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This is something I think you should know about, I leave it to you to decide whether it is a bug or not.

Camera details: Fuji X-T3 shooting in F-Log at 1 stop over exposed (1 to 2 stops recommended), 10-bit interframe HEVC at 200mbps.

Cinelerra settings: Preferences YUV colour space BT709, YUV colour range JPEG. Off camera clips are imported as they come, no transcoding first.

I have two types of footage, some with clear blue Mediterranean sky, some with cloudy English sky. To produce a good quality output from blue sky, without 8-bit style banding, Format Colour model needs to be set to RGBA-FLOAT. However if I import cloudy shots, often highlight details are missing with or without applying a Fuji LUT. On the waveform monitor those cloudy shots straight line at 100, trying to pull the highs down, no matter what effect I apply, only darkens the image. If I set Colour model to YUVA-8 Bit the full waveform shows in the monitor and the detail is restored, however when I try to colour correct and increase saturation, the highlights start to turn magenta and it does not make any difference which effect I use. It can be done with care, but if I use the same model for blue sky I get banding. 😣 

I have tried resetting colour space and range, the effects I use and the stack order, with or without a LUT. Camera exposure needs to be at least 1 stop over to get the best out of F-Log.

I get no similar problems with the other NLEs I have tried including Flowblade, Kdenlive, Olive, Shotcut, so I am afraid, sadly, I am off to one of those to complete my latest project.

This topic was modified 4 weeks ago by DeJay
3 Answers
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Any undesirable behavior is considered a bug. So far I have taken some sky pictures in jpeg format, loaded them into Cinelerra, and read up on "banding".  I am trying to produce a good test case to show GG using the Videoscope plugin but I simply do not understand it enough to provide a demonstration of the problem (it is an inexpensive Sony camera but that should not make a difference).  I have informed him of the issue but right now he is still "gone off the reservation" and is seeing if he can get Cinelerra working on Windows (but why?).

 

There have been similar type reports of this in the past but we have never been able to see the problem so it could be addressed fully.  If we can produce an exact demonstration, then there might be a way to fix it.  If at some point, someone has time and motivation to send 2 jpegs that will clearly demonstrate the blue skies / grey skies problem, then at least we have a better starting point.

@phylsmith2004

Phyl, from my point of view you are looking at it from the wrong perspective, maybe I did not explain it well enough. The problem is losing highlight detail when working in RGBA-FLOAT. The illustration of YUVA and, therefore, magenta highlights and blue sky banding was to show that a. The full waveform is there in YUV but RGBA chops it off and b. that YUV is not useable for my footage. There is no banding when working in RGBA.

I attempted to attach some PNG screenshots from Cinelerra, but the post will only accept one at a time, sorry to do it this way........

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Usually the magenta cast in the highlights is an indication of low dynamic range that also leads to clipping and banding. I would exclude Fuji and since it goes well in the other NLEs, I would say that the blame is in some step or plugin of CinGG that reduces the video to 8 bit and maybe even to yuv420. Finding the weak step is impossible for me, because each step has its own way of treating and transforming colour spaces as it pleases.
Try looking at a post of mine here on the forum, to see if some advice works for you:
https://www.cinelerra-gg.org/forum/forum-miscellaneous/color-management-in-cinelerra-gg-infinity/

@andreapaz

I agree but, if you look at my reply to Phyl (which was posted after yours), you will see that my problem is RGBA-FLOAT performance, since it does not seem to be able to handle full range 10-bit log footage input properly. There is no way I want to reduce it to 8-bit until I have to for output and my tests in YUVA-8 Bit were just to see what happens.

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@DeJay

Thanks for the clarification and the png's.  GG has made an improvement and it is in the new builds released today.  We do not know for sure if it fixes the "loss of highlight detail" that you are experiencing, but it seems to for us.  PLEASE let us know if it does or does not correct the problem.  We have to get this understood and fixed for sure.

This post was modified 3 weeks ago by PhyllisSmith

@phyllissmith

Thanks Phyl and GG, it has corrected the issue. I tested with two different cloudy sky projects and with some blue sky in case it has affected that, which it hasn't.

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