Texture Paint Color Picker Interpreted as Gamma Corrected #88646

New Issue

Jamell Moore · 2021-05-28T09:49:47+02:00

Jamell Moore commented

2021-05-28 09:49:47 +02:00

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: NVIDIA GeForce GTX 1050 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 465.89

Blender Version
Broken: 3.0.0 alpha

Description of Issue

I'm not sure if there is a bug, if there is a doc issue or neither so I'm asking in multiple places.

The Blender Documentation states:

In Blender, the RGB and HSV/HSL values are in Scene Linear color space, and are therefore not Gamma corrected. On the contrary, Hex are automatically Gamma corrected for the sRGB Color Space. For more information, see Color Management.

Note that Vertex Paint works in sRGB space, and the RGB representation of the same colors will be different between the paint tools and the materials that are in linear space.

But when painting to a linear texture target in texture paint mode, RGB colors appear to be interpreted as gamma corrected srgb for display. Then converted to linear before painting.

This is evident from the color values when using the color sampling tool in image view mode:

This also seems to be supported by the fact that in code, brush.color is converted to linear using IMB_colormanagement_display_to_scene_linear_v3 in image editor texture paint mode.

In paint_image.c L404, the color_correction condition is true when the texture is linear, so the display to scene conversion is applied.

if (color_correction) {
    IMB_colormanagement_display_to_scene_linear_v3(color, display);
}

If the color picker is gamma corrected whilst in this mode, it's confusing to for the user because the documentation states otherwise.

To add to the confusion, brush.color has a PropertySubType of PROP_COLOR_GAMMA but is converted to linear before use.

The code states that PROP_COLOR_GAMMA "is used for colors that would be color managed before display". Therefore I'm interpreting that colors with the type PROP_COLOR_GAMMA are Linear - they will be gamma corrected before display.

Am I interpreting this incorrectly!?

Sorry for the long description.

Steps to see discrepancy

From start-up create an image in texture paint mode, with a floating point buffer. This should be linear.
Go into image paint mode
Select the rgb(0,5, 0.5, 0.5) from the color picker
Paint a stroke so that you can sample it
Go back to image view mode and use the sample tool to check the color values before and after color management
You will see that the unmanaged color values are 0.214 and the color managed values are 0.5
Now turn off color management in the render properties tab
Paint another stroke with the same color
Sample the colors again and you will see that both the unmanaged color and the managed color have values of 0.5.
This is evidence that the color is converted to linear. Is this a bug or a design decision?

**System Information** Operating system: Windows-10-10.0.19041-SP0 64 Bits Graphics card: NVIDIA GeForce GTX 1050 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 465.89 **Blender Version** Broken: 3.0.0 alpha **Description of Issue** I'm not sure if there is a bug, if there is a doc issue or neither so I'm asking in multiple places. The Blender Documentation states: > In Blender, the RGB and HSV/HSL values are in Scene Linear color space, and are therefore not Gamma corrected. On the contrary, Hex are automatically Gamma corrected for the sRGB Color Space. For more information, see Color Management. > Note that Vertex Paint works in sRGB space, and the RGB representation of the same colors will be different between the paint tools and the materials that are in linear space. But when painting to a linear texture target in texture paint mode, RGB colors appear to be interpreted as gamma corrected srgb for display. Then converted to linear before painting. This is evident from the color values when using the color sampling tool in image view mode: ![texture_paint_color_management_report_02.jpg](https://archive.blender.org/developer/F10148249/texture_paint_color_management_report_02.jpg) ![texture_paint_color_management_report_03.jpg](https://archive.blender.org/developer/F10148264/texture_paint_color_management_report_03.jpg) This also seems to be supported by the fact that in code, `brush.color` is converted to linear using `IMB_colormanagement_display_to_scene_linear_v3` in image editor texture paint mode. In paint_image.c L404, the color_correction condition is true when the texture is linear, so the display to scene conversion is applied. ``` if (color_correction) { IMB_colormanagement_display_to_scene_linear_v3(color, display); } ``` If the color picker is gamma corrected whilst in this mode, it's confusing to for the user because the documentation states otherwise. To add to the confusion, brush.color has a `PropertySubType` of `PROP_COLOR_GAMMA` but is converted to linear before use. The code states that `PROP_COLOR_GAMMA` "is used for colors that would be color managed before display". Therefore I'm interpreting that colors with the type `PROP_COLOR_GAMMA` are Linear - they will be gamma corrected before display. Am I interpreting this incorrectly!? *Sorry for the long description.* **Steps to see discrepancy** - From start-up create an image in texture paint mode, with a floating point buffer. This should be linear. - Go into image paint mode - Select the rgb(0,5, 0.5, 0.5) from the color picker - Paint a stroke so that you can sample it - Go back to image view mode and use the sample tool to check the color values before and after color management - You will see that the unmanaged color values are 0.214 and the color managed values are 0.5 - Now turn off color management in the render properties tab - Paint another stroke with the same color - Sample the colors again and you will see that both the unmanaged color and the managed color have values of 0.5. - This is evidence that the color is converted to linear. Is this a bug or a design decision?

Jamell Moore commented

2021-05-28 09:49:47 +02:00

Added subscriber: @JamellMoore