Bug with Offset Filter- Aliasing appears with high values

[mattnava]

If you use the Offset filter on a large canvas and input high values for the offset, the image quality gets degraded. I was testing on a canvas that is 2048x2048, and the effect is clear. Things become very aliased, thin lines get turned into blocky pixels. The higher the offset value, the more extreme the aliasing becomes.

This becomes an issue for authoring seamless textures, where the offset functionality needs to be lossless as it gets repeated many times.

[Lucky Clan]

Please send step-by-step instruction, and give us your iPad model.

[mattnava]

Hey I’m finally updating this issue with repro steps and examples- the bug still exists. I’m on iPad Pro (12.9-inch) (6th generation).


1 make an image that is 2048 x 2048.
2 use filter- render- clouds to make some black and white shapes.
3 use levels to increase the contrast a bit to make the issue easier to see.
4 use filter- distort- offset, and set the horizontal amount to 2048. Edges should be set to repeat (seamless).
5 zoom in and observe that despite the fact that this operation should result in the image being unchanged (because we shifted it the same amount as the width of the canvas), every other column of pixels is now duplicated from its neighboring column. The image has lost data.


Attached is a close up showing the issue. The left side shows what happens when you do an offset filter, and the right side shows the original pixels.

[mattnava]

On more bit of info, this doesn’t seem to happen on a 100 x 100 pixel canvas with a 100 pixel sized offset, I’m not sure at exactly what size it starts to happen