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ATSC Broadcast Color Spec
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Nice article/exchange about DV, super-black, super-white, etc.
https://www.larryjordan.biz/articles/lj_white.html
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Thank you all for chiming in on this thread! The last few posts have cleared things up for me as well as support what I believed was going on all along in FCP.
Despite not starting the thread, some of these issues had been bothering me for a while. Being an FCP only editor at an FCP based facility, it first started bugging me when my clients’ exports from their AVID’s didn’t have proper black/white levels when brought into FCP. Furthering the madness was how I now know FCP handles levels – between either FCP or the corresponding AJA, Blackmagic, etc. capture cards, the output signal is in fact proper 16-235. What was confusing things the most for me is that within FCP, all of its channel controls go from 0-255 like computers/graphics, instead of 16-235 which is correct for broadcast video. So, after having understood all of this for years in terms of video signals, it was mostly how FCP “represents” things within itself as a program that was throwing me for a loop.
All in all, I’m not versed at all in AVID, but when my clients export Quicktimes from their AVID with rec.709, the levels are wrong in FCP. When they export with RGB, black is black in FCP. I still can’t figure that out, but at least I now know what’s going on with 16-235 in FCP outside of that issue.
Thanks guys.
Chad Brewer
Senior Broadcast Videotape Operator
TeleVersions, LLC -
Chris, the latter half of your post answered my question perfectly. I actually did some additional digging and found that digital still uses the value of 0 and 255 for sync pulses.
Like I mentioned in a previous post, I use After Effects to conform my footage as it’s color managed. It allows up to 253 for spectral highlights.
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[Chris Wiggles] “It appears to me, at least I have always assumed, that FCP displays much as QT displays video on playback: it expands the range to 0-255. But that the actual video is 16-235.
So for instance if you just pop a DVD in, or a test DVD, your computer will re-map that on playback by default to the 0-255 range, thus clipping below 16 and above 235 in the video.”
Video signal is 0-255. Is the luminance that have to be kept between 16-235.
On display, the 100% Y’ value (b235, 100 IRE) must be mapped-back to 8b RGB as 255x255x255 = Pure White.
Everything on top of 100 IRE is clipped as white too because we have not more RGB values to represent them.
With 10b RGB monitors this is not like that.DVDs do not allows this head-room for super-blacks-whites. When you making the MPEG-2/DVD compliant, all values below 0% or over 100% gets clipped.
[Chad Brewer] “All in all, I’m not versed at all in AVID, but when my clients export Quicktimes from their AVID with rec.709, the levels are wrong in FCP. When they export with RGB, black is black in FCP.”
As Steven Jobs would say: ” Mapping is a world of pain”.
Each NLE, Graphic application, and some codecs seems to fallow his own rules.
rafael
rafael -
Hi Chad,
When we bring 8b RGB to that sequence, 0-RGB (Black) should be 16 (0 IRE > Y’ = 0), while 255-RGB (White) should be 235 (100 IRE > Y’ = 100%)).The problem is that FC behaves in different ways depending where the graphics come from:
a) If you are importing the graphic (PS, PNG,..):
– By default are mapped to 16-235.
– But if you set the famous “SuperWhites” option, the mapping will be to 16-255.
Make a test with a white still from PS and see how the Waveform changes when you check/uncheck “SuperWhites”.b) If you are generating the White in FC: That will depends on the tool that is generating the white.
– The two Color Mattes, now works properly, mapping 0-255 to 16-235. Those values doesn’t change whether your sequence is set to SuperWhites or no.
– The TEXT GENERATOR/ BORIS: Generates 0-255 RGB values that will be mapped depending if the sequence is set to SuperWhites or not.
[Chad Brewer] ” if I choose a color in FCP that is 255x255x255 it is 100 IRE on the scope where 235x235x235 is not 100IRE.”
Those values you are setting, are RGB. They haven’t been been mapped yet.
The secret is the SuperWhites.
Your 235-235-235 will be pure White (100 IRE) as soon as you change your sequence to “SuperWhites”.
So if you use in Boris-3D the default 234x234x234, that will be Gray on a normal sequence.
If you change to “SuperWhites”, you will see that the Gray becomes White on your scope.Don’t miss this:
https://www.kenstone.net/fcp_homepage/video_levels_nattress.html
The graphics for the RGB-YUV mapping are very clear.
rafael -
Rafael, thanks for the further helpful info. Much appreciated!
Chad Brewer
Senior Broadcast Videotape Operator
TeleVersions, LLC
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