[sane-devel] various questions

[Henning Meier-Geinitz]

Hi,

On Fri, Mar 15, 2002 at 03:00:38PM -0600, Frank Zago wrote:
> - apparently the optical resolution is 300*1200dpi. However if the Y
> resolution goes beyond 300, the image is stretched. eg a 300*600 scan will
> give an image twice longer than a 300*300 image. Is there a software
> algorithm to correct that?

Mustek scanners also have max resolutions of e.g. 600*1200. I just
inflate the x-direction if the resolution is >600 dpi. For an example,
look at the mustek backend and search for "/* need to enlarge
x-resolution? */" (function fix_line_distance_pro()).

> - the twain driver asks for some data at the beginning of the scan.
> 30720 bytes are returned, independantly of the resolution or area scan. I
> assume this is some calibration data. How can I use that, or how can I find out
> how to use it or what it is exactly? I assume this is then used to modify
> the gamma table that is sent just after.

The scanners I know do something like this: Scan some calibration
lines, e.g. 10. These are scanned from a white strip, some scanners
also have a black line that mark the beginning of the scan area (and
the black point). The one line of calibration data is sent back. This
data is calculated from the mean value of the 10 lines.

That's for calibrating the ccd "pixels" (or CIS elements) so I don't
think it affects gamma directly.

> - the twain driver, in color mode, shows 4 gamma tables: rgb, red, green
> and blue. How is it handled by the frontends? Has rgb a priority over the
> three color tables? What should be the option name of the rgb table?

Depends on what rgb gamma actually means. I'm using the three colors
and the normal (gray) gamma table in color mode. The latter is
"intensity gamma" (SANE_NAME_GAMMA_VECTOR).

Bye,
  Henning