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Additive v. Subtractive Colors

The six main colors of photography are divided into two categories, additive and subtractive.

Additive Colors Subtractive Colors
Red, green, blue Cyan, magenta, yellow

The additive colors, red, green, and blue, are also called the primary colors.

Cyan, magenta, and yellow, the subtractive colors, are also called the complementary or secondary colors.

How They're Produced

The additive colors are produced by light sources, such as by the glowing phosphors of a cathode-ray tube monitor.

The subtractive colors are produced by light reflecting off of surfaces, such as a photograph in a magazine.

Some of the light that strikes the surfaces is being absorbed, or subtracted, by the surfaces.

Additive Colors Subtractive Colors
Red, green, blue Cyan, magenta, yellow
Produced by light sources Produced when light strikes a surface and some of the light is absorbed (subtracted), and the rest is reflected.

Why Additive?

Red, green, and blue are called additive colors because when two of them are added (mixed), one of the subtractive colors is produced.

For example, in the photograph below, when blue and red are added, or mixed, magenta light is produced.

Combining all three additive colors with equal intensities produces white.

Here are all of the mixes.

Blue + Red

Magenta

Blue + Green

Cyan

Green + Red

Yellow

Red + Green + Blue White
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Additive Colors: Red, Green, & Blue

Why Subtractive?

When you look at an image of a barn on a page in a magazine, you're looking at four layers of color.

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Subtractive Colors: Cyan, Magenta, Yellow

(Black is used for offset printing.)

On a magazine page, the full-color barn image below is created from the above four images printed in register.

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Think of subtractive colors as absorbers or subtractors of color.

When light strikes the barn image in a magazine, the inks absorb or subtract colors.

What One Subtractive Color Subtracts

A single subtractive color subtracts or absorbs one of the additive colors.

Single Subtractive Color Subtracts Reflects Seen As
Cyan Red Green & Blue Cyan
Magenta Green Red & Blue Magenta
Yellow Blue Red & Green Yellow

What Two Subtractive Colors Subtract

Two subtractive colors produce an additive color because each of the two subtractive color absorbs (subtracts) an additive color.

For example, when magenta and yellow are combined, they absorb (subtract) green and blue, respectively, leaving red to be seen.

Two Subtractive Colors Subtracts Reflects Seen As
Magenta + Yellow Green & Blue Red Red
Cyan + Yellow Red & Blue Green Green
Cyan + Magenta Red & Green Blue Blue
Cyan + Magenta + Yellow Red, Green, & Blue Black Black

Combining all three subtractive colors with equal intensities produces black, because all colors are subtracted.

However, mixing equal amounts of cyan, magenta, and yellow inks doesn't yield a satisfactory black.

Therefore, the CMYK color space adds black, the K in CMYK, to the subtractive colors.

Because cyan was nicknamed blue in printing plants, the b in blue could be confused with the b in black.

Therefore, the K designation for black was adopted.

The K is from the word key.