> This slide isn't particularly dark, but the image I get with a gamma of
> 1.0 is simply unusable. A histogram shows that it has almost no
> pixels with a value above about 150 (out of 255). This is with the
> recommended 150% exposure. Applying a gamma and white point correction
> to the scanned image does fix it up, but, as I pointed out, it leaves
> an image with very many large gaps in its histogram and markedly reduced
> color resolution.
150% is not by any means a recommended value (it's just the HP default
value for slides). Try a higher value and you'll get a better picture
with a somewhat smoother histogram. You mustn't set it too high
though otherwise you loose all detail in the highlights.
> Is it the right thing to do, to acquire an 8-bit/channel image with a
> flat 1.0 gamma curve, then apply a gamma of 2.2 to the result?
No it's not the right thing to do but it's the best that can be done
right now...
> I agree there--the densitometric data should be in the frontend. My
> concern is that possible the HP PS R032 can't output a usable 24-bit
> image unless there is a (10x8?) tone map downloaded to it (which seems to
> be happening in the VueSmart logs).
As far as I understood it Vuesmart does the tonemapping in software.
You might have mistaken the calibration data for the tonemap.
Revision 032 of the photosmart doesn't seem to allow any tonemap up or
downloading so we will actually be forced to do it in software.
> I just wanted to see how VueSmart was doing such a good job! So far, I
> haven't managed to get a comparable image from xscanimage/hp backend. Doing
> so will require either manipulation of 10-bit data in software or
> downloading a (10x8?) tone map to the scanner.
Yes, the current state of affairs does suck somewhat. I'm writing a
new frontend for the KDE project that will address these and other
concerns but it will be a few months till a public release though.
> By the way, what does the 10x8 notation mean? Map 10-bit data to 8-bit?
Yep!
-- -- Ewald
-- Source code, list archive, and docs: http://www.mostang.com/sane/ To unsubscribe: echo unsubscribe sane-devel | mail majordomo@mostang.com