I can detect largest contour the answer sheet (20 questions, each have 4 alternative)
After the draw largest contour, what shall I do?
Divide matris the rectangle by 20x4 cell? Or find countour again but this time inside the rectangle?
I dont know what I need. Just I want to get which is marked.
public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
return findLargestRectangle(inputFrame.rgba());
}
private Mat findLargestRectangle(Mat original_image) {
Mat imgSource = original_image;
hierarchy = new Mat();
//convert the image to black and white
Imgproc.cvtColor(imgSource, imgSource, Imgproc.COLOR_BGR2GRAY);
//convert the image to black and white does (8 bit)
Imgproc.Canny(imgSource, imgSource, 50, 50);
//apply gaussian blur to smoothen lines of dots
Imgproc.GaussianBlur(imgSource, imgSource, new Size(5, 5), 5);
//find the contours
List contours = new ArrayList();
Imgproc.findContours(imgSource, contours, hierarchy, Imgproc.RETR_LIST, Imgproc.CHAIN_APPROX_SIMPLE);
hierarchy.release();
double maxArea = -1;
int maxAreaIdx = -1;
MatOfPoint temp_contour = contours.get(0); //the largest is at the index 0 for starting point
MatOfPoint2f approxCurve = new MatOfPoint2f();
Mat largest_contour = contours.get(0);
List largest_contours = new ArrayList();
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();
Imgproc.approxPolyDP(new_mat, approxCurve, contourSize*0.05, true);
if (approxCurve.total() == 4) {
maxArea = contourarea;
maxAreaIdx = idx;
largest_contours.add(temp_contour);
largest_contour = temp_contour;
}
}
}
MatOfPoint temp_largest = largest_contours.get(largest_contours.size()-1);
largest_contours = new ArrayList();
largest_contours.add(temp_largest);
Imgproc.cvtColor(imgSource, imgSource, Imgproc.COLOR_BayerBG2RGB);
Imgproc.drawContours(imgSource, contours, maxAreaIdx, new Scalar(0, 255, 0), 1);
Log.d(TAG, "Largers Contour:" + contours.get(maxAreaIdx).toString());
return imgSource;
}
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