On 20/05/2014 18:42, Octavio Alvarez wrote:
On 05/20/2014 12:27 AM, Octavio Alvarez wrote:
So far, I have repeated some of the tests with scanimage only and
target_code seems to be too high for my taste. 0x8000 seems like a lot
better value. I'm still testing though.
Hi, Stef. I have made some tests using scanimage only. I, effectively,
don't get the artifacts anymore. Thanks a lot! However, you were right,
the image quality has problems.
Using target_code = 0xe000, the currently coded value, I get a bluish
and saturated image. I tried lowering target_code across multiple values
down to 0x4000. The lower the value, the better the quality but the
darker the image.
At 0xb000, the horizontal extremes of the image are white balanced but
it is still noticeably bluish towards the center. This is, two small
vertical correctly white-balanced sections are noticed at the left and
right extremes.
For example, at 0x8000, the image is not saturated anymore, and the
image is way better white-balanced overall. However, the image is
noticeably darker image (75% of the histogram with typical white at 55%
luminosity). There is still a noticeably vertical stripe towards the
blue, a bit off the center towards the right.
At 0x4000, I don't get bluish stripes and perfect white-balance, but it
results in only half of the histogram.
I tried tweaking the "o" value (offset?) but I didn't seem to find any
kind of pattern, except that if I set it too high I get badly colored
stripes, so I just left them at their original values.
Thanks again.
Hello,
the offset shouldn't be touched. For some undocumented reason the
ASIC needs it to have the shading coefficients match the right pixels.
target_code is giving the desired target value for white. Once this
value is correct : not too low, and not too high to avoid
"solarization", you should turn to tuning gamma values. They are defined
in genesys_devices.c for the CCD_HP3670. Currently it is 1.0 for each
color channels, and this need to be adjusted. This will improve the
histogram.
Regards,
Stef
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