Forums Technical Discussion Missing Unpremultiplied Option in New COPS File Node

Missing Unpremultiplied Option in New COPS File Node

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maartennielen
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In the new COPS, the file node does not have an option to load images unpremultiplied, which results in a very dark image. Since I often need to load TGA files with alpha for my work, I'm looking for a good workaround. The old COPS file node does have this option.
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Edited by maartennielen - 2025年3月24日 04:36:21

Attachments:
example.tga (1.0 MB)

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Heileif
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Workarounds.

Unpremult = rgb divided with the alpha.

Premult = rgb multiplied by the alpha.
Edited by Heileif - 2025年3月13日 11:18:41
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maartennielen
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Yeah, thanks for the fast reply. The File node gives a different outcome compared to manually premultiplying or unpremultiplying the correct image without the alpha. So I think something is broken in the File node since the results don’t match. I’ll make an example file
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maartennielen
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Here is an example file. I don't see any way to restore the image by dividing or multiplying with the alpha. As far as I know, this only happens with TGA files.
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example.tga (1.0 MB)

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ajz3d
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My guess is that you should be importing the image as Raw for the Un-premultiply (Premultiply COP) to work correctly.
In the File COP, change the "Incoming Colorspace" to "Raw", or check the "Raw" flag for the C AOV.
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maartennielen
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Thank you for your reply! Yeah, I also assumed that would be the solution. I think I’ve tried almost every possibility, but I have a feeling it’s a bug. I attached the TGA file in my last post if you want to try it.
Edited by maartennielen - 2025年3月24日 17:41:08

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example2.jpg (160.3 KB)

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ajz3d
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Now with File COP set to "Raw", drop a Premultiply COP and unpremultiply the image.
Edited by ajz3d - 2025年3月24日 18:02:42
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maartennielen
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Thank you! It’s working now! I don’t know why I couldn’t get it to work before. I did try dividing by the alpha but got a broken result. I just tried it again, and everything seems fine now.
Edited by maartennielen - 2025年3月24日 18:13:42
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johnmather
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This has been fixed in 20.5.549. You can disable the new "Pre-multiply if Necessary" parm on the file node.
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maartennielen
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Thank you very much!
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