[Hot News] Colour Multiplexing on B&W Atari Video Game

[moderator]

<h3>From Andrew Davie</h3>
I was a very interested reader of some of your site's information on early colour television systems, particularly those that interleaved red/green/blue frames to achieve a colour display. Your members might be interested in details on the work on low-resolution colour images done by members of the homebrew community programming for the 1977 video game console, the Atari 2600.

The Atari 2600 has a single-colour capability for two 8-pixel wide 'sprites', which can themselves be multiplexed on a single line to give a 48 pixel wide 'bitmap' display. Single colour. Experiments in the past few years has seen the development of display technology that manages to produce 'full' colour images using these limitations. The full colour is achieved by displaying each scanline alternately with red pixels, green pixels, blue pixels - and on alternate frames 'rolling' the red/green/blue lines either up or down. At the same time, each line's pixels display only the red/green/blue component of the pixels, depending on the current 'line colour'; being drawn. Further refinements to this technique involve using television interlace to reduce the number of frames required from 3 (one red, one green, one blue - all interleaved) to 2 (it's tricky, but I'll be happy to explain in more detail if this is considered on-topic for your members).

One other thing, the 'full' colour range is achieved (even though we only have always-on or always-off red/green or blue) by dithering the component frames (which are 1-bit colour images). The combination of dithering and 'interleaved' frame colours surprisingly produces quite reasonable colour images with very low technology.

I just thought this had some parallels to experiments in early colour TV, and might interest some of your members - and I'll be happy to provide sample images/videos and/or further explanations if requested.

http://www.taswegian.com/TwoHeaded/Atari2600/cb2.mpg gives a VERY brief and hard-to-see example, running on 1977 hardware (each scanline is only ever a single colour, with no shading - pixels are either on or off).