Auto perspective correction using OpenCV and Java

Question

I'm looking at perspective correction for images taken from an Android camera, similar as defined in this question posted earlier. However, I'm not able to get my hands on proper working Java code.

If anyone has made it work on Java, please help.

Answer 1

I found an answer to my query here. Have put little refined code snippet below:

public static void correctPerspective() {

    String fileName = "IMG_20141024_132131.jpg";
    Mat imgSource = Highgui.imread(fileName, Highgui.CV_LOAD_IMAGE_UNCHANGED);
    // convert the image to black and white does (8 bit)
    Imgproc.Canny(imgSource.clone(), imgSource, 50, 50);

    // apply gaussian blur to smoothen lines of dots
    Imgproc.GaussianBlur(imgSource, imgSource, new org.opencv.core.Size(5, 5), 5);

    // find the contours
    List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
    Imgproc.findContours(imgSource, contours, new Mat(), Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_SIMPLE);

    double maxArea = -1;
    MatOfPoint temp_contour = contours.get(0); // the largest is at the
                                                // index 0 for starting
                                                // point
    MatOfPoint2f approxCurve = new MatOfPoint2f();

    for (int idx = 0; idx < contours.size(); idx++) {
        temp_contour = contours.get(idx);
        double contourarea = Imgproc.contourArea(temp_contour);
        // compare this contour to the previous largest contour found
        if (contourarea > maxArea) {
            // check if this contour is a square
            MatOfPoint2f new_mat = new MatOfPoint2f(temp_contour.toArray());
            int contourSize = (int) temp_contour.total();
            MatOfPoint2f approxCurve_temp = new MatOfPoint2f();
            Imgproc.approxPolyDP(new_mat, approxCurve_temp, contourSize * 0.05, true);
            if (approxCurve_temp.total() == 4) {
                maxArea = contourarea;
                approxCurve = approxCurve_temp;
            }
        }
    }

    Imgproc.cvtColor(imgSource, imgSource, Imgproc.COLOR_BayerBG2RGB);
    Mat sourceImage = Highgui.imread(fileName, Highgui.CV_LOAD_IMAGE_UNCHANGED);
    double[] temp_double;
    temp_double = approxCurve.get(0, 0);
    Point p1 = new Point(temp_double[0], temp_double[1]);
    // Core.circle(imgSource,p1,55,new Scalar(0,0,255));
    // Imgproc.warpAffine(sourceImage, dummy, rotImage,sourceImage.size());
    temp_double = approxCurve.get(1, 0);
    Point p2 = new Point(temp_double[0], temp_double[1]);
    // Core.circle(imgSource,p2,150,new Scalar(255,255,255));
    temp_double = approxCurve.get(2, 0);
    Point p3 = new Point(temp_double[0], temp_double[1]);
    // Core.circle(imgSource,p3,200,new Scalar(255,0,0));
    temp_double = approxCurve.get(3, 0);
    Point p4 = new Point(temp_double[0], temp_double[1]);
    // Core.circle(imgSource,p4,100,new Scalar(0,0,255));
    List<Point> source = new ArrayList<Point>();
    source.add(p1);
    source.add(p2);
    source.add(p3);
    source.add(p4);
    Mat startM = Converters.vector_Point2f_to_Mat(source);
    Mat result = warp(sourceImage, startM);

    Highgui.imwrite("corrected.jpg", result);
}

public static Mat warp(Mat inputMat, Mat startM) {

    int resultWidth = 1200;
    int resultHeight = 680;

    Point ocvPOut4 = new Point(0, 0);
    Point ocvPOut1 = new Point(0, resultHeight);
    Point ocvPOut2 = new Point(resultWidth, resultHeight);
    Point ocvPOut3 = new Point(resultWidth, 0);

    if (inputMat.height() > inputMat.width()) {
        // int temp = resultWidth;
        // resultWidth = resultHeight;
        // resultHeight = temp;

        ocvPOut3 = new Point(0, 0);
        ocvPOut4 = new Point(0, resultHeight);
        ocvPOut1 = new Point(resultWidth, resultHeight);
        ocvPOut2 = new Point(resultWidth, 0);
    }

    Mat outputMat = new Mat(resultWidth, resultHeight, CvType.CV_8UC4);

    List<Point> dest = new ArrayList<Point>();
    dest.add(ocvPOut1);
    dest.add(ocvPOut2);
    dest.add(ocvPOut3);
    dest.add(ocvPOut4);

    Mat endM = Converters.vector_Point2f_to_Mat(dest);

    Mat perspectiveTransform = Imgproc.getPerspectiveTransform(startM, endM);

    Imgproc.warpPerspective(inputMat, outputMat, perspectiveTransform, new Size(resultWidth, resultHeight), Imgproc.INTER_CUBIC);

    return outputMat;
}