Deck 1: Imaging

Question 1

Define resolution of an image

Answer 1

The resolution of an image is the smallest size of thing that can be distinguished.

Question 2

Give a situation were resolution can be important?

Answer 2

In an ultrasound scan, if a baby has a heart defect the ultrasound scanner must be able to detect it.

Question 3

Give two examples of were resolution limits the quality of an image.

Answer 3

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.

Question 4

What is a piezoelectric crystal, whats its use?

Answer 4

Pulse generator detector, frequency of piezoelectric crystal is 3MHz.

Question 5

What is the wavelength and speed of a piezoelectric crystal?

Answer 5

The wavelength of ultrasound is 0.5mm, and the speed of ultrasound is 1500m/s.

Question 6

How does an ultrasound scanner build an image?

Answer 6

An ultrasound scanner builds up an image from the strength and time delay of reflected pulses.

Question 7

What is the highest frequency people can hear up to?

Answer 7

20KHz

Question 8

Period

Answer 8

Period,T, seconds - the time taken for a whole vibration ( for a wave to complete a whole wavelength).

Question 9

Frequency, Hz

Answer 9

The number of vibrations per second passing a given point.

Question 10

What is computer tomography?

Answer 10

The big computing job of working out what is producing all the reflections in an ultrasound scan.

Question 11

Right out the electromagnetic spectrum from the longest wavelengths to the shortest.

Answer 11

1) Long-wave radio
2) Ultrahigh frequency
3) microwave
4) Infrared
5) Visible light
6) Ultraviolet
7) X-ray
8) Gamma-ray

Question 12

In the electromagnetic spectrum, in which direction does the frequency and photon energy increase?

Answer 12

Long-wave radio starts with the lowest frequency and photon energy to gamma ray which has the highest.

Question 13

In the electromagnetic spectrum,in which direction does the wavelength increase?

Answer 13

Gamma ray having the lowest and long-wave radio having the largest.

Question 14

What is the frequency and wavelength of long-wave radio waves?

Answer 14

The frequency of long-wave radio is 10^5Hz and the wavelength is 10^4m.

Question 15

What is the frequency and wavelength of micro waves?

Answer 15

The frequency of microwaves is 10^11Hz and the wavelength is 10^-2m.

Question 16

What is the frequency and wavelength of ultraviolet waves?

Answer 16

The frequency of ultraviolet waves is 10^16Hz and wavelength is 10^-7m.

Question 17

The frequency and wavelength of gamma rays?

Answer 17

The frequency of gamma rays is 10^20Hz and wavelength is 10^-12m.

Question 18

Explain how a CCD works?

Answer 18

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.

Question 19

Explain how the scanning tunneling microscope works.

Answer 19

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.

Question 20

What is a bit?

Answer 20

A bit is a memory location storing either a 1 or 0.

Question 21

What is a byte?

Answer 21

8 bits.

Question 22

The better the resolution of an image the more of what does it have?

Answer 22

More information stored for it.

Question 23

How many alternatives are there for 8 bits?

Answer 23

2^8= 256

Question 24

The amount of information something has =

Answer 24

The number of bits it has.

Question 25

If the number of bits something has increases by one, what happens to the number of alternatives?

Answer 25

The number of alternatives doubles.

Question 26

The amount of information that something has is measured on what sort of scale?

Answer 26

It is measured on a plus scale and increases by equal additions.

Question 27

The number of alternatives something has is measured on what?

Answer 27

Measured on a times scale and increases by equal multiples.

Question 28

How is the number of alternatives,n, calculated from the amount of information something has?

Answer 28

Number of alternatives, N=I^2 - I = information in bits

Question 29

How is the amount of information something calculated?

Answer 29

Log2(number of alternatives)=information

Question 30

3 bytes = how many bits?

Answer 30

3x8= 24 bits

Question 31

Why are logarithmic scales used?

Answer 31

Logarithmic scales are used to show many orders of magnitudes on on graph.

Question 32

What does a logarithmic scale increase by?

Answer 32

It increases by equal multiples.

Question 33

What is the length of the diameter of the Earth?

Answer 33

1 mega meters

Question 34

What is the size of a small town?

Answer 34

1 kilo meters

Question 35

What is the width of a human hair?

Answer 35

10^-5 meters.

Question 36

What is the size of a microchip element?

Answer 36

1 micro meter

Question 37

What is the size of a molecule?

Answer 37

1 nano meter.

Question 38

Why can digital images be manipulated more than photographs?

Answer 38

Because you can manipulate the numbers corresponding to the pixels of the image.

Question 39

IMAGE PROCESSING: Removing noise

Answer 39

Replace each pixel by the median of its value and those of its neighbours.

Question 40

IMAGE PROCESSING: Smoothing sharp edges

Answer 40

Replace each pixel by the mean of its value and those of its neighbours.

Question 41

IMAGE PROCESSING: Finding edges

Answer 41

Subtract the N,S,E and W neighbours from four times the value of each pixel.

Question 42

What lenses do we have in the eye?

Answer 42

We have the cornea and another adjustable lens behind that.

Question 43

What is the retina briefly?

Answer 43

The retina is built from light sensitive elements that emit signals to the brain.

Question 44

What are cones?

Answer 44

Cones are the light sensitive elements of the eye which work best in bright light and detect colours.

Question 45

What are rods?

Answer 45

Rods are light sensitive elements in the eye which are sensitive to dim light but do not distinguish colours.

Question 46

What is the rod to cone ratio in the retina like?

Answer 46

Many more rods than cones.

Question 47

What is the fovea?

Answer 47

The fovea is an area in the retina which detects fine detail,it is packed with cones.

Question 48

Explain how the eye is good at detecting edges.

Answer 48

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.

Question 49

What is the focus point?

Answer 49

The focus point is the point where all the light is bent towards on point where they all cross.

Question 50

A powerful lens has a long or short focal length?

Answer 50

Short

Question 51

What does a lens add the waves coming into it?

Answer 51

1/f curvature

Question 52

What is the power of a lens measured in?

Answer 52

Power of a lens = 1/f and is measured in dioptres.(1/v and 1/u is also measured in dioptres)

Question 53

Explain what happens to the wave fronts of waves as it enters glass and as it leaves.

Answer 53

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.

Question 54

Refractive index glass=

Answer 54

Speed of light in a vacuum / Speed of light in glass

Question 55

Explain why glass of the same refractive index as oil will disappear when submerged in it.

Answer 55

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.

Question 56

What is the only thing a lens changes about incoming light?

Answer 56

It adds curvature and thats it. (Does not change its general direction).

Question 57

What is the lens equation?

Answer 57

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.

Question 58

Explain the cartesian graph rules

Answer 58

1)Measure from the lens. 2) Count distances to the right positive 3)Count distances to the left as negative.

Question 59

How is the linear magnification of a lens calculated?

Answer 59

image/ object or image distance/object distance

Question 60

In m=v/u , what does a negative sign of m indicate?

Answer 60

Negative sign of m indicates inversion of image.

Question 61

In m=v/u what does a value of less than 1 for m indicate?

Answer 61

Indicates diminution