[sane-devel] pixma MP810 working with sane

[Nicolas]

Hi, 

Concerning the vertical lines at 4800/2400 dpi for MP810, I'm wondering
whether:

- this is a normal behavior of the scanner (which would mean that it has
to be compensated by the backend), 
- or if it's an alignment problem of the sensor, the lines corresponding
each one to a particular sensor cell, but only at high dpi, the sensor
uses all its cells to scan.

I think it may be interesting that other MP810 users could give feedack
on the current CVS backend, if possible, that's why I copy also the
sane-devel list

Do you know if there's an alignment procedure for MP810 ? This is
usually the case when you get a new scanning device.

Have you the possibility to test the Canon Windows driver, and see if it
behaves the same ? 

FYI, the particular image encoding used by pixma devices at high dpi
(giving a subset of images to be merged) is the same on newer generation
devices (like MP610 with CIS sensor, or MP970 with CCD), but for those
models, there's no effect of vertical lines, all cells are correctly
aligned up to 4800 dpi. 

Also, I've not seen samples of scanned images for other older pixma
devices (like MP600, MP960, ...), currently not supporting 2400 or 4800
dpi mode, but I'would be interested to know if those devices produces
also such image subsets (which means it could be very easy to have them
fully supported also by the pixma backend).

Last point concerning the white lines at the bottom: this is simply due
to the color planes shifting, as the backend algorithm to shift the
color planes uses only that portion of the image that will contain data
for the 3 colors. The bottom of the scanned image contains 2 and 1 color
zones only, due to the color shift. 
So this is a little limitation for pixma CCD sensors, you must select a
scan zone a little bit bigger at the bottom, then remove the image
bottom white zone, that is padded on purpose by the backend to keep the
image size the frontend expects.
Another solution would have been to send to the frontend a smaller
image, but this may raise some errors then in the frontend ...

Nicolas

Le mardi 02 septembre 2008 à 00:38 +0200, Arne a écrit :
> Hi Nicolas,
> 
> here is the output from some scantests with the code you sent me:
> 
> http://81.137.198.200/tmp/scantests2.tar.bz
> 
> It's about 14 MB.
> 
> I have scanned two small pictures at 4800dpi, 2400dpi and 1200dpi (the 
> 1200dpi is so you can see how it's supposed to look like).
> 
> The 4800dpi now has corect proportions and no duplication so there is 
> some improvement, but it's still very fringed similar to the 2400dpi.
> 
> Also in all resolutions there is always the bottom section that just stays 
> white (despite it should contain scanned data as it's part of the selected 
> area), I'm not sure if that's a xsane prblem or a MP810 driver specific 
> problem?
> 
> Best regards,
> Arne
> 
> 
> On Mon, 1 Sep 2008, Nicolas wrote:
> 
> > Hi Arne, 
> > 
> > I've added a small change to file pixma_mp150.c (attached), this should
> > merge the 2 parts of the 4800 dpi image you get.
> > 
> > The remaining resolutions should be unchanged.
> > 
> > Could you give a try, and send the result of a small 4800 dpi scan ?
> > 
> > Nicolas
> >