Sculpt Paint: Mask by color produces an empty mask with a threshold of 0.0 #98838

New Issue

Floatharr · 2022-06-13T10:52:52+02:00

Floatharr commented

2022-06-13 10:52:52 +02:00

System Information
Operating system: Windows-10-10.0.19043-SP0 64 Bits
Graphics card: NVIDIA GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 512.95

Blender Version
Broken: version: 3.2.0, branch: master, commit date: 2022-06-08 10:22, hash: e05e1e3691

Short description of error
It is impossible to make a precise color selection from two similar colors with Mask by Color alone, because a threshold near or at 0 produces an empty mask. I consider this a bug because according to the comment in the source code, this functionality isn't working as intended. Quote directly from source code:

https://developer.blender.org/D8157

/* sculpt_mask_by_color_delta_get returns values in the (0,1) range that are used to generate the
 * mask based on the diference between two colors (the active color and the color of any other
 * vertex). Ideally, a threshold of 0 should mask only the colors that are equal to the active
 * color and threshold of 1 should mask all colors. In order to avoid artifacts and produce softer
 * falloffs in the mask, the MASK_BY_COLOR_SLOPE defines the size of the transition values between
 * masked and unmasked vertices. The smaller this value is, the sharper the generated mask is going
 * to be. */

For completeness, here is a real world scenario where it is tedious to mask the pants, shirt, or skin because the colors are too close together for the Mask by Color tool.

Exact steps for others to reproduce the error

Apply two similar colors to a subdivided surface with the paint tool, and try to mask only one of them. The only way to produce a sharp mask is with the Increase Contrast operator when the Threshold is fine tuned to work with it.
blender_3Yh12TUXry.mp4

**System Information** Operating system: Windows-10-10.0.19043-SP0 64 Bits Graphics card: NVIDIA GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 512.95 **Blender Version** Broken: version: 3.2.0, branch: master, commit date: 2022-06-08 10:22, hash: `e05e1e3691` **Short description of error** It is impossible to make a precise color selection from two similar colors with Mask by Color alone, because a threshold near or at 0 produces an empty mask. I consider this a bug because according to the comment in the source code, this functionality isn't working as intended. Quote directly from source code: https://developer.blender.org/D8157 ``` /* sculpt_mask_by_color_delta_get returns values in the (0,1) range that are used to generate the * mask based on the diference between two colors (the active color and the color of any other * vertex). Ideally, a threshold of 0 should mask only the colors that are equal to the active * color and threshold of 1 should mask all colors. In order to avoid artifacts and produce softer * falloffs in the mask, the MASK_BY_COLOR_SLOPE defines the size of the transition values between * masked and unmasked vertices. The smaller this value is, the sharper the generated mask is going * to be. */ ``` For completeness, here is a real world scenario where it is tedious to mask the pants, shirt, or skin because the colors are too close together for the Mask by Color tool. ![image.png](https://archive.blender.org/developer/F13155082/image.png) **Exact steps for others to reproduce the error** Apply two similar colors to a subdivided surface with the paint tool, and try to mask only one of them. The only way to produce a sharp mask is with the Increase Contrast operator when the Threshold is fine tuned to work with it. [blender_3Yh12TUXry.mp4](https://archive.blender.org/developer/F13155118/blender_3Yh12TUXry.mp4)

Floatharr commented

2022-06-13 10:52:52 +02:00

Added subscriber: @Floatharr

Omar Emara commented

2022-06-20 09:31:20 +02:00

Added subscriber: @OmarEmaraDev

Omar Emara commented

2022-06-20 09:31:20 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Omar Emara commented

2022-06-20 09:31:20 +02:00

If the distance between the two colors is close to zero and the threshold is close to zero, then len = (-len + threshold) / MASK_BY_COLOR_SLOPE; will also be close to zero. Which I guess is not the expected behavior.

If the distance between the two colors is close to zero and the threshold is close to zero, then `len = (-len + threshold) / MASK_BY_COLOR_SLOPE;` will also be close to zero. Which I guess is not the expected behavior.

Philipp Oeser removed the

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Sculpt Paint: Mask by color produces an empty mask with a threshold of 0.0 #98838