Image Processing Basics - Digital Signal Processing: Fundamentals and Applications - page 684

Coding DC Coefficients.................................................................................................. 737
Coding AC Coefficients .................................................................................................. 737
14.7.4 Image Compression Using Wavelet Transform Coding ...............................................738
14.8 Creating a Video Sequence by Mixing Two Images ....................................................................... 745
14.9 Video Signal Basics ................................................................................................................... 746
14.9.1 Analog Video .........................................................................................................747
PAL Video ..................................................................................................................... 752
SECAM Video................................................................................................................ 752
14.9.2 Digital Video .........................................................................................................753
14.10 Motion Estimation in Video ....................................................................................................... 755
14.11 Summary ................................................................................................................................. 757

OBJECTIVES:
In today's modern computers, media information such as audio, images, and video have become necessary
for daily business operations and entertainment. In this chapter, we will study the digital image and its
processing techniques. This chapter introduces the basics of image processing, including image
enhancement using histogram equalization and filtering methods, and proceeds to study pseudo-color
generation for object detection and recognition. Finally, the chapter investigates image compression
techniques and the basics of video signals.

14.1 IMAGE PROCESSING NOTATION AND DATA FORMATS
The digital image is picture information in a digital form. The image can be filtered to remove noise to
enhance it. It can also be transformed to extract features for pattern recognition. The image can be
compressed for storage and retrieval, as well as transmitted via a computer network or a communi-
cation system.
The digital image consists of pixels. The position of each pixel is specified in terms of an index
for the number of columns and another for the number of rows. Figure 14.1 shows that a pixel pð 2 ; 8 Þ
has a level of 86 and is located in the second row, eighth column. We express it in notation as

pð 2 ; 8 Þ¼ 86 (14.1)

The number of pixels in the presentation of a digital image is its spatial resolution , which relates to the
image quality. The higher the spatial resolution, the better quality the image has. The resolution can be
fairly high, for instance, as high as 1,600 1,200 (1,920,000 pixels ¼ 1.92 megapixels), or as low as
320 200 (64,000 pixels ¼ 64 kilopixels). In notation, the number to the left of the multiplication
symbol represents the width, and that to the right of the symbol represents the height. Image quality
also depends on the numbers of bits used in encoding each pixel level, which will be discussed in next
section.

14.1.1 8-Bit Gray Level Images
If a pixel is encoded on a gray scale from 0 to 255, where 0 ¼ black and 255 ¼ white, the numbers
in between represent levels of gray forming a grayscale image . For a 640 480 8-bit image, 307.2