CircleFinder.java

import java.awt.image.BufferedImage;
import java.util.ArrayList;
import java.util.List;

public class CircleFinder {
   
    private int threshold;
    private int numberOfCircles;
    private int minRadius;
    private int maxRadius;
    
    public CircleFinder(int threshold, int numberOfCircles, int minRadius, int maxRadius) {
    	this.numberOfCircles = numberOfCircles;
        this.threshold = threshold;
        this.minRadius = minRadius;
        this.maxRadius = maxRadius;
    }
    
    /*
     * Detect circles on the given image
     */
    public List<Circle> circleDetection(BufferedImage image, double[][] sobel) throws Exception {        
        // sets a 3D integer space array to contain 'hits' circles
        int[][][] accumulator = new int[image.getWidth()][image.getHeight()][maxRadius];
        int max = 0;

        for (int x = 0; x < image.getWidth(); x++)
            for (int y = 0; y < image.getHeight(); y++) {
                /*
                 * checks if the pixel is above threshold, checks if its coordinates are valid and increases accumulator
                 */
                if (sobel[x][y] > threshold) {
                    for (int rad = minRadius; rad < maxRadius; rad++) {
                        for (int t = 0; t <= 360; t++) {
                            Integer a = (int) Math.floor(x - rad * Math.cos(t * Math.PI / 180));
                            Integer b = (int) Math.floor(y - rad * Math.sin(t * Math.PI / 180));

                            // checks if a or b are outside the bounds of the image, then ignore them
                            if (!((0 > a || a > image.getWidth() - 1) || (0 > b || b > image.getHeight() - 1))) {
                                accumulator[a][b][rad] += 1;
                                if(accumulator[a][b][rad] > max){
                                    max = accumulator[a][b][rad];
                                }
                            }
                        }
                    }
                }
            }
        
        List<Circle> circles = new ArrayList<>();
        for (int x = 0; x < image.getWidth(); x++)
            for (int y = 0; y < image.getHeight(); y++)
                for (int rad = minRadius; rad < maxRadius; rad++)
                    circles.add(new Circle(x, y, rad, accumulator[x][y][rad]));
        
        return circles;
    }
    
    public int getNumberOfCircles() {
    	return this.numberOfCircles;
    }
}