 |
Chapter 12 Image Processing |
 |
|
Chapter 12 Image Processing |
|
The ImageProducer interface defines the methods that ImageProducer objects must implement. Image producers serve as sources for pixel data; they may compute the data themselves or interpret data from some external source, like a GIF file. No matter how it generates the data, an image producer's job is to hand that data to an image consumer, which usually renders the data on the screen. The methods in the ImageProducer interface let ImageConsumer objects register their interest in an image. The business end of an ImageProducer--that is, the methods it uses to deliver pixel data to an image consumer--are defined by the ImageConsumer interface. Therefore, we can summarize the way an image producer works as follows:
There's a sense in which you have to take this process on faith; image consumers are usually well hidden. If you call createImage(), an image consumer will eventually show up.
Every Image has an ImageProducer associated with it; to acquire a reference to the producer, use the getSource() method of Image.
Because an ImageProducer must call methods in the ImageConsumer interface, we won't show an example of a full-fledged producer until we have discussed ImageConsumer.
The addConsumer() method registers ic as an ImageConsumer interested in the Image information. Once an ImageConsumer is registered, the ImageProducer can deliver Image pixels immediately or wait until startProduction() has been called.
Note that one image may have many consumers; therefore, addConsumer() usually stores image consumers in a collection like a Vector or Hashtable. There is one notable exception: if the producer has the image data in memory, addConsumer() can deliver the image to the consumer immediately. When addConsumer() returns, it has finished with the consumer. In this case, you don't need to manage a list of consumers, because there is only one image consumer at a time. (In this case, addConsumer() should be implemented as a synchronized method.)
The isConsumer() method checks to see if ic is a registered ImageConsumer for this ImageProducer. If ic is registered, true is returned. If ic is not registered, false is returned.
The removeConsumer() method removes ic as a registered ImageConsumer for this ImageProducer. If ic was not a registered ImageConsumer, nothing should happen. This is not an error that should throw an exception. Once ic has been removed from the registry, the ImageProducer should no longer send data to it.
The startProduction() method registers ic as an ImageConsumer interested in the Image information and tells the ImageProducer to start sending the Image data immediately. The ImageProducer sends the image data to ic and all other registered ImageConsumer objects, through addConsumer().
The requestTopDownLeftRightResend() method is called by the ImageConsumer ic requesting that the ImageProducer retransmit the Image data in top-down, left-to-right order. If the ImageProducer is unable to send the data in that order or always sends the data in that order (like with MemoryImageSource), it can ignore the call.
The FilteredImageSource class combines an ImageProducer and an ImageFilter to create a new Image. The image producer generates pixel data for an original image. The FilteredImageSource takes this data and uses an ImageFilter to produce a modified version: the image may be scaled, clipped, or rotated, or the colors shifted, etc. The FilteredImageSource is the image producer for the new image. The ImageFilter object transforms the original image's data to yield the new image; it implements the ImageConsumer interface. We cover the ImageConsumer interface in ImageConsumer and the ImageFilter class in ImageFilter. Figure 12.1 shows the relationship between an ImageProducer, FilteredImageSource, ImageFilter, and the ImageConsumer.
Constructors
The FilteredImageSource constructor creates an image producer that combines an image, original, and a filter, filter, to create a new image. The ImageProducer of the original image is the constructor's first parameter; given an Image, you can acquire its ImageProducer by using the getSource() method. The following code shows how to create a new image from an original. ImageFilter shows several extensive examples of image filters.
![[Graphic: Figure 12-1]](figs/jawt1201.gif)
Image image = getImage (new URL
("http://www.ora.com/graphics/headers/homepage.gif"));
Image newOne = createImage (new FilteredImageSource
(image.getSource(), new SomeImageFilter()));
The ImageProducer interface methods maintain an internal table for the image consumers. Since this is private, you do not have direct access to it.
The addConsumer() method adds ic as an ImageConsumer interested in the pixels for this image.
The isConsumer() method checks to see if ic is a registered ImageConsumer for this ImageProducer. If ic is registered, true is returned. If not registered, false is returned.
The removeConsumer() method removes ic as a registered ImageConsumer for this ImageProducer.
The startProduction() method registers ic as an ImageConsumer interested in the Image information and tells the ImageProducer to start sending the Image data immediately.
The requestTopDownLeftRightResend() method registers ic as an ImageConsumer interested in the Image information and requests the ImageProducer to retransmit the Image data in top-down, left-to-right order.
The MemoryImageSource class allows you to create images completely in memory; you generate pixel data, place it in an array, and hand that array and a ColorModel to the MemoryImageSource constructor. The MemoryImageSource is an image producer that can be used with a consumer to display the image on the screen. For example, you might use a MemoryImageSource to display a Mandelbrot image or some other image generated by your program. You could also use a MemoryImageSource to modify a pre-existing image; use PixelGrabber to get the image's pixel data, modify that data, and then use a MemoryImageSource as the producer for the modified image. Finally, you can use MemoryImageSource to simplify implementation of a new image type; you can develop a class that reads an image in some unsupported format from a local file or the network; interprets the image file and puts pixel data into an array; and uses a MemoryImageSource to serve as an image producer. This is simpler than implementing an image producer yourself, but it isn't quite as flexible; you lose the ability to display partial images as the data becomes available.
In Java 1.1, MemoryImageSource supports multiframe images to animate a sequence. In earlier versions, it was necessary to create a dynamic ImageFilter to animate the image. Constructors
There are six constructors for MemoryImageSource, each with slightly different parameters. They all create an image producer that delivers some array of data to an image consumer. The constructors are:
The parameters that might be present are:
Width of the image being created, in pixels.
Height of the image being created, in pixels.
The ColorModel that describes the color representation used in the pixel data. If this parameter is not present, the MemoryImageSource uses the default RGB color model (ColorModel.getRGBDefault()).
The array of pixel information to be converted into an image. This may be either a byte array or an int array, depending on the color model. If you're using a direct color model (including the default RGB color model), pix is usually an int array; if it isn't, it won't be able to represent all 16 million possible colors. If you're using an indexed color model, the array should be a byte array. However, if you use an int array with an indexed color model, the MemoryImageSource ignores the three high-order bytes because an indexed color model has at most 256 entries in the color map. In general: if your color model requires more than 8 bits of data per pixel, use an int array; if it requires 8 bits or less, use a byte array.
The first pixel used in the array (usually 0); prior pixels are ignored.
The number of pixels per line in the array (usually equal to w). The number of pixels per scan line in the array may be larger than the number of pixels in the scan line. Extra pixels in the array are ignored.
A Hashtable of the properties associated with the image. If this argument isn't present, the constructor assumes there are no properties.
The pixel at location (x, y) in the image is located at pix[y * scan + x + off]. ImageProducer interface methods
In Java 1.0, the ImageProducer interface methods maintain a single internal variable for the image consumer because the image is delivered immediately and synchronously. There is no need to worry about multiple consumers; as soon as one registers, you give it the image, and you're done. These methods keep track of this single ImageConsumer.
In Java 1.1, MemoryImageSource supports animation. One consequence of this new feature is that it isn't always possible to deliver all the image's data immediately. Therefore, the class maintains a list of image consumers that are notified when each frame is generated. Since this list is private, you do not have direct access to it.
The addConsumer() method adds ic as an ImageConsumer interested in the pixels for this image.
The isConsumer() method checks to see if ic is a registered ImageConsumer for this ImageProducer. If ic is registered, true is returned. If ic is not registered, false is returned.
The removeConsumer() method removes ic as a registered ImageConsumer for this ImageProducer.
The startProduction() method calls addConsumer().
The requestTopDownLeftRightResend() method does nothing since in-memory images are already in this format or are multiframed, with each frame in this format.
In Java 1.1, MemoryImageSource supports animation; it can now pass multiple frames to interested image consumers. This feature mimics GIF89a's multiframe functionality. (If you have GIF89a animations, you can display them using getImage() and drawImage(); you don't have to build a complicated creature using MemoryImageSource.) . An animation example follows in Example 12.3 (later in this chapter).
The setAnimated() method notifies the MemoryImageSource if it will be in animation mode (animated is true) or not (animated is false). By default, animation is disabled; you must call this method to generate an image sequence. To prevent losing data, call this method immediately after calling the MemoryImageSource constructor.
The setFullBufferUpdates() method controls how image updates are done during an animation. It is ignored if you are not creating an animation. If fullBuffers is true, this method tells the MemoryImageSource that it should always send all of an image's data to the consumers whenever it received new data (by a call to newPixels()). If fullBuffers is false, the MemoryImageSource sends only the changed portion of the image and notifies consumers (by a call to ImageConsumer.setHints()) that frames sent will be complete.
Like setAnimated(), setFullBufferUpdates() should be called immediately after calling the MemoryImageSource constructor, before the animation is started.
To do the actual animation, you update the image array pix[] that was specified in the constructor and call one of the overloaded newPixels() methods to tell the MemoryImageSource that you have changed the image data. The parameters to newPixels() determine whether you are animating the entire image or just a portion of the image. You can also supply a new array to take pixel data from, replacing pix[]. In any case, pix[] supplies the initial image data (i.e., the first frame of the animation).
If you have not called setAnimated(true), calls to any version of newPixels() are ignored.
The version of newPixels() with no parameters tells the MemoryImageSource to send the entire pixel data (frame) to all the registered image consumers again. Data is taken from the original array pix[]. After the data is sent, the MemoryImageSource notifies consumers that a frame is complete by calling imageComplete(ImageConsumer.SINGLEFRAMEDONE), thus updating the display when the image is redisplayed. Remember that in many cases, you don't need to update the entire image; updating part of the image saves CPU time, which may be crucial for your application. To update part of the image, call one of the other versions of newPixels().
This newPixels() method sends part of the image in the array pix[] to the consumers. The portion of the image sent has its upper left corner at the point (x, y), width w and height h, all in pixels. Changing part of the image rather than the whole thing saves considerably on system resources. Obviously, it is appropriate only if most of the image is still. For example, you could use this method to animate the steam rising from a cup of hot coffee, while leaving the cup itself static (an image that should be familiar to anyone reading JavaSoft's Web site). After the data is sent, consumers are notified that a frame is complete by a call to imageComplete(ImageConsumer.SINGLEFRAMEDONE), thus updating the display when the image is redisplayed.
If setFullBufferUpdates() was called, the entire image is sent, and the dimensions of the bounding box are ignored.
This newPixels() method is identical to the last, with one exception: consumers are notified that new image data is available only when frameNotify is true. This method allows you to generate new image data in pieces, updating the consumers only once when you are finished.
If setFullBufferUpdates() was called, the entire image is sent, and the dimensions of the bounding box are ignored.
These newPixels() methods change the source of the animation to the byte or int array newpix[], with a ColorModel of newmodel. offset marks the beginning of the data in newpix to use, while scansize states the number of pixels in newpix per line of Image data. Future calls to other versions of newPixels() should modify newpix[] rather than pix[].
You can create an image by generating an integer or byte array in memory and converting it to an image with MemoryImageSource. The following MemoryImage applet generates two identical images that display a series of color bars from left to right. Although the images look the same, they were generated differently: the image on the left uses the default DirectColorModel; the image on the right uses an IndexColorModel.
Because the image on the left uses a DirectColorModel, it stores the actual color value of each pixel in an array of integers (rgbPixels[]). The image on the right can use a byte array (indPixels[]) because the IndexColorModel puts the color information in its color map instead of the pixel array; elements of the pixel array need to be large enough only to address the entries in this map. Images that are based on IndexColorModel are generally more efficient in their use of space (integer vs. byte arrays, although IndexColorModel requires small support arrays) and in performance (if you filter the image).
The output from this example is shown in Figure 12.2. The source is shown in Example 12.2.
![[Graphic: Figure 12-2]](figs/jawt1202.gif)
import java.applet.*;
import java.awt.*;
import java.awt.image.*;
public class MemoryImage extends Applet {
Image i, j;
int width = 200;
int height = 200;
public void init () {
int rgbPixels[] = new int [width*height];
byte indPixels[] = new byte [width*height];
int index = 0;
Color colorArray[] = {Color.red, Color.orange, Color.yellow,
Color.green, Color.blue, Color.magenta};
int rangeSize = width / colorArray.length;
int colorRGB;
byte colorIndex;
byte reds[] = new byte[colorArray.length];
byte greens[] = new byte[colorArray.length];
byte blues[] = new byte[colorArray.length];
for (int i=0;i<colorArray.length;i++) {
reds[i] = (byte)colorArray[i].getRed();
greens[i] = (byte)colorArray[i].getGreen();
blues[i] = (byte)colorArray[i].getBlue();
}
for (int y=0;y<height;y++) {
for (int x=0;x<width;x++) {
if (x < rangeSize) {
colorRGB = Color.red.getRGB();
colorIndex = 0;
} else if (x < (rangeSize*2)) {
colorRGB = Color.orange.getRGB();
colorIndex = 1;
} else if (x < (rangeSize*3)) {
colorRGB = Color.yellow.getRGB();
colorIndex = 2;
} else if (x < (rangeSize*4)) {
colorRGB = Color.green.getRGB();
colorIndex = 3;
} else if (x < (rangeSize*5)) {
colorRGB = Color.blue.getRGB();
colorIndex = 4;
} else {
colorRGB = Color.magenta.getRGB();
colorIndex = 5;
}
rgbPixels[index] = colorRGB;
indPixels[index] = colorIndex;
index++;
}
}
i = createImage (new MemoryImageSource (width, height, rgbPixels,
0, width));
j = createImage (new MemoryImageSource (width, height,
new IndexColorModel (8, colorArray.length, reds, greens, blues),
indPixels, 0, width));
}
public void paint (Graphics g) {
g.drawImage (i, 0, 0, this);
g.drawImage (j, width+5, 0, this);
}
}
Almost all of the work is done in init() (which, in a real applet, isn't a terribly good idea; ideally init() should be lightweight). Previously, we explained the color model's use for the images on the left and the right. Toward the end of init(), we create the images i and j by calling createImage() with a MemoryImageSource as the image producer. For image i, we used the simplest MemoryImageSource constructor, which uses the default RGB color model. For j, we called the IndexColorModel constructor within the MemoryImageSource constructor, to create a color map that has only six entries: one for each of the colors we use. Using MemoryImageSource for animation
As we've seen, Java 1.1 gives you the ability to create an animation using a MemoryImageSource by updating the image data in memory; whenever you have finished an update, you can send the resulting frame to the consumers. This technique gives you a way to do animations that consume very little memory, since you keep overwriting the original image. The applet in Example 12.3 demonstrates MemoryImageSource's animation capability by creating a Mandelbrot image in memory, updating the image as new points are added. Figure 12.3 shows the results, using four consumers to display the image four times.
// Java 1.1 only
import java.awt.*;
import java.awt.image.*;
import java.applet.*;
public class Mandelbrot extends Applet implements Runnable {
Thread animator;
Image im1, im2, im3, im4;
public void start() {
animator = new Thread(this);
animator.start();
}
public synchronized void stop() {
animator = null;
}
public void paint(Graphics g) {
if (im1 != null)
g.drawImage(im1, 0, 0, null);
if (im2 != null)
g.drawImage(im2, 0, getSize().height / 2, null);
if (im3 != null)
g.drawImage(im3, getSize().width / 2, 0, null);
if (im4 != null)
g.drawImage(im4, getSize().width / 2, getSize().height / 2, null);
}
public void update (Graphics g) {
paint (g);
}
public synchronized void run() {
Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
int width = getSize().width / 2;
int height = getSize().height / 2;
byte[] pixels = new byte[width * height];
int index = 0;
int iteration=0;
double a, b, p, q, psq, qsq, pnew, qnew;
byte[] colorMap = {(byte)255, (byte)255, (byte)255, // white
(byte)0, (byte)0, (byte)0}; // black
MemoryImageSource mis = new MemoryImageSource(
width, height,
new IndexColorModel (8, 2, colorMap, 0, false, -1),
pixels, 0, width);
mis.setAnimated(true);
im1 = createImage(mis);
im2 = createImage(mis);
im3 = createImage(mis);
im4 = createImage(mis);
// Generate Mandelbrot
final int ITERATIONS = 16;
for (int y=0; y<height; y++) {
b = ((double)(y-64))/32;
for (int x=0; x<width; x++) {
a = ((double)(x-64))/32;
p=q=0;
iteration = 0;
while (iteration < ITERATIONS) {
psq = p*p;
qsq = q*q;
if ((psq + qsq) >= 4.0)
break;
pnew = psq - qsq + a;
qnew = 2*p*q+b;
p = pnew;
q = qnew;
iteration++;
}
if (iteration == ITERATIONS) {
pixels[index] = 1;
mis.newPixels(x, y, 1, 1);
repaint();
}
index++;
}
}
}
}
Most of the applet in Example 12.3 should be self-explanatory. The init() method starts the thread in which we do our computation. paint() just displays the four images we create. All the work, including the computation, is done in the thread's run() method. run() starts by setting up a color map, creating a MemoryImageSource with animation enabled and creating four images using that source as the producer. It then does the computation, which I won't explain; for our purposes, the interesting part is what happens when we've computed a pixel. We set the appropriate byte in our data array, pixels[], and then call newPixels(), giving the location of the new pixel and its size (1 by 1) as arguments. Thus, we redraw the images for every new pixel. In a real application, you would probably compute a somewhat larger chunk of new data before updating the screen, but the same principles apply.
|
 |
|
| ColorModel |  |
ImageConsumer |
| This HTML Help has been published using the chm2web software. |
![[Graphic: Figure 12-3]](figs/jawt1203.gif)