Hands-On Image Processing with Python

Haar-like features

Haar-like features are very useful image features used in object detection. They were introduced in the first real-time face detector by Viola and Jones. Using integral images, Haar-like features of any size (scale) can be efficiently computed in constant time. The computation speed is the key advantage of a Haar-like feature over most other features. These features are just like the convolution kernels (rectangle filters) introduced in Chapter 3, Convolution and Frequency Domain Filtering. Each feature corresponds to a single value computed by subtracting a sum of pixels under a white rectangle from a sum of pixels under a black rectangle. The next diagram shows different types of Haar-like features, along with the important ...