Java(TM) Boutique - Using Rasters for Image Processing, Part 2

Tutorials : Using Rasters for Image Processing, Part 2 :

Create a WritableRaster Object from a Specific SampleModel Object

If you want to create a WritableRaster object from a specific SampleModel object, for instance, PixelInterleavedSampleModel, SinglePixelPackedSampleModel, MultiPixelPackedSampleModel, or BandedSampleModel, this a set of methods is dedicated to performing just that task:

public static WritableRaster createInterleavedRaster(DataBuffer DB, int w, int h, int scanlineStride , int pixelStride, int[] bandOffsets, Point location): This method creates a WritableRaster object based on the PixelInterleavedSampleModel and using the specified DataBuffer object. The location parameter represents the origin coordinates of the raster. If the parameter is null, then the origin coordinates will be (0,0). You can obtain the number of bands from bandOffsets.length.
public static WritableRaster createPackedRaster(DataBuffer DB, int w, int h, int scanlineStride, int[] bandMasks, Point location): This method creates a WritableRaster object based on the SinglePixelPackedSampleModel and using the specified DataBuffer 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 bandMasks array contain an entry for every color band so the bandMasks.length represents the number of image color bands.
public static WritableRaster createPackedRaster(DataBuffer DB, int w, int h, int bitsPerPixel, Point location): This method creates a WritableRaster object based on the MultiPixelPackedSampleModel and using the specified DataBuffer 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 bitsPerPixel parameter specifies the number of bits for each pixel.
public static WritableRaster createBandedRaster(int dataType, int w, int h, int bands, Point location): This creates a WritableRaster object based on the BandedSampleModel. band represents the number of bands, dataType represents the data type for storing samples (can be only TYPE_BYTE, TYPE_USHORT, and TYPE_INT) and location represents the origin coordinates of the raster. If location is null than the (0,0) coordinates will be used.

Now, if you know how to create a raster using WritableRaster class, you can use the setter methods of this class to modify it:

setPixel: This method uses an int array of samples for setting a pixel in the DataBuffer. The pixels coordinates are (x,y):
```
public void setPixel(int x,int y,int[] intArray)(x,y)
```
Similar tow the above method, these methods use an array of float and an array of double, respectively:
```
public void setPixel(int x, int y, float[] floatArray)
public void setPixel(int x, int y, double[] doubleArray)
```
setPixels: This method uses an int array of samples for setting all pixels into the (x,y,w,h) rectangle. Every int array element represents one sample:
```
public void setPixels(int x, int y, int w, int h, int[] intArray)
```
Similar to the above method, these methods use an array of float and an array of double, respectively:
```
public void setPixels(int x,int y,int w,int h,float[] floatArray)
public void setPixels(int x,int y,int w,int h,double[] doubleArray)
```
setSample: This method sets the int sample for the pixel from the (x,y) coordinates in the DataBuffer. The sample's band is specified by the b parameter:
```
public void setSample(int x,int y,int b,int s)
```
Similar to the above method, the next two methods use a float sample and a double sample respectively:
```
public void setSample(int x,int y,int b,float s)
public void setSample(int x,int y,int b,double s)
```
setSamples:

int

(x,y,w,h)

int

intArray

b

public void setSamples(int x,int y,int w,int h,int b,int[] intArray)

float

double

public void setSamples(int x,int y,int w,int h,int b,float[] floatArray)
public void setSamples(int x,int y,int w,int h,int b,double[] doubleArray)

Exctracting a Raster from Image and BufferedImage Objects

As you have seen, the Raster and WritableRaster classes define sets of methods for creating rasters. However, these methods aren't generally used for manually creating rasters—they are instead used for extracting rasters from images. In Java, these images can be encapsulated by the Image and BufferedImage objects.

The first step for extracting a raster from an Image object is to obtain the pixels from it, using the PixelGrabber class (click here to find a good presentation of this class). The second step is to create DataBuffer and SampleModel objects. Of course, to create these objects, you will use the pixels that have been extracted with PixelGrabber class. The last step is to call a specific method from the Raster or WritableRaster class.

Listing 1 shows an example of extracting a raster from an Image object. In addition to drawing the raster portion on the screen, the application converts the Raster object to a BufferedImage object. This type of conversion was addopted for all the applications in this section. If you'd rather, you can also draw the raster on the screen like you did in Part I.

Figure 1. RasterFromImage.java: Left side: original picture, right side: raster.

The second example in this section extracts a raster from a BufferedImage. This is simpler than extracting a raster from an Image, because the BufferedImage class defines a set of methods that can be used for extracting rasters. The most commonly used methods are:

public Raster getData(): This extracts a raster from the whole image.
public Raster getData(Rectangle rect): This extracts a raster from the image equal to the rectangle area, rect.
public WritableRaster getRaster(): This returns a WritableRaster from the image.

Listing 2 uses public Raster getData(Rectangle rect) to extract a raster from a BufferedImage object. The BufferedImage object is obtained from an Image object. After it obtains the raster, the application converts it back to a BufferedImage and draws it on the screen.

Note: The output of this application is the same as the output of the RasterFromImage.java application.

The application in Listing 2 demonsrates a simple way to extract a raster from a BufferedImage. However, there are many ways to extract a raster from a BufferedImage. Here are some examples:

Example 1:

int W,H;
    BufferedImage BI=null;
    ...
    BI=new BufferedImage(W,H,BufferedImage.TYPE_INT_RGB);
    ...
    WritableRaster WR1=Raster.createWritableRaster
	(BI.getSampleModel(),null);
    WritableRaster WR2=WR1.createCompatibleWritableRaster
	(BI.getWidth()/2,BI.getHeight()/2);      
    BI.copyData(WR1); //or
    //BI.copyData(WR2);

Example 2:

    int W,H;
    BufferedImage BI=null;
    ...
    BI=new BufferedImage(W,H,BufferedImage.TYPE_INT_RGB);
    ...
    Rectangle rect=new Rectangle(0,0,BI.getWidth()/3,BI.getHeight()/3);        
    Raster R=BI.getData(rect);  //or for the whole image                      
    //Raster R=BI.getData();

Example 3:

	int W,H;
    BufferedImage BI=null;
    ...
    BI=new BufferedImage(W,H,BufferedImage.TYPE_INT_RGB);
    ...
    WritableRaster R=BI.getRaster();

Example 4:

    int W,H;
    BufferedImage BI=null;
    ...
    BI=new BufferedImage(W,H,BufferedImage.TYPE_INT_ARGB);
    ...
    //the bit masks must be compatible with the BufferedImage format
    //the below BM array must corespond to BufferedImage.TYPE_INT_ARGB
    int[] BM=new int[]{0xff0000,0xff00,0xff,0xff000000};
    WritableRaster WR=Raster.createPackedRaster
	(DataBuffer.TYPE_INT,50,50,BM,null);
    BI.copyData(WR);

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