Unit 1 - computing IGCSE revision

An image

a series of pixels that are converted to binary, which is processed by a computer

Resolution

the number of pixels in the image

Colour depth

the number of bits used to represent each colour

The file size and quality of the image…

increases as the resolution and colour depth increase

Sample rate

number of samples taken in a second

Sample resolution

number of bits per sample

Calculate sound file size

Sample rate x duration x sample resolution

Calculate image file size

Colour depth x image height x image width

File size units in ascending order

Bit, nibble, byte, kilobyte, megabyte, gigabyte, terabyte

How many bits in a byte

8

How many bytes in a kilobyte

1000

Why is compression needed?

less bandwidth required, less storage space required, shorter transmission time

Lossless process

An algorithm is used when compressing data with the lossless method. Repetitions within text/sound/image are identified. These repetitions are put in a table and are given an index. With Lossless data previous data can still be accessed.

Lossy process

An algorithm is used when compressing data with the lossy method. Unnecessary data is removed to reduce the file size. This change can sometimes not be detected by the human eye. File size is reduced by reducing resolution or colour depth, reducing sample rate or resolution.

Analogue sound to digital

1. Analogue sound is recorded in sound waves

2. The sample rat is set

3. The sample resolution is set

4. In the same increments, a sample is taken of the audio

5. The sample is turned into binary code