unit 3 - data representation Flashcards
what is binary?
a base 2 system of numbers using only 1 and 0
what is 1 bit?
a 0 or 1
what is 1 byte?
8 bits
what is a kilobyte?
1000 bytes
what is a megabyte in kB?
1000 kB
what is a gigabyte in mB?
1000 mB
what is a terabyte in GB?
1000 GB
what is a petabyte in TB?
1000 TB
what are the uses of binary?
it is used to store numbers and do binary arithmetic with
what does a binary shift to the right represent?
dividing by 2 - moves all the bits one place to the left
what does a binary shift to the left represent?
multiplying by 2 - moves all the bits one place to the right
what is an overflow error?
when the result of a binary arithmetic calculation is too long for a computer to process
what are the possible states of binary?
256, 128, 64, 32, 16, 8, 4, 2, 1
what is the most significant bit?
the bit with the largest value - furthest to the left
what is the least significant bit?
the bit with the smallest value - furthest to the right
how to convert binary (0001 1100) to decimal
example:
128 64 32 16 8 4 2 1
0 0 0 1 1 1 0 0
16 + 8 + 4 = 28
what is the largest number that can be held in 8 bits?
numbers between 0 (0000 0000) and 255 (1111 1111)
2^8 - 1 = 255
what is hexadecimal?
a base 16 number system, 0-9 A-F
how many values can be held in hex?
256 values - from 0 - 255
what are the advantages of using hexadecimal?
- simpler to remember
- quicker to type
- fewer digits so less error prone
- easier to convert between hex and decimal
hexadecimal (2A) to decimal conversion
2 (comes in groups of 16s) + A (10 in hex)
(2 x 16) + 10 = 42 in decimal
multiply left hand digit by 16 and then add the units
decimal (18) to hex conversion
- divide the decimal by 16 to get the number of 16s (left had digit) -> 18/16 = 1 r 2
- the remainder is the units -> 2
- the hex value for decimal 18 is 12
binary (1110 0101) to hex conversion
- divide the binary into two niblle of 4 bits
1110 0101 - convert each nibble into a decimal and then into its hex value and rejoin
1110 = 14 = E + 0101 = 5 = 5 in hex - so 1110 0101 = E5 in hex
hex (3B) to binary conversion
- split the two hex characters and convert to binary
3 = 0011 B = 1011 - so 3B = 0011 1011
what are the rules of binary addition?
- 0 + 0 = 0
- 0 + 1 = 1
- 1 + 0 = 1
- 1 + 1 = 0 carry the 1
- 1 + 1 + 1 = 1 carry 1
- 1 + 1 + 1 + 1 = 1 carry the 1 over two columns
what is ASCII?
a code for representing english characters with numbers with each character being represented with a binary number
it includes: numbers 0-9, upper and lowercase A-Z, punctuation symbols and the space character
how many characters can be held in 7-bit ASCII?
128
what is a character set?
a set of letters, symbols and digits that can be represented by a computer
what are two examples of character sets?
ASCII and unicode
what can a computer’s memory and storage only hold?
can only hold binary 1s and 0s
how many characters can be encoded in extended ASCII?
256 different characters because it is 8 bit
what is unicode?
it represents other characters from different languages so it has been developed to use 16 bits - 65, 536 combinations
what is a pixel?
a picture element - the smallest identifiable area of an image.
what is the function of a pixel?
each pixel is given a single colour and is given a binary value, which represents the colour.
a pixel’s colour can be changed by changing this value
what is a bitmap?
an image composed of pixels with a fixed resolution
what is the colour depth?
the number of bits per pixel
what does an increase in colour depth mean?
it means that more bits are used to represent each pixel so the overall size will increase
what is the equation to calculate file size in bytes?
(image width x image height x colour depth) / 8
what is the equation to calculate file size in bits?
image width x image height x colour depth
what is the image resolution?
the concentration of pixels within a specific area- defined by image width and height in pixels
what does a higher amount of pixels in a given area mean for the image?
higher imagine resolution so the quality of the image will be better
what does the size of the image depend on?
the number of pixels
what does having more pixels per inch mean for the image?
the image is sharper but the file size is higher
what are some bitmap image file formats?
GIF, JPG, PNG
how can we find colour depth?
pixel = n bits
combinations = 2^n
what are the colour values of individuals expressed as and why?
in software they are represented as decimal RGB values and in hexdecimal - this is because it is easier for people to read, write, remember and reduce errors if copied
what do the RGB values range between?
0-255
what is image metadata?
information other than the image data that is stored with a file, including:
- colour depth in bits per pixel
- resolution (height and width in pixels)
- date created
- author
sometimes this the reason why file sizes don’t always add up
what is the difference between digital and analogue
- sound waves are measured in analogue which are continuously changed
- but it must be stored in a digital format, which is discrete
what is sampling?
soundwaves being measured at regular intervals converting the waveform into a numerical representation - that is how sound is digitised
what does a analogue to digital converter do? and why?
takes signals and converts them into a digital representation because sound must be converted into a digital form to be stored and processed by a computer
what is a sample?
a measure of amplitude at a point in time
what is sample resolution?
the number of bits used to store each sample
what do more bits per sample mean for the sound quality and the file size?
- enables the height of the wave to be more accurately measured
- but also increases file size
what is the sample rate?
number of samples taken per second
the greater the frequency, the greater the ccuracy and file size
what is sample rate measured in?
hertz
1Hz = 1 sample per second
what is the equation for calculating the file size of a sound file?
sample resolution x sample rate x number of seconds
- divide by 8 to get the answer in bytes
what are the common sample rate and resolution for a CD audio?
sample rate: 44.1 kHz or 44100 Hz
sample res: 16 bits
what is the sample resolution?
the number of bits used to record each measurement
what is the human hearing rate?
20Hz - 20,000Hz
what is lossy compression?
- removes unnecessary sounds that we can’t easily hear or that least affect the perceived playback quality
- it is compressed by removing some detail from the original
what are the advantages of lossy?
- you can save lots of storage because lossy can easily compress 10MB into 1MB
- useful for storing, downloading and streaming
what are the disadvantages of lossy
- permanently loses data that can’t be returned and may result in digital artifacts
- can’t be used on text or software files
- lose quality on images and audio
what is lossless compression?
date compression technique in which the files can be reduced by compression but doesn’t not lose any information
how does lossless compression work?
the algorithm finds groups of repeating data and records the data once along with the number of repetitions
what are the benefits of compression?
- smaller files, fewer packets, faster transmission, hence less traffic
- reduces download times
- reduces space taken up on a disk/server
- reduces amount of bits required to store data
examples of lossy compression:
JPEG, MP3, MP4
examples of lossless compression:
PNG, ZIP, GIF
what is huffman encoding?
a form of lossless compression based on certain characters appearing more often than others. it uses the repeated patterns in the original pattern and encodes each pattern in a dictionary
what is (RLE) run length encoding?
an algorithm to compress data that uses frequency/word pairs to reduced the amount of data stored
what is compression?
algorithms which reduce file sizes, often used with sound, image and video files
what are the two types of compression?
lossy and lossless
what are digital artifacts?
small mistakes that appear on images and videos as a result of lossy compression
