[sane-devel] image lines is -1 according to sane_get_parameters

[Olaf Meeuwissen]

m. allan noah writes:

> That is the backend's indication that it does not know the length of
> the paper. The backend should have some option where you set the
> height of the image you want it to scan. If you do not tell it, it
> tells you that it does not know. I imagine you use an Avision scanner?
>
> On Mon, Oct 22, 2012 at 7:27 PM, dabicho <tsukebumi at gmail.com> wrote:
>> Hi.
>> I am writing a front-end.
>> In previous version, after sane_start, sane_get_parameters would tell
>> me how much memory I would need to allocate for the image.
>> I am using 1.0.22-5 (from fedora) to support a new scanner, but after
>> sane_get_parameters I am told the image is "-1" lines high.
>> What does that mean? I have not received any error, and xsane works alright.
>> or how sould I go about it as a turn around?
>>
>> any pointer please?

See the API specification for sane_get_parameters():

  Member lines specifies how many scan lines the frame is comprised of.
  If this value is -1, the number of lines is not known a priori and the
  frontend should call sane_read () until it returns a status of
  SANE_STATUS_EOF.

There are situations where you want to scan the whole document but the
device cannot determine in advance how long it is.  Think an ECG for
example.

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