1. Digital Video
Chapter 6

2. Outline Video = Motion Pictures Analog Television Video
Digital Television Video
Analog vs. Digital Video

3. Animation is different.
What is Video?
Take many pictures per second, sequence them in order, and play them back at about the same rate as they were taken.
Animation is different.
Take/make pictures at a slower rate
then play them back at a faster rate.
Obviously, not live, not real-time.

4. Video Recording How to store it
Technology is pretty much the same as general photography
Optical device that can capture light and store it.
How to store it
Negative film (analog)
Digital device
Magnetic film
Hard drive
Flash memory
Challenge: Video requires taking and storing many picture per second.

5. Motion (moving) Pictures
Motion Pictures: the first widely-viewed form of real life captured video
Captured on Film Stock (Negative Film) – Pioneered
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
Movie Cameras store images on negative film.
Very Mechanical
Lots of moving parts
Surprisingly few electronics
TV Cameras do NOT use negative film
Signal is either
Broadcasted over wires
Saved on Cassette Tapes/Reals

8. Modern TV Camera vs. Camcorder
Higher quality, more expensive
Interfaces with lot of different devices for
Broadcast
Recording
Camcorders
Lower quality all-around
Self contained
Recording device is usually part of the camera.

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 atoms which 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 × 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 Video = Motion Pictures Analog Television Video
Digital Television Video
Analog vs. Digital Video

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

17. Analog Broadcast TV 3 standards for analog television broadcast.
standards = technical details
Encoding format
Transmission format.
Standards include
frame rate
scan lines in each frame.

18. 3 Standards NTSC - National Television Systems Committee
North America, Japan, Taiwan, Caribbean and South America.
PAL - Phase Alternating Line
Australia, New Zealand, Western Europe and Asia.
SECAM - Séquentiel Couleur avec Mémoire
France, the former Soviet Union, and Eastern Europe.
Africa and parts of Asia are mostly influenced by their colonial histories.

19. Frame Rates Video Type Frames Per Second (fps) NTSC 29.97 PAL 25 SECAM
Motion Picture Film 24
NTSC was 30 fps for black-and-white TV, Frame rate was lowered to 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 pixels at 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
Artifact Example

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 covers the 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 ( lines).
The area you do NOT see is called the overscan
TV Broadcast (especially News), has to be careful not to display important information in the 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 Video = Motion Pictures Analog Television Video
Digital Television Video
Analog vs. Digital Video

34. Interlacing & Digital HDTV
An interlaced signal is not meant for LCD and Plasma display technology
LCD and Plasma TVs display an entire frame in one burst (called a refresh).
CRT technology naturally displays lines drawn from top to bottom, rapidly.

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
640 x 480 progressive
24 fps
30 fps
60 fps
640 X 480 interlaced
704 X 480 progressive
704 X 480 interlaced

41. High-Definition Digital TV Signals
1280 × 720 progressive (720p)
24 fps (720/24p)
30 fps (720/30p)
60 fps (720/60p)
1920 X 1080 interlaced (1080i)
60 fps (1080/60i)
1920 X 1080 progressive (1080p)
24fps (1080/24p)
30 fps (1080/30p)

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 Video = Motion Pictures Analog Television Video
Digital Television Video
Analog vs. Digital Video

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
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 rate i.e., 30 frames per second vs. say 60
Quantization Level is still
The color depth i.e., 8 bit color vs. say 24-bit