Representing Images, Sound and Other Data Flashcards
Describe Analogue Data
Continuous
No Limits to the values that the data can take
Can be changed as frequently as required
Smooth curves which feature sharp peaks
Describe Digital Data
Discrete
Can only take particular values
Can only take one of a specific range of values
Can only change values at specified intervals
What does a DAC stand for
Digital to Analogue converter
How does a DAC work
It reads a bit pattern representing an analogue signal and outputs an alternating, analogue, electrical current
What outputs an analogue signal
Temperature sensors and microphones
What does ADC stand for
Analogue to Digital Convertor
How does an ADC work
Takes a reading of an analogue signal at regular intervals
Records the value through sampling
Samples are taken at a specific frequency
Once the signal is recorded - it can be stored digitally as a bit pattern representing its amplitude
What are bitmap graphics and how do they work ————
A way a computer can represent an image
An image is broken down into pixels - each pixel is assigned a binary value
How is the resolution of an image represented ———–
Number of dots per square inch
OR
Number of pixels in an image
How big is a dot ——
A pixel
What determines the colour of a pixel ————–
The binary value assigned to it
What is the colour depth —————-
Number of bits assigned to a pixel in an image
How do you calculate the storage required to represent a bitmap image and what does this method tell you ————
Resolution x Colour Depth
Minimum amount of bits required due to the files containing metadata
What do vector graphics represent and how and what are the properties stored in ————–
Images using geometric objects and shapes
A list
Why can vector graphics be scaled without losing quality ———–
They use shapes instead of pixels
Uses for Vector Graphics ————
Simple images such as company logos
Uses for bitmapped graphics ————
Storing photos
Why do vector graphics frequently use less storage space than bitmapped graphics ———————
Information is stored for each shape rather than for every single pixel
How do computers represent sound
As a sequence of samples
What does a sample take
Discrete digital values
What is the sampling rate
Number of Samples per second
Measured in Hz
What is the sample resolution
Number of bits allocated to each sample
What comes with higher sample resolutions
Greater audio quality and increased file size
How can the size of a sound sample be calculated
Sample rate x sample resolution x length of sample
What is the Nyquist Theorem
Sampling rate of a digital audio file must be at least twice the frequency of the sound
What does MIDI stand for
Musical Instrument Digital Interface
When are MIDIs used
With electronic musical instruments which can be connected to computers
How does a MIDI work
Stores sound as a series of event messages - each of which represents an event in a piece of music
Advantages of MIDI over samples
Easy manipulation of music without loss of quality (lossless)
Notes can be transposed and the duration of notes can be altered
Smaller in Size
What are the two types of compression
Lossy and Lossless
What is Lossy Compression
Compression where some information is lost
Quality of File is Reduced
The extent to which file size can be reduced is not limited
What is Lossless Compression
Compression where no information is lost
There is no loss of quality
There is a limit to how much file can be compressed
Define Encryption
The process of scrambling data so that it cannot be understood if intercepted in order to keep it secure during transmission
What is Plaintext
Unencrypted information
What is Ciphertext
Encrypted information
What is a cipher
A type of encryption method
What is a Vernam Cipher
A one time pad cipher which requires the key to be random
How does a Vernam Cipher work
Align the characters of the plaintext and the key
Convert each character to binary using an information coding system
Apply a logical XOR operation to the two bit patterns
Converting the result back to a character
How many bit patterns can series of bits represent
2^n
What does the size of an image dtermine
Number of rows and columns of pixels that create the image
Relationship between size and resolution
Inversely proportional
Formula for resolution
Width in pixels x height in pixels
