Bitmap colour depth

Because a bitmap image is really just a long string of 1s and 0s (binary digits, bits), it has no idea about the concept of colour.

We could store each colour as 24 bits (or 32 bits if we need transparency).
That would allow us to store pretty much any colour, but it does mean that images which only use a few colours would take up a lot more storage than they need to.

To fix this, we can store a bit depth, which will tell the program reading the image how many bits each pixel’s colour takes up.

The colours represented by each number is stored in a colour map.

Example: black and white images

If we store a black and white image, there are only two possible colours each pixel can have. We can represent a black-and-white image with just 1 bit per pixel (a 0 for black and a 1 for white, for example), and so our colour depth would be one bit.