DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

Introduction to
video compression 14
Directly storing or transmitting Y’C B C R digital video
requires immense data capacity – about 20 megabytes
per second for SDTV, or about 120 megabytes per
second for HDTV. First-generation studio digital VTRs,
and today’s highest-quality studio VTRs, store uncompressed
video; however, economical storage or transmission
requires compression. This chapter introduces
the JPEG, M-JPEG, and MPEG compression techniques.
Data compression
Data compression reduces the number of bits required
to store or convey text, numeric, binary, image, sound,
or other data, by exploiting statistical properties of the
data. The reduction comes at the expense of some
computational effort to compress and decompress.
Data compression is, by definition, lossless: Decompression
recovers exactly, bit for bit (or byte for byte), the
data that was presented to the compressor.
Binary data typical of general computer applications
often has patterns of repeating byte strings and
substrings. Most data compression techniques,
including run-length encoding (RLE) and Lempel-Ziv-
Welch (LZW), accomplish compression by taking advantage
of repeated substrings; performance is highly
dependent upon the data being compressed.
Image compression
Image data typically has strong vertical and horizontal
correlations among pixels. When the RLE and LZW
algorithms are applied to bilevel or pseudocolor image
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