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difference signals (r-y) (b-y) must not raise above 700 mV or fall below 0 mV when measured with 350mV offset

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Laura Fernandez
difference signals (r-y) (b-y) must not raise above 700 mV or fall below 0 mV when measured with 350mV offset
on Nov 17, 2016 at 10:15:14 am

Hello everybody.

I have a project and I have to respect the next sentence:

programs color difference signals (R-Y, B-Y) should not rise above 700 mV or fall below 0 mV when measured with a 350 mV offset.

I ONLY have davinci resolve to solve this. Im working with 10 bit depth

How can I know if I am going over the limit in this signals??? Which waveform should I use for keeping this okei?? The vectorscope? or the waveform with RGB activated? Which will be the davinci limits for that 350mV offset??

For the Luminance I use the waveform and I respect the 64-940 limits, but if i change that waveform to RGB I see the colors can be over the luminance limit and that scare me. So i dont know if i only have to care about the vectorscope regarding to the chrominance....

Please help me!

I know there are other conversations already about this Issue, but theyre all about luminance levels.

Thank you very much in advance!!!!!


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Joseph Owens
Re: difference signals (r-y) (b-y) must not raise above 700 mV or fall below 0 mV when measured with 350mV offset
on Nov 17, 2016 at 4:59:55 pm

[Laura Fernandez] "I know there are other conversations already about this Issue, but theyre all about luminance levels."

This is an old analog "legal gamut" specification that applies to Standard Def 601 CAV (Component Analog Video) standards. Where did this come from? Are you delivering Betacam SP?

Its about as relevant today as 7.5 IRE pedestal in Standard Definition composite analog video.

You cannot measure it in RGB, because that's not what it is.

Here's the situation you are looking at:
http://jp.tek.com/datasheet/wfm1125-opt-0a-0b-0c-and-0d

Scroll down this datasheet and you will find a waveform example of Y, Pb, Pr and you will see where the 350 mV offset comes from and why there is a 0-700 mV excursion boundary. We don't measure things this way anymore.

jPo, CSI

"I always pass on free advice -- its never of any use to me" Oscar Wilde.


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Laura Fernandez
Re: difference signals (r-y) (b-y) must not raise above 700 mV or fall below 0 mV when measured with 350mV offset
on Nov 18, 2016 at 3:43:50 am

Thank you very much for the info. Nop, there is no betacam, so maybe I dont have to worry about it??

I would like to ask you something regarding to the luminance

For the luminance limit I am respecting the space 64-940 in the da vinci waveform. (we are working in 10 bit depth).
- I am also limiting the RGB waveform to this limits. (is that necessary?), also looking all the time to the vectorscope for not exceeding the limits.
- Should I absolutely respect this limits (for luminance and RGB?? No single little part should exceed these limits?? Or can I pass through them a little bit? because the blacks are completely milky and it look actually bad.

Beside to all this. I have the broadcast safe option ON in color management to a -10 - 110 (would be better 0-100? , or -20 - 120?) My question to this tool: Is this something that works at the exporting moment?? If I activate this tool do I need to respect the (64-940) limits on the Waveform?. Or, if I am respecting the limits in the waveform I dont need to activate this tool??. or viceversa??

They also say I hace to "use the standard ITU-R-BT.709 gamma curves and colorimetry. This excludes masters with all other gamma curves, including log curves."

In the Davinci the actual input/timeline/output color space is Rec.709 Gamma 2.4. (the monitor is in gamma 2.2). Should I change the Input,timeline,Output color Space to just REC.709??

THANKS!!!!!!


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Glenn Sakatch
Re: difference signals (r-y) (b-y) must not raise above 700 mV or fall below 0 mV when measured with 350mV offset
on Nov 18, 2016 at 2:44:05 pm

I find many spec sheets are out of date, as they become more of an "add this to it" scenario rather than starting fresh. Unfortunately many of the people in charge of handing them out dont kow what they are asking for inside the specs anyway.

Glenn


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Joseph Owens
Re: difference signals (r-y) (b-y) must not raise above 700 mV or fall below 0 mV when measured with 350mV offset
on Nov 18, 2016 at 6:07:00 pm

[Laura Fernandez] "In the Davinci the actual input/timeline/output color space is Rec.709 Gamma 2.4. (the monitor is in gamma 2.2). Should I change the Input,timeline,Output color Space to just REC.709??
"


Which is the result of over-thinking things when the blizzard of formats gets thrown at non-technical operators.

"Just Rec709" should result in a 0-100 IRE output at 2.4 gamma, which is the standard. Your monitor should also conform with the data profile that is being sent to it.

There will be more talk now about source-reference and display-referenced profiles and colorspaces. If there is any advantage to the ACES workflow, this might be it, but it requires the understanding that the image is being placed in a universal colorspace and its flow-through values are dependent on the IDT/ODT transforms.

If you are complaining that the blacks are "milky", its because the concept of 64-940 is not strictly relevant to the bit-depth resolution of the source media, but how those data values relate to 0-100 IRE. 709 mapping places "64" at 0 IRE and "940" at 100 IRE. The scalars on the waveform display effectively don't correspond to anything. For the sake of simplicity, take the bottom to be zero and the top to 100 if you are operating in 709 linear.

jPo, CSI

"I always pass on free advice -- its never of any use to me" Oscar Wilde.


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