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Colour levels confusion when exporting TIFF image

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Juan Juig
Colour levels confusion when exporting TIFF image
on Jan 20, 2018 at 12:45:08 pm

Hello,

I have exported a still TIFF image from Avid Media Composer. Outside of avid, the image seemingly has different gamma than the original video, even though when I reimport it back into avid, the Y waveforms seem to be identical and in the preview window the re-imported image and original video also seem identical.

What's odd is that when I compare the original video and the exported TIFF in Davinci Resolve, the waveforms are different and in the preview window the image is different (has different gamma, contrast).

How is it possible that the image and video seem identical (in terms of waveform and preview) in Avid, while in Davinci the waveforms and previews are different.


Export settings for TIFF: No compression, automatic bit depth, 100 quality, color levels 601/709 (if I use RGB option the image outside of Avid seems okay and in Resolve the waveforms are identical to the original video, when I re-import that back to Avid the blacks seem crushed and the waveform is different from the original).

I am using Avid Media Composer 7.

Original video file: Quick time wrapper, DNxHD 175X (24fps), exported from Davinci Resolve.


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Job ter Burg
Re: Colour levels confusion when exporting TIFF image
on Jan 20, 2018 at 2:47:51 pm

This makes perfect sense, the video is Rec709 legal, so blacks at 16, whites at 235, whereas your computer monitor (and graphics software) expects blacks to be between 0 and 255. Hence the option to maintain levels as they are (601/709, maintain, 16-235), or expand to full swing ('RGB', 0-255). http://www.jobterburg.nl/Publications/601_709_RGB.pdf


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Juan Juig
Re: Colour levels confusion when exporting TIFF image
on Jan 20, 2018 at 3:22:26 pm

That indeed would make sense if all the levels would be between 16 and 235. But the waveform sometimes shows parts that are out of this range. Meaning that these parts would be crushed if I exported them as RGB.

The colour grader that exported the files was working in Rec 709 full swing in 10bit colour space. When I play the video in VLC it seems right. Also if I export the same as source from Avid, VLC shows the video "the right way" (and on a computer monitor!) even though there was no remapping done. Why does the washed out colour problem occur with tiff export?


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Glenn Sakatch
Re: Colour levels confusion when exporting TIFF image
on Jan 21, 2018 at 10:44:50 pm

Don't forget, when you look at these in Resolve, it is also making an assumption on video levels, as is Avid.
So just because they don't look the same, doesn't mean Avid did something wrong, or Resolve did something wrong, it could simply be that Resolve in interpreting them incorrectly. It defaults to Auto for the interpretation, which I find to be wrong about 50 percent of the time. I would guess a tiff sequence probably needs to be set to full data levels in Resolve in the clip attributes.

Glenn


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Juan Juig
Re: Colour levels confusion when exporting TIFF image
on Jan 22, 2018 at 3:21:57 pm

But here's the thing: I know for a fact that inside Avid (at least within version 7) everything looks washed out.

Also: my video file from resolve was exported as "full levels" and in Avid I can see that colour levels are often out of legal (16-235) range. And that's how it's meant to be.

If I export the video (that is now imported to Avid and also has 'illegal' values) with same as source 601/709 quicktime setting the export looks right in VLC player and different from Avid preview. Which is absolutely fine. I always have in mind that Avid's preview (in my version: 7) is not accurate and shows footage as if it had less contrast.

But my problem is the following: the still TIFF that I export from Avid looks exactly like the the preview in Avid. Meaning that it is also different from Same as source export.

And that is what I find odd. Could it be that the pictures use different standard colour space than videos and therefore behave differently with same export settings? Could it be an internal Avid 7.0 version bug?

Best regards


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