[sane-devel] Avision: Non-standard papersize requires additional left offset?

[m. allan noah]

This happens because the backend does not pad your input values when
it sends them to the scanner. The sane standard does not specify
whether this is required or not. The avision backend author chose not
to. Many (if not most) other backends do make this correction. If you
are able to produce a patch which adds this capability, I will apply
it.

allan

On Fri, Jan 8, 2010 at 10:38 AM, Crypto <crptdngl71 at gmx.net> wrote:
> Hi,
>
> I came across this while using gscan2pdf to scan a number of postcard-sized
> sheets.
>
> Because the format is unknown to gscan2pdf (and the underlying scanner
> backend) at first I have entered the dimensions of the sheets manually.
>
> The sheets are 105mm x 148mm in size.
>
> My scanner is an Avision AV200 and I have noticed that the sheets are not
> scanned properly unless I add an additional left offset in the "Change
> Papersize" form.
>
> The paper guides of the scanner's sheet feeder are mounted in such a way that
> all paper sizes that fit into the scanner sheet feeder are centered in the
> sheet feeder, i.e. that the center of the sheets always is positioned at the
> same vertical line in the middle of the available scan area.
>
> BUT: I have noticed that the underlying scanner backend seems to assume that
> instead of a centered paper position the left side of the paper always is
> "line 0". I have found that because when I try to scan the postcard-sized
> sheets  I have a certain area of the sheets that is not scanned (the right
> half of it) and therefore I keep getting only about half way scanned sheets.
>
> In the "Change Papersize" form I can enter an additional left offset of about
> 56mm and this "moves" the sheets to the left but leaves an area of that size
> which seems to be unused yet scanned. It means that I can now scan the full
> area of the sheets but I get an area which is scanned unnecessarily and is
> wasted.
>
> So why do I need to enter an additional left offset at all to scan smaller than
> A4 sized sheets? Why does the backend not automatically adjust the offset (if
> it is one, or bug?) to scan smaller than A4 sized sheets?
>
> Thanks for any hint,
> Crypto.
>
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