Actually, I should step back a little from that statement. It might make a difference, but I don't know how the Gimp handles dpi. If the software behaves properly, it shouldn't make a difference. If it doesn't, then that might, indeed, be the problem.
I'll leave it to Rob to say yea or nay on that one.
Heh. Well, don't zoom in on it. That'll cause pixellation every time! Now that I know what I'm looking at, in terms of the workspace, I know exactly where the problem is, and that's the magnification. Don't try and judge the quality of your image at anything other than 100%; that's what your audience is going to be seeing it at, after all.
It looks terrific at actual size--better than the 600 px version, in fact--so there's really no need to worry about what it looks like zoomed in. If you want to make images that scale upward nicely without ever seeing that pixellation, take a look at Inkscape, a vector drawing program.
It looks a little better with multiply (see below), and I guess I could make it less opaque to get a similar effect to burn, but the pixelation was just bugging me.
It is your choice of burn as an overlay mode.
Here are 4 useful ones for this kind of work:
Burn is done by inverting the back later, dividing by the front layer then invert back again. It effectively boosts the contrast and saturation:
255-((255-B)*255)/(F+1) (formula from Beginning GIMP, from Novice to Professional)
So because your pattern fill is highly contrasted you get colour blow-outs of the back layer (that look like pixelation).
Here is that paper bg with a gradient using burn (top is normal blend, bottom is burn):
I personally use overlay, and duplicate the overlay layer if the effect isn't dark enough.
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Thanks Rob - I ended up using a double burn layer with playing around with the opacity. That solved a lot of my problems, as did making my pattern a smaller one. I guess it's a matter of trying a bunch of things and seeing how they work. One thing's for sure, I'm learning a lot more about Gimp than I knew before and that's all good.
Thanks again - when I'm done with the Zombie tutorials, I'll post the results.