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ATSC Broadcast Color Spec
updated 12 years ago
6 Members
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17 Posts
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Out of curiosity, since the switch to digital broadcasting, is the broadcast community still recommending Rec.709 with 16-235 levels or since the picture itself isn’t part of additional data transfer, that you’ve seen Rec.709 with full swing 0-255?
Out of safety/ignorance I’ve been conforming all my tv work with 16-235.
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I don’t know (interesting thought though).
At the end of last year I had to provide 2 versions of the same items both on tape and electronically, so I made one set (the ones going to tape) normally, i.e., 16-235, then made the electronic versions and encoded them to the specs I was given. As the specs didn’t mention the video levels I didn’t alter them, so they got 16-235, and they passed tech review. So I guess I’ll stick with 16-235 until told otherwise…
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Maybe Dave LaRonde (who I know from reading here is well versed in FCP) or someone else can help explain. These color issues between different NLE’s have messed with my mind from time to time.
We are an FCP based facility and I know very little about AVID.
Every time a client gives us a Quicktime from their AVID in rec.709, it appears to be mapped over 16-235 and black/white levels are wrong coming out of FCP, wrong on all the scopes regarding what digital black and white should be, basically it’s washed out as black comes in around 10IRE and whites barely hit 100IRE. If they export from AVID with RGB instead of rec.709, then the levels seem to be on (or at least close enough) for outputting from FCP. I could be wrong, but it seems to me that FCP is based on full swing 0-255 because everything including graphics that adheres to that space is proper coming out of FCP, verified on scopes. FCP plug-ins that allow RGB value inputs are also using 0-255 scales.So, are the color specs really different between different NLE’s or is rec.709 truly 16-235 across all HD video and FCP has an internal conversion algorithm that maps it out as 0-255 when it’s really 16-235? My scopes tell me that 0x0x0 is 0IRE and 255x255x255 is 100IRE…
Chad Brewer
Senior Broadcast Videotape Operator
TeleVersions, LLC -
I could be wrong as I don’t cut with FCP, but it sounds like it MAY be their gamma shift issue. I conform/color correct all of my footage with After Effects on a calibrated monitor because it’s an ICC color managed application.
I found this on another forum:
FCP assumes that you are working on a 1.8 system and therefore need a gamma adjustment to match the 2.2 broadcast gamma. So FCP automatically adjusts the gamma for certain imported footage. The rules are as follows since FCP 5.1.2:– Quicktime movies that use Y’CbCr codecs (like Uncompressed, DV, etc.), get no adjustment (assumed to be 2.2 from the start).
– Quicktime movies using RGB codecs (like Animation) and still images (like TIFF) use the setting in Imported Still/RGB Video Gamma (either Source, 1.8, 2.2, 2.22 and Custom). This is kind of new in recent versions (I can’t remember when it was added), but in the past, all RGB video codecs got an automatic adjustment of 1.22 (got brighter). Now it’s controlled by the same setting as for still images.Things were more complicated before FCP 5.1.2 where there rules were different and files were also adjusted on export (for example TIFF would get a .824 gamma shift – made darker). This doesn’t happen anymore.
You can test the whole thing by creating a gradient in FCP and viewing it with the Waveform Monitor in the Video Scopes:
– Create a grad, view it in the scope and you’ll see it as a straight line going diagonally.
– Export the grad as a TIFF. Import the image back into FCP with the Imported Still gamma set to Source. The grad will now appear brighter and the scope will show a bump in the mid tones duo to the applied gamma adjustment of 1.22.
– Now change the gamma for the imported clip (cmd + 9 on the clip in the sequence). Under Format > Gamma change it to 1.8. Nothing will change because any still imported into FCP is assumed to be set to 1.8.
– Now change the gamma to 2.2 and you’ll see it revert to the original grad with the same straight slope in the scope.There’s more to this once you start adding Motion (which again assumes that everything coming in is 1.8 and exports everything as 1.8).
Working for TV and need to be sure of your content? Use a broadcast monitor. Only then can you spot all these differences and will you know exactly what will be displayed on a TV.
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Chad So, are the color specs really different between different NLE’s or is rec.709 truly 16-235 across all HD video and FCP has an internal conversion algorithm that maps it out as 0-255 when it’s really 16-235? My scopes tell me that 0x0x0 is 0IRE and 255x255x255 is 100IRE…
It’s nothing to do with different NLEs, although some will modify inputs and outputs differently to others. Black=16 and White=235 is correct. Quick guide to rec.709 here: https://en.wikipedia.org/wiki/Rec._709
(IIRC the full spec is behind a paywall) -
Slight revision my last post – I’ve just found the ITU-R 709 official recommendations here: https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.709-5-200204-I!!PDF-E.pdf
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Angelo/Andrew,
Thanks for the responses. I don’t believe it’s a gamma issue at all as I’ve done color correction on these types of clips where gamma never had to be corrected, only lifts and highlights were translating incorrectly.
I’ve previously read the rec.709 specs in detail and I’m trying to gather how FCP handles the values. What I’m looking for clarification on is whether the video signal values are 16-235, but FCP has been designed to handle them/map them to 0-255 like computer graphics software, e.g. it behaves consistently like a program like Photoshop. Some say 0-15 is reserved for super-black and 236-255 is for super-white. If that is the case, then in FCP super-black and super-white are either below 0 or above 255 as translated on this scale…
So, is it just an issue of how FCP is designed to interpret what is always 16-235 for black/white in the video signal? Seeing the differences between AVID and FCP is what has made me curious about this.
Chad Brewer
Senior Broadcast Videotape Operator
TeleVersions, LLC -
As far as I’m aware, FCP doesn’t change the levels unless you tell it to (the difference with Avid is that Avid puts that option in your face when you import, whereas FCP doesn’t), so where you have footage that comes from a video camera the levels will be as the broadcasting spec and signals over 235/100% are essentially overexposure (giving you the chance to correct it rather than just clip it).
As an experiment, I’ve just imported an image from photoshop and peak level is at 255, so FCP isn’t changing anything automatically.
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[Angelo Lorenzo] “Out of curiosity, since the switch to digital broadcasting, is the broadcast community still recommending Rec.709 with 16-235 levels or since the picture itself isn’t part of additional data transfer, that you’ve seen Rec.709 with full swing 0-255?”
8b Digital Video is always mapped at 16-239 (Luma 0-100%).
There is room for highlights and “SuperBlacks”, so you will need to adjust those (and Chroma and RGB) to the very specs of your distribution system.
rafael -
Hey Rafael,
So, can you offer answers to my posts in this thread regarding how the signal appears to be mapped from 0-255 in FCP. For example, if I choose a color in FCP that is 255x255x255 it is 100IRE on the scope where 235x235x235 is not 100IRE. Is this just how FCP happens to map the signal?Thanks.
Chad Brewer
Senior Broadcast Videotape Operator
TeleVersions, LLC
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