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Clip attributes for logC material: Video or data level?

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Ole Slyngstad
Clip attributes for logC material: Video or data level?
on Mar 18, 2014 at 5:12:27 pm
Last Edited By Ole Slyngstad on Mar 18, 2014 at 5:19:45 pm

I’m grading footage from Arri Alexa in Davinci Resolve 10. The file format is 2K ProRes 4444 in logC.

But I’m a little confused with the level input intepretation for these files. For the “Levels” setting in the “Clip Attributes” in the Media/Edit tab I can choose between Auto, Data and Video for the clips. What setting is optimal for logC material?

ProRes 4444 is considered a data container and Resolve therefore automatically interpret these files as data when I set it to Auto.

But I wanna understand how these files should be interpreted correctly, and therefore I don’t wanna just set clip attributes to “Auto” levels and let Resolve do the choice for me. I grade on a 709 monitor with video levels out to my monitor while Resolve works full range internally.

When I use Resolves built in Arri Alexa LogC to Rec709 LUT with the “Data” setting on the clips, lowest black is more like dark grey and is placed somewhere close to level 32 on Resolves internal waveform monitor (10 bit).

When I choose “video levels” in clip attributes, Resolve does the video to data scale, and the LUTs black level looks better and are much closer to 0. But now the highlights appear to be more clipped. I guess I could recover highlight information by reducing the gain in the highlights or by a roll off. I always use the LUT as the final node in the chain and sometimes as an output LUT if all the clips are of the same file type/format.

So what’s considered to be the best method in Resolve for working with logC files? Selecting data levels probably gives me more latitude but I manually have to push the blacks from 32 down to 0 internally (64 on my monitor). Maybe it’s a good thing? Video levels gives me instant blacks and I don’t have to manually adjust the shadows but then there’s the risk of losing info.


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Juan Salvo
Re: Clip attributes for logC material: Video or data level?
on Mar 18, 2014 at 5:39:28 pm

Resolve's auto is handling it correctly, it's meant to be read as data. It's LogC as in log, as in NOT video gamma, as in needs to be graded.

http://JuanSalvo.com
http://theColourSpace.com


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Ole Slyngstad
Re: Clip attributes for logC material: Video or data level?
on Mar 18, 2014 at 7:10:33 pm
Last Edited By Ole Slyngstad on Mar 21, 2014 at 2:46:02 pm

Thanks for your reply, Juan. I would presume that too, but I've just found this info from ARRIs website on Alexa's technical specs:

http://www.arri.com/camera/digital_cameras/cameras/camera_details/?product=...

Far down on the page under In-camera Recording it says: "All codecs record legal range video with embedded audio, timecode and metadata. [...] Codec: ProRes 4444."

From reading this I believe that it would actually be right to tell Resolve to interpret the Alexa clips as video instead of data, since the Alexa codec records "legal video"? The selection between these two options for Alexa's footage has troubled me, as I periodically get better grading results with selecting video level inputs rather than data.

But this would also mean that Resolve inherently interprets these files the wrong way and therefore preforms an unnecessary stage of legalization on the footage. One of the world's leading grading systems should be able to import Alexa's footage (one of the most widely used digital cinema cameras available) in a proper way.


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Guillaume Cottin
Re: Clip attributes for logC material: Video or data level?
on Oct 22, 2014 at 5:28:44 pm

Yes. All ProRes codecs are by definition Legal range, including Log-C ProRes 4444.
I have also seen that Resolve handles the levels incorrectly, resulting in the Arri LogC to 709 LUT to produce lifted blacks.


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Juan Salvo
Re: Clip attributes for logC material: Video or data level?
on Oct 22, 2014 at 7:16:30 pm

[Guillaume Cottin] " All ProRes codecs are by definition Legal range"

Not quite. RGB containers like ProRes4444 actually generally expect a full/data range signal. YUV containers, like ProRes422 OTOH, generally expect a Legal/scaled signal.

http://JuanSalvo.com
http://theColourSpace.com


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Guillaume Cottin
Re: Clip attributes for logC material: Video or data level?
on Oct 22, 2014 at 8:17:45 pm

This is incorrect. From Arri's website:
"Apple specifies that ProRes should be legal range. Our tests have shown that an extended range ProRes file can result in clipping in some Apple programs. However, the difference between legal and extended coding are essentially academic, and will not have any effect on any real world images."
ProRes codecs CAN contain extended range data (some external recorders like the KiPro do it), but legal range is always the expected setting. In this regard, Arri respects Apple's specifications.
Resolve 10 misinterprets ProRes 4444 footage.


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NubusAvid
Re: Clip attributes for logC material: Video or data level?
on May 22, 2015 at 7:47:05 am

To add weight to Guillaume’s comments, my testing shows that Resolve (11 lite) always applies a studio to full range level change to ProRes 444 QT files.
Assimilate Scratch (play) does the same.
So does Nuke.
As Guillaume says; not such an insurmountable problem with Alexa footage, which is studio (legal) range, but anything full range will be clipped.
Media Composer 8 seems the only software that handles ProRes 444 correctly.
The way MC interpreted ProRes444 was corrected after V7.02, but was not documented anywhere.

Check for yourselves.
Herewith a clip containing superblack (0) and black (16):
http://courtyard.livedrive.com/item/08207bfc7cbf49a08cf2dc2721c33fc0

The superblack bars left and right of the grey bars are there when ingested into MC8.



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NubusAvid
Re: Clip attributes for logC material: Video or data level?
on May 22, 2015 at 7:52:40 am

To add weight to Guillaume’s comments, my testing shows that Resolve (11 lite) always applies a studio to full range level change to ProRes 444 QT files.
Assimilate Scratch (play) does the same.
So does Nuke.
As Guillaume says; not such an insurmountable problem with Alexa footage, which is studio (legal) range, but anything full range will be clipped.
Media Composer 8 seems the only software that handles ProRes 444 correctly.
The way MC interpreted ProRes444 was corrected after V7.02, but was not documented anywhere.

Check for yourselves.
Herewith a clip containing superblack (0) and black (16):
http://courtyard.livedrive.com/item/08207bfc7cbf49a08cf2dc2721c33fc0

The superblack bars left and right of the grey bars are there when ingested into MC8.



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