[sane-devel] Canon LiDE 90

[Pierre Willenbrock]

Guillaume Gastebois schrieb:
> Hello,
> 
> I need a little bit more informations befor testing (sorry for my poor knowledge
> in scanner)
> 
> Selon Pierre Willenbrock <pierre at pirsoft.dnsalias.org>:
> 
>> I don't know why the image colors are reversed, but it may be worth
>> trying to flip the sign bits in Genesys_Frontend. If that does nothing,
>> we need to handle that in code(or i am missing some setting of the gl841).
>> The other thing you have seen is the half-resolution mode, used for
>> greater speed when doing lower(i.E. not full) resolutions.
>>
> 
> How do you explain yhat with half resolution the image seems to be grayscale and
> without it seems to be lineart ?

If you look closely, you see that the image is not exactly lineart. When
doing half resolution, the sensitivity of the scanner sensor changes,
and thus needs a different afe setup. That should be handled gracefully
by the offset/gain calibration, once those are working.

>>> Subsidary question : what is the small white (perhaps black) rectangle
>>> in the middle up off page (for calibration) ?
>> That may be a small metal clamp holding the glass or the calibration
>> strip. That is the black(i.E. white) part at the very top.
>>
> Under this small rectangle I have a vertical more clear line(same height). Is it
> because I need to tweek calibration area (without this small rectangle) ?
> 
>> To summarize, it is a good idea to have bit 4 on, bit 5 is the half
>> resolution switch. I'd put 0x10 into the 0x6c gpio register.
>>
>> As for the calibration area, you will need to change some code:
>> * comment out genesys_gl841.c:4220:(line numbers may differ)
>>   status = gl841_feed(dev, 280);/*feed to white strip. canon lide 35 only.*/
>> * the same for genesys_gl841.c:4821:
>>   status = gl841_feed(dev, 280);/*feed to white strip. canon lide 35 only.*/
>>
>> then you can try what happens when you turn on the led_calibration and
>> the coarse_gain_calibration. offset_calibration needs a bit more
>> changes. i think i am having the code needed lying around somewhere.
>> essentially, the offset calibration needs to be done with leds off.
>> the shading calibration does need even more changes.
>>
> Where to find led_calibration, coarse_gain_calibration ? How to turn them on ?
> For personnal information : what is shading calibration ????

They are called by genesys_flatbed_calibration, i think i requested to
comment them out earlier.

There are three things to calibrate for:
1) the mapping from sensor voltages to numbers, to not lose color space
by clipping lower brightness to 0 or higher brightness to 65535.
ideally, you don't ever see 0 or 65535 from the afe. This is mainly the
job of offset/gain calibration, but the led-exposure is a factor to this.
2) the color intensities relative to each other. We try to get each
colored LED to lead to similar voltages in the sensor during its
exposure. This is calibrated by led_calibration
3) Variations between the sensor cells. each sensor cell has it's own
sensitivity and black voltage, so there needs to be a
per-pixel-correction. This is done by shading_calibration.

Additionally, the shading_calibration is by-color, so this is the place
where we map each color channel to the correct range, as the
led_calibration is not that exact.

> 
>> Additionally, if you can't get the afe to switch the sign, you need to
>> do that in the calibration functions(i.E. 65535-value).
>>
> 
> Only in calibration function ?

For now, that should be enough. We are not interested in the actual
output image, yet.

Regards,
  Pierre

> 
> Regards
> Guillaume
> 
>> Regards,
>>   Pierre
>>
>