NTSC Pennant?

[old_tv_nut]

Originally Posted by W.B.

It seems, based on the colors as registered in this JPEG file, that 205° would be the RGB position for -I, 24° for +I, 275° for +Q and 95° for -Q, would that sound correct? (Being that RGB values are different from the phase positions in video language.) I had done my own research of position values in Photoshop and Corel Photo-Paint 11, and had come up with:
- 204° for -I
- 24° for +I
- 272° for +Q
- 92° for -Q

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.