Manipulating and Displaying Images

Filtering a BufferedImage

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 actual 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 , RescaleOp , or ThresholdOp
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 ImageOps program illustrates the use of four different image filter operations: low-pass, sharpen, lookup, and rescale.

 

You can see the complete code for this program in ImageOps.java. To run the applet, you will also need this HTML file, ImageOps.html, which includes the applet and these two images files: bld.jpg and boat.gif.

The sharpen filter is performed 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.

Here is the code that constructs and applies the sharpen filter to the BufferedImage :

float[][] data = {{0.1f, 0.1f, 0.1f,
                   0.1f, 0.2f, 0.1f,
                   0.1f, 0.1f, 0.1f},
                   SHARPEN3x3_3};
...
int iw = bi[i].getWidth(this);
int ih = bi[i].getHeight(this);
int x = 0, y = 0;
...
AffineTransform at = new AffineTransform();
at.scale((w-14)/2.0/iw, (h-34)/2.0/ih);
BufferedImage bimg = new
              BufferedImage(iw,ih,BufferedImage.TYPE_INT_RGB);
...
x = i==0?5:w/2+3; y = 15;
Kernel kernel = new Kernel(3,3,data[i]);
ConvolveOp cop = new ConvolveOp(kernel,
                                ConvolveOp.EDGE_NO_OP,
                                null);
cop.filter(bi[i],bimg);

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. For more information about how kernels work with ConvolveOp, see the Image Processing and Enhancement section in the Java 2D Programmer's Guide.

Manipulating and Displaying Images