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Don't use "Noise -> Median". You'll see some people recommending it, but the results are deceptively poor.

The dark area here is among the hardest type of screening to filter cleanly. The sparse white dots need to be filtered evenly across the surface, or they'll leave ugly little checkered splotches:



The median noise filter, at first glance, seems like it's doing a good job here, removing the white dots for further filtering.

But that's completely wrong. The dots are there for a reason: they affect the brightness of the area. This filter is removing them entirely, which darkens everything and kills luminescence (brightness) detail. The dots aren't there by accident--they need to be filtered, not just removed.