Re: How do color printers reproduce pics with photo quality?

Hi April,

All printers work by applying a pigment (ink or wax) to paper. Color printers work by using several colors of pigment, usually cyan (light blue), magenta (pinkish red), yellow, and black. Why these particular colors? Because they are the three "primary colors" for pigments. By combining these colors in varying amounts, a printer can produce almost any color imaginable. It is difficult to get a deep black using cyan, magenta, and yellow, so most printers contain black pigment as well. The black is used for dark portions of pictures and for printing text.

It is often difficult to accurately mix the primary colors. To deal with this, printers either don't mix the colors, or just mix them a little to produce a small number of printable colors. The printable colors are applied to the paper as very tiny dots. Your eyes combine the dots into the colors you see. For example, a grouping of yellow and cyan dots would appear to be green. This technique, called "dithering", was invented by the painter Georges Seurat (though painters call it "pointillism"). You can see Seurat's paintings here.

There are many methods for applying the pigment to the paper. Listed below are the most popular methods, roughly in order from lowest to highest print quality:

• Dot matrix printers store their ink in a ribbon. This ribbon is struck by tiny pins that "punch" the ink onto the paper. The big problem with dot matrix printing is that the pins have to be large enough to strike the ribbon without breaking. This means that the dots can't be extremely small, and the print quality remains fairly poor. Dot matrix printers are seldom used these days.
• Ink-jet printers use packs of liquid ink. This ink is sprayed onto the paper, and dries quickly. A high quality ink-jet can print hundreds of dots in a single inch. This is the most common type of color printer for home computers.
• Laser printers use a laser beam to give an electric charge to a rotating drum. The ink sticks to the charged portions of the drum, and then sticks to the paper. A laser printer can print over a thousand dots in an inch. The paper must go through the printer four times, once for each color.
• Thermal wax (dye-sublimation) printers use a ribbon coated with colored wax. A small, heated print head melts the wax onto the paper. This is very similar to the way a dot matrix printer works. The difference is that there is a great deal of control over how much of each pigment is melted into a single dot, resulting in many more color possibilities for each dot, and a much nicer picture. Thermal wax printers can be very expensive to use, with costs of $3 - $5 per page.
• Solid ink printers are fairly new. They use a combination of techniques from the ink-jet and thermal wax printers. The pigment is stored in solid blocks of wax. To print, the wax is melted and sprayed onto the paper.
• Thermal-autochrome printers, also new technology, use special paper with the ink already in it. A heated print head uses various heat levels to "pull" the ink out of the paper. This process is similar to the way photographs are developed.