[sane-devel] Resolution: range or list?

[m. allan noah]

On Wed, Aug 1, 2018 at 6:18 PM, Brian Potkin <brian at copernicus.org.uk> wrote:
> On Wed 01 Aug 2018 at 09:48:01 -0400, m. allan noah wrote:
>
>> Most inexpensive scanners only support a few discrete resolutions. I
>> would not be surprised if the older version of that backend was
>> scaling the scanner's output to simulate a range. You'd have to ask
>> the author.
>
> That is interesting; thanks, I'll make an inquiry about it.
>
> So - whatever the backend gets from the scanner is possibly altered by
> the backend in both cases. Is there any relatively easy way to know what
> resolutions a scanner firmware does support before the information is
> massaged by a backend?
>

Relatively easy? No, you'd have to read the specs on the scanner or
the source of the backend, or ask the author.

But, I wonder why it matters? Even a scanner which provides a complete
range of resolutions is doing the same scaling internally. The optical
sensor in any scanner has a discrete element size, which sets both the
upper limit of resolution, and the list of easily derived resolutions.
This is done in hardware by effectively ignoring a subset of the
elements in the sensor- hence the 1/2, 1/3, 1/4, 1/6, 1/8 scale that
you see in your HP. If you had a Fujitsu (which has a 50-600 dpi range
in hardware), you would find that 300 dpi scans are fast, and 301 dpi
scans are slow. That particular behavior is pretty common.

allan
-- 
"well, I stand up next to a mountain- and I chop it down with the edge
of my hand"