Alpha channel is not respected by emission (or some/any other) shaders, connected to one of two duplicated image texture nodes, one with alpha on and the other with alpha off. #50032

New Issue

Ales Volcini · 2016-11-15T03:10:19+01:00

Ales Volcini commented

2016-11-15 03:10:19 +01:00

System Information
Windows 7, Linux Mint 17.3 (in VirtualBox)
AMD R9 Nano

Blender Version
Broken: 2.78a

Short description of error
See screenshot - Cube is glowing instead of glowing only at the bottom.

Exact steps for others to reproduce the error
Have a png or tga texture file, RGB channel for diffuse and alpha to specify emission region.
Create a mesh, switch to cycles, import the texture, duplicate it, set up other nodes, set alpha to off for the texture connected to the diffuse node. Render will be invalid one.
Pack one of the textures to blend file, render will become valid.
Unpack it again, preview is still valid until F12 rendering, but the render result is again invalid. Preview also becomes invalid after some parameter change happens (eg. emission strength is changed).

See attached blend file emission test1.zip.

It appears there is the same effect if emission shader is swapped for a different one. I also noticed texture preview hints at the correct result, if the alpha mode is set to straight and the incorret result, if the alpha mode is set to premultiplied. Material preview however does not reflect any changes. My guess is Alpha mode: Straight is somehow ignored.

Ales

**System Information** Windows 7, Linux Mint 17.3 (in VirtualBox) AMD R9 Nano **Blender Version** Broken: 2.78a **Short description of error** See screenshot - Cube is glowing instead of glowing only at the bottom. ![Screenshot.png](https://archive.blender.org/developer/F400874/Screenshot.png) **Exact steps for others to reproduce the error** Have a png or tga texture file, RGB channel for diffuse and alpha to specify emission region. Create a mesh, switch to cycles, import the texture, duplicate it, set up other nodes, set alpha to off for the texture connected to the diffuse node. Render will be invalid one. Pack one of the textures to blend file, render will become valid. Unpack it again, preview is still valid until F12 rendering, but the render result is again invalid. Preview also becomes invalid after some parameter change happens (eg. emission strength is changed). See attached blend file [emission test1.zip](https://archive.blender.org/developer/F400879/emission_test1.zip). It appears there is the same effect if emission shader is swapped for a different one. I also noticed texture preview hints at the correct result, if the alpha mode is set to straight and the incorret result, if the alpha mode is set to premultiplied. Material preview however does not reflect any changes. My guess is Alpha mode: Straight is somehow ignored. Ales

Ales Volcini commented

2016-11-15 03:10:19 +01:00

Changed status to: 'Open'

Ales Volcini commented

2016-11-15 03:10:19 +01:00

Added subscriber: @avolcini

Joel Godin commented

2017-01-02 05:24:05 +01:00

Added subscriber: @FloridaJo

Joel Godin commented

2017-01-02 05:24:05 +01:00

I see that when I use your png, but when I create one from Gimp I'm not seeing that.
Can you try this image attached in place of test003.png

I see that when I use your png, but when I create one from Gimp I'm not seeing that. Can you try this image attached in place of test003.png ![JTest2.png](https://archive.blender.org/developer/F425940/JTest2.png)

Ales Volcini commented

2017-01-02 13:50:21 +01:00

I don't think it's a file type related problem, a tga texture has the same result.
I came across this problem with textures used for Valve Source engine, where there is a diffuse channel combined with an emission one (or transparency, bump etc. (i.e. noncolor data, however this texture setting does not change anything visible in this setup).

Since I could not extract only the alpha channel, I duplicated the image texture node, made one a single-user copy so they didn't share alpha setting, switched off alpha in one for the diffuse shader (since black alpha affects color, too) and used only the alpha in second to select regions with emission. Before I tried with straight and premultiplied alpha, too, with no effect.

I used your texture, it does the same (see emission test3.blend in a zip below). Just switch 'viewport shading' to 'rendered' mode and when you'll click "pack an image as embedded", it will render in a way (i think) it should be - where alpha is 0, non-glowing. Funny thing: the material preview (on the right side of screenshots) is ok in both cases. Using same texture in two separate files renders ok. A case with both textures packed renders ok, too. It's just the case when the texture source is in the same actual file even if it's 'single-user copy'.

emission tests.zip

Emission test3.blend before'pack' (incorrect): After (correct):

I also attached another test - emission test2.blend - with texture (also made with gimp, first one was made with gimp too, so that's not related to a program).

Before (incorrect render): After 'pack' (correct render):
Funny again, the material preview on the right side seems ok in both cases.

I don't think it's a file type related problem, a tga texture has the same result. I came across this problem with textures used for Valve Source engine, where there is a diffuse channel combined with an emission one (or transparency, bump etc. (i.e. noncolor data, however this texture setting does not change anything visible in this setup). Since I could not extract only the alpha channel, I duplicated the image texture node, made one a single-user copy so they didn't share alpha setting, switched off alpha in one for the diffuse shader (since black alpha affects color, too) and used only the alpha in second to select regions with emission. Before I tried with straight and premultiplied alpha, too, with no effect. I used your texture, it does the same (see emission test3.blend in a zip below). Just switch 'viewport shading' to 'rendered' mode and when you'll click "pack an image as embedded", it will render in a way (i think) it should be - where alpha is 0, non-glowing. Funny thing: the material preview (on the right side of screenshots) is ok in both cases. Using same texture in two separate files renders ok. A case with both textures packed renders ok, too. It's just the case when the texture source is in the same actual file even if it's 'single-user copy'. [emission tests.zip](https://archive.blender.org/developer/F426290/emission_tests.zip) Emission test3.blend before'pack' (incorrect): ![Screenshot before.jpg](https://archive.blender.org/developer/F426278/Screenshot_before.jpg) After (correct): ![Screenshot after.jpg](https://archive.blender.org/developer/F426280/Screenshot_after.jpg) I also attached another test - emission test2.blend - with texture (also made with gimp, first one was made with gimp too, so that's not related to a program). Before (incorrect render): ![Screenshot3.jpg](https://archive.blender.org/developer/F426286/Screenshot3.jpg) After 'pack' (correct render): ![Screenshot4.jpg](https://archive.blender.org/developer/F426288/Screenshot4.jpg) Funny again, the material preview on the right side seems ok in both cases.

blender-admin commented

2017-01-25 14:02:59 +01:00

This issue was referenced by blender/cycles@0f7a17a023

This issue was referenced by blender/cycles@0f7a17a0230787dfd062a6c702d044de04325e4f

blender-admin commented

2017-01-25 14:02:59 +01:00

This issue was referenced by ced20b74e5

This issue was referenced by ced20b74e58f3dd33840f2a62f6f1f19714b35d7

Sergey Sharybin commented

2017-01-25 14:14:10 +01:00

Changed status from 'Open' to: 'Resolved'

Sergey Sharybin closed this issue

2017-01-25 14:14:10 +01:00

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Alpha channel is not respected by emission (or some/any other) shaders, connected to one of two duplicated image texture nodes, one with alpha on and the other with alpha off. #50032