Commodore Colors

 From an article by Philip "Pepto" Timmermann

Commodore VIC-II Color Analysis (Preview)

The C=64 (with its VIC-II chip) features a palette of 16 colors.
cCommodore C64 colors.PNG

Black, White and the three Greys are no colors and the "light"-versions of Red, Green and Blue are just brighter versions of Red, Green and Blue. That leaves us with eight unique colors.

Since the color-palette of the VIC-II has been made for the TV-system, we aren't talking a RGB-color-space, but a YUV-one (for PAL-TV that is), that we can convert to RGB later.

"Y" in the YUV-color-space is the Luma-signal which is just the "black&white-part" (the brightness) of the colors. "U" and "V" are color-difference signals, which together describe the hue and the saturation of the colors.

color wheel.PNG

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bilherd's picture

OMG, don't even get me started on VIC2 colors.  One of these days I'll post an article "Colors, Colors, Colors!" as there is just so much to say.  But in regards to this, I used it as a basis color model for my C128 Media Player (video portion).  It gives fairly reasonable emulation of VIC2, but some colors still seem a bit off.  There are some different luminances between chips, so I played with them a bit... but never found anything that was very good.  (Note it does give good/reasonable but not very good.)
After further research, I'm thinking the problem may be a difference between NTSC and PAL color generation.  As far as I can tell, the phase angles were meausred from PAL chips.  Now PAL has an orthogonal color axis: U and V are 90 degrees apart in color space.  But in NTSC the I and Q axes are about 73 degrees apart in color space.  Note I am talking about color space... for actual QAM generation the two signals are 90 degrees apart in either case.  Well this is my understanding, I don't have a dual-channel O-Scope with phase-locked-loop to verify this!
So I think Pepto's article is a very informative, but just wondering if anyone has any more info as to how the NTSC color phase (or colors in general) would differ from PAL?  For example, he seems to use U as his reference phase (zero degrees) and equates it with Blue... but YUV Blue is not exactly 0 degrees; it is something like 10 degrees off!

For example if the color wheel runs from Red = 0 degrees to Green = 120 degrees to Blue = 240 degrees, then the U axis corresponds to 250 degrees and V is 340 (-20) degrees. Another thing: the I of YIQ is nearly opposite, being the orange/flesh hue at 22 degrees (the Q axis at 275 degrees).
Err, sorry this is really hard to talk about without several diagrams to refer to... so I guess I need to make that web page :/  But still, any info about how the YIQ colors of the VIC2 differ from PAL (in particular, phase angles) would be informative!

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