Post by @gsuberland@chaos.social

2026-03-12 22:16 UTC

@emilyyoung@tech.lgbt @moira@mastodon.murkworks.net it's because you want to keep the picture out of the noise floor. if your brightness range goes all the way down to 0V then any noise superimposed on the signal appears in your black regions, and that's where your eye is most sensitive. PAL inverted the luma for the same reason. that way any of the noise floor ends up in the white portion where you can't really see it, and the blacks come out nice and solid.

Replies (2)

@gsuberland@chaos.social 2026-03-12 22:19

@emilyyoung@tech.lgbt @moira@mastodon.murkworks.net if you want a cool book on this subject, check out A Technical Introduction to Digital Video by Charles Poynton. the title says digital but it covers all the analogue gubbins too. it's got all sorts of interesting tidbits in there about video modulation schemes, colour representation, and demodulation tricks.

Open ##2944918
@emilyyoung@tech.lgbt 2026-03-12 22:21

@gsuberland@chaos.social @moira@mastodon.murkworks.net Yeah, I've been reading up on how NTSC's colour subcarrier was chosen to fit between the peaks of the luma signal to reduce interference in the low end. They knew what they were doing, even though by today's standards it seems very limited. Properly formatted signals and calibrated equipment looked and looks pretty good! If only NTSC land had the foresight to do what PAL did and ... "Alternated" the colour "Phase" between "Lines". Wouldn't have needed a tint control then, though my limited understanding is that the 29.97Hz timing drift vs 30Hz had a similar effect of reducing interference between lines.

Open ##2944919