alt Hacker News> broadcast systems historically used 16-235
For 8-bit, 16 maps to 7.5IRE which is the well understood legal black. Mapping 235 means they mapped peak to 110IRE. This is based on a 0-120IRE scale. This gets weird as the broadcast limit for video was 100IRE allowing for the chroma to reach 110IRE. So if you're trying to limit your white values to 235, that'll be higher than is broadcast safe. Of course, nobody cares about NTSC broadcast limits any more. However, to this day, I still see out of spec tapes marked as "broadcast master" that have been ingested for streaming use. It drives me crazy to this day, and it's only getting worse as people don't even have scopes to adjust the VTR's TBC properly.
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Ugh. Sudden flashbacks to having to switch analog output between Japanese NTSC (no pedestal) and US NTSC (with pedestal) without getting weird noise in the black regions.
But IIRC the MPEG-2 standard had luma==235 -> 100IRE for all of the analog formats (pal/ntsc-j/ntsc/secam) so I'm not sure why you say that would violate the broadcast limits?
> For 8-bit, 16 maps to 7.5IRE which is the well understood legal black. Mapping 235 means they mapped peak to 110IRE.
Generally no -- in an 8-bit NTSC-M Rec. 601 system, 16 maps to E'Y = 0 at 7.5 IRE, and 235 maps to E'Y = 1 at 100 IRE. See https://www.poynton.ca/pdf/Poynton-1996-TechIntrDigiVide.pdf
The "16" digital black level is independent of the "7.5 IRE" analog setup. E.g. in Japan with an 8-bit "NTSC-J" Rec. 601 system, my understanding is that 16 still maps to E'Y = 0 which is now at 0 IRE, and 235 is still E'Y = 1 at 100 IRE.