[sane-devel] Well known option consensus

[abel deuring]

Étienne Bersac wrote:

>   \section{Papersize}
> 
>   When using an Automatic Document Feeder, the user generally cannot
>   preview. If the page being scanned is smaller than the maximum size
>   supported by the hardware/backend, the frontend cannot determine
>   the location of the document on the scan surface, and cannot limit
>   the values of the scan area (tl-x/y and br-x/y) to match.
> 
>   If the backend implements options for the frontend user to set the
>   paper size, the backend should limit the range of the scan area to 
>   that defined by the paper. The scan area is then relative to paper
>   origin, not scan surface origin.
> 
>   \begin{options}
>     \option{paper-width}{\FIXED}{\MM}{Paper width.}
>     \option{paper-height}{\FIXED}{\MM}{Paper height.}
>   \end{options}


Now things become really tricky ;) Some Fujitsu ADF scanners (and
probably also devices from other manufacturers) have a so-called
"overscan mode". In overscan mode, the scan window is larger than
the page size; for pixels outside tha page area, you get a
background colour (you can even select between white and black
background). This allows to detect and correct skewed scans and to
check the page size by "analyzing" the image.

So, stating that the scan window should not be larger than the page
size is not such a good idea...

It might be better if the backend tells the frontend, if scan window
coordinates are relative to the entire scan area or to the selected
page size.

Abel