Chapter 1 - Information Representation + Multimedia Flashcards
Binary
Base 2 number system based on the values of 1 and 2 only
Bit
Abbreviation for binary digit
One’s compliment
Each binary digit in a number is reversed to allow both negative and positive numbers to be represented
Two’s compliment
Each binary digit is reversed and 1 is added to represent positive and negative numbers
Sign and magnitude
Binary number system where the left-most bit represents the sign (0=+, 1=-) and the remaining bits the binary value
Hexadecimal
Base 16 number system (0-9, A-F)
Memory dump
Contents of a computer memory output to a screen/computer
BCD
Binary coded Decimal
Number system that uses 4 bits to represent each denarydigit
ASCII code
Coding system for all the characters on a keyboard and control codes
Character set
List of characters defined by computer hardware and software so that the computer can understand human characters
Unicode
Coding system which represents all the languages of the world (first 128 are the same as ASCII)
Byte
Smallest unit of memory in a computer system
Uses of BCD
Representation of digits on a clock/calculator display
Difference between upper and lowercase in Unicode
Add 32 to uppercase to get lowercase (causes the 6th bit from the right to change to a 1)
Difference between ASCII and Unicode (2)
1 vs 4 byte character representation
Only English vs all languages of the world
Goals for Unicode (5)
Universal standard for all languages +writing systems
Reserve part of code for private use
Create unambiguous coding (each 16/32 bit value always represents the same thing)
Uniform encoding where each character is 16 or 32 bits
More efficient coding system than ASCII
Bit-map image
System that uses pixels to make up an image
Pixel
Smallest picture element that makes up an image
Colour depth
Number of bits used to represent the colours in a pixel eg 8 bit colour depth is 2^8=256 colours
Bit depth
Number of bits used to represent the smallest unit in a sound/image file (larger the depth, the better the quality)
Image resolution
Number of pixels that make up an image
Screen resolution
No. Of horizontal and vertical pixels that make up a screen display.
What happens if the screen resolution is smaller than the image resolution
The whole image cannot be shown on the screen or the original image will become lower quality
Resolution
Number of pixels per column and per row on a monitor/TV screen
Pixel density
Number of pixels per square centimetre
Vector graphics
Images that use 2D points to describe lines + curves + their properties that are grouped to form geometric shapes
Sampling resolution
Number of bits used to represent sound amplitude (bit depth)
Sampling rate
Number of sound samples taken per second (horizontal/line of propagation)
Rate at which the DAC can translate the digital output into analogue voltages
Frame rate
Number of video frames that make up a video per second
What to consider when storing images as pixels (3)
At least 8 bits per pixel are needed
True colour requires 3 bytes per pixel
Number of bits used to represent a pixel is the colour depth
Difference between bit depth and colour depth
No. Of bits used to represent a single pixel determines the colour depth. The higher the bit depth the more possible colours can be represented
How to find pixel density
Add the squares of the resolution size
Find the square root
Divide by screen size
Drawback of high resolution images
Large file size
What to do when saving a bit-map image
Include a file header which has things like file type (eg. .jpeg), file size, image resolution, bit depth and any type of data compression employed
How can vector graphics be designed (2)
Computer aided design (CAD)
Application which uses a canvas on a screen
Contents of vector graphic drawing list (4)
Command used for each object that makes up the graphic image
Attributes that define properties that make up each object (thickness, line colour etc.)
Relative position of each object
Relative positions of objects to each other (so that up-scaling won’t reduce the quality)
Vector graphic images vs Bit-map images (5)
Made up of geometric shapes requiring definitions/attributes - tiny pixels of different colours
Need to change each of the geometric shapes to edit - can edit each of the pixels
Made up of simple geometric shapes so don’t require large file size -very large file size (pixels)
Limited no. of geometric shapes so not very realistic - usually very realistic
File formats usually .svg, .cgm, .odg
Vector graphic images vs Bit-map images (5)
Made up of geometric shapes requiring definitions/attributes - tiny pixels of different colours
Need to change each of the geometric shapes to edit - can edit each of the pixels
Made up of simple geometric shapes so don’t require large file size -very large file size (pixels)
Limited no. of geometric shapes so not very realistic - usually very realistic
File formats usually .svg, .cgm, .odg
When should a vector graphic be used (2)
If the image needs to be resized
If the image needs to be drawn to scale
When should bit-map images be used (2)
If the image needs to look real
If there are file restrictions (consider the image resolution of image to ensure size not too big)
Sound
Analogue Transmitted by causing oscillations of particles within a medium. The human eye picks up these oscillations (changes in air pressure) and interprets them as sound. Each wave has a frequency and wavelength and amplitude which specifies the loudness of the sound
How sound is stored
It is digitised using an Analogue to Digital Converter. It is filtered to remove frequencies out of the human hearing range, then the sound waves are sampled at a given time rate and approximate amplitude values are stored
How is sampling used to record a sound clip (3)
Amplitude of the sound wave is determined at set time intervals
An approximate representation of the sound wave is given
Wave is encoded as a series of binary digits
Pros of a high sampling rate/resolution (3)
Larger dynamic range
Better sound quality
Less sound distortion
Cons of higher sampling rate/resolution (3)
Produces large file size
Takes longer to transmit/download sound files
Requires greater processing power
Features of recorded sound editing software (8)
Edit start/stop times + duration of a sample
Extract + save/delete part of sample
Alter frequency + amplitude of the sample
Fade in + out
Mix/merge multiple sound tracks and sources
Combine various sound sources together and alter their properties
Remove noise to enhance one sound wave in a multiple of waves
Convert between different audio formats
Lossless file compression
File compression method where the original file can be restored following decompression
Lossy file compression
File compression method where parts of original file cannot be recovered during decompression (some detail is lost)
JPEG
Joint Photographic Expert Group
Form of lossy file compression based on the inability of the eye to spot certain colour changes and hues
MP3/MP4 files
File compression method used for music and multimedia files
Perceptual music shaping
Method where eg. sounds outside normal range of hearing of humans are eliminated during compression
Audio compression
Method to reduce size of a sound file using perceptual music shaping
Bit rate
No. Of bits per second that can be transmitted over a network. Its a measure of the data transfer rate over a digital telecoms network
RLE
Run length encoding
Lossless file compression technique used to reduce text and photo files in particular
Most common forms of file compression (2)
Lossless file compression
Lossy file compression (JPEG/MP3)
File compression applications (3)
MPEG 3 and MPEG 4
Photographic (bit-map) images
RLE
MPEG-3
Uses audio compression (perceptual music shaping) to convert music and other sounds into a MP3 file format (lossy compression), reducing the size by about 90%.
What perceptual music shaping removes (2)
Sounds outside human hearing range
If 2 sounds are played simultaneously, the softer one is eliminated
MPEG-4
Allows storage of multimedia files rather than just sound.
Photographic (bitmap) images
JPEG, reduces the image by a factor between 5 and 15
Scalable Vector graphics (svg) are defined in XML text files, allowing them to be compressed
RLE
Run Length Encoding
Form of lossless file compression that reduces the size of a string of adjacent, identical data by encoding it into 2 values.
1st: number of identical items
2nd: code of the data item
General methods to compress movie files (3)
Reduce the sampling rate
Reduce sampling resolution
Reduce frame rate
General methods to compress image files (3)
Crop the image
Decrease the colour/bit depth
Reduce the image resolution
