1 / 46

Digital Video

Digital Video. Chapter 6. Outline. What is Video?. Video Recording. Motion (moving) Pictures. Motion Pictures: the first widely-viewed form of real life captured video Captured on Film Stock (Negative Film) – Pioneered 1900-1920 Still used today. Television.

blade
Télécharger la présentation

Digital Video

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Digital Video Chapter 6

  2. Outline

  3. What is Video?

  4. Video Recording

  5. Motion (moving) Pictures • Motion Pictures: the first widely-viewed form of real life captured video • Captured on Film Stock (Negative Film) – Pioneered 1900-1920 • Still used today

  6. Television • Real-time Analog Signal transmitted over a wire • Pioneered 1950 • At first, TV was only live. • Later, stored on Magnetic Tapes and re-broadcasted • Pioneered 1956 • Even Later, TV signals and Movies stored on Consumer VCRs and VHS cassette tapes – 1971 • VCR – Video Cassette Recorder • VHS – Video Home System

  7. Movie Cameras vs. TV Cameras

  8. Modern TV Camera vs. Camcorder

  9. Digital Movies • Most major motion pictures are still shot on negative film (analog technology) • Film is high resolving medium (as good as the best digital capturing technology) • Academy camera US Widescreen: • 21 × 11 mm 2970 × 1605 • Anamorphic Panavision ("Scope"): • 21 × 17.5 mm 2970 ×2485 • Super-35: • 24 x 10 mm 3390× 1420

  10. Digitizing Film • Converting the Film (analog) to digital form. • Film Scanners are used • Prices range from $100 to $20,000 • Google “Negative Film Scanners”

  11. How Film Works • Film has millions of light-sensitive silver halide crystals (silver + halogen) • held together by electrical attraction. • When crystals are struck by light, silver ions build up uncharged atomswhich forms a latent image • Developing chemicals create a visible image by building up the metallic silver where ever the uncharged atoms formed, i.e., the latent image.

  12. Film Width • Each image is stored sequentially on film role. • To achieve higher resolution, you can increase the width of the film • Only part of the width can be used to capture images 35mm 21mm

  13. Film Width & Orientation • 35mm Film can achieve High Definite (HD) resolutions • HD Wide Screen 1920+ × 1080+ • 70mm can go way beyond the HD seen on BluRay and HD DVD. • IMAX used 70mm film and changes the orientation. • 10000 X 7000 is possible.

  14. Direct Digital Capture for Movies • Digital Video Cameras are just starting to be widely used for filming movies • Speeds up the processing. • Eliminates a step: Film  Digital Media Storage • Digital editing can immediately begin • Interestingly, in Hollywood, there is great resistance to direct digital capture • Union resistance • Puts technicians out of work

  15. Outline

  16. Analog TV Broadcast • Is now ancient history, as of February 2009. • Or is it?

  17. Analog Broadcast TV

  18. 3 Standards

  19. Frame Rates NTSC was 30 fps for black-and-white TV, Frame rate was lowered to 29.97 fps to accommodate for color encoding.

  20. Lines • Old televisions (CRT technology) are made up of horizontal lines. • Lines are drawn (refreshed) across the screen one line at a time. • NTSC frame: 525 lines (480 picture safe zone). • PAL and SECAM frames: 625 lines (576 picture save zone).

  21. Columns? • The signal breakdown into lines (rows) is needed for CRT technology to properly display the picture • In principle, the rows could have been continuous and the signal could be broken down into columns

  22. No Pixels • Analog video signals transmit each line as a continuous signal, i.e., no pixelsat all. • The only reason the signal is broken down into rows is for 2D display on a CRT. • The laws of physics limit how fast the electrical signal can be sent, the resolution is only limited by the speed and density of the signal.

  23. Progressive Scan vs. Interlacing • Progressive Scan: Computer monitors (CRT) display lines from top to bottom in one pass. • Interlacing: Television Standards (NTSC, PAL, and SECAM) display the picture in two passes: • first pass is odd-numbered lines (upper field) • second pass is even-numbered lines (lower field)

  24. Interlacing – Progressive Scan

  25. Interlacing • The original video may have had all the lines (odd and even) for each frame • But, the broadcast signal only includes half the lines for each frame • Each frame alternates • Frame 1 odd lines • Frame 2 even lines • Frame 3 odd lines • Frame 4 event lines • …

  26. Why Interlace? • It removes the flicker effect, without the need to increase the frame rate. • Progressive Scan at 15 frames per second flickers, i.e., a noticeable blinking, like a strobe light. • To remover the flicker, you’d have to increase the frame rate, which would require sending more data • 24+ frames per second instead of 15.

  27. Refreshing • 60 Hertz • each pixel is refreshed 60 times per second. • With Interlacing, you only have to refresh a pixel 30 times a second with no noticeable difference. Time

  28. Refreshing • Interlacing + latency Time

  29. Interlacing Artifacts Upper Field & Lower Field Demo • http://media.pearsoncmg.com/ph/esm/esm_wong_dmp_1/chapter06/ylwong-video-interlace-fields.html Artifact Example • http://media.pearsoncmg.com/ph/esm/esm_wong_dmp_1/chapter06/ylwong-dv-interlace-demo.mov

  30. Overscan • CRTs distort the signal near the edges the picture tube. • Caused by noise in the signal • By design, the plastic frame of the TV coversthe distorted area. • The size of the covered area depends on the quality of both the CRT and the signal

  31. Overscan & Save Zones • For NTSC The signal sent is larger (525 lines) than what you see (480-520 lines). • The area you do NOTsee is called the overscan • TV Broadcast(especially News), has to be carefulnot to display importantinformation inthe overscan area. • 480 lines is the save zone

  32. TV Color Format • Remember how Digital Images were encoded using RGB or CYMK. • Analog TV actually breaks the color signal into only two parts • Luminance (Brightness) • Chrominance (Hue/Color) • When there were only B&W TV’s the signal was only a luminance signal. • Chrominance was added later and it lengthened the signal, which decreased the Frame rate.

  33. Outline

  34. Interlacing & Digital HDTV

  35. Interlacing & Digital HDTV • While LCD technology can achieve refresh rates of over 200 Hertz (200 frames per second)… • The problem is that an analog TV signal is interlaced (sends half the lines 30 times a second). • Also, until recently TV signals were analog.

  36. Analog  Digital Problem • With an analog signal, LCD or Plasma TVs have to • Wait for two frames (odd lines then even) and put them together, or • Interpolate (approximate) the missing lines Both require added hardware One of the reasons these TVs are more expensive One of the reason they should be cheaper in the future, i.e., no need to worry about analog signals anymore

  37. Which do you think is better? • Wait for two frames (odd lines then even) and put them together, or • Interpolate (approximate) the missing lines

  38. Interpolation

  39. HDTVs and Analog Signals • The video quality of HDTVs (high resolution LCD or Plasma) appears poor when given an analog signal. • Because the • Interlaced signal need to be interpolated to a progressive signal (now a minor issue) • Signal can only be up-converted to a NTSC safe area frame 640 X 480 • Consider that a 20” LCD ($150) has 1280 X 1024 pixels. Over 4 times as many pixels as the received signal. • Buying an HTDV without a digital video source is a waste of money.

  40. Standard-Definition Digital TV Signals

  41. High-Definition Digital TV Signals

  42. What Signal will be transmitted when Broadcast TV goes Digital? • It can be any one of the Standard or High Definition formats I just listed. • 720/24p will probably be the standard definition default • 1080/24p will likely be the HD default • 1080i was supposed to be used because it works nicer with CRTs, but CRTs will be phased out of existence soon. • Depends on the TV network’s system or your signal provider. • TV Network = ABC, NBC, Local Affiliates, etc. • Signal provider = DirectTV, TimeWarner, etc.

  43. Outline

  44. Analog Video Signal • The details here are not 100% correct, but the principle is… • Like the Bohr Model of the Atom • Think of an analog TV signal as a wave • The amplitude (height) indicates the brightness • The frequency (pattern) indicates the color • A segment of the signal generates a line on the CRT

  45. Digital TV Signal • This is closer to being 100% correct • Think of a digital signal as a wave • Where wave/no wave indicate 1 or 0 • 1 0 0 0 0 0 1 1 0 1 0 0 1 0 0 1 1 1 0 0 • Each frame is encoded as bitmap/raster image just as we previously studied. • Color is RBG 24-bit • Obviously, compression is used

  46. Digital Video Fundamentals • Sampling rate is… • Capture resolution or each frame i.e., 640 X 480 vs. say 1920 X 1080 • Capture ratei.e., 30 frames per second vs. say 60 • Quantization Level is still • The color depthi.e., 8 bit color vs. say 24-bit

More Related