M150: Data, Computing and Information

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M150 Data, Computing and Information
Unit Three Crossing the boundary analogue
universe, digital world
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4- Crossing the boundary

• Images
• If you want to reduce a picture to numbers, you
  must divide it into discrete parts (squares) and
  then transform the result into numbers.
• Take an image.
• Put a border.
• Divide it into a grid of equal sized squares.

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4- Crossing the boundary

• If the square is entirely grey make it white.
• If the square is entirely colored (mauve) make it
  black.
• If the square contains both grey and color and if
  more than the third of the square is mauve then
  it will become black otherwise it will become
  white.

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4- Crossing the boundary

• In the resulting image, assign the number 0 if
  the color is white and 1 if the color is black.
• We obtain a binary image, each mapped square is
  called pixel (picture element), such image
  transformation is called bitmap encoding (each
  number is only
• either 0 or 1, and computers use bits
• to store 0s and 1s)
• A pixel is a short for picture element
• (square) that we have mapped to 0 or 1.
• To improve the quality of the image,
• you must increase the number of
• the squares (pixels) and make
• each square smaller

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4- Crossing the boundary

• Resolution
• Depends on the number and the size of the pixels
• If we go on and on increasing the resolution of
  the picture, making the pixel size smaller and
  smaller, we will move closer and closer to an
  image that appears completely smooth.
• We can never reach a perfectly smooth image by
  this process to do this one would need
  infinitely small pixels.
• We can never reach an analogue representation by
  digital means, only approximate to it.

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4- Crossing the boundary

• One bit was allocated to each pixel in the image,
  0 or 1, either black or white (no way of handling
  color).
• Allocating more bits to each pixel will result in
  shades between black and white.
• 2 bits will result in 11 black, 00 white, 01
  light gray, and 10 dark gray.
• Three bits per pixel will give us (23) eight
  shades, from black to white four bits per pixel
  gives us (24) 16 shades and so on.
• A mapping of shades of grey between black and
  white in a black and white bitmap is known as
  grayscale.
• The range of numbers to which a pixel can be
  mapped is termed the pixel amplitude

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4- Crossing the boundary

• Color is an example of an analogue property.
• We are trying to map infinite number of colors to
  a finite number
• Colors are represented in a different way.
• Any color can be made out of a mixture of three
  basic shades Red, Green and Blue (R, G, B). ? RGB
  model
• Each shade is represented by a byte (8 bits),
  giving values ranging from 0 to 255.
• As a total we have 256 x 256 x 256 shades of
  color (16,777,216)
• Red is (255, 0, 0) since it is all Red and 0
  Green and 0 Blue.
• Green is (0, 255, 0).
• Blue is (0, 0, 255).
• White is (255, 255, 255), all the color spectrum.
• Black is (0, 0, 0), no color what so ever.

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4- Crossing the boundary

• When dealing with images, sometimes large amounts
  of memory are required.
• Two important models
• RGB model
• The primary colors are red, green and blue.
• CMYK model (other model)
• The primary colors that are reflected off paper
  are not red, green and blue but cyan
  (blue-green), magenta and yellow.
• The K stands for a special black ink used to add
  crispness.

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4- Crossing the boundary

• Interlude diagrams
• Some types of visual information can be
  represented more economically than in a bitmap
  (less waste of memory).
• The huge majority of the pixels will just be
  white, the background to the picture. The only
  information all these white pixels give us is the
  simple fact that the background color is white.
• To reconstruct the diagram we need information
  about what sort of object it is (line, square),
  the size, the position and the color of them
• Shapes, line thickness, coordinates, all have
  their numerical representations in a computer.

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4- Crossing the boundary

• First assign a number to each type of object
  (rectangle, circle, arrow, line and the text).
• Second record the size and position (Cartesian
  coordinates x, y axes) of each object.
• Third Identify the color.
• Finally put all information together and produce
  a final set of numbers

• A circle is defined by its radius and the
  coordinates of its center.
• A rectangle by the coordinates of its upper left
  and lower right corners.
• Lines and arrows by their starting and ending
  points.
• The text area by the coordinates of its top left
  corner

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4- Crossing the boundary

• Vector graphics
• The way (sort) of encoding of visual information.
• Opposed to the bitmap approach (raster graphics)
• Advantages of vector graphics
• Very compact form of encoding.
• The resulting image is scalable we can easily
  shrink or stretch the size of it without any loss
  of information.
• Disadvantages of vector graphics
• Works with fairly simple images
• Need complex program to interpret the number and
  display them as diagram
• Drawing packages the programs that allow us to
  draw and display vector graphics
• Painting packages the systems for constructing
  and displaying raster graphics (bitmap)

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4- Crossing the boundary

• Several formats exist for image digitizing,
  depending on the allowed loss of precision (ex
  bmp, png, jpg, gif, etc)
• Making image move
• A Video or a movie, is a series of images that
  slightly differ one from another, passing them
  one after the other at a certain speed will give
  the illusion of movement.
• A picture would be called a frame.
• The speed of flipping the frames one after the
  other is called frame rate (fps).
• Transferring such an enormous amount of digital
  information over a network would be slow.

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4- Crossing the boundary

• We have to find some way of reducing the amount
  of storage that moving images need. The vector
  graphics approach will not work for complex
  image, so we must look for a way of compressing
  bitmapped visual information.
• There are many standards for image and film
  compression.
• Standards for image compression
• JPEG (Joint Photographic Experts Group)
• GIF (Graphics Interchange Format) standards.
• (Both standards reduce the number of bits used to
  store each pixel)
• For video, the dominant standard is MPEG (Moving
  Picture Experts Group), which is now used in most
  digital camcorders.

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4- Crossing the boundary

• Image and video capture devices
• Scanner, digital cameras and camcorders are the
  main devices used for transforming images and
  video into digital form inside the computer.
• Digital still camera and camcorders
• Widely and cheaply available
• No film, contains removable memory card
• Get a compressed digital image (usually JPEG
  format)
• Camcorder record in MPEG format (store on tape)
• Both devices works by means of an electronic
  chips called a charge-coupled device (CCD)
• A CCD is basically an array of tiny cells, that
  respond to light by generating a tiny electric
  charge (the amount of charge depends on the
  intensity and color)

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4- Crossing the boundary

• Scanner
• Making a digital image of the page and then
  passing this image to an OCR system to
  distinguish the various characters.
• A scanner works by moving a sensing point rapidly
  across the image, in a series of lines.
• The scanner measures the brightness (luminance)
  and the coloring (chrominance) of a series of
  points along each line.
• The quality of the resulting bitmap will depend
  on the number of lines the scanner follows across
  the specimen, and the number of measurement
  points along each line.
• Most scanners come with software that will
  compress the bitmap into a number of formats,
  including JPEG and GIF.

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4- Crossing the boundary

• Sound and music
• Hearing is the second most relied on sense for a
  human being (another analogue feature of the
  world).
• A sound consists of a waveform (tuning fork
  instrument).
• Displacement how far an air moves backwards and
  forwards
• Cycle (wave or period) represent the time
  between adjacent peaks ( or trough)
• Frequency the number of
• cycles completed in a fixed time
• (decide how low or high pitched
• the note sounds)
• Amplitude maximum displacement
• (how loud the sound is)

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4- Crossing the boundary

• In order to digitize a sound waveform, we take
  samples of the sound at small time intervals,
  such a process is called sampling
• The number of times/second we take a sample is
  called the sampling rate.
• The smaller the interval the better.
• We can never make a perfect digital
  representation of an analogue quantity.

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4- Crossing the boundary

• It is impossible to make a perfect digital coding
  of an analogue picture, because we will always
  lose information between the pixels, so we will
  always lose information between the times we
  sample a waveform.
• The process of digitizing a sound consists into
  sampling it and then associating a number to each
  sample (quantization).
• The smaller the interval of taking the samples,
  the more accurate our representation of the
  analogue sound will be.
• Smaller intervals will mean, more samples and
  therefore more bits to quantize them, which means
  more storage space.
• Sound waves samples are generally mapped to
  16-bits.
• Several formats exist for sound digitizing,
  depending on the allowed loss of precision (ex
  mp3, wav, mid, etc).
• Sound capture devices microphone

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5- Going back

• Semantics the meaning attached to words and
  symbols.
• When we take image, video and sound across the
  boundary (digitized and stored on the computer),
  they are stripped of their meaning. They just
  become numbers, their human associations lost.
• If their meaning is to be regained, they must be
  transported back from the digital to the human
  world
• If we need to view an image or replay a sound we
  need some output devices.

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5- Going back

• Regaining meaning
• Machine on which image is stored will have to get
  the image back to us by means of a device that
  can render it into a form meaningful to the human
  eye (output device)
• The process of sending a digital representation
  back across the boundary, consists of three
  stages
• Identifying the suitable output device (depends
  on the user for example screen or printer)
• Arrange the numbers into a form suitable for the
  output device (sometime it is a very complex
  especially in cases where the information has
  been compressed).
• Interpret the code by the output device (carried
  out by specialized electronics in the output
  devices).

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5- Going back

• For the second stage (Arranging the numbers )
• The digital world can only be manipulated from
  inside by other digital things. In this case, the
  necessary arrangements are made by a special
  class of digital encoding a program.
• A program is a set of binary words (a word is a
  group of four bytes)
• Each word of the program has a special
  significance to the machines central processor
  it stands for an instruction.
• When a computers central processor reads one of
  these words it carries out the instruction that
  the word stands for.
• The digital representations mean nothing in
  themselves.

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5- Going back

• Types of output devices
• Monitors
• All computers are supplied complete with a
  monitor which opens a window onto the machines
  digital world.
• There are two main types of monitor
• The CRT (cathode ray tube) A CRT monitor looks
  like a television screen, and works in a similar
  way to a TV or a scanner. A beam of electrons is
  fired from a gun at the back of the tube onto a
  glass screen on the front. The beam sweeps across
  this screen in the same raster scanning pattern.
  The front of the tube is coated in a
  phosphorescent material that glows as the
  electron beam hits it.
• LCD (liquid crystal display) flat (they have no
  electronic gun) works on the principle of passing
  light through a special material. The molecules
  change orientation when an electrical voltage is
  applied to them
• The CRT monitors have color accuracy.
• The LCD monitors use less power, takes up little
  space and does not flicker.

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5- Going back

• The resolution actually displayed on the screen
  is not decided by the monitor itself, but by the
  program that prepares the digital encodings for
  display.
• Printers
• Inkjet, work by firing tiny droplets of liquid
  ink at the paper.
• Can print in both color and black and white.
• Color cartridge use color model (CMYK).
• Cheap but ink cartridges are expensive.
• Laser, work by firing a laser beam and burning
  powder ink on paper.
• Produce very high quality.
• Color lasers are available but expensive.

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5- Going back

• Plotters
• A plotter is a special type of printing device
  mostly used by architects, engineers and map
  makers.
• Printed output is produced by moving a pen
  across the paper.
• Suitable for line drawings.
• In contrast with monitors and printers they
  produce an analogue output directly.
• Loudspeakers
• Produce an analogue output (sound).
• The audio program inside the boundary converts
  the digital encoding of the sound to a series of
  electrical pulses that are sent to the speaker.

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6- What if? changing the digital world

• Using appropriate software, computers will help
  you simulate what happens in the real world.
• We can create digital models of natural phenomena
  and then write programs to manipulate them
• Simulations help us study problems through models
  
• (Example the earths climate).
• Computer scientists will create a model, a
  simplification including only features directly
  affecting the system being modeled (abstraction).

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6- What if? changing the digital world

• The climate model
• The weather is created by the interaction of
  earths atmosphere with the land, the oceans and
  the energy of the sun.
• The air pressure, temperature, humidity, wind
  speed, and so on are the key factors.
• The GCM (General Circulation Model) is an
  atmospheric model.
• The earths surface is split into a rectangular
  grids.
• Each rectangle is divided into layers splitting
  the atmosphere into 3-D boxes.
• Each box contains a sample number of points
  (sampling) where temperature, pressure, humidity,
  wind speed, and other features are recorded
  (quantization).

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6- What if? changing the digital world

• The climate model needs to follow certain laws in
  order to be accurate
• The Navier-Stokes equations which relate the
  movement of air, to the earths rotation,
  friction and pressure.
• The thermodynamic equation which relates in
  temperature variations to heat from the sun,
  condensation, and from other sources.
• The laws describe how things change in relation
  to one another over time how air flows, how
  things warm up and cool, how matter clumps
  together. Now, if we write and run a program that
  applies the laws to the model, we can show how
  things will change as time goes on (predicate the
  future)

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6- What if? changing the digital world

• Simulated prediction of weather patterns

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6- What if? changing the digital world

• Imaginary worlds
• Human imagination associated with appropriate
  software will allow the creation virtual worlds
  in computer memory.
• AlphaWorld
• Does not exist in space (purely digital world)
• It is a virtual world where a virtual is a term
  used to describe any entity that does not really
  exist, but is simulated by the action of a
  computer.
• AlphaWorld is open to anyone who has an internet
  connection.
• I can select or create a digital representative
  of myself, called an avatar, a word now used to
  refer to all sorts of digital being or agent, and
  send that into AlphaWorld.