[sane-devel] Backend for plustek Opticbook 3600

[Chris Berry]

> 	Hello,
>
> 	I am facing the same issues than you while adding support for the HP3670. I
> eventually found that one of my decoding script was buggy and hide most of AFE
> accesses. I have appended the fixed version. By decoding usbsnoop again, you
> may find more AFE writes to be coded in backend. That may fix the red tint
> issue you have. I wouldn't be surprised if only write to red gain was showing
> in decoded log, leaving other channels untouched.
>
Ok I have decoded another log file using this revision, you are correct 
there are many more writes to the fe showing up but they do not really 
mean anything more to me :(. I have attached the fe_writes.log file, 
which is just a straight grep of the fe writes with the new decoded log 
file. If you could look at it and tell me what you think is happening, 
the only reasonable things I can gather is that there are:

* init style writes (0x00 -> 0x70, 0x01 -> 0x80, everything else -> 0x00)
* possible offset settings (0x05-0x07 seem to be set to 0x80 and 0xff 
repeatedly)
* offset (0x05-0x07) and gain (0x02-0x04) seem to be set arbitrarily at 
various times.

I'm not sure if any of this is relevant but whenever I set the 
offset/gain values in genesys_devices they seem to make little (if any) 
difference to the scans.

> 	You'll also have to look at the base gamma coefficient in the Genesys_Sensor
> entry for your model.
>
I've had a look at this and I take it you mean this section:
    float red_gamma;
    float green_gamma;
    float blue_gamma;
    uint16_t *red_gamma_table;
    uint16_t *green_gamma_table;
    uint16_t *blue_gamma_table;

I've tried changing the floats but there doesn't seem to be much 
difference, maybe I should wait until I fix the shading issue then tweak 
this?

I assume the gamma_table entries are just initialisers for the tables.

> 	When doing a calibrated scan, the REG01_DVDSET bit is set to activate shading
> calibration. Clearing it may side step issues with shading calibration, but
> defeat the purpose of calibration.
I was slightly worried that's what I had done here, i've restored it to 
the original values :P

> When tuning shading calibration, you must
> look at the black/white_shading.pnm and black/white_average pnm files that are
> written when full debug is enabled. With proper offset and gain values, you
> must have a full black picture (with some values slightly above 0) and a full
> white one. If not, the computed shading calibration coefficient will be bogus
> and you'll get black scans.
>
> Regards,
> 	Ste
>

Ok i've also attached the black/white_shading/average files. If I 
understood you correctly the black_shading.pnm should be all white and 
not the pretty purple colour it is now and conversely the white should 
not look as it does. I have tried altering the offset and gain in 
gen_devices but this doesnt seem to do anything :(. Any other 
suggestions about how I move forward with the shading? I think as soon 
as the shading is sorted I might be there with this project and ready to 
commit to the dev version.

Also I currently have OFFSET_CALIBRATION and DARK_CALIBRATION flags set 
for the scanner, how do I know if I should be using these (as opposed to 
COARSE_CALIB and DARK_WHITE_CALIB)?

Sorry I have given you quite an essay to read there but at the minute I 
have a few assignments to deal with so i'm just trying to juggle 
everything but again thanks for all the help and time you have given me. 
One other thing I wanted to ask is about a new release? I've seen a lot 
of chat on the mailing list about this but I just wondered if you knew 
any more specifics?

I only ask because I am taking this project on as part of my University 
course and the ideal end result for me is to have the drivers present in 
a SANE stable release,so if I could do this by the next release that 
would be perfect :)

Thanks

Chris


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