data representation Flashcards
(32 cards)
What does analogue mean?
continuously changing
Why can’t computers store analogue sound?
Because analog sound has infinite data so it’s impossible to store it all.
What is the name of the device that takes real world analogue signals and converts them to a digital representation?
Analogue-to-digital converter (ADC)
How does a computer convert analogue sound waves to digital sound data?
1) analogue sound is received by a microphone
2) This is converted to an electrical analogue signal
3) The signal amplitude (height of wave) is measured at regular intervals this is called sampling.
4) The values are rounded to a level this is called quantisation
5) The values are stored as a series of binary values
What is a sample a measure of?
A sample is a measure of amplitude at a point in time.
What are the two things that determine digital sound data’s accuracy?
sample resolution and sample rate.
What is sample resolution?
The sample resolution is the number of bits used to store each sample.
What is sample rate?
The sample rate is the frequency at which you record the amplitude of the sound i.e the number of samples per second.
What is sample rate usually measured in?
Hertz
What is the formula to calculate a sound file size?
file size = sample rate x sample resolution x number of seconds
What is the sample rate and sample resolution of a cd?
sample rate:44.1kHz
sample resolution: 16 bits
What is a vector graphic?
An image made up of lines and shapes with specific properties such as: line style, line colour, fill colour, start point and end point.
How does a computer store a photograph taken by a digital camera.
The computer breaks down the image into its smallest elements (pixels).
What does pixel stand for?
Picture element
What is the size of an image expressed as
Width in pixels by height in pixels e.g 600 pixels x 400 pixels
What is the use of pixels in images called?
Bitmap
How many possible colours are there in 8 bits per pixel ?
256
What is colour depth?
The number of bits per pixel. i.e the number of colours a pixel can be.
Why is increasing the colour depth good ?
It makes the image more faithful to how it actually looks
What is resolution?
It is how dense the pixels in the image are. i.e How detailed the image looks.
What is pixel density measured in?
pixels per inch (PPI)
What normally happens when you try to enlarge an image of the internet?
The image goes blurry because the software tries to make up for the pixels that don’t exist
What is the normal pixel density of an image off the internet?
72PPI
What does file size of an image depend on?
colour depth and the number of pixels in the image.
