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When I try to use an image that has an alpha channel, the image has glowing around the parts where there is transparency. Below are images to better explain my issue. Both are using the same image with exactly the same node setup and Cycles render engine.

In Blender 2.90.1 it looks like this: In Blender 2.90.1 it looks like this

and in Blender 2.79 it works as expected: Blender 2.79

This is the image i'm using. It is a TIF file created in Photoshop Blender 2.79

Is this a bug or has something changed in the way alpha is handled? I haven't used 2.90.1 version for long as I only recently updated from 2.79

EDIT: After packing the TIFF file into the blend file, the glowing disappeared. Then after unpacking the image and adding it to a new image texture node, the glowing appeared again.

Looks like Blender 2.90.1 treats external and packed files differently.

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  • $\begingroup$ Hello :). What happens if you plug the alpha channel directly into the Alpha input of Pricipled BSDF? And don't use the mix node? $\endgroup$ Oct 13, 2020 at 21:00
  • $\begingroup$ Hi. The result is the same. $\endgroup$
    – nyaol9
    Oct 13, 2020 at 21:57
  • $\begingroup$ I would suspect that for some reason the input values are larger than 1.0. Could you try to add a Map Range node with Clamp enabled between the Image node and the Principled BSDF? Does the glow also occur when only the color is connected? $\endgroup$
    – Robert Gützkow
    Oct 13, 2020 at 22:16
  • $\begingroup$ I added the map range node with clamp enabled. The texture turned grayscale as expected but I could still see the glow around the holes like before (just not so bright as it was only grayscale). I also tried to connect the texture color to the Principled BSDF and disconnected the alpha socket of the texture node completely, after that the glow disappeared along with the transparent holes. $\endgroup$
    – nyaol9
    Oct 13, 2020 at 22:39
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    $\begingroup$ Photoshop has completely bungled alpha. All of Blender’s eight bit imports are unassociated, so I suspect it might be interpreting the TIFF incorrectly as unassociated alpha and it is associated? On the upside, Blender finally displays alpha properly thanks to @atmind. $\endgroup$
    – troy_s
    Oct 14, 2020 at 1:45

1 Answer 1

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With image packaged into blend it works for me as expected. The issue appears when TIFF is unpacked and used linked from directory. Troy_s probably will be able to explain the issue, I don't have a knowledge in this area. I can just say how to avoid the issue here.


  • your TIFF doesn't use Transparency but channel "Alpha" (that is also why option "Save Transparency" is grey when you are saving your TIFF

enter image description here

  • to avoid the issue copy alpha channel and paste into Mask channel for "Background" layer.

enter image description here

  • Then when you save with "Layers", "Save Transparency" is available.

enter image description here

  • This TIFF is rendered fine in Blender.

enter image description here

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  • $\begingroup$ Here is an image of my TIFF save options: imgur the save transparency option is grayed out for some reason but the "Save alpha channels" option is enabled in the "Save as" window that appears before the TIFF options window. Color space is RGB and bit depth is 8bit. $\endgroup$
    – nyaol9
    Oct 13, 2020 at 22:44
  • $\begingroup$ I attached the blend file to the question now. $\endgroup$
    – nyaol9
    Oct 14, 2020 at 11:14
  • $\begingroup$ This method worked and now the transparency works in Blender. Though its weird that saving the image from photoshop and using the alpha channel instead of a layer mask works when the image is packed into the blend file. This sounds like a bug and should be looked into. $\endgroup$
    – nyaol9
    Oct 14, 2020 at 15:05
  • $\begingroup$ As Troy_s commented it can be on Photoshop side, I don't really know how these things works. Also Robert's comment is right, there is RGB larger than 1. So it is definitely clear Alpha channel participates on RGB appearance. I'm more curious how blender handles packed TIFF without issue ... :) $\endgroup$
    – vklidu
    Oct 14, 2020 at 15:18
  • $\begingroup$ I might be wrong here but it seems like Blender treats the alpha channel of external images as premultiplied alpha regardless of what has been chosen in the properties panel. If you read here in the Blender docs it says that premultiplied alpha is useful for emissive effects and that sounds like what is happening here with RGB larger than 1, causing the glowing effect. $\endgroup$
    – nyaol9
    Oct 14, 2020 at 15:38

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