Photography: Capture to Presentation, 2nd Edition Page 417 (417 of 672)

Chapter 15 Digital Darkroom Basics
On the standard RGB color wheel, Figure 15-29,
the additive and subtractive primaries alternate
and thus are paired on opposite sides: red is
opposite cyan, blue is opposite yellow, and green
is opposite magenta. The colors in each pair are
known as complementary colors.
Color correction
Familiarity with the complementary
color pairs is important when correcting color
images using a
Curves
adjustment layer. With
this method, adjustments can be made to the
composite RGB curve, which affects the image
as a whole, or to the individual color channels
(providing much more precise control). For
example, a photo taken under industrial fluores-
cent or mercury vapor lighting often will have an
overall green color cast.
Figure 15-29. A standard RGB color wheel. Comple-
mentary colors (red/cyan, blue/yellow, green/magenta)
are opposite each other on the wheel.
Figure 15-30. Correcting a color cast. A—Fluorescent lighting has given this photo of a subway station a strong
green cast. B—Using a
Curves
adjustment layer, the green channel can be adjusted to correct the color.
A B
Correct the Color Cast:
1. Create a Curves adjustment layer and switch to the green channel (since green is the problem color).
2. Click on the Target adjustment tool button, located to the left of the channel indicator. Move the cursor
(which appears as an eyedropper tool) to an area where the color cast is most noticeable. A small circle will
appear on the diagonal line of the tone graph. This indicates the graph location for the pixel values being
sampled.
3. Click the mouse button, and the cursor will change to the Target adjustment tool (a double-headed arrow).
Drag the tool downward to reduce green and increase its complementary color, magenta,
Figure 15-30.
If
you drag too far, you will see the image taking on a distinct magenta cast.
(Continued)
417

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Extracted Text (may have errors)

Chapter 15 Digital Darkroom Basics
On the standard RGB color wheel, Figure 15-29,
the additive and subtractive primaries alternate
and thus are paired on opposite sides: red is
opposite cyan, blue is opposite yellow, and green
is opposite magenta. The colors in each pair are
known as complementary colors.
Color correction
Familiarity with the complementary
color pairs is important when correcting color
images using a
Curves
adjustment layer. With
this method, adjustments can be made to the
composite RGB curve, which affects the image
as a whole, or to the individual color channels
(providing much more precise control). For
example, a photo taken under industrial fluores-
cent or mercury vapor lighting often will have an
overall green color cast.
Figure 15-29. A standard RGB color wheel. Comple-
mentary colors (red/cyan, blue/yellow, green/magenta)
are opposite each other on the wheel.
Figure 15-30. Correcting a color cast. A—Fluorescent lighting has given this photo of a subway station a strong
green cast. B—Using a
Curves
adjustment layer, the green channel can be adjusted to correct the color.
A B
Correct the Color Cast:
1. Create a Curves adjustment layer and switch to the green channel (since green is the problem color).
2. Click on the Target adjustment tool button, located to the left of the channel indicator. Move the cursor
(which appears as an eyedropper tool) to an area where the color cast is most noticeable. A small circle will
appear on the diagonal line of the tone graph. This indicates the graph location for the pixel values being
sampled.
3. Click the mouse button, and the cursor will change to the Target adjustment tool (a double-headed arrow).
Drag the tool downward to reduce green and increase its complementary color, magenta,
Figure 15-30.
If
you drag too far, you will see the image taking on a distinct magenta cast.
(Continued)
417

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Section III Digital Postprocessing
416
described earlier in this text, the images displayed
on your computer screen or television are RGB
images: all the colors you see are combinations of
varying amounts of red, blue, and green light. On
the screen, tiny phosphor dots of red, blue, and
green glow when struck by a beam of electrons,
transmitting the color. Light Emitting Diode
displays (LEDs) and Liquid Crystal Displays
(LCDs) operate on different principles, but have
the same visual effect. Red, green, and blue are
referred to as the additive primaries, since their
light is added together to make a color.
Images that are printed on paper or
other opaque base material cannot depend on
transmitted light to convey colors to the eye.
Instead, they make use of reflected light. A
different set of colors (cyan, magenta, and yellow)
is used for printed images. Each color blocks,
or subtracts, a specific color and reflects others.
Yellow absorbs the blue wavelengths of light but
reflects red and green, magenta absorbs green
but reflects red and blue, while cyan absorbs red
and reflects blue and green. For this reason, cyan,
magenta, and yellow are called the subtractive
primaries. (Refer to Chapter 4, Light and Exposure
for additional information.)
Alter Contrast Using Curves
1. With the image open, click on the
Curves
icon in
the
Adjustments
panel.
2. Click on the midpoint of the diagonal line to
anchor it at that point. A small black dot will
appear at the center of the graph line.
3. Click on the line at a point midway between
the center and the lower-left corner, then drag
it a small distance diagonally down and to the
right. Note that the line is now a curve from the
midpoint to the lower-left corner. The line from the
midpoint to the upper-right corner has assumed
a matching (but opposite) curved shape,
Figure 15-28.
4. The image will have become more contrasty, with
the tonal range extended. The degree of contrast
change depends on the distance the point was
moved—the farther the line curves away from the
diagonal, the greater the change.
5. To decrease contrast, the curve is moved in the
opposite direction, curving upward from the lower
left corner to the midpoint and downward from
the midpoint to the upper-right corner. The tonal
range is decreased, flattening the image.
Figure 15-28. With the curve anchored in the
middle, a change in the lower portion of the line
is mirrored in the upper portion. This mildly
S-curved line represents a moderate increase in
the contrast of the image. If a color image (or a
desaturated RGB file like this one) is being adjusted,
changes can be made independently to each of the
three color channels.
When working with a color image, contrast
of the red, green, and blue color channels can
be adjusted individually for greater control.
The desired channel can be selected using the
Channel
box above the tone graph.
RGB
is the
default; when it is displayed, contrast adjustments
are applied to all three channels simultaneously.
Contrast also can be adjusted locally (in a
selected area). Such a change might be made to
bring up detail in the somewhat dark foreground
of a landscape. This is equivalent to the
conventional darkroom process of using different
contrast filters to expose selected areas of a print.
First, a selection is made, and then the contrast
adjustment is carried out. The change will affect
only the selected area.
Correcting and Adjusting
Color
Working with color images, as compared to
black-and-white, can be considered three or four
times as complicated, since color images consist
of either three channels (red, blue, and green)
or four (cyan, magenta, yellow, and black). As

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418
Section III Digital Postprocessing
A color correction method that does not
offer control as precise as the
Curves
adjustment
layer, but is somewhat less complex to use, is
the
Color Balance
adjustment layer. It presents
the three pairs of complementary colors,
with a slider control for each pair. To make
a color correction, the appropriate slider is
moved toward the color that is to be increased,
Figure 15-32. The color balance can be adjusted
differently, if desired, in the image’s shadows,
midtones, and highlights.
Figure 15-32. This photo, taken with incandescent light
on daylight-balanced film, is much too yellow. The
Color
Balance
command can be used to add blue, effectively
decreasing the yellow. The amount of decrease can be
different in shadow, midtone, or highlight areas.
Color
Balance
is quicker and easier to use than Curves, but
control is less precise.
Figure 15-31. To brighten the image, the composite
curve is pulled slightly upward. The proper amount
of adjustment can be judged by changes on the
displayed image.
4. The changes in the green and blue curves may
cause the image to darken somewhat. To lighten
the entire image, switch to the composite (RGB)
curve and pull diagonally up to the left on the
midpoint of the curve,
Figure 15-31.
Color adjustment
The
Hue/Saturation
adjustment layer can be
used to fine-tune colors in an image. It permits
selection of any of the six primary colors in the
image (red, green, blue, cyan, magenta, yellow)
and adjusting the hue, saturation, and brightness
of the chosen color.
As shown in Figure 15-33, the
Hue
slider
can shift a given color toward its neighbors
on the color wheel (the two colors that are its
components). If the selected color is red, for
example, sliding the control to the left will change
the red values in the image to magenta; sliding
to the right will change them to yellow. Such
extreme shifts are seldom made—more often, you
would make the red just a bit more magenta or
a bit more yellow. The
Saturation
slider changes
the intensity (strength) of the color; the
Lightness
slider alters the overall brightness.
Similar changes can be made with
the
Replace Color
command or the
Color
Replacement
tool. The
Replace Color
command’s
dialog box, Figure 15-34, has a preview window
that shows (in white) the color selected for
replacement. The selection is made by using an
eyedropper to sample the desired area of the
image. Moving the
Fuzziness
slider in the dialog
box will expand or contract the selection in the
preview window. The selected color is replaced
by using the Hue, Saturation, and
Lightness
sliders.
The
Color Replacement
tool is selected from
the toolbox (right click on the
Brush
tool to see it).

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Page 11Section I The Basics click to expand contents

Page 151Section II Shooting click to expand contents

Page 375Section III Digital Postprocessing click to expand contents

Page 487Section IV Traditional Processing click to expand contents

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