1/2- Imaging Flashcards
Relationship between radius and curvature?
Curvature= 1/r
Define magnification.
For linear magnification, magnification = image distance/ object distance
Define resolution of a digital image.
The scale of the smallest detail that can be distinguished,
Equation for the amount of info in an image:
amount of info in an image=
no. pixels *bits per pixel
Describe changing brightness.
Increasing brightness of each pixel by the same amount until the brightest pixel in the image is coded to the largest value.
Explain how noise is removed from an image.
Smoothing, where the value of a pixel is replaced by the median or mean of its value and the pixels surrounding it.
Define noise in an image.
Random “speckles” across an image.
What is edge detection?
The average value of the pixels neighbours is subtracted from each pixel.
Why is edge detection used?
It removes uniform areas of brightness and picks out the places where the gradient of the brightness changes abruptly (the edges).
How is contrast improved?
Images where the full range of pixel values aren’t used are “stretched out” across the full range of values.
What range of wavelengths does visible light cover?
700-400 nm
Define a polarised wave.
When a transverse wave vibrates in one plane only.
What is sampling of a signal?
When the displacement of a continuous analogue signal is measured at small time intervals and converted into a digital string of binary numbers.
Relationship between number of levels and number of bits.
No. levels= 2^N
Where N is the number of bits.
Equation for resolution of a sample:
no. quantisation levels
Equation for max useful number of levels?
Total noisy signal variation / noise variation
Equation linking no. bits and Vnoise and Vtotal
b=log2(Vtot/Vnoise)
What are the two conditions of sampling?
The signal cant contain frequencies above a certain maximum.
The min sampling rate must be greater than double the highest frequency component.
Why cant signals contain frequencies above a certain maximum?
Lower frequency signals called aliases (which aren’t present in original signal) will be generated.
Define bit rate and state its units.
The rate of transmission of digital information.
Hz or bit/s
Equation for bit rate.
samples per second * bits per sample
Equation for duration of signal?
no. bits / bit rate
