Current LCD screens have three colors per pixel, Red, Blue, and Green (RGB). Common graphics chips store the three colors as eight bits (byte) each, so 24 bits

Current LCD screens have three colors per pixel, Red, Blue, and Green (RGB). Common graphics chips store the three colors as eight bits (byte) each, so 24 bits per pixel. So a 500 by 500 pixel image would have 3 by 500 by 500 bytes or 750,000 bytes. The Windows BMP format stores images this way. GIF files reduce the number of colors to 256 by using a table in the file that has 256 entries of 3 bytes. The image is reduced to one byte (an index to the table) for each pixel. Then that is heavily compressed. JPG (simplistic description) stores the difference between pixels, losing some quality. GIMP is a free, open source image manipulation program. One feature is a color picker where you can enter RGB values by slider or hex value. Then you can draw lines, dots, etc in that color. It can export the resulting image in many different file formats. All of the other image or photo editing software has this feature.