Data Representation Flashcards
What is data?
Basic values or facts.
What is information?
Data that has been organised or processed in a useful manner
What is multimedia?
Several different types of media.
What is data compression?
Reducing the amount of space needed to store a piece of data.
What is bandwidth?
The number of bits or bytes that can be transmitted from one place to another in a given period of time.
What is the compression ratio?
The size of the compressed data divided by the size of the uncompressed data.
This should be a number between 1 and 0, and the closer it is too 0 the tighter the compression
What is lossless compression?
Data compression in which there is no loss of information.
What is lossy compression?
data compression in which there is loss of information.
What is analog data?
A continuous representation of data.
What is digital representation?
A discrete representation of data.
What does digitize mean?
The act of breaking down information into discrete pieces.
What does Pulse-code modulation mean?
Variation in a signal that jumps sharply between two extreams.
What does Reclock mean?
The act of reasserting an original digital signal before too much degeneration occurs.
What is overflow?
A situation where a calculated value can not fit into the number of digits reserved for it.
What is the radix point?
The dot that separates the whole part from the fractional part in the real number of any base?
What is a character set?
A list of the characters and the codes used to represent each one
What is keyword encoding?
Replacing a frequently used word with a single charterer.
What does ascii stand for ?
What is Ascii?
Amrecian Stranded Code for Information Interchange.
Originally used 7 bits allowing for 128 different unique characters, and the eighth bit was used as a check bit which helped ensure proper transmission. However it was soon changed to use the eighth bit allowing for 256 unique characters.
The first 32 characters are not simple characters that can be printed to the screen, but are reserved for special purposes such as back space.
What does Unicode Stand for?
What is Unicode?
Why do we have it
The extended verion of ASCII that uses 256 bit is enough for the English language but not enough to be used internationally. Unicode’s goal was to be able to represent every single charecter from every single language.
It uses 16-bit encoding per character but is flexible so that it can use more spaces per character if needed.
The ASCII values are a subset of Unicode, and Unicode is a super-set of ascii.- the first 256 characters are the same.
What is keyword encoding?
Replacing frequently used words with a single character.
Longer words save more space as more text is reduced however the frequnelty used words text to be shorter.
Cons:
- The character can not be part of the original text, or t would be unknown when that character appeared it would be ambiguous.
- UpperCase and lowercase versions of the same word would have to have be represented differently.
What is Run-Length Encoding?
Replacing a long series of a repeated character with a count of the repetition.
This can be very usuful for texts such as DNA in which a there would be long runs.
It works by having a flag followed by the charecter followed by the number of times it appears. IE AAAAA becomes *A5.
Cons:
-It is only worth encoding if the carecter is repeated more then 3 times as that is longer then the encoded version.
What is Huffman encoding?
How does it work?
Using a variable length binary digit to represent a single character, ensuring that the most frequently used characters have the shortest codes.
An important factor of the Huffmann encoding method is that no bit string used to represent a character is a prefix for any other bit string used to represent a character. Therefore we can scan from left to right across the bit string, and when a bit pattern matches, that bit string is translated to the character.
What is the process of huffman encoding?
First calculate frequency of characters if not given
Generate Huffman Tree
Calculate number of bits using frequency of characters and number of bits required to represent those characters.
How does a stereo produce sounds that we hear?
A stereo produces an electrical signal to the speaker, and this is an analogue representation of the sound. This causes the speaker to then vibrate, which vibrates the air, in turn vibrating the membrane in our ear.
What are real numbers?
Numbers with a whole part and a fractional part.
What is sampling?
The process of perodically measuring the voltage leve of a signal and recording this as a numeric value.
To get an accurate sound we should sample at 40,000 times per second.
What is MP3?
MP3 is a popular audio format, due to its strong compression ratio. It employs both lossless and lossy data compression.
It first analyses the frequencies, and discards any that are out of the human hearing range. The remaining bit stream is then compressed further using huffman encoding.
How is color represented?
When representing colour, we represent as a RGB (red green blue) value, with three numbers representing the amount of each colour. The colour depth is the number of bits used to represent the colour. Hi-colour has a 16 bit colour depth, using 5 bits for each of RGB, and the extra bit sometimes used to represent transparency. True-colour uses a 24 bit colour depth so each colour is represented by 8 bits. This gives a scale from 0 to 255. So a RGB colour would look like (200, 192, 45).
What are pixels?
Dots of colour in a picture.
What is the resolution?
Number of pixels in an image.
What is raphster graphics?
Representing a picture as a collection of pixels.
Common formatts are JPEG, PNG, GIF, Bitmaps.
What is a Bitmap?
A type of raphster graphics, with true colour depth, or less to reduce file size. Suited to RLE..
What is a GIF?
Tye of raphster graphics, that is made up of only 256 different colors, but each gif is made from a differnt set of colours - this is known as Indexed colour. GIFS are suited to graphics with few colors.
What is PNG?
–Intended to replace GIFs
– Greater compression with wider range of color depths
– No animation
What are JPEGS?
• JPEG – Averages hues over short distances as human vision tends to blur colors together within small areas. • Essentially the same idea used in MP3 – Adjustable degree of compression most suited for storing photography.
What are vector graphics?
•A format that describes an image in terms of lines
and geometric shapes
•A vector graphic is a series of commands that
describe shapes using mathematical properties
(e.g. direction, length, thickness, color)
•For some types of images, the file sizes can be
smaller than with raster graphics because not
every pixel is described.
Pros and cons of vector graphics?
Vector graphics can be resized mathematically
and changes can be calculated dynamically as
needed.
Vector graphics are good for line art (e.g.
diagrams) and cartoon-style drawings
Vector graphics are not good for representing
images of the real-world
What is Codecs?
Refers to methods used to compress film.
Almost all Codecs use Lossy data compression to reduce the huge amount of data associated with film.
What is temporal compression?
Temporal compression
A technique based on differences between
consecutive frames: If most of an image in two frames
has not changed, why should we waste space
duplicating information?
What is spatial compression?
Spatial compression
A technique based on removing repetitive information
within a frame: This problem is essentially the same as
that faced when compressing still images
