information rep and multimedia Flashcards
analogue data
- data obtained by measurement of physical property
- any value from a contiuous range of values
- continuous electrical signals
ASCII
- only english alphabets can be represented
- each character encoding takes up 7 bits, 128 possible characters
- smaller storage space
bandwidth
rate of data transfer
Binary coded decimal (BCD)
practical applications:
- a string of digits on any electronic device displaying numbers (calculators)
- accurately measuring decimal fractions
- electronically coding denary numbers
bitmap images
images stored as an array of individual pixels. a bitmap image is created by combining pixels.
colour depth/bit depth
number of bits allocated to represent each pixel’s colour -> colour depth depends on bit depth
compression
the reduction of file size
digital data
- data that has been stored as binary value (0s and 1s)
- discrete electrical signals
drawing list
set of commands defining the vector
drawing objects
a mathematically defined construct of shapes
Extended ASCII
- includes most European languages’ alphabets
- extended to 8 bits, 256 possible characters
features of vector graphics
- stores a set of instructions about how to draw the shape
- individual elements of vector graphics can be grouped
- each geometric shape needs to be changed to alter the design
- does not require a large file size
- not very realistic as the number of shapes are limited
- file formats: .svg, .cgm, .odg
- can be resized without pixelation
storing commands, not individual pixels - can be transferred and downloaded quicker
features or graphic editing software
Ready Crabs Bring Revenge
- re-size: increase/decrease the size of the image
- crop: remove certain parts of the image
- blur: reduce the focus
- red-eye reduction: reduces red light reflected from human eye
file header
contains info regarding the image such as image size, number of pixels, types of compression, colour depth, file location
formula for bit rate
bit rate = sampling rate x sampling resolution
file size = bit rate x length of sound
formula for size calculation
width pixels x height pixels x colour depth
hexadecimal base and applications
base 16
- defining colours in HTML
- defining media access control (MAC) addresses
- assembly language and machine code
- debugging via memory dumps
high resolution images -> increase in file size
impacts:
- the number of images that can be stored on the hard drive
- the time to download images from the internet
- the time it takes to transfer images from device to device
how images are encoded into digital format
- images are stored as bitmap images
- each image is made up of pixels
- each pixel is of a single colour
- each colour has a unique binary number
- sequence of binary numbers is stored in each image
how sampling is used to record the sound clip
- amplitude of sound wave is determined
- at set time interval
- to get an approximation of the sound wave
- encoded as a sequence of binary numbers
- increased sampling rate will improve the accuracy of the recording
image resolution
- measured in pixels per inch, value determines the amount of detail an image has
- high image resolution means that there are more pixels per inch, resulting in more pixel info and creating high quality images
lossless compression
- data is not lost
- file can be decompressed as the original
lossless is used when
accuracy of data is important
lossy file compression
data is lost and the decompressed file is not the same as the original
lossy is used when
- accuracy of data is unimportant
- smaller file size is needed
- for sound files (.mp3), .jpeg images
- sound files compression utilizes perceptual coding to remove certain parts (frequencies) of sound that are less audible to human hearing
media access control (MAC) address
every device on a network has a MAC address which identifies it uniquely. data packets sent to switches will have a MAC address identifying the source of the data
metadata
data/information about data
e.g: file name, file format, colour depth
modifying image resolution
- pixels can be removed to fit the screen
- instead of modifying, simply zoom in to enlarge it to full-screen size; causes image to become pixelated as the pixel density is reduced and can cause image quality to become deteriorated
pixel
smallest picture element
pixel density
number of pixels per square inch
property
data about the shapes
quantization error
the difference between the analogue signal and the closest digital value at each sampling instant
reasons why files need to be compressed
- data files can be very large
- it would take a long time to transfer the non compressed file / compressed files will download faster
- a higher bandwidth would need to transmit the uncompressed file
run length encoding (RLE)
- looks for runs of consecutive pixels of the same colour
- then reduces file size of a sequence of elements with adjacent and identical elements
- stores the colour value once and the number of times it occurs
- lossless
sampling
taking measurements of sound at regular time intervals
sampling rate
number of samples taken per second
higher sampling rate -> higher accuracy
sampling resolution
number of bits used to store each sample
screen resolution
number of pixels which can be viewed horizontally and vertically on the screen
- if screen res < image res, the whole image cannot be shown on the screen or the original image will be a lower quality
true colour
requires 3 bytes per pixel which gives more than one million colours
Unicode
- superset for ASCII + extended ASCII - recognised by various global languages
- greater range of characters, as it uses 2 or 4 bytes per character
- 2 or 4 times more storage space per char
vector graphics
images made up of drawing objects, the properties of each object determine its shape and appearance
perceptual coding
used to remove certain parts (frequencies) of sound that are less audible to human hearing
