Image Processing Toolbox

Introduction

Overview

This chapter introduces you to the fundamentals of image processing using MATLAB and the Image Processing Toolbox. It describes the types of images supported, and how MATLAB represents them. It also explains the basics of working with image data and coordinate systems.

Words You Need to Know

An understanding of the following terms will help you to use this chapter. For more explanation of this table and others like it, see Words You Need to Know in the Preface.

Words
Definitions

Binary image
An image containing only black and white pixels. In MATLAB, a binary image is represented by a uint8 or double logical matrix containing 0's and 1's (which usually represent black and white, respectively). A matrix is logical when its "logical flag" is turned "on." We often use the variable name BW to represent a binary image in memory.

Image type
The defined relationship between array values and pixel colors. The toolbox supports binary, indexed, intensity, and RGB image types.

Indexed image
An image whose pixel values are direct indices into an RGB colormap. In MATLAB, an indexed image is represented by an array of class uint8, uint16, or double. The colormap is always an m-by-3 array of class double. We often use the variable name X to represent an indexed image in memory, and map to represent the colormap.

Intensity image
An image consisting of intensity (grayscale) values. In MATLAB, intensity images are represented by an array of class uint8, uint16, or double. While intensity images are not stored with colormaps, MATLAB uses a system colormap to display them. We often use the variable name I to represent an intensity image in memory. This term is synonymous with the term "grayscale."

Multiframe image
An image file that contains more than one image, or frame. When in MATLAB memory, a multiframe image is a 4-D array where the fourth dimension specifies the frame number. This term is synonymous with the term "multipage image."

RGB image
An image in which each pixel is specified by three values -- one each for the red, blue, and green components of the pixel's color. In MATLAB, an RGB image is represented by an m-by-n-by-3 array of class uint8, uint16, or double. We often use the variable name RGB to represent an RGB image in memory.

Storage class
The numeric storage class used to store an image in MATLAB. The storage classes used in MATLAB are uint8, uint16, and double. Some function descriptions in the reference chapter of this User's Guide have a section entitled "Class Support" that specifies which image classes the function can operate on. When this section is absent, the function can operate on all supported storage classes.

Words	Definitions
Binary image	An image containing only black and white pixels. In MATLAB, a binary image is represented by a `uint8` or `double` logical matrix containing 0's and 1's (which usually represent black and white, respectively). A matrix is logical when its "logical flag" is turned "on." We often use the variable name `BW` to represent a binary image in memory.
Image type	The defined relationship between array values and pixel colors. The toolbox supports binary, indexed, intensity, and RGB image types.
Indexed image	An image whose pixel values are direct indices into an RGB colormap. In MATLAB, an indexed image is represented by an array of class `uint8`, `uint16`, or `double`. The colormap is always an m-by-3 array of class `double`. We often use the variable name `X` to represent an indexed image in memory, and `map` to represent the colormap.
Intensity image	An image consisting of intensity (grayscale) values. In MATLAB, intensity images are represented by an array of class `uint8`, `uint16`, or `double`. While intensity images are not stored with colormaps, MATLAB uses a system colormap to display them. We often use the variable name `I` to represent an intensity image in memory. This term is synonymous with the term "grayscale."
Multiframe image	An image file that contains more than one image, or frame. When in MATLAB memory, a multiframe image is a 4-D array where the fourth dimension specifies the frame number. This term is synonymous with the term "multipage image."
RGB image	An image in which each pixel is specified by three values -- one each for the red, blue, and green components of the pixel's color. In MATLAB, an RGB image is represented by an m-by-n-by-3 array of class `uint8`, `uint16`, or `double`. We often use the variable name `RGB` to represent an RGB image in memory.
Storage class	The numeric storage class used to store an image in MATLAB. The storage classes used in MATLAB are uint8, uint16, and double. Some function descriptions in the reference chapter of this User's Guide have a section entitled "Class Support" that specifies which image classes the function can operate on. When this section is absent, the function can operate on all supported storage classes.

Using the Image Processing Toolbox Images in MATLAB and the Image Processing Toolbox