Representing images, sound and other data key terms

Bit pattern

A sequence of binary digits used to represent data.

Representation

An agreed way of assigning meaning to a bit pattern so that it can be interpreted as a particular form of data.

Analogue

Describes data or a signal that varies continuously.

Digital

Describes data or a signal represented using separate, distinct values or levels.

Analogue-to-digital converter (ADC)

A device that converts a continuously varying analogue signal, such as the output from an analogue sensor, into a digital representation.

Digital-to-analogue converter (DAC)

A device that converts a digital signal into a corresponding analogue signal, commonly for digital audio output.

Bitmap

An image represented using pixels, with bits stored to describe each pixel.

Metadata

Information stored in an image file about the image, such as its width, height and colour depth.

Vector graphic

An image represented as a list of geometric objects, with the properties of each object stored in the representation.

Primitive

A simple geometric object or shape, such as a rectangle, circle or line, used to create a vector graphic.

Vector graphic

A graphic represented using shapes and paths, allowing the image to be resized while generally retaining the sharpness of its shapes.

Bitmapped graphic

A graphic represented as a grid of individual pixels.

Sample resolution

The number of bits used to represent the value of each sound sample.

Sampling rate

The number of samples taken from a sound each second.

MIDI

A system for representing a musical performance using instructions and event messages rather than a complete recording of the sound.

Event message

A piece of MIDI information that describes a musical event, such as a note starting or stopping, as part of a timed sequence.

Lossless compression

A compression method that preserves all original data so that the original file can be reconstructed exactly.

Run length encoding

A lossless compression technique that represents consecutive repeated values by recording the value and the number of repetitions.

Ciphertext

The encrypted form of a plaintext message.

Computational security

Security based on an encryption algorithm being sufficiently difficult to break with the available ciphertext, time and computational resources, rather than being mathematically impossible to break.