Quote:This scan is just bot high fidelity enough (600dpi jpg) for the extreme close ups I need to do.
For a scan, 300 ppi (photo quality) is sufficient. 600 ppi is really a maximum but it depends on the scanner, 1200 ppi usually an interpolation and not always better quality, just larger.
From your posts you are doing some extreme manipulation. Try thinking of other ways. Get someone with a good camera, good lighting, good macro lens and take a photograph of the area of the painting you are interested in.
This with a cr*p camera (mobile phone), poor lighting (sun is setting here), and a 10 euro clip-on macro lens.
It is the center of a postage stamp. An area about 1 cm x 1 cm