[sane-devel] Colour problem with Canon Maxify MB5150

[Ralph Little]

Hi,

On 2021-05-19 8:46 a.m., Dr Rainer Woitok wrote:
> Greetings,
>
> since our good ol'  Canon Pixma MX885  has eventually reached its End Of
> Life, we've bought a Canon Maxify MB5150.  And because
>
>    http://www.sane-project.org/sane-mfgs.html
>
> listed this scanner  as using the same  "pixma" backend  as the MX885, I
> just had to update the IP address in "~/.config/sane/pixma.conf" to acc-
> ess the new scanner via "scanimage".   However, scanning the same single
> page from flatbed or via ADF produced significantly different results:
>
>   - The PNG file from the flatbed clearly showed the original paper hav-
>     ing been rather thin, since some colours from the reverse side shone
>     slightly through, and the background colour having been faintly grey
>     rather than white.   In other words, this PNG file was a fairly good
>     copy of the original.
>
>   - But the PNG file from the ADF did show almost no shine through and a
>     more or less purely white background.  Dark colours appeared slight-
>     ly darker and light colours slightly lighter than the original.  The
>     effect was somewhat similar to using ImageMagick's "-normalize" opt-
>     ion.
>
> While this sort of normalization seems good to have,  if one needs it, I
> would prefer controlling it  via options to "scanimage"  rather than via
> the scanning source.
>
> Is there some way  to prevent this normalization effect  for the  MB5150
> when scanning via ADF?
>
> Oh, almost forgot:  using "media-gfx/sane-backends" version 1.0.31-r2 on
> Gentoo.
>
Some of the pixma devices seems to have a completely different engine
for generating scans from the ADF compared to the flatbed.
For ADF, they return JPEG data to SANE instead of the normal raster data
that we get from flatbed.
I have no idea why that would be the case but they do use the same sensors.

For a number of pixma devices that do this, we tend to see a very good
image from the ADF, and a poor one from the flatbed.
It seems like the machine does some processing on the image to balance
it when it comes through the ADF that it doesn't do when sending raster
data.

It's weird, but that's what I experience.
Presumably their WIndows drivers do some post-processing to the flatbed
raster data to rebalance it.

Cheers,
Ralph