Fwd: Re: [sane-devel] Lexmark experimental backend]

[Fred Odendaal]

Stef,

I tried a few scans with the latest code. It seems to find the start 
position much better. It even works when I have Top-left x and y set to 
something other than 0, which was broken for me before.

However, the colours are way off for my scanner. All the colour scans I 
do are saturated to blue (white becomes blue). This becomes worse as I 
increase the resolution. Also, there is a lot of back tracking at 300dpi 
for a full page scan. I don't think the acceleration curves have been 
set correctly for this resolution and image size. Actually, it's 
probably just width and resolution to determine the acceleration curves.

If you need me to do any testing, or send you any logfiles let me know.
Fred.

Stéphane VOLTZ wrote:
> Le Dimanche 28 Mai 2006 20:20, Fred Odendaal a écrit :
>   
>> Stef,
>>
>> You are correct about the dot. I've attached 2 files:
>> find_start_lexmark1.pnm - This was with SANE_DEBUG_SANEI_USB=255
>> find_start_lexmark2.pnm - This was with SANE_DEBUG_SANEI_USB unset.
>>
>> As you can see the picture gets better with usb logging turned off. I
>> think the real problem function is
>> sanei_lexmark_x1100_search_home_bwd(). It should have stopped the scan
>> head and positioned it inside the dot. The white space at the top of
>> each file is the distance past the dot that the scan head moved in the
>> reverse direction. In this function after the scan is stopped from
>> moving in the backward direction it is moved forward half the distance
>> of the dot plus the maximum no. of lines the buffer will hold. This is
>> done by the call to sanei_lexmark_x1100_move_fwd(). When I comment this
>> line out the picture gets even better. In other words, this function
>> isn't moving forward, but continuing backwards making our position even
>> worse!
>>
>> The sanei_lexmark_x1100_find_start_line() function is working as it
>> should. It simply scans what should be enough lines to scan past the dot
>> into white space and return the number of white lines past the dot.
>> Since the distance to the scanning area from the dot is known we simply
>> subtract how far past the dot we've moved from this number to see how
>> far we still have to go.
>>
>> regards,
>> Fred O.
>>     
>
> 	Hello,
>
> 	you wre right, the trouble was with  sanei_lexmark_x1100_search_home_bwd()
> which was scanning too far. To correct it, I made it read only one line of
> data (2500 bytes) at a time. So when it finds the dot and then stop, it is
> right on it. So we don't need to move forward a little. Now origin finding is
> slower but much more reliable.
> 	This change uncovered a bug in the way I modified rewind. So I had to change
> it. It now goes back by the bottom right y coordinate plus a fixed amount
> which is the distance between start of visible area and the "origin dot".
> 	I tweaked a little the calibration values. Picture are now close to the
> quality of my other scanner.
>
> 	I think that the current version is in good shape.
>
> Regards,
> 	Stef
>
> -------------------------------------------------------
>
>   
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