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

Bertrik Sikken bertrik at zonnet.nl
Thu Jul 20 17:12:17 UTC 2006


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m. allan noah wrote:
> On Tue, 18 Jul 2006, Bertrik Sikken wrote:
> 
> 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?
> 
> As far as I know, xsane automatically calculates and downloads a gamma
> table for brightness / contrast / gamma if the backend advertises it.
> 
> 
>> interesting! do you know of a backend that does this? i would like to
>> see the option structures which are used... of course, not everyone uses
>> xsane, so i might have to steal the code from it :)

I built the gamma table support into the niash backend (I think I also
looked at other backends then, as an example). Look for optGammaTable
in niash.c

Regards,
Bertrik
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