Re: [gentoo-user] Scanner and weird streaking

[Michael]

On Friday, 30 December 2022 13:42:04 GMT Dale wrote:
> Michael wrote:
> > On Friday, 30 December 2022 02:28:32 GMT Dale wrote:
> >> Howdy all,
> >>
> >> I have a HP scanjet 4570c flatbed scanner.  I bought it used years ago
> >> and most of the time, it works just fine.  On occasion tho, I get
> >> something weird.  When I scan something, it adds some pinkish colored
> >> streaks.  I took a scrap sheet of paper and scanned the back of it. I
> >> used a magic marker on some text that was there, also drew a smiley face
> >> on it as well.  Anyway, the side with print is on the opposite side.
> >> Basically, it is also seeing the back side of the paper.  I'm not sure
> >> if that could cause this weird streaking but wanted to mention it.
> >
> > I've come across the pink hue artefact on an old HP scanner, but can't
> > recall the model.  It is not related to the print of the opposite side
> > becoming visible, which is caused by a high light exposure setting.  You
> > need to reduce the exposure to a level where you can see the primary
> > print clear enough, without the back side bleeding through.
>
> I kinda figure that.  It is pretty bright.  I don't recall seeing a
> setting for it but I may not have seen it.  I mostly tried different
> color settings, resolution and such.  Goes to show tho, it is
> sensitive.  ;-)

If the scanner front end doesn't offer an exposure tweak, you could try post-
processing of the scanned image using Gimp, or some other image editing 
software.  Reduce exposure until the reverse side print dissipates, while the 
front remains clear enough.

Alternatively, on a simpler set of controls playing with brightness and 
contrast could get you close enough.


> >> At first, I thought it was something on the glass so I disassembled the
> >> thing and cleaned it as best as I could.  When I put it back together, I
> >> concentrated on the back side of the glass, since I have to disassemble
> >> it to clean it.  I also clean the side the document goes on regularly.
> >> If it changed, I can't tell it.  Another odd thing, the streaks change
> >> depending on the document.  Sometimes you can barely see it, other times
> >> it is awful.  I've not been able to reason out what makes the difference
> >> tho.
> >
> > Cleaning the glass won't affect the pink hue.  I dismantled the scanner
> > and
> > cleaned the glass too, with no improvement.
> >
> >> I've got about the same results using Scanlite, Scanpage and XSane
> >> software.  XSane may be a tiny bit better but it does vary at times.
> >> There's not a lot of settings available.  I tend to use either 100dpi or
> >> 300 dpi for resolution thingy. I fiddled around a bit but it doesn't
> >> seem to help.  This is a link to the page I described above.  It's a
> >> little sizey so I didn't want to attach, for those who have email
> >> clients that puke a lot.  lol
> >>
> >> https://freeimage.host/i/HTQLpWb
> >>
> >> You may notice that it is a little heavier at the top and gets lighter
> >> as it goes down.  I've checked the glass, I can't find anything that
> >> would cause this.  Is my scanner just going bad?  Am I doing something
> >> wrong with a setting or something?  Any ideas?  Thoughts?
> >
> > The pink hue is probably due to the scanner bar going bad.  Some fixes,
> > which did not work in my case, are as follows:
> >
> > 1. Reset internal chipset:  Plug it in, switch it on, then pull the power
> > lead, followed by the USB.  Wait for a minute or longer to discharge, then
> > reconnect, power on and try to see if the problem is fixed.
> >
> > 2. Overheating: More of a problem in the summer.  Use a desk fan while
> > operating to see if it makes a difference.
> >
> > If none of the above work, then the scanner bar needs replacing.  Probably
> > time for a new scanner, unless you can find a donor scanner for the
> > scanner
> > bar.
>
> Well, bummer.  I was afraid it was going bad.  I knew it moved the light
> thing back and forth and all but know there is a lot more to it than
> that.  If it was a consistent streak, I'd think a bad CCD or whatever
> that chip that grabs the image is called nowadays.  This tho, wasn't
> looking like that.
>
> I may disassemble it again and check all the cables. Disconnect and
> reconnect everything and hope for a bad or lose connection.  Now let us
> pray.

The pink hue is visible signal noise captured in the image.  This may be 
internal, the scanner sensor is drifting outside its spec, or it could be some 
external source.  Do you always use the scanner in the same position on your 
desk, or does it give different results depending on location?  Strong 
electromagnetic interference may exacerbate the problem.


> Given I only use Linux, know of any good and commonly available flatbed
> scanner models?  I'm fine with used ones as long as they work.  I like
> the one I got since when I'm done, it stands upright in my closet and
> takes up very little floor space.  It does a really good job. I've even
> scanned in pictures and they looked good, when it wasn't doing the
> streak thing.
>
> Thanks.
>
> Dale
>
> :-)  :-)

I only have a very old 23 year old CanoScan N650U flat bed scanner with just 
one button on it!  It has worked faithfully for years with no problems, but my 
scanning needs are simple.

In case you are looking for used items on ebay, beware what you're buying may 
be in a worse state than what you are trying to replace.  Business clearance 
items can prove to be a bargain, but without testing in your environment you 
can't be sure.