Compositor RGB Curves artefacts with 'film like' option when using individual channels (only works correctly with the 'master' curve) #60940

New Issue

Paul R · 2019-01-28T01:53:05+01:00

Paul R commented

2019-01-28 01:53:05 +01:00

System Information
Operating system: SUSE Leap 15.0
Graphics card: NVidia GTX 560ti (official drivers)

Blender Version
Broken: 2.80, 5632e1b525, x86_64 linux, 2019-01-24 (buildbot)

Short description of error
Compositor RGB Curves node gives false colours when set to 'Film like' and when any of R,G,B channels are adjusted. Adjustment of C channel alone is OK.

sidenote; Constant hue adjustment is definitely an interesting feature to have! But since film often has various hue shifts going on, if anything, 'Standard' is possibly closer with a typical S-curve - a bias to cyan, magenta, yellow in the highlights corresponding to the curve shoulder.

'Hue hold' or 'Hue lock' could be alternative names.

Example .blend
compositor_rgbcurves_film-like_artefacts.blend

Exact steps for others to reproduce the error
Load attached .blend, render.

Ref:
https://developer.blender.org/rB4de7c0c3105a80d244dd9f2078c310331873a16b

Notes:

Muting the noise texture hides the issue in this example.
Stepping through the emission strength from 0.0 to 1.0 gives varying results. Might be a clue to the cause?

**System Information** Operating system: SUSE Leap 15.0 Graphics card: NVidia GTX 560ti (official drivers) **Blender Version** Broken: 2.80, 5632e1b52586, x86_64 linux, 2019-01-24 (buildbot) **Short description of error** Compositor RGB Curves node gives false colours when set to 'Film like' and when any of R,G,B channels are adjusted. Adjustment of C channel alone is OK. ![rgb_curves_film-like_artefacts_example_2.png](https://archive.blender.org/developer/F6426691/rgb_curves_film-like_artefacts_example_2.png) sidenote; Constant hue adjustment is definitely an interesting feature to have! But since film often has various hue shifts going on, if anything, 'Standard' is possibly closer with a typical S-curve - a bias to cyan, magenta, yellow in the highlights corresponding to the curve shoulder. 'Hue hold' or 'Hue lock' could be alternative names. **Example .blend** [compositor_rgbcurves_film-like_artefacts.blend](https://archive.blender.org/developer/F6426720/compositor_rgbcurves_film-like_artefacts.blend) **Exact steps for others to reproduce the error** Load attached .blend, render. Ref: https://developer.blender.org/rB4de7c0c3105a80d244dd9f2078c310331873a16b Notes: - Muting the noise texture hides the issue in this example. - Stepping through the emission strength from 0.0 to 1.0 gives varying results. Might be a clue to the cause?

Paul R commented

2019-01-28 01:53:05 +01:00

Added subscriber: @intracube

Jeroen Bakker was assigned by Brecht Van Lommel

2019-01-28 07:58:03 +01:00

Jeroen Bakker commented

2019-02-22 15:08:13 +01:00

This comment was removed by @Jeroen-Bakker

*This comment was removed by @Jeroen-Bakker*

Jeroen Bakker was unassigned by Dalai Felinto

2019-12-23 16:35:16 +01:00

Dalai Felinto commented

2019-12-23 16:35:16 +01:00

Added subscriber: @Jeroen-Bakker

Philipp Oeser commented

2020-02-07 13:07:54 +01:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2020-02-07 13:07:54 +01:00

Not knowing the internals well, this really looks "off".
It is especially apparent with soft, gradient like areas, so it breaks quickly with Bloom (like in this case), Glare, Blur and such...

There is a similar example in the comments of 4de7c0c310.
Would have to check the implementations in other software to get a sense if this is "broken by design" or an actual bug in the shuffling of channels or so...

Not knowing the internals well, this really looks "off". It is especially apparent with soft, gradient like areas, so it breaks quickly with Bloom (like in this case), Glare, Blur and such... There is a similar example in the comments of 4de7c0c310. Would have to check the implementations in other software to get a sense if this is "broken by design" or an actual bug in the shuffling of channels or so...

Philipp Oeser commented

2020-02-07 13:34:04 +01:00

Maybe it is also expected to break if done on a particular channel [and not done on the "master" C curve only]?

Maybe it is also expected to break if done on a particular channel [and not done on the "master" `C` curve only]?

Paul R commented

2020-02-07 13:52:00 +01:00

In #60940#867434, @lichtwerk wrote:
Not knowing the internals well, this really looks "off".

Hi, I think it was explained that the film option is only designed to work with adjustments to the 'C' (luminance) channel.

So the simple solution would be to disable the R,G,B channels in that mode.

> In #60940#867434, @lichtwerk wrote: > Not knowing the internals well, this really looks "off". Hi, I think it was explained that the film option is only designed to work with adjustments to the 'C' (luminance) channel. So the simple solution would be to disable the R,G,B channels in that mode.

Philipp Oeser self-assigned this 2020-02-07 14:53:20 +01:00

Philipp Oeser commented

2020-02-07 14:53:20 +01:00

Also reconfirmed with @Jeroen-Bakker that this is only correctly working with the C curve.
So fix is a UI thing: will hide the Film like option when in R G or B curves, and hide R G B when in Film like...

Also reconfirmed with @Jeroen-Bakker that this is only correctly working with the `C` curve. So fix is a UI thing: will hide the `Film like` option when in `R` `G` or `B` curves, and hide `R` `G` `B` when in `Film like`...

Philipp Oeser changed title from ~~Compositor RGB Curves artefacts with 'film like' option~~ to Compositor RGB Curves artefacts with 'film like' option when using individual channels (only works correctly with the 'master' curve)

2020-02-07 14:54:22 +01:00

Alex P commented

2020-10-31 18:22:15 +01:00

Added subscriber: @Alex-9

Philipp Oeser removed their assignment 2020-11-17 14:16:53 +01:00

Roman commented

2021-07-21 13:42:42 +02:00

Added subscriber: @rwman

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Compositor RGB Curves artefacts with 'film like' option when using individual channels (only works correctly with the 'master' curve) #60940