Multimedia Systems Part 12

Mahdi Vasighi www.iasbs.ac.ir/~vasighi

Department of Computer Science and Information Technology, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran To discuss:

• Types of video signals • Analog Video • Digital Video Types of Video Signals

Video Signals can be classified as

1. Composite Video 2. S-Video 3. Component Video Types - Composite Video

• Used in broadcast TV’s • Compatible with B/W TV • Chrominance ( I & Q or U & V) & Luminance (Y) signals are mixed into a single carrier wave, which can be separated at the receiver

• Mixing of signals leads interference & create crosstalk and visual defects (dot crawl) Types – S-Video

o S stands Super / Separated o Uses 2 wires, one for luminance & the other for chrominance signals o Less cross talk Pin 1 Ground (Y) Pin 2 Ground (C) Pin 3 Intensity (Luminance) Pin 4 Color (Chrominance)

o Humans have much higher acuity for luminescence part of images than for the color part of color images. o we can send less accurate color information than must be sent for intensity information Types – Component Video

o Each primary is sent as a separate video signal.

. The primaries can either be RGB or a luminance- chrominance transformation of them (e.g., YIQ, YUV). . Best color reproduction . Requires more bandwidth and good synchronization of the three components Types – Component Video

SONY Bravia KDL-46XBR4 Analog Video

o Represented as a continuous (time varying) signal o Brightness is a monotonic function of the voltage o Sweeping an electrical signal horizontally across the display one line at a time. o Progressive scanning traces through a complete picture (a frame) row-wise for each time interval. o high-resolution computer monitor (1/72 s) Analog Video

Interlaced scanning • The odd-numbered lines are traced first, then the evens. • “odd” and “even” fields make up one frame. • TV and in some monitors • Invented because of transmission limitation (avoid flicker) Analog Video

voltage is one-dimensional (it is simply a signal that varies with time). how do we know when a new video line begins? • a small voltage offset from zero to indicate black. • another value, such as zero, to indicate the start of a line. (blacker-than-black) • synchronization is so important

one scan line of NTSC composite video. Analog Video

The vertical retrace and sync ideas are similar to the horizontal one, except that they happen only once per field. V-sync pulses are composed of pulse trains distributed on several lines NTSC

NTSC (National Television System Committee) TV standard is mostly used in North America and Japan. o It uses the familiar 4:3 aspect ratio o NTSC follows the interlaced scanning system o uses 525 scan lines per frame at “29.97” frames per second (fps). Why 29.97? o 525x29.97 =15,734 lines/sec, 63.6 μs for each line o 10.9 μs (Horizontal retrace)+52.7 μs (active line signal) NTSC

Vertical retrace 20 lines reserved for control information at the beginning of each field (odds or even). 485 active video lines per frame

Horizontal retrace almost 1/6 of the raster at the left side is blanked for horizontal retrace and sync. The non-blanking pixels are called active pixels. NTSC

. analog signal with no fixed horizontal resolution . Pixel clock is used to divide each horizontal line of video signal into samples [240-500].

. composite video signal is a signal in which all the components required to generate a video signal are embedded in a single signal. . The three main components of a composite signal are:

 The luma signal (or luminance)  The chroma signal (or color)  The synchronization signal NTSC

A typical waveform of an all-white NTSC composite video signal

NTSC uses YIQ color model

Quadrature modulation C = I cos(Fsct) + Q sin(Fsct). The frequency of C is Fsc ≈ 3.58MHz

composite = Y + I cos(Fsct) + Q sin(Fsct) NTSC

A typical waveform of an all-white NTSC composite video signal NTSC PAL

PAL (Phase Alternating Line)

. Widely used in Western Europe, China, India and … . Uses 625 scan lines per frame, at 25 frames/second . 4:3 aspect ratio and interlaced fields . Uses the YUV color model . Uses an 8 MHz channel and allocates a bandwidth of . 5.5 MHz to Y, and 1.8 MHz each to U and V.