Look at a screen with a magnifying glass and you will see tiny red, green and blue lights (subpixels). Look at a magazine photo and you will see tiny dots of cyan, magenta, yellow and black ink, called a halftone. From a normal distance, the eye blends both into smooth color.
Key idea
A screen adds red, green and blue light. A printer subtracts with cyan, magenta, yellow and black dots on white paper. The two can show different ranges of colors.
Why it works
A screen makes yellow by lighting its red and green subpixels; a printer makes red by overlapping magenta and yellow dots. The range of colors a device can show is called its gamut. Some glowing screen colors, especially very bright greens, blues and oranges, lie outside what inks can reach on paper, so they print duller.
Worked example: Two ways to make red
How does a screen make red, and how does a printer make red?
- A screen gives off light: it lights its red subpixels and leaves green and blue dark.
- A printer subtracts: magenta ink absorbs green light and yellow ink absorbs blue light.
- Together the two inks leave mostly red light to bounce back from the paper.
Answer: Screen: red light alone. Printer: magenta and yellow ink.
Common mistake
Expecting a bright screen color to print exactly the same. The screen glows; paper only reflects. Designers check colors in print-preview modes, choose inks for special jobs, and expect the brightest screen colors to come out a little quieter on paper.
Painters found a related idea by hand. Georges Seurat placed small dots of color side by side so they would blend in the viewer's eye (see Seurat and Pointillism).