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After straightening out UV islands, I often find that there is a lot of "Noise" in the positions of the vertices in my UV map. This results in small distortions when applying a texture to the mesh. Sometimes the "Minimize stretch" tool in the UV editor will fix this, but most of the time I just get a result like this:[![enter image description here][1]][1]

This issue is also very inconsistent. Just small changes to the geometry will drastically effect whether or not this happens. In fact, it was hard to get a screenshot of it, since adding a few sharpening loops to my mesh fixed the issue for most of the UV islands.

EDIT:

here is a file demonstrating the issue.

[1]: https://i.stack.imgur.com/tJ3PV.png

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  • $\begingroup$ The effect of minimize stretch is going to depend on your actual mesh object, which isn't shown. It should be trying to adjust UV in a way to minimize change in UV / change in position. It does this in iterations, available in the operator panel for the operation, because minimizing stretch on one face may exacerbate for it another face. I can't promise to be able to help with this, but a file with the actual mesh under consideration would help people take a look at the issue. $\endgroup$
    – Nathan
    Nov 21, 2021 at 23:38
  • $\begingroup$ @Nathan I attached a .blend file. It's hard to get a good example of the issue, since I mostly smooth the UVs manually when this occurs. This file should show the problem, but please note that it is usually more extreme than this, since these UVs have already been manually smoothed. $\endgroup$
    – SupaKoopaTroopa64
    Nov 23, 2021 at 21:26

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The fix for the issues caused by minimize stretch operation is to mirror your UV map for the affected islands-- ie, scale each UV map by -1 in the X axis. (Or the Y axis. It doesn't matter which.)

If we take a look at the mesh and the UV map that you've provided, we can see that there's a difference in coordinate handedness between the world position of the verts and the UV position of the verts (for the bad islands): moving up the strand moves it in the +V, but moving right along a ring in a strand (looking down from the normal, with the "top" being the +V side of the strand) moves it in -U.

I don't know exactly how Blender calculates stretch in order to minimize it, but it's very easy to imagine it getting confused by this difference in coordinate handedness. We can see that when we mirror the bad UVs, we get appropriate operation from minimize stretch:

enter image description here

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