Practical Computer Vision with SimpleCV

Chapter 5. The Impact of Light

All vision systems depend on quality images, and quality images in turn depend on light. Because of this, the quality of the light in the vision system environment is a key factor to its success. This chapter takes a deeper look at light and how to use it to illuminate a vision system, including:

• The different types of light sources available

• Ways to evaluate light sources

• Looking at how the target object interacts with light

• Removing unwanted ambient light

• Reviewing different lighting techniques

• Calibrating the camera

• Using color to segment an image

Introduction

One of the most common mistakes of beginning computer vision developers is to overlook lighting and its effect on image quality and algorithm performance. Lighting is a critical component in any vision system and can be the difference between success and failure. After all, without lighting, computer vision would be the study of black rooms with black objects. That would actually make vision programming incredibly easy, but not terribly useful. Instead the lighting should help accomplish three main goals:

• Maximize the contrast of the features of interest

• Be generalized enough that it works well from one object to the next

• Be stable within the environment, particularly over time

Note that in any environment, light radiates from one or more sources and then bounces onto an object (or irradiates it). When filming the object, that surface then radiates the incident light into the camera. It is important to ...