When i paint some textures on my UV-Texture, the image is sometimes pixelated. I don't know how i can adjust the best zoom size of the stencil texture. How can i ensure best quality?
Generally, you should be aware of two things:
In your case, I'm not sure how big you build the background image, but if it's 2048 x 2048 px, then, in the current zoom level, the stencil texture may probably covers about 10% of the whole area, which means 648 x 648 px around, far from enough, isn't it?
Besides, your stencil texture seems sort of a gravel texture, which means the detail unit is quite small. Obviously, you need enough pixels on the background image to at least cover the detail of the a unit gravel, in order to preserve the original detail as you want.
My suggestion is: try not to have the background image over zoomed in while painting.