Seems alright to me. How are you trying to use it?

As usual, the lack of code makes hard to answer, since we must try to guess what error you did...
For example, it can be the issue addressed in the Why are text and graphics so ugly and blocky? article...

God I've been stupid. I compared the code shown above to mine, and I realised I forgot to call background() in the draw() function. Thank you for helping me.