Raster images are made up of pixels stored as an array of numerical values representing each pixel. There are two types: grayscale images representing shades of gray using 1-8 bits per pixel, and color images using a 3-tuple of red, green, and blue pixel values to represent colors. Color images are more common as they closely resemble real-world color experiences. Pixels in color images use a certain number of bits, such as 3 or 8 bits, for each color value in the 3-tuple to represent different color intensities and combinations that produce colors other than red, green, and blue.