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  1. PO
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    <p>There is the code computes the affine transformation matrix using the library Opencv (it shows how to trasform your trapezoid to rectangle and how to find transformation matrix for futher calculations):</p> <pre><code>//example from book // Learning OpenCV: Computer Vision with the OpenCV Library // by Gary Bradski and Adrian Kaehler // Published by O'Reilly Media, October 3, 2008 #include &lt;cv.h&gt; #include &lt;highgui.h&gt; #include &lt;stdlib.h&gt; #include &lt;stdio.h&gt; int main(int argc, char* argv[]) { IplImage *src=0, *dst=0; // absolute or relative path to image should be in argv[1] char* filename = argc == 2 ? argv[1] : "Image0.jpg"; // get the picture src = cvLoadImage(filename,1); printf("[i] image: %s\n", filename); assert( src != 0 ); // points (corners of ) CvPoint2D32f srcQuad[4], dstQuad[4]; // transformation matrix CvMat* warp_matrix = cvCreateMat(3,3,CV_32FC1); // clone image dst = cvCloneImage(src); // define all the points //here the coordinates of corners of your trapezoid srcQuad[0].x = ??; //src Top left srcQuad[0].y = ??; srcQuad[1].x = ??; //src Top right srcQuad[1].y = ??; srcQuad[2].x = ??; //src Bottom left srcQuad[2].y = ??; srcQuad[3].x = ??; //src Bot right srcQuad[3].y = ??; //- - - - - - - - - - - - - -// //coordinates of rectangle in src image dstQuad[0].x = 0; //dst Top left dstQuad[0].y = 0; dstQuad[1].x = src-&gt;width-1; //dst Top right dstQuad[1].y = 0; dstQuad[2].x = 0; //dst Bottom left dstQuad[2].y = src-&gt;height-1; dstQuad[3].x = src-&gt;width-1; //dst Bot right dstQuad[3].y = src-&gt;height-1; // get transformation matrix that you can use to calculate //coordinates of point Pxy cvGetPerspectiveTransform(srcQuad,dstQuad,warp_matrix); // perspective transformation cvWarpPerspective(src,dst,warp_matrix); cvNamedWindow( "cvWarpPerspective", 1 ); cvShowImage( "cvWarpPerspective", dst ); cvWaitKey(0); cvReleaseMat(&amp;warp_matrix); cvReleaseImage(&amp;src); cvReleaseImage(&amp;dst); cvDestroyAllWindows(); return 0; </code></pre> <p>Hope it will be helpfull!</p>
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    1. POTransform point position in trapezoid to rectangle position
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    1. USAnn Orlova
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      1. VTUpMod
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    1. COHi Ann, I am not really looking for an image to transform. However I understand that I get a transformation matrix from this example, but what do you exactly mean by "//coordinates of rectangle in src image".
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      1. USSebastian Borggrewe
    2. COSorry, not rectangle,I meant the corners of your trapazoid in src image.
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      1. USAnn Orlova
 

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