Although a CD-ROM device has a storage capacity of a few gigabits, its average data-read throughput is only a few Megabits per second (about 1.2 Mbps to 1.5 Mbps for the common 1 × read speed CLV CDs). The resulting delay is intolerably large considering that a delay as small as 1 to 2 seconds is needed to conduct an interactive “slide show,” and a much smaller delay (on the order of 0.1 second) is required for video transmission or playback. In fact, a single uncompressed color image or video frame with a medium resolution of 500 × 500 pixels would require 100 seconds for transmission over an Integrated Services Digital Network (ISDN) link having a capacity of 64,000 bits per second (64 Kbps). The function of compression is often referred to as coding, for short.Ĭoding techniques are crucial for the effective transmission or storage of data-intensive visual information. In this way, a much greater reduction in bit rate can be attained as compared to lossless compression, which is necessary for enabling many real-time applications involving the handling and transmission of audiovisual information. The goal of lossy compression is to achieve the best possible fidelity given an available communication or storage bit rate capacity or to minimize the number of bits representing the image signal subject to some allowable loss of information. The number of bits representing the signal is typically expressed as an average bit rate (average number of bits per sample for still images, and average number of bits per second for video). The goal of lossless image compression is to represent an image signal with the smallest possible number of bits without loss of any information, thereby speeding up transmission and minimizing storage requirements. Lina J.Karam, in The Essential Guide to Image Processing, 2009 16.1 INTRODUCTION
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