[sane-devel] Can I change resolution offerings for Epson V200 Photo scanner?

[Olaf Meeuwissen]

2cv67 <2cv67 at free.fr> writes:
> On 17/04/12 01:48, Olaf Meeuwissen wrote:
>> Care to explain about those negatives? 
> Sure (my negatives for Image Scan! for Linux):
> [snip]

Thanks for the detailed feedback.  I still have to work my way through
the threads on ubuntuforums.org but I'll try to summarize and forward
your comments to those that call the shots on Image Scan! for Linux.

>>> This means I really only have 300/600/1200/2400/4800 as usable values.
>> Only if you insist on using the same resolution in *both* directions.
>> If you use different resolutions for the X and Y directions, you really
>> should make sure they are incorporated in the image's metadata.  If you
>> don't, chances are you get weirdly elongated images in one direction.
>>
> Sorry, you lost me there.
> Obviously (OK - should never say that) if I scan a circle, I want to
> see a circle.
> That means, with XSane for instance, the only lowish dpi's which work
> for me are 300x300 & 600x600.
> Anything else gives me an ellipse.
> I don't know what to make of "make sure they are incorporated in the
> image's metadata"?

Let's say you're scanning a circle that with a 1 inch diameter at
300x300 dpi.  Then you get a 1x1 inch, 300x300 pixel image.  That will
display as a circle just about anywhere, even without resolution
information, because normally the x/y resolutions are the same.

Now scan that same circle at 300x600 dpi.  You get a 1x1 inch, 300x600
pixel image.  Now, without any resolution information, this will indeed
display as an ellipse because there is no way you can tell that the x/y
resolution aren't the same.  If the image were to contain resolution
information however, an image viewer would be able to figure out that it
is really a 1x1inch image and display your circle as a circle.

The thing is, without resolution information in the image, you can't
determine its physical size (i.e. the 1x1 inch in the above example).

Makes sense?

> And there are no X options between 75 & 300 anyway, which is where I
> would want to be for routine stuff.
> I don't care much how the scanner, the backend or the frontend decide
> to split the work, all I want is to be able to select a good
> compromise between image size & visible detail depending on the
> intended use.

Point well taken.  From a backend developer's point of view, I'd like to
expose the devices capabilities directly and have the frontend deal with
giving the user a good experience.  This is *not* an easy job, but as
far as I'm concerned, the onus is on Simple Scan and its likes.

>>> 2. Can I do anything to get other values - preferably with same X&  Y,
>>> particularly 75/100/150 ?
>> You're best bet is probably post-processing of the image with something
>> like `convert` for command-line based work (part of the imagemagick and
>> graphicsmagick packages) for example, or the GIMP if you prefer a GUI.
> That prospect could drive me back to Windows if Image Scan ever
> disappears. ;)
> I really, really understand why Ubuntu needs Simple Scan for ordinary users.
> But it also needs to work.

For that you have to make clear to the Simple Scan developers how you
expect it to work when you, for example, select 150dpi.  Do you expect
an image at 150x150dpi?  Exactly matching the scan area you selected?
Or is an image at at least 150x150dpi and including at least the scan
area you selected what you would expect?

Based on the information I've seen, it seems that Simple Scan just gives
you an image at a resolution that is at least 150dpi.  If that is what
the developers had in mind, then it "works" as far as they're concerned.

> I wish it well!
>
> Thanks again for the detailed explanations, Olaf, & thanks to all
> working to get Linux scanning up to speed, hopefully for ordinary
> users.

Hope that helps,
-- 
Olaf Meeuwissen, LPIC-2           FLOSS Engineer -- AVASYS CORPORATION
FSF Associate Member #1962               Help support software freedom
                 http://www.fsf.org/jf?referrer=1962