Median filter of a pgm image

Question

I have to write a program that replaces each pixel with the median value of it and its 8 neighbors. What I have will compile but when i try to create a new image im getting multiple errors. Help is appreciated.

Here's the stacktrace:

Exception in thread "main" java.lang.ClassCastException: [I cannot be cast to java.lang.Comparable
at java.util.ComparableTimSort.countRunAndMakeAscending(ComparableTimSort.java:290)
at java.util.ComparableTimSort.sort(ComparableTimSort.java:171)
at java.util.ComparableTimSort.sort(ComparableTimSort.java:146)
at java.util.Arrays.sort(Arrays.java:472)
at ImageProcessing.median(ImageProcessing.java:25

And here's my code:

public static int [] [] median(int [] [] image) {
    int height = image.length;
    int width = image[0].length;
    int [] [] result = new int [height] [width];

    for (int col = 0 ; col < image.length ; col++) {
        result[0][col] = image[0][col];
        result[height - 1][col] = image[height - 1][col];
    }

    for (int row = 0 ; row < image[0].length ; row++) {
        result[row][0] = image[row][0];
        result[row][width - 1] = image[row][width - 1];
    }

    for (int row = 1 ; row < height - 1 ; row++) {
        for (int col = 1 ; col < width - 1 ; col++) {
            Arrays.sort(image);
            result[row][col] = image[row][col] / 2;
        }
    }
    return result;
}

Answer 1

The error you are getting is because in the last pair of loops, your call to Arrays.sort(image) is attempting to sort the rows of the image.

Instead of calling Arrays.sort(image), you'll need to build up a list of the nine pixel values you want to look at (the pixel itself and its eight neighbors). Then sort that, and write the median value to result.