[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:

> Allan,
> I don't have an answer, but I'd like to comment that I sure could use such a 
> feature.
> 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.
> Thanks,
> 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.
>> anyone?
>> allan

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