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correction of distorted grid in image ??

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tomos:
does anyone know of software that would correctly align a grid in an image:

What I would use it for:

Say I have a photo or scan of a drawing on graph paper. The graph will be more or less distorted depending on means of capture. (Also sometimes the graph-paper itself doesn't have an accurate grid cause of age etc, or sometimes it's photocopied or simply cause it's paper)

The ideal software would atomatically recognise the grid & correct any distortion in the image.
But of course manually marking points on the grid wouldn't kill me  :D

There is stuff like this for correcting lens distortion in digital cameras but this requires more then "just" that correction.
I know photogrammetry uses software to align points in an image in order to correct an image of, say, the face of a building, but beyond that .. (also prob. very expensive as geared to 3D as well)

thanks for any suggestions, tom

I've also posted that in http://www.imaging-resource.com/ forums. It's a good site for camera info but not so busy on the software front.
I would also appreciate any ideas of where I might get ideas for this.

f0dder:
Hm, dunno if a specific app exists, but photo morphing software might do what you need? Usually you set up some control points (has always been a grid for the stuff I've played with), and can then move those control points around... dunno if it's accurate enough for your uses.

tsaint:
does anyone know of software that would correctly align a grid in an image:

What I would use it for:

Say I have a photo or scan of a drawing on graph paper. The graph will be more or less distorted depending on means of capture. (Also sometimes the graph-paper itself doesn't have an accurate grid cause of age etc, or sometimes it's photocopied or simply cause it's paper)
-tomos (February 14, 2007, 11:24 AM)
--- End quote ---
This might not be exactly what you want Tom, but its related. I use an application called "whiteboard photo" in this circumstance.
Every lesson, I take a photo of the whiteboard Ive been doing maths on. The photos have perspective distortions, as well as looking bad (the white isnt white etc)
Whiteboard photo's purpose is to "clean" those photos by fixing the colour and the perspective problem.
For the latter, it does this by suggesting a moveable trapezium you set around the outline of the board, and this trapezium gets transfomed to a rectangle. (ie eliminating distortion)
Re the colour problem... I have tried setting white balance and messing about in both photoshop and psp ... Whiteboard photo worked much easier and better.
This colour aspect might be relevant to you depending on how you obtained your images (eg photo of a page from a book)

A negative is the price, listed at $249 (go to http://www.polyvision.com/products/wbp.asp for info), but note that a long time ago it used to be $79. When I came to buy it, I hunted around and found a place on the net STILL selling it for $79 (I think I searched for "pixid" who used to own the software)
tony

mouser:
there is defintely software for doing such distortion corrections - maybe look for photoshop filters.

tomos:
Hm, dunno if a specific app exists, but photo morphing software might do what you need? Usually you set up some control points (has always been a grid for the stuff I've played with), and can then move those control points around... dunno if it's accurate enough for your uses.-f0dder (February 14, 2007, 05:36 PM)
--- End quote ---

f0dder, sounds interesting - I had a look, but couldnt tell from what I found on google - what software are you using?

tony - thanks for that idea,
I've actually read about that elsewhere -
If the edge of board is curved in photo (say from wide angle shot) does it correct that as well ?
-
I suspect it wont be up to what i want ... because of the irregular nature of some of the distortion - especially from photocopied images - but I will go have a look (as you say, full price is very expensive for what it does)


Am trying out a couple of photoshop filters but havent found anything appropriate yet. Problem is there seems to be millions of them out there (& this was supposed to be a time saving exercise  :)  -  )

thanks, tom

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