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Flatten or Rasterize after a crop introduces small transparent edge(s)

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I've noticed this for a while but didn't think to post.


You have an image. Make sure 'force pixel alignment is off'. Perform a crop. Then either rasterize the layer or flatten the document and many times there will be a small 1px transparent edge(s) on the image.


If it is completely transparent shouldn't it be cropped away?


Using 'force pixel alignment' fixes this but it seems that it is not accurate behavior with it off.

Work site: Pixel and Poly


Introduction to astronomy and the universe website (all images were created with Affinity Photo and Affinity Designer): The Universe from A to Z

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It actually is accurate behavior because of anti-aliasing. If the edge of an object isn’t exactly aligned to a pixel edge it’s bleeding into the next pixel with a varying amount of transparency, depending on the amount of misalignment. It might not even be visible to the plain eye but it’s there for the computer that does the calculation, and that’s why you get a (semi) transparent edge.


Nice tutorial explaining anti-aliasing in icon design showing the issue in the second image: http://mezzoblue.com/archives/2007/07/11/icon_design/

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