The basic data structure in MATLAB® is the array, an ordered set of real or complex elements. This object is naturally suited to the representation of images, real-valued ordered sets of color or intensity data.
MATLAB stores most images as two-dimensional matrices, in which each element of the matrix corresponds to a single discrete pixel in the displayed image. (Pixel is derived from picture element and usually denotes a single dot on a computer display.) For example, an image composed of 200 rows and 300 columns of different colored dots would be stored in MATLAB as a 200-by-300 matrix.
Some images, such as truecolor images, represent images using a three-dimensional array. In truecolor images, the first plane in the third dimension represents the red pixel intensities, the second plane represents the green pixel intensities, and the third plane represents the blue pixel intensities. This convention makes working with images in MATLAB similar to working with any other type of numeric data, and makes the full power of MATLAB available for image processing applications.
For more information on how Image Processing Toolbox™ assigns pixel indices and how to relate pixel indices to continuous spatial coordinates, see Image Coordinate Systems.