1.1 Data representation
Binary - Base 2 number system based on values 1 and 0
Overflow - the result is larger than which can be stored in the given number of bits
Hexadecimal - Base 16 number system uses values from 0-9 and A-F
BCD - Number system which uses 4 bits to represent each denary digit.
● The BCD(Binary coded Decimal) is mostly used for RTC clock displays or calculators
● Normally used where arithmetic processing is required
Advantages Disadvantages
● Easy to convert for Humans ● Wastes Space (10-15 are not used)
● Easy to add → less calculation errors ● Requires more memory than Binary
Converting between Positive and Negative
One’s Complement - Each binary digit is reversed to allow both negative and positive numbers to be represented
Two’s complement - Each binary digit is reversed and 1 is added to produce another method of representing
positive and negative numbers in binary.
Sign and Magnitude - Where the leftmost digit is used to represent the sign of the remaining bits of a number
system. (0 - positive, 1 - Negative)
Uses of Each Number System
● All computers communicate in a binary number system as they can only be 1 or 0 and since there are
millions of tiny capacitors which can be represented by on or off (0-1).
Measuring Size of Computer Memories
● Kilo uses denary prefixes on the powers of 10
● Kibi uses binary prefixes on the powers of 2
ASCII code - Coding system for all characters on a
keyboard and control codes.
(7 bits for ASCII, 8 bit extended ASCII)
Character set - A list of characters which have been
define by computer hardware and software and computers
can understand human characters
Unicode - Coding system which represents all languages
in the world
32 bits
,How to represent words using ASCII?
● Each character has its own unique code
● The character is replaced by its code
● Codes are stored in order of the words
1.2 MultiMedia
Bitmap Images
Encoding Bitmap Images (Mark Scheme) Varying Image and Screen Resolutions
● The images are stored as bitmaps
● Each image is made up of pixels 1. Higher image resolution (2000) on a smaller
● each pixel is of a single colour screen resolution(1000), the image will need to be
● Each colour has a unique binary number resized which can be done in 2 ways:
● Sequence of binary digits representing pixels ●
combine to form a bitmap image ● Crop the image
● Remove some pixels to fit the resolution
Pixel Density - The number of pixels per square (lower quality)
centimetre
If we want to display a lower image resolution on a
higher screen resolution then there will not need to
be any modification done to the image but rather
enlarge it which may lead to the image becoming
pixelated
Bitmap Image - system that uses pixels to make up an image
Pixel - The smallest Element making up bitmap images
File Header - Contains information about the bitmap image
Colour depth - The number of bits used to represent the colours in a pixel (8 bit reps 256 colours)
Bit Depth - The number of bits used to represent the smallest unit in a sound or image file.
Image Resolution - The total number of pixels which make up a bitmap image (pixel height * pixel Length)
Screen Resolution - The amount of pixels which can be viewed horizontally and vertically on a screen
(pixel height * pixel Length)
.
Structure of Bitmap Images How are bitmap images Encoded?
● Header Bitmap images are encoded by first typing in the header
○ file size info and then going through and assigning the bit values
○ file type of the pixels from bottom to top and left to right.
○ image resolution
○ Dimensions Formula for File Size
○ bit depth File Size = Image Resolution * Colour Depth
○ Compression Algorithm
● Body (the codes to the colours)
● Ending signal
, Image Quality can be increased Advantages Drawbacks
by: ● More accurate Image ● Higher file size
● Colour depth ● Higher upload time
● Higher download time
● Image resolution
● More Processing Power
Vector Graphics - images which use 2D points to describe the lines and the curves which are grouped to form
geometric shapes.
● Made with Computed Aided Software (CAD).
● When displaying the vector graphics there is a drawing list:
○ Drawing list - lIsts all the shapes involved in the image (different shapes)
○ Property - data about the shapes (colour of the shapes, fill shape)
○ Also may contain the position of each of the shape
● Printing Out Vector Images needs to be converted to Bitmap Images to match the format of the printers
Vector Bitmap
Made up of geometric shapes which require Made up of pixels of different colours
definition and attribute. (Commands)
Smaller File SIze (instructions) Larger File Size (each pixel)
Not Realistic (Shapes) Realistic (Pixels)
Not Easily Compressible Easily Compressible
Easily Change Shape Hard to change the shape → Pixelation
SVG JPEG, PNG
Sound Files
Sampling - The process in which the ● The amplitude of the waves are measured
amplitude of sound waves of analogue data is ● This is taken per unit of timed intervals
measured at different points/intervals at a time. ● Approximate representation of the sound wave is given
MARK SCHEME → ● The sound wave is encoded as binary digits
● Increasing the Sampling Rate and Resolution will
increase the accuracy of the sound wave sampled
Sampling Resolution - The Number of bits ● Number of Bits to store each sample
used to each Sample sound file ● Known as bit depth
MARK SCHEME → ● Usually 8,16,24,32 bit
Sampling Rate - Number of sound samples taken per second
Advantages Disadvantages Features of Sound Editing Software:
● Cut/Delete
More Accurate File Size ● Copy Paste
(less time between Longer to Download/Transmit ● Changing the amplitude/Frequency
samples) More Processing Power ● Removing Background noise
Less Sound Distortion ● Changing between different audio formats
More dynamic Range ● Mixing sounds
, Video Files
Frame Rate - The number of video frames Recorded/Displayed Each Second
Temporal redundancy - Pixels in the same location have the same value in continuous frames
● Only the difference is recorded
Spatial Redundancy - Continuous Pixels in a single frame have the same value
File Compression
Lossless File Compression - file compression Lossy file compression – file compression method
method where the original file can be restored after a where parts of the original file cannot be recovered
compression algorithm by simply decompressing the during decompression, so some of the original detail is
file. lost.
● No Data is removed during compression but ● Original Data is removed during compression
rearranged to makes data more efficient and cannot be recovered after decompression
● Useful Where: ● Useful Where:
○ High Precision of accuracy ○ Smaller file achieved (10% compression)
○ Requested a PNG or Flac File ○ Faster to transmit/Download
■ Data in Spreadsheets ○ Humans cannot hear the difference
○ No high accuracy needed
● Drawbacks: ○ Requested a JPEG or MP3 file
○ Only 50 % compression achieved
● Drawbacks
○ No of high accuracy
RLE- A lossless file compression technique used to reduce text and photos files in particular.
● This is a form of Lossless file compression
● This is sued when there are a lot of adjacent repeating data
● This is where no data is removed but re-arranged
● The repeating string (Run) is broken down into 2 values.
○ First value is the number of identical data
○ Second Value represents the code of the actual data (ASCII code)
● RLE is only effective when there is a long run of repeated units.
To use lossy in Image
● Reduce bit depth
● Reduce image resolution
Lossy in Sound
● Sampling rate
● Sampling resolution
Binary - Base 2 number system based on values 1 and 0
Overflow - the result is larger than which can be stored in the given number of bits
Hexadecimal - Base 16 number system uses values from 0-9 and A-F
BCD - Number system which uses 4 bits to represent each denary digit.
● The BCD(Binary coded Decimal) is mostly used for RTC clock displays or calculators
● Normally used where arithmetic processing is required
Advantages Disadvantages
● Easy to convert for Humans ● Wastes Space (10-15 are not used)
● Easy to add → less calculation errors ● Requires more memory than Binary
Converting between Positive and Negative
One’s Complement - Each binary digit is reversed to allow both negative and positive numbers to be represented
Two’s complement - Each binary digit is reversed and 1 is added to produce another method of representing
positive and negative numbers in binary.
Sign and Magnitude - Where the leftmost digit is used to represent the sign of the remaining bits of a number
system. (0 - positive, 1 - Negative)
Uses of Each Number System
● All computers communicate in a binary number system as they can only be 1 or 0 and since there are
millions of tiny capacitors which can be represented by on or off (0-1).
Measuring Size of Computer Memories
● Kilo uses denary prefixes on the powers of 10
● Kibi uses binary prefixes on the powers of 2
ASCII code - Coding system for all characters on a
keyboard and control codes.
(7 bits for ASCII, 8 bit extended ASCII)
Character set - A list of characters which have been
define by computer hardware and software and computers
can understand human characters
Unicode - Coding system which represents all languages
in the world
32 bits
,How to represent words using ASCII?
● Each character has its own unique code
● The character is replaced by its code
● Codes are stored in order of the words
1.2 MultiMedia
Bitmap Images
Encoding Bitmap Images (Mark Scheme) Varying Image and Screen Resolutions
● The images are stored as bitmaps
● Each image is made up of pixels 1. Higher image resolution (2000) on a smaller
● each pixel is of a single colour screen resolution(1000), the image will need to be
● Each colour has a unique binary number resized which can be done in 2 ways:
● Sequence of binary digits representing pixels ●
combine to form a bitmap image ● Crop the image
● Remove some pixels to fit the resolution
Pixel Density - The number of pixels per square (lower quality)
centimetre
If we want to display a lower image resolution on a
higher screen resolution then there will not need to
be any modification done to the image but rather
enlarge it which may lead to the image becoming
pixelated
Bitmap Image - system that uses pixels to make up an image
Pixel - The smallest Element making up bitmap images
File Header - Contains information about the bitmap image
Colour depth - The number of bits used to represent the colours in a pixel (8 bit reps 256 colours)
Bit Depth - The number of bits used to represent the smallest unit in a sound or image file.
Image Resolution - The total number of pixels which make up a bitmap image (pixel height * pixel Length)
Screen Resolution - The amount of pixels which can be viewed horizontally and vertically on a screen
(pixel height * pixel Length)
.
Structure of Bitmap Images How are bitmap images Encoded?
● Header Bitmap images are encoded by first typing in the header
○ file size info and then going through and assigning the bit values
○ file type of the pixels from bottom to top and left to right.
○ image resolution
○ Dimensions Formula for File Size
○ bit depth File Size = Image Resolution * Colour Depth
○ Compression Algorithm
● Body (the codes to the colours)
● Ending signal
, Image Quality can be increased Advantages Drawbacks
by: ● More accurate Image ● Higher file size
● Colour depth ● Higher upload time
● Higher download time
● Image resolution
● More Processing Power
Vector Graphics - images which use 2D points to describe the lines and the curves which are grouped to form
geometric shapes.
● Made with Computed Aided Software (CAD).
● When displaying the vector graphics there is a drawing list:
○ Drawing list - lIsts all the shapes involved in the image (different shapes)
○ Property - data about the shapes (colour of the shapes, fill shape)
○ Also may contain the position of each of the shape
● Printing Out Vector Images needs to be converted to Bitmap Images to match the format of the printers
Vector Bitmap
Made up of geometric shapes which require Made up of pixels of different colours
definition and attribute. (Commands)
Smaller File SIze (instructions) Larger File Size (each pixel)
Not Realistic (Shapes) Realistic (Pixels)
Not Easily Compressible Easily Compressible
Easily Change Shape Hard to change the shape → Pixelation
SVG JPEG, PNG
Sound Files
Sampling - The process in which the ● The amplitude of the waves are measured
amplitude of sound waves of analogue data is ● This is taken per unit of timed intervals
measured at different points/intervals at a time. ● Approximate representation of the sound wave is given
MARK SCHEME → ● The sound wave is encoded as binary digits
● Increasing the Sampling Rate and Resolution will
increase the accuracy of the sound wave sampled
Sampling Resolution - The Number of bits ● Number of Bits to store each sample
used to each Sample sound file ● Known as bit depth
MARK SCHEME → ● Usually 8,16,24,32 bit
Sampling Rate - Number of sound samples taken per second
Advantages Disadvantages Features of Sound Editing Software:
● Cut/Delete
More Accurate File Size ● Copy Paste
(less time between Longer to Download/Transmit ● Changing the amplitude/Frequency
samples) More Processing Power ● Removing Background noise
Less Sound Distortion ● Changing between different audio formats
More dynamic Range ● Mixing sounds
, Video Files
Frame Rate - The number of video frames Recorded/Displayed Each Second
Temporal redundancy - Pixels in the same location have the same value in continuous frames
● Only the difference is recorded
Spatial Redundancy - Continuous Pixels in a single frame have the same value
File Compression
Lossless File Compression - file compression Lossy file compression – file compression method
method where the original file can be restored after a where parts of the original file cannot be recovered
compression algorithm by simply decompressing the during decompression, so some of the original detail is
file. lost.
● No Data is removed during compression but ● Original Data is removed during compression
rearranged to makes data more efficient and cannot be recovered after decompression
● Useful Where: ● Useful Where:
○ High Precision of accuracy ○ Smaller file achieved (10% compression)
○ Requested a PNG or Flac File ○ Faster to transmit/Download
■ Data in Spreadsheets ○ Humans cannot hear the difference
○ No high accuracy needed
● Drawbacks: ○ Requested a JPEG or MP3 file
○ Only 50 % compression achieved
● Drawbacks
○ No of high accuracy
RLE- A lossless file compression technique used to reduce text and photos files in particular.
● This is a form of Lossless file compression
● This is sued when there are a lot of adjacent repeating data
● This is where no data is removed but re-arranged
● The repeating string (Run) is broken down into 2 values.
○ First value is the number of identical data
○ Second Value represents the code of the actual data (ASCII code)
● RLE is only effective when there is a long run of repeated units.
To use lossy in Image
● Reduce bit depth
● Reduce image resolution
Lossy in Sound
● Sampling rate
● Sampling resolution
