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noise types and filterings

scanning_dust
it shows up mainly on bright tones and dark tones. small dusts on bright can be erased easily by ordinary filtering, but other dusts need to be erased by the clone stamp or the patch tool.

paper_texture
it resembles to scanning_dust because they're the issue of physical structure of scanned materials. in other works, they are 3D noises.
this noises on bright tones are eaisly erased by the same way of the above, but I still couldn't get how to kill this noises on darks.

bleed through
get an accurate levels is the first step. then apply strong filter with the color range selection with white, or masking on dark~mid tones.

screening
it exists on mid~dark tones, and separated 2 types of noises.
1) chroma screening noise: just remove CrCb masking brights.
2) luminous screening noise: it mainly exists as white spots on the darks. it's better to use 2 pass filtering (darken+normal) than 1 pass filtering. also don't forget to mask on bright tones.

jpeg_artifacts
poke the man who scanned it.