Chapter 1- Imaging

An overview of the first chapter of the advancing physics OCR book

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  • Created by: R_Hall
  • Created on: 03-12-12 19:00

The Nature of Waves

  • A progressive wave carries energy and information without transferring material
  • Waves carry energy- electromagnetic waves heat, x-rays and gamma rays ionise, sounds makes things vibrate, wave power can generate electricity and wave sources lose energy (as give it to the waves)
  • Reflection- a wave is bounced back when hits a boundary
  • Refraction- the wave changes direction when it enters a different medium
  • Frequency= 1/period
  • Speed of wave= wavelength x frequency
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Forming Images With Lenses

  • When light meets a boundary of mediums, some is reflected back into the 1st medium and the rest is transmitted
  • The more optically dense a material is, the more slowly light travels in it
  • Absolute refractive index= speed of light in a vacuum/ speed of light in material
  • Lenses change the curvature of wavefronts via refraction
  • A lens adds curvature- they slow down the light travelling through the middle for a longer time than for the edges
  • Focal length (f) is the distance between the lens axis and the focus
  • More powerful the lens- more strongly will curve the wave- shorter focal length
  • Power (dioptres)= 1/ focal length
  • Curvature= 1/radius of curvature
  • The linear magnification of a lens (m)= size of image/ size of object
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Information in Images

  • The binary system uses two digits, 1 and 0
  • A single binary digit is a bit, and 8 bits make up a byte
  • The number of bits in a string of info determines how many alternatives the string can code for
  • Each pixel in an image is represented by a binary number
  • The value of the binary number gives the colour (or shade of gray) of the pixel
  • In coloured images, each pixel is described by three binary numbers (one for each primary colour- red, blue and green)
  • Addition of false colour is used to highlight certain, important features
  • Noise is unwanted interference affecting a signal
  • Noise can be removed by replacing each pixel with the median of itself and the 8 pixels surrounding it
  • Any odd values are removed and the image is smoother
  • Finding edges is useful when working out if there is something useful in the image (not just noise)
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