Revise Multimedia - Graphics for Cambridge 9618 (1.2.1)

Imagine a vast grid. Each square in this grid is a pixel, and we can colour it in. This is the fundamental principle of a bitmap image. These images are composed of a fixed number of pixels, and the quality of the image is directly tied to the density of these pixels (resolution) and the variety of colours available for each one (colour depth).

For your exam, you must be able to calculate the storage requirement for an uncompressed bitmap image. This calculation depends directly on the image's dimensions and its colour depth. The base unit for this calculation is bits, which can then be converted into bytes, kilobytes, megabytes, etc.

$File Size (in bits) = Image Width (pixels) \times Image Height (pixels) \times Colour Depth (bits)$

Remember the standard conversions for file storage units: 8 bits = 1 byte, 1024 bytes = 1 kilobyte (KB), 1024 KB = 1 megabyte (MB). While some contexts use 1000, for Cambridge A-Level, using powers of 2 (1024) is the standard convention unless specified otherwise.

Instead of storing a grid of pixels, vector graphics store a list of instructions. These instructions define objects like lines, curves, circles, and polygons, along with their attributes such as line colour, fill colour, and thickness. When you view a vector image, your computer reads these instructions and renders the image on the screen. This is why they are perfectly scalable.