handrawn - evidently I can't upload .pspimage files, I've tried. So even if I did, you wouldn't be able to work with it as the layers aren't preserved... Unless I'm missing something, haha.

Anyway, are you suggesting I merge one of the window layers to the background layer so that the blending is preserved? That is a good idea, except that then my people passing behind the window (and in front of the background) will still not be passing behind a blended layer.

Trev - yeah, I've tried the PNG Optimizer as you'll see above. My actual issue is getting the blend modes to stay blended when the background is not visible and then it is saved.