Digital Image Processing The electronic camera/frame grabber/computer combination has made it easy to digitize, store and manipulate images. These possibilities have made a great impact on optical metrology in recent years. Digital image processing has evolved as a specific scientific branch for many years. Many of the methods and techniques developed here are directly applicable to problems in optical metrology. In this chapter we go through some of the standard methods such as edge detection, contrast stretching, noise suppression, etc. Besides, algorithms for solving problems specific for optical metrology are needed. Such methods will be treated in Chapter 11. . | Optical Metrology. Kjell J. Gasvik Copyright 2002 John Wiley Sons Ltd. ISBN 0-470-84300-4 10 Digital Image Processing INTRODUCTION The electronic camera frame grabber computer combination has made it easy to digitize store and manipulate images. These possibilities have made a great impact on optical metrology in recent years. Digital image processing has evolved as a specific scientific branch for many years. Many of the methods and techniques developed here are directly applicable to problems in optical metrology. In this chapter we go through some of the standard methods such as edge detection contrast stretching noise suppression etc. Besides algorithms for solving problems specific for optical metrology are needed. Such methods will be treated in Chapter 11. THE FRAME GRABBER A continuous analogue representation the video signal of an image cannot be conveniently interpreted by a computer and an alternative representation the digital image must be used. It is generated by an analogue-to digital A D converter often referred to as a digitizer a frame-store or a frame-grabber . With a frame grabber the digital image can be stored into the frame memory giving the possibility of data processing and display. The block diagram of a frame grabber module is shown in Figure . These blocks can be divided into four main sections 1 the video source interface 2 multiplexer and input feedback LUT 3 frame memory 4 display interface. The video source interface The video source interface performs three main operations 1 signal conditioning 2 synchronization timing and 3 digitalization. In the signal condition circuitry the signal is low-pass filtered with a cut-off frequency of 3-5 MHz to avoid aliasing see Section . Some frame grabbers also have programmable offset and gain. 250 DIGITAL IMAGE PROCESSING Figure Block diagram of frame grabber Before A D conversion the video signal must be stripped from its horizontal and vertical sync signals. The pixel .
