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Graphics Format

The GameTank's standard video hardware renders a 128×128 pixel framebuffer to a color composite video signal. On a typical television about 100 horizontal lines will be visible. The image is presented with borders on the left and right side, the color of which is determined by the rightmost pixel in the buffer.

Each pixel in the image is represented by a single byte that encodes Hue, Saturation, and Luminosity in 3, 2, and 3 bits respectively.

This is functionally identical to a 8-bit indexed color mode, with a fixed palette with 200 unique colors

Three Hue bits encode eight different colors that can be selected. In order these are Green, Yellow, Orange, Red, Magenta, Violet, Blue, and Cyan. Each of these selections represents a different phase offset of the NTSC color carrier.

Two Saturation bits control the amplitude of the color carrier signal, which results in four possible color intensities. Setting saturation to zero eliminates the color carrier, resulting in a shade of black, gray, or white. Colors with different hues, zero saturation, and the same Luminosity will be identical.

Three Luminosity bits control the brightness of a color by determining the low frequency voltage component of the video signal. Higher numbers tend towards white while lower numbers tend towards black.

graphics/format.txt · Last modified: 2023/08/22 19:36 by clyde