff
#009100 #009155 #0091aa #0091ff #00b600 #00b655 #00b6aa #00b6ff
#00da00 #00da55 #00daaa #00daff #00ff00 #00ff55 #00ffaa #00ffff
#240000 #240055 #2400aa #2400ff #242400 #242455 #2424aa #2424ff
#244800 #244855 #2448aa #2448ff #246d00 #246d55 #246daa #246dff
#249100 #249155 #2491aa #2491ff #24b600 #24b655 #24b6aa #24b6ff
#24da00 #24da55 #24daaa #24daff #24ff00 #24ff55 #24ffaa #24ffff
#480000 #480055 #4800aa #4800ff #482400 #482455 #4824aa #4824ff
#484800 #484855 #4848aa #4848ff #486d00 #486d55 #486daa #486dff
#489100 #489155 #4891aa #4891ff #48b600 #48b655 #48b6aa #48b6ff
#48da00 #48da55 #48daaa #48daff #48ff00 #48ff55 #48ffaa #48ffff
#6d0000 #6d0055 #6d00aa #6d00ff #6d2400 #6d2455 #6d24aa #6d24ff
#6d4800 #6d4855 #6d48aa #6d48ff #6d6d00 #6d6d55 #6d6daa #6d6dff
#6d9100 #6d9155 #6d91aa #6d91ff #6db600 #6db655 #6db6aa #6db6ff
#6dda00 #6dda55 #6ddaaa #6ddaff #6dff00 #6dff55 #6dffaa #6dffff
#910000 #910055 #9100aa #9100ff #912400 #912455 #9124aa #9124ff
#914800 #914855 #9148aa #9148ff #916d00 #916d55 #916daa #916dff
#919100 #919155 #9191aa #9191ff #91b600 #91b655 #91b6aa #91b6ff
#91da00 #91da55 #91daaa #91daff #91ff00 #91ff55 #91ffaa #91ffff
#b60000 #b60055 #b600aa #b600ff #b62400 #b62455 #b624aa #b624ff
#b64800 #b64855 #b648aa #b648ff #b66d00 #b66d55 #b66daa #b66dff
#b69100 #b69155 #b691aa #b691ff #b6b600 #b6b655 #b6b6aa #b6b6ff
#b6da00 #b6da55 #b6daaa #b6daff #b6ff00 #b6ff55 #b6ffaa #b6ffff
#da0000 #da0055 #da00aa #da00ff #da2400 #da2455 #da24aa #da24ff
#da4800 #da4855 #da48aa #da48ff #da6d00 #da6d55 #da6daa #da6dff
#da9100 #da9155 #da91aa #da91ff #dab600 #dab655 #dab6aa #dab6ff
#dada00 #dada55 #dadaaa #dadaff #daff00 #daff55 #daffaa #daffff
#ff0000 #ff0055 #ff00aa #ff00ff #ff2400 #ff2455 #ff24aa #ff24ff
#ff4800 #ff4855 #ff48aa #ff48ff #ff6d00 #ff6d55 #ff6daa #ff6dff
#ff9100 #ff9155 #ff91aa #ff91ff #ffb600 #ffb655 #ffb6aa #ffb6ff
#ffda00 #ffda55 #ffdaaa #ffdaff #ffff00 #ffff55 #ffffaa #ffffff
With RGB332 addition/subtraction of colors can be approximated in a very fast way using the OR/AND operation -- however this only works sometimes (check visually). For example if you need to quickly brighten/darken all pixels in a 332 image, you can just OR/AND each pixel with these values:
brighten by 3: | 0x6d (011 011 01)
brighten by 2: | 0x49 (010 010 01)
brighten by 1: | 0x24 (001 001 00)
darken by 1: & 0xdb (110 110 11)
darken by 2: & 0xb6 (101 101 10)
darken by 3: & 0x92 (100 100 10)
TODO: conversion to/from RGB24