C HAPTER 5: F UNDAMENTAL C ONCEPTS IN V IDEO 1

T YPES OF V IDEO S IGNALS Component video Higher-end video systems make use of three separate video signals for the red, green, and blue image planes. This kind of system has three wires and connectors connecting the camera or other devices to a TV or a monitor. Use component video to take advantage of the superior picture found in such signal sources as HDTV and progressive DVD 2

T YPES OF V IDEO S IGNALS Composite video Color (“chrominance") and intensity (“luminance") signals are mixed into a single carrier wave. This is the type of signal used by broadcast color TVs; it is downward compatible with black-and-white TV. 3

T YPES OF V IDEO S IGNALS S-video Also known as Separated-Video or Super-video A video color format that combines the three YUV video signals into two channels. Brightness/luma (Y) is in one channel, and color/chroma (U and V) are in another. S-video provides a sharper image than composite video, but is not as good as component video. 4

B ASIC V IDEO P ROPERTIES Representation of Video Signals Visual Representation To present the observer with as realistic as possible a representation of a scene Transmission of Video Signals Television Systems Video Digitization Digital Television 5

V ISUAL R EPRESENTATION In order to accurately convey both spatial and temporal aspects of a scene, the following properties are considered 1. Vertical Details and Viewing Distance The geometry of a television image is based on the ratio of the picture width W to the picture height H (W/H), called the aspect ratio. – Conventional aspect ratio is 4:3. The angular field of view is determined by the viewing distance, D, and is calculated as D/H. 2. Horizontal Detail and Picture Width – Can be determined from the aspect ratio 3. Total detail content of a picture – Since not all lines (horizontal and vertical) are visible to the observer, additional information can be transmitted through them. 6

V ISUAL R EPRESENTATION 4. Depth perception – Depth is a result of composing a picture by each eye (from different angles) – In a flat TV picture Perspective appearance of the subject matter Choice of focal length of the camera lens and changes in depth focus 5. Luminance – RGB can be converted to a luminance (brightness signal) and two color difference signals (chrominance) for TV signal transmission 7

V ISUAL R EPRESENTATION 6. Temporal Aspects of Illumination A discrete sequence of still images can be perceived as a continuous sequence. The impression of motion is generated by a rapid succession of barely differing still pictures (frames). Rate must be high enough to ensure smooth transition. Rate must be high enough so that the continuity of perception is not disrupted by the dark intervals between pictures The light is cut off, briefly, between these frames. 8

V ISUAL R EPRESENTATION 7. Continuity of Motion Continuity is perceived with at least 15 frames per second. To make motion appear smooth in a recorded film (not synthetically generated), a rate of 30 frames per second is needed. Films recorded with 24 frames per second look strange when large objects close to the viewer move quickly. NTSC (National Television Systems Committee) Standard Original: 30 frames/second Currently: frames/second PAL (Phase Alternating Line) Standard 25 frames per second 9

V ISUAL R EPRESENTATION 8. Flicker If the refresh rate is low, a periodic fluctuation of the perceived brightness can result. Minimum to avoid flicker is 50 Hz. Technical measures in movies and TV have allowed lower refresh rates. The Refresh rate is the number of times a display's image is repainted or refreshed per second. A refresh rate of 75 Hz means the image is refreshed 75 times in one second. 10

S IGNAL F ORMATS RGB YUV YIQ Composite Signals Instead of sending each component on one channel, send them all Computer Video Formats Current video digitization hardware differ in Resolution of digital images (frames) Quantization Frame rate Motion depends on the display hardware (Figure 5-4 page 86) 11

S IGNAL F ORMATS Computer Video Formats Color Graphics Adapter (CGA) Resolution: 320 x bits / pixel Enhanced Graphics Adapter (EGA) Resolution: 640 x bits / pixel Video Graphics Array (VGA) Resolution: 640 x bits / pixel Super Video Graphics Array (SVGA) Resolution: 1024 x 768, 1280 x 1024, 1600 x bits / pixel Video accelerators are needed to avoid reduced performance at higher resolutions Check the storage requirements of the above systems! 12

A NALOG V IDEO Each frame of video is represented by a fluctuating voltage known as an analog wave form. A composite signal has brightness, colour and synchronisation elements combined in the one signal. NTSC, PAL and SECAM are the three most widely used composite video signals.  Analog to Digital Video NTSC, PAL and SEACAM signals are analog (wave based). Computers store video in a digital format. The process of digitizing video is known as capturing or sampling. 13

T ELEVISION S YSTEMS Conventional Systems NTSC : National Television System Committee Originated in the US Uses color carriers of approx MHz or approx MHz. With suppressed color carrier, it uses quadrature amplitude modulation Refresh rate: 30Hz # horizontal lines:

T ELEVISION S YSTEMS Conventional Systems SECAM (stands for Système Electronique Couleur Avec Mémoire, the third major broadcast TV standard) France and Eastern Europe With suppressed color carrier, it uses frequency modulation Refresh rate: 25Hz # horizontal lines:

T ELEVISION S YSTEMS Conventional Systems PAL : Stands for Phase Alternating Line a TV standard widely used in Western Europe, China, India, and many other parts of the world. Uses color carriers of approx MHz With suppressed color carrier, it uses quadrature amplitude modulation Refresh rate: 25Hz # horizontal lines:

Table below gives a comparison of the three major analog broadcast TV systems. 17 TV System Frame Rate (fps) # of Scan Lines Total Channel Width (MHz) Bandwidth Allocation (MHz) YI or UQ or V NTSC PAL SECAM

D IGITAL V IDEO The advantages of digital representation for video are many. For example: Video can be stored on digital devices or in memory, ready to be processed (noise removal, cut and paste, etc.), and integrated to various multimedia applications; Direct access is possible, which makes nonlinear video editing achievable as a simple, rather than a complex, task; Repeated recording does not degrade image quality; Ease of encryption and better tolerance to channel noise 18

T ELEVISION S YSTEMS High-Definition TV (HDTV) Research began in Japan, 1968 Third Technological Shift (after black and white and color TV) The goal was to “integrate” the viewer with the events happening on the screen 19

T ELEVISION S YSTEMS High-Definition TV (HDTV) Resolution More than 1000 scanning lines Approximately double the resolution of conventional TV Higher video bandwidth About five times that of conventional TV Resolutions Recommended High 1440 Level: 1440 x 1152 High Level: 1920 x 1152 Later, 2k x 2k pixels Frame Rate No agreement on a fixed frame rate worldwide 50 or 60 frames per second 20

T ELEVISION S YSTEMS High-Definition TV (HDTV) Aspect Ratio Originally 16:9 Currently 4:3 Interlaced and/or progressive scanning formats Conventional systems supported interlaced scanning formats HDTV supports both. Viewing Conditions Screen area should be bigger than 8000cm 2 for “real” scenes 21

D IGITIZATION OF V IDEO S IGNALS Goes through Sampling, Quantization and Coding. Just like audio Composite Coding Sample the entire analog signal Simple but has many drawbacks Depends on the TV standard used Since luminance information is more important than chrominance information, it takes more bandwidth. Component Coding Based on the separate digitization of the components Luminance (Y) is sampled at 13.5 MHz whereas chrominance components (U and V) are sampled at 6.75 MHz. 22

D IGITAL T ELEVISION DVB (Digital Video Broadcasting) started in Europe in the early 90s after considerable progress in video compression techniques More precisely DTVB (Digital TeleVision Broadcasting) MPEG-2 for source coding of audio/video data Satellite Connections, CATV networks and (S)MATV (Small) Master Antenna TV systems were suitable for digital TV distribution DVB-S (Satellite) and DVB-C (Cable) were adopted by the European Telecommunications Standards Institute ETSI as official standards. Multichannel Microwave Distribution Systems (MMDS) are another possibility. 23

D IGITAL T ELEVISION Advantages Increased number of programs can be transmitted over a TV channel Adaptable video/audio quality to each application Exceptionally secure encryption systems for pay-per-view Additional services (video on demand, data broadcast,...) Computers and TV convergence 24