Book Image

OpenCV for Secret Agents

By : Joseph Howse
Book Image

OpenCV for Secret Agents

By: Joseph Howse

Overview of this book

Table of Contents (15 chapters)
OpenCV for Secret Agents
Credits
About the Author
Acknowledgments
About the Reviewers
www.PacktPub.com
Preface
Index

Detecting circles and lines


From The Living Headlights (our project in Chapter 5, Equipping Your Car with a Rearview Camera and Hazard Detection), we are already familiar with one technique to detect circles. We treated the problem as a special case of blob detection and we used an OpenCV class, SimpleBlobDetector, which allows us to specify many detection criteria such as a blob's size, color, and circularity (or noncircularity, that is linearity).

A blob is a shape filled with a solid (or nearly solid) color. This definition implies that many circular or linear objects are not detectable as blobs. In the following photo we see a sunlit desk with a china teapot, china bowl, and pewter bowl:

The bowls and the lid of the teapot have approximately circular outlines in this top-down view. However, they are unlikely to pass the detection as blobs because the interior of each shape is multicolored, especially in uneven light.

Blob detection starts with a simple threshold filter (marking bright regions...