Bitmap image

Unlike a vector image which stores the mathematical instructions for how to draw the image, a bitmap image (which we sometimes call a ‘raster image’) stores the image as a grid of pixels, where each pixel has a specific color value.

Think of it like a big table, each containing a code which corresponds to a specific colour.

For example, if we have a 3x3 bitmap image, it might look something like this:

R G B
G R G
B G R

(where I’m using R G and B to represent colours which can be drawn).

Metadata

Bitmap images are a grid of pixels, but how does the computer know how many rows and columns there are?

That’s stored in the metadata. See bitmap metadata for more details!