So far I've made the simplifying assumption that each pixel can be filtered independently of its neighbors. This isn't always true. For example a Gaussian blur or a sharpen or unspeckle filter, requires a substantial amount of information about other parts of the image.
When a filter must take into account the values of pixels other
than the ones being filtered, it's no longer possible to use the
simple RGBFilter class. Instead you have to work
directly with java.awt.image.ImageFilter. You must
override the two setPixels() methods to implement your
filter.
public void setPixels(int x, int y, int width, int height,
ColorModel model, byte[] pixels, int offset, int scan)
public void setPixels(int x, int y, int width, int height,
ColorModel model, int[] pixels, int offset, int scan)