Lecture 03: Multimedia Data (Video)

Transcription

1 Lecture 03: Multimedia Data (Video) Date: Prof. Pallapa Venkataram PET Unit, Dept. of ECE, Indian Institute of Science, Bangalore

2 Organization: Multimedia Data (Recap of Image and Audio) Color in Image and Video Color models in images and video Multimedia Data: Video Types Formats Analog and Digital Video

3 Recap (Lecture 02) Graphics and Image Data Data Types: 1-bit, 8-bit gray, 24-bit color, 8-bit color File Formats GIF, JPEG, PNG, TIFF, PS and PDF Audio Sampling Theorem, SNR, SQNR Musical Instrument Digital Interface (MIDI)

4 Color in Image and Video

5 Color Models in Images Color Models in Images RGB Color Model for CRT displays A color in the RGB color model is described by indicating how much of each of the red, green, and blue is included. The color is expressed as an RGB triplet (r,g,b), each component of which can vary from zero to a defined maximum value. If all the components are at zero the result is black; if all are at maximum, the result is the brightest representable white.

6 Color Models in Images Color Models in Images Subtractive Color: CMY Color Model This stands for cyan-magenta-yellow In contrast to color on the monitor, the color in printing acts subtractive and not additive. The C-M-Y coordinates are just the complements of the R-G-B coordinates. Transformation from CMY to RGB,

7 Color Models in Videos YUV Color Model Color Models in Video YUV codes a luminance (luma) signal equal to Y (for gamma corrected signals) Chrominance (chroma) refers to the difference between color and luminance. U = B Y V = R Y

8 Color Models in Videos YUV Color Model Color Models in Video

9 Color Models in Videos YIQ Color Model Color Models in Video YIQ is used in analog NTSC color TV broadcasting I and Q are rotated version of U and V

10 Color Models in Videos YCbCr Color Model Color Models in Video Digital video uses YCbCr model closely related to YUV YUV is changed to YCbCr by scaling Cb and Cr shifted between 0 and 1.

11 Video Data: Types of Video Signals Analog Video Digital Video

12 Component video Types of Video Signals High-end video systems, such as for studio Three separated video signals --Red,Green and Blue image plane Three wires connecting to Camera or other devices to TV or monitor Giving the best color reproduction No crosstalk between the different channels Requiring more bandwidth and good synchronization Besides RGB, YIQ, YUV and other model can be used

13 Composite video Types of Video Signals Chrominance and luminance signals mixed into a single carrier wave Chrominance --I and Q ( or U and V) Only one wire some interference Used by broadcast color TV, downward compatible with black-and-white TV In NTSC TV,I and Q combined into chrominance signal, at the higher frequency end of the channel.

14 S-video Separated video or Super-video Types of Video Signals Two wires: One for luminance and Another for a composite chrominance Less crosstalk Black and White: crucial for visual perception Humans better spatial resolution for grey-scale image Color information less accurate

15 AVI Format Windows Media Format MPEG Format QuickTime Format RealVideo Format Shockwave (Flash) Format Formats

16 Analog Video Analog signal : f(t) time-varying images Progressive scanning Scanning a complete frame row-wise for each interval High-resolution monitor an interval of 1/72 second Interlaced scanning Odd-numbered lines first, then even-numbered lines odd and even fields make up a frame Reducing perceived flicker High-speed action image blurred Vertical retrace and horizontal retrace Two-dimensional scene transformed into one-dimensional signal.

17 Analog Video Scan lines Object resolutions and bandwidth

18 Analog Video Television Standards for analog TV NTSC Video: USA, Canada, Japan and Korea PAL Video: Germany, England and China SECAM Video: France, Russia Downward compatible with black-and-white TV system Parameters Consistence: scan method, scan row-frequency, field frequency, frame frequency, image carrier-frequency, audio carrierfrequency Signal transmission Consistence: Luminance signal, two chrominance signals.

19 Analog Video NTSC Video: National Television Standards Committee 4:3 length and width ratio; 525 line per frame; 30 frames per second (30 fps); Horizontal scan frequency, =15,734 lines; Horizontal scan,1/6 of raster reserved; Horizontal resolution sample number per line; Time per line:1/15,734=63.6usec ( ); Interlace scan,262.5lines/fields;

20 Analog Video NTSC Video: National Television Standards Committee

21 Analog Video NTSC Video: National Television Standards Committee The spectrum shows: The picture carrier at 1.25MHz, total bandwidth 6MHz The color subcarrier F sc 3.58MHz, high-end of the channel, the center frequency =4.83MHz Audio carrier 4.5MHz, center frequency =5.75MHz

22 Analog Video PAL Video: Phase Alteration Line 625 scan lines, 25 frames/second, 4:3 aspect ratio Color Model YUV,Y Luminance, U and V Two Chrominance Y = 0.299R G B U = R-0.289G B V = 0.615R G B In PAL standard: Y with bandwidth 5.5 MHz, U and V with bandwidth 1.8 MHz respectively HDTV (High Definition Television): Y and U, V have the same bandwidth

23 Analog Video Comparison of NTSC, PAL and SECAM

24 Standards distribution Analog Video

25 Digital Video Advantages of digital representation Storing video on digital devices or in memory Ready to be processed and integrated into various multimedia applications Direct access Repeated recording without degradation of quality Ease of encryption and better tolerance to channel noise

26 Chroma subsampling Digital Video Human vision : see color with less resolution than Black and White Per four original pixels, how many pixel values really sent? 4:4:4 indicates no subsampling 4:2:2 indicates horizontal subsampling of Cb and Cr with factor 2 4:1:1 indicates horizontal subsampling of Cb and Cr with factor 4 4:2:0 indicates horizontal and vertical subsampling of Cb and Cr with factor 2, respectively 4:2:0 scheme generally used in JPEG and MPEG

27 Chroma subsampling Digital Video

28 Digital Video Digital video CCIR standard CCIR (Consultative Committee for International Radio) CCIR-601 : one important standard for component digital video, further become ITU-R-601 standard For NTSC standard: 525 lines;858 pixels (where, 720 is visible); 4:2:2 scheme; One pixel --two bytes; CCIR 601(NTSC)date rate: bytes 8bits/byte 216Mbps

29 Digital Video Digital video CCIR standard

30 Digital Video CIF standard CIF - Common Intermediate Format The idea of CIF: a format for lower bit-rate QCIF - Quartar-CIF, more lower bit-rate The resolution of CIF/QCIF can be divided by 8 or 16

31 CIF standard Digital Video

32 High Definition TV Digital Video The first generation HDTV based on analog signal, in the late 1970s by Sony and NHK 1,125lines;60fields/second (Interlaced) 16:9 aspect ratio; DBS (Direct Broadcast Satellite); 24 Mhz 1995,ATSC (Advanced Television System Committee) Digital TV standard recommended by FCC( Federal Communication Commission) ACATS (Advisory Committee on Advanced Television Service) MPEG2 Chosen as the compression standard Main Level to High Level of the Main Profile AC-3 for Audio; 5.1 channel Dolby surround sound

33 Digital Video Digital format support by ATSC

34 Questions

35 Thank You