91
A
N INTRODUCTION TO COLOR
90
Changes in hue rotate the original
color values though a color space
and reassigns a new hue based on
the new position in that space. In
this example, the original image
was rotated 180°. For more on the
hue, saturation, and brightness
palette, see page 81.
Two color spaces are displayed at
the bottom of the palette. The top
bar indicates the color space of
the original image. The bottom bar
displays the relative shift to the
color space. In the example, the
reds have been shifted to green
and the yellows to lavender.
Original color space
New color space
Hue corrections
HSB color model (p. 81)
Adding or subtracting equal parts of red, green, and blue will have no affect on the
color balance. However, it can change the overall image brightness and contrast.
Usually, no more than two color channels are needed to color balance an image.
Color balancing is a skill that develops with practice. While the human eye is
extremely sensitive in making comparative judgements, it is a poor tool when making
absolute measurements of color. Initially, it can be very difficult to distinguish
between blue and cyan, and red and magenta. However, adjusting the wrong color
channel never improves an image; subtracting blue from an image that is too cyan
will give a green cast to the image.
If the image is too
RED
GREEN
BLUE
CYAN
MAGENTA
YELLOW
Decrease the amount of green.
Decrease the amount of blue.
Increase the amount of red.
Increase the amount of green.
Increase the amount of blue.
Decrease the amount of red.
Knowing the complementary colors is very important in color balancing. If the image
has a specific color cast, either subtracting the color or adding its complementary
color will create a natural looking image.
Complementary colors
RED
GREEN
BLUE
CYAN
MAGENTA
YELLOW
Primary (RGB) and secondary (CMY) colors
Complementary colors (p. 90)
The RGB color model is an additive process that uses the primary colors of light:
red, green, and blue. An additive color system mixes the three colors to recreate the
entire spectrum of light. If all three colors are mixed, white light is produced.
Television sets and computer monitors use RGB to create images.
The CMY color model is a subtractive process that uses the secondary colors: cyan,
magenta, and yellow. A subtractive color system recreates color with pigments and
dyes to absorb unwanted color. If all three colors are mixed, black is produced. Film-
based photography is a subtractive process. Printing technology is also a subtractive
process, but, unlike photographic systems, it requires a black channel (K). Because
of the imperfections of printing inks, cyan, magenta, and yellow cannot produce a
true black when mixed, printers use what is called a four-color process (CMYK) to
reproduce images.
In photography, red, green, and blue are the primary colors. The secondary colors,
cyan, magenta, and yellow, are made from combining the primary colors: cyan =
blue + green, magenta = blue + red, and yellow = red + green. The primary and sec-
ondary colors are grouped in complementary pairs: red and cyan, green and magen-
ta, and blue and yellow.
C
OLOR EXAMPLES
Hue
Saturation
Lightness
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