PNG is always 100% quality. There is no setting to it. It's lossless compression.

I don't understand your sentence that combines the words "resolution" and "kilobytes". You're compressing. An ultra high resolution image consisting of mostly rectangles of solid color would compress to very small values, so telling us your file size is in kilobytes doesn't actually tell us anything at all.

What is your problem. Are you concerned with dimensions of your image? (image size?)

Are you concerned with the number of pixels used to represent your props? (resolution, which is actually image size?)

Are you concerned with pixellated edges of your rendered objects? (antialiasing which is all about render settings and nothing to do with PNG VS JPG)

If it's the last one, you need to increase pixel samples in render settings and you probably need to adjust post filtering in render settings. However,  I'm sorry to say I can no longer remember if/where those are in P6.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)