Text, Sound and Images Quick Revision

Vocabulary flashcards covering character sets (ASCII, Extended ASCII, Unicode), bitmap image representation, metadata, and digital sound sampling from the Text, Sound and Images revision guide.

Character Set

A list of characters that have been defined by computer hardware and software, necessary so that the computer can understand human characters.

ASCII

Standing for American Standard Code for Information Interchange, it is a character set for all the characters on a standard keyboard and control codes. Standard ASCII uses $7\text{ bits}$ and represents $128\text{ characters}$ ($0$ to $127$ in denary or $00$ to $7\text{F}$ in hex).

Control Characters

Non-printing ASCII codes from $0$ to $31$, such as carriage return and line feed.

Extended ASCII

A character set that uses $8\text{ bits}$, allowing for $256\text{ characters}$ ($0$ to $255$ in denary or $00$ to $\text{FF}$ in hex). It adds $128$ extra characters (codes $128\text{–}255$) for non-English alphabets and graphical/special symbols.

Unicode

A character set that represents all the languages of the world. It uses $16\text{-bit}$ or more (capable of representing over $65,000\text{ characters}$ and emoji) and is backward compatible with ASCII for its first $128\text{ characters}$.

Bitmap Image

An image made up of pixels arranged in a 2D grid (matrix), where each pixel is represented by a binary number.

Pixel

Derived from the term 'picture element', this is the smallest element used to make up an image on a display.

Colour Depth

The number of bits used to represent the colours of a pixel (to store the colour of each pixel).

Image Resolution

The total number of pixels in an image (width $\times$ height), or the number of pixels in the X-Y direction of an image (such as $4096 \times 3072\text{ pixels}$).

Metadata

Data included in an image file that identifies how the file should be displayed, such as the colour depth and image resolution.

Pixelated (Image)

The result of zooming into a bitmap image, where pixel density is diminished to such a degree that the actual pixels themselves become visible.

Pixel Density

The number of pixels per square inch.

Frequency

A property of a sound wave describing how fast the wave vibrates, which determines pitch.

Wavelength

The physical distance between peaks of a sound wave.

Amplitude

The height of a sound wave, which determines loudness.

Analogue to Digital Converter (ADC)

A hardware converter used to digitize continuous analogue sound waves by sampling their amplitude at regular intervals.

Sampling

The process of converting continuous analogue sound waves into digital form by measuring the sound wave's amplitude at regular time intervals and storing each measurement as a binary number.

Sampling Rate

The number of sound samples taken per second in digital sound recording, measured in Hertz ($\text{Hz}$).

Sampling Resolution (Bit Depth)

The number of bits used to represent sound amplitude in digital sound recording, representing the smallest unit or individual sample in a sound file.