[sane-devel] Backend for plustek Opticbook 3600

[Pierre Willenbrock]

Chris Berry schrieb:
> On 02/24/2010 10:33 AM, Pierre Willenbrock wrote:
>> stef schrieb:
>>   
>>> Le mercredi 24 février 2010 03:00:16 Chris Berry, vous avez écrit :
>>>     
>>>> Hey Stef,
>>>>
>>>> I think I have sorted out the white shading data but the black is still
>>>> a mystery. I have uploaded some files to the project site (here
>>>> http://sites.google.com/site/bez625/updates-1/update240210 ) these are
>>>> at shading lines set to 400 but for the scan to work even a little
>>>> bit I
>>>> needed to change the lines to 20 (this removes the light blue lines at
>>>> the bottom of the white_shading.pnm).
>>>>
>>>> As you will be able to see the black_shading400.pnm is all white, I
>>>> have
>>>> no idea how to alter this. You can see from the white_shading400.pnm
>>>> the
>>>> full calibration area so I am at a loss really. Have you encountered
>>>> this problem before?
>>>>
>>>> Thanks
>>>>
>>>> Chris
>>>>
>>>>        
>>>     Hello,
>>>
>>>     judging from the 2 pictures, there is no black area to scan. You
>>> should then
>>> rather use the GENESYS_FLAG_DARK_WHITE_CALIBRATION (like the lide 35)
>>> flag
>>> instead of GENESYS_FLAG_DARK_CALIBRATION. The shading data will be
>>> taken from
>>> an all white area and black data will be inferred from the small
>>> black areas
>>> still in the picture.
>>>     
>>>      
>> GENESYS_FLAG_DARK_WHITE_CALIBRATION is just a way to scan the black and
>> white strip in one go. Chris, you should try to figure out if the
>> backend goes through genesys_dark_shading_calibration with
>> GENESYS_FLAG_DARK_CALIBRATION, and if so, why the lamp does not switch
>> off.
>>
>> Regards,
>>    Pierre
>>
>>    
> Hi Pierre / Stef,
> 
> I was wondering the same thing but the lamp does indeed go off. I'm not
> sure why the scan is so light, I had no idea which area it was scanning
> from.... I have been playing with the dark_white calibration and i seem
> to be getting somewhere, here (
> http://sites.google.com/site/bez625/updates-1/update240210lateron ) are
> some scans.
> 
> Should I abandon the work with DARK_WHITE and see if I can fix the issue
> with DARK_CALIBRATION?

Hi Chris,

DARK_WHITE mode uses static thresholds on the scanned data to determine
whether a given pixel is white or black, so it will find nearly nothing
in the black category. DARK_CALIBRATION should be working on any scanner
that can successfully disable its lamp, still leaving the analog data
processing powered. Obviously, the scanning head should be about the
calibration area, so there is no external light even with the lid open.

In short: try to figure out what goes wrong in DARK_CALIBRATION.
DARK_WHITE_CALIBRATION will not help you. Perhaps the lamp needs more
time to turn off?

Regards,
  Pierre