#rgbi — Public Fediverse posts

RGBI Macaw

Experimenting with the idea of creating an image with the RGBI colorcsheme. RGBI stands for Red, Green, Blue, Intensity. It's basically the colorscheme used by the text-mode console on Linux - with the six primary colors plus black and white, and with bright and dark versions of each of those colors.

#Pixel #PixelArt #Animal #Bird #Parrot #Macaw #Retro #RetroArt #RetroAesthetic #8Bit #8BitArt #RGB #RGBI #GIMP #Digital #DigitalArt #Art #Artwork #MastoArt #ArtistOnMastodon

RGBI Macaw

Experimenting with the idea of creating an image with the RGBI colorcsheme. RGBI stands for Red, Green, Blue, Intensity. It's basically the colorscheme used by the text-mode console on Linux - with the six primary colors plus black and white, and with bright and dark versions of each of those colors.

#Pixel #PixelArt #Animal #Bird #Parrot #Macaw #Retro #RetroArt #RetroAesthetic #8Bit #8BitArt #RGB #RGBI #GIMP #Digital #DigitalArt #Art #Artwork #MastoArt #ArtistOnMastodon

The #CGA color palette is an interesting example of creative problem solving. The question is: how to describe colors in RGB color space on four bits?

Three bits are simple — we just give a bit to each channel, and we get eight colors, three basic colors and their combinations: black, red, green, blue, cyan, magenta, yellow and white. But what should we do about the fourth bit?

We could add it to one of the channels but we'd get quite an asymmetric palette — say, RGB211 would give us three shades of red, of green, some violets, but no orange.

CGA uses #RGBI color space instead — the bits corresponding to the basic colors give ⅔ brightness, and the fourth bit adds ⅓ "intensity" to all colors. So we get 8 "dark" colors, same as listed above, and 8 "bright" colors: red and light red, green and light red, and so on.

And why is that ⅔ and ⅓, and not half-half? Because if we used halves, we'd have two identical grays; the "bright black" and "dark white" would be the same. And with ⅔ + ⅓, we get two different shades of gray instead.

But creativity doesn't end here. Originally, the "dark yellow" apparently was not considered "pleasant". So for this specific color, the intensity of green is tuned down to ⅓, giving brown.

It should probably be noted here that with larger screen resolutions (read: larger than 160x100), CGA wasn't able to fully utilize all these 16 colors. Nevertheless, we still see traces of this basic color palette to this day, for example in some implementations of ECMA-48 console color sequences.

https://en.wikipedia.org/wiki/Color_Graphics_Adapter#Color_palette

#retro

Paleta kolorów karty graficznej #CGA to ciekawy przykład kreatywnego rozwiązywania problemów. Otóż, jak zapisać kolor w przestrzeni RGB na czterech bitach?

Na trzech prosto — dajemy po bicie na każdy kanał, i dostajemy osiem kolorów; trzy podstawowe i ich kombinacje: czarny, czerwony, zielony, niebieski, cyjan, różowy, żółty i biały. Co jednak zrobić z czwartym bitem?

Moglibyśmy go dodać do któregoś kanału, ale wówczas dostalibyśmy dosyć niesymetryczną paletę — np. RGB211 oferuje trzy odcienie czerwieni, zieleni, jakieś fiolety, ale brak pomarańczu.

Zamiast tego, CGA używa przestrzeni #RGBI — bity odpowiadające kolorom podstawowym odpowiadają ⅔ jaskrawości koloru, a czwarty bit dodaje ⅓ "intensywności" do wszystkich kolorów. Tak więc dostajemy 8 "ciemnych" kolorów, jak wymienione wyżej, i 8 "jasnych": czerwony i jasnoczerwony, zielony i jasnozielony, itd.

A dlaczego ⅔ i ⅓, a nie po połowie? Bo gdyby dawać po połowie, to kolor szary by się powtórzył, jako "jasny czarny" i "ciemny biały". A tak dostajemy dwa odcienie szarości.

Na tym jednak pomysłowość się nie kończy. Oryginalnie, ciemny wariant żółtego był "brzydki", jak najwyraźniej uznano. Dlatego też ten jeden kolor obniża jaskrawość zieleni do ⅓, dając kolor brązowy.

Trzeba tu zaznaczyć, że przy większych rozdzielczościach (czyli większych niż 160x100), CGA nie była w stanie w pełni wykorzystać 16 kolorów. Niemniej, ślady tej podstawowej palety widzimy do dziś, chociażby w niektórych implementacjach konsolowych sekwencji kolorów ECMA-48.

https://en.wikipedia.org/wiki/Color_Graphics_Adapter#Color_palette

#retro

@dryak Oh boy! I really just learned the "classic" Windows Console palette was even "more broken", I wasn't aware so far. This would also mean there would be a very dark "dark white" and a second "black", but no, those two were adjusted...

Also found they only changed that in #Win10, but instead of going for a real #RGBI palette with brown adjustment, they picked pretty arbitrary values creating a new less greenish "dark yellow" 🤦‍♂️
https://devblogs.microsoft.com/commandline/updating-the-windows-console-colors/

Indeed, I remember seeing lots of very regular dithering in Windows 3.x ... so you probably have a point here 😉

BTW, the color difference you see in these Windows screenshots is the classic "dark yellow vs brown" issue.

Quick background, with digital #RGBI signals (like used with #CGA), you couldn't have brown, but high-quality monitors (including IBM's own, but also a Commodore 1084 I have here) had extra circuitry adjusting dark yellow to brown by reducing the green component. With #CGA on a cheap monitor or a TV set, you still had "dark yellow".

#VGA finally moved to analog #RGB and used brown. Still many terminals today (including #Windows #Console) have dark yellow in their default palettes.

#dos2ansi must rely on the default palette when the terminal supports only 8 or 16 colors, but with a 256-color terminal, it uses "original" CGA/VGA colors. And of course, there's a switch to disable the "brown adjustment" 😎

Screenshot from #xterm on#FreeBSD showing both modes, actually this example looks like it might have been designed with "dark yellow" in mind.

#retrocomputing #ansiart