Blurring functions for Android bitmaps

BlurUtilities.java

import android.graphics.Bitmap;
import android.graphics.Color;

/**
 * Blurring functions for Android bitmaps
 *
 * Sliding window algorithm inspired by http://elynxsdk.free.fr/ext-docs/Blur/Fast_box_blur.pdf
 * 
 * Released into the public domain
 * 
 * Created by chedabob on 30/03/2014.
 * https://gist.github.com/chedabob/9870984
 * 
 */
public class BlurUtilities {

    /**
     * Approximates a gaussian blur to within 3% by performing 3 box blurs on the source
     * @param input The input bitmap
     * @param radius The radius of the blur function in pixels
     * @return Blurred bitmap
     */
    public static Bitmap approxGaussianBlur (Bitmap input, int radius) {

        Bitmap temp = null;

        for (int i = 0; i < 3; i++) {
            if (temp == null) {
                temp = boxBlur(input,radius);
            }
            else {
                temp = boxBlur(temp,radius);
            }
        }
        return temp;
    }

    /**
     * Box blur using a sliding window
     * @param input The input bitmap
     * @param radius The radius of the blur function in pixels
     * @return Blurred bitmap
     */
    public static Bitmap boxBlur(Bitmap input, int radius) {
        return horizontalPass(verticalPass(input, radius), radius);
    }

    /**
     * Horizontal motion blur component of the box blur
     * @param input The input bitmap
     * @param radius The radius of the blur function in pixels
     * @return Horizontally blurred bitmap
     */
    private static Bitmap horizontalPass(Bitmap input, int radius) {

        int width = input.getWidth();
        int height = input.getHeight();

        int [] pixels = new int [width * height];
        input.getPixels(pixels,0,width,0,0,width,height);

        int [] outPixels = new int [width * height];
        input.getPixels(outPixels,0,width,0,0,width,height);

        for (int y = 0; y < height; y++) {
            int averageR = 0, averageG = 0, averageB = 0;

            for (int x = 0; x < width; x++) {
                if (x == 0) {
                    for (int i = -radius; i <= radius; i++) {
                        int pixel = pixels[(y * width) + wrapValue(x + i, width)];
                        int r = Color.red(pixel);
                        int g = Color.green(pixel);
                        int b = Color.blue(pixel);

                        averageR += r;
                        averageG += g;
                        averageB += b;
                    }
                } else {
                    int currentRightMost = pixels[(y * width) + wrapValue(x + radius, width)];
                    int previousLeftMost = pixels[(y * width) + wrapValue((x - 1) - radius, width)];

                    int currentR = Color.red(currentRightMost);
                    int currentG = Color.green(currentRightMost);
                    int currentB = Color.blue(currentRightMost);

                    int prevR = Color.red(previousLeftMost);
                    int prevG = Color.green(previousLeftMost);
                    int prevB = Color.blue(previousLeftMost);

                    averageR -= prevR;
                    averageG -= prevG;
                    averageB -= prevB;

                    averageR += currentR;
                    averageG += currentG;
                    averageB += currentB;
                }

                int newColor = Color.argb(255, clampColour(averageR / (2 * radius + 1)), clampColour(averageG / (2 * radius + 1)), clampColour(averageB / (2 * radius + 1)));
                outPixels[(y * width) + x] = newColor;
              }
        }

        return Bitmap.createBitmap(outPixels,width,height,input.getConfig());
    }

    /**
     * Vertically motion blur component of the box blur
     * @param input The input bitmap
     * @param radius The radius of the blur function in pixels
     * @return Vertically blurred bitmap
     */
    private static Bitmap verticalPass(Bitmap input, int radius) {
        int width = input.getWidth();
        int height = input.getHeight();
        int [] pixels = new int [width * height];
        input.getPixels(pixels,0,width,0,0,width,height);

        int [] outPixels = new int [width * height];
        input.getPixels(outPixels,0,width,0,0,width,height);

        for (int x = 0; x < width; x++) {

            int averageR = 0, averageG = 0, averageB = 0;

            for (int y = 0; y < height; y++) {

                if (y == 0) {
                    for (int i = -radius; i <= radius; i++) {
                        int pixel = pixels[(wrapValue(y + i, height )* width) + x];
                        float r = Color.red(pixel);
                        float g = Color.green(pixel);
                        float b = Color.blue(pixel);

                        averageR += r;
                        averageG += g;
                        averageB += b;
                    }
                } else {
                    int currentRightMost = pixels[ (wrapValue(y + radius, height) * width) + x ];
                    int previousLeftMost = pixels[ (wrapValue((y- 1) - radius, height) * width) + x ];

                    int currentR = Color.red(currentRightMost);
                    int currentG = Color.green(currentRightMost);
                    int currentB = Color.blue(currentRightMost);

                    int prevR = Color.red(previousLeftMost);
                    int prevG = Color.green(previousLeftMost);
                    int prevB = Color.blue(previousLeftMost);

                    averageR -= prevR;
                    averageG -= prevG;
                    averageB -= prevB;

                    averageR += currentR;
                    averageG += currentG;
                    averageB += currentB;
                }

                int newColor = Color.argb(255, clampColour(averageR / (2 * radius + 1)), clampColour(averageG / (2 * radius + 1)), clampColour(averageB / (2 * radius + 1)));
                outPixels[(y * width) + x] = newColor;
            }
        }

        return Bitmap.createBitmap(outPixels,width,height,input.getConfig());
    }

    /**
     * Clamps a colour between 0 and 255
     * @param input Value to clamp
     * @return Clamped value
     */
    private static int clampColour(int input) {
        if (input < 0) { return 0; }
        if (input > 255) { return 255;}
        return input;
    }

    /**
     * Clamps a pixel value between 0 and max
     * @param value The value to clamp
     * @param max The max the value can be
     * @return The clamped value
     */
    private static int wrapValue(int value, int max) {
        if (value < 0) {return 0;}
        if (value >= max) { return max - 1; }

        return value;
    }
}