[sane-devel] Reflecta ProScan 7200

[Vleeshouwers, J.M.]

Hi Michael,

That took me quite a while to think through, I'm stll not ready with
everything yet. I think we need some kind of a document that accumulates all
we have come to know. Maybe we should also try to agree on the names we use.
I'm trying to compose it, but: not ready yet...

What surprises me is the difference you discovered. I attach my INQUIRY
response so you can check if there are more differences except for byte 74
(which equals 0x30 for the Crystalscan scanner). I would not expect large
differences. Perhaps it is only a small change in the use of bit 3 in MODE
SELECT byte 9 ("required speed").
If I send 0x02 (instead of 0x0a) to the scanner for quality mode, COPY gives
an error, and REQUEST SENS gives 70 0005 000000000600000000 2000 = ILLEGAL
REQUEST, INVALID command OPERATION CODE.
Would it be worthwhile to check for differences in more detail, for example
in the startup sequence?

I think it's probably best to continue focussing on the SCSI-DC command.
It seems logical to have exposure time, gain and offset for the R, G and B
channels, and for "quality" mode your experiments show where they are in the
23-byte sent by the DC-command. But the "normal"-mode results are strange.
You are right about the very dark scans I get (the raw data, Cyberview
corrects for this). But it is strange that "normal" mode seems to do away
with all pixel values in the lower half of the dynamic range, and expands
the upper half (by a factor 2). That is what seems to be happening in
"normal" mode, isn't it?
We should check if we are missing context. Could it be that some of the
unidentified 0xDC-information sets a shadow-highlight range of 50% to 100%?
Might "normal" mode work by simply setting this range? Maybe the
DC-information is interpreted by the scanner depending on the modes
("startup" mode (0x00) with very simple settings, a "normal" mode (0x08) with
more parameters, and a "quality" mode (0x02/0x0a) with the most extensive
parameter set.)

Did you experiment with byte 15 (after the RGB-gains)? I notice 0x00 switches
off the light during a scan, and non-0x00-values turn it on. I do not know
if it is more than just switch on/off, but if we can specify the light
intensity, we have an extra parameter to consider.

Did you find a relationship of the exposure time specified in the INQUIRY
reponse (min 100 max 2500) to the range you find? I do not see a factor 25
between min and max?

The (almost) exponential gain curves look like ones I found in datasheets
(e.g.http://focus.ti.com/general/docs/lit/getliterature.tsp?
genericPartNumber=vsp3100&fileType=pdf). Having an analytical description is
nice, but not absolutely required; a look-up table for the relationship
between the gain parameter value and the actual gain will also work. This
table can be derived from your experiments, I'll describe how in the reference
document.

I have made a small program to communicate with the scanner outside of
SANE, because I found I sometimes needed some more flexibility. I intend
to use it for documenting my experiments as well, so I'm thinking of adding
a facility to run the experiments based on a text script. If I see what
is still asking for an explanantion, this effort may be worthwhile.

Yours,

Jan
________________________________________
From: Michael Rickmann [mrickma at gwdg.de]
Sent: Wednesday, May 18, 2011 6:47 PM
To: Vleeshouwers, J.M.
Cc: sane-devel at lists.alioth.debian.org
Subject: Re: [sane-devel] Reflecta ProScan 7200

Hi Jan,
now what I found.

< huge snip >

Regards
Michael
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