Manipulating saturation of colors (e.g via HSV or RGB curves, but also within color picker) shifts HUE #69562
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Reference: blender/blender#69562
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System Information
Operating system: Linux-4.15.0-58-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 430.40
Blender Version
Broken: version: 2.81 (sub 8), branch: master, commit date: 2019-09-05 10:52, hash:
b6e7e173ec
Short description of error
To desaturate a color you plug a HSV or RGB curves node. But the more you light up the color the more hue shifts. I've tested it with eyedropper in blender and gimp. Dragging the right side control of the RGB curves node (making darker) doesn't shift hue.
If i'm doing something wrong, then what's a correct way to desaturate a color without hue shifting?
Exact steps for others to reproduce the error
Open up the attached file
Fire the render
From the Picker node pick the color from the render view
Compare the hues on both nodes
color_hue_shift_bug.blend
Added subscriber: @YegorSmirnov
#82631 was marked as duplicate of this issue
#75876 was marked as duplicate of this issue
#79212 was marked as duplicate of this issue
#79220 was marked as duplicate of this issue
#70352 was marked as duplicate of this issue
Added subscriber: @lichtwerk
Tempted to confirm this, not 100% sure though, checking...
Same is true for compositing...
Added subscribers: @troy_s, @brecht
Actually not sure about this...
ui_scene_linear_to_color_picker_space
in color picker code I also get the same values for hue there [even after desaturation].Without diving deeper [which I really want to do sooner than later], I'll have to pass this on to someone else I guess...
CC @brecht
CC @troy_s
Added subscriber: @VictorMukayev
I think this is the same issue as the original report in #41287 (Color Picker applies color management incorrectly in 2.71).
I don't really understand the context of that entire discussion, but I think what we should do is:
In implementation this is not entirely simple because all those widgets point to the same HSV value in memory, so we have to be careful to convert everything as appropriate.
Agree with @brecht.
The issue here is the tip of a larger iceberg, and perhaps it can be resolved in the right direction. The core issue is that the HSV code is legacy, and was based on the nonlinear assumptions behind sRGB. Rightfully so, given how old it is. Although the discussion of hue linearity is complex, at the simplest level, as long as the RGB light ratios hold, the chromaticity angle will hold.
A potential path to solution:
Added subscriber: @frameshift
Would this be the cause of the HSV colour picker returning crazy RGB ratios when using an alternative OCIO config?
I believe the “crazy” ratios are a byproduct of a number of anachronistic / legacy issues:
Added subscriber: @MrBeep
Added subscriber: @Jeroen-Bakker
D6653: ColorManagement: PoC Windowmanager Areas addresses a step into the direction of solving this issue. I set this to TODO as it needs a design how to fix the color picker related issues.
Added subscribers: @Leroy-Xie, @JacquesLucke, @iss
Manipulating saturation of colors via HSV or RGB curves shifts HUEto Manipulating saturation of colors (e.g via HSV or RGB curves, but also within color picker) shifts HUEAdded subscribers: @cheteron, @Garek, @mano-wii
Added subscribers: @blanchsb, @ankitm
This issue was referenced by
f193b1afb3
Changed status from 'Confirmed' to: 'Resolved'