The Engineer's Guide to Standards Conversion - Snell

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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 2
Page 1 and 2: The Engineer’s Guide to Standards
Page 3: INTRODUCTION Standards conversion u
Page 7 and 8: One solution to large area flicker
Page 9 and 10: A further advantage of digital circ
Page 11 and 12: changing. In short it is a form of
Page 13 and 14: To prevent aliasing, a band limitin
Page 15 and 16: The theoretical vertical bandwidth
Page 17 and 18: 2.4 Kell effect In conventional tub
Page 19 and 20: 2.6 Quantizing error It is possible
Page 21 and 22: unpredictable and gives the system
Page 23 and 24: clairvoyant powers. Shortening the
Page 25 and 26: 2.8 Composite video For colour tele
Page 27 and 28: Line n received with phase error
Page 29 and 30: 2.9 Composite decoding The reason f
Page 31 and 32: Vertical spatial frequency Temporal
Page 33 and 34: A single pixel has meaning over the
Page 35 and 36: 3.2 Line doubling Input samples Out
Page 37 and 38: Input samples A B C D Sample value
Page 39 and 40: a) Data in Phase select b) FILTER R
Page 41 and 42: Vertical frequency Stop band Tempor
Page 43 and 44: Vertical axis Time axis Fig 3.5.4 b
Page 45 and 46: Vertical frequency Unsuppressed = M
Page 47 and 48: a) Drama aperture +525 c/ph Vertica
Page 49 and 50: 3.7 Motion compensated standards co
Page 51 and 52: This is because relative motion res
Page 53 and 54: a) Input fields Interpolation axis
Page 55 and 56:
SECTION 4 - APPLICATIONS 4.1 Up and
Page 57 and 58:
It is possible to identify the 3:2
Page 59 and 60:
Published by Snell & Wilcox Ltd. Du
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The Engineer's Guide to Standards Conversion - Snell

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