[filmscanners] Vuescan and multipass algorithm

["" <ake.vinberg@home.se>]

I noticed the other day a peculiarity with Vuescan's multipass algorithm. I
scanned transparencies using a flatbed, did 16-pass scans. (Very noisy
scanner, especially after being powered on a few hours.)

The output images seem to be calculated by averaging the value in each
pixel. The result is a smooth noise level, but no real noise elimination.

As an experiment, I scanned 16 passes and did the noise elimination myself
in Photoshop, using Apply Image in Darken mode. This mode takes the lowest
value for each color in each pixel. The resulting image was very clean!
Noise was completely gone, and real-life Dmax was much better. Colors did
not seem to be affected, except for improved contrast.

So: It would be great to have the option in Vuescan to choose algorithm in
multipass scans, between Average and Minimum.

Does this sound reasonable?

Best regards,

Åke

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