Apple Aperture Digital Photography Fundamentals - Manual (Page 33)

Chapter 2 How Digital Images Are Displayed 33
Understanding How a Digital Image Is Displayed
Photographers display their digital images in two basic ways: onscreen or in print. The
method by which an image is displayed onscreen and the way it is displayed as a print
hanging on a wall are completely different. Computers, televisions, and video and
digital still cameras create color images by combining red, green, and blue (RGB)
primary colors emitted from a light source. This approach is based on the additive color
theory. Printed images require an external light source from which to reflect light.
Printing technology uses subtractive color theory, typically with four primary
colors: cyan, magenta, yellow, and black.
Additive vs. Subtractive Color
Images with color elements derived from the light source itself are considered to have
additive color, while images that subtract or absorb certain wavelengths of light,
reflecting back specific colors to the viewer, are considered to have subtractive color.
Because of these differences, an image displayed with additive color (for example, on
an LCD display) will always look different from the same image displayed with
subtractive color (such as on a magazine cover). The reason for this is that digital
devices like LCD displays combine red, green, and blue light in different combinations
to produce the desired color. All colors combined at their maximum intensities create
white, and the absence of color creates black. On the other hand, a printed piece like a
magazine cover combines cyan (C), magenta (M), and yellow (Y) inks in different
combinations to create a color that reflects the proper color of light. Black ink (K) is
added to the image last to generate pure black on the page. The addition of ink creates
a darker color, and the absence of ink creates a lighter color. This color process is also
known as CMYK.
Red Yellow
Blue
Additive color
White
Magenta Cyan
Green
Subtractive color
Red
Yellow
Blue
Black
Magenta Cyan
Green
B
R G
Y
C M
K