Quote:
Originally Posted by old_tv_nut
I'll have to check out the code when I get back home. This simulation was done in Photoshop by writing custom Photoshop filters to do the matrixing, chroma modulation, filtering, and demodulation, would you believe? I just love perverting software to do things I want that it never was intended to do.
By defining the +/- I and +/- Q subcarrier peaks to fall on pixel locations, modulation and demodulation can be simulated by multiplying by a pattern of
(+1,0,-1,0) or (0,+1,0,-1).
The +I channel should be at 33° electrically with respect to scaled R-Y and scaled B-Y, and the other three phases at 90° increments. You have to be careful that you are working with properly scaled R-Y (divided by 1.14 if I recall correctly) and B-Y (divided by 2.03 if I recall correctly) before converting to I,Q. The values you found may be correct when calculating angles in the RGB domain, that is, with straight R-Y and B-Y.
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I found that +(R-Y) in RGB domain was 340°, while -(R-Y) was 160°; +(B-Y) was 250° and -(B-Y) [a.k.a. NTSC 'burst'] was 70°; and G-Y=0 values were 43° and 223°. I also found the +/-I and +/-Q values through taking the YCbCr calculations in color bars and changing the luma from 16 to 126.
I am aware that RGB values are different from what is registered on color vectorscopes.