Raster Image

A raster graphics image is a data structure epresenting a generally rectangular grid of pixels, or points of color, viewable via amonitor, paper, or other display medium. Raster images are stored in image files with varying formats. Or a raster image is a class representing a rectangular array of pixels. A Raster encapsulates a DataBuffer that stores the sample values and a SampleModel that describes how to locate a given sample value in a DataBuffer.

A Raster defines values for pixels occupying a particular rectangular area of the plane, not necessarily including (0, 0). The rectangle, known as the Raster's bounding rectangle and available by means of the getBounds method, is defined by minX, minY, width, and height values. The minX and minY values define the coordinate of the upper left corner of the Raster. References to pixels outside of the bounding rectangle may result in an exception being thrown, or may result in references to unintended elements of the Raster's associated DataBuffer. It is the user's responsibility to avoid accessing such pixels.

A SampleModel describes how samples of a Raster are stored in the primitive array elements of a DataBuffer. Samples may be stored one per data element, as in a PixelInterleavedSampleModel or BandedSampleModel, or packed several to an element, as in a SinglePixelPackedSampleModel or MultiPixelPackedSampleModel. The SampleModel is also controls whether samples are sign extended, allowing unsigned data to be stored in signed Java data types such as byte, short, and int.

Although a Raster may live anywhere in the plane, a SampleModel makes use of a simple coordinate system that starts at (0, 0). A Raster therefore contains a translation factor that allows pixel locations to be mapped between the Raster's coordinate system and that of the SampleModel. The translation from the SampleModel coordinate system to that of the Raster may be obtained by the getSampleModelTranslateX and getSampleModelTranslateY methods.

A Raster may share a DataBuffer with another Raster either by explicit construction or by the use of the createChild and createTranslatedChild methods. Rasters created by these methods can return a reference to the Raster they were created from by means of the getParent method. For a Raster that was not constructed by means of a call to createTranslatedChild or createChild, getParent will return null.

The createTranslatedChild method returns a new Raster that shares all of the data of the current Raster, but occupies a bounding rectangle of the same width and height but with a different starting point. For example, if the parent Raster occupied the region (10, 10) to (100, 100), and the translated Raster was defined to start at (50, 50), then pixel (20, 20) of the parent and pixel (60, 60) of the child occupy the same location in the DataBuffer shared by the two Rasters. In the first case, (-10, -10) should be added to a pixel coordinate to obtain the corresponding SampleModel coordinate, and in the second case (-50, -50) should be added.

The translation between a parent and child Raster may be determined by subtracting the child's sampleModelTranslateX and sampleModelTranslateY values from those of the parent.

The createChild method may be used to create a new Raster occupying only a subset of its parent's bounding rectangle (with the same or a translated coordinate system) or with a subset of the bands of its parent.

All constructors are protected. The correct way to create a Raster is to use one of the static create methods defined in this class. These methods create instances of Raster that use the standard Interleaved, Banded, and Packed SampleModels and that may be processed more efficiently than a Raster created by combining an externally generated SampleModel and DataBuffer.


You can see the below image to look at the pixels.