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stig olsen
709 export / ranges
on Jun 8, 2012 at 1:31:36 pm

709 export
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Hi,

I do all my grading in Davinci with the normal (legal) scaling on which means I get legal waveforum values (16-235) both in Davinci and Avid. This is a good solution for TV-commercial work. When I render from Avid to file delivery for TV, I simply export my legal values to RGB as it will be remapped back to 709 on the encoder (adstream / Adtoox) used before broadcast.

But, when I export the same TV-file for web delivery I need to compensate a little.
If I export 709 it will look ok, but not as good as on the monitor (set up for 16-235) as the monitor read 16 as black. A computer monitor dont. That will give me a little dull image, but the details are there. How do you compensate for this export?

There is no solution to export RGB for web delivery because it will blow out the highlights and cranck the shadows if the luma fills the waveforms from 16-235.



Stig


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Job ter Burg
Re: 709 export / ranges
on Jun 8, 2012 at 1:47:55 pm

I leave it 709, export same-as-source or QT Ref, and then when encoding for the web I set a Black Restore and White Restore in Squeeze.

You can however export as RGB. That will remap your legal 16-235 to 0-255, and that should be fine.

I don't think your assumption of blown-out highlights is correct. If your luma range in Avid/DaVinci is between 16 and 235, an RGB export will remap that to 0-255, and nothing will be crushed or clipped.

Also see this document for some tests:
http://www.xs4all.nl/~terburg/Publications/601_709_RGB.pdf

Do note that using Quicktime (which is what Avid uses when you do anything other than Same-As-Source or QT Reference) to export to certain codecs (like ProRes and H264) will cause gamma shifts. Better to handle it in a decent external encoder.

On a sidenote: I'm no big supporter of the double remap you are using (709 to RGB then RGB to 709), as it is bound to cause rounding errors. In essence, you are doing two passes of rendered color corrections on top of each other, the second undoing the first. Not a clean workflow, in my book.

But I'm not sure if you can get your encoder to go around it.


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Daniel Frome
Re: 709 export / ranges
on Jun 8, 2012 at 2:11:08 pm

Avid 709/RGB function is a tad more tricky than you're describing.

In Avid speak, exporting with the 709 setting means "don't change any values."
Exporting RGB means "shift the 16-235 values to 0-255"

[stig olsen] "That will give me a little dull image, but the details are there. How do you compensate for this export?"

This means that your video actually has color values outside the 709 legal range. And exporting as 709 from Avid does not mean your file is 709 legal. As said above, it only means that Avid won't change the values on your export. That's why, when you export as RGB, you're losing some data -- as there was information in the 0-16 / 235-255 range that you are now pushing out - since the RGB option is simply going to force the 16/235 marks and extrapolate out to 0-255. I hope this make sense and I have described it properly.

Sorenson Squeeze, when using the Mainconcept H264 encoder, has the option to properly remap these values. See screenshot:


I THINK the highlighted option is what you're looking for (a 709 export, but with 0-255 range), but I can't be sure. Experiment with the different values and check the results. Hope this helps.


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stig olsen
Re: 709 export / ranges
on Jun 8, 2012 at 2:25:02 pm

Thank you guys, I follow you.

My waveform only show values between 16 and 235, but when viewing this file when exported as RGB, it really do give blown out hightlights.
Daniel, you say I loose some data when I export RGB, that is what Im experiencing. Job, you are experiencing the opposite?

Thank you both for the black restore tip. Then I guess I will export 709 for web and use the black restore option. I didnt know it existed.

About the double remap thing. The adstream/Adtoox decoder (those who approve the upload for TV in norway) tell me they need the film in RGB (full range) as they remap it back to 16-235. If I deliver 16-235 they will double-remap the film and it will look bad on TV. Thats why I have to do it this way. Any other solution?

Stig


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Daniel Frome
Re: 709 export / ranges
on Jun 8, 2012 at 2:32:59 pm

[stig olsen] "The adstream/Adtoox decoder (those who approve the upload for TV in norway) tell me they need the film in RGB (full range) as they remap it back to 16-235"

Well then they leave you with no choice, probably just keep doing what you're doing.

Read this to learn more:
http://terburg.home.xs4all.nl/Publications/601_709_RGB.pdf


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stig olsen
Re: 709 export / ranges
on Jun 8, 2012 at 2:41:42 pm

I have read the documenta and find most of it to be correct, except the luma expanding when exporting RGB.
I have always experienced that my whites are blown out when exporting RGB even though my values are between 16-235.
What are your opinion on that?


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stig olsen
Re: 709 export / ranges
on Jun 8, 2012 at 3:16:48 pm

Daniel, can you please follow this thread? http://community.avid.com/forums/p/109958/637214.aspx#637214


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Daniel Frome
Re: 709 export / ranges
on Jun 8, 2012 at 3:26:30 pm

No, if I have a proper 235 white, and I export as RGB, the white renders out as proper 255 white - not blown out, but very bright of course.. But again - this is viewing on a computer monitor. If you view on your 16-235 monitor, then of course it will look blown out.


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stig olsen
Re: 709 export / ranges
on Jun 8, 2012 at 3:36:11 pm

Ok, maybe my computer monitor is set to 16-235... I will try the file on some other systems and laptop at home.


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Job ter Burg
Re: 709 export / ranges
on Jun 8, 2012 at 5:19:40 pm

Download the HD Test Chart from Belle-Nuit.com. Open it on your desktop. Do you see brightness difference between 255 and 251? If not, you need to turn down the contrast on your computer monitor.


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Job ter Burg
Re: 709 export / ranges
on Jun 8, 2012 at 5:18:37 pm

Stig, as I wrote in the other thread, if you cannot distinguish between the 231 and 235 whites in the document, then your monitor is not set up correctly, and you should turn down the contrast.

Or, and this is also very possible, a straight remap from 16-235 to 0-255 might just look different on a computer monitor, and you may prefer to use a LUT with a slight gamma curve to have it look nicer on your computer screen.


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stig olsen
Re: 709 export / ranges
on Jun 11, 2012 at 9:02:26 am

You are correct, I downloaded the chart and my contrast was set wrong.
Thank you guys!


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