The Java 2D API defines several filtering operations for BufferedImage objects. Each image-processing operation is embodied in a class that implements the BufferedImageOp interface. The image manipulation is performed in the image operation's filter method. The BufferedImageOp classes in the Java 2D API support 
  • Affine transformation 
  • Amplitude scaling 
  • Lookup-table modification 
  • Linear combination of bands 
  • Color conversion 
  • Convolution 

To filter a BufferedImage using one of the image operation classes, you 

  1. Construct an instance of one of the BufferedImageOp classes: AffineTransformOp, BandCombineOp, ColorConvertOp, ConvolveOp, LookupOp, or RescaleOp. 
  2. Call the image operation's filter method, passing in the BufferedImage that you want to filter and the BufferedImage where you want to store the results. 
Example: ImageOps

The following applet illustrates the use of four image-filter operations: low-pass, sharpen, lookup, and rescale.
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You can see the complete code for this applet in ImageOps.java. The applet uses these two image files: bld.jpg and boat.gif. 

The sharpen filter is performed by using a ConvolveOp. Convolution is the process of weighting or averaging the value of each pixel in an image with the values of neighboring pixels. Most spatial-filtering algorithms are based on convolution operations. 

To construct and apply the sharpen filter to the BufferedImage, this sample uses code similar to the following snippet.  
public static final float[] SHARPEN3x3 = {
                            0.f, -1.f, 0.f,
                            -1.f, 5.0f, -1.f,
                            0.f, -1.f, 0.f};
BufferedImage dstbimg = new 
              BufferedImage(iw,ih,BufferedImage.TYPE_INT_RGB);
Kernel kernel = new Kernel(3,3,SHARPEN3x3);
ConvolveOp cop = new ConvolveOp(kernel,
                                ConvolveOp.EDGE_NO_OP,
                                null);
cop.filter(srcbimg,dstbimg);

The Kernel object mathematically defines how each output pixel is affected by pixels in its immediate area.The definition of the Kernel determines the results of the filter. 

                                                                                                           

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