T3: Data Representation

What is the binary number system?

A base 2 number system using only 0 and 1.

What is the denary number system?

A base 10 number system using digits 0-9.

How many bytes do most computers use to represent integers?

4 bytes

How many bits are in one byte?

8 bits.

What is a nibble?

4 bits or half a byte.

What is the size of 1 kilobyte (KB)?

1000 bytes.

What is the size of 1 megabyte (MB)?

1000 kilobytes or 1000x1000 bytes.

What is the size of 1 gigabyte (GB)?

1000 megabytes.

What is the size of 1 terabyte (TB)?

1000 gigabytes.

What does the Most Significant Bit (MSB) represent?

The bit with the largest value, located furthest to the left.

What does the Least Significant Bit (LSB) represent?

The bit with the smallest value, located furthest to the right.

What is hexadecimal?

A number system that uses base 16.

How do you convert hexadecimal to decimal?

Multiply the left-hand digit by 16 and add the units digits.

How do you convert decimal to hexadecimal?

Divide the decimal number by 16 to find the left-side hex digit; the remainder gives the units.

What is an overflow error in binary addition?

An error that occurs when the result of an addition exceeds the number of bits the computer can handle.

What effect does a binary shift left have?

It doubles the number.

What effect does a binary shift right have?

can very quickly multiply/divide a binary number by factor of 2, Loss of accuracy can occur if 1 or more bits are removed

What are character sets? + examples

Sets of letters, symbols, and digits that can be represented by a computer. ASCII and Unicode

What is ASCII + what language it represents?

A character set that encodes 128 characters into 7 bits binary codes, English

What is the difference between 7-bit and 8-bit ASCII?

7-bit ASCII encodes 128 characters, while 8-bit ASCII can encode 256 characters.

What does Unicode store and no. of bits?

16 bits (65536 combinations) and stores other characters from other languages + emojis

What is a bitmap image?

An image made up of pixels, where each pixel has a binary value representing its color.

What does image resolution refer to?

The concentration of pixels within a specific area

What does PPI and DPI mean?

PPI = Pixels per Inch DPI = Dots per Inch

What is color/bit depth + what can it be determined by?

The number of colors a pixel can represent, determined by the number of bits per pixel.

How to calculate colour/bit depth?

2^n n = number of bits

How does increasing bit depth affect image quality?

Higher bit depth allows for a greater range of colors and better image quality/resolution

What happens to file size when the physical size of an image increases?

No change in file size.

What do PBM images represent?

Portable bitmap images with 0 for white and 1 for black.

How is a (PBM) monochrome image represented in binary?

As a bit pattern, e.g., 0111, 0011, 0101, 1000. 0 = white, 1 = black

Why is hexadecimal used to represent colours?

Numerical values + hex easier for people to read, write + remember, Reduce errors if copied

How many bits are required to store one color in RGB format?

8 bits.

What is the total number of bits required for a whole pixel in RGB?

24 bits (16.8 million colours)

What does the term 'metadata' refer to in image files?

Data about data, such as color depth and resolution.

What is the purpose of an Analog to Digital Converter (ADC)?

To convert analog signals into digital signals.

What does sample resolution determine in sound sampling?

How closely the wave is sampled on the y-axis and number of bits used to record each measurement

What is the unit of measurement for sampling rate?

Hertz (Hz).

How do you calculate the size of a sound file in bits?

File size (bits) = sampling rate x resolution x duration.

How to improve recording quality?

more frequently sample sound (increase sample rate), more accurately record wave height

What is lossy compression?

Compression that removes some data, negatively affecting quality.

What are examples of a lossless music file format?

FLAC (Free Lossless Audio Codec), ALAC, WMA

What is the difference between lossy and lossless compression?

Lossy compression loses some data; lossless retains all original data.

What is Run Length Encoding (RLE)?

A compression technique that encodes data as frequency/data pairs.

What are the benefits of using compression?

Smaller files lead to faster transmission times and reduced traffic.

What file format is commonly used for photos with lossy compression?

JPEG.

How does sampling rate increase sound quality?

Improves recording quality by capturing more data points.

What is the purpose of a Digital to Audio Converter (DAC)?

To convert digital signals back into audio outputs.

What is the maximum number of colors that can be represented in a 24-bit image?

16.8 million colors.

What does a higher bit depth in sound sampling indicate?

More bits used per sample, leading to more accurate wave height measurement.

What is the significance of compression algorithms?

They reduce file size for easier storage and transmission.

What is the impact of digital artifacts in lossy compression?

They can cause visible or audible errors in images and sound.

How does lossless compression differ from lossy in terms of data retention?

Lossless compression retains all original data, while lossy does not.

What is the formula for calculating image size in bytes?

Size in Bytes = Width x Height x Colour Depth / 8.

What is the role of sampling rate in digital sound representation?

It affects the level of detail and accuracy in the digital representation.

How to Calculate Sound File Sizes

Files size (bits) = sampling rate x resolution x duration

Sampling rate?

how often sound is measured in Hz

Sampling resolution?

no. bits per sample

Higher values in sample rate and resolution?

better quality but larger file size

How to improve recording quality

More frequently we sample sound

More accurately we record wave height

What does lossy compression do MP3

Removes sounds that we can't easily hear or that least affect the perceived playback quality

How does lossy compression affect sound quality

Negatively affect sound quality: leaves out some data from original

What does lossless compression do?

Reduce file size when compressed but doesn't lose any info

Lossless music file formats

FLAC (Free Lossless Audio Codec)

ALAC (Apple Lossless Audio Codec)

WMA Lossless (Windows Media Audio)

Compression definition

algorithms which reduce file size

Decompression definition

process where compressed data is restored to its original format

Lossy Compression Types

JPG, GIF, MP3

Lossless compression Types

PNG, TIFF

What are digital artefacts

small mistakes from permanently losing data in lossy compression

How does lossless image compression work?

finds groups of repeating data and records the data once along with the number of repetitions

Run Length Encoding

Using frequency/data pairs to encode each run length of the same coloured pixel

Why Use Compression

Often used for files + data that are sent via the internet

Download times reduced

Data allowances go further

Possible to transmit video + music data streams as fast as they are playing

Benefits of Compression 6

Smaller files = fewer packets = Quicker to complete transmission

Reduces traffic over the internet

Reduces download times of video, sound + image files

Streaming is also possible as data can be sent as fast as the rate it is played

Images inside web pages appear faster

Reduces space on disk/servers

Buffering definition

when download speed is slower than the playback speed

Instructions to make a Huffman Tree DON't NEEd

1. Calculate how many times each character appears in the string.

2. Put these in order of least to most frequent.

3. Place the two least common characters along with their frequency in a binary tree. This is done by combining these in a new node and adding the individual frequencies of each character together.

4. Update the table showing the combined characters.

5. Take the next two frequent characters and repeat steps 3 and 4 using single letters first until all characters are combined.

File usage + type of compression of JPEG

photos, lossy

File usage + type of compression of PNG

images/photos, may include transparency, lossless

File usage + type of compression of ZIP

document compression, lossless

File usage + type of compression of GIF

simple images, may include animation, lossless

File usage + type of compression of MP4

video file format, lossy

File usage + type of compression of MP3

music format, lossy

File usage + type of compression of FLAC/ALAC

Lossless Music format (free/apple), lossless

Compression formula

(original-new) / original x 100

sound formula

rate resolution x time / 8

Binary --> Hex Conversion

1.Take binary number of 8 bits

2.Divide into two nibbles - 4 bits

3.Convert each nibble into its hex value the rejoin E.g. 11100101 = E5

How to calculate the number of possible combinations with number of bits

2^n n = number of bits (columns of 1s and 0s)

Why use Hex rather than Binary? 4

Much simpler to remember a hex value than a binary value, Quicker to write or type since hex digit only takes up 1 digit rather than 4 bits, People less likely to make an error with fewer digits, Easy to convert between hex and binary