[sane-devel] Why is the background of the scanned image not a constant grayscale

[m. allan noah]

On Tue, 13 May 2003, Peter Chen wrote:

> Hi,
> 
> I still do not quite understand. When I tried to scan the same image using
> Twain, there was no gray background. What could be the reason?

thats interesting. when you scan a white sheet of paper via twain and 
sane, is the sane one more gray? if so, i bet the twain driver is 
interpolating gamma on the whole of the scan or bumping the contrast up, 
and shifting the light gray to white.

> 
> And I could not find the option to set the option brightness/contrast when I
> ran: scanimage --help -d fujitsu:/dev/usb/scanner0.
> 

you did not find it because it is not there. this would have to be done in 
software, cause the scanner does not provide hardware ability to do this. 
try setting up some script to do b/c adjustments on the image from the 
unix command line.

allan

> Thanks,
> 
> Peter
> 
> ----- Original Message -----
> From: "m. allan noah" <anoah@pfeiffer.edu>
> To: "Peter Chen" <peterchenn@hotmail.com>
> Sent: Tuesday, May 13, 2003 8:43 AM
> Subject: Re: [sane-devel] Why is the background of the scanned image not a
> constant grayscale
> 
> 
> >
> > ok, a few points:
> >
> > 1. never, ever send someone the routing numbers on the lower edge of a
> > check.
> >
> > 2. the gray background that you see cannot be avoided. it is the
> > reflection of the wight stripe on the opposite read head. open your
> > scanner, and notice the bottom read head has a white plastic stripe bellow
> > it. the top read head has a wight plastic stipe above it. these line up
> > when the unit is closed.
> >
> > 3. immediately around the check, there is a darker line. this is a shadow
> > caused but the thickness of the edge of the check. there is no way to
> > avoid it.
> >
> > 4. if you scan the check in the middle of the adf, you would need to set
> > the -l to something higher, to cut off the background, then you dont have
> > to deal with it. you just have to cut it off, or turn up the
> > brightness/contrast to make the back completely wight.
> >
> > allan
> >
> > On Mon, 12 May 2003, Peter Chen wrote:
> >
> > > Hi,
> > >
> > > I scanned one check using the command:
> > >
> > > scanimage -d fujitsu:/dev/usb/scanner0 --format=tiff
> > > -l 0 -t 0 -x 100 -y 200 --mode=Gray --rif=yes > ttt.tiff
> > >
> > > then on my Windows machine, I converted it to jpg file.
> > >
> > > I did not try SCSI yet.
> > >
> > > Thanks,
> > >
> > > Peter
> > >
> > > ps: pls also see the comments below.
> > >
> > >
> > > ----- Original Message -----
> > > From: "m. allan noah" <anoah@pfeiffer.edu>
> > > To: "SANE Mailing List" <sane-devel@mostang.com>
> > > Sent: Friday, May 09, 2003 1:56 PM
> > > Subject: Re: [sane-devel] Why is the background of the scanned image not
> a
> > > constant grayscale
> > >
> > >
> > > > 1. what mode are you scanning in, grayscale, lineart, color?
> > > grayscale
> > > >
> > > > 2. what do you mean by layer? the fujitsu driver returns only one
> frame to
> > > > the front end, so there should not be a case where there is multiple
> pixel
> > > > data available for one physical pixel.
> > > Sorry, I was not very clear. Please see the jpg file attached. You can
> see
> > > outside the edge of the check, there is another layer which is not
> totally
> > > white nor totally black.
> > >
> > > >
> > > > 3. does this happen with other front-ends?
> > > Yes, I used scanimage, and it was the same thing. Actually, I created a
> > > bitmap file using the data from sane_read in my application to display
> it in
> > > Kylix.
> > >
> > > >
> > > > 4. does this happen with the scsi connection instead of usb?
> > > Sorry, I did not try it yet.
> > >
> > > >
> > > > 5. could you send me directly a copy of an image where you see this?
> > > Sure. Please see attched jpg file. If you need the tiff or bmp file, let
> me
> > > know.
> > >
> > > >
> > > > allan
> > > >
> > > > On Fri, 9 May 2003, Peter Chen wrote:
> > > >
> > > > > Hi,
> > > > >
> > > > > I set up the tl_x, tl_y, br_x and br_y, scanned one image and found
> that
> > > > > there was another layer between the real image and the dark
> background.
> > > It
> > > > > was a rectangle, not of constant grayscale. The scanner is Fujitsu
> > > fi-4120c.
> > > > >
> > > > > Could somebody pls tell me how to get rid of this layer? Since when
> I
> > > scan
> > > > > images using Twain, there is not such a layer.
> > > > >
> > > > > The reason that I want to get rid of the layer is I need to do some
> edge
> > > > > detection and deskewing. If the background is a constant black (or
> > > white),
> > > > > then it would be much easier to implement the algorithm.
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Peter
> > > > > _______________________________________________
> > > > > Sane-devel mailing list
> > > > > Sane-devel@www.mostang.com
> > > > > http://www.mostang.com/mailman/listinfo/sane-devel
> > > > >
> > > >
> > > > --
> > > > "so don't tell us it can't be done, putting down what you don't know.
> > > > money isn't our god, integrity will free our souls" - Max Cavalera
> > > >
> > > > _______________________________________________
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> > > > Sane-devel@www.mostang.com
> > > > http://www.mostang.com/mailman/listinfo/sane-devel
> > > >
> > >
> >
> > --
> > "so don't tell us it can't be done, putting down what you don't know.
> > money isn't our god, integrity will free our souls" - Max Cavalera
> >
> >
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-- 
"so don't tell us it can't be done, putting down what you don't know.
money isn't our god, integrity will free our souls" - Max Cavalera