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The Apple II has a very weird graphics mode in which each byte stores seven pixels plus a palette bit. On a monochrome monitor, the palette bit is unused and th
by kmeisthax 5y ago
The Apple II has a very weird graphics mode in which each byte stores seven pixels plus a palette bit. On a monochrome monitor, the palette bit is unused and the seven pixel bits just become black or white dots on the screen. On an NTSC color TV there's an additional color signal added to each block of seven pixels, and through the use of artifact color the seven dots per byte becomes three-and-a-half color dots per byte.
At first I thought this might be referring to the palette bit - as this was almost certainly intended for B&W operation that bit is free to be used for other purposes. However, that's the high bit. Using the low bit would mean every seventh column of pixels would need to be white. Either that, or the engineer in question misremembered something and actually meant to say the palette bit.
- tenebrisalietum 5y agoI can't find any information or examples on it at the moment, but doesn't the palette bit shift the remaining 7 pixels one pixel when viewed as monochrome?
- a1369209993 5y agoIIRC, it shifts them half a pixel, regardless of whether it's color or monochrome, and that's why it affects the palette. In color mode, the on/off pixels form a psuedo-sine wave, and the phase of this wave determines the color: if it's on even pixels you get green, if it's on odd you get purple, if it's on even-and-a-half you get orange, and if it's on odd-and-a-half you get blue (give or take which alignments are even/odd and half/whole, since I can't remember, but that's the basic idea).