# 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
• 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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