55 lines
4.3 KiB
Markdown
55 lines
4.3 KiB
Markdown
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# RGB332
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RGB332 is a general 256 color [palette](palette.md) 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](kiss.md)/[suckless](suckless.md)" and often [good enough](good_enough.md) (especially with [dithering](dithering.md)) as it saves memory, avoids headaches with [endianness](byte_sex.md) 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](embedded.md). It is also in the [public domain](public_domain.md), unlike some other palettes, so it's additionally a legally safe choice. RGB332 also has a "sister palette" called [RGB565](rgb565.md) which uses two bytes instead of one and so offers many more colors.
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A disadvantage of plain 332 palette is the linearity of each component's intensity, i.e. lack of [gamma correction](gamma_correction.md), 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).
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The RGB values of the 332 palette are following:
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```
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#000000 #000055 #0000aa #0000ff #002400 #002455 #0024aa #0024ff
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#004800 #004855 #0048aa #0048ff #006d00 #006d55 #006daa #006dff
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#009100 #009155 #0091aa #0091ff #00b600 #00b655 #00b6aa #00b6ff
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#00da00 #00da55 #00daaa #00daff #00ff00 #00ff55 #00ffaa #00ffff
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#240000 #240055 #2400aa #2400ff #242400 #242455 #2424aa #2424ff
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#244800 #244855 #2448aa #2448ff #246d00 #246d55 #246daa #246dff
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#249100 #249155 #2491aa #2491ff #24b600 #24b655 #24b6aa #24b6ff
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#24da00 #24da55 #24daaa #24daff #24ff00 #24ff55 #24ffaa #24ffff
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#480000 #480055 #4800aa #4800ff #482400 #482455 #4824aa #4824ff
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#484800 #484855 #4848aa #4848ff #486d00 #486d55 #486daa #486dff
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#489100 #489155 #4891aa #4891ff #48b600 #48b655 #48b6aa #48b6ff
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#48da00 #48da55 #48daaa #48daff #48ff00 #48ff55 #48ffaa #48ffff
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#6d0000 #6d0055 #6d00aa #6d00ff #6d2400 #6d2455 #6d24aa #6d24ff
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#6d4800 #6d4855 #6d48aa #6d48ff #6d6d00 #6d6d55 #6d6daa #6d6dff
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#6d9100 #6d9155 #6d91aa #6d91ff #6db600 #6db655 #6db6aa #6db6ff
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#6dda00 #6dda55 #6ddaaa #6ddaff #6dff00 #6dff55 #6dffaa #6dffff
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#910000 #910055 #9100aa #9100ff #912400 #912455 #9124aa #9124ff
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#914800 #914855 #9148aa #9148ff #916d00 #916d55 #916daa #916dff
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#919100 #919155 #9191aa #9191ff #91b600 #91b655 #91b6aa #91b6ff
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#91da00 #91da55 #91daaa #91daff #91ff00 #91ff55 #91ffaa #91ffff
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#b60000 #b60055 #b600aa #b600ff #b62400 #b62455 #b624aa #b624ff
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#b64800 #b64855 #b648aa #b648ff #b66d00 #b66d55 #b66daa #b66dff
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#b69100 #b69155 #b691aa #b691ff #b6b600 #b6b655 #b6b6aa #b6b6ff
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#b6da00 #b6da55 #b6daaa #b6daff #b6ff00 #b6ff55 #b6ffaa #b6ffff
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#da0000 #da0055 #da00aa #da00ff #da2400 #da2455 #da24aa #da24ff
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#da4800 #da4855 #da48aa #da48ff #da6d00 #da6d55 #da6daa #da6dff
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#da9100 #da9155 #da91aa #da91ff #dab600 #dab655 #dab6aa #dab6ff
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#dada00 #dada55 #dadaaa #dadaff #daff00 #daff55 #daffaa #daffff
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#ff0000 #ff0055 #ff00aa #ff00ff #ff2400 #ff2455 #ff24aa #ff24ff
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#ff4800 #ff4855 #ff48aa #ff48ff #ff6d00 #ff6d55 #ff6daa #ff6dff
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#ff9100 #ff9155 #ff91aa #ff91ff #ffb600 #ffb655 #ffb6aa #ffb6ff
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#ffda00 #ffda55 #ffdaaa #ffdaff #ffff00 #ffff55 #ffffaa #ffffff
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```
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With RGB332 addition/subtraction of colors can be [approximated](approximation.md) in a very fast way using the [OR](or.md)/[AND](and.md) 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:
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```
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brighten by 3: | 0x6d (011 011 01)
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brighten by 2: | 0x49 (010 010 01)
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brighten by 1: | 0x24 (001 001 00)
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darken by 1: & 0xdb (110 110 11)
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darken by 2: & 0xb6 (101 101 10)
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darken by 3: & 0x92 (100 100 10)
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```
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TODO: conversion to/from RGB24
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