Colour and Sound: Part 1: Introduced and Compressed Dan Eaves CSE5060 – Multimedia Applications on...
47
Colour and Sound: Part 1: Introduced and Compressed Dan Eaves CSE5060 – Multimedia Applications on the Web, Semester 2, 2006 Lecture 2 Note: Non-anime images are from Ted’s Photographics: http://www.ted.photographer.org.uk Very highly recommended! Please spend some time at this wonderful site.
Colour and Sound: Part 1: Introduced and Compressed Dan Eaves CSE5060 – Multimedia Applications on the Web, Semester 2, 2006 Lecture 2 Note: Non-anime
Colour and Sound: Part 1: Introduced and Compressed Dan Eaves
CSE5060 Multimedia Applications on the Web, Semester 2, 2006
Lecture 2 Note: Non-anime images are from Teds Photographics:
http://www.ted.photographer.org.uk Very highly recommended! Please
spend some time at this wonderful site.
Slide 2
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced2 Colour onto Screen Computers use RGB colour Red Green
Blue The process is additive. There are three electron guns at the
back of the TV tube. There are three types of phosphors (rare
earths) which coat the inside of the front of the monitor. There is
a grid (mask) or set of vertical wires (aperture grill) through
which the electrons go on their way from the gun to the face of the
monitor. (Aperture grill is better.) Each position on the screen
has the three phosphors. The colour of the position is their
combined light.
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced8 Monitors: Aperture Grill versus Shadow Mask
Slide 9
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced9 LCD Displays For liquid crystal displays A freak of
nature. Such crystals are Liquid Present a twisted path (blocks
light) But electricity untwists it, so light can get through!
Voila
Slide 10
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced10 From Digital Home Magazine: How LCDs work
Slide 11
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced11 Plasma Displays 3 florescent lights (red, green, blue)
in each pixel position
Slide 12
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced12 Plasma Display Problems 3 florescent lights are big
There is no likelihood of making them really small So plasma
displays always have to be big and low resolution But for a home
theatre wall display at 16x9 HDTV resolution theyre wonderful. Note
that 16x9 aspect ratio Note that HDTV resolution is (in theory) up
to 1920 x 1080 pixels(i) at 16x9, but a current 50 inch Sony $9,500
plasma display has a 1280 x 768(p) resolution Note the i and p:
interlaced or progressive: both those last are actually (sort of)
the same resolution.
Slide 13
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced13 Aspect Ratios When TV developed in 1940s, took the
then standard motion picture ratio: 4x3 Movie industry responded to
perceived threat from TV by inventing a new standard, 16x9 Other
countries responded to US TV standard (NTIS) by specifying
alternative incompatible standards to protect their electronics
industries, e.g., the PAL standard used in Australia Different
standards have different number of horizontal lines, different
screen refresh rates Aint competition wonderful!
Slide 14
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced14 Getting Colour onto the Screen We can specify an
intensity of each of the three colours in the range of 0 to 255.
255 by 255 by 255 = about 16,700,000. This takes 24 bits, 8 for
each colour If we want pure red, we set: Red = 255 Green = 0 Blue =
0 This translates to the intensity of the beams of electrons
striking the different phosphors. What do we get when: Red = 255
Green = 255 Blue = 255
Slide 15
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced15 But Wait, Theres More... True colour can be either 24
or 32 bits deep. Both of these have a palette of 16.7 million
colours. If present, the 8 extra bit are called the alpha channel.
This contains transparency information: How well can you see
through this pixel, on a scale of 0-255 Primarily used as masks in
animation where images are overlaid to build the final result.
(Note: you can also call 32 bit colour 4 channel colour) Alpha
channels dont exist in transmitted image. Here just because you
will be using then in Flash
Slide 16
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced16 Anti-Aliasing (I use a 16 colour picture so the effect
is clear)
Slide 17
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced17 Anti Aliasing When digitized (and compressed) curved
lines get the jagged edges. You can make these look less bad by
dithering in some pixels in colours between those of the line and
the background where the jagged parts are.
Slide 18
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced18 Anti Aliasing The Actual Pixels The Visual Effect
Slide 19
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced19 Anti Aliasing Used all the time Built into digital
cameras Built into compression programs Built into products like
PhotoShop Built into products like Flash/Shockwave Even with
PhotoShop, hand retouching is done with great frequency for high
(perceived) quality images Foxing (fooling) the eye is the basis
for much of the substance of computer graphics, including
compression!
Slide 20
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced20 Compression Introduced We Shall Return! Because
pictures take up so much space, we have to compress them Reduce the
number of colours Store constant information only once Reduce the
size of images Use vector graphics Used by Flash/Shockwave Used for
animations Used for simple static images There are a number of
different static image raster compression formats
Slide 21
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced21 Raster versus Vector Graphics Raster = The invisible
dot that moves across the (TV, Monitor) screen, Puts something in
each pixel position. Then does a flyback from the bottom right to
top left positions. Driven by storage of data (2-24 bits) for each
pixel position. Supports highly detailed images, e.g., photographs
File sizes are typically big, sometimes very big. Vector = A line
(any line, not necessarily straight, but which can be described by
a mathematical formula. Formulas are converted into bit maps
(raster images) These are displayed on the screen Supports low
detail images, e.g., cartoons and drawings File sizes are typically
small, sometimes very small. Vector graphics trade computer
processing for file size.
Slide 22
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced22 GIF/PNG GIF Graphics Interchange Format is: A lossless
compression (so not very compressed) Maximum of 8 bit colour (256
different colours) One colour can be invisible (transparent) Very
fast to decompress Universally used for headings, buttons, etc.
Works by recognizing areas of rows of pixels of the same colour and
not storing actual pixel by pixel data but start/stop/colour
information That is, where possible works like a scanner and sends
addresses of changes rather than all pixels. Sends all pixels where
necessary. Useless for photographs
Slide 23
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced23 JPG/JPEG JPG - Joint Photographers Expert Group Lossy
compression What you get after decompression isnt what you started
with Tuned to the human vision system: Starts by eliminating colour
differences the eye cant see Degree of compression under your
control You specify the degree of compression, from unnoticeable to
horrible Many colours (up to 24 bits) No transparent colour Used
for photographs
Slide 24
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced24 Raster Graphics Data is stored for each pixel
position. With an image that is 500 x 300 there are 150,000 pixel
positions. 500 * 300 = 150,000 * 3 (bytes) = 450,000 * 24 images
per second * 60 seconds per minute * 60 minutes per hour And then,
of course, theres sound
Slide 25
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced25 The Tragedy of Raster Graphics Remember, modems are
serial (1 bit at a time) so thats, say, 1-3 mbits a second Weep!
Bash head against wall! Bewail fate! If a page contains 400 words @
5 letters per word and 5 characters of extra HTML per word we get:
(400 * 5) + (400 * 5) = 4,000 characters = 4,000 bytes no time at
all Drat, drat, drat. Well need to compress, use vector graphics,
reduce the number of colours, compress again.
Slide 26
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced26 Vector Graphics Like Corel Draw, Flash and Illustrator
files (note: can have raster background image(s) in these. Lines
and outline shapes are stored as mathematical formulas Fills are
stored as a few bytes. A program reconstructs the always necessary
raster image from the vectors, stores the results in the video
cards frame buffer, and shows the results on a raster device (your
screen). Image size can be increased or decreased without loss of
detail or introduction of artefacts (e.g., moire effects) So we
have very small files but lots of processing work on the way to
displaying the results. Flash/Shockwave are currently the only
standard ways of using vector graphics on the web. But new
standards are being developed to extend web use of vector graphics
their chance of success is ????? TrueType and PostScript fonts are
vector graphics formats.
Slide 27
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced27 A Shift: Digital Sound Music on CD works as follows:
Each chunk of data represents the amplitude of the sound at a
moment in time with a number ranging from 0 to 65,535 -- 44,000
samples are taken per second per stereo channel. So data storage
per second is 44,100 samples * 2 bytes per sample * 2 channels =
176,000 bytes per second. So a 3 and a half minute song takes
176,000 * 60 * 3.5 = 36,960,000 bytes of storage space Hummmmm.
Were going to have problems with sound, too. Your CD music is the
equivalent to uncompressed raster graphics MP3 is the equivalent
to.JPG/.JPEG compression, as it is both lossy and the degree of
loss (and compression) is under user control. Standard MP3 gets a
standard length song down to, say 3- 4 meg. (Estimate using a 90%
compression factor)
Slide 28
Part 2: Speeding Things Up
Slide 29
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced29 Good Sources As always, Wikipedia.Wikipedia Good
Australian broadband site: Whirlpool.Whirlpool Note especially the
Broadband Choice link. Recent OECD study (Dec., 2005) of worldwide
broadband usageOECD study
Slide 30
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced30 Broadening the Bandwidth Alternatives are: ISDN
(international standard digital network) Cable modems (fiber optics
to local hub, coaxial to your house) Cable (point to point) DSL
(digital subscriber line), aka ADSL (A = asymmetrical) BoP
(broadband over powerlines) Satellite WebTV - Combining your TV, a
specialised web computer and a remote control with keyboard, using
existing cable connections.
Slide 31
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced31 ISDN (International Standard Digital Network) Comes in
two flavours: Uses existing POTS for digital (not analog)
transmission. Primarily for home use Initially provided two
64kbit/s data links and 1 voice link Available in selected suburbs
Not very expensive at lower speeds, very expensive at higher ones.
Uses special lines (fiber/coaxial) Primarily for business use Many
speeds and combinations available Available in most CBDs Predates
Web and Internet
Slide 32
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced32 Cable Modems (Australian) pay TV wiring works like
this: Fiber optics into near neighborhood hub. Coaxial cable from
hub to home. All channels are broadcast all the time. There is
extra bandwidth available (in both links) So a.5 - 1.5 mbyte/s
connection possible But: Less in local link, which would be shared
across all cable modem users in immediate neighborhood. Pay TV less
popular that anticipated, so wiring incomplete No economies of
scale in modem replacements, due to Australias unique position re
cable TV Some suppliers (e.g., Optus) may be rationing bandwidth.
Note: Pay TV elsewhere is a mix of usually less sophisticated
technologies, but 9 million cable modems in use in USA.
Slide 33
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced33 DSL Digital Subscriber Line or ADSL for Asymmetric
Digital Subscriber Line Uses the existing TWP (twisted wire pair)
telephone line, which is split (ADSL): 0-4,000 kHertz for voice.
4,000 25.875 kHertz up link (varies by standard) 25.875 1104 kKertz
down link (varies by standard) Intended for The Last Mile (from
local exchange to customer) Line/signal quality falls with distance
Signal is faster on the down link and slower on the up link. Data
rate is distance to exchange dependent: Theoretical downlink
maximum speed varies from 8 to 24 mbps, with different protocols
and standards. But max speed may be down to 128 kbps in some (bad)
situations. Above ca. 5.5km, DSL isnt possible. Hummmmmmm...
Slide 34
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced34 ADSL in Australia From Telstra/Big Pond From Telstra
competition Telstra has been criticised for limiting their ADSL
DSLAM speed to a maximum of 1.5 Mbit and 256 kbit/s (download and
upload respectively), whereas the maximum ADSL speed possible is 8
Mbit and 1 Mbit (download and upload respectively). The reason
Telstra limit their DSLAM speed is so as to not kill off its own
ISDN service which charges hugely expensive premiums for 2 Mbit/s
speeds. Wikipedia, DSL Around the World, accessed April 13, 2006.
DSLAM = Digital subscriber line access multiplexer
Slide 35
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced35 ADSL in Australia 2: From Whirlpools Broadband
ChoiceWhirlpools Broadband Choice I supplied my phone number and
requirements (speed, volume, price willing to pay, etc) I got: Your
telephone line is connected to the Warranwood exchange. This
exchange has been enabled for ADSL service. In terms of pricing,
Warranwood is classed as Metro. Please note that while the
Warranwood exchange supports ADSL, this is no guarantee that your
physical phone line is up to scratch. A conclusive test can only be
done upon registering for a service. And a list of 20+ DSL and
cable plans available (including the cable service Im using. I set
this up before DSL was available.)
Slide 36
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced36 ADSL Take-up Currently 2nd broadband technology of
choice in USA ADSL = 6.5 per 100 inhabitants by Dec., 2005 (versus
9 per 100 inhabitants with cable modems, 1.3 per 100 other mainly
satellite) Currently 1 st in Australia: relative figures are: ADSL
= 10.8 per 100 inhabitants by Dec., 2005 (versus 2.6 per 100
inhabitants with cable modems, 0.4 per 100 other mainly satellite)
Speed in theory averages about 1.5mbits / second down, 256kbits /
second up. (So 25+ times faster than voice modem) Less congestion
problem than cable models, at least in theory.
Slide 37
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced37 Near Future Technologies Wi-Fi Wi-Fi Wireless
Broadband Works without phone lines G3 phones limited to ca. 384
kbps. Unwired Is examplem available in Sydney and (from April,
2006) Melbourne CBDsUnwired Speeds from 256/64 to 1024/256 kpbs for
$55 $120 per month Highly limited coverage really just CBD Requires
line-of-sight link, so just like cell phone, with dead spots Google
is Wi-Fiing up all of San Francisco in 2005-6 for free as an
experiment.
Slide 38
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced38 Near Future Technologies BOP (Broadband over
Powerwires Different Scopes Complete path Last mile Within site
(home or office) Primary Problem Very noisy environment Transformer
problem In US, most homes have own high to low voltage transformer
In Europe, each 10-100 homes have own transformer As there must be
a relay station around each transformer, cost is much higher per
customer in US. Much promised over last 15 years
Slide 39
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced39 Satellites Two classes of connection: One-way
satellite link: Landline-based upload, with Direct satellite
download That is, traffic from you to the satellite goes down the
phone line of the ISP, to the satellite company and up to the
satellite from there. The response goes directly from satellite to
the antenna on your roof. The traditional internet satellite link.
Two-way satellite link Data goes up from your antenna, as well as
being received by it. Requests relayed down by satellite. (4 trips)
Requires a slightly larger antenna (.75 x 1.1 m.) Requires a very
accurately aimed antenna. Such a service recently introduced in the
US by StarBand 55,000 customers after 4 months (March, 2001)
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced41 Satellites, 3 Three classes of satellites:
Geosynchronous (GEO) always over exactly the same place Has to be
at altitude of exactly 35,786 km over the equator. (Slots are
running out, but you only need three for full coverage.) And the
speed of light comes in! 40,000+ km up, 40,000km down, maybe 20,000
across = 100,000 km trip, = a half of a second -- called latency
Problem is in lack of synchronisation for conversations Problem is
in acknowledgment of successful reception of packets. Trend is to
use undersea cables for voice, satellite for data transfers (in
non-packet form.) Medium Earth Orbit (MEO) Less latency, but still
too much Require a number of satellites because dont stay over the
same location
Slide 42
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced42 Satellites, 4 Medium Earth Orbit (MEO) Less latency,
but still too much Require a number of satellites because dont stay
over the same location
Slide 43
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced43 Satellites, 5 Low Earth Orbit (LEO) Need lots because
moving relative to the surface, so say 288 (plus spares) satellites
at 1,375 km altitude Speed of light isnt a problem Coordinating
across satellites is a problem Will handle voice, data & video
all as Internet IP packets Was initial plan of Teledesic (from
McCaw and Gates)
Slide 44
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced44 Satellites, 6 Additional Problem: the IP in TCP/IP
TCP/IP assumes Low latency Low bit error rates Relatively symmetric
bandwidth (All those little packets have to be acknowledged.)
Satellite Telecommunications are characterised by: High latency
High bit error rates Highly asymmetric bandwidth (esp. with
landline based uploading) Solution of choice Convert to a non-IP
protocol designed for satellite communications. (Whoops)
Slide 45
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced45 Satellites, 7 Some conclusions LEO eliminates latency
but requires an enormous investment. (And nobody is going to invest
in satellites for awhile) For file transfers, any satellite is
great, without TCP/IP. If you are isolated, and need
bandwidth...
Slide 46
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced46 The Dark Fiber Problem In the late 1990s (Internet
boom) A huge amount of optical fiber was laid. Within countries
(esp. US) Between countries The assumption was that Computer line
use would follow exponential growth curve of 1995-2000. The boom
ended and wavelength division multiplexing increased existing fiber
capacity by 100x There is currently (2006) still huge over capacity
in fiber This has greatly slowed the investment in other
technologies
Slide 47
Rev. 26 July, 2006CSE5060 Lecture 2: Colour and Sound
Introduced47 Shrinking the Content To fit more through the eye of
the needle, we can Make the eye bigger (increase bandwidth) or
Shrink the content Better compression The vector graphics approach,
e.g., Send instructions to build things, not the things themselves.
We trade (much) faster transmission for (much) increased local
processing. It is hard (but not impossible) to digest a photograph
or movie. Background transmission Send stuff in advance of need
behind the scenes Examples, streaming audio, video, media Streaming
means: It keeps being sent automatically after you first ask for it
It starts playing before it is fully transmitted Has fallbacks for
not keeping up (dropped frames, etc.)