On 4/2/21 6:56 PM, Kevin Parker via cctalk wrote:
If there is anyone on the list familiar with scanners I'd be most
grateful for some advice please.
I'm definitely not an expert. But I have opinions.
Some time ago I bought a HP 8270 sheet feed (full duplex) scanner
NOS. I wanted to digitise a whole heap of old computer documentation
and for a little while I've been working through the big heap of
stuff. But for quite some time I've had an issue with scans that go
through the sheet feeder (irrespective of whether I do them double
sided or not). Basically the problem is that anything that goes via
the sheet feeder has issues with "streaks" in the document whereas
anything done on the flat bed is perfect (I have some links to some
examples below).
The thing that smacks me in the face is the difference in -- what I
think is called -- the white balance.
It may be that the white balance is /so/ /far/ /off/ for the sheet
feeder that things can't compensate and you're into the realm of sensors
interpreting noise differently between adjacent pixels. It's almost as
if the different horizontal pixels have different levels of sensitivity
or are being over driven such that they can't compensate. I really
notice it on the right hand side of the black canted center window and
the blue in the upper left window. It's noticeable in in the text fade
out in the lower left window too.
By way of clarity, anything done on the flatbed the lamp traverses
the flat bed to do the scan. For sheet fed items the lamp is moved to
specific slot on the scanner and the sheet feeder takes over wrapping
the document past the lamp. Given that flat bed scans are OK I don't
think its an issue with the lamp.
When I looked at the flat bed scan first, I didn't see anything wrong.
Then I noticed the 2nd link. ;-)
I've done the following things to try to resolve the issue with no joy:
* Checked for any specific settings
* Tried doing scans in grayscale
* Tried increasing the resolution (default is 300dpi) to slow the
speed that the document is fed through the feeder.
The only time that I've ever had anything scan weird, even remotely like
your sheet feed example, is when the item to be scanned isn't /close/
/enough/ to the scanning surface. E.g. the middle spine / gutter
(?terms?) of a book / magazine that I can't lay completely flat on the
scanner.
It sounds like the sheet feeder may be part of the lid and that it can
be lifted / moved away from the scanning bed. As such, I'll suggest
making sure that the lid / sheet feed scanner is properly closed and not
gaping in any way.
According to HP the issue is a cleanliness one i.e. dirt on the glass
can cause reflections. I've followed their instructions for cleaning
the glass but still no joy.
Based on how the flatbed example looks, I don't think that it's a dirt
issue.
Unless there is another piece of glass that is between the flatbed as
part of the body of the sheet feeder that needs to be cleaned.
Flatbed example.
https://drive.google.com/file/d/1jYiFzERiZiaq7-WoTiQ2eIzITn6giviR/view?usp=sharing
That looks really good to me.
Sheet feed example.
https://drive.google.com/file/d/1WF4SHbwV3bVET_bzwIUiULywbCGZBf_V/view?usp=sharing
Oy vey!
Thank you!!!
Good luck.
--
Grant. . . .
unix || die
