Image Editor "Erase Alpha" brush erases all channels of float images #86868

New Issue

Sam Brubaker · 2021-03-24T01:15:55+01:00

Sam Brubaker commented

2021-03-24 01:15:55 +01:00

System Information
Linux 64-bit

Blender Version
Broken: 2.92
Note: In versions 2.83 and earlier, Alpha was not premultiplied (this started in 4212b6528a, unsure if this should be the case if we are only looking at the Color without Alpha?).

Short description of error
Erasing the alpha on float images erase the RGB channels as well.
erase_alpha_bug.mp4

Exact steps for others to reproduce the error

Open the attached file. (Left image is a Non-float while right image is Float, both have Alpha channel. We are seeing only the RGB channels).
Use the brush "Erase Alpha" to erase part of the non-floating-point image (on the left).
Use shift-click to sample the pixel-values of this image. The RGB channels have NOT actually been affected and the image only appears to have been premultiplied.
Use the brush "Erase Alpha" on the floating-point image (on the right).

Use shift-click to sample the pixel-values of this image. ALL channels were erased!

It may look like the same bug as #86866 but it isn't! The brush works as expected; it's the RGB display that's wrong.
image editor bug.blend

**System Information** Linux 64-bit **Blender Version** Broken: 2.92 Note: In versions 2.83 and earlier, Alpha was not premultiplied (this started in 4212b6528a, unsure if this should be the case if we are only looking at the Color without Alpha?). **Short description of error** Erasing the alpha on float images erase the RGB channels as well. [erase_alpha_bug.mp4](https://archive.blender.org/developer/F12885725/erase_alpha_bug.mp4) **Exact steps for others to reproduce the error** - Open the attached file. (Left image is a Non-float while right image is Float, both have Alpha channel. We are seeing only the RGB channels). - Use the brush "Erase Alpha" to erase part of the non-floating-point image (on the left). - Use shift-click to sample the pixel-values of this image. The RGB channels have **NOT** actually been affected and the image only appears to have been premultiplied. - Use the brush "Erase Alpha" on the floating-point image (on the right). # Use shift-click to sample the pixel-values of this image. **ALL** channels were erased! It may look like the same bug as #86866 but it isn't! The brush works as expected; it's the RGB display that's wrong. [image editor bug.blend](https://archive.blender.org/developer/F9906271/image_editor_bug.blend)

Sam Brubaker commented

2021-03-24 01:15:55 +01:00

Added subscriber: @rocketman

blender-admin commented

2021-03-24 01:15:55 +01:00

#91207 was marked as duplicate of this issue

blender-admin commented

2021-03-24 01:15:55 +01:00

#86866 was marked as duplicate of this issue

Germano Cavalcante commented

2021-03-26 16:58:50 +01:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2021-03-26 16:58:50 +01:00

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

Germano Cavalcante commented

2021-03-26 16:58:50 +01:00

Thanks for the report, I can confirm the problem.

I don't know what the industry standard is but I think the other channels shouldn't be erased when you use an "Erase Alpha" brush.
In any case, this should be consistent across different image formats.

For the number of related reports I dare to set this bug as a high priority (for now).

(Personally, I think the pre-multiplication should be optional).
(I also mentioned about this on #86764).

Thanks for the report, I can confirm the problem. I don't know what the industry standard is but I think the other channels shouldn't be erased when you use an "Erase Alpha" brush. In any case, this should be consistent across different image formats. For the number of related reports I dare to set this bug as a high priority (for now). --- (Personally, I think the pre-multiplication should be optional). (I also mentioned about this on #86764).

Germano Cavalcante commented

2021-03-26 17:20:15 +01:00

@rocketman, with the edits I made, I would say that this report was even more similar to the #86866 (sorry about that).
But the idea of the pre-multiplied alpha has already been described in other reports.
So I'll merge then.

@rocketman, with the edits I made, I would say that this report was even more similar to the #86866 (sorry about that). But the idea of the pre-multiplied alpha has already been described in other reports. So I'll merge then.

Germano Cavalcante changed title from ~~Image Editor appears to multiply the RGB channels by the Alpha channels when non-float images are displayed in RGB~~ to Image Editor "Erase Alpha" brush erases all channels

2021-03-26 17:22:50 +01:00

Sam Brubaker commented

2021-03-26 17:38:13 +01:00

It's a funny issue because the behavior of the Erase Alpha brush appears to be ONE bug when in fact there are two different bugs. And now I don't know which bug report is which! This is exactly what I was afraid would happen, lol

Yuki Hashimoto commented

2021-07-01 03:54:01 +02:00

Added subscriber: @hzuika

Philipp Oeser commented

2021-09-06 10:46:19 +02:00

Added subscribers: @CoderTiger, @lichtwerk

ZYC commented

2021-12-26 10:03:58 +01:00

Added subscriber: @fatboyzzfatboyzz

Yuki Hashimoto commented

2022-02-24 13:03:55 +01:00

I have submitted a patch to fix this problem.
However, I don't know if this is a bug or the default behavior.
For your information, this brush function seems to have been implemented in 8f9150871c.

I have submitted a patch to fix this problem. However, I don't know if this is a bug or the default behavior. For your information, this brush function seems to have been implemented in 8f9150871c.

Evan Wilson commented

2022-02-25 12:08:37 +01:00

Added subscriber: @EAW

Philipp Oeser commented

2022-03-25 15:04:58 +01:00

Added subscriber: @Jeroen-Bakker

Philipp Oeser commented

2022-03-25 15:04:58 +01:00

CC @Jeroen-Bakker

Jeroen Bakker commented

2022-05-09 14:52:34 +02:00

This requires a design. For images I think it should do what it says erase alpha. This means for premultiplied images it should only effect the alpha channel.
Currently it does not. There has been some discussions lately about this brush and would like the Sculpt, paint, texturing project to determine what should be done.

The image editor didn't change this behavior it only made it visible. Will remove the eevee/viewport from this issue as it isn't related to that module.

This requires a design. For images I think it should do what it says erase alpha. This means for premultiplied images it should only effect the alpha channel. Currently it does not. There has been some discussions lately about this brush and would like the Sculpt, paint, texturing project to determine what should be done. The image editor didn't change this behavior it only made it visible. Will remove the eevee/viewport from this issue as it isn't related to that module.

Brecht Van Lommel commented

2022-05-11 15:18:45 +02:00

Added subscriber: @brecht

Brecht Van Lommel commented

2022-05-11 15:18:45 +02:00

This is a result of float images always being associated alpha by convention. I think that given that convention, the erase brush affecting all channels is correct. If you make it affect just alpha it will be more consistent when looking at just the RGB channels, but less consistent when looking at the full RGBA channels.

It would be good to support unassociated alpha for float images, but I don't think we should change the behavior for associated alpha images.

This is a result of float images always being associated alpha by convention. I think that given that convention, the erase brush affecting all channels is correct. If you make it affect just alpha it will be more consistent when looking at just the RGB channels, but less consistent when looking at the full RGBA channels. It would be good to support unassociated alpha for float images, but I don't think we should change the behavior for associated alpha images.

Sam Brubaker commented

2022-05-11 17:01:16 +02:00

In #86868#1356811, @brecht wrote:
If you make it affect just alpha it will be more consistent when looking at just the RGB channels, but less consistent when looking at the full RGBA channels.

I disagree; there are numerous cases where I am editing an image with associated alpha and would still like only to affect the alpha channel. What brush would I use then, besides "Erase Alpha"?

> In #86868#1356811, @brecht wrote: >If you make it affect just alpha it will be more consistent when looking at just the RGB channels, but less consistent when looking at the full RGBA channels. I disagree; there are numerous cases where I am editing an image with associated alpha and would still like *only* to affect the alpha channel. What brush would I use then, besides "Erase Alpha"?

Julien Kaspar commented

2022-05-12 10:25:29 +02:00

Added subscriber: @JulienKaspar

Julien Kaspar commented

2022-05-12 10:25:29 +02:00

We agreed to lower the priority since this doesn't need urged fixing and has been high priority for a long time. But discussion on the issue and working towards a fix can continue.

Evan Wilson changed title from ~~Image Editor "Erase Alpha" brush erases all channels~~ to Image Editor "Erase Alpha" brush erases all channels of float images

2022-05-20 07:05:44 +02:00

Philipp Oeser removed the

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Image Editor "Erase Alpha" brush erases all channels of float images #86868

Use shift-click to sample the pixel-values of this image. ALL channels were erased!