Does it lower the vertical luma resolution or just the chroma?
lets say you have a white screen with a black vertical line.
1,1,1,0,1,1,1
1,1,1,0,1,1,1
1,1,1,0,1,1,1
1,1,1,0,1,1,1
1,1,1,0,1,1,1
with a comb filter:
luma(x) = [ composite(x) + composite(x - scanline) ] / 2
chroma(x) = [ composite(x) - composite(x - scanline) ] / 2
luma:
1,1,1,0,1,1,1
1,1,1,0,1,1,1
1,1,1,0,1,1,1
1,1,1,0,1,1,1
1,1,1,0,1,1,1
chroma:
0,0,0,0,0,0,0
0,0,0,0,0,0,0
0,0,0,0,0,0,0
0,0,0,0,0,0,0
0,0,0,0,0,0,0
it works perfectly. But for a horizontal line:
1,1,1,1,1,1,1
1,1,1,1,1,1,1
0,0,0,0,0,0,0
1,1,1,1,1,1,1
1,1,1,1,1,1,1
with a comb filter:
luma(x) = [ composite(x) + composite(x - scanline) ] / 2
chroma(x) = [ composite(x) - composite(x - scanline) ] / 2
luma:
1,1,1,1,1,1,1
1,1,1,1,1,1,1
.5,.5,.5,.5,.5,.5,.5
.5,.5,.5,.5,.5,.5,.5
1,1,1,1,1,1,1
chroma:
0,0,0,0,0,0,0
0,0,0,0,0,0,0
-.5,-.5,-.5,-.5,-.5,-.5,-.5
.5,.5,.5,.5,.5,.5,.5
0,0,0,0,0,0,0
It doesn't work so well.
Do comb filters band pass the chroma signal after it seperates them from the composite signal?
When I wrote the last post, I realized that the comb filtered chroma signal doesn't resemble any meaningful chroma information.
0,0,0,0,0,0,0
0,0,0,0,0,0,0
-.5,-.5,-.5,-.5,-.5,-.5,-.5
.5,.5,.5,.5,.5,.5,.5
0,0,0,0,0,0,0
If you subtract the signal by it's neighboring "pixels"
chroma(x) = chroma(x)/2 - chroma(x - wavelegnth/2) / 4 - chroma(x + wavelegnth/2) / 4
you get:
0,0,0,0,0,0,0
0,0,0,0,0,0,0
0,0,0,0,0,0,0
0,0,0,0,0,0,0
0,0,0,0,0,0,0
when you subtract the filtered chroma from the composite signal you get the luma:
0,0,0,0,0,0,0
0,0,0,0,0,0,0
1,1,1,1,1,1,1
0,0,0,0,0,0,0
0,0,0,0,0,0,0