Java Image Data

Image Data Classes,

Class: DataBuffer
Extends: Object

Class: Raster
Extends: Object

Class: SampleModel
Extends: Object

Class: WriteableRaster
Extends: Raster

The basic unit of image data storage is the DataBuffer. The DataBuffer is a kind of raw storage that contains all of the samples for the image data but does not maintain a notion of how those samples can be put together as pixels. The information about how the samples are put together as pixels is contained in a SampleModel. The SampleModel class contains methods for deriving pixel data from a DataBuffer. Together, a DataBuffer and a SampleModel constitute a meaningful multi-pixel image storage unit called a Raster.

A Raster has methods that directly return pixel data for the image data it contains.
* Raster - a read-only object that has only accessors
* WritableRaster - A writable object that has a variety of mutators

There are separate interfaces for dealing with each raster type. The RenderedImage interface assumes that the data is read-only and does not contain methods for writing a Raster. The WritableRenderedImage interface assumes that the image data is writeable and can be modified.

Data from a tile is returned in a Raster object. A tile is not a class in the architecture; it is a concept. In the Java 2D API, the implementation of the WritableRenderedImage (BufferedImage) is defined to have a single tile. This, the getWritableTile method will return all the image data. Other methods that relate to tiling will return the correct degenerative results.

RenderedImages do not necessarily maintain a Raster internally. Rather, they can return requested rectangles of image data in the form of a (Writable)Raster (through the getData, getRect, and get(Writable)Tile methods). This distinction allows RenderedImages to be virtual images, producing data only when needed. RenderedImages do, however, have an associated SampleModel, implying that data returned in Rasters from the same image will always be written to the associated DataBuffer in the same way.

The Java 2D BufferedImage also adds an associated ColorModel, which is different from the SampleModel. The ColorModel determines how the bands are interpreted in a colorimetric sense.