Color Without Color: Apple II Computer Graphics #Apple #Hacking #Video #AppleII
A great write-up by paleotronic on how Steve Wozniak was able to get color from monochrome for the Apple II computer:
Released in 1977, the Apple II was one of the first personal computers marketed towards households rather than businesses. It was a complete computer – it had a keyboard for data entry and the ability to connect to a CRT monitor or a television set. However, unlike its competitors, the TRS-80 Model I and the Commodore PET 2001, the Apple II was able to display colour – but remarkably, it accomplished this without a dedicated colour video chip. The Apple II’s video hardware is actually monochrome!
So how does it display colours? The Apple II’s designer, Apple co-founder and chief engineer Steve Wozniak, discovered that if he repeated portions of the outgoing digital luminance signal (black or white) and injected it into the “colorburst” or NTSC colour signal, various patterns of pixels produced lines of different colours.
The “native” monochrome resolution of the Apple II is 280 pixels wide by 192 pixels deep. Each pixel is either on (1) or off (0). Steve found that using blocks of two pixels, he would get black (00), purple (01), green (10) and white (11). By shifting the timing of the colour signal, Steve was able to get an additional two colours, blue (01) and orange (10). This left him with a “high resolution” graphics mode (HGR) of 140×192.
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