Chapter 7

Geometric operations

What Will we Learn?

- What do geometric operations do to an image and what are they used for?
- What are the techniques used to enlarge/reduce a digital image?
- What are the main interpolation methods used in association with geometric operations?
- What are affine transformations and how can they be performed using MATLAB?
- How can I rotate, flip, crop, or resize images in MATLAB?
- What is image registration and where is it used?

7.1 Introduction

Geometric operations modify the geometry of an image by repositioning pixels in a constrained way. In other words, rather than changing the pixel values of an image (as most techniques studied in Part I of this book do), they modify the spatial relationships between groups of pixels representing features or objects of interest within the image. Figure 7.1 shows examples of typical geometric operations whose details will be presented later in this chapter.

Geometric operations can be used to accomplish different goals, such as the following:

- Correcting geometric distortions introduced during the image acquisition process (e.g., due to the use of a fish-eye lens).
- Creating special effects on existing images, such as twirling, bulging, or squeezing a picture of someone's face. ...