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POAffine Transform, Simple Rotation and Scaling or something else entirely?
 

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  1. POAffine Transform, Simple Rotation and Scaling or something else entirely?
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    <p>The scenario goes like this: I have a picture of a paper that I would like to do some OCR. So take the image below as my input example:</p> <p><img src="https://i.stack.imgur.com/Spl0H.jpg" alt="orig_image"></p> <p>After successfully detecting the area that corresponds to the paper I'm left with a <code>vector&lt;Point&gt;</code> of 4 coordinates that define its location inside the image. Note that these coordinates will probably not correspond to a perfect rectangle due to the distance of the camera and angle when the picture was taken. For viewing purposes I connected the points in the sub-image so you can see what I mean:</p> <p><img src="https://i.stack.imgur.com/nVd0p.jpg" alt="detected_image"></p> <p>In this case, the points are: [1215, 43] , [52, 67] , [56, 869] and [1216, 884]</p> <p>At this moment, I need to adjust these points so they become aligned horizontally. What do I mean by that? If you notice the area of the sub-image above, it is a little rotated: the points on right side of the image are positioned a little higher than points on the other side.</p> <p>In other words, we have image <strong>A</strong>, which was exaggerated on purpose to look a little more distorted/rotated than reality, and then image <strong>B</strong> - which is what I would like as the final result of this procedure:</p> <p>A) <img src="https://i.stack.imgur.com/GJ575.jpg" alt="bad_rect"> B) <img src="https://i.stack.imgur.com/ijOyl.jpg" alt="ok_rect"></p> <p>I'm not sure <strong>which techniques</strong> could be used to achieve this transformation. The application also needs to <strong>detect automatically</strong> how much rotation needs to be done, as I don't have control over the image acquisition procedure. </p> <p>The purpose is to have a new <code>Mat</code> with the <em>normalized</em> sub-image. I'm not worried about a possible image distortion right now, I'm just looking for a way to identify how much rotation needs to be done on the sub-image and how to apply it and get a more <em>rectangular area</em>.</p>
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