Re: HP Photosmart R032 problem

john allen pitney (pitney@students.uiuc.edu)
Tue, 16 Mar 1999 10:53:12 -0600

On Tue, Mar 16, 1999 at 05:22:39PM +0100, Ewald R. de Wit wrote:
> john allen pitney (pitney@students.uiuc.edu) wrote:
>
> > 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.

Hmm, it seems like the tooltip recommended 150% for normal slides. I'll
experiment with it.

> > 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...

Hmm, OK. Maybe I should put together some example scans. I think we can
do better than what I'm seeing. Maybe there's a config problem on my end.

> > 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.

Well, from the log I put up
(http://www.students.uiuc.edu/~pitney/vuesmart1.log)

I interpreted this as a tone map download:

time 0 command 0a flags 54 status 01 length 5 *a5T
time 0 command 0a flags 54 status 01 length 5 *a6D
time 0 command 0a flags 54 status 01 length 8 *a1024W
time 0 command 0a flags 54 status 01 length 1024

According to http://www.dmo.hp.com/devexchange/nam/scanjet/sclv9.htm the
*a6D means a 10x8 tone map is about to be downloaded. Am I reading this
right? I take that last line above to be the downloading of 10-bits
worth of gamma table.

> > 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.

KDE!?! :-) Anyway, enjoy your project. I think that xscanimage/hp backend
is pretty close right now, it just needs a few more tweaks.

> > By the way, what does the 10x8 notation mean? Map 10-bit data to 8-bit?
>
> Yep!

Thanks!

John

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