1.1 Text, Images, Sound, Memory Units Flashcards
What is a bitmap image?
A collection of pixels where each pixel is assigned a value that represents it’s colour.
What is a pixel?
Short for picture element
The smallest block of colour in an image
What is colour/bit depth?
The number of bits used to represent the colour of a single pixel
How many colours can be stored using 1-bit?
2
There are 2 possible values - 0 or 1
How many colours can be stored using 2-bits?
4
There are 4 possible values (00, 01, 10, 11)
How many colours can be stored using 4-bits?
16
Range of possible value is 0000 - 1111 = 0 - 15
For n bits you can store 2^n different colour codes.
How many colours can be stored using 12 bits?
4096 (2^12)
What is image resolution?
The number of pixels in the image e.g. 600 px x 400 px = 240 000 px
How do you calculate the size of an image?
image size = number of pixels x colour depth
If a 12-bit colour depth is used and the image size is 800 x 600 pixels, what is the minimum file size for the image in bytes?
Number of pixels = 800 x 600
Number of bits per pixel = 12
Total number of bits = 12 x 800 x 600 = 5760000
Number of bytes = 5760000 ÷ 8 = 720000 bytes
What is meant by image metadata?
Image files usually also contain metadata .
Metadata means ‘data about data’
It provides additional information about the image.
Computers needs this data to interpret the file
Give 3 examples of image metadata
file format - eg JPG, GIF, BMP, PNG
resolution
colour depth
time/date the image was taken
camera settings
GPS data
Explain how captured camera images are converted to digital photo files
Image is turned into pixels
Pixels form a grid
Each pixel is give a binary value
Each pixel is given a colour
Pixels are stored in the correct sequence
Meta data is also stored about the image e.g. dimensions/resolution/colour depth
Different file formats are used e.g. JPEG
What happens when you increase the colour depth of an image?
The quality of the image increases
You are more accurately able to represent the range of colours
Also increases the memory size of the image
What happens when you increase the number of pixels in an image?
The density of pixels in the same sized area increases
More pixels per inch, improving sharpness
Can enlarge without visible loss of quality
Increases the memory size of the image
What is an ADC?
Analogue-to-digital converter
Samples and converts an analogue signal into an equivalent digital signal
What is a DAC?
Digital-to-analogue converter
Converts a digital signal into an equivalent electrical analogue signal
What is the difference between analogue and digital signals?
Analogue signals cover a whole continuous range of values.
Digital signals change in discrete steps e.g. have only two values - off (0) and on (1)
What is the sample/sampling rate?
The number of samples taken per second of sound
1 Hertz (Hz) is one sample per second.
Audio CD is 44.1KHz
What is the sample/sampling resolution?
The number of bits used to store each sample / measurement of the height of the wave
Also known as bit depth
What is the bit rate?
The number of bits required to store 1 second of sound
Bit Rate = Sample Rate x Sample Resolution
A typical audio CD has a bit rate of 16 bits per sample, per channel. The sample rate is 44.1KHz and there are 2 channels. How many bytes of storage are needed for 5 seconds?
44,100 samples taken each second.
5 x 44100 = 220 500 samples on one channel for 5 secs
220 500 x 2 = 441 000 samples on both channels
16 bits = 2 bytes for each sample
441 000 x 2 bytes = 882 000 bytes.
Advantage: A higher sample rate and sample resolution means _______
Advantage: A higher sample rate and sample resolution means better quality music
Disadvantage: A higher sample rate and sample resolution means _________
Disadvantage: A higher sample rate and sample resolution means _________
more bandwidth required for transmission
more memory space required for storage.
State 3 advantages of digital sound
It can be edited and manipulated easily by computer equipment.
It is more portable
It can be played over and over again without deterioration.
It can be easily copied on a computer.
Digital audio files can be easily emailed, downloaded and streamed by users.
How are analogue sounds recorded in binary?
The amplitude (height) of the wave is measured and sampled at regular intervals
How often the height is measured is known as the sample rate
The sample resolution is the number of bits used to measure the height
State 3 different character sets
ASCII
Extended ASCII
Unicode
UTF-8
What is a character set?
A character set is a complete set of the characters and their character codes that can be recognised by a computer system.
What is character code?
A value/binary number that represents a character
What is ASCII?
American Standard Code for Information Interchange.
A character set used to represent 128 characters
It uses 7 bits
How many characters can be represented using ASCII?
Uses 7 bits so …
000 0000 to 111 1111 = 0 to 127 = 128 unique characters (2^7)
How many bits per character does extended ASCII use?
8
How many characters can be represented using extended ASCII?
Uses 8 bits so …
0000 0000 to 1111 1111 = 0 to 255 = 256 unique characters (2^8)
How many bits per character does Unicode use?
16
How many characters can be represented using Unicode?
Uses 16 bits so … 65536 unique characters (2^16)
The first 128 characters are the same as ASCII
Describe the difference between ASCII and Unicode
ASCII uses 7 (or 8 bits) and can represent 128 (or 256 characters)
Unicode uses 16 bits and can represent 2^16 characters.
Describe one advantage of Unicode over ASCII
Uses more bits per character so …
… can represent a wider range of characters and therefore more languages
Describe one disadvantage of Unicode over ASCII
Uses more bits per character so …
… will take up more memory/storage space
If the 7 bit character code for A = 100 0001. What is the 7 bit character code for C?
A = 100 0001 = 65 B = 100 0010 = 66 C = 100 0011 = 67
How many bits in a byte?
How many bits in a nibble?
How many nibbles in 4 bytes?
How many bits in a byte? 8
How many bits in a nibble? 4
How many nibbles in 4 bytes? 8
Put the following memory units in ascending (smallest to largest) order of size?
terrabyte (TB), byte, kilobyte (KB), megabyte (MB), bit, nibble, gigabyte (GB)
bit, nibble, byte, kilobyte (KB), megabyte (MB), gigabyte (GB), terrabyte (TB)
How many bytes are in 1 kilobyte (KB)?
1024 (2^10)
How would you convert from bits to MiB?
Division
bits -> bytes -> KB -> MB
/ 8 / 1024 / 1024
How would you convert from TB to GB?
Multiplication
TB -> GB
x 1024 (or x 2^10)
A 32-second sound clip will be recorded. The sound will be sampled 16000 times a second. Each sample will be stored using 8 bits. Calculate the file size in kilobytes. You must show all of your working (3 marks)
2 marks from …
16000 * 32 = 512000
512000 / 1024 = 500
Or
16000 * 8 = 128000
12800 * 32 = 409600
409600 / 8 = 51200
512000 / 1024 = 500
1 mark for final answer
500
List all of the memory units in descending (largest to smallest) order of size?
terrabyte (TB)
terrabyte (TB)
gigabyte (GB)
megabyte (MB)
kilobyte (KB)
byte
nibble
bit
How many bytes are in 1 Terrabyte(TB)?
1024 x 1024 x 1024 x 1024 bytes
or
2^40 bytes
The Rock says …
What is MIDI?
- Musical Instrument Digital Interface
- Communication protocol that allows electronic musical instruments to communicate with each other
- 8-bit serial transmission (asynchronous)
State 3 example MIDI commands
- Instrument - which instrument is being played.
- Pitch - frequency of the note
- Volume - how the note is played loud or soft.
- Duration - length of the note (on and off)
- Tempo - speed at which the music is played
State 3 advantages of MIDI
- File sizes are smaller
- All aspects of the sound can be edited
- Effects can be applied to individual instruments
- No interference or background noise during recording
State 3 disadvantages of MIDI
- Dependent on quality of sound card for overall sound
- Can not store vocals
- Effects are limited
- Less realistic sounds than actual instruments
