Deck 1: Imaging Flashcards
Define resolution of an image
The resolution of an image is the smallest size of thing that can be distinguished.
Give a situation were resolution can be important?
In an ultrasound scan, if a baby has a heart defect the ultrasound scanner must be able to detect it.
Give two examples of were resolution limits the quality of an image.
1) In an image, were there are just 256 possible different shades of grey, a change of intensity smaller than this cannot be distinguished.
2) The number of pixels of the image.
What is a piezoelectric crystal, whats its use?
Pulse generator detector, frequency of piezoelectric crystal is 3MHz.
What is the wavelength and speed of a piezoelectric crystal?
The wavelength of ultrasound is 0.5mm, and the speed of ultrasound is 1500m/s.
How does an ultrasound scanner build an image?
An ultrasound scanner builds up an image from the strength and time delay of reflected pulses.
What is the highest frequency people can hear up to?
20KHz
Period
Period,T, seconds - the time taken for a whole vibration ( for a wave to complete a whole wavelength).
Frequency, Hz
The number of vibrations per second passing a given point.
What is computer tomography?
The big computing job of working out what is producing all the reflections in an ultrasound scan.
Right out the electromagnetic spectrum from the longest wavelengths to the shortest.
1) Long-wave radio
2) Ultrahigh frequency
3) microwave
4) Infrared
5) Visible light
6) Ultraviolet
7) X-ray
8) Gamma-ray
In the electromagnetic spectrum, in which direction does the frequency and photon energy increase?
Long-wave radio starts with the lowest frequency and photon energy to gamma ray which has the highest.
In the electromagnetic spectrum,in which direction does the wavelength increase?
Gamma ray having the lowest and long-wave radio having the largest.
What is the frequency and wavelength of long-wave radio waves?
The frequency of long-wave radio is 10^5Hz and the wavelength is 10^4m.
What is the frequency and wavelength of micro waves?
The frequency of microwaves is 10^11Hz and the wavelength is 10^-2m.
What is the frequency and wavelength of ultraviolet waves?
The frequency of ultraviolet waves is 10^16Hz and wavelength is 10^-7m.
The frequency and wavelength of gamma rays?
The frequency of gamma rays is 10^20Hz and wavelength is 10^-12m.
Explain how a CCD works?
When an image is formed, each element stores a charge in proportion to the brightness of the light that has fallen on it. To record an image the charges are shunted in sequence from one element to the next until they reach the edge were the value is read as a potential difference.
Explain how the scanning tunneling microscope works.
It has a support and control arm which has an ultra-sharped needle which scans across the surface, electrons from the atoms “tunnel” into the tip and make a current the microscope moves the needle to keep this current constant and then the movements are recorded to make an image of the materials surface.
What is a bit?
A bit is a memory location storing either a 1 or 0.
What is a byte?
8 bits.
The better the resolution of an image the more of what does it have?
More information stored for it.
How many alternatives are there for 8 bits?
2^8= 256
The amount of information something has =
The number of bits it has.
If the number of bits something has increases by one, what happens to the number of alternatives?
The number of alternatives doubles.
The amount of information that something has is measured on what sort of scale?
It is measured on a plus scale and increases by equal additions.
The number of alternatives something has is measured on what?
Measured on a times scale and increases by equal multiples.
How is the number of alternatives,n, calculated from the amount of information something has?
Number of alternatives, N=I^2
- I = information in bits
How is the amount of information something calculated?
Log2(number of alternatives)=information
3 bytes = how many bits?
3x8= 24 bits
Why are logarithmic scales used?
Logarithmic scales are used to show many orders of magnitudes on on graph.
What does a logarithmic scale increase by?
It increases by equal multiples.
What is the length of the diameter of the Earth?
1 mega meters
What is the size of a small town?
1 kilo meters
What is the width of a human hair?
10^-5 meters.
What is the size of a microchip element?
1 micro meter
What is the size of a molecule?
1 nano meter.
Why can digital images be manipulated more than photographs?
Because you can manipulate the numbers corresponding to the pixels of the image.
IMAGE PROCESSING: Removing noise
Replace each pixel by the median of its value and those of its neighbours.
IMAGE PROCESSING: Smoothing sharp edges
Replace each pixel by the mean of its value and those of its neighbours.
IMAGE PROCESSING: Finding edges
Subtract the N,S,E and W neighbours from four times the value of each pixel.
What lenses do we have in the eye?
We have the cornea and another adjustable lens behind that.
What is the retina briefly?
The retina is built from light sensitive elements that emit signals to the brain.
What are cones?
Cones are the light sensitive elements of the eye which work best in bright light and detect colours.
What are rods?
Rods are light sensitive elements in the eye which are sensitive to dim light but do not distinguish colours.
What is the rod to cone ratio in the retina like?
Many more rods than cones.
What is the fovea?
The fovea is an area in the retina which detects fine detail,it is packed with cones.
Explain how the eye is good at detecting edges.
The rods and cones in the retina are connected to those near them. The connections are inhibitory. A lot of light on one rod or cone turns down the sensitivity of its neighbours. This make the eye a good detector of sharp edges.
What is the focus point?
The focus point is the point where all the light is bent towards on point where they all cross.
A powerful lens has a long or short focal length?
Short
What does a lens add the waves coming into it?
1/f curvature
What is the power of a lens measured in?
Power of a lens = 1/f and is measured in dioptres.(1/v and 1/u is also measured in dioptres)
Explain what happens to the wave fronts of waves as it enters glass and as it leaves.
When the wave go into glass the wave fronts become a lot closer together. When the waves leave the glass the wave fronts become further apart.
Refractive index glass=
Speed of light in a vacuum / Speed of light in glass
Explain why glass of the same refractive index as oil will disappear when submerged in it.
Since they both have the same refractive index, no light will be reflected or refracted since the light does not speed up or slow down.
What is the only thing a lens changes about incoming light?
It adds curvature and thats it. (Does not change its general direction).
What is the lens equation?
1/v=1/u+1/f
- Were v length from lens to virtual image
- Were u is length from image source to les
- f is the focal length.
Explain the cartesian graph rules
1)Measure from the lens. 2) Count distances to the right positive 3)Count distances to the left as negative.
How is the linear magnification of a lens calculated?
image/ object or image distance/object distance
In m=v/u , what does a negative sign of m indicate?
Negative sign of m indicates inversion of image.
In m=v/u what does a value of less than 1 for m indicate?
Indicates diminution
