If you are looking for information on the first edition of this book, it is here.
If you are looking for information on the second edition of this book, it is here.
Chapter 8. Computer Vision
Feb 2020. Ch 8 Computer Vision has now been updated to use OpenCV directly rather than SimpleCV (which is no longer being maintained. The Recipes in Chapter 8 have remained the same, but it does mean that the code in GitHub has changed quite a lot.
You can find instructions on installing OpenCV 4 on a Raspberry Pi 4 here.