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Reasons for the palette of the PAL VCS ?


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The pal VCS as a weird palette with :

- colors seems "interlaced"

- there are 3 identical gradients of greys


Today I took another look at this, and emited the hypothesis that color are arranged that way because it helps with generating the PAL signal. So I converted the palette to YUV, and here is how the $x0 colors (taken from wikipedia) are translated :


What is there to be seen ? If you compare an odd numbered value with the next (even) one, you will get almost the same luminance, almost same V as the other color, and about opposite U (well, except for $40)...


Could it mean that, instead of shifting the phase of the color, the pal TIA inverts the first bit of the colors on even lines to select a color that is already phase inverted ?


That would also explain why we have two grey scales for $0x and $1x, but not why the last two lines of the palette are also greyscales.


If I understand the Color Select Decode in the NTSC TIA (page 5) corectly, the delay cells are selected based one the color like this :

Delay [ ][ ][ ][ ][ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
Color  2  3  4  5  6  7  8  9  A  B  C  D  E  F

Where E and F might give the same colors as 3 and 2.


If we want an opposite phase for conecutiv color numbers, the PAL version might look like this :

Delay [ ][ ][ ][ ][ ][ ][ ][ ][ ][ ][ ][ ][ ][ ]
Color  2  4  6  8  A  C  E  F  D  B  9  7  5  3

but now colors 5 and 3 might be the same as 2 and 4. If you use a counter to generate a gradient, some colors might even be reversed.


Could that be a reason to suppress colors E and F ? Or is there something in the timing of the PAL signal or in the speed of the cells (they don't seem to be synchronized with the 4,453125MHz clock ?*) that would prevent from having two more colors ?




* : or are they ? I'm not strong with reading schematics !


Edited by Windless
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