Perspective correction of UIImage from Points

Question

I\'m working on a app where I\'ll let the user take a picture e.g of a business card or photograph.

The user will then mark the four corners of the object (which the

Answer 1

I'm not sure if you've tried the Opencv library yet, but it has a very nice way to deskew an image. I've got here a small snippet that takes an array of corners, your four corners for example, and a final size to map it into.

You can read the man page for warpPerspective on the OpenCV site.

cv::Mat deskew(cv::Mat& capturedFrame, cv::Point2f source_points[], cv::Size finalSize)
{
    cv::Point2f dest_points[4];

    // Output of deskew operation has same color space as source frame, but
    // is proportional to the area the document occupied; this is to reduce
    // blur effects from a scaling component.
    cv::Mat deskewedMat = cv::Mat(finalSize, capturedFrame.type());

    cv::Size s = capturedFrame.size();

    // Deskew to full output image corners
    dest_points[0] = cv::Point2f(0,s.height); // lower left
    dest_points[1] = cv::Point2f(0,0);        // upper left
    dest_points[2] = cv::Point2f(s.width,0);  // upper right
    dest_points[3] = cv::Point2f(s.width,s.height);  // lower right

    // Build quandrangle "de-skew" transform matrix values
    cv::Mat transform = cv::getPerspectiveTransform( source_points, dest_points  );
    // Apply the deskew transform
    cv::warpPerspective( capturedFrame, deskewedMat, transform, s, cv::INTER_CUBIC );

    return deskewedMat;
}