2
$\begingroup$

On trying to answer this question, I can't subtract information from the alpha channel without running into borders that persist from the UV mapping node. Those borders come from the original image's alpha channel.

When I map a mask using the UV mapping node, I would have expected to get only the information from the mask in the image (meaning the mask on a black background), but the image gets some alpha information from the render layer as well. That information I cannot subtract from the alpha channel.

This is the setup I'm after, that shows the error:

enter image description here

and the result of the subtract operation:

enter image description here

If you look at the mask going through the UV map, there are some edges that are not part of the mask at all, but are the edges of the original alpha channel of the image used in the texture.

The object in the scene is just an EXR image imported as plane, mapped to a principled bsdf, that uses the Alpha channel of the image as Alpha on the shader.

enter image description here

Here's the blend file

EDIT:

If I ignore the alpha channel on the original image, the mask shows correctly, but now the edges of the UV map show.

enter image description here

$\endgroup$
0
$\begingroup$

This difference is in the original alpha channel.

Same view, same zoom level:

enter image description here

enter image description here

$\endgroup$
3
  • $\begingroup$ The question is why subtracting a mask does not take away those pixels. $\endgroup$ – susu Jan 17 at 22:07
  • $\begingroup$ If you notice the problem appears before mixing the render layer, in the Map UV, where I would expect only the mask to be present with no other information from the image itself. $\endgroup$ – susu Jan 17 at 22:20
  • $\begingroup$ Oh, you're right, hmm... $\endgroup$ – Allen Simpson Jan 18 at 3:45

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.