Very impressive! I'm surprised by how well this works (especially for those bricks!).
There are still some patterns that can be spotted, I think you should try maybe rotating some of those splotches to get rid of those (there is a great video I watched which goes into way more detail about this and is definitely worth looking at for you youtube.com/watch?v=-VgtSL5ZpYc ).
I think it would also be cool to have different types of splotches , as the current one doesn't work to well with grids for example. While you're at it, the UI could definitely use some tooltips (what the heck does radius do??).
It would also be really cool if you could somehow add some functionality to crop out certain things in the image, especially if the shape isn't a perfect rectangle, as the way we take pictures (phone or screenshots) are in rectangular format, but some of the things I might want to tile could be skewed or a different shape entirely (triangle, hexagon, etc).
I've also noticed, that the texture look weirdly darker, but not really in a way that can be fixed with the brightness or contrast sliders :|
But apart from that, great work! All I want now is a mac version so I don't have to break out my old computer to use this :D