White outline around alpha in texture paint (when using multiple layers) #69106

New Issue

Syntex · 2019-08-24T00:21:24+02:00

Syntex commented

2019-08-24 00:21:24 +02:00

System Information
Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 417.22

Blender Version
Broken: version: 2.81 (sub 3), branch: master, commit date: 2019-08-22 20:40, hash: 1de7717ed7 and 2.8 release
Worked: Never. As far as I can remember this has always been an issue.

Short description of error
When painting with multiple layers in texture paint mode, there is a white outline around the alpha channel. (You have to be in material view to see the 2 layers at the same time)
The first layer is just a solid red color & the second layer's alpha is set to 0 and then I painted on the layer with green color.
The layers are mixed together using the MixRGB node with the second layer's alpha set as the mix factor.
IMPORTANT: the brush falloff needs to be set to the last preset or the issue is not as visible because the change in alpha value is smoother

The white outline is not visible if I render the scene in cycles, which makes me think that this is a bug. If it's not a bug, it's most likely a limitation of the "Mix" blend mode.

This issue makes the texture paint mode unusable for any serious work that needs more than 1 layer.

Exact steps for others to reproduce the error
Unwrap the default cube U> smart UV project, switch to texture paint workspace, add a base color texture & a second base color texture with alpha set to 0,
switch to material view, go to the shader editor & Mix the 2 base color textures together using the MixRGB node.
The first base color texture goes to the "Color1" input & the second base color texture with alpha goes to the "Color2" input.
Connect the alpha output of the second base color texture to the MixRGB node's alpha input. Then paint on the second base color layer with a hard edged brush (last falloff preset) and you get white outlines around your brush strokes.

Here's a .blend file where i reproduced the issue.
white outline.blend

**System Information** Operating system: Windows-10-10.0.17134 64 Bits Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 417.22 **Blender Version** Broken: version: 2.81 (sub 3), branch: master, commit date: 2019-08-22 20:40, hash: `1de7717ed7` and 2.8 release Worked: Never. As far as I can remember this has always been an issue. **Short description of error** When painting with multiple layers in texture paint mode, there is a white outline around the alpha channel. (You have to be in material view to see the 2 layers at the same time) The first layer is just a solid red color & the second layer's alpha is set to 0 and then I painted on the layer with green color. The layers are mixed together using the MixRGB node with the second layer's alpha set as the mix factor. ***IMPORTANT: the brush falloff needs to be set to the last preset or the issue is not as visible because the change in alpha value is smoother*** ![falloff.PNG](https://archive.blender.org/developer/F7696108/falloff.PNG) ![Texture paint layers white outline.PNG](https://archive.blender.org/developer/F7695973/Texture_paint_layers_white_outline.PNG) The white outline is not visible if I render the scene in cycles, which makes me think that this is a bug. If it's not a bug, it's most likely a limitation of the "Mix" blend mode. ![Rendered view with cycles.PNG](https://archive.blender.org/developer/F7695978/Rendered_view_with_cycles.PNG) This issue makes the texture paint mode unusable for any serious work that needs more than 1 layer. **Exact steps for others to reproduce the error** Unwrap the default cube U> smart UV project, switch to texture paint workspace, add a base color texture & a second base color texture with alpha set to 0, switch to material view, go to the shader editor & Mix the 2 base color textures together using the MixRGB node. The first base color texture goes to the "Color1" input & the second base color texture with alpha goes to the "Color2" input. Connect the alpha output of the second base color texture to the MixRGB node's alpha input. Then paint on the second base color layer with a hard edged brush (last falloff preset) and you get white outlines around your brush strokes. Here's a .blend file where i reproduced the issue. [white outline.blend](https://archive.blender.org/developer/F7696088/white_outline.blend)

Syntex commented

2019-08-24 00:21:24 +02:00

Added subscriber: @Syntex3D

blender-admin commented

2019-08-24 00:21:24 +02:00

#81474 was marked as duplicate of this issue

Philipp Oeser commented

2020-01-06 14:35:37 +01:00

Added subscribers: @PabloDobarro, @fclem, @Jeroen-Bakker, @lichtwerk

Philipp Oeser commented

2020-01-06 14:35:37 +01:00

Changed status from 'Needs Triage' to: 'Needs Developer To Reproduce'

Philipp Oeser commented

2020-01-06 14:35:37 +01:00

Hi and thx for the report (sorry for the massive delay in answering here)!

To me this seems to be tied to the mode the Texture Interpolation on the Image Texture node?
If I set this to Closest (instead of Linear) for the Image with alpha, this seems to be displaying just fine...

Please also check b98e6743dc... for Filtering in Texture Slots > Material vs Single Image mode

@PabloDobarro , @fclem, @Jeroen-Bakker: I assume this is to be expected behavior? (or is there something wrong with how this is displayed with Linear interpolation?)

Hi and thx for the report (sorry for the massive delay in answering here)! To me this seems to be tied to the mode the `Texture Interpolation` on the `Image Texture` node? If I set this to `Closest` (instead of `Linear`) for the Image with alpha, this seems to be displaying just fine... Please also check b98e6743dc... for Filtering in `Texture Slots` > `Material` vs `Single Image` mode @PabloDobarro , @fclem, @Jeroen-Bakker: I assume this is to be expected behavior? (or is there something wrong with how this is displayed with `Linear` interpolation?)

Jeroen Bakker commented

2020-01-06 15:24:11 +01:00

Seems to be a render difference between cycles and eevee. Perhaps this could be solved by premultiplying the texture when used in eevee, but that will give other artifacts. Point is that in this case the texture is not setup for linear interpolation, so will leave these borders. IMO current solution is that the user should fix the texture to be usable for linear interpolation.

I would vote to put this as a known issue. EEVEE works as it is designed, but can be improved by new developments.

Seems to be a render difference between cycles and eevee. Perhaps this could be solved by premultiplying the texture when used in eevee, but that will give other artifacts. Point is that in this case the texture is not setup for linear interpolation, so will leave these borders. IMO current solution is that the user should fix the texture to be usable for linear interpolation. I would vote to put this as a known issue. EEVEE works as it is designed, but can be improved by new developments.

Philipp Oeser commented

2020-01-06 15:31:31 +01:00

In #69106#842793, @Jeroen-Bakker wrote:
IMO current solution is that the user should fix the texture to be usable for linear interpolation.

How would you do this (with this kind of falloff)?

> In #69106#842793, @Jeroen-Bakker wrote: > IMO current solution is that the user should fix the texture to be usable for linear interpolation. How would you do this (with this kind of falloff)?

Syntex commented

2020-01-07 09:19:44 +01:00

Thanks for the replies :)
The issue happens when using anything other than the default smooth brush curve, if you increase the hardness even a little bit with a custom curve, you get the white artifacts on the edges.

When using "closest" interpolation instead of "linear" on the image texture node, the white outline indeed goes away but so does the smoothing, so that's not an option in this case.
Are the changes mentioned in b98e6743dc in the newest alpha build because I couldn't find them from anywhere? @lichtwerk

How would I "fix the texture to be usable for linear interpolation"? @Jeroen-Bakker

I still haven't found a way to fix this issue so any help would be appreciated

Thanks for the replies :) The issue happens when using anything other than the default smooth brush curve, if you increase the hardness even a little bit with a custom curve, you get the white artifacts on the edges. ![linear interpolation with smooth brush.PNG](https://archive.blender.org/developer/F8264080/linear_interpolation_with_smooth_brush.PNG) When using "closest" interpolation instead of "linear" on the image texture node, the white outline indeed goes away but so does the smoothing, so that's not an option in this case. Are the changes mentioned in b98e6743dc in the newest alpha build because I couldn't find them from anywhere? @lichtwerk How would I "fix the texture to be usable for linear interpolation"? @Jeroen-Bakker I still haven't found a way to fix this issue so any help would be appreciated

Philipp Oeser commented

2020-01-07 09:34:25 +01:00

Not sure if these help (since you can only set it to Closest), but here they are:

Not sure if these help (since you can only set it to `Closest`), but here they are: ![T69106_a.png](https://archive.blender.org/developer/F8264125/T69106_a.png) ![T69106_b.png](https://archive.blender.org/developer/F8264128/T69106_b.png)

Syntex commented

2020-01-07 10:11:36 +01:00

Oddly that fixes the issue on the tansparent layer but now I'm unable to paint on the green solid color layer because the mode is set to "Single image".

I just created a new transparent texture in the "Single image" mode with linear interpolation & alpha set to 0, and swapped that texture to the second image texture node & painted on it with red color.

Linear interpolation seems to work correctly in single image mode but not in material mode.

This is still not a fix because now I'm unable to paint on the green image texture layer.

Oddly that fixes the issue on the tansparent layer but now I'm unable to paint on the green solid color layer because the mode is set to "Single image". I just created a new transparent texture in the "Single image" mode with linear interpolation & alpha set to 0, and swapped that texture to the second image texture node & painted on it with red color. ![single image_new transparent layer_linear interpolation.PNG](https://archive.blender.org/developer/F8264149/single_image_new_transparent_layer_linear_interpolation.PNG) Linear interpolation seems to work correctly in single image mode but not in material mode. This is still not a fix because now I'm unable to paint on the green image texture layer.

Syntex commented

2020-01-07 10:21:33 +01:00

Nevermind, it actually works perfectly if you switch the image in "single image" mode. I was able to paint more green in the green layer.
You can switch layers by pressing the button circled in my screenshot.

This 100% fixes the issue. I wonder why it doesn't work properly in "material" mode though

Thanks for helping :)

Nevermind, it actually works perfectly if you switch the image in "single image" mode. I was able to paint more green in the green layer. You can switch layers by pressing the button circled in my screenshot. ![it actually works.PNG](https://archive.blender.org/developer/F8264157/it_actually_works.PNG) This 100% fixes the issue. I wonder why it doesn't work properly in "material" mode though Thanks for helping :)

Jeroen Bakker commented

2020-01-07 11:45:14 +01:00

The original texture had a strong white color with full transparency. When interpolating this white color appears and was rendered.
So with fixing the texture the fully transparent color could have been changed to remove the undesired color interpolation.

The original texture had a strong white color with full transparency. When interpolating this white color appears and was rendered. So with fixing the texture the fully transparent color could have been changed to remove the undesired color interpolation. ![image.png](https://archive.blender.org/developer/F8264218/image.png)

Philipp Oeser commented

2020-01-07 12:10:23 +01:00

In #69106#843320, @Jeroen-Bakker wrote:
So with fixing the texture the fully transparent color could have been changed to remove the undesired color interpolation.

Ah, thx for clarification @jbakker.
So I guess this requires a little paintover with Affect Alpha unchecked:

> In #69106#843320, @Jeroen-Bakker wrote: > So with fixing the texture the fully transparent color could have been changed to remove the undesired color interpolation. Ah, thx for clarification @jbakker. So I guess this requires a little paintover with Affect Alpha unchecked: ![image.png](https://archive.blender.org/developer/F8264239/image.png)

Will Brown commented

2020-01-20 00:04:37 +01:00

Added subscriber: @will.brown039

Will Brown commented

2020-01-20 00:04:37 +01:00

Hi I stumbled on this and I thought I'd add something,
If you open the source image in an image editor view, you can set the alpha mode to "Premultiplied", which will automatically multiply the RGB values by the alpha so they blend properly. Then you can paint without the white outlines.

It's odd that you have to open an image editor view to see the "Alpha" option, since you can change the "Image Source" and "Colour Space" options right on the Texture Node in the shader graph.

Another thing, it looks like the difference between Cycles and Eevee is because one treats "Straight" as "Independent RGB/Alpha" and the other treats it as "Premultiplied RGB/Alpha". If you set the alpha mode to "Premultiplied" or "Channel Packed", you get the same look in both renderers.

Hi I stumbled on this and I thought I'd add something, If you open the source image in an image editor view, you can set the alpha mode to "Premultiplied", which will automatically multiply the RGB values by the alpha so they blend properly. Then you can paint without the white outlines. ![premultiplied_change.png](https://archive.blender.org/developer/F8288658/premultiplied_change.png) It's odd that you have to open an image editor view to see the "Alpha" option, since you can change the "Image Source" and "Colour Space" options right on the Texture Node in the shader graph. ![premultiplied_result.png](https://archive.blender.org/developer/F8288660/premultiplied_result.png) Another thing, it looks like the difference between Cycles and Eevee is because one treats "Straight" as "Independent RGB/Alpha" and the other treats it as "Premultiplied RGB/Alpha". If you set the alpha mode to "Premultiplied" or "Channel Packed", you get the same look in both renderers.

Philipp Oeser commented

2020-01-20 10:56:37 +01:00

Added subscribers: @WilliamReynish, @brecht

Philipp Oeser commented

2020-01-20 10:56:37 +01:00

Thx for digging @will.brown039
Indeed this seems to be the (my) cause of confusion as well (should have thought about this before).

In #69106#842793, @Jeroen-Bakker wrote:
Perhaps this could be solved by premultiplying the texture when used in eevee, but that will give other artifacts.

So we already have the freedom to choose here, it is just not obvious. [@Jeroen-Bakker: not sure which artifacts this causes?]

In #69106#853164, @will.brown039 wrote:
It's odd that you have to open an image editor view to see the "Alpha" option, since you can change the "Image Source" and "Colour Space" options right on the Texture Node in the shader graph.

You can do it in the Node Editor, too, if you go to the sidebar and inspect the properties of that Image Texture Node.
(you have more settings in the sidebar than on the node itself, I think this is to keep nodes more compact...)

However, since this came up, maybe it makes sense in this case to add it to the node directly @WilliamReynish, @brecht?
(screenshot above is already with the patch below, so you can choose the Alpha directly on the node)
P1223: T69106_snippet



diff --git a/source/blender/editors/space_node/drawnode.c b/source/blender/editors/space_node/drawnode.c
index 35c9082b54c..5b35ecd0398 100644
--- a/source/blender/editors/space_node/drawnode.c
+++ b/source/blender/editors/space_node/drawnode.c
@@ -734,6 +734,13 @@ static void node_buts_image_user(uiLayout *layout,
   uiItemL(split, IFACE_("Color Space"), ICON_NONE);
   uiItemR(split, &colorspace_settings_ptr, "name", 0, "", ICON_NONE);
 
+  uiLayout *split_alpha = uiLayoutSplit(layout, 0.5f, true);
+  uiItemL(split_alpha, IFACE_("Alpha"), ICON_NONE);
+  uiItemR(split_alpha, imaptr, "alpha_mode", 0, "", ICON_NONE);
+  Image *ima = (Image *)imaptr->data;
+  bool is_data = IMB_colormanagement_space_name_is_data(ima->colorspace_settings.name);
+  uiLayoutSetActive(split_alpha, !is_data);
+
   /* Avoid losing changes image is painted. */
   if (BKE_image_is_dirty(imaptr->data)) {
     uiLayoutSetEnabled(split, false);

Thx for digging @will.brown039 Indeed this seems to be the (my) cause of confusion as well (should have thought about this before). > In #69106#842793, @Jeroen-Bakker wrote: > Perhaps this could be solved by premultiplying the texture when used in eevee, but that will give other artifacts. So we already have the freedom to choose here, it is just not obvious. [@Jeroen-Bakker: not sure which artifacts this causes?] > In #69106#853164, @will.brown039 wrote: > It's odd that you have to open an image editor view to see the "Alpha" option, since you can change the "Image Source" and "Colour Space" options right on the Texture Node in the shader graph. You can do it in the Node Editor, too, if you go to the sidebar and inspect the properties of that Image Texture Node. (you have more settings in the sidebar than on the node itself, I think this is to keep nodes more compact...) ![image.png](https://archive.blender.org/developer/F8289384/image.png) However, since this came up, maybe it makes sense in this case to add it to the node directly @WilliamReynish, @brecht? (screenshot above is already with the patch below, so you can choose the `Alpha` directly on the node) [P1223: T69106_snippet](https://archive.blender.org/developer/P1223.txt) ``` diff --git a/source/blender/editors/space_node/drawnode.c b/source/blender/editors/space_node/drawnode.c index 35c9082b54c..5b35ecd0398 100644 --- a/source/blender/editors/space_node/drawnode.c +++ b/source/blender/editors/space_node/drawnode.c @@ -734,6 +734,13 @@ static void node_buts_image_user(uiLayout *layout, uiItemL(split, IFACE_("Color Space"), ICON_NONE); uiItemR(split, &colorspace_settings_ptr, "name", 0, "", ICON_NONE); + uiLayout *split_alpha = uiLayoutSplit(layout, 0.5f, true); + uiItemL(split_alpha, IFACE_("Alpha"), ICON_NONE); + uiItemR(split_alpha, imaptr, "alpha_mode", 0, "", ICON_NONE); + Image *ima = (Image *)imaptr->data; + bool is_data = IMB_colormanagement_space_name_is_data(ima->colorspace_settings.name); + uiLayoutSetActive(split_alpha, !is_data); + /* Avoid losing changes image is painted. */ if (BKE_image_is_dirty(imaptr->data)) { uiLayoutSetEnabled(split, false); ```

Brecht Van Lommel commented

2020-01-20 14:37:22 +01:00

Don't add the alpha setting to the node. For correct behavior it almost never needs to be changed, it will encourage users to use the wrong workaround, which then breaks usage of the image in other renderers or tools.

If you open the source image in an image editor view, you can set the alpha mode to "Premultiplied", which will automatically multiply the RGB values by the alpha so they blend properly.

That is not what the option does. It specifies that the image file on disk contains premultiplied colors, and will then use that information to convert the image to the alpha format expected by Blender.

Don't add the alpha setting to the node. For correct behavior it almost never needs to be changed, it will encourage users to use the wrong workaround, which then breaks usage of the image in other renderers or tools. > If you open the source image in an image editor view, you can set the alpha mode to "Premultiplied", which will automatically multiply the RGB values by the alpha so they blend properly. That is not what the option does. It specifies that the image file on disk contains premultiplied colors, and will then use that information to convert the image to the alpha format expected by Blender.

Philipp Oeser commented

2020-01-20 14:43:15 +01:00

@brecht: thx for clarification (think I still need some more reading on the subject)

Will Brown commented

2020-01-21 06:18:35 +01:00

@brecht If setting the mode to Premultilpied means that the image data is read as already premultipled, then why does alpha_mode == IMA_ALPHA_PREMUL lead to IMB_colormanagement_imbuf_to_byte_texture() multiplying the RGB by alpha, when it's preparing the texture data in gpu_texture_create_from_ibuf()? If it thinks the data is already premultiplied, isn't that redundant?

Sorry if that's a dumb question, I'm just a bit confused following through the code

@brecht If setting the mode to `Premultilpied` means that the image data is read as already premultipled, then why does `alpha_mode == IMA_ALPHA_PREMUL` lead to `IMB_colormanagement_imbuf_to_byte_texture()` multiplying the RGB by alpha, when it's preparing the texture data in `gpu_texture_create_from_ibuf()`? If it thinks the data is already premultiplied, isn't that redundant? Sorry if that's a dumb question, I'm just a bit confused following through the code

Brecht Van Lommel commented

2020-01-21 13:42:46 +01:00

Changed status from 'Needs Developer To Reproduce' to: 'Archived'

Brecht Van Lommel closed this issue

2020-01-21 13:42:46 +01:00

Brecht Van Lommel self-assigned this 2020-01-21 13:42:46 +01:00

Brecht Van Lommel commented

2020-01-21 13:42:46 +01:00

You're right, it does end up premultiplying the colors in that case, I wasn't very clear. However it will also unpremultiply the image when loading from disk, which can break things depending on the tool or image file.

The reason for this issue is fb03f50, and it was an intentional change.

Basically, we made to choice to make Eevee behave the same as most game engines for compatibility, while Cycles does texture interpolation as typically found in production renderers. GPU hardware does not support accurate texture interpolation with good performance. It assumes zero alpha areas are still filled with color. By premultiplying the colors you can make it work for some images, while other images will have problematic dark edges.

You're right, it does end up premultiplying the colors in that case, I wasn't very clear. However it will also unpremultiply the image when loading from disk, which can break things depending on the tool or image file. The reason for this issue is fb03f50, and it was an intentional change. Basically, we made to choice to make Eevee behave the same as most game engines for compatibility, while Cycles does texture interpolation as typically found in production renderers. GPU hardware does not support accurate texture interpolation with good performance. It assumes zero alpha areas are still filled with color. By premultiplying the colors you can make it work for some images, while other images will have problematic dark edges.

Richard Antalik commented

2020-10-09 14:00:25 +02:00

Added subscribers: @AdrianoOliveira, @iss, @mano-wii, @Diogo_Valadares

Werner Lang commented

2022-09-02 16:22:41 +02:00

Added subscriber: @Punky

Werner Lang commented

2022-09-02 16:22:41 +02:00

I dont't get it. Is there a solution?
I try to paint landscapes (ala unreal engine) with multiple textures: http://kwyn.net/tex_pic.html and get a similar problem. I tried thousend of different things 😉 and still get this effect:
.
Any advice (apart from constant falloff, as smoohting leads to the same effect)?

I dont't get it. Is there a solution? I try to paint landscapes (ala unreal engine) with multiple textures: http://kwyn.net/tex_pic.html and get a similar problem. I tried thousend of different things 😉 and still get this effect: ![grafik.png](https://archive.blender.org/developer/F13452019/grafik.png). Any advice (apart from constant falloff, as smoohting leads to the same effect)?

Brecht Van Lommel commented

2022-09-02 16:25:13 +02:00

Please try one of the community support forums:
https://www.blender.org/community/

Please try one of the community support forums: https://www.blender.org/community/

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White outline around alpha in texture paint (when using multiple layers) #69106