7.2: From two colors to millions

24-bit color

16-bit color

8-bit color

These images display color at different bit depths. The difference between 24 bpp and 16 bpp is subtle.

What is pixel depth?

Pixel depth, also known as bit depth, determines how many unique colors are available for a given computer display, or how many unique colors are encoded in a digital image:

RGB channels

Every pixel in a color digital image is created through a combination of the red, green and blue primaries, often referred to as color channels.

MONOCHROME IMAGES: Early computer monitors displayed two colors, black and white. Each pixel had one bit of data available, and pixels were dithered to give the illusion of shades of gray.


GRAYSCALE IMAGES: With expanded the memory available for video display, computer screens could display 255 shades of gray, plus white. Each pixel had eight bits, or one byte, of data available. These were the same screens used for monochrome, but with more video RAM.


INDEXED COLOR: A color screen is capable of displaying millions of colors, but the first color computers still had the same eight bits of video memory per pixel. Pictures were displayed with the best palette of 256 colors (28). The palette was different for each picture. Colors were dithered to simulate a wider color range.


TRUE COLOR: Today, computers have high-speed video boards with plenty of RAM. Each pixel is supported by 24 bits of memory, eight bits for each channel of red, green and blue. The screen can display 16,777,216 colors (224).