Text, Sound & Images

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Notes

Character Sets

A **character set** is all characters and symbols a computer can represent; each character has a unique binary code.
Character sets are ordered logically (e.g., code for 'B' is one more than code for 'A').
They provide a standard for computers to communicate; without one, the same binary code could be interpreted differently.
The number of representable characters = 2^(number of bits used).
Two common character sets: **ASCII** (7-bit, 128 characters) and **UNICODE** (minimum 16-bit, 65,536+ characters).
ASCII covers English letters, digits, and some symbols; cannot represent other languages or emojis.
**Extended ASCII** uses 8 bits (256 characters), adding mathematical operators and symbols like ©.
UNICODE supports characters from all major languages and special symbols like emojis; uses more storage than ASCII.

Representing Sound – Sampling

Sound is originally **analogue**; it must be converted to digital via **Analogue-to-Digital conversion (A2D)**.
The process measures the **amplitude** of the sound wave at regular intervals; each measurement is a **sample**.
Each sample is stored as a binary value; the collection of samples forms a digital representation of the wave.
The digital wave can be stored on secondary storage and played back by reversing the process.

Sample Rate and Sample Resolution

**Sample rate** is the number of samples taken per second, measured in **Hertz (Hz)** (1 Hz = 1 sample/second).
Higher sample rate → digital wave closer to original → better quality, but larger file size.
A typical audio CD uses a sample rate of **44.1 kHz** (44,100 samples per second).
**Sample resolution** (or bit depth) is the number of bits stored per sample.
Higher sample resolution → more possible amplitude values → better quality, but larger file size.
Both high sample rate and high sample resolution increase playback quality and file size.

Bitmap Images

A **bitmap image** is made up of a grid of **pixels** (picture elements).
A **pixel** is the smallest element of a bitmap image; each pixel is stored as a binary code representing its colour.
More colours and more detail → higher quality → more binary data needed.

Resolution and Colour Depth

**Resolution** is the total number of pixels in an image, calculated as width × height (in pixels).
Higher resolution → more detail → larger file size.
**Colour depth** is the number of bits used per pixel; determines the number of possible colours (2^colour depth).
Examples: 1-bit → 2 colours (black & white); 8-bit → 256 colours; 24-bit → 16.7 million colours (True Colour).
Higher colour depth → more colours → larger file size.
File size = width × height × colour depth (in bits).
A balance between quality and file size must be considered.

Analogue sound wave (blue) sampled at regular intervals to produce a digital wave (red). Vertical dashed lines show sample points.

A bitmap image is a grid of pixels; each pixel stores a binary code representing its colour.

Practice questions

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1.What is a character set?
Easy
- AAll the characters and symbols that can be represented by a computer system
- BA set of instructions for encoding images
- CA collection of fonts used in word processing
- DA standard for compressing text files
2.How many bits does standard ASCII use to represent a character?
Easy
- A7 bits
- B8 bits
- C16 bits
- D32 bits
3.Which character set can represent characters from all major languages around the world?
Easy
- AASCII
- BExtended ASCII
- CUNICODE
- DEBCDIC
4.If an image has a resolution of 100 × 100 pixels and a colour depth of 4 bits, how many bits are needed to store the image?
Medium
- A10,000 bits
- B40,000 bits
- C100,000 bits
- D400,000 bits
5.What is the sample rate of a typical audio CD?
Medium
- A44.1 kHz
- B22.05 kHz
- C96 kHz
- D192 kHz
6.Which of the following is a benefit of using UNICODE over ASCII?
Medium
- AUNICODE uses fewer bits per character
- BUNICODE can represent emojis and symbols from many languages
- CUNICODE is faster to process
- DUNICODE requires less storage space
7.A sound recording has a sample rate of 44.1 kHz and a sample resolution of 16 bits. If the recording is 10 seconds long, what is the approximate file size in bits? (Ignore any compression or header.)
Medium
- A7,056,000 bits
- B44,100 bits
- C705,600 bits
- D441,000 bits
8.An image has a colour depth of 24 bits. How many different colours can it represent?
Hard
- A256
- B65,536
- C16,777,216
- D24

Slides

Character Sets

A character set is all the characters and symbols a computer can represent.
Each character has a unique binary code; codes are ordered logically.
The number of bits determines how many characters can be represented.

What is a character set?

A set of colours used in images
All the characters and symbols a computer can represent
A type of compression algorithm
A method of sampling sound

ASCII Character Set

ASCII uses 7 bits, representing up to 128 characters.
Extended ASCII uses 8 bits, representing up to 256 characters.
ASCII only covers English letters, digits, and some symbols; no emojis or non-English characters.

ASCII uses ____ bits, providing up to ____ characters.

UNICODE Character Set

UNICODE uses a minimum of 16 bits, representing over 65,000 characters.
It supports characters from all major languages and symbols like emojis.
UNICODE was created to overcome ASCII's limitations.

Which of these are true about UNICODE?

It uses 7 bits
It can represent emojis
It supports characters from many languages
It was created before ASCII

Representing Sound: Sampling

Sound is analogue; it must be converted to digital via analogue-to-digital conversion (ADC).
The amplitude of the sound wave is measured at regular intervals called samples.
Each sample is stored as a binary value.

What is a sample in digital sound?

A measurement of the sound wave's amplitude at a point in time
The number of bits per second
A type of compression
The colour depth of an image

Sample Rate and Sample Resolution

Sample rate is the number of samples taken per second, measured in Hertz (Hz).
Higher sample rate gives better quality but larger file size.
Sample resolution is the number of bits per sample; higher resolution means better quality and larger file size.

Sample rate is measured in ____ . A typical audio CD uses a sample rate of ____ kHz.

Bitmap Images

A bitmap image is made up of pixels, the smallest element of the image.
Each pixel is stored as a binary code representing its colour.
Resolution is the total number of pixels (width × height).
Colour depth is the number of bits per pixel.

What is a pixel?

A unit of sound measurement
The smallest element of a bitmap image
A type of compression
A character in a character set

Resolution and Colour Depth Impact

Higher resolution means more pixels, leading to larger file size.
Higher colour depth means more bits per pixel, also increasing file size.
There is a trade-off between image quality and file size.

An image with a colour depth of 1 bit can represent ____ colours. An image with a colour depth of 24 bits can represent ____ colours.

Calculating File Size

File size (bits) = width × height × colour depth.
For sound: file size = sample rate × sample resolution × duration.
Always consider the units (bits vs bytes).

An image is 100×100 pixels with a colour depth of 8 bits. What is the file size in bits?

10,000 bits
80,000 bits
100,000 bits
800,000 bits

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