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4a: Describe how digital images are composed of individual elements
Keyword
Definition
bitmap
a digital image which is described by a grid of coloured pixels
digital
something that has been represented using binary 0s and 1s
element
the simplest building block or part
image
a digital picture
pixel
a picture element which describes the colour of a small part of an image
vector
a digital image which is described by shapes of different sizes and colours
4b: Recall that the colour of each picture element is represented using a sequence of binary digits
Keyword
Definition
bit
a binary digit (0 or 1)
bit sequence
a pattern of more than one bit where each bit represents a different part of some data (e.g. different pixels in an image)
bitmap
a type of digital image that is represented by a grid of coloured pixels
colour
different wavelengths of light that the human brain interprets as different hues of the rainbow
pixel
a picture element which is a small coloured dot that makes up part of a bitmap image
representation
a way of describing something (using binary 0s and 1s to describe a digital image)
vector
a type of digital image that is represented by shapes of different colours and sizes
4c: Define key terms such as 'pixels', 'resolution', and 'colour depth'
Keyword
Definition
bit
an individual binary digit of 0 or 1
bitmap
a type of digital image that is represented by a grid of coloured pixels
colour depth
the number of bits used to represent individual colours in a digital image.
digital image
a picture that has been created or converted so that it can be represented by binary 0s and 1s, so that it can be stored or displayed on a computer
pixel
an individual picture element which makes up a single coloured dot in a grid to form part of a digital bitmap image
resolution
the total number of pixels in a bitmap image which is calculated by the width x height
vector
a type of digital image that is represented by shapes of different sizes and colours
4d: Describe how an image can be represented as a sequence of bits
Keyword
Definition
bit
a single binary digit of 0 or 1
bitmap image
a digital image represented by a sequence of bits which describe the colour of each pixel in a grid going from the top left, row by row, down to the bottom right
pixel
a single picture element (a coloured picture dot that makes up part of a digital bitmap image)
vector image
a digital image represented by a sequence of bits that describe instructions to draw shapes in specific colours, coordinates and sizes
4e: Describe how colour can be represented as a mixture of red, green, and blue, with a sequence of bits representing each colour's intensity
Keyword
Definition
black
a lack of colour which is made up of an absence of any visible light
blue
a colour (with the shortest wavelength and highest frequency) of light visible to humans
colour
a property of visible light which is interpreted by the human brain as different shades/hues of the rainbow
colour intensity
a measure of the brightness or dullness of a colour
green
a colour (with wavelength and frequency in the middle) of light visible to humans
red
a colour (with the longest wavelength and lowest frequency) of light visible to humans
visible spectrum
the range of colours that a human eye can detect (all the colours of the rainbow)
white
a colourless light that is made up of an equal intensity combination of visible light at all wavelengths within the visible spectrum
4f: Compute the representation size of a digital image
Keyword
Definition
bit
individual binary digit (0 or 1)
colour depth
the number of bits used to represent any of the colours in an image
height
the number of pixels found in one column up or down a bitmap image
pixel
an individual picture element made up of a single coloured dot
representation size
a measure of how many bits are needed to represent an image (calculated by width x height x colour depth)
resolution
the number of pixels in a bitmap image (calculated by width x height)
width
the number of pixels found in one row across a bitmap image
4g: Describe the trade-off between representation size and perceived quality for digital images
Keyword
Definition
colour depth
the number of bits used to represent any colour in a digital image. A higher colour depth will appear to use more realistic or natural colours but will require more bits to be stored or transferred
digital image
a picture which has been represented by binary 0s and 1s
perceived quality
an indication of how detailed an image appears to the human eye
representation size
the total number of bits needed to represent a digital image
resolution
the total number of pixels used in a bitmap image (calculated by width x height). A higher resolution will appear more detailed but will require more bits to be stored or transferred.
trade-off
a balancing act where an improvement in one area will mean another area suffers
4h: Perform basic image editing tasks using appropriate software and combine them in order to solve more complex problems requiring image manipulation
Keyword
Definition
brush
a tool used to draw on an image
crop
slice off some of the edges of an image
export
save an image from graphics editing software
file format
the type of file used to export a digital image (e.g. JPG or PNG)
import
load an image into graphics editing software so that it can be edited
layers
separate images that can be drawn on top of each other without destroying the pixel data from overlapping areas
transform
changing an image to scale, rotate, move or flip it
4i: Explain how the manipulation of digital images amounts to arithmetic operations on their digital representation
Keyword
Definition
arithmetic operation
a mathematical calculation (like adding, subtracting, dividing or multiplying)
erase
rubbing out part of an image (or setting the opacity of the pixels to 0)
grayscale
an image where all pixels are different shades of gray (or the red, green and blue values for individual pixels are all the same)
image manipulation
changing the colours of pixels within a digital image
opacity
the opposite of transparency (fully opaque means not at all transparent)
pixel
an individual picture element which is a single coloured dot in a bitmap image
4j: Describe and assess the creative benefits and ethical drawbacks of digital manipulation
Keyword
Definition
creative benefit
being able to do something with software that looks great
digital manipulation
using software to edit something on a computer
ethical drawback
something that can cause moral or psychological harm
realism
how natural, accurate or realistic an image appears
4k: Recall that sound is a wave
Keyword
Definition
frequency
a measure of how many times a sound wave goes up and down each second
sound
vibrations that can be detected by a human ear and are interpreted by the brain as noise, speech or music
vibrations
changes in air pressure that can cause sound
wave
something that oscillates (goes up and down) in a predictable pattern
wavelength
a measure of the distance between two peaks of a sound wave
4l: Explain the function of microphones and speakers as components that capture and generate sound
Keyword
Definition
analogue signal
an electronic signal where the voltage could be any value rather than just on or off
component
electronic device that makes up part of a gadget or computer
digital signal
an electronic signal made up of 0s (voltage switched off) and 1s (voltage switched on)
microphone
a device which converts the changes in air pressure caused by sound into an electronic signal where the voltage changes instead
speaker
a device which converts an electronic signal into sound by moving the air so it vibrates at the frequency as the changes to the electronic signal's voltage
4m: Define key terms such as 'sample', 'sampling frequency/rate', 'sample size'
Keyword
Definition
amplitude
how loud or quiet a sound is at any moment in time
bass
sounds with a low frequency that sound low pitched to humans
Hertz
the unit used to measure frequencies (meaning one per second)
sample
a measurent taken of the amplitude of a sound wave at a particular moment in time
sample size
the number of bits needed to represent each individual sample
sampling frequency
the number of samples taken every second
treble
sounds with a high frequency that sound high pitched to humans
4n: Describe how sounds are represented as sequences of bits
Keyword
Definition
amplitude
a measure of how loud or quiet a sound is at any moment in time
audio stream
a sequence of bits that represents sound by describing the amplitude of each sample in turn
bit
an individual binary digit (0 or 1)
bit rate
the number of bits that are needed to represent each second of sound
sample rate
the number of samples recorded every second
sample size
the number of bits that are need to represent each individual sample
4o: Calculate representation size for a given digital sound, given its attributes
Keyword
Definition
bit
individual binary digit (1 or 0)
byte
8 bits
kilobyte
1000 bytes
megabyte
1000 kilobytes
recording length
the duration of a recording of a sound wave
sample rate
the number of samples of a sound wave taken every second
sample size
the number of bits used to represent each sample of a sound wave
sound size
the number of bytes needed to store a sound. Calculated by: sample rate (in Hz) x sample size (in bits) x recording length (in seconds) / 8 (because there are 8 bits in a byte)
4p: Explain how attributes such as sampling frequency and sample size affect characteristics such as representation size and perceived quality, and the trade-offs involved
Keyword
Definition
perceived quality
the more closely the digital representation of a sound matches the original analogue sound wave, the better quality the sound will appear to people listening
representation size
the number of bytes needed to store or transfer an audio recording
sample size
the number of bits used to represent each sample of a sound wave. A higher value means the digital representation is closer to the original analogue sound but the recording will take up more bytes of storage.
sampling frequency
the number of samples of a sound wave taken every second. A higher value means the digital representation is closer to the original analogue sound but the recording will take up more bytes of storage.
trade-off
a balancing act where improving one thing will have a negative effect elsewhere
4q: Recall that bitmap images and pulse code sound are not the only binary representations of images and sound available
Keyword
Definition
bitmap image
a way of representing images by describing the colours of individual pixels in a grid
MIDI sound
Musical Instrument Digital Interface (a technique for representing sound by describing the length and pitch of musical notes)
PCM sound
Pulse-Code Modulation (a technique for representing sound by sampling the amplitude of sound waves at regular intervals)
vector image
a way of representing images by describing the size and position of coloured shapes
4r: Define 'compression', and describe why it is necessary
Keyword
Definition
compression
reducing the number of bits required to represent data (such as sound or images)
lossless compression
an algorithm that can reduce the number of bits required to represent sound or images without any reduction of quality
lossy compression
an algorithm that can significantly reduce the number of bits required to represent sound or images by reducing the quality in a way that can't be reversed
