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POExecuting cv::warpPerspective for a fake deskewing on a set of cv::Point
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  1. POExecuting cv::warpPerspective for a fake deskewing on a set of cv::Point
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    copied!<p>I'm trying to do a <a href="http://nuigroup.com/forums/viewthread/3414/">perspective transformation</a> of a set of points in order to achieve a <a href="http://felix.abecassis.me/2011/10/opencv-rotation-deskewing/">deskewing</a> effect:</p> <p><a href="http://nuigroup.com/?ACT=28&amp;fid=27&amp;aid=1892_H6eNAaign4Mrnn30Au8d">http://nuigroup.com/?ACT=28&amp;fid=27&amp;aid=1892_H6eNAaign4Mrnn30Au8d</a></p> <p>I'm using the image below for tests, and the <strong>green</strong> rectangle display the area of interest.</p> <p><img src="https://i.stack.imgur.com/r8fmh.jpg" width="300" height="350"></p> <p>I was wondering if it's possible to achieve the effect I'm hoping for using a simple combination of <code>cv::getPerspectiveTransform</code> and <code>cv::warpPerspective</code>. I'm sharing the source code I've written so far, but it doesn't work. This is the resulting image:</p> <p><img src="https://i.stack.imgur.com/206aG.jpg" width="100" height="130"></p> <p>So there is a <code>vector&lt;cv::Point&gt;</code> that <strong>defines the region of interest</strong>, but the points are <strong>not stored in any particular order</strong> inside the vector, and that's something I can't change in the detection procedure. Anyway, <strong>later</strong>, the points in the vector are used to define a <code>RotatedRect</code>, which in turn is used to assemble <code>cv::Point2f src_vertices[4];</code>, one of the variables required by <code>cv::getPerspectiveTransform()</code>.</p> <p>My understanding about <strong>vertices</strong> and how they are organized <strong>might be one of the issues</strong>. I also think that using a <strong><code>RotatedRect</code> is not the best idea</strong> to store the original points of the ROI, since the <strong>coordinates will change</strong> a little bit to fit into the rotated rectangle, and <strong>that's not very cool</strong>.</p> <pre><code>#include &lt;cv.h&gt; #include &lt;highgui.h&gt; #include &lt;iostream&gt; using namespace std; using namespace cv; int main(int argc, char* argv[]) { cv::Mat src = cv::imread(argv[1], 1); // After some magical procedure, these are points detect that represent // the corners of the paper in the picture: // [408, 69] [72, 2186] [1584, 2426] [1912, 291] vector&lt;Point&gt; not_a_rect_shape; not_a_rect_shape.push_back(Point(408, 69)); not_a_rect_shape.push_back(Point(72, 2186)); not_a_rect_shape.push_back(Point(1584, 2426)); not_a_rect_shape.push_back(Point(1912, 291)); // For debugging purposes, draw green lines connecting those points // and save it on disk const Point* point = &amp;not_a_rect_shape[0]; int n = (int)not_a_rect_shape.size(); Mat draw = src.clone(); polylines(draw, &amp;point, &amp;n, 1, true, Scalar(0, 255, 0), 3, CV_AA); imwrite("draw.jpg", draw); // Assemble a rotated rectangle out of that info RotatedRect box = minAreaRect(cv::Mat(not_a_rect_shape)); std::cout &lt;&lt; "Rotated box set to (" &lt;&lt; box.boundingRect().x &lt;&lt; "," &lt;&lt; box.boundingRect().y &lt;&lt; ") " &lt;&lt; box.size.width &lt;&lt; "x" &lt;&lt; box.size.height &lt;&lt; std::endl; // Does the order of the points matter? I assume they do NOT. // But if it does, is there an easy way to identify and order // them as topLeft, topRight, bottomRight, bottomLeft? cv::Point2f src_vertices[4]; src_vertices[0] = not_a_rect_shape[0]; src_vertices[1] = not_a_rect_shape[1]; src_vertices[2] = not_a_rect_shape[2]; src_vertices[3] = not_a_rect_shape[3]; Point2f dst_vertices[4]; dst_vertices[0] = Point(0, 0); dst_vertices[1] = Point(0, box.boundingRect().width-1); dst_vertices[2] = Point(0, box.boundingRect().height-1); dst_vertices[3] = Point(box.boundingRect().width-1, box.boundingRect().height-1); Mat warpMatrix = getPerspectiveTransform(src_vertices, dst_vertices); cv::Mat rotated; warpPerspective(src, rotated, warpMatrix, rotated.size(), INTER_LINEAR, BORDER_CONSTANT); imwrite("rotated.jpg", rotated); return 0; } </code></pre> <p>Can someone help me fix this problem?</p>
 

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