CODEWITHSUNDEEP
javaimage-processingconvolution
Roshan Prabhakar
Roshan Prabhakar

Reputation: 174

Image Convolution not working according to the actual algorithm

I have implemented a convolution filter in java. I did this a while back in ap cs but now I actually need it for something, so I re implemented it to make sure I still know how to do it. Unfortunately I lost my working copy so I can't compare current code to my previous working code. I am pretty sure I am implementing the algorithm correctly, but the code is still not working properly. Can an experienced programmer please explain what I am doing wrong.

Here is the Convolution class:

import java.awt.*;
import java.util.Arrays;

public class ConvolutionFilter {

    private int[][] image;
    private int[][] weights;
    private double[][] doubleWeights;

    private int[][] convolved;

    public ConvolutionFilter(int[][] image, int[][] weights) {

        this.image = image;
        this.weights = weights;

        convolve();
    }

    public void convolve() {

        int sum;
        int[][] convolved = new int[image.length][image[0].length];

        for (int r = 0; r < convolved.length - weights.length - 1; r++) {
            for (int c = 0; c < convolved[r].length - weights.length - 1; c++) {
                sum = 0;
                for (int i = 0; i < weights.length; i++) {
                    for (int j = 0; j < weights[i].length; j++) {
                        sum += image[r + i][c + j] * weights[i][j];
                    }
                }
                convolved[r][c] = sum / weight();
            }
        }

        this.convolved = convolved;
    }

    public int numWeights() {
        return weights.length * weights[0].length;
    }

    public int weight() {
        int sum = 0;
        for (int r = 0; r < weights.length; r++) {
            for (int c = 0; c < weights[r].length; c++) {
                sum += weights[r][c];
            }
        }
        if (sum == 0) return 1; else return sum;
    }

    public int[][] getConvolved() {
        return convolved;
    }

}

Any help is appreciated!

Upvotes: 2

Views: 191

Answers (1)

user555045
user555045

Reputation: 64904

To adapt this to RGB, the arithmetic should be done per channel instead of over the packed representation, for example (not tested)

public void convolve() {
    int[][] convolved = new int[image.length][image[0].length];
    double invScale = 1.0 / weight();

    for (int r = 0; r < convolved.length - weights.length - 1; r++) {
        for (int c = 0; c < convolved[r].length - weights.length - 1; c++) {
            int rsum = 0, gsum = 0, bsum = 0;
            for (int i = 0; i < weights.length; i++) {
                for (int j = 0; j < weights[i].length; j++) {
                    int pixel = image[r + i][c + j];
                    int w = weights[i][j];
                    rsum += ((pixel >> 16) & 0xFF) * w;
                    gsum += ((pixel >> 8) & 0xFF) * w;
                    bsum += (pixel & 0xFF) * w;
                }
            }
            rsum = (int)(rsum * invScale);
            gsum = (int)(gsum * invScale);
            bsum = (int)(bsum * invScale);
            convolved[r][c] = bsum | (gsum << 8) | (rsum << 16) | (0xFF << 24);
        }
    }

    this.convolved = convolved;
}

Upvotes: 1

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