[sane-devel] brightness/contrast/gamma LUT ideas?
m. allan noah
anoah at pfeiffer.edu
Tue Jul 11 00:10:01 UTC 2006
are you using lineart mode? the threshold option should help...
On Mon, 10 Jul 2006, Jim McQuillan wrote:
> I don't have an answer, but I'd like to comment that I sure could use such a
> I'm using the Fujitsu fi-5120C scanner, as you know, because you helped me
> get it working.
> And so far, it's working really well. I did find one issue though. I'm
> scanning both sides of the page at the same time, and i've found that
> documents printed on 20lb paper are getting some "bleed through". That is,
> the scan of the front is actually showing some of the stuff that is on the
> back of the page.
> Also, the scans come out looking somewhat "dirty". Again, because I think
> light from the other side is bleeding through.
> I tried printing the same documents on 28lb paper, and the scans look
> beautiful, no bleeding is seen.
> This turns out to be a big issue, because when I scan the document printed on
> 20lb paper, the two images tarred together and compressed with bzip are
> taking about 2.7mb. While the same document printed on 28lb paper compresses
> down to about 900kb. HUGE difference in compressability.
> I'm thinking that if I could reduce the brightness of the light, it may not
> bleed through so badly.
> Jim McQuillan
> jam at Ltsp.org
> m. allan noah wrote:
>> recent model fujitsu scanners dont have native brightness/contrast/gamma
>> support, instead they use an 256x256 or 1024x256 bit look up table to
>> convert the raw scan data before 8 bit output.
>> while it is true that the 8bit square LUT could be done after scanning with
>> no data loss, most command line front-ends dont do this, and the 10 bit lut
>> has 'access' to more data that never gets out of the scanner, so i would
>> like to extend the backend to provide at least brightness/contrast for
>> these scanners.
>> i need suggestions or pointers to code that i could use. what things i can
>> find are far over my head, but i have a simple brightness adjustment that
>> shifts the linear slope of the in-out function up or down, and a crude
>> contrast setting that changes the slope of the function around the center
>> of the table. i think both of these methods are likely too simplistic.
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