What image program do you use?
For me, I use GIMP, but a little trick I've found is that if you have the whole image selected and it's 513x513 and greyscale, and press Ctrl + C to copy it, and then press Ctrl + Shift + V (or whatever it is for other image programs, it just pastes into a new window) and then press Flatten Image, and then save over the old one, it usually works for me.