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What you should do is : <ol> <li>Feed the 4 corners that you have found and the 4 real corners of the image to <a href="http://opencv.willowgarage.com/documentation/cpp/imgproc_geometric_image_transformations.html#cv-getperspectivetransform" rel="nofollow"><code>cv::getPerspectiveTransform</code></a>. It will give you a matrix of the perspective transformation that will warp the quadrangle to the whole image.</li> <li>Use <a href="http://opencv.willowgarage.com/documentation/cpp/imgproc_geometric_image_transformations.html#warpPerspective" rel="nofollow"><code>cv::WarpPerspective</code></a> to create the image you want.</li> </ol> The links will take you to the documentation. EDIT : You could use <code>cv::findHomography</code> to do step 1. But this is more about having a lot of corresponding points and outliers. EDIT : Here is an example. It is with the C interface but you could easily make it to work with the c++ <pre><code>#include <stdio.h> #include "highgui.h" #include "cv.h" int main( int argc, char** argv ) { // cvLoadImage determines an image type and creates datastructure with appropriate size IplImage* img = cvLoadImage( argv[1], CV_LOAD_IMAGE_COLOR); IplImage* img1 = cvCreateImage( cvSize(img->width, img->height), img->depth, img->nChannels ); cvNamedWindow( "out", CV_WINDOW_AUTOSIZE ); cvShowImage( "out", img1 ); // create a window. Window name is determined by a supplied argument cvNamedWindow( argv[1], CV_WINDOW_AUTOSIZE ); // Display an image inside and window. Window name is determined by a supplied argument cvShowImage( argv[1], img ); // The part you need // Here is the points that you take the image from (the small quadrangle) CvPoint2D32f first[4] = { {0,0}, {(img->width /4)* 3, img->height /4 }, { img->width /4 ,(img->height /4) *3}, {(img->width /4)* 3,(img->height /4) *3}, }; // Here are the points that you draw the quadrangle into (the four corners) CvPoint2D32f second[4] = { {0,0}, {img->width,0}, {0,img->height}, {img->width,img->height} }; // The part you need CvMat *transform = cvCreateMat(3,3, CV_32F); cvGetPerspectiveTransform(first,second, transform); cvWarpPerspective(img, img1, transform, CV_INTER_LINEAR+CV_WARP_FILL_OUTLIERS, cvScalarAll(0)); // End of part you need cvShowImage( "out", img1 ); // wait indefinitely for keystroke cvWaitKey(0); // release pointer to an object cvReleaseImage( &img ); // Destroy a window cvDestroyWindow( argv[1] ); } </code></pre> You should replace the array <code>first</code> with end points of the quadrangle you have found. EDIT : Here are some samples. I haven't looked them very well. <a href="http://www.adaptive-vision.com/en/technical_data/documentation/filters/GeometricImageTransformations/index.html" rel="nofollow">Geometric Image Transformations</a> <a href="http://www.adaptive-vision.com/en/technical_data/documentation/filters/GeometricImageTransformations/cvGetPerspectiveTransform.html" rel="nofollow">cvGetPerspectiveTransform</a>
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1. POadjust corners and crop the image openCV
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1. COcan you provide any link or example regarding this.
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