Video

1
Video

• And by this I mean Digital video.

2
Process

• Process is as complex as the project
• But basically
• Planning
• Shooting
• capturing
• Editing
• Post production
• distribution

3
Planning

• Well come back to this in practical sessions.

4
Shooting

• Shooting footage is the process of recording
  images
• With digital video there are a number of
  recording options
• DV tape
• Memory sticks
• Internal hard drives
• External hard drives
• By far the most common method is recording to DV
  tape.

5
The technology

• DV (digital video) cameras record video data
  directly as digital data
• Some video creators still prefer analogue
  technologies because they give a certain look and
  feel to the recorded footage
• But much footage recorded on analogue devices is
  converted to digital files for the editing
  process.

6
The technology

• Digital video like digital audio allows for
  reproduction and repeated transfer between
  technologies without the loss of quality
• Copying analogue information often causes
  information loss and so degrades the footage
• The breakthrough in digital video was the high
  bandwidth transfer from recording device to
  editing software
• Usually done now through IEEE 1394
  firewire/I-link specification
• USB2 almost as good
• All pcs on 5th floor have firewire

7
Digital Video Cameras

• Images as photons (basic unit of light) are
  focused by a lens on a detector
• Usually detector is a CCD Charged Couple Device
• Has thousands of tiny sensors which when struck
  by photons create an electrical charge.
• The amount of this charge is converted into a
  digital value and then recorded
• Good at this point to remember that light is not
  digital so the recording process creates a loss
  of information
• There are strong arguments about how much this
  matters both with video and audio

8
Digital Video Cameras

• Quality issues
• The CCD
• Better cameras have multiple CCDs
• colour information on single ccd cameras is
  gained by RGB filters over the ccd
• 3 CCD cameras have one CCD for each colour
  R,G,and B and the incoming light is split off to
  each CCD using a prism
• Better quality CCDs have a greater density of
  sensors
• Larger CCDs are needed for larger lenses

9
Digital Video Cameras

• Interlacing
• Televisions produce(d) images in the past (and
  still do now to a greater or lesser extent) by
  scanning a beam of electrons on the inside
  surface of the screen
• Scan travels from left to right
• From bottom to top
• The frequency of the electrical power (its not a
  continual stream) comes in the UK at 50 hertz (50
  pulses a second)
• The image fades before another pulse to redraw
  can be utilised this causes flickering
• Developed a method of interlacing 2 fields
• So each image made up of 2 interlaced images, one
  drawn very rapidly after the other
• This stopped the picture flickering on the screen

10
Digital Video Cameras

• Interlacing

11
Digital Video Cameras

• Interlacing
• Video cameras as a legacy of this interlacing,
  capture 2 fields.
• They capture 30 fps but actually capture 60
  images a second, each frame being constructed
  from 2 passes which make these 2 fields
• Modern display devices no longer require this
  interlacing but it still survives mostly for
  commercial and political reasons

12
Digital Video Cameras

• Interlacing so what?
• Not an interesting aside because interlacing has
  repercussions.
• Computer generated moving images, such as those
  made in 3D programs dont need to be interlaced.
  And by default arent because single passes where
  the whole frame is rendered give better quality.
• Causes issues when compositing high quality CGI
  and live footage

13
Digital Video Cameras

• Progressive scanning
• Good DV cameras now offer 24p (mostly in US, we
  get 25p)
• Record 24 frames per second in progressive mode
  i.e. the whole frame is captured in one pass.
• Progressive scanning allows for a much better fit
  between shot footage and CGI.
• Interlaced frames can make editing difficult
• 24fps is the standard for motion pictures (film)
• In the past, digital video was never considered
  of broadcast quality but with the advent of high
  quality CCD technology and progressive scanning
  at 24p it now is

14
Digital Video Cameras

• PAL and NTSC video standards
• Phase Alternation by Line (perfect at last)
• Parts of Europe including UK
• National Television Standards Committee (never
  the same colour)
• USA and Americas
• Both are analogue systems which further compound
  the anachronistic fit between tv output and DV
  recording

15
Digital Video Cameras

• PAL
• 625 scanned lines in fields at 50hz
• Only 576 of these lines carry image
• The fields are refreshed 50 times per second
• Giving 25 frames per second
• Cine film is 24 fps so little problem displaying
  cine films but are slightly speeded
• Bigger issue with NTSC which is approx 30fps

16
Digital Video Cameras

• PAL
• There are 720 pixels and 576 lines
• 1.251
• So the ratio is not the same as a standard
  television screen which is 43
• 1.331
• For this reason, DV pixels are not square but are
  thinner to fit on a standard 43 screen
• This is known as the pixel aspect ratio

17
Digital Video Cameras

• PAL
• Cameras often offer 2 aspect ratios for
  recording, 43 or 169
• 43 Standard
• 169 widescreen
• Need to be sure of how you wish to output your
  video when shooting as a 169 aspect ratio gives
  1.771 which means that the pixels have to be
  wider to fit the 43 aspect ratio of a standard
  tv.
• 169 closer to the cine aspect ratio of 1.66 1

18
Digital Video Cameras

• HD
• Coming soon
• 1920x1080 much more detail possible will be
  digitally transmitted, not as analogue signals
• Need better displays
• Expensive cameras at the moment.
• Sony, Canon making hand held ones for under
  1000!

19
Lenses

• The quality of these can have great impact on the
  quality of footage and the price of the camera..
• Commonly fitted with motor driven zoom lenses
• Zoom lenses simply mean the focal length can be
  altered
• This might mean they can act as telephoto lenses
  bringing distant objects closer but restricting
  the depth of field
• Or macro lenses, allowing close-ups of small
  objects
• Zoom lenses described in terms of the spread
  between their longest and shortest focal lengths
• So a lens that can zoom between 100 and 400 mm is
  know as a 4x zoom.
• More expensive for larger range.
• Digital zoom is a trick, it simply enlarges the
  image that was captured and so results in a
  poorer quality image
• Its basically a process of cropping the image

20
Features

• Most DV cameras offer standard features such as
  switching between auto and manual modes for focus
  and exposure control
• Some offer image stabilisation which reduces
  jitters due to camera shake
• Optical stabilisation is much better that digital
  stabilisation which often causes a reduction in
  quality
• New systems float the CCDs in a shockproof
  liquid

21
Features

• Zebra stripes are a useful feature for checking
  overexposure banding appears on image areas
  where the white balance is too high
• The ability to switch off colour viewfinders is
  also very useful as it is much easier to get
  light levels and focus correct in monochrome
• CCDs are usually infra red sensitive so some dvs
  come with built in infrared light for night
  shooting

22
Audio

• Almost all DV cameras allow audio capture but
  built in mics are usually poor quality even if
  audio can be recorded at 48Khz (better than CD
  quality)
• Options for external mics are very useful.
• Poor quality audio can ruin good visual footage
• Or consume vast quantities of time and effort
  later making it right
• Can always record onto better audio devices and
  edit the audio later.