Is it a bug or is it because I'm a beginner ?

I’m new in photo editing, so I may be confused, and probably I am.
Here is my issue.
I like to make my own wallpapers with shots from films I like. I have a decent screen (Eizoo CG277) and I’m on W10. My screen has an AdobeRGB profile, and is in 10 bits.

  • So I take with FFMpeg a shot from my 4K disk, and a screenshot with my player (MPC-BE)
  • So I have 2 files, the screenshot with "real’ colors in sRGB, and a 4K file (so very desatured).
  • Then I try to retrieve the “original” colors by comparison with the sRGB shot.

So there begins my confusion.

  • The sRGB screenshot doesn’t come from a camera, so I put “none” on the color profile for screen preview, and the result is OK.

  • For the 4K source, I put “included in source” because source is in AdobeRGB, work space also in AdobeRGB.

  • Then I do all stuff to have the 4K picture looking like the sRGB shot.

  • But, when I watch pixels off gamut, it’s OK for the sRGB, but mostly off gamut for the 4K version (in the blue for the shot I’m working on). And if I try to be in gamut, I don’t have the same colors.

  • When I save the file in AdobeRGB as a wallpaper, it looks good for me.

  • I have to say that the off gamut is not one color, it’s a variation of color, many values of color are “off gamut”.

  • Sorry again if this topic is more a “general” topic than focused on ART.

  • Where am I wrong ?

  • Could it be a bug ?

I haven’t used ffmpeg and can’t understand why the 4k image would be desaturated. Can’t you just load the video in, select the frame you want, and export as image? I’ve done this on proprietary software and never had an issue with colours.

When you use FFmpeg, it exports the frame “as is” without treatment to look like HDR, so the frame is washed out. It seems that there is something to do with gamma correction (not linear curve, the logarithmic one). But I must search about this.
The problem of my player is that it exports the image in 24 bits, 8 bits by channel. And to have a good upscale, I have to use a 48 bits frame. And the player doesn’t export in the original scale (4K) but the current scale instead (the size of you screen). So, not good at all. At least with FFmpeg, I have the real source frame, the one encoded on disk, without any transformation.

@Teto Welcome to the forum!

Without the files, there is no way of knowing what you mean exactly. Please share (drag and drop them directly or put them in an archive first if you don’t want them to be displayed). Keep them vague because they are probably copyrighted material.

My guess is that both images don’t have an embedded ICC profile and so you may have to apply them in whatever app you decide to use. Don’t worry about the working profile. What you should concentrate on is the input profile. If the input is correct, the rest should be consistent. Again, I don’t have the sample files, so that is all I can say for now.

See if my understanding is correct here: You started with log video, which by nature looks washed out and desaturated. You then applied the corrective log tonal curve so the video now has proper contrast and saturation, but when you export the still, it exports the original washed out version instead of the corrected?

If so, perhaps ffmpeg will only export a still of rendered footage, and the log corrections have not yet been rendered? Or perhaps there is a setting you can tick telling stills to export with corrections applied? Having not used ffmpeg its hard for me to know.

If my understanding is wrong, then like Afre suggests, it could be a colour profile issue.

If my understanding is right, but you absolutely cannot export a log corrected image out of ffmpeg, then you should be able to apply the correct log curve in ART, or any image editor. You can apply them as LUTs. They are usually freely downloadable from the video camera manufacturers website. However setting input profile to ‘none’ is not correct. Input profile needs to match the profile embedded in your image , otherwise the colours will be off.

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@everyone :Many thanks for all you answers. In fact there’s a filter in FFmpeg (hidden feature as the filter is not in documentation) that takes the source picture (so washed out) and retrieve original colors (feature discovered yesterday). No need of a LUT, and I don’t like them, as I’d spend more time to find a LUT that would fit the scene, that tonemap manually the picture with ART.

The only thing that I have to check is keeping the tonemapped picture as close as possible to the source, aka keep the file and its content in 48 bits, because Gigapixel (an upscaling program) works wayyyy better with files in 16 bits by channel.

FFMpeg can be cumbersome sometimes, as you have many many options, so I have to check the ones which keep the output the most faithful possible to the input (high color range, pixels value) , between how to handle source, the filter used and how to save the picture.

Anyway, I won’t bother anyone until my tests are done, in the end of August. And if you want I’ll give the command line. Thanks again.

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You do not understand. ALL log footage has a corresponding LUT, designed to retrieve proper contrast and colour. It would take you less time implementing the corresponding LUT (simply google the LUT for your camera, download, and apply) than it would to manually adjust the tonemap. (It would do exactly what that ‘hidden feature’ does, except in a way specifically designed for your footage). This LUT does not have to “fit the scene”. It only has to fit the camera. It is a technical LUT, not a creative LUT.

Tonemapping will not change the bit depth. To maintain a 16 bit image, all you have to do is export a 16 bit image firstly out of ffmpeg, then out of ART.

First, sorry for the delay, I was unavailable for a month.
It seems I was not that clear in my first post, but my pictures don’t come from a camera, but are screenshots from 4K films that I want to transform in wallpapers for my desktop.
So by definition I can’t have the lut, at least easily.

When I do a capture (via FFMpeg) of a frame, from my disc, I have an image made to be displayed on a hdr device, but without all steps done by the 4K player. FFMpeg doesn’t do that (and developers don’t care, it seems), so I don’t have the Hybrid Log-Gamma correction applied to my screenshot, so I have a washed-out picture in the end.

After a long time without solution (and I wasn’t able to try things during this month) I figured that yes, I had to find a lut that could fit my needs. I found one, that does a color grading with a result very close to the result I want, even if it’s not perfect. It’s a 3D-Lut (.cube) that I can use with Gimp (and G’Mic).

If someone has lut that does perfectly the Hybrid Log-Gamma correction, please tell me. :slight_smile:

(Anyway thanks to everyone, I have answers to my questions)

You can try LUTcalc, an on line tool that creates LUTs from one gamma and color space to another. Info: https://cameramanben.github.io/LUTCalc/
To run: https://cameramanben.github.io/LUTCalc/LUTCalc/index.html
You can choose as Rec Gamma: Display, REC 2100 HLG
Other settings will be easy to figure out.

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Oh, many thanks !
I found another one but the results were not that good.
And meanwhile I found a free lut creator (GrossGrade) that allowed me to construct my own 3D-lut. Not perfect, but good enough, I finish with ART.
But I’ll try your tool, maybe it’s the graal. I’ll tell you if it’s the case.
Thanks again !

Edit : OK, I already found this one, and I wasn’t able to have what I wanted. Thanks anyway for your help ! :slight_smile:

Now, I really have to thank you, sir.

Short story : I tried this tool when I started to search a 3D-LUT, a week ago. As a beginner in color management (I mean, color grading and LUT), I tried things and ultimately failed. So I let it down, goodbye, whatever.

Now, after reading your post this morning, I tried it again, but this time, as I spent all week on the subject, I understood what was going on, so now I can proudly announce to the world that I found and created the LUT I wanted for my needs, and a high quality one !

Thanks again, I can move on now. :smiley:
This topic can be closed too. :slight_smile:

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