Introduction to Digital Television - CinemaSource

1 Introduction toDigital TelevisionCinemaSource Technical Bulletins. Copyright 2002 by CinemaSource , rights reserved. Printed in the United States of America. No part of this bulletin may be used or reproduced in any manner whatsoever without written permission,except in brief quotations embodied in critical reviews. CinemaSourceis a registered federal information contact: The CinemaSource Press, 18 Denbow Rd. Durham, NH 03824 CinemaSource ,18 Denbow Rd., Durham, NH One: Basic Video Concepts3 Chapter 1: Basic Video Concepts Understanding Video Resolution ---------------------------------------- --------Page 4 Understanding Progressive Scanning ---------------------------------------- --Page 7 Popular Line Doublers and Scalers ---------------------------------------- -----Page 10 Understanding Component Video ---------------------------------------- -------Page 11 Understanding Aspect Ratios ---------------------------------------- -------------Page 16 Cables for DTV

2 ---------------------------------------- -------------------------------Page 26 Chapter 2: Digital Signals Explained What is a Digital Signal ---------------------------------------- --------------------Page 28 Understanding Video Compression ---------------------------------------- ----Page 30 Chapter 3: The History of Digital Television The history of DTV ---------------------------------------- --------------------------Page 39 Behind The Scenes of the Grand Alliance ------------------------------------Page 46 Introduction to Digital TelevisionThis guide is a collection of articles related to the rollout of digitaltelevision (DTV).

3 The articles have been chosen from various sources andeach explains a particular segment of the complex DTV puzzle. We hopethat you find this guide useful. Please fell free to email us atCinemaSource if you have any comments or One: Basic Video ConceptsThe term resolution is used to quantify a displaydevice s ability to reproduce fine detail in a videoimage. In a solid state imaging device (LCD, DILA,DLP), the resolution is simply the number of pixels on theimaging elements. In a raster scanned CRT-baseddevice,it is a very different mechanism and there is asignificant difference between horizontal and verticalresolution.

4 Vertical Resolution of a CRT:Below we have a diagram that shows how an electronbeam is scanned across a picture tube faceplate to forma NTSC video image. The technique of interlacing theimages was developed to minimize that bandwidth of thesignal and reduce flicker in the maximumvertical resolution is simply the number of scan linesvisible in the number is the number ofhorizontal scan lines (525) minus the retrace lines (43).Thus the maximum vertical resolution of a NTSC display is525 -43 = 482 lines. With an HDTV image, the image isswept faster with the result of more lines of Resolution of a CRT:Horizontal resolution is a completely different mechanismin a CRT-based device.

5 The horizontal resolution is afunction of how fast you can turn the electron beam onand off. The image above illustrates this. Here acheckerboard pattern is being displayed by making theelectron bean turn on and off very rapidly. Note: Byconvention, video resolution is measured in pictureheights, whether it is vertical resolution or horizontalresolution. So the horizontal resolution is the number ofresolvable vertical lines across a width of the display equalto the picture height. For a 4:3 display this is equivalent to75% of the resolvable lines across the full width of One:Basic VideoConceptsChapter One: Basic Video Concepts5 Horizontal Resolutionof Various VideoSources6 Chapter One: Basic Video ConceptsProjectorRequirementsFor HDTVMany thanks to Greg Rogersof The Perfect Vision for hispermission to reprint thisHDTV material.

6 You can visithis web site requirements can be separated into twocategories. First are the minimum requirements todisplay the HDTV format signals. These includeHorizontal Scan Rates, Horizontal Retrace Time andVertical Retrace Time. If these requirements are not met,then the projector will not sync to the signals and nostable picture will be produced. Second are therequirements necessary to achieve the maximum qualitydelivered by the HDTV format. Even if the secondrequirements are not fully met, the picture quality from anHDTV source should still exceed that delivered by SDTV sources.

7 In most cases a video display device s vertical resolutionfor a 4:3 picture will be approximately the same as thehorizontal resolution in TV Lines (referenced to a 4:3picture height). This assumes that the spot size isapproximately round (this will require good adjustment ofastigmatism and focus) and that the horizontal resolutionis not limited by the RGB bandwidth. Only a handful of projectors will have sufficiently smallspot sizes to truly display the full vertical resolution of the1080I format. On the positive side, some modestoverlapping of the scan lines will help hide the interlacingartifacts from this format.

8 There is a very fine balancingact going on here that makes for the interesting debatebetween proponents of the 720 Pand 1080I formats. The1080I format should produce a 50% improvement inhorizontal and vertical resolution over 720P, but CRTandoptical limitations in projectors (and aperture-grille andshadow-mask limitations in direct view TVs) will limit thatsignificantly. But those same limitations partially obscurethe visibility of the fine line-twitter and other interlaceartifacts of the 1080I format. So the debate goes onbetween proponents of the 1080I and the 720 Pformats asthe networks and others choose up sides for the bestHDTV signal.

9 Video Projector Requirements For HDTVC hapter One: Basic Video Concepts7 Since debuting in the late 1930s, Television receiversand the images they display, have evolvedcontinuously and prodigiously. From small,marginally acceptable, B&W affairs Television images havemorphed into enormous, full color, theater-like this remarkable change can be attributed to theunrelenting R&D efforts on the parts of hundreds of videotechnology companies, and individuals, all in pursuit ofprogress and "competitiveadvantage". Yet despite themagnitude of this effort, andmajor advancements incomponentry, such astransistors, integrated circuitsand microprocessors, the NTSC color signal remains firmlyrooted in the past.

10 Raster Scanning 101 Raster scanning is the standardprocess by which CRT-baseddisplay devices create videoimages. There are other ways toderive images from CRTdisplays, such as vector-basedmethods (used in some air traffic control displays andmilitary applications), but by far the most common methodused is raster scanning. Raster scanning refers to themethod by which video images are actually "assembled"on the face of the CRT. But before we dig into theprincipals of scanning, let's consider how standard picturetubes actually generate light. It starts with a device located deep in the neck of allpicture tubes called an electron gun.