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From: "OkinawaDolphin " <OkinawaDolphin@Hotmail.com>
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Subject: Re: Correction of Perspective Distortion
Date: Fri, 1 Feb 2008 07:29:02 +0000 (UTC)
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Roger Stafford,

choosing four points that correspond to the corners of a 
rectangle in the original image (which is not available) 
might indeed solve the problem. In the images I have there 
are lines that can be assumed to be parallel and small 
objects that can be taken as corners of rectangles. There 
are also medium sized objects that are approximately 
rectangular in the real world.

I wonder how I should choose a quadrilateral. What is large 
enough? Should the quadrilateral in the image cover more 
than half the image area? Should it cover 2/3 or 3/4? Would 
1/10 be enough? It seems that this is the challenge.