Blur brush foxes me.

[iconoclast]

1 minute ago, R C-R said:

I think it is a bug too, one related to hardware acceleration ... at least assuming that for you on Windows like for me on my Mac that disabling it makes the brush preview behave as expected.

Yes, but it is not clear to me if it is worth it, because I do not use this brush very often and I'm not sure about the disadvantages of disabling Open CL. Hope this will be fixed soon, so that we don't have to bother our brains about it any longer.

[Patrick Bell]

It is not that it is subtle, it just doesn't seem to work on some images. I can load some images and clearly see the blurring. I think the issue is that if already a bit blurred it may not recognise the edges.  In those images where it works it is working on already recognised edges. If I export and try to increase the blur (where it has worked in the original image) I cannot do so.

[PaulEC]

The effect will also vary depending on the size/dpi of the picture.

[iconoclast]

And to get a meaningful impression of its effect you should watch it with zoom factor 100% (1:1).

Also the help file says that the effect of the brush is cumulative. So to blur more, you have to paint more. It's a little bit like modelling. Very subtle.

Also important is that you choose the right size for this brush, because this will determine the blur radius. And usually you should use a soft brush head, not a hard one.