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Chapter 1: Imaging (1.3:Storing and Manipulating the Image (Image…

- - - - This is a screen covered by millions of PIXELS
        
        Each pixel stores electric charge when light falls on it- the brighter the light on the pixel, the greater the chsrge stored on it
  - - - On may be a high potential difference
      - Off may be low
      - This is a BINARY system
    - - Pixels have 256 shades of grey, with each shade recorded as number from 0 to 255
      - N = 2^b or b= log2N
        
        Where b is the number of bits available
      - The number of bits required to store 256 alternatives is only eight, a group of eight that is called a BYTE, so one bite can store 256 alternatives
  - - - A dim image can be brightened by increasing the value on each pixel by the same amount until the brightest pixel in the image is coded at 255
    - - Noise in images refers to the random speckles across the image; this can be reduced by smoothing, where the value of each pixel is replaced with the median or mean of its value and those around it
    - - To enhance edges in an image, the average value of the pixels neighbours is subtracted from each pixel; this removes uniform areas of brightness and picks out the places where the gradient of the brightness changes abruptly – at the edges
    - - An image with little contrast will not use the full range of pixel values. An image may only use the values between 75 and 150. To improve the contrast the range is stretched across the 256 possible values so the 75 becomes 0 and 150 becomes 255
- - - - The first filter allows through the vertical component of the wave and the second filter only allows through the horizontal component of the wave
    - - If the intensity varies as the filter rotates the source is emitting polarised light
  - - - Transverse waves are polarised if they vibrate in one plane only; and polarised transverse waves vibrate in a randomly changing plane
    - - But the two fields are right angles to each other and to the direction of travel of the wave
        
        The electric field oscillates in the vertical plane. The magnetic field oscillates in a horizontal plane
    - - If the waves are polarised the direction of oscillation will not be fixed
- - - - WORKED EXAMPLE
    - - These are called Plane Wave-Fronts
  - - - A ray of light points along the direction of motion of the wave-front and is always at right angles to the wave-front
      - FIGURE 3 page 1
  - - - The intensity of light at this point, the focus of the lens, can be great enough to start a fire
      - In terms of rays: the burning glass works by bending the parallel rays from the Sun and focusing them together at the focus
      - In terms of waves: the lens works by altering the curvature of the waves, changing the plane waves that strike it from the Sun into spherical ripples that converge on a focus
    - - A converging lens adds a curvature of 1/f to wave-fronts
      - 1/f is the power of the lens; measured in DIOPTRES (D)
- - - - Curvature of waves leaving the lens = Curvature of waves entering the lens + Curvature added by lens
      - Distance from lens to image of the source (image distance) is represented by v
        
        Image distance is different to focal length, because the focal point is the point at which parallel waves from a very distant object are brought to focus
      - Distance from lens to source (object distance) is represented by u
      - Curvature of waves leaving lens = 1/v
        
        Curvature of waves entering the lens = 1/u
        
        Lens equation= 1/v = 1/u + 1/f
        
        WORKED EXAMPLE
      - The focal length is the distance from the centre of the lens to the focal point, and is a constant for a particular lens with a fixed shape
        
        Waves from a nearer object are brought together beyond the focal point- the image distance(v) is greater than focal length(f); except for very distant objects
  - - - Linear Magnification, m = image distance(v)/object distance(u)
    - - When m is less than 1, the image appears smaller than its source