#26 Gamma correction from scanner?

[Detlef Peukert]

Hello,
can somehow use the gamma correction from the scanner? Even the default value of 1.8 is not enough. For example, if I use simplescan, the scan is wonderful. Or I edit with Gimp (brightness / contrast) and there (from the scanner), then the scan is synonymous okay. My scans are still too dark, too low in contrast. I use an Epson ET-2550 via network scan.
Thanks for your help...

Regards - Poi

[Jeffrey Ratcliffe]

Please start gscan2pdf from the command line with

gscan2pdf --log=log

open the scan dialog, quit, and post the log file.

[Detlef Peukert]

Hallo Jeffrey,
tx for answer. Here is the log file... :-)

Regards from germany.

[Jeffrey Ratcliffe]

Apologies for the late reply.

Your log file shows two sets of gamma option, gamma-correction "Selects the gamma correction value from a list of pre-defined devices or the user defined table, which can be downloaded to the scanner", and individual red, blue, green settings, which seem to expect multiple values.

It is not clear to me how to download the gamma-correction table to the scanner, and never owning a scanner which expected multiple values for an option, I have not been able to test those type of options well.

I'm guessing that simplescan scans in colour and then postprocesses to get the desired result.

You could achieve the same by scanning in colour and then either thresholding to black and white or using a user-defined tool (e.g. with imagemagick) to get the greyscale result you want.

Alternatively, using the scanimage tool from the command line, if you can find the set of options that get you the result you want, I can look at improving the GUI in gscan2pdf to be able to achieve those options more easily.

You can get help with scanimage from the SANE mailing list:

http://lists.alioth.debian.org/pipermail/sane-devel/

[Detlef Peukert]

Hi...

It is not clear to me how to download the gamma-correction table to the scanner

can not you use the settings of the scanner? Instead of loading a gamma correction into the scanner? I have to scan many documents for a DMS. That makes the work pretty hard.

But thank you for your cool support !!
Best regards.

[Jeffrey Ratcliffe]

The options that gscan2pdf offers you in the second tab onwards of the scan dialogue are exactly those offered by the scanner backend, and exactly the same offered by the scanimage command line tool.

Therefore, I suspect that simplescan is not giving you the scanner setting directly.

My suggestion to you is to find the scan options needed to get a reasonable results from scanimage. The same options should also work with gscan2pdf.

If you can't get scanimage to give you reasonable results, ask for help at

http://lists.alioth.debian.org/pipermail/sane-devel/

Perhaps there is a problem with the scanner backend. sane-devel is the best starting point in that case.