Image Processing Toolbox

Geometric Operations

Overview

This chapter describes the geometric functions, which are basic image processing tools. These functions modify the geometry of an image by resizing, rotating, or cropping the image. They support all image types.

The chapter begins with a discussion of interpolation, an operation common to most of the geometric functions. It then discusses each of the geometric functions separately, and shows how to apply them to sample images.

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

Aliasing
Artifacts in an image that can appear as a result of reducing an image's size. When the size of an image is reduced, original pixels are downsampled to create fewer pixels. Aliasing that occurs as a result of size reduction normally appears as stair-step patterns (especially in high contrast images), or as Moire (ripple-effect) patterns.

Anti-aliasing
Any method for preventing aliasing (see above). The method discussed in this chapter is interpolation (see below).

Bicubic interpolation
Output pixel values are calculated from a weighted average of pixels in the nearest 4-by-4 neighborhood.

Bilinear interpolation
Output pixel values are calculated from a weighted average of pixels in the nearest 2-by-2 neighborhood.

Geometric operation
An operation that modifies the spatial relations between pixels in an image. Examples include resizing (growing or shrinking), rotating, and shearing.

Interpolation
The process by which we estimate an image value at a location in between image pixels.

Nearest neighbor interpolation
Output pixel values are assigned the value of the pixel that the point falls within. No other pixels are considered.

Words	Definitions
Aliasing	Artifacts in an image that can appear as a result of reducing an image's size. When the size of an image is reduced, original pixels are downsampled to create fewer pixels. Aliasing that occurs as a result of size reduction normally appears as stair-step patterns (especially in high contrast images), or as Moire (ripple-effect) patterns.
Anti-aliasing	Any method for preventing aliasing (see above). The method discussed in this chapter is interpolation (see below).
Bicubic interpolation	Output pixel values are calculated from a weighted average of pixels in the nearest 4-by-4 neighborhood.
Bilinear interpolation	Output pixel values are calculated from a weighted average of pixels in the nearest 2-by-2 neighborhood.
Geometric operation	An operation that modifies the spatial relations between pixels in an image. Examples include resizing (growing or shrinking), rotating, and shearing.
Interpolation	The process by which we estimate an image value at a location in between image pixels.
Nearest neighbor interpolation	Output pixel values are assigned the value of the pixel that the point falls within. No other pixels are considered.

Troubleshooting Interpolation