sane-project-backends/doc/gt68xx/gt68xx.TODO

gt68xx.TODO -*-text-*-

General:
--------

- some sort of fixed lookup-table may be necessary to compensate for the
  non-linear CCD/CIS behaviour. A gamma value is not good enough. Or maybe line
  calibration can be used for that?
- Some Plustek scanners are advertised with e.g. 1200x2400 but the maximum
  vertical resolution seems to be limited to the horizontal one. Check if
  that's really the case.
- Keep a log of all gain/offset combinations already tested and break if
  one is repeated to avoid endless loops.
- Print commands that are send to the scanner in clear text.
- Try to implement non-blocking USB bulk reads, check libusb CVS.

CCD:
----

Mustek BearPaw 2400 TA Plus:
- some lines at the beginning of each image have wrong colors (linedistance?)
  This seems to happen with other scanners, too.
- 600 dpi no backtrack, 1200, 2400 dpi backtrack (gray), check with windows for
  color
- 600 dpi 12 bit seems to work in pixel mode only (but long lines are too big!)

Mustek BearPaw 1200 TA:
- similar color problem as 2400 TA Plus, doesn't always happen?

Mustek BearPaw 2448 TA Plus:
- all modes are slow (massive backtracking). If connected to a USB2 port, the
  backtracking ich much less despite this scanner can't do USB2. Strange.
- Sometimes there is a USB protocol error when cancelling the scan?
- top borders move with resolution (happened in the early days with 2400 TA!)
- gray scans have different brightness
- scan motor is bumpy and freezes sometimes, looks like accelaration is too big
  (firmware problem?)
- vertical stripes
- TA settings are wrong
- no backtrack >= 600 dpi (also gray!)
- don't move before and after scan
- check jpeg output, maybe this can be used for faster scans

Plustek 1248U:
- Linedistance seems to have problems in the first few and the last lines.
- Gain and offset values are quite high. Optimum values are not reached. Problem
  with coarse calib? Better algorithm needed.
- Images in color mode sometimes look too redish (result of above problem).
- quite slow when full width is selected. Lots of backtracking.
- Check if pixel mode is possible.
- Check again 600x1200 dpi.

Plustek U16B:
- 600 dpi 16 bit is limited to about half the size of the scan area because
  only pixel mode works and 16k is the maximum buffer size.
- After scanning, a run of sane-find-scanner leads to a protocol error and
  scanning does no longer work.

Genius ColorPage Vivid 1200XE
- 16 bit per color is advertized but this mode doesn't seem to work
  (only 12 bit)?
- 1200x1200 and 1200x2400 dpi doesn't seem to work despite being advertized
- Y-positioning varies slightly with resolution (some mm)

CIS:
----

- It may be necessary to do an additional exposure calibration before the
  offset/gain calibration to compensate for different intensities of the
  colored leds. Especially for the Mustek 2400 CU Plus.
- Changing exposure doesn't seem to have any effect during calibration
  sometimes while it has an effect on the final image?

Mustek BearPaw 1200 CU
- ok

Mustek BearPaw 1200 CU Plus (0x021b)
- ok, but similar exposure problems as 2400 CU Plus

Mustek BearPaw 2400 CU Plus
- ok, but exposure setting may need to be done automatically if the intensity
  of the colors varies for different scanners.
- calibration/exposure has sometimes sharp jumps in intensity. Reason is
  unknown.

Mustek ScanExpress A3 USB
- still slight vert. stripes
- why is line distance setup necessary?
- line distance varies with resolution (0,5,5 at 300 dpi, 0, 6, 7 with 150 dpi)
- exposure doesn't seem to have any effect

Mustek ScanExpress 1248 UB
ok

Plustek OpticSlim 2400
- only upto 1200 dpi vertical works
- only 8 and 12 bit work, 16 doesn't (check Windows)
- exposure is extremely high and seems to have similar problems as with other
  CIS scanners (reaches limit also)

Mustek ScanExpress 2400 USB
- make it work (nobody seems to have this device)

Visioneer OneTouch 7300
- 16 bit doesn't seem to work despite beeing advertized