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The Engineer’s Guide to Decoding & Encoding
by John Watkinson
HANDBOOK
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SERIES
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The Engineer’s Guide to Decoding & Encoding
by John Watkinson
John Watkinson is an independent author, journalist and consultant in
the broadcast industry with more than 20 years of experience in research
and development.
With a BSc (Hons) in Electronic Engineering and an MSc in Sound and
Vibration, he has held teaching posts at a senior level with The Digital
Equipment Corporation, Sony Broadcast and Ampex Ltd., before forming
his own consultancy.
Regularly delivering technical papers at conferences including AES,
SMPTE, IEE, ITS and Montreux, John Watkinson has also written
numerous publications including “The Art of Digital Video”,
“The Art of Digital Audio” and “The Digital Video Tape Recorder.”
Engineering with Vision
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INTRODUCTION
The subject of encoding and decoding has become increasingly important with
the trend towards the use of component technology in production.
This handbook treats the entire subject of encoding and decoding from first
principles leading up to today’s most sophisticated technology.
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CONTENTS
Section 1 - Introduction to composite video
Page 2
1.1 What is composite video?
1.2 Brief history of NTSC PAL and SECAM
1.3 Quadrature modulation
1.4 NTSC encoding
1.5 PAL encoding
1.6 SECAM encoding
1.7 Digital encoding
Section 2 - Spectral analysis of composite video
Page 15
2.1 Sampling theory
2.2 Aperture effect
2.3 Two and three dimensional sampling spectra
2.4 Spectrum of NTSC
2.5 Spectrum of PAL
2.6 Colour framing and Sc-H phase
Section 3 - Composite decoding
Page 31
3.1 Introduction
3.2 Simple Y/C separation
3.3 Field combs
3.4 Line combs
3.5 Adaptive filters
3.6 Multi-dimensional filtering
3.7 Chroma demodulators
3.8 NTSC demodulation
3.9 PAL demodulation
3.10 Digital decoders
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SECTION 1 - INTRODUCTION TO COMPOSITE VIDEO
1.1 What is composite video?
This book is concerned with advanced encoding and decoding of composite
video. Composite video was originally designed as monochrome compatible system
for broadcasting in which subcarrier based colour information was added to an
existing line standard in a way which allowed existing sets to display a monochrome
picture. A further criterion was that the addition of colour should not increase the
bandwidth of the TV channel. In that respect composite video has to be viewed as
an early form of compression. Although designed for transmission, the baseband
composite signals could be recorded on videotape. In the case of NTSC and PAL,
vision mixing was also possible on composite signals. As a result early colour
studios were entirely composite. There was one coder at the camera control unit and
one decoder at the viewer’s TV set.
Since the introduction of colour, new processes such as slow motion, standards
conversion, DVEs, graphics and so on have come into being. These have in common
the fact that they cannot operate upon composite signals. All processes which
manipulate the image spatially will render meaningless any subcarrier based colour
information. In a composite environment such devices need an input decoder and an
output encoder and clearly these need to be of high quality. Television is currently
in a state of change with many new transmission formats proposed. Some of these
work in components, but if such formats are adopted it will be some time before
composite transmission ceases. Other proposals seek to increase the performance of
composite signals. In both cases a requirement for quality coding and decoding is
clear. Even if a utopian component world came about tomorrow, decoding would
still be necessary to view the enormous composite archives which have built up.
Whilst the techniques vary, all composite signals have in common the need to
include a subcarrier based chroma signal within the luminance band in such a way
that it will be substantially invisible on an unmodified monochrome TV set. This is
achieved in much the same way in all three systems.
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