Gaussian Blur Image

public static GreenfootImage blur(BufferedImage image, int[] filter, int filterWidth) {
        if (filter.length % filterWidth != 0) {
            throw new IllegalArgumentException("filter contains a incomplete row");
        }

        final int width = image.getWidth();
        final int height = image.getHeight();
        final int sum = IntStream.of(filter).sum();

        int[] input = image.getRGB(0, 0, width, height, null, 0, width);

        int[] output = new int[input.length];

        final int pixelIndexOffset = width - filterWidth;
        final int centerOffsetX = filterWidth / 2;
        final int centerOffsetY = filter.length / filterWidth / 2;

        // apply filter
        for (int h = height - filter.length / filterWidth + 1, w = width - filterWidth + 1, y = 0; y < h; y++) {
            for (int x = 0; x < w; x++) {
                int r = 0;
                int g = 0;
                int b = 0;
                for (int filterIndex = 0, pixelIndex = y * width + x;
                filterIndex < filter.length;
                pixelIndex += pixelIndexOffset) {
                    for (int fx = 0; fx < filterWidth; fx++, pixelIndex++, filterIndex++) {
                        int col = input[pixelIndex];
                        int factor = filter[filterIndex];

                        // sum up color channels seperately
                        r += ((col >>> 16) & 0xFF) * factor;
                        g += ((col >>> 8) & 0xFF) * factor;
                        b += (col & 0xFF) * factor;
                    }
                }
                r /= sum;
                g /= sum;
                b /= sum;
                // combine channels with full opacity
                output[x + centerOffsetX + (y + centerOffsetY) * width] = (r << 16) | (g << 8) | b | 0xFF000000;
            }
        }

        BufferedImage result = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
        result.setRGB(0, 0, width, height, output, 0, width);
        return createGreenfootImageFromBI(result);
    }