[sane-devel] xsane-0.87 released

Henning Meier-Geinitz henning@meier-geinitz.de
Wed, 17 Jul 2002 20:41:35 +0200


On Tue, Jul 16, 2002 at 06:07:31PM +0200, Oliver Rauch wrote:
> a threshold value is something that is clear to me.
> a brightness value can be implemented in a comparable way to a threshold value.

That was done in the mustek_usb backend. They used brightness as
inversed threshold. That's done in the backend, the scanner seems to
only scan gray or color.

I have changed the mustek_usb backend.

> but what makes a contrast value for a lineart image?

Don't ask me, ask Mustek :-)

> The contrast is defined by the two colors that are used: black and white.
> I do not understand what the contrast value does change.

Hm, the threshold is applied to the gray image before/during the
conversion to lineart. Maybe the same is true for contrast?

In the Mustek backend, contrast in lineart mode is send to the
scanner, that means, it's done by the scanners firmware.
And changing the value does change the image. But I can't find out,
what's done exactly.

I haven't changed the mustek backend, because brightness and contrast
are used for different scanners in different ways and i don't want to
break anything.