Java(TM) Boutique - Using Rasters for Image Processing, Part 1

Tutorials : Using Rasters for Image Processing, Part 1 :

Scanline, Pixel Stride, Scanline Stride, and Band Offsets

Before you can create a DataBuffer and a SampleModel, you'll need understand a few things about the representation of samples in DataBuffers:

Scanline: This defines a row of pixels from the image region that you want to process.
Pixel stride: This defines the distance, represented in DataBuffer elements, between the samples of two pixels, where the samples are on the same scanline and belong to the same band.
Scanline stride: This defines the distance, represented in DataBuffer elements, between a sample on a scanline and the sample on the next scanline but on the same column. The scanline stride value can be smaller or bigger than the scanline value, but in general they are equal (as shown in Figure 5).
Bands offsets: This defines the distance, represented in DataBuffer elements, from the beginning of a block to the first sample from a band.

Figures 5 represents the architectures for the PixelInterleavedSampleModel and SinglePixelPackedSampleModel classes. Obviously, their interpretation depends on the storage model.

Figure 5. Class Architectures: The image shows the architectures for PixelInterleavedSampleModel and SinglePixelPackedSampleModel.

Creating a DataBuffer Object

To create a DataBuffer object, first obtain an instance of one of the DataBufferXXX classes. You will learn how to do that for the DataBufferByte class and the principle is the same for the other DataBufferXXX. The constructors of the DataBufferByte class are:

public DataBufferByte(int size): This creates a data buffer object containing only one block. The dimension of this block is specified by the size argument.
public DataBufferByte(int size, int blocks): This creates a data buffer object containing a blocks number of blocks, the dimensions of which are specified by the size argument.
public DataBufferByte(byte[] array, int size): This creates a data buffer object containing only one block, using the byte array array. The dimension of the block is specified by the size argument. Obviously, the array must contain at least size elements.
public DataBufferByte(byte[] array,int size, int offset): This creates a data buffer object containing only one block, using the byte array. The dimension of the block is specified by the size argument. The offset argument represents the offset of the array. Obviously, the byte array must contain at least offset+size elements.
public DataBufferByte(byte[][] arrays, int size): This creates a data buffer object that containing arrays.length blocks. The dimensions of the blocks are specified by the size argument. Obviously, each array must have at least size elements.
public DataBufferByte(byte[][] arrays,int size, int[] offsets): This creates a data buffer object that containing arrays.length blocks. The dimensions of the blocks are specified by the size argument and the offsets array represent the offsets into each byte array. Obviously, each array must have at least size+offset elements.

Figure 6. A DataBuffer Object: The image shows the architecture for a DataBuffer object.

The following code illustrates how to create a DataBufferByte object without offset:



int z=50;

byte[] pixels = new byte[z];

DataBufferByte DB=new DataBufferByte(pixels,z);

And with offset=10:



int offset=10;

int z=50+offset;

byte[] pixels = new byte[z];

DataBufferByte DB=new DataBufferByte(pixels,z,offset);

Common Methods in All DataBufferXXX Classes

To extract one or more arrays from a data buffer, use the following methods in all DataBufferXXX classes:

public data_type[] getData()

public data_type[] getData(int block): This returns the array corresponding to the specified block.

public data_type[][] getBankData()

Where data_type[]/data_type[][] can be byte[]/byte[][], int[]/int[][], short[]/short[][], float[]/float[][], or double[]/double[][] depending of the DataBufferXXX class. This affirmation is valid for all the above methods.

To extract an integer value from a DataBuffer, use the following methods in all DataBufferXXX classes:

public int getElem(int i): This returns from the first block an integer value from the i index.
public int getElem(int block, int i): This returns from the specified block an integer value from the i index.

To obtain a float value, use the following two methods:

public float getElemFloat(int i): This returns from the first block a float value from the i index;.
public float getElemFloat(int block, int i): This returns from the specified block a float value from the i index;.

Or, to obtain a double value from a DataBuffer use the following two methods:

public double getElemDouble(int i): This returns from the first block a double value from the i index;.
public double getElemDouble(int block, int i): This returns from the specified block a double value from the i index;.

The set a DataBuffer element to an integer value, use the following methods in all DataBufferXXX classes:

public void setElem(int i, int value): This sets the element from the i position to the specified integer value. The used block is the first one.
public void setElem(int block, int i, int value): This sets the element from the i position to the specified integer value. The used block is specified by the block argument.

To set a DataBuffer element to a float value, use the following two methods:

public void setElemFloat(int i, float value): This sets the element from the i position to the specified float value. The used block is the first one.
public void setElemFloat(int block, int i, float value): This sets the element from the i position to the specified float value. The used block is specified by the block argument.

Or, to set a DataBuffer element to a double value use the following two methods:

public void setElemDouble(int i, double value): This sets the element from the i position to the specified double value. The used block is the first one.
public void setElemDouble(int block, int i, double value): This sets the element from the i position to the specified double value. The used block is specified by the block argument.

All DataBufferXXX classes inherit a series of methods for obtaining information about data buffers from the DataBuffer superclass. Among these methods are: getOffset, getOffsets, getSize, getNumBanks, getDataTypeSize, and getDataType.



int offset=10;

int z=50+offset;

byte[] pixels = new byte[z];

�

DataBufferByte DB=new DataBufferByte(pixels,z,offset);                 

        int GNB=DB.getNumBanks();

        int GS=DB.getSize();

        int GO=DB.getOffset();

               System.out.println("Number of blocks:"+GNB);

               System.out.println("Blocks dimension:"+GS);

               System.out.println("Offset:"+GO);                  

	      DB.setElem(0,122);

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