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Transform node with bicubic filtering distorts image
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System Information
Win 7 64bit

Blender Version
Broken: 2.79

Short description of error
With untouched settings every other option gives proper "difference" result, except Bicubic.

Exact steps for others to reproduce the error
Open file, switch between filtering options and see difference from source image.



Event Timeline

I see that too.
Don't know enough about nodes to know if its a bug or not.

Even in cycles you see a difference. I thing that the difference is by what is determined as the dead center of the pixel coordinate. (lower left verses precise center). But will need more testing (if this is the case) and discussion about what should be the correct implementation.

Brecht Van Lommel (brecht) triaged this task as Normal priority.

This is what a plain bicubic filter is expected to do. The filter area for a bilinear filter is exactly 1 pixel, and so there will be no influence from neighboring pixels if the image is not transformed and the pixel centers are aligned properly. A bicubic filter has a larger filter area and will blur the image.

What would be useful is a smarter filter, that can for example detect when to do bicubic or bilinear filtering depends on the parameters. I'm not sure the current state should be considered a bug.