Image compression - GCSE Computing

The bitmap image format described earlier has a binary number for every single pixel in the image. The accuracy of the image is only limited by the resolution and colour depth of the format. No data is missing and so this is called an 'uncompressed image' format. Uncompressed image files can be huge.

For example a 1000 pixel x 1000 pixel image with 24 bit depth has a file size of

1000 x 1000 x 24/3 bytes = 8 Megabytes.

This is massive, making it impractical for web sites and awkward as an email attachment.

A very popular way of using fewer bytes is to 'compress' the file. This works by looking…