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In the following code, I have carried out the following steps:

1. Loaded an image from sdcard.

1. Converted it to HSV format.

2. Used inRange function to mask out the red color.

1. Used findContours to find the contours.

2. Find the largest contour from those contours.

3. Created an ROI around the largest contour using boundingRect and submat functions.

1. Converted this ROI Mat to HSV format.

1. Iterated through the ROI Mat, and check for each pixel if it lies within the largest contour. I used the method pointPolygonTest to find this out, but it returns -1 for every pixel, as can be seen from the Log.i output I have pasted here. The question is why? How can I correct this.

   private Scalar detectColoredBlob() {
       rgbaFrame = Highgui.imread("/mnt/sdcard/DCIM/rgbaMat4Mask.bmp");
   
       Mat hsvImage = new Mat();
       Imgproc.cvtColor(rgbaFrame, hsvImage, Imgproc.COLOR_BGR2HSV);
       Highgui.imwrite("/mnt/sdcard/DCIM/hsvImage.bmp", hsvImage);// check
   
       Mat maskedImage = new Mat();
       Core.inRange(hsvImage, new Scalar(0, 100, 100), new Scalar(10, 255, 255), maskedImage);
       Highgui.imwrite("/mnt/sdcard/DCIM/maskedImage.bmp", maskedImage);// check
   
       List<MatOfPoint> contours = new ArrayList<MatOfPoint>();
       Imgproc.findContours(maskedImage, contours, new Mat(), Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_SIMPLE);
   
       // \/ We will use only the largest contour. Other contours (any other possible blobs of this color range) will be ignored.
       MatOfPoint largestContour = contours.get(0);
       double largestContourArea = Imgproc.contourArea(largestContour);
       for (int i = 1; i < contours.size(); ++i) {// NB Notice the prefix increment.
           MatOfPoint currentContour = contours.get(i);
           double currentContourArea = Imgproc.contourArea(currentContour);
           if (currentContourArea > largestContourArea) {
               largestContourArea = currentContourArea;
               largestContour = currentContour;
           }
       }
       MatOfPoint2f largestContour2f = new MatOfPoint2f(largestContour.toArray());// Required on Line 289. See http://stackoverflow.com/questions/11273588/how-to-convert-matofpoint-to-matofpoint2f-in-opencv-java-api
   
       Rect detectedBlobRoi = Imgproc.boundingRect(largestContour);
       Mat detectedBlobRgba = rgbaFrame.submat(detectedBlobRoi);
       Highgui.imwrite("/mnt/sdcard/DCIM/detectedBlobRgba.bmp", detectedBlobRgba);// check
   
       Mat detectedBlobHsv = new Mat();
       Imgproc.cvtColor(detectedBlobRgba, detectedBlobHsv, Imgproc.COLOR_BGR2HSV);
       Highgui.imwrite("/mnt/sdcard/DCIM/roiHsv.bmp", detectedBlobHsv);// check
   
       for (int firstCoordinate = 0; firstCoordinate < detectedBlobHsv.rows(); firstCoordinate++) {
           for (int secondCoordinate = 0; secondCoordinate < detectedBlobHsv.cols(); secondCoordinate++) {
               Log.i(TAG, "HAPPY " + Arrays.toString(detectedBlobHsv.get(firstCoordinate, secondCoordinate)));
               if (Imgproc.pointPolygonTest(largestContour2f, new Point(firstCoordinate, secondCoordinate), false) == -1) {
                   Log.i(TAG, "HAPPY ....................... OUTSIDE");
               }
           }
       }
       Highgui.imwrite("/mnt/sdcard/DCIM/processedcontoured.bmp", detectedBlobHsv);// check