ibm pc

CGA Color Palettes

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The infamous default 4-color palette with pink, cyan, black and white is probably the first thing that comes to mind when somebody starts to talk about CGA. I previously wrote a post about 16-color modes available for composite monitors but it’s good to add also something about the palettes for RGBI TTL monitors. These started to be used heavily when people stopped using TVs with their IBM PC compatibles.

The CGA palettes were designed for good viewing on NTSC TVs. That’s the reason behind the strange color combinations. The default one can, however, be modified using a video chip register – it replaces pink with red but also disables color burst on the composite output. Such trick was used in many games, but it did nothing on newer cards (EGA/VGA).

CGA also supports changing the color 0 (usually black) to any other color. Several games used this with the default palette to get blue, cyan, pink and white which allowed for better color transitions. Anyway, the easiest way to get more visually appealing games was to use the second palette – red, green, yellow and black.

Bright Text on 1-bit Displays

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XT-class Toshiba laptops started to use “double-scan CGA” displays with a resolution of 640×400 in the late 80s. This allowed for better graphics and much sharper text in comparison with ordinary CGA solutions. However, the LCDs which Toshiba used worked only in 1-bit mode so there were no shades of grey (blue). Lower resolutions in graphics emulated (four) colors using 2×2 patterns. The text mode, on the other side, emulated the intensity bit (bright text) using bolt characters.

Toshiba experimented a lot with hi-res fonts in ROM and I’m not pleased with the results. Standard (thin) font is hard to read and not visually appealing. Fortunately, it is possible at least to swap the bold and standard fonts using a keyboard shortcut. It is strange that the highlighted characters are in fact less readable then but overall experience is still better than with the default setup.