Scanning software

Scanning software should deliver maximum information in the best possible form. It’s not necessary to avoid further processing, but it’s important to keep it possible and to perform processing steps that can be made automatically without losing important information. Choosing right scanning tools is important as mistakes in this process may result in the necessity of repeated scanning and processing. How is it with scanning negative films on Epson Perfection 2480 Photo?

The original Epson scanning software on Windows usually produces good results, but one must be careful to actually receive them. Obvious selections are setting colors to 48-bit (or 16-bit in case of bw negatives) and resolution to

  1. “Improvement” options should be all disabled, especially dust removal

that in my experience actually doesn’t remove any dust but removes many details instead (this is a pure software algorithm, the hardware doesn’t support any dust removal features). Note that unsharp masking has to be disabled for each scanned film field individually. When you forget it, you receive bad results when you try to apply unsharp masking later yourself. Usually the software produces good colors (better than I’m able to get from the negative by other means now) although manual corrections are often necessary during post-processing, as is common with color negatives. It happened to me once with a few strongly overexposed film fields that the software has chosen very aggressive color clipping and I had to adjust histogram settings and rescan the given fields again. The Epson software requires a lot of mouse clicks (on average more than 2 for each scanned field) and suffers from memory leaks, requiring occasional restarts.

On Linux the scanning process is more challenging. The SANE driver supports all the crucial hardware features and scanning half a film strip requires just a single scanner button press (when you use scanbuttond) and no mouse clicks. But here is a small 1:1 sample of what you receive (contrast is much increased in all the examples to demonstrate the problems more clearly):

epson-sane-quality.png

Note two things:

  1. The very ugly stripe about one quarter from the left in the image. This is not a scratch on the film, this is a systematic defect.
  2. The regular pattern of vertical one pixel wide darker and brighter stripes around edges of dark areas.

As for the special ugly stripe, it helps turning quality settings off (i.e. removing the ‘–high-quality=yes –quality-cal=yes’ scanimage command line options). I guess their meaning is reversed in the driver by mistake. So here is new result:

epson-sane.png

The extra stripe is gone, but the regular stripe pattern is still there. I’ve no idea why it’s there but I’ve seen something similar in the samples from other scanners on the net so it’s likely to be some common hardware feature. FWIW, scanning direction is vertical here. No such apparent stripes are present when the same image is scanned with the Epson software on Windows:

epson-epson.png

So I tried to get rid of the stripes by averaging each two neighboring stripes into a new “neutral” stripe. This operation shouldn’t lower resolution of the image, it may just soften it (and the actual scanner resolution doesn’t correspond to the scanned image size anyway). So it should be safe. Here is what I received after applying the following imagemagick commands:

convert -crop 199x158+0+0 image.png crop1.png
convert -crop 199x158+1+0 image.png crop2.png
composite -blend 50% crop1.png crop2.png result.png

epson-fixed.png

I think the result is pretty close (except for contrast adjustments) to what Epson software produces, so it’s probably the way to go.

All the things presented here may look clear and simple. But it took me long time coming from the first naive scanning attempts to discovering why the scanned images don’t look well and finally finding out all what’s described above. Now I know supporting a piece of hardware doesn’t mean just providing raw low-level drivers to the hardware. The hardware specific post-processing part is also very important and the user may receive poor results if this part is missing.

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