The Blue Filter Example

Here's a simple filter that extracts only the blue parts of an image.

import java.awt.image.*;

public class BlueFilter extends RGBImageFilter {

  public BlueFilter() {
      canFilterIndexColorModel = true;

  public int filterRGB(int x, int y, int rgb) {
    return rgb & 0xFF0000FF; 


canFilterIndexColorModel is set to true because the filtering is independent of position. The bitwise and operator, &, is used to select only the first eight bits and last eight bits of the rgb value. The transparency level is stored in the first eight bits. Thu blue component of the pixel is stored in the last eight bits. FF is 11111111 so all blue and transparency bits are retained. The remaining bits vanish.

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Copyright 1997, 2003 Elliotte Rusty Harold
Last Modified November 12, 2003