Imaging and signalling

Created by

Summer Evans

Cards (36)

What expression can be used to calculate the number of alternatives produced by a given number of bits?
$N=$ $2^b$
What expression can be used to calculate the number of bits required for a given number of values?
$b=$ $log_2 N$
What is meant by the resolution of an image?
The resolution of an image is the smallest distance between which two points can be distinguished
What equation is used to calculate resolution?
$Resolution=$ $width /number$
What are the 4 main ways of processing an image?
Removal of noise
Edge detection
Increasing contrast
Changing brightness
The process of noise removal is to:
Replace the value of the pixel by the mean of the 8 immediately surrounding pixels
What is meant by the term 'real image'?
An image that can be projected onto a screen
In the wave model of light, what can be said about the direction of the waves motion and its wavefronts?
The wavefronts are perpendicular to the direction of the waves motion
What are plane wavefronts?
Wave fronts parallel to eachother and appear to have no curvature
What condition is required for a wave to have plane wavefronts?
The wave should come from a very distant source
How does a converging lens affect wavefronts of light?
The lens adds curvature of 1/f to the wavefront
What is the lens equation?
$1/v=$ $1/u +$ $1/f$
What expression is used to calculate the power of a lens?
1/f
What is the unit for power of a lens?
Dioptres, D
Why are object distance values negative?
It is measured in the opposite direction to the image and focal length
What are the equations for linear magnification?
$H_i /H_o$ $D_i /D_o$
What do modern cameras use to store images?
CCD (charged coupled devices)
What is a CCD?
It is a screen covered with pixels that store charge when light is incident on them
What is a binary system?
A system that can take 2 values, on or off
What is the process of edge detection?
Get the average value of the 8 pixels surrounding it and subtract it from the pixel
What is the process of increasing image contrast?
Multiply each pixel by a fixed number so that the image spreads across all available values
What is the process of increasing image brightness?
Add a fixed value to each pixel to brighten it
What is the difference between analogue and digital signals?
Analogue signals can continuously vary between values, whereas digital can only take fixed values
What process is used to convert analogue signals to digital?
Sampling
What does the process of sampling involve?
It involves taking frequent measurements of analogue signals and then rounding them to the nearest value
What problem can arise when carrying out sampling?
It can produce quantisation errors, which is a difference between the quantisation level and the actual level
What is a positive and negative of analogue signals?
✅️ more detailed than digital signals
❌️ cannot be easily amplified due to noise
Four advantages of digital signals
noise resistant
Easy to send, store and receive
Faster transmission
Easily compressed
Two disadvantages of digital signals
Lack of detail
Easily scrambled
What equation can be used to calculate the maximum level of useful quantisation levels
Total noisy signal variation
-------------------------
Noise variation
State an equation linking the number of quantisation levels used and the image resolution
Resolution=p.d rangeof signals
-----------------
Number of levels
What is the minimum sampling rate that can be used when converting analogue to digital?
The minimum sampling rate must be at least twice the the highest frequency in the signal
What can happen if sampling rate is too low?
Aliasing can occur
A low signal may be produced from a high frequency from the rate being too infrequent
What is bit rate?
The rate of information transmission
What is the equation used to calculate bit rate?
Rate=
sample per second x bits per sample
What is the relationship between bits and bytes?
A byte is 8 bits