[sane-devel] XSane/Epson problems and comments

[Oliver Rauch]

Juhana Sadeharju schrieb:
> 
> Hello. Some Xsane/Sane-Epson notes:
> 
> Summary: I want save the scanned image "as is" without effects
> and without value range clippings at bottom or top. The design
> of sane/xsane seems to make this difficult to optain. I need
> help in finding suitable settings.
> 
> I would like to have all Epson developers documentations?
> Where I may download them?
> 
> I suggest to read the rest of the mail paragraph by paragraph.

When you set gamma=1.0, brightness=0 and contrast=0 in the xsane main
window then xsane does use a linear gamma table gamma[0]=0,... gamma[i]=i.

The headers in the files created by xsane do not store the correct gamma values
in all available version. This already is corrected for xsane-0.89.

In most cases it does not make sense to do the image enhancement independent
from scanning because 
- a lot of scanners do scan with e.g. 12 or 14 bits/sample but only can output
  8 bits/sample. You get better results when you use the scanner internal gamma correction
- even when the scanner can output more than 8 bits/sample you do not need more then
  8 bits/sample in most cases. So doing a gamma correction and storing the image
  with 8 bits/sample reduces the file size and creates images with good results.

If you think you need to do the conversion after scanning simply set
gamma=1.0, brightness=0.0 and contrast=0.0 in the xsane main window
and xsane does not touch the data.

Best regards
Oliver

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