3.3 - Image & Sound Representation (6 + 7) Flashcards
made in line with spec
what is a pixel?
tiny single point in a graphical image which makes up a picture
how is each pixel displayed?
using a binary representation
what is a bitmap?
the binary stored data representing an image
what is the term ‘pixel’ short for?
picture element
what is a VDU?
a virtual display unit
how do VDUs display pictures?
dividing the display screen into thousands of pixels (arranged into rows and columns)
how do you display the size of a bitmap (in pixels)?
width of image (in pixels) x height of image (in pixels)
define colour depth
the number of bits used to represent each pixel
what is the image resolution?
in terms of pixels
width x height
how does a bitmap represent an image using pixels and colour depth?
- bitmap images are organised as a grid of coloured squares (pixels)
- each colour of image is stored as a binary number
- bits of info are stored in the bitmap
how does the number of pixels and colour depth affect the file size of a bitmap image?
the higher number of pixels and higher colour depth, the larger the file size
how do you calculate the size (in bits) of an image?
image width x image height x colour depth
how do you calculate the size of an image in bytes?
(image width x image height x colour depth depth) / 8
- same as bits (just divide by 8)
what is metadata?
extra details about an image (location, colour depth, file name, camera details)
define image resolution
a measure of pixel density and the quality of the image (by the distance between two adjacent pictures)
sound is …….. and must be converted to a ……….. ……….. for …… and ……….. in a computer
analogue, digital form, storage, processing
what process is carried out for digital versions of sound to be made?
and explain briefly what it is
sampling, a sound measurement taken at a given point in a sound file
what is a sample?
a measure of amplitude at a point in time
describe the processes in which a sound wave is converted to a sound file
- measure the amplitude of sound wave at specific intervals (sampling)
- convert values to binary
- store into the sound file
what is the sampling rate?
the number of samples taken in a second (measured in hertz)
what is the sample resolution?
number of bits used to store each sample
how does a sampling rate for a sound file affect the size?
makes the file larger (as it has more samples to store)
formula to calculate file size based on sampling rate and resolution? (sound)
sample rate x sample resolution x number of seconds x channels
describe how a physical image can be represented in a bitmap
- bitmap images organised as a grid of coloured squares (pixels)
- each colour stored as a binary number
- bits of information are stored in the bitmap
what is sampling?
when analogue sound is converted into a set of binary numbers
what is an ADC?
a device that converts real-world analogue signals into digital signals
define a bit rate
the amount of information used to describe one second of sound (ie. the number of bits per second)
formula to calculate bit rate?
sample rate x bit depth x number of channels
what are the advantages of digital signals?
they are easy to copy, transmit and store
what does a DAC do?
converts a binary stored version of a recording to voltage that speakers can reproduce
what is the common sampling rate for sound files?
44.1 kH
how would a greater number of samples per second affect a sound file?
higher quality of sound, larger file size (greater data stored)
