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In the compositor node editor, I have an image node -> a blur node (Gaussian, X=100, Y=100) -> composite node.

The unblurred image looks like this (There is a black square on a white background and a white square on a black background): There is a black square on a white background and a white square on a black background

The blurred image looks like this: white square bigger than black square

Notice how in the blurred image, the white square is bigger than the black square. Is there a way I can blur the image "The other way" so that the white square is smaller than the black square?

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  • $\begingroup$ Try the dilate/erode node $\endgroup$
    – susu
    Sep 29 '20 at 0:36
  • $\begingroup$ @susu it does help a bit $\endgroup$ Sep 29 '20 at 2:25
  • $\begingroup$ @RobinBetts I think it should be an answer anyway - it's pretty much spot-on in my mind :-) $\endgroup$ Sep 29 '20 at 14:02
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With a little encouragement from @Rich Sedman, copied from comment:

The white square looks bigger, because of the conversion after compositing to sRGB for your display device. Arithmetically, inside the compositor, the squares are the same size. If you go to Color Management and switch the View Transform to 'Raw', you can see that.

You could use gamma correction after blurring in the compositor, to change that, but you would have to be be aware, that were you to use the squares for masking or suchlike, that part of the pipeline would become non-linear.

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  • $\begingroup$ Thank you so much! I will try for a bit. $\endgroup$ Sep 29 '20 at 20:34
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Can also use some RGB curves, maybe (?)

enter image description here

Eventually, add another blur (with lower values) after the last RGB curves.

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