Scct2013 topic4 video


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Scct2013 topic4 video

  1. 1. OVERVIEW Introduction to Video Analogue Video Digital Video 2
  2. 2. INTRODUCTION TO VIDEO Moving pictures – film and video:  a series of still images presented at a speed that gives the illusion of motion Film uses a photo emulsion that reacts to the different wavelengths that reproduces images  Analog film records images on transparent medium projected onto a screen Video uses electronic circuits to capture information  Analog video records images as continuously varying electrical voltages that produce images on a CRT or projection screen Film and video rely on the trick of human eyes – 3 persistence of vision
  3. 3. INTRODUCTION TO VIDEO CONT… What is video?  A series of electronically captured still images display in rapid succession to achieve the illusion of motion Two types of video:  Analogue  Digital Video vs. Animation? Recall topic 1.1 4
  4. 4. VIDEO SIGNAL Light = electromagnetic radiation The variation in light wavelength that represent brightness and colour can be rendered accurately by electronic circuit. Electronic waveforms signal = analogue signal Analogue video utilizes fluctuations in the electronic waveform to represent brightness and colour. Analogue video signal – continuous signal 5
  5. 5. VIDEO SIGNAL CONT… To capture the electronic waves form digitally, we have to represent them as finite binary numbers. The transformation from waveforms to numbers is never always 100% correct. Digital representation of analog signal has to be balanced between accuracy and functionality. 6
  6. 6. VIDEO – FRAMES AND FRAME RATE Frame rate (Scan rate) – how fast the frames are displayed.  Standard frame rate:  film = 24 fps  25 or 29.97 fps (depending on video standard)  Lowering frame rate (e.g. 8 fps) can result in video with jerky movements or flickers.  Generally, frame rate of 15 fps = natural movement; use for Internet. What happens if we raise the frame rate? 7
  7. 7. VIDEO – RESOLUTION AND ASPECT RATIO Resolution = number of scan lines that fit on screen Aspect ratio = width divided by height 8
  8. 8. VIDEO IMAGE Video image is created by an electron gun in the CRT. The electronic signal illuminates lines of phosphorus dots on the screen. Methods to illuminate or scan the image:  Interlaced scan alternates the scanning between odd numbered lines in the frame and even numbered lines in the frame (NTSC).  Progressive scan scans each line of the image sequentially (computer monitor). 9
  9. 9. VIDEO COLOUR SIGNALSComposite Video Component Video Combines two signals:  Colors are represented  Luminance or amount separately. of brightness in the  Red, Green, Blue light image. signals combine to  Chrominance or color create color range. hue in the image.  Better color quality. Inexpensive to create and transmit. Video captured in component color. NTSC standard = composite color. 10 Computer monitors = component color.
  10. 10. ANALOGUE VIDEO11
  11. 11. ANALOGUE VIDEO Analogue video consist of series of images produced by continuous analogue signals. Ref: 12
  12. 12. ANALOGUE VIDEO In an analogue video signal, each frame is represented by a fluctuating voltage signal. This is known as analogue waveform. Composite analogue video has all its components (brightness, colour, synchronisation information, etc.) combined into one signal. 13
  13. 13. ANALOGUE VIDEO – FORMATS & STANDARDS A broadcast television standard:  NTSC - National Television Standards Committee  Developed in the US and first used in 1954  The oldest existing broadcast standard.  Consists of 525 horizontal lines of display and 60 vertical lines.  Scanning method (interlacing)  Only one type exists - NTSC M.  PAL - Phase Alternating Line  Developed in Germany and first used in 1967.  A variant of NTSC, PAL uses a 625/50-line display.  Different types use different video bandwidth and audio carrier specifications.  Common types are B, G, and H. (Less common - D, I, K, N, & M)  These different types are generally not compatible with one another.  In England and much of Europe 14
  14. 14. ANALOGUE VIDEO – FORMATS & STANDARDS CONT  SECAM - Système Électronique pour Couleur avec Mèmoire.  Developed in France and first used in 1967.  Uses a 625/50 line display.  Different types use different video bandwidth and audio carrier specifications.  Types B and D are usually used for VHF.  Types G, H, and K are used for UHF.  Types I, N, M, K1 and L are used for both VHF and UHF.  These different types are generally not compatible with one another. What’s the TV standard in Malaysia? 15
  15. 15. DIGITAL VIDEO16
  16. 16. DIGITAL VIDEO Digital video uses binary numbers to represent image data Two sources of digital video:  Convert existing analog video to digital.  Create or purchase digital footage. 17
  17. 17. ANALOGUE VS. DIGITALAnalogue Video Digital Video Continuous signal –  Digital or discrete-time fluctuating voltage signal – in binary signal number Reduces in quality over  Stable/enduring quality the time or when  Random access duplicates Linear access 18
  18. 18. DIGITAL VIDEO QUALITY Factors contribute to quality  Screen resolution  Number of horizontal and vertical pixels used to present the video image.  Colour resolution  the number of colours displayed on the screen at one time.  Frame rate - Number of individual video frames displayed per second.  The higher the frame rate, the smoother the video  Compression method  Algorithm used to compress and decompress the video. Developers can adjust these factors to optimize delivery of digital video. 19
  19. 19. SCREEN RESOLUTION Screen resolution (or output resolution) - number of horizontal and vertical pixels used to present the video image.  impacts processing, storage, and transmission requirements. High quality digital video (DV) format is 720 X 480 (or 350,000 pixels at rates of 30fps).  CD-Rom and Internet are too slow to deliver that much data.  Solution: reduce the display size, which reduces the number of pixels/second to output. Why does the video degrade Why is YouTube when viewed at full videos are best at screen? 20 smaller size?
  20. 20. DIGITAL VIDEO - COMPRESSION Compression is key to successful delivery of digital video. Three strategies for compressing video:  Intra-frame: re-encodes within the frame.  Inter-frame: eliminates intervening frames saving only changes between the frames.  Variable bit rate (VBR)  CBR (constant bit rate) assigns same number of bits per second to all parts of the video.  VBR assigns more bits to complex scenes and fewer bits to simpler scenes. 21
  21. 21. DIGITAL VIDEO COMPRESSION Choosing compression depends on:  Output destination  DVD  Internet  Editing capability  Detailed editing tasks  Limited editing tasks  Type of images in video  Complex scenes  Similar scenes 22
  22. 22. INTRA-FRAME Lossless strategy could be Run-length encoding (RLE).  Result: smaller more efficient file with all the original data. Lossy strategy commonly used is M-JPEG.  Individual images are compressed and linked together as motion sequences.  Best for video editing as every frame is preserved despite data being lost from each separate frame. 23
  23. 23. INTER-FRAME MPEG compression identifies:  I-frames: "intra-frame" or complete compressed frames  P-frames: predictive frames record more significant changes.  B-frames: bidirectional frames record smaller changes between the I and P frame. Good choice for distributing video. Not appropriate for recording and editing video 24
  24. 24. VARIABLE BIT RATE Constant Bit Rate encoding uses same number of bits per second for simple and complex video. Variable Bit Rate assigns more bits to complex scenes and fewer bits to simpler scenes.  Common option in video editing software. 25
  25. 25. COMMON VIDEO CODECS MPEG  MPEG-1 (short videos on Video CD—optical disc format).  MPEG-2 (transmission of video for television).  MPEG-4 (video over the web). M-JPEG (less-compressed higher quality files without inter-frame loss) RealVideo (proprietary codec for streaming video on web) DV (uses M-JPEG, suitable for authoring or 26 archiving)
  26. 26. DIGITAL VIDEO - FORMATS & STANDARDS Developers use these  Common video file formats to render the final formats project in a form suitable for  Windows Video file (.avi) delivery  D1  Movie file (.mpg or .mpeg)  D2 and D3  Windows Media Video file (.mwv)  DV  CD Video  MPEG-4 file (.mp4)  DVD video  QuickTime Movie file  Quicktime (.mov, .qt)  Video for Windows  Any others?  Real Video. 27
  27. 27. DIGITAL VIDEO CHALLENGES Large file sizes  Every second of uncompressed digital video requires 30MB of storage. Hardware performance  Computer processors, memory and bus size must deliver digital video to the screen at full motion frame rates. Distribution methods  DVD players.  High speed network bandwidth Digital video made possible by:  Compression algorithms  Fast computer hardware  DVD storage  Gigabit bandwidth. 28
  28. 28. DIGITAL VIDEO Quality is long lasting Quality for duplicates is almost the same as the original Allow random search/access of content Can be compressed for better and easier storage and distribution 29
  29. 29. MORE ON VIDEO..Things to consider: When to use  When video can say something that would be impossible or difficult to say with medium such as graphics, photos, or text. Where to place  In the page  In a separate context User Interaction with Video  No control – video play immediately  User control – play/stop buttons 30
  30. 30. USES OF VIDEO Consumer use  Corporate Use  Television  Corporate video  Home entertainment  Live video / video on  Etc.. ? demand  Video surveillance system 31
  31. 31. SUMMARY Introduced video – definition and concept Two categories of video Ref and Readings:    Barfield, L. (2004). Design for New Media: Interaction design for multimedia and the web. Essex, England: PearsonAddison Wesley. 32