Posted By
IstvanV
on 2007-09-13
12:28:24
|  Re: So I want to do plus/4 gfx...
When referring to normalization vs. not normalization, I meant different scale factors applied to U and V. The following simple program reproduces the colors of YAPE 0.76 with good accuracy (usually +/- 1 error for the integer RGB values):
http://www.sharemation.com/IstvanV/yapecolors.c
It can be compared to the code I posted on 2007-09-02, which is based on plus4emu 1.2.1 (there are a few minor color changes in 1.2.2, but that is not relevant). U and V are both multiplied by 0.18 there before the standard conversion, while in yapecolors.c, U is multiplied by 0.15 and V is multiplied by 0.21. The reason why I use the same scale factors for both U and V is that this way the hue and saturation are more consistent between the calculated colors and the screenshots (i.e. I get less variation in the chroma level), and also the phase angles for simple colors like red or green result in "pure" colors. But I could be wrong, or have a bad TV card.
I did not read the articles yet, but will have a look later. By the way, in digital video, U and V actually have the same range like I assumed it was the case in YAPE, although the colorspace is more accurately called YCbCr then. In analogue video, the V level is higher I think (by the 0.615/0.436 ratio), so if the TED generates a color subcarrier with a more or less constant amplitude, then my formulas are correct.
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