The Engineer's Guide to Standards Conversion.pdf

The Engineer’s Guide to Standards Conversion

by John Watkinson

HANDBOOK

SERIES

The Engineer’s Guide to Standards Conversion

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

INTRODUCTION

Standards conversion used to be thought of as little more than the job of

converting between NTSC and PAL for the purpose of international program

exchange. The application has recently become considerably broader and one of the

purposes of this guide is to explore the areas in which standards conversion

technology is now applied. A modern standards converter is a complex device with

a set of specialist terminology to match. This guide explains the operation of

converters in plain English and defines any terms used.

CONTENTS

Section 1 - Introduction

Page 2

1.1 What is a standards converter?

1.2 Types of converters

1.3 Converter block diagram

Section 2 - Some basic principles

Page 7

2.1 Sampling theory

2.2 Aperture effect

2.3 Interlace

2.4 Kell effect

2.5 Quantizing

2.6 Quantizing error

2.7 Digital filters

2.8 Composite video

2.9 Composite decoding

Section 3 - Standards conversion

Page 29

3.1 Interpolation

3.2 Line Doubling

3.3 Fractional ratio interpolation

3.4 Variable interpolation

3.5 Interpolation in several dimensions

3.6 Aperture synthesis

3.7 Motion compensated standards conversion

Section 4 - Applications

Page 52

4.1 Up and downconverters

4.2 Field rate doubling

4.3 DEFT

SECTION 1 - INTRODUCTION TO STANDARDS CONVERSION

1.1 What is a standards converter?

Strictly speaking a television standard is a method of carrying pictures in an

electrical wave form which has been approved by an authoritative body such as the

SMPTE or the EBU. There are many different methods in use, many of which are

true standards. However, there are also signals which are not strictly speaking

standards, but which will be found in everyday use. These include signals specific to

one manufacturer, or special hybrids such as NTSC 4.43.

Line and field rate doubling for large screen displays produces signals which are

not standardised. A practical standards converter will quite probably have to accept

or produce more than just “standard” signals. The word standard is used in the

loose sense in this guide to include all of the signals mentioned above. We are

concerned here with baseband television signals prior to any RF modulation for

broadcasting. Such signals can be categorised by three main parameters.

Firstly, the way in which the colour information is handled; video can be

composite, using some form of subcarrier to frequency multiplex the colour signal

into a single conductor along with the luminance, or component, using separate

conductors for parallel signals. Conversion between these different colour

techniques is standards conversion.

Secondly, the number of lines into which a frame or field is divided differs

between standards. Converting the number of lines in the picture is standards

conversion.

Thirdly, the frame or field rate may also differ between standards. Changing the

field or frame rate is also standards conversion. In practice more than one of these

parameters will often need to be converted. Conversion from NTSC to PAL, for

example, requires a change of all three parameters, whereas conversion from PAL to

SECAM only requires the colour modulation system to be changed, as the line and

field parameters are the same. The change of line or field rate can only be performed

on component signals, as the necessary processing will destroy the meaning of any

subcarrier. Thus in practice a standards converter is really three converters in

parallel, one for each component.

1.2 Types of converters

Fig 1.2.1 illustrates a number of applications in which some form of standards

conversion is employed. The classical standards converter came into being for

international interchange and converted between NTSC and PAL/SECAM.

However, practical standards converters do more than that. Many standards

converters are equipped with comprehensive signal adjustments and are sometimes

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