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5.4 Managing and Manipulating Rasters

A BufferedImage object uses a Raster to manage its rectangular array of pixel data. The Raster class defines fields for the image's coordinate system--width, height, and origin. A Raster object itself uses two objects to manage the pixel data, a DataBuffer and a SampleModel. The DataBuffer is the object that stores pixel data for the raster (as described on page 81), and the SampleModel provides the interpretation of pixel data from the DataBuffer (as described on page 81).

5.4.1 Creating a Raster

In most cases, you don't need to create a Raster directly, since one is supplied with any BufferedImage that you create in memory. However, one of the BufferedImage constructor methods allows you to create a Raster by passing in a WritableRaster.

The Raster class provides a number of static factory methods for creating Rasters with the DataBuffers and SampleModels you specify. You can use these factories when implementing RasterOp filtering classes.

5.4.2 Parent and Child Rasters

The Raster class incorporates the concept of parent and child rasters. This can improve storage efficiency by allowing you to construct any number of buffered images from the same parent. The parent and its children all refer to the same data buffer, and each child has a specific offset and bounds to identify its image location in the buffer. A child identifies its ownership through its getParent method.

To create a subraster, you use the Raster.createSubRaster method.When you create a subraster, you identify the area of its parent that it covers and its offset from the parent's origin.

5.4.3 Operations on a Raster

The Raster class defines a number of ways to access pixels and pixel data. These are useful when you're implementing the RasterOp interface, which provides raster-level filtering and manipulation of image data, or when implementing any method that needs to perform low-level pixel manipulation.

The Raster.getPixel methods let you get an individual pixel, which is returned as individual samples in an array. The Raster.getDataElements methods return a specified run of uninterpreted image data from the DataBuffer. The Raster.getSample method returns samples of an individual pixel. The getSamples method returns a band for a particular region of an image.

In addition to these methods, you can also access the data buffer and the sample model through instance variables of the Raster class. These objects provide additional ways to access and interpret the Raster's pixel data.

5.4.4 The WritableRaster Subclass

The WritableRaster subclass provides methods for setting pixel data and samples. The Raster associated with a BufferedImage is actually a WritableRaster, thus providing full access to manipulate its pixel data.