Bitmap Graphics

Definitions

Name	Definition
Bitmap image	Bitmap images are stored as a series of pixels.
Pixel	A pixel is a single point in a graphic image with an assigned colour. Many of them on a screen are assigned a colour in a specific place to recreate a bitmap image.

Colour Depth

Colour depth is either the number of bits used to indicate the colour of a single pixel, in a bitmap image, or the number of bits used for each colour component of a single pixel. This means the number of bits needed to code an image. For example an image will only need 1 bit colour depth for black and white, i.e. a 0 for white or 1 for black, such as the following image...

although if an image has 24 bit colour depth, it can code up to 16777216 colours, such as the following image...

Resolution

Resolution is determined by the height and width of an image file, for example:

This square has a total of 10000 pixels because it is 100 pixels high and 100 wide. You multiply the height by the width. This image was downsized from a larger image to this resolution.

The image above is the same image but downsized to the larger resolution of 200 x 200. This resolution is double the previous image so it looks of equal quality even though it is double the resolution.

File Size

File Size of a bitmap file links nicely to this all as it is essentially the Colour Depth multiplied by the Resolution. This is because for every pixel there needs to be a colour assigned to it. Hence, an image, 100 pixels high, 500 pixels wide, with a colour depth of 24, bits would have the size of (100*500*24=) 1,200,000 bits or (100*500*25/8=) 150,000 bytes if it would be a bitmap image.