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TOPIC: Color correction effect: Please allow more than 8 bit precision also in the tab "Curves".

Color correction effect: Please allow more than 8 bit precision also in the tab "Curves". 1 month, 1 week ago #220975

  • schrauber
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As a rule, the GPU precision set in the project settings is used within the effect path (also in the preview, and for 8-bit export). I like that.
Now I noticed that color corrections which are created using the curves seem to work internally with about 8 bits, independent of the project settings (tested in the preview and the free-8-bit export.

For testing I used the "Colour Gradient" effect, and set it to very dark.

Reference test (OK):
- I increased the brightness with the "Gain" parameter (1000%) in the colour correction effect
- When changing the GPU precision, as expected, clear differences were visible.

Test with curves:
- I adjusted the steepness of the curve so that it should do almost the same as in the test before
- When changing the GPU precision, I unexpectedly did not see any significant quality improvements when I switched to higher GPU precision.

See the video:
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The same results from both tests for free-8-bit export.

I can't test if the 10 bit export would use a higher GPU precision in this test.
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Re: Color correction effect: Please allow more than 8 bit precision also in the tab "Curves". 1 month, 1 week ago #221155

  • hugly
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I haven't tested 10-bit export, but I will do it.

This might fit into the feature request as well: From what I see, I suspect that the LUT effect ignores GPU precision of 16-bit and above.

Cube LUTs are by design 8 bit, as far as I know, but when interpolating values, the interpolation could well target 16-bit precision and above.

If my assumption is correct, please consider interpolation to the available/adjusted precision and not only to 8-bit.
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Re: Color correction effect: Please allow more than 8 bit precision also in the tab "Curves". 1 month, 1 week ago #221167

  • hugly
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schrauber wrote:
I can't test if the 10 bit export would use a higher GPU precision in this test.

I changed the luma settings on the gradient to 9.3 % to get the full range on the scopes and made some tests. I can confirm your finding.

With GPU precision set to 16 percent, I don't see any difference between 8-bit and 10-bit export, for both variants, Main.Gain at 1000% and Curves.RGB at 255/23.

I would have expected to see a difference at least for the gradient adjusted with Main.Gain, but I don't see any, do you? I don't know what that means.

I've attached the generating sequence and the two exported files (h.264 and Cineform).
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Re: Color correction effect: Please allow more than 8 bit precision also in the tab "Curves". 1 month, 1 week ago #221169

  • schrauber
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Thanks for the test.

hugly wrote:
I've attached the generating sequence and the two exported files (h.264 and Cineform).


In the rar file I find this video:
Gradient - Main vs Curves 1080p24 h.264  10-bit 420.mp4

Is the ... "10-bit" ... a typo in the name of this mp4 file?
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Last Edit: 1 month, 1 week ago by schrauber.

Re: Color correction effect: Please allow more than 8 bit precision also in the tab "Curves". 1 month, 1 week ago #221170

  • hugly
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YES, sorry, but not on the avi file.
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Re: Color correction effect: Please allow more than 8 bit precision also in the tab "Curves". 1 month, 1 week ago #221173

  • David Rasberry
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hugly wrote:
I haven't tested 10-bit export, but I will do it.

This might fit into the feature request as well: From what I see, I suspect that the LUT effect ignores GPU precision of 16-bit and above.

Cube LUTs are by design 8 bit, as far as I know, but when interpolating values, the interpolation could well target 16-bit precision and above.

If my assumption is correct, please consider interpolation to the available/adjusted precision and not only to 8-bit.


Cube LUTS are written in three different levels of precision, none of them 8 bit:
17x17X17, 33x33x33, 64x64x64.

Cube LUTS don't describe RGB bit values directly but complex mathematical relations between colors and values in a 3D matrix. Bit values are all interpolated according to the bit depth of the video.

Most camera field monitors that accept viewing LUTS only accept 17x.

affinityspotlight.com/article/1d-vs-3d-luts/
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Last Edit: 1 month, 1 week ago by David Rasberry.

Re: Color correction effect: Please allow more than 8 bit precision also in the tab "Curves". 1 month, 1 week ago #221174

  • hugly
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Thank you for the information.

I was relying on an answer I got on the forum some time ago. Good to know that 3D LUTs are not 8-bit.

Most 3D-LUTs I have here are 33x33x33, so it shouldn't be problem to interpolate correctly to a given GPU precision of 16-bit integer, for instance. However, my observation that they don't might also be not correct, as mentioned, but perhaps worth checking?
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Re: Color correction effect: Please allow more than 8 bit precision also in the tab "Curves". 1 month ago #221302

  • gr00by
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Now I noticed that color corrections which are created using the curves seem to work internally with about 8 bits, independent of the project settings (tested in the preview and the free-8-bit export.


Maybe that's why my videos had some issues after color correction (I was using curves for delog).
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