We do not propose to describe the processing of dynamically changing images in this introduction. It is appropriate-given that many static images are derived from video cameras and frame grabbers-to mention the standards that are associated with the three standard video schemes that are currently in worldwide use- NTSC, PAL, and SECAM. This information is summarized in Table 3.
Standard
NTSC
PAL
SECAM
Property
Images / Second
29.97
25
25
Ms / image
33.37
40.0
40.0
Lines / image
525
625
625
(horiz./vert.)=aspect radio
4:3
4:3
4:3
interlace
2:1
2:1
2:1
Us / line
63.56
64.00
64.00
Table 3: Standard video parameters
In a interlaced image the odd numbered lines (1, 3, 5.) are scanned in half of the allotted time (e.g. 20 ms in PAL) and the even numbered lines (2, 4, 6,.) are scanned in the remaining half. The image display must be coordinated with this scanning format. The reason for interlacing the scan lines of a video image is to reduce the perception of flicker in a displayed image. If one is planning to use images that have been scanned from an interlaced video source, it is important to know if the two half-images have been appropriately "shuffled" by the digitization hardware or if that should be implemented in software. Further, the analysis of moving objects requires special care with interlaced video to avoid 'Zigzag' edges.
Tools
Certain tools are central to the processing of digital images. These include mathematical tools such as convolution, Fourier analysis, and statistical descriptions, and manipulative tools such as chain codes and run codes. We will present these tools without any specific motivation. The motivation will follow in later sections.
