1: Imaging_checked Flashcards
Define Frequency
The number of whole vibrations (or oscillations), f, passing a given point each second.
Frequency is measured in Hertz, Hz
The frequency is the inverse of the period
f = 1/T
Define Period
The time, T, taken for a whole vibration (oscillation)
Unit of Period is ‘second’, s
The frequency is the inverse of the period
f = 1/T
Define Phase Difference
The amount by which one wave lags behind another wave.
Phase difference is measured in degrees or radians
What do lenses do?
Lenses change the curvature of the incident wavefront by refraction.
A lens adds curvature to waves as they pass through it. If waves are uncurved before passing through the lens, and parallel to the lens axis, they will be given spherical curvature, centred on the focus (or focal point) of the lens.
Explain how a converging lens curves wavefronts by changing the speed of the wave
A converging lens curves the wavefronts by slowing down the part of the wave (or light) travelling through the middle of the lens more than parts of wave (or light) at the lens edges.
All points on a wavefront take the same amount of time to get to the focus point.
The more powerful (thicker) the lens, the more it will curve the wavefronts that travel through it - so the shorter its focal length
What is the focal length?
The focal length, f, is the distance between the lens axis and the focus
What is the lens power equation (D)?
lens power = 1 / f (focal length in metres)
Lens power is measured in Dioptres
What is the curvature of wave equation
Curvature = 1 / r
(radius or distance in metres)
What is the lensmaker equation words and symbols?
The lens equation states: curvature of waves leaving lens = curvature of waves before entering lens + curvature added by lens
1/v = 1/u + 1/f
- v = image distance (lens to image formed)
- u = object distance (lens to source)
- f = focal length
why is object distance (1/u) negative
You always measure distances from the lens axis, and count distances to the right as poitive; and distances to the left as negative
(Just like drawing graphs)
Describe the wavefronts of a distant light source. What curvature will a converging lens give them
If you’ve got a distant light source, the wavefronts approaching the converging lens will be flat (1/u = 0)
The converging lens will then give them a curvature of 1/f
Describe the wavefronts if the source is at the focus of the lens
If the source is at the focus of the lens, the wavefronts will start off curved w/ negative curvature.
This is because u is measured as a negative distance.
This -ve curvature is then cancelled out by the +ve curvature added by the converging lens - so the wavefronts will be made flat
What are the linear magnification equations for height and distance
linear magnification =
image height (m) / object height (m)
image distance (m) / object distance (m)
v/u
What is a bit?
A single binary digit {i.e. 0 or 1}
What is a byte?
A byte is a group of 8 bits
What is a pixel?
A pixel is the smallest unit of a digital image or graphic that can be displayed and represented on a digital display device.
What is the equation for number of arrangements [or alternatives] of bits(b)?
N = 2b
- N = number of levels or alternatives ot arrangements
- b = number of bits
How do you calculate number of bits, b, from number of arrangements N?
b = log2N
- b = number of bits
- N = number of levels or alternatives or arrangements
What is the equation to calculate image resolution?
Resolution = width of image / number of pixels across object
Resolution is measured in metres per pixel [mpixel-1]
What is the equation to calculate amount of information in an image?
Amount of information = total number of pixels * bits per pixel
In processing a digital image, what does adding a fixed number to each value of a pixel do?
Adding a fixed number to each value of pixel increases the brightness (if the fixed number is +ve) - each pixel has a higher number therefore has a lighter colour.