Flashcards in Coding systems Deck (25):
What is ASCII?
A binary coding system for storing characters
Seven (or eight, for the more recent extended ASCII) bits are used, with each permutation representing a different character. As a result, it can only represent 128 or 256 characters
What is unicode?
A binary coding system that has superseded ASCII
It has backwards compatibility with ASCII. There are two common encodings, UTF-8 and UTF-16, which use 8 and 16 bits respectively. It can represent every character in use in the world
Describe the parity bit method of error checking
A bit appended to a binary data transmission to check for errors. If the transmissions contains an even number of 1s then the parity bit will be 0, else it will be 1, i.e. it makes the number of 1s even. If the number of 1s is the data received is odd, then it is therefore incorrect
Describe the majority voting method of error checking
Each bit is transmitted three times, i.e. 101 would be transmitted as 111000111. Therefore, if there are not three consecutive 1s or 0s, there is an error. In this case, the bit with the most occurrences is chosen, i.e. 001 would be assumed to be 0
Describe the check digit method of error checking
Some operation is performed on all digits to obtain a one digit number, i.e. repeatedly adding up the digits until a one digit number is reached. This digit is then appended to the number. When the transmission is received, the number is checked to see if it produces the same check digit. To overcome the problem of two digits being swapped around not having an effect on the check digit, each digit may first be multiplied by a different weight, starting at 2, i.e. 23045 would become 2*6+3*5+0*4+4*3+5*2
What is the resolution of an image?
width*height (in pixels)
Describe bitmapped graphics
Each pixel is stored individually using one or more bits. They may also contain metadata, normally found at the beginning of the file and including information such as the image's width, height and colour depth
What is the colour depth of an image?
The number of bits allocated to the colour of each pixel in a bitmapped image
How many different colours may an image with a colour depth of n contain?
What is the relationship between the file size of an image, its resolution, and its colour depth?
file size=resolution*colour depth
Describe vector graphics
They are created using objects and coordinates. For example, a line could be stored with just two sets of coordinates, a triangle with three, etc. Other information may include thickness, colour, etc.
Give two advantages of vector graphics compared to bitmapped graphics
*Smaller file size due to not having to store information about every pixel
*No pixellation occurs when enlarged
What is sampling/analogue to digital conversion?
The process of converting analogue sound waves into digital form
Explain how analogue to digital conversion works
A series of readings at fixed intervals are taken from the wave, recording the amplitude
What is the sampling resolution in analogue to digital conversion?
The number of bits allocated to each sample
What is the relationship the file size of an audio file produced through analogue to digital conversion, the sampling rate, the length of recording, and the sampling resolution?
file size=sampling rate*length*sampling resolution
What does Nyquist's theorem state?
To faithfully recreate an analogue signal in digital form, the sample rate should be at least twice the value of the highest frequency in the sampled signal
What is compression?
The process of reducing the number of bits required to represent data
What is lossless compression?
Compression where the compressed file has the same quality as the uncompressed file
What is lossy compression?
Compression where some data is discarded and so the resultant file is of worse quality
Explain how run length encoding can compress data
It eliminates repeated data, i.e. aaaaa may be turned into 5a
Explain how dictionary based encoding can compress text files
Common strings are coded in some way. For example, "tion" may be replaced with a "1". It can then be decoded again by looking up what string each numeric token corresponds to