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Why are scanned pages always tilted to the right ?

Posted: 12 May 2010, 05:44
by DSpider
Image

Notice the red space markers.

Some pages are more noticeable than others but the result is always the same. It kinda bothers me because I read them on an iPod touch with Good Reader's lock scroll option and the tilting is very pronounced if I zoom right up to the edge (which would be recommended because tiny screen is tiny).

Using v0.9.8.1 on Windows XP.

Previous versions have had the same problem but I didn't thought about asking why because most of the time I read them on my computer screen where you don't really notice it. Is there something I can do besides manually tilting each page at the "Deskew" section ? Because it takes forever to go through 492 pages and it doesn't have an "Apply To ..." button there.

Re: Why are scanned pages always tilted to the right ?

Posted: 12 May 2010, 06:42
by phaedrus
Maybe I'm missing something here but what are your input images like? Are you sure your camera(s) are exactly in line and/or the images are not suffering from some minor distortion that'd affect the de-skewing? I've not noticed the problem myself but will take a closer look when I get the chance.

I appreciate the desire to apply certain settings across all images I'd be all for that - content selection is one that I'd previously suggested but it's fairly low on Tulon's list of things to do - there are times I really wish I knew how to do these coding things and was able to help out :-)

Cheers, P.

Re: Why are scanned pages always tilted to the right ?

Posted: 12 May 2010, 07:04
by DSpider
I'm using a flatbed scanner. The funny thing is it's sitting on my desk to my right and because of the slight angle the scans should come out tilted to the left... which most do, especially when I edit the covers in GIMP. I always need to tilt them a few degrees to the right to straighten them out.

It's probably the ST algorithm. Was ST tested with flatbed scanners too or just digital cameras ?

Re: Why are scanned pages always tilted to the right ?

Posted: 12 May 2010, 08:36
by Tulon
ST's Deskew stage can only rotate images, not tilt them. Rotation is done in such a way that would make lines of text horizontal. If your pages weren't rectangular to begin with, it produces results like yours. Usually it's not a problem though.

Re: Why are scanned pages always tilted to the right ?

Posted: 12 May 2010, 14:01
by DSpider
So you're saying it's the scanner ? Maybe I am pressing a little too hard on one side (because of the position of my chair relative to the scanner) but how come EVERY page is tilted to the right ? I mean, ST can properly deal with stuff like this but not flatbed scanned material ?

Re: Why are scanned pages always tilted to the right ?

Posted: 12 May 2010, 14:22
by Tulon
DSpider wrote:So you're saying it's the scanner ? Maybe I am pressing a little too hard on one side (because of the position of my chair relative to the scanner) but how come EVERY page is tilted to the right ? I mean, ST can properly deal with stuff like this but not flatbed scanned material ?
It's probably caused by the book not being pressed hard enough to the scanner.
The example you mention demonstrates experimental dewarping, which I had to turn off, as otherwise I would get complains about it every other day. It clearly needs more work.