TV Technology

1
TV Technology

• DSIM Week 7

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Lecture Outcomes

• Light and The Eye
• TV Global standards PAL, NTSC, Secam
• Interlaced and Progressive scan images
• The TV signal
• Sampling explained
• Video Compression (colour subsampling)
• High Definition Video

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What is Light?

• Light is made up of different wavelengths of
  energy.
• Colour we see falls into the bracket of the
  visible spectrum.
• Red has the longest wavelength and blue has the
  shortest.

4
Light Theory

• White light is actually made from a mixture of
  full red, full green and full blue wavelengths as
  shown below.
• RGB can make all colours in the visible spectrum.
  Mixing pairs of the primary colours makes the
  secondary colours (cyan, magenta and yellow).

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How We See Light The Eye

• Light is gathered through the pupil and focused
  by the lens onto the retina.
• The retina is covered in light sensitive cells
  called rods and cones.
• Tiny electrical pulses are sent down the optical
  nerve to the brain where they are assembled into
  an image.

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How The Eye Deals Detects Light

• 95 of the retina is made of rods and are
  sensitive to luminance (brightness/intensity/black
  or white info) and work at low light levels
  only.
• 5 of the retina is made of cones that are
  sensitive to chrominance (colour) and work in
  only good light levels.
• This is why in darkness we see black and white
  and edges.

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The Eye

• There three cones are all sensitive to a
  different wavelengths of light.
• We have cones sensitive to red, green and blue
  light.
• We are most sensitive to green, less to red and
  even less to blue.
• We actually see 60 green, 29 red and 11 blue
• All video devices work on the same principles as
  the eye and because we are least sensitive to
  colour. This is where the most compression is
  used. This is explained more further on in this
  presentation.

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TV Display Basics

• The television lights up by thousands of tiny
  dots of phosphors with 3 high-energy beams of
  electrons.
• In most systems, there are three phosphor colours
  -- red, green and blue -- which are evenly
  distributed on the screen.
• By combining these colours in different
  proportions, the television can produce the
  entire colour spectrum.

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What Colour Systems do Cameras and TVs use?

• Standard televisions use 8bit RGB colour
• A low to mid range video camera uses 8bit RGB
  too.
• A top end camera uses 10bit RGB (like our studio
  cameras and digital betacam)

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How a Camera deals with light

• RGB is split via a prism onto its corresponding
  CCD
• The data sent to a colour matrix where it is
  converted into luminance and chrominance.

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The CCD charge coupled device

• They come in 2 sizes
• 2/3 inch CCDs (high end broadcast cameras)
• 1/3 inch CCDs (DV cameras)
• 2/3in have more photoreceptors per chip (average
  about 400,000). Less than half a megapixel. You
  could state this is the DPI of the CCD.
• 1/3in average about 200,000 to 330,330. About a ¼
  of a megapixel in digital camera terms.

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Global TV Standards and Frames Sizes
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Global TV Standards - NTSC

• NTSC TV
• National Television Standards Committee
• Used in North and Central America and Japan
• 525 lines of horizontal resolution
• Runs at 60Hz of vertical frequency (60 cycles per
  sec) at 110 volts of AC

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Global TV Standards - SECAM

• SECAM
• Sequential Couleur Avec Memoireor Sequential
  Colour with Memory
• Used in France, Iran and Iraq to name a few
• 625 lines of horizontal resolution
• Runs at 50Hz of vertical frequency (50 cycles per
  sec) at 220 volts of AC
• Adopted in 1967

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Global TV Standards - PAL

• PAL TV
• Phase Alternative Line
• A German invented system
• Used in most of Europe, Africa, Australia, and
  South America
• 625 lines of horizontal resolution
• Runs at 50Hz of vertical frequency (50 cycles per
  sec) at 220 volts of AC

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Global Electricity Standards

• Australia 230V 50 Hz
• Canada 120V 60 Hz
• France 230V 50 Hz
• Hong Kong 220V 50 Hz
• Japan 100V 50 Hz (Eastern Japan)
• Japan 100V 60 Hz (Western Japan)
• Mexico 127V 60 Hz
• Singapore 230V 50 Hz
• South Africa 220 / 230V 50 Hz
• USA 120V 60 Hz
• United Arab Emirates 220V 50 Hz
• http//kropla.com/electric2.htm

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Standard Definition TV Frame Sizes

• What frame size is an analogue PAL TV image?

768 x 576
What frame size is a digital PAL TV image?
720 x 576
A Pal TV runs at how many individual images per
second?
25
A NTSC TV runs at how many images per second?
29.97 its common to round it up to 30fps
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Whats Better PAL or NTSC?
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Pal V NTSC data rate per frame comparison

• PAL is 25fps whilst NTSC is 30fps
• NTSC and PAL have the same date rate per second
  but why is PAL better quality?
• Well the data per frame is 20 higher than NTSC

This is not all too see the next slide
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Pal V NTSC lines of resolution

• Pal has 625 individual lines making up the 25
  frames.
• NTSC has 525 individual lines making up the 30
  frames.
• So per frame PAL has 100 more lines of vertical
  resolution per frame (or 16 more).

So PAL has 16.7 more data per frame and 16 more
vertical resolution per frame than NTSC.
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What happens when NTSC and PAL are transferred to
Film?

• Film 24fps NTSC is 30fps PAL is 25fps
• NTSC needs a 20 reduction (24/30x10080 or 20
  less) in the numbers of frames. So 6 frames per
  second are dropped.
• PAL needs a 4 reduction (24/25x10096 or 4)
  and so drops just one frame per second.
• So whats better for video to film transfer?

PAL OF COURSE!!! Remember PAL has 16 more data
per frame too
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Interlacing and Progressive Scanningexplained
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Interlaced Scanning

• The image is made up of 625 individual lines and
  therefore the TV set draws 15,625 lines per
  second (625x25)

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Interlaced Scanning

• Half of the 625 lines are drawn first. This is
  called field 1.
• The first field draws is called the odd field as
  it draws the odd numbers 1,3,5,7, etc
• The second half of the lines are called field 2
  and this draws the even numbered lines 2,4,6,8
  etc
• This is also called 50i recording, for 50
  interlaced images per second.
• Field 1 and Field 2 1 Frame

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Interlaced TV Image
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Progressive Scan

• A progressive scan draws each of the scan lines
  one after another in numerical order e.g.
  1,2,3.625
• This gives a sharper image that an interlaced
  image.
• This is called 25p recording.
• There are no fields in a progressive scan just a
  single frame.

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Progressive Scan (De-interlaced image a field
removed)
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(No Transcript)
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InterlacedScan
Progressive Scan
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25p Cameras

• The Panasonic AXG DV100 can record a 25p image.
  How does it do this?
• It only records the first field and then copies
  this to the second field.
• Progressive scan images are sharper and clearer
  because the are full frame scans.
• These cameras produce a higher quality image than
  the Canon XL1s because the CCDs have more
  photosensors per chip.
• You can use these in third year.

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To understand this you need to understand what a
single scan line is and how it works.
You now understand how a TV draws a picture but
how can a waveform make a TV picture?
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Scan Line TV Signal

• This is an electronic signal for one scan line
  of a single TV picture.

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TV Signal

• The signal contains all the
• luminance information
• the colour info
• the retracing information

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Scan Line TV Signal

• The majority of this signal is the luminance
  (brightness/intensity) level of the picture that
  the TV is drawing.
• The colour information is also combined into this
  signal in the colour burst.

Key Back PorchThe area of a composite video
signal defined as the time between the end of the
colour burst and the start of active video. Also
loosely used to mean the total time from the
rising edge of sync to the start of active
video. Front PorchThe area of a composite video
waveform between the end of the active video and
the leading edge of sync.
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Active Video

• The active video signal is a waveform that shows
  the brightness/intensity level of the picture.
• The lowest level represents a black or very dark
  image. This is a 0.5 volt signal.
• The highest level represents white and is the
  maximum brightness. This is a 2v signal.
• A waveform in this area will be continually
  rising and failing depending on the image it is
  drawing unless its a white picture or a black
  picture.

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Question

• For a single scan line of video draw the graph
  which would represent the varying voltage of the
  image below.

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Sync Tip / Horizontal Retrace

• The sync tip or horizontal retrace is what tells
  the electron beam to end the current scan
  (picture) line its drawing and move back to the
  left hand side of the screen to start to draw the
  next line.

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Colour burst

• The colour information is added to the luminance
  signal.
• It is a sine wave with the different colours
  being identified by the phase difference between
  it and the colour burst reference signal.

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What is In Phase and out of Phase
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Phases changed explained

• The top and bottom sine wave are out of phase.
• The top signal is the reference signal e.g the
  starting signal.
• Depending on what degree out of phase the colour
  signal is determines the electronics in the TV
  drawn a different colour,.

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Colour Burst

• Depending on how out of phase the colour signal
  is compared to the reference signal a different
  colour will be drawn.

Notice the colours are RGB (primary) and Cyan,
Magenta and Yellow (secondary)
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Colour bars

• Why use colour bars?
• They are used for matching the output of two
  cameras in a multi-camera shoot and to set up a
  video monitor. They are made up from the primary
  and secondary colours.

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Recording Signals through Sampling

• How does sampling a signal actually work?
• Sampling is the process used to convert an
  analogue signal into its electrical and
  equivalent.
• Recording devices translate sound or light into a
  voltage.
• The decimal number recorded is then converted
  into its binary (0 and 1s) equivalent. This is
  called analogue to digital conversion.

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Sampling Made Simple

• To reproduce this signal we have sampled it at 4
  sample points.
• We have a 1 signal split into 8 possible voltage
  points.
• Whats the bit depth of this scale?
• 238
• We amount of times per second we sample is called
  the frequency. In this case its 4 or correctly
  termed 4Hz

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Sample Plot Table
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What happens when we reproduce this waveform from
the sampled points?
As you can see with such a low sampling frequency
the waveform cannot be accurately reproduced.
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How could we reproduce the signal accurately?

• Increase bit depth and increase the sampling
  frequency
• CD quality audio is sampled at 44100 times per
  second at a bit depth of 16bit (65536 levels to
  break up the 1 voltage)
• This means a very accurate signal can be
  reproduced.
• The voltages recorded at then converted into
  digital numbers (binary 0s and 1s) and stored.

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What rate is Video Sampled?

• Video is sampled at these following rates
• 444 at 10bit Latest Sony FDW 9500 and Thompson
  Viper only
• 422 at 10 bit Our Studio Camera / Digital
  Betacam
• 411 at 8 bit NTSC DV cameras
• 420 at 8 bit PAL DV Cameras
• This is called Colour Subsamping

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What does 422 actually mean?

• Firstly, this is a ratio
• The first 4 represents the luminance and is said
  to be sampled at fully.
• The 22 are the colour components (red and blue)
• The second number is the red component and is
  sampled at half the rate of the luminance
• The third number is the blue component and is
  sampled at half the rate of the luminance.
• The luminance video sampling frequency is
  actually sampled at 13.5Mhz (13.5 million times
  per second)
• The colour is therefore half of 13.5Mhz 6.75

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What does this result in?

• Already you only have 50 of the colour being
  sampled compared to black and white info.
• Why? Well are eyes are less sensitive to colour
  (remember 95 of our vision is b/w)
• What are the effects?
• Less detail in the colour grading of shadows and
  less tints.

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More 422

• However, remember 422 is 10bit.
• So there are 1024 shades of RGB coming off the
  cameras image recording device (CCD). This does
  reproduce very accurate colour.
• On the downside Film can be said to be 444
  because it is uncompressed and does not do
  selective sampling like video.

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What does 411mean?

• Remember this is 411 at 8 bit
• Luminance is fully sampled
• Red and blue is sampled at a quarter of the rate
  of luminance.
• So already you only have 25 of the colour being
  sampled on each of the scan lines.
• Thats 13.5Mhz sampling on the luminance, and
  3.75MHz on the colour.
• 411 cameras are used for NTSC TV only
• There are only 256 shades of RGB too as its 8
  bit!
• So what are the knock on effects? Well its not
  good to do a chroma-key with a 411 as theres
  hardly any colour!

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What does 420 mean?

• Remember this is 420 at 8 bit
• Luminance (y) is sampled fully
• What does the 20 part mean?
• Well, the red and blue are sampled at half the
  resolution of the luminance.
• But only the red content is sampled on field 1.
  Blue is sampled on Field 2.
• So Y is sampled at 13.5Mhz and red and blue are
  sampled at 6.75Mhz but alternating between red
  and blue depending on the field.

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420 continued

• All DV cameras (Canon and Panasonic) are 420 at
  8 bit
• There are only 256 shades of RGB too as its 8
  bit!.
• So what are the knock on effects? Well its not
  good to do a chroma-key with a 420 as theres
  hardly any colour!
• Theres more too! DV Cameras also include more
  compression 51 too so the 25 of colour I
  compressed 5 times more so reducing the colour to
  6 of the original.

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Lets look at the Data Rate

• The uncompressed data rate of video can be worked
  out by the following equation.
• Image size (width x height) x colour bit depth x
  frames per second
• 720x576 x 24 x 25 248000000B/s or 248Mb/s
• The 24 is made up from 3 colour channels of 8
  bits each
• 720 x 576 is the frame size for digital TV
• 25 is the PAL frame rate

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What about 422?

• This is worked out slightly differently.

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422 continued

• 422 compression is generally always 10bit. It
  is quoted in the technical spec of the cameras
  running at 277MB/s.
• Where the extra info come from?
• Well, It has 4 channels of 16bit 48K Audio
• It also has massive amount of error correction
  added to ensure all the 0s and 1s are
  transmitted and can reproduced correctly in the
  right order. As it is SDI connection and not
  firewire (serial digital interface)
• All the data (video and audio) is pushes down one
  cable. This pushes the totally uncompressed data
  rate to 554MB/s.
• Sony Digital Betacam of 422 is quoted to be
  compressed 21. The 554MB/s is compressed to
  277MB/s.

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420 at 8bit Data rate
This is DV compression. It is then compressed a
further 51 making the data rate 25MBs.
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To Wrap up Compression

• 422 10bit has a higher sampling frequency than
  420
• A higher bit depth (4 times as many shades of
  RGB) and therefore higher data rate.
• 422 use less compression after the colour
  subsampling.
• 422 cameras also have 2/3 of inch size CCD
  instead of 1/3 on 420 cameras so more light is
  recordable too.
• Also they have more photoreceptors on the CCDs so
  a higher dot per inch too.

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Colour in Cameras

• With all the knowledge of video compression now
  you should understand that colour is the heavily
  compressed.
• Only studio cameras or 422 cameras should be
  used for chromakey.

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• What happens when you shoot on the studio cameras
  and record to mini dv?
• Is there any point?
• Yes Why when Mini DV is 420.
• Its like by passing the problems of the XL1 lens
  and CCDs.
• Bigger CCDs, more photosensors per chip so
  higher quality images.

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The Canon XL2

• The Canon XL2 is the latest Canon camera
• It has 3x 1/3" true 169 with 800.000 pixels per
  CCD
• Thats 3 or 4 times higher than the XL1 and twice
  as many as the Panasonic AXG DV100.
• Also has a 50i 25p frame rate
• XLR connectors built in

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The Future - High Definition
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HDTV - What is it?

• High Definition TV
• Some of the basic features of HDTV are
• Higher picture clarity
• Larger pictures
• More colours (5 times the resolution of normal
  standard definition TV sampling at 13.5Mhz x 5
  67.5million samples per second at full
  resolution)
• Wider pictures (all 169)
• Multi-channel digital CD quality sound

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Broadcasting HD - TV

• Starting in UK in late 2006 on the Sky network
  using the European 720p standard.
• BBC intends to produce all content in HD by 2010

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Show the HD IMAGES
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What Video Formats are High Definition

• Sonys HDCAM 422 at 10bit and 444 RGB with
  2.2megapixel CCDs
• Panasonic DVCPro HD 422 at 8 bit with
  1Megapixel CCDs
• Thompson Viper 444 at 10bit with 9.2megapixel
  CCDs
• Sony HDV (the HD for the DV market) 420 at 8
  bit.
• JVC HDV

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How does it work?

• It uses intra frame (within the frame)
  compression but no inter frame.
• It uses 25 I-frames per second

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Is HD interlaced or Progressive Scan?
Its both
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High Definition TV Frame Sizes

• What is the maximum frame size of HDCAM?

1920 X 1080i
What frame size is a Panasonic DVCPROHD?
1280 x 720p
A Pal TV runs at how many individual images per
second?
25
A NTSC TV runs at how many images per second?
29.97 its common to round it up to 30fps
IInterlaced scan PProgressive scan
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HDV High Definition Digital Video
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HDV Cameras

• HDV is an entry-level HD format which is ideally
  suited to videographers, low-budget filmmakers
  and corporate or institutional productions.
• Uses an MPEG-2 video format and MPEG-1 audio
  layer 2 running at 384kbps (48K 16bit)
• It allows HD pictures to be captured on a mini dv
  tape.
• A down converter to standard def is also
  featured.

True 169 CCD Frame Sizes 1440x1080i or
1280x720p
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HDV MPEG-2 Versus DV
25MBs DV Intra-frame formats
MPEG-2 Encoding
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How Does HDV work?

• HDV uses an MPEG-2 Transport stream as its data
  file
• What is an MPEG-2?
• A highly efficient compression format used in
  digital television, DVD-video and now HDV
  camcorders
• It runs at a data rate of 25MBs at 1080i or
  19MBs at 720p
• It uses interframe compression

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HDV MPEG-2 compares to traditional video formats
The B and P frames are mathematically calculated
based upon the main I frame. The inbetween
frames record changes in movement only and not
the repeated information. The HDV format runs at
19-25Mbps, it needs the highly efficient MPEG-2
to put HD size images on to Mini DV tape.
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What is compression looking for?

• Repetition in information.
• The following sentence has repetition
• The cat sat on the mat.
• The word the is repeated twice
• Instead of copying the word twice you copy it
  once and then create a reference point that
  states use the word the again.
• This information is called redundancy and it is
  removed in compression.
• The core and essential information is called the
  entropy.
• Removing the one word from this sentence reduces
  the data amount by 17.
• (This is called lossless encoding as all the
  original sentence can be perfectly recreated
  data)

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Problems with HDV

• HDV is a pain for an editor why?

Its very CPU intensive as the MPEG has to be
uncompressed into 25fps, create the effect like
transition and them recompress to MPEG-2. The
HDV format runs in MPEG -2 all the time unless
you choose to uncompress to add an edit or a
effect.

• Will this effect the quality?

Mmm maybe not sure until we can test it
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Conclusion

• PAL and NTSC Standards
• Interlacing and Progressive scanning
• A scan line TV Signal
• Phases
• Colour burst
• Active image
• Sampling and resolutions
• Wheres as the colour gone (Colour Sub Sampling)
• 444 compression
• 422 compression
• 420 compression
• High Definition Camera Technology
• HDV Camera Technology

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Glossary

• Interlaced ScanThe process whereby each frame of
  a picture is created by first scanning half of
  the lines and then scanning the second set of
  lines, which are interleaved between the first to
  complete the picture. Each half is referred to as
  a field. Two fields make a frame.
• IREAn arbitrary unit of measurement equal to
  1/100 of the excursion from blanking to reference
  white level. In NTSC systems, 100 IRE equals
  714mV and 1-volt p-p equals 140 IRE.
• LumaThe monochrome or black-and-white portion of
  a video signal. This term is sometimes
  incorrectly called "luminance," which refers to
  the actual displayed brightness
• NTSCNational Television Systems Committee. A
  group that established black-and-white television
  standards in the United States in 1941 and later
  added colour in 1953. NTSC is used to refer to
  the systems and signals compatible with this
  specific colour-modulation technique
• PALPhase alternate line. PAL is used to refer to
  systems and signals that are compatible with this
  specific modulation technique.
• Progressive ScanThe process whereby a picture is
  created by scanning all of the lines of a frame
  in one pass
• Interlaced ScanThe process whereby each frame of
  a picture is created by first scanning half of
  the lines and then scanning the second set of
  lines, which are interleaved between the first to
  complete the picture. Each half is referred to as
  a field. Two fields make a frame