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Using Rasters for Image Processing, Part 2
by Anghel Leonard
In Part 1 of this series, you learned about the rasters concept as well as what raster components you need in order to use them in Java applications.
Part 2 will explain how to define a Raster/WritableRaster as a single object in a few different ways. First, you will learn how to create a raster from an array of pixels, from an Image, and from an BufferedImage object. You will also learn how to convert a raster to an Image/BufferedImage object and how to apply the Java2D filters to rasters. Complete applications for extracting rasters and for filter rasters with the ConvolveOp, AffineTransformOp and BandCombineOp classes are provided.
Creating a Raster Using the Raster and WritableRaster Classes
As you learned in Part 1, to create a raster, you need a DataBuffer object and a SampleModel object. Since you already know how to obtain these objects, it's time to learn how to use them.
To create a raster, you use two classes from the java.awt.image package: Raster and WritableRaster. Because the Raster class is abstract, its constructors are declared protected. This means you can't create instances of the raster class. So, to create Raster objects, you use a set of static methods from the Raster class. Each of these static methods returns a WritableRaster object—except the createRaster method, which returns a Raster object. The createRaster method looks like this:
public static Raster createRaster(SampleModel SM, DataBuffer DB, Point location):
This creates a Raster object using the specified SampleModel and DataBuffer objects. The location parameter represents the origins of the raster. If this parameter is null then the origins are (0,0).
Point P=new Point(0,0);
Raster R=Raster.createRaster(SM,DB,P);
// In this case, P can be replace with null
After you've made a Raster object with the createRaster method, you can use it to gain access to the raster's pixels using the getPixel, getPixels, getSample, and getSamples methods:
- getPixel: The following method returns an array of integers representing the samples of the specified pixel. The pixel coordinates are
(x,y):
public int[] getPixel(int x, int y, int[] intArray):
Similar to the above method, these methods respectively return an array of float and an array of double:
public float[] getPixel(int x,int y,float[] floatArray)
public double[] getPixel(int x,int y,double[] doubleArray)
- getPixels: The following method returns an array of integers representing the raster's samples. This method stores one sample per array element, so you must know the number of color bands in order to identify the samples of one pixel. The raster is delimitated by the
x, y, w, and h parameters. The x and y parameters represent the origins of the raster, w is the width, and h is the height:
public int[] getPixels(int x,int y,int w,int h,int[] intArray):
Similar to the above method, these methods respectively return an array of float and an array of double:
public float[] getPixels(int x,int y,int w,int h,loat[] floatArray)
public double[] getPixels(int x,int y,int w,int h,double[] doubleArray)
- getSample: The following method returns an
int representing a sample of the pixel from the (x,y) coordinates. The sample belongs to the color band specified by the band parameter.
public int getSample(int x,int y,int band):
Similar to the above method, these methods return a float and a double, respectively:
public float getSampleFloat(int x,int y,int band)
public double getSampleDouble(int x,int y,int band)
- getSamples: The following method returns an array of integers representing all samples from the specified raster and the specified band, one sample per array element. The raster is delimitated by the
x,y,w,h parameters. The x,y prameters represents the origins of the raster, w is the width and h is the height of it.The band parameter represents the color band that contains all samples that will be extracted.
public int[] getSamples(int x,int y,int w,int h,int band,int[] intArray)
Similar to the above method, these methods returns a float and a double, respectively:
public float[] getSamples(int x,int y,int w,int h,int band,float[] floatArray)
public double[] getSamples(int x,int y,int w,int h,int band,double[] doubleArray)
As you can see, the Raster class doesn't contain methods for modifying its pixel's properties. To modify them, you must obtain an WritableRaster object. The WritableRaster class provides some setter methods that can be used to modify the pixels of a raster. This class also inherits from the Raster class the getter methods listed above. The WritableRaster object can be obtained using the following static methods from the Raster class:
-
public static WritableRaster createWritableRaster(SampleModel SM, DataBuffer DB, Point location): This method creates a WritableRaster object using the specified SampleModel and DataBuffer objects. The location parameter represents the origin coordinates of the raster. If this parameter is null, then the origin coordinates will be (0,0).
Point P=new Point(0,0);
WritableRaster R=Raster.createWritableRaster(SM,DB,P);
// In this case, P can be replace with null
public static WritableRaster createWritableRaster(SampleModel SM, Point location): This method creates an WritableRaster object using the specified SampleModel object. The location parameter represents the origin coordinates of the raster. If this parameter is null, then the origin coordinates will be (0,0).
The two above methods can be used for any SampleModel object.
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