Apple II SeriesSee also: Apple II graphics
The Apple II series features a 16-color composite video YPbPr palette, that comprises 15 different colors plus a duplicate gray.
Number — name Y Pb (rel.) Pr (rel.) Number — name Y Pb (rel.) Pr (rel.) 0 — black 0 0 0 8 — brown 0.25 -0.5 0 1 — magenta 0.25 0 0.5 9 — orange 0.5 -1 1 2 — dark blue 0.25 0.5 0 10 — grey #2 0.5 0 0 3 — purple 0.5 1 1 11 — pink 0.75 0 0.5 4 — dark green 0.25 0 -0.5 12 — green 0.5 -1 -1 5 — grey #1 0.5 0 0 13 — yellow 0.75 -0.5 0 6 — medium blue 0.5 1 -1 14 — aqua 0.75 0 -0.5 7 — light blue 0.75 0.5 0 15 — white 1 0 0
Although a bit disordered, some facts can be established:
- there are five levels for the luminance and five levels (two negatives, zero and two positives) for the chroma;
- colors 15 to 8 are the exact YPbPr complementary from the 0 to 7 (also their binary complements), so only eight colors are actually implemented and the rest obtained by inverting the YPbPr levels (hence the duplication of the gray at indexes 5 and 10);
- PbPr levels are chosen to get a regular distribution of the colors in the YPbPb color space within 16 entries and having the maximum (±Pb,±Pr) colors at Y=0.5.
The original Apple II has two graphic modes, along with a 40 columns text mode and some mixed graphic+text modes.
- Low resolution 40×48, 16-color graphic mode, with a 7:4 pixel aspect ratio.
When an RF modulator is employed to plug the Apple II into an NTSC TV set, many colors vary, and, dramatically, the brown and light blue, which when converted from YCbCr to YIQ color space by the RF modulator and to RGB by the TV's built-in demodulator, lie deeply outside of the RGB gamut. The first image simulates a native composite video monitor display, and the second an NTSC TV display:
- High resolution 280×196, 6-color mode.
In fact, high resolution mode is able to light the pixels only in four colors: purple, green, orange and medium blue (pixels off are always black). Pixels on at even columns can be purple or blue, and at odd columns can be green or orange, and any of this purple-green or blue-orange color pairs can be selected for every seven consecutive pixels. A single pixel on also spreads through half of the surrounding pixels on each side. So when a purple-green or green-purple (or blue-orange/orange-blue) pixel pair are both on, this results in an on-screen mixed 2:1 aspect ratio "white pixel", and this is the sixth "color".
Due these color arrangements, the high resolution mode is usually documented to have a "practical resolution" of 140×192 instead of 280×196. It is more simply to think this way for programmers but not more exact, so some surprises usually arise: a vertical line can be of a pure solid color when it has an odd number (1, 3, 5...) of pixels wide alternatively on and off (the off pixels seem to be "on" by the color spread of the aside on ones), but can be "white" when it has any number greater than one of pixels wide, all on; when two vertical, one pixel wide blue and green or orange and purple lines are drawn together, they also becomes colorized bluish, redish, yellowish or greenish "white", depending on the combination, etc.
The way to produce colors in high resolution mode is a pure analog tricky collateral effect. When RGB monitors and adapters became available for the Apple IIgs, users felt than the good oldies high resolution software and games did not look the same. But the Apple IIgs was able to use 4,096 RGB colors with new software, and the original-compatible high resolution 6-color mode was then considered outdated. The first image simulates native composite video monitor display, and the second a RGB monitor display:
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