CODEWITHSUNDEEP
javaopencv
NSaid
NSaid

Reputation: 751

OpenCV Java - Changing pixel color

I am trying to determine a way to change the pixel color of my masks from black to a different color. Unfortunately, I have not be able to determine a way to do this task. Essentially, what I am trying to do is take this image: mask

and convert the black portions to a color with values (255, 160, 130). I have tried several methods to try and achieve my goal. These include draw contours, setTo, and looping through the matrix. Unfortunately all of these attempts have failed. I have included the code and the resulting outcomes below.

Draw Contours method

System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
        Mat img = Imgcodecs.imread(
                "C:\\Users\\Hassan\\Documents\\School\\Me\\COMP5900 Y\\Project\\Project\\src\\resources\\face.jpg");
        Mat img_grey = new Mat();
        Mat grad = new Mat(), grad_x = new Mat(), grad_y = new Mat();
        Mat abs_grad_x = new Mat(), abs_grad_y = new Mat();

        int ddepth = CvType.CV_32F;
        int scale = 1;
        int delta = 0;

        Imgproc.GaussianBlur(img, img, new Size(3, 3), 0, 0, Core.BORDER_CONSTANT);
        Imgproc.cvtColor(img, img_grey, Imgproc.COLOR_BGR2GRAY);

        // Apply Sobel
        Imgproc.Sobel(img_grey, grad_x, ddepth, 1, 0, 3, scale, delta, Core.BORDER_DEFAULT);
        Imgproc.Sobel(img_grey, grad_y, ddepth, 0, 1, 3, scale, delta, Core.BORDER_DEFAULT);

        // converting back to CV_8U
        Core.convertScaleAbs(grad_x, abs_grad_x);
        Core.convertScaleAbs(grad_y, abs_grad_y);

        // Total Gradient (approximate)
        Core.addWeighted(abs_grad_x, 0.5, abs_grad_y, 0.5, 0, grad);

        Photo.fastNlMeansDenoising(grad, grad);
        Imgproc.GaussianBlur(grad, grad, new Size(3, 3), 0, 0, Core.BORDER_CONSTANT);

        // isolate background
        Mat background = new Mat();
        Imgproc.threshold(grad, background, 2, 255, Imgproc.THRESH_BINARY);

        // draw contours
         List<MatOfPoint> contours = new ArrayList<>();
         Mat hierarchy = new Mat();
         Imgproc.findContours(background, contours, hierarchy, Imgproc.RETR_TREE, Imgproc.CHAIN_APPROX_NONE);
         Mat drawing = Mat.zeros(background.size(), CvType.CV_8UC3);

         List<MatOfPoint> hullList = new ArrayList<>();
         for (MatOfPoint contour : contours) {
             MatOfInt hull = new MatOfInt();
             Imgproc.convexHull(contour, hull);
             Point[] contourArray = contour.toArray();
             Point[] hullPoints = new Point[hull.rows()];
             List<Integer> hullContourIdxList = hull.toList();
             for (int i = 0; i < hullContourIdxList.size(); i++) {
                 hullPoints[i] = contourArray[hullContourIdxList.get(i)];
             }
             hullList.add(new MatOfPoint(hullPoints));
         }

         for (int i = 0; i < contours.size(); i++) {
             Scalar color = new Scalar(255, 160, 130);
             Imgproc.drawContours(drawing, contours, i, color);
             //Imgproc.drawContours(drawing, hullList, i, color );
         }

Draw Contours

Note here, that I also tried using Imgproc.RETR_EXTERNAL as well, but that produced a completely black image. Also the name of the HighGui window is called "flood fill", but I just forgot to update the name.

setTo

// replace find and draw contours portion of code above
Mat out = new Mat();
background.copyTo(out);
out.setTo(new Scalar(255, 160, 130), background);

setTo

Iterating through matrix

   // replace draw contours portion of code above
   for (a = 0; a < background.rows(); a++) {
        for(b = 0; b < background.cols(); b++) {
            if(background.get(a,b)[0] == 0) {
                //background.put(a, b, CvType.CV_16F, new Scalar(255, 160, 130));
                double[] data = {255, 160, 130};
                background.put(a, b, data);
            }
        }
    }

iterating over matrix

The loop is promising, but I know it will not be efficient as I have 2 other masks that I would like to update as well. Could you please suggest an efficient method, that allows me to set the value for all three channels?

Thanks

Upvotes: 1

Views: 2261

Answers (1)

Sariq Shaikh
Sariq Shaikh

Reputation: 1124

I am not sure why you are doing many operations on the image but to me it looks like applying the mask and replacing the color efficiently. So if there are other complexities than please let me know.

Below is the code I was looking for in Java.

public static void main(String s[]) {
    System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
    Mat matr =Imgcodecs.imread("/home/shariq/Desktop/test.png");
    Mat result = new Mat();
    //create a mask based on range
    Core.inRange(matr, new Scalar(0), new Scalar(50), result);
    Imgcodecs.imwrite("/home/shariq/Desktop/test_in.png", result);
    //apply the mask with color you are looking for, note here scalar is in hsv
    matr.setTo(new Scalar(130,160,255),result);
    Imgcodecs.imwrite("/home/shariq/Desktop/result.png", matr);
}

We are creating a mask for the pixel values between 0-50 for black color using inRange method.

Core.inRange(matr, new Scalar(0), new Scalar(50), result);

This mask in result variable is than applied to original matrix using setTo method. The replacement color value is provided in HSV format through Scalar object. new Scalar(a,b,c) in HSV can be understand in RGB like this Red = c, Green = b and Blue = a.

matr.setTo(new Scalar(130,160,255),result);

Its quite fast compared to iterating the pixels one by one.

Upvotes: 1

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