Topic 5.6 - Representing Images, Sound and other Data (incomplete) Flashcards
How do bit patterns represent images
image height * image width * colour depth (in bits)
Difference between Analogue and Digital Data
Analogue data is continuous meaning there are no limits
Digital data is discrete meaning it can only take particular values
Analogue data can change as quickly as required
Digital data can only change at specific intervals
Difference between Analogue and Digital Signals
Analogue signals are smooth curves
Digital signals have sharp edges
How does an Analogue to Digital Converter (ADC) work
Works by taking a reading of an analogue signal at regular intervals and recording the value; called sampling
Samples are taken at a specific frequency (in Hertz (Hz)) which determines number of samples taken per second.
Needs to be a high frequency for better accuracy in reproducing the signal
Once signal has been recorded, it is stored digitally as a bit pattern
How does a Digital to Analogue Converter (DAC) work
Device reads the bit pattern of the audio signal and outputs an analogue electrical current
What is the most common use for a Digital to Analogue Converter (DAC)
To convert a digital audio signal into an analogue signal
What are ADC’s used for
Many sensors like microphones and thermometers which output analogue signals.
Explain how bitmaps are represented
An image is broken down into pixels
Each pixel is given a binary value which represents a colour
What is resolution
The number of pixels per square inch.
What is meant by the term Pixel
Picture element
A small square that makes up an image
More pixels = Higher resolution
What is colour depth
The number of bits stored for each pixel
if the colour depth is 5 then there will be 2^5 colours available.
What is the size of an image in pixels
Width of the image in pixels
*
Height of the image in pixels
What is the calculation for the storage required of a bitmapped image
Width * Height * Colour Depth(in bits)
What are some common examples of metadata
Location, time, date
How does vector graphics represent images
By using objects and shapes (rectangles, circles, lines)
The properties of each object & shape are stored as a list
What are the typical properties of objects used in vector graphics
Height
Width
Fill Colour
Start Position
Advantages of Bitmap Graphics over Vector Graphics
Used for storing photographs and highly detailed images
Vectors can only store simple images
Advantages of Vector Graphics over Bitmap Graphics
Images can be scaled with no loss of quality
Bitmap cant
Vectors use less storage space since they only have to store information about each shape rather than each pixel.
Explain Digital Representation of Sound
Computers represent sound as a sequence of samples which each hold a specific digital value
The number of bits allocated to each sample is called the sample resolution
A greater sample resolution results in greater audio quality but greater file size
What is the calculation for the size of a sound sample
Duration of sample (in secs)
*
The sampling rate (in Hz)
*
The sample resolution
What is The Nyquist Theorem
The sampling rate of a digital audio file must be at least twice the frequency of the sound.
Otherwise the sound may not be accurately represented.
What is the purpose of Musical Instrument Digital Interface (MIDI)
Allows electronic musical instruments to be able to communicate with each other
How does MIDI work
Instead of storing samples of sound, MIDI stores sound as a series of event messages.
Each event message represents an instruction in a piece of music. E.G. :
Duration of a note
Instrument being used
Volume of note
Which note is being played
What are the advantages of using MIDI to represent music
Easy to manipulate music without loss of quality
Smaller file size
Lossless files
