Example of removing rainbow artifacts from gloss warped stock when scanning.

[slackercrurster]

When scanning gloss stock that is warped it is hard to get a good contact with the scanner glass. In this example the warped gloss stock produced a rainbow type of defect while scanning.

Weighting the scanner lid can help get good contact with the original. Foam backer board must be used under the scanner lid as the flatbed scanner lid provides poor contact. 18 pounds of weight was used here. If you go above 22 - 24 pounds on the scanner lid, an Epson V600 scanner may break. Every scanner is different; you check its weight limits out for yourself. In the old days we had vacuum frames. They provided perfect contact...but we had no scanners!





Unweighted scan of RPPC



Crop of unweighted scan defect area.



Crop of weighted scan defect area.

Full report:

Scan With Rainbow Defects Weighted / Unweighted Comparisons D. D. Teoli Jr. A. C. : D. D. Teoli Jr. A. C. : Free Download, Borrow, and Streaming : Internet Archive

 

[koraks]

a rainbow type of defect

Newton rings.
Nite that your solution works (and indeed I use it frequently) for reflective materials. The problem with (e.g.) prints isn't just Newton rings, but also (even more so) issues like uneven exposure across the print if the paper isn't perfectly flat - think of wavy FB or alt process prints. I generally use the foam-padded pressure mat that came with my scanner and weigh it down with something reasonably heavy that's handy. A couple of pounds does the trick. There's very little point in weighting down the entire scanner lid (just leave it up/open) and in fact you don't want to do that especially if you have a transparency unit in there. Weighting down the lid is ineffective and may damage it.