12.10 Image Processing

Both Java 1.0 and 1.1 included a complex API for filtering images on the fly as they were downloaded over a network connection. Although this API is still available in later versions of Java, it is not commonly used, nor is it demonstrated in this book. Java 2D defines a simpler API based on the BufferedImageOp interface of the java.awt.image package. This package also includes several versatile implementations of the interface that can generate the image-processing effects illustrated in Figure 12-11. Example 12-13 shows the code used to produce Figure 12-11. The code is straightforward: to process a BufferedImage, simply pass it to the filter( ) method of a BufferedImageOp.

Figure 12-11. Image processing with BufferedImageOp

Example 12-13. ImageOps.java

package je3.graphics; import java.awt.*; import java.awt.geom.*; import java.awt.image.*; import java.awt.color.*; /** A demonstration of various image processing filters */ public class ImageOps implements GraphicsExample {     static final int WIDTH = 600, HEIGHT = 675;         // Size of our example     public String getName( ) {return "Image Processing";}// From GraphicsExample     public int getWidth( ) { return WIDTH; }             // From GraphicsExample     public int getHeight( ) { return HEIGHT; }           // From GraphicsExample     Image image;     /** This constructor loads the image we will manipulate */     public ImageOps( ) {         java.net.URL imageurl = this.getClass( ).getResource("cover.gif");         image = new javax.swing.ImageIcon(imageurl).getImage( );     }          // These arrays of bytes are used by the LookupImageOp image filters below     static byte[  ] brightenTable = new byte[256];     static byte[  ] thresholdTable = new byte[256];     static {  // Initialize the arrays         for(int i = 0; i < 256; i++) {             brightenTable[i] = (byte)(Math.sqrt(i/255.0)*255);             thresholdTable[i] = (byte)((i < 225)?0:i);         }     }     // This AffineTransform is used by one of the image filters below     static AffineTransform mirrorTransform;     static {  // Create and initialize the AffineTransform         mirrorTransform = AffineTransform.getTranslateInstance(127, 0);         mirrorTransform.scale(-1.0, 1.0);  // flip horizontally     }     // These are the labels we'll display for each of the filtered images     static String[  ] filterNames = new String[  ] {         "Original", "Gray Scale",  "Negative",  "Brighten (linear)",         "Brighten (sqrt)", "Threshold", "Blur", "Sharpen",         "Edge Detect", "Mirror", "Rotate (center)", "Rotate (lower left)"     };     // The following BufferedImageOp image filter objects perform     // different types of image processing operations.     static BufferedImageOp[  ] filters = new BufferedImageOp[  ] {         // 1) No filter here.  We'll display the original image         null,         // 2) Convert to Grayscale color space         new ColorConvertOp(ColorSpace.getInstance(ColorSpace.CS_GRAY), null),         // 3) Image negative.  Multiply each color value by -1.0 and add 255         new RescaleOp(-1.0f, 255f, null),         // 4) Brighten using a linear formula that increases all color values         new RescaleOp(1.25f, 0, null),         // 5) Brighten using the lookup table defined above         new LookupOp(new ByteLookupTable(0, brightenTable), null),         // 6) Threshold using the lookup table defined above         new LookupOp(new ByteLookupTable(0, thresholdTable), null),         // 7) Blur by "convolving" the image with a matrix         new ConvolveOp(new Kernel(3, 3, new float[  ] {               .1111f,.1111f,.1111f,             .1111f,.1111f,.1111f,             .1111f,.1111f,.1111f,})),         // 8) Sharpen by using a different matrix         new ConvolveOp(new Kernel(3, 3, new float[  ] {               0.0f, -0.75f, 0.0f,             -0.75f, 4.0f, -0.75f,             0.0f, -0.75f, 0.0f})),         // 9) Edge detect using yet another matrix         new ConvolveOp(new Kernel(3, 3, new float[  ] {               0.0f,  -0.75f, 0.0f,             -0.75f, 3.0f, -0.75f,             0.0f,  -0.75f, 0.0f})),         // 10) Compute a mirror image using the transform defined above         new AffineTransformOp(mirrorTransform,AffineTransformOp.TYPE_BILINEAR),         // 11) Rotate the image 180 degrees about its center point         new AffineTransformOp(AffineTransform.getRotateInstance(Math.PI,64,95),                               AffineTransformOp.TYPE_NEAREST_NEIGHBOR),         // 12) Rotate the image 15 degrees about the bottom left         new AffineTransformOp(AffineTransform.getRotateInstance(Math.PI/12,                                                                 0, 190),                               AffineTransformOp.TYPE_NEAREST_NEIGHBOR),     };     /** Draw the example */     public void draw(Graphics2D g, Component c) {         // Create a BufferedImage big enough to hold the Image loaded         // in the constructor.  Then copy that image into the new         // BufferedImage object so that we can process it.         BufferedImage bimage = new BufferedImage(image.getWidth(c),                                                  image.getHeight(c),                                                  BufferedImage.TYPE_INT_RGB);         Graphics2D ig = bimage.createGraphics( );         ig.drawImage(image, 0, 0, c);  // copy the image         // Set some default graphics attributes         g.setFont(new Font("SansSerif", Font.BOLD, 12));  // 12pt bold text         g.setColor(Color.green);                          // Draw in green         g.translate(10, 10);                              // Set some margins         // Loop through the filters         for(int i = 0; i < filters.length; i++) {             // If the filter is null, draw the original image; otherwise,             // draw the image as processed by the filter             if (filters[i] == null) g.drawImage(bimage, 0, 0, c);             else g.drawImage(filters[i].filter(bimage, null), 0, 0, c);             g.drawString(filterNames[i], 0, 205);      // Label the image             g.translate(137, 0);                       // Move over             if (i % 4 == 3) g.translate(-137*4, 215);  // Move down after 4         }     } }