Incorrect blending of image with alpha

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Borek Lupoměský

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Incorrect blending of image with alpha

PostThu Apr 20, 2017 12:59 pm

I am using Fusion to add animated title to Resolve. I export from Fusion as PNG frames with alpha channel. The clip is then put on top of other footage in the timeline and it blends using the alpha channel. This works fine -- as long as the title is not resized in any way. Once you zoom the title layer, or it is implicitly resized because of project frame settings, ugly dark fringe appears around the letters. You can see this in the linked image (note the zoom values).

My original idea was that Resolve is interpolating the title in gamma-corrected space instead of linear space (the correct way). But I couldn't recreate the effect in Photoshop, so I am not sure if that's what is happening. Any ideas?

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Igor Riđanović

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Re: Incorrect blending of image with alpha

PostThu Apr 20, 2017 8:23 pm

That's interesting. Premult settings for the PNG clip in Resolve should not be the reason for this artifact, but I'd try changing the premult to see if it makes any difference.

I't almost as if a different algorithm is used for RGB and for Alpha. Try changing the scaling algorithm in the Project Settings or in the Inspector.
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Borek Lupoměský

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Re: Incorrect blending of image with alpha

PostFri Apr 21, 2017 6:44 am

The example uses premultiplied alpha -- without it it's wrong even without any resizing. I tried to change the scaling options, but it is slightly different each time, but always wrong.

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