[sane-devel] brightness/contrast/gamma LUT ideas?

[Jim McQuillan]

m. allan noah wrote:
>
> are you using lineart mode? the threshold option should help...

No, i'm using Greyscale, because there's some shaded regions, and I 
really need the scanned document to look good.

Jim.


>
> allan
>
> 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
>>>
>>
>