A Raster Image is esentially an image made of different coloured dots.
The more colours/shades the larger the file.
Raster graphics are bitmaps. A bitmap is a grid of individual pixels that collectively compose an image. Raster graphics render images as a collection of countless tiny squares. Each square, or pixel, is coded in a specific hue or shade. Individually, these pixels are worthless. Together, they’re worth a thousand words