[sane-devel] Reflecta ProScan 7200

[Vleeshouwers, J.M.]

Hi Michael,

A short update on a couple of settings (mode normal/quality, auto-exposure, auto-gamma, and ICE).
For details see: http://www.stadspartijeindhoven.nl/jv/SettingsAnalysis.ods I'm not completely ready with all settings yet, but If you
have suggestions for additional tests, let me know.

Setting mode to "quality" results in a recalibration before each scan, whereas in "normal" mode the scanner
only calibrates when the scanner is switched on. Apart from that, a bit is set in MODE SELECT byte 7. I do not notice
other settings changes.

Setting auto-exposure results in a double scan when asking a preview. The first scan probably assesses the appropriate
exposure settings, and the second is the actual preview. The effect is noticable in the preview. Perhaps if I wouldn't
have asked a preview, this additional scan would have happened before the actual scan, but I didn't check. Remarkably,
the SCSI 0A command for SET EXPOSURE TIME does not change. The only output command with new data in between the exposure
scan and the preview scan is a SCSI D7. Apparently exposure related settings are part of what's being sent here.

Setting auto-gamma does not lead to any changes at all. Does that make any sense?

When setting ICE, in MODE SELECT byte 4 an additional bit is set, which results in sending RGBI-data to Cyberview instead
of just RGB. The infrared-channnel can be converted into a monochrome picture which shows the dust and scratches,
and some vague contours of the original slide. I did not yet check if the RGB-data is original or has the scratches
removed.

The settings do not appear to influence these SCSI-commands:
- SCSI 08 (READ CALIBRATION INFORMATION)
- SCSI 0A (WRITE - SET SCAN FRAME)
- SCSI 0A (WRITE - SET EXPOSURE TIME)
- SCSI 0A (WRITE - SET HIGHLIGHT SHADOW)
- SCSI 0A (WRITE 17, function unknown)
- SCSI 0A (WRITE - REQUEST CALIBRATION INFORMATION)
- SCSI 18 (COPY)
- SCSI 1B (SCAN)
- SCSI D2 (? RELEASE)
The remaining commands are infuenced:
- SCSI 15 (MODE SELECT)
- SCSI 0F (READ SCAN PARAMETERS)
- SCSI D7 (? READ CUSTOM DATA)
- SCSI DC (? WRITE CUSTOM DATA)

About the interpretation of DC and D7 (and probably bytes 12 and 13 of SCSI 0F as well):

No, I did not see any larger amounts of data written to the scanner. I suppose only very basic calibration parameters
are being sent, nothing else. Is it possible that the calibration scan data (1+13+31 lines) are used by Cyberview to do
shading correction?
Why do you think the first six DC-bytes are 12-bit RGB-values? The most-significant 4 bits are used sometimes, and apart
from that there is some unbalance I cannot explain. If interpreted as 2-byte integers, most of the time the three values
are around 3000. But sometimes they double or even triple, and in a couple of cases the first value is the only one that
deviates. I don't see any logical reasons for that. Might these 2-byte values represent floating point numbers? They are
not IEEE half-precision values, I checked that. Would there be any use for floats?
The D7-data returned by the scanner show something similar in bytes 6-11. If they refer to RGB respectively, what could
be the reason that the first value is 1.5 times the 2nd and 3rd?
When interpreted as 2-byte integers, bytes 0-5 have three values which resemble numbers I found in discussions about
16-bit CCD saturation. These values are updated after the scanner has sent out calibration data (1+13+31 lines).
I can imagine the scanner presents this information for calibration purposes, right?

To be continued, I suppose.

Jan