Signaling Flashcards
How do you calculate the number of bytes given the number of bits
Divide the number of bits by 8
How do you calculate the possible number of alternatives in a binary string and hence the number of bits from the number of alternatives
2^bits
log2((N)umber of alternatives)
In a coloured image, how many binary numbers are used to represent each picture element and what are they used for
3, one for red, one for blue and one for green
What are the 2 definitions of image resolutions and how do you calculate each one
- The length represented by each pixel. To calulate, take the real width of the object in real life and divide that by the number of pixels used to represent that width
- The number of pixels in the format width by height
How can you increase the amount of information in an image
Use more bits per pixel
How do you calculate the total amount of information in an image
Number of pixels times the bits per pixel
What is the difference between changing brightness and changing contrast of an image
Changing brightness adds a fixed value to each pixel, so the difference between each pixel remains the same.
Changing contrast multiplies each pixel by a fixed value, which causes the difference between each pixel to increase.
Describe the process of adding false colour to an image and the benefits of it
Take the values of an image and assign them different colours (I.e. if a value of 50 is grey and a value of 100 is dark grey, then 2 could be pink and 4 could be green)
The brighter, higher contrast colour allows for important details within the image to be highlighted
What is noise and how is it reduced within images
Interference in the signal.
In images, we can replace each pixel with the median of the 8 surrounding pixels and itself
Describe the process to find the edges in an image
- Multiply the value of a pixel by 4
- Subtract the values of the pixels in the cardinal directions
- If the answer is negative, the value is treated as 0
- Invert the colours, so now any pixels not on the edge become white
In what scenario does edge dectection NOT work?
If there is a gradual change in colours
Why are digital signals resistant to noise, but analogue is not?
A reciever must reconstruct a wave that is recieves, and if there is noise in the signal, then it may reconstruct it inaccurately. When the number of inputs is restricted, such as in a digital signal, it reduces the chance of the signal being reconstructed inaccurately.
Describe the process to digitise an analogue signal.
- Take the value of the signal at regular intervals then match it to the closer digital value
- Convert the digital values into binary values
Describe what determines resolution of signals and how it affects the quality of digitisation of a signal
Resolution is determined by the number of bits used per value. If more bits are used, then you have a large number of closesly spaced digital values and the reconstructed signal will be a lot closer to the analogue signal
Where would you use a high and low resolution signal and why
High - CDs. They use a 16 bit recording so that the recorded music is similar to the original
Low - Telephone lines. The conversations had need to be audible, but don’t need to be accurately reprasentative of the person’s voice
What are the advantages of digital signals?
- Sent, recieved and reproduced more easily due to a limited number of values
- Easily compressed and manipulated
- Noise isn’t really a problem
- Digital can represent multiple types of media
- Computers can easily process digital signals
What are the disadvantages of digital signals?
- Can’t reproduce analogue signals exactly
- Can be reproduced easily, which leads to piracy (hardly a downside)
- Easier for information to be stolen
Define the fundamental frequency and describe how you find it
The fundamental frequency is the lowest frequency wave that makes up a sound wave. To find it, find the shortest repeating part of the sound wave and calculate the inverse of it.
Why do we want to limit the number of bits we use in resolution and how do we calculate the number we use?
If the original signal contains noise, then a high resolution will reproduce all the noise. To calculate the actual number of bits we use, we take log 2 of the (total variation in the signal divided by the variation caused by the noise)
Why is important to have a high sample rate?
If the sampling rate is too low, detail can be lost, or aliases can be created (low frequency signals that are reconstructed from the samples that weren’t in the original signal)
What is the theory to determine minimum sample rate?
Nyquist theory, sample at 2 times the highest frequency
What two things are rate of transmission dependant on and how do you calculate it. Add the units
The sample rate and the number of bits per sample.
Multiply the sample rate by the bits per sample
It’s in bits per second
