GaussianGlowFilter.java

/*
** Copyright 2005 Huxtable.com. All rights reserved.
*/

package com.jhlabs.image;

import java.awt.Color;
import java.awt.image.BufferedImage;
import java.awt.image.Kernel;

/**
 * A filter which applies Gaussian blur to an image. This is a subclass of ConvolveFilter
 * which simply creates a kernel with a Gaussian distribution for blurring.
 * 
 * This is a copy and slightly modified version of the GaussianFilter written by Jerry Huxtable
 */
public class GaussianGlowFilter extends ConvolveFilter {

    static final long serialVersionUID = 5377089073023183684L;

    protected float radius;
    protected Kernel kernel;

    private Color glow = Color.white;
    
    /**
     * Construct a Gaussian filter
     */
    public GaussianGlowFilter() {
        this(2);
    }

    /**
     * Construct a Gaussian filter
     * @param radius blur radius in pixels
     */
    public GaussianGlowFilter(float radius) {
        setRadius(radius);
    }

    public GaussianGlowFilter(float radius, Color glow) {
        this(radius);
        this.glow = glow;
    }

    /**
     * Set the radius of the kernel, and hence the amount of blur. The bigger the radius, the longer this filter will take.
     * @param radius the radius of the blur in pixels.
     */
    public void setRadius(float radius) {
        this.radius = radius;
        kernel = makeKernel(radius);
    }
    
    /**
     * Get the radius of the kernel.
     * @return the radius
     */
    public float getRadius() {
        return radius;
    }

    public BufferedImage filter( BufferedImage src, BufferedImage dst ) {
        int width = src.getWidth();
        int height = src.getHeight();

        if ( dst == null )
            dst = createCompatibleDestImage( src, null );

        int[] inPixels = new int[width*height];
        int[] outPixels = new int[width*height];
        src.getRGB( 0, 0, width, height, inPixels, 0, width );

        convolveAndTranspose(kernel, inPixels, outPixels, width, height, alpha, CLAMP_EDGES, glow);
        convolveAndTranspose(kernel, outPixels, inPixels, height, width, alpha, CLAMP_EDGES, glow);

        dst.setRGB( 0, 0, width, height, inPixels, 0, width );
        return dst;
    }

    public static void convolveAndTranspose(Kernel kernel, int[] inPixels, int[] outPixels,
            int width, int height, boolean alpha, int edgeAction, Color glow) {
        float[] matrix = kernel.getKernelData( null );
        int cols = kernel.getWidth();
        int cols2 = cols/2;

        for (int y = 0; y < height; y++) {
            int index = y;
            int ioffset = y*width;
            for (int x = 0; x < width; x++) {
                float r = 0, g = 0, b = 0, a = 0;
                int moffset = cols2;
                for (int col = -cols2; col <= cols2; col++) {
                    float f = matrix[moffset+col];

                    if (f != 0) {
                        int ix = x+col;
                        if ( ix < 0 ) {
                            if ( edgeAction == CLAMP_EDGES )
                                ix = 0;
                            else if ( edgeAction == WRAP_EDGES )
                                ix = (x+width) % width;
                        } else if ( ix >= width) {
                            if ( edgeAction == CLAMP_EDGES )
                                ix = width-1;
                            else if ( edgeAction == WRAP_EDGES )
                                ix = (x+width) % width;
                        }
                        int rgb = inPixels[ioffset+ix];
                        // only apply the matrix to the alpha channel.
                        a += f * ((rgb >> 24) & 0xff);
                        // set the glow color to get rid of the dark described on 
                        // http://www.jhlabs.com/ip/blurring.html under Alpha Channels
                        r=glow.getRed();
                        g=glow.getGreen();
                        b=glow.getBlue();
                    }
                }
                // TODO not sure about this. Multiply by 4 so that we have a bigger glow.
                // There is probably a function to get a better glow effect.
                int ia=Math.min((int)(a*4), 255);
                int ir = PixelUtils.clamp((int)(r+0.5));
                int ig = PixelUtils.clamp((int)(g+0.5));
                int ib = PixelUtils.clamp((int)(b+0.5));
                outPixels[index] = (ia << 24) | (ir << 16) | (ig << 8) | ib;
                index += height;
            }
        }
    }

    /**
     * Make a Gaussian blur kernel.
     */
    public static Kernel makeKernel(float radius) {
        int r = (int)Math.ceil(radius);
        int rows = r*2+1;
        float[] matrix = new float[rows];
        float sigma = radius/3;
        float sigma22 = 2*sigma*sigma;
        float sigmaPi2 = 2*ImageMath.PI*sigma;
        float sqrtSigmaPi2 = (float)Math.sqrt(sigmaPi2);
        float radius2 = radius*radius;
        float total = 0;
        int index = 0;
        for (int row = -r; row <= r; row++) {
            float distance = row*row;
            if (distance > radius2)
                matrix[index] = 0;
            else
                matrix[index] = (float)Math.exp(-(distance)/sigma22) / sqrtSigmaPi2;
            total += matrix[index];
            index++;
        }
        for (int i = 0; i < rows; i++)
            matrix[i] /= total;

        return new Kernel(rows, 1, matrix);
    }

    public String toString() {
        return "Blur/Gaussian Blur...";
    }
}