For more on digitAl photogrAphy, visit http://www.shortCourses.Com 67
One way to evaluate
the tonal range is with
a histogram that charts
the various levels of
brightness in the image.
http://www.photocourse.com/itext/hue/
and shadow areas or the image may be too dark or light. In these cases you
may want to adjust or expand the image’s tonal range.eVAluAting ColorS
The human eye perceives color in terms of three characteristics—hue, satura-
tion, and brightness and there is even a color model based on these charac-
teristics, called HSB. The color monitor uses a different color model called
RGB because images are displayed using varying amounts of red, green, and
blue light. When evaluating images, you can think in terms of these two mod-
els—one to evaluate colors and the other to look for color casts.
To evaluate colors in an image, think of them in terms of hue, saturation, and
brightness because these three aspects can be adjusted.- Hue is unique in one respect, it is the actual color, as measured by its wave-
length, while the other two characteristics (saturation and lightness) modify
the hue in some way. The hue can be red, orange, yellow, green, blue, purple,
or any intermediate color between those pairs. - Saturation, sometimes called chroma, is the strength or purity of the
color. If you adjust saturation through its entire range, colors go from rich
and vibrant to dark gray. - Lightness, also called luminance or brightness, is the relative lightness or
darkness of the color. Brightness is reduced by adding black to the color mix
and increased by adding white. If you adjust brightness through its entire
range, colors go from white to black. This is the only one of the three color
attributes that gray scale images have.
As you decrease
saturation (top), colors
become muddier and
finally gray. As you
decrease lightness
(bottom), colors
become darker and
eventually black.
Hues can be arranged
on a color circle or
wheel.
A color cast is usually caused when one or more of the three color compo-
nents (red, green, and blue) are too high or low over the entire image. This
can be caused by not setting white balance correctly, by photographing a
scene illuminated by more than one type of light source, or even a subject
picking up reflections from a colored surface. Color casts are very noticeable
when shooting during sunrises and sunsets—but there we usually like the
effects. It’s easiest to identify a color cast by looking at areas that should be
neutral white or gray. If these areas have any colors mixed in, the image has aTiP
a neutral color has
equal amounts of
red, green, and blue
and appears as a
shade of gray.Click for a movie
on adjusting hue,
saturation and
brightness.
evAluAting your imAges—bAsiCs