SOT: Scanning old computer docs

[Grant Taylor]

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