[sane-devel] Insights from a newbie backend writer...

Tue, 12 Apr 2005 21:39:51 -0400

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Thanks for the tip. I hadn't actually thought of looking at the 
calibration data as an image.

There are no other data transfers between calibration scans. That and 
the fact that its a CIS scanner (cheaper, lower quality) lead me to 
believe that its not adjusting individual pixel gains for each sensor.

The Windows .ini file has a bunch of other clues, like:
Calibrate=1 // [1:Enable Calibration]
DoPixelDC=1 // [1:Enable Dark Compensation]
PixelDCDarkLevel=1
ScanPixelDCLines=16
CalibrationYDPI=300
CalibrationLines=30
GainTargetCode=0xEFEFEF
ScanTargetCodeRed=260
ScanTargetCodeGreen=262
ScanTargetCodeBlue=259
TargetVGARed=6
TargetVGAGreen=6
TargetVGABlue=6
CalibrationSkipLines=8
CalibrationBackwardLines=95
etc...

I'll probably take a break from this for a while (really busy at work), 
but I think I have enough clues with the calibration images to continue 
when I get back at it.

regards,
Fred Odendaal

Earle F. Philhower, III wrote:

>Hi Fred,
>
>Don't give up yet, some suggestions you probably already heard below...
>
>--- Fred Odendaal <freshshelf@rogers.com> wrote:
>  
>
>>So, I'm thinking "I've got a degree in comp. sci. How difficult can it 
>>be to write a scanner driver?" 
>>    
>>
>...big snip...
>  
>
>>Finally after many Windows scans and log files at various different 
>>sizes, resolutions, and colour or gray  scale mode I start writing the 
>>backend. It only took me about 2 weeks before I could scan on Linux, but 
>>this is the easy part! What I soon discovered is something called 
>>CALIBRATION. At 600x1200dpi colour resolution the Windows driver 
>>actually does ~20 scans off to the side of the glass flat bed. I have no 
>>idea what its doing. By looking at the usb logs it appears to be setting 
>>the gain and the dc offset in a gradual fashion over several calibration 
>>scans.
>>    
>>
>
>Dump the received binary data to an image and then just see which
>control register they're iterating over.  Then it's just a matter of
>figuring what they want the end image to look like (ie. adjust offset
>down until black pixels are < XXX, then increase gains until white
>pixels are near YYY).  The received calibration image was really helpful
>when I was trying to figure out what the heck the Microtek driver
>was doing!
>
>It may also be adjusting the individual pixel gains for each sensor
>element.  If there's a really large download of slowly varying #s
>between scans that might be a pointer.
>
>Good luck,
>
>
>
>
>		
>__________________________________ 
>Do you Yahoo!? 
>Make Yahoo! your home page 
>http://www.yahoo.com/r/hs
>
>  
>

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Thanks for the tip. I hadn't actually thought of looking at the
calibration data as an image. 
 
There are no other data transfers between calibration scans. That and
the fact that its a CIS scanner (cheaper, lower quality) lead me to
believe that its not adjusting individual pixel gains for each sensor. 
 
The Windows .ini file has a bunch of other clues, like: 
Calibrate=1&nbsp; // [1:Enable Calibration] 
DoPixelDC=1&nbsp; // [1:Enable Dark Compensation] 
PixelDCDarkLevel=1 
ScanPixelDCLines=16 
CalibrationYDPI=300 
CalibrationLines=30 
GainTargetCode=0xEFEFEF 
ScanTargetCodeRed=260 
ScanTargetCodeGreen=262 
ScanTargetCodeBlue=259 
TargetVGARed=6 
TargetVGAGreen=6 
TargetVGABlue=6 
CalibrationSkipLines=8 
CalibrationBackwardLines=95 
etc... 
 
I'll probably take a break from this for a while (really busy at work),
but I think I have enough clues with the calibration images to continue
when I get back at it. 
 
regards, 
Fred Odendaal 
 
 
Earle F. Philhower, III wrote:
<blockquote
 cite="mid20050411055927.94869.qmail@web30209.mail.mud.yahoo.com"
 type="cite">
 <pre wrap="">Hi Fred,

Don't give up yet, some suggestions you probably already heard below...

--- Fred Odendaal <a class="moz-txt-link-rfc2396E" href="mailto:freshshelf@rogers.com">&lt;freshshelf@rogers.com&gt;</a> wrote:
  </pre>
  <blockquote type="cite">
    <pre wrap="">So, I'm thinking "I've got a degree in comp. sci. How difficult can it 
be to write a scanner driver?" 
    </pre>
  </blockquote>
  <pre wrap=""><!---->...big snip...
  </pre>
  <blockquote type="cite">
    <pre wrap="">Finally after many Windows scans and log files at various different 
sizes, resolutions, and colour or gray  scale mode I start writing the 
backend. It only took me about 2 weeks before I could scan on Linux, but 
this is the easy part! What I soon discovered is something called 
CALIBRATION. At 600x1200dpi colour resolution the Windows driver 
actually does ~20 scans off to the side of the glass flat bed. I have no 
idea what its doing. By looking at the usb logs it appears to be setting 
the gain and the dc offset in a gradual fashion over several calibration 
scans.
    </pre>
  </blockquote>
  <pre wrap=""><!---->
Dump the received binary data to an image and then just see which
control register they're iterating over.  Then it's just a matter of
figuring what they want the end image to look like (ie. adjust offset
down until black pixels are &lt; XXX, then increase gains until white
pixels are near YYY).  The received calibration image was really helpful
when I was trying to figure out what the heck the Microtek driver
was doing!

It may also be adjusting the individual pixel gains for each sensor
element.  If there's a really large download of slowly varying #s
between scans that might be a pointer.

Good luck,

__________________________________ 
Do you Yahoo!? 
Make Yahoo! your home page 
<a class="moz-txt-link-freetext" href="http://www.yahoo.com/r/hs">http://www.yahoo.com/r/hs</a>

  </pre>
</blockquote>
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