Chapter 1: Imaging Flashcards
What is the Wave Equation?
v = fλ
How can images be recorded electronically?
With microsensors, such as charge-coupled devices (ccd)
How can images be recorded on an atomic scale?
By scanning methods; such as an atomic force microscope (AFM) or a scanning tunnelling microscope (SEM and TEM)
How are images stored digitally?
As an array of pixels, each of which is defined by a number.
How can images be smoothed?
By different types of averaging techniques. They can also be sharpened with edge detection.
What is the lens equation?
1/v=1/f+1/v
What does the Cartesian convention state?
You should measure from the lens to the right as positive and from the lens to the left as negative. Therefore, u is always negative whilst v is positive.
When does refraction occur?
When a wave changes speed by moving from one medium into another.
What makes a material optically denser than another?
It slows down light more than another material.
What is the purpose of a lens?
Lenses add curvature to wavefronts
What is the focal length equal to for parallel incoming rays of light?
The image distance
What is the lens power equation?
P = 1/f
What are the units of optical power?
Dioptres (D)
What is curvature defined as?
1/radius of curvature
What is the equation for magnification?
m = size of image / size of object;
m=v/u
What is the focal length of a lens?
The distance between the lens axis and the focus.
What happens to a wave as it passes through a thin converging (convex) lens?
The rays of light will converge to the focal point.
What is a bit?
A single digit (0 or 1)
What is a byte?
8 bits
Number of bits =
amount of information
Equation for number of possible alternatives, N
N = 2^I
or
log_2(N)=I
What is an image?
An array of pixels each needing an 8, 16 or 24 bit colour code.
How many possible alternatives does 8 pixels give?
N = 2^I = 2^8 = 256
What is a CCD?
Array of tiny sensors mounted on a chip, detecting light levels. Information from each sensor is recorded and converted to a pixel value.
How do you reduce the noise in an image?
You replace the value of a pixel by the median value of the pixel and its eight neighbouring pixels.
How do we detect edges?
Using the Laplace rule: multiply a pixel’s value by 4 and then subtract the values of the pixels to the pixel’s north, south east and west from it.
Types of image
ultrasound, visible light, radar, IR, X-rays, electron scattering…
What is RESOLUTION?
The smallest object or distance distinguishable.,
What is the equation for the displacement at any one point in a wave?
s = A sin(2πft - ϕ)
Name an application of gamma rays
Sterilisation of medical instruments; medical imaging
Name an application of X rays
medical imaging
Name an application of UV light
sun beds/security markers
Name an application of visible light
photography, seeing
Name an application of IR radiation
fibre optic communication
Name an application of microwaves
cooking food; satellite communications
Name an application of radio waves
broadcasting and communication
Name a typical source of gamma rays
Decay of a radioactive nucleus
Name a typical source of X rays
Inner shell atomic electron transitions
Name a typical source of UV rays
Atomic electron transitions
Name a typical source of visible light
Outer shell atomic electron transitions
Name a typical source of infrared rays
vibrations of atoms and molecules
Name a typical source of microwaves
electrons in resonant cavities
Name a typical source of radio waves
electrons oscillating/accelerating and decelerating in an aerial.
