I have this 1754x1240 texture which I use for vintage effect in background images in my iOS app. iPad screen size is quite large 1536x2048 and when I apply this texture directly to an image that size it doesn't look very nice.
I tried downscaling this texture and cloning it all over the image but then in the edges there are abrupt transitions, which doesn't look nice neither. I tried gaussian blurring for the edges but couldn't get it to work. Is there any way to extend a part of this texture (with smooth transitions between repeated parts) so I can apply it to an arbitrary size image? Hope I'm clear.
There's really no big trick to it. There's no automatic way to simply create a smooth tillable image from scratch. And, if you want to retain the rough edges that's not at all possible withut cloning.
It merely takes some attention to cloning, healing, and covering seams once you've duplicated portions of the image.
If you are looking for a seamless pattern, crop the image to a square. Then use Filter > Other > Offset and input half the width and half the height and click OK. This will result in an image with seams in the middle. Simply use cloning or healing tools to blend those seams. The result will be a seamless pattern which you can tile.