Importing own textures

[Essemmgee]

I hope this is not too dumb; whenever I use the supplied canvas/paper textures I get an overall tiling effect (presumably where the edges of the samples don't quite match). As I work a lot with dry brush/crayon techniques this is rather undesirable as it shows as an uneven grid pattern on the finished A/W. I was wondering whether I might be able to install my own scan of a full size texture (say 400mm x 300mm), but despite scouring the forums I have been unable to locate details on how to do this - or even if it is a wise move or just plain stupid.

I would be grateful for any advice or links.

Thank you.

[Essemmgee]

Whoopsie, sorry. Posted this in the wrong form