As we read earlier, we modify the curve by using anchors or the free form
pencil. By far, anchors are used more often. Once the anchors have
been created, we reposition them in order to reshape the curve. We can
reposition an anchor one of three ways.
When we make a change, the curve will automatically reshape itself
The Curves dialog box shows the input digital tonal range on the X axis and
the output, or modified, digital tonal range on the Y axis. The curve
default is a straight line because Adobe Photoshop maps input tones 1:1 to
output tones. By reshaping the curve we are remapping the input tones to
new output tones. Using Figure 1 as an example, one of the anchor points
has been dramatically lowered. The red arrows in Figure 1 show both the
before and after tones. The vertical arrow coming from the X axis shows
this anchor was originally a light tone. The horizontal arrow touching the
Y axis shows us the new tone it has been remapped to, which is a darker tone.
One of the nice features of the Curves control is its ability to show us
where a tone in our image is on the curve. With the Curves dialog box
open, mouse over the image while holding down the left mouse button. As we
do this, a bouncing ball will move along the curve. The ball is showing us
the tone of the area the cursor is currently over.
Generally speaking, when the curve is flattened (made more horizontal), the
full input tonal range is being compressed into a smaller output tonal range.
Shadow areas (black and dark tones) will become lighter and highlight areas
(white and light tones) will become darker. The flattening of the curve
causes a reduction in the contrast of an image because the two extreme ends of
the output tonal range are being forced closer together. The input tonal
range remains 0 to 255. But by flattening the curve, the output tonal
range is some number higher than 0 and a number lower than 255. An example
of a flattened curve can be seen in Figure 2. The red line shows the
position of the original, unadjusted curve.
Figure 3 shows a steepened curve. On the adjusted curve, the darker
tones that are flat lined on the bottom left of the curve are all being mapped
to solid black (output tone 0). The lighter tones that are flat lined on
the upper right of the curve are all being mapped to solid white (output tone
255). All the remaining tones on the new curve are being spread out.
Specifically, any tone that is below the point of intersection between the
adjusted curve and the red line is being mapped to a tone that is darker than
itself. Any tone that is above the point of intersection is being mapped
to a tone that is lighter than itself. The steeping of the curve causes an
increase in the contrast of an image because some tones are becoming darker
while others are becoming lighter.
There is an almost infinite number of ways that a curve can be shaped. In
Table 2 below, most of the common shapes are shown. Review Table 2 to
learn about these shapes and how they affect an image. Table 2 gives the
equivalent Levels adjustment, when there is one. The red line in each of
the dialog boxes in Table 2 shows the position of the default curve.
To see examples of how the Curves control affects an image, be sure to
Take the Test.
|Red Line Represents Default Curve
||Equivalent Levels Adjustment
Place an anchor on tone 127 and move it horizontally to the right.
|Darkens overall image. The effect tapers off as it approaches white
||Move gamma slider to the right.
Place an anchor on tone 127 and move it horizontally to the left.
|Lightens overall image. The effect tapers off as it approaches white
||Move gamma slider to the left.
Lower white anchor, raise black anchor.
|Lowers contrast. Removes solid white and black. The effect tapers
off as it approaches mid tone. The more the curve approaches horizontal,
the more contrast decreases.
||Move both Output Levels black and white sliders inward. Example 3
more accurately replicates the Levels adjustment than Example 11.
Move white anchor to the left, move black anchor to the right.
|Increases contrast. Increases the number of solid whites and solid
blacks. The effect tapers off as it approaches mid tone. The more the
curve approaches vertical, the more contrast increases.
||Move Input Levels white and black sliders inward. Many
photographers consider Levels the better control for this kind of
adjustment because of its clipping preview feature. Read the
Clipping Preview page for more information.
Raise black anchor only
|Lightens shadows. The effect tapers off as it approaches white.
||Move Output Levels black slider inward.
Move black anchor to the right
|Darkens shadows. The effect tapers off as it approaches white.
||Move Input Levels black slider inward.
Move white anchor to the left
|Lightens highlights. The effect tapers off as it approaches black.
||Move Input Levels white slider inward.
Lower white anchor.
|Darkens highlights. The effect tapers off as it approaches black.
||Move Output Levels white slider inward.
Place multiple anchors on the curve and only move the white anchor down.
|Darkens highlights. However, the tapering effect is eliminated
because only highlights are darkened and the remaining curve is
unchanged. Compare to previous adjustment.
||None. This is an example of the control the Curves command gives
that we cannot replicate with Levels. The closest we can come is to
move the white Output Levels slider inward.
Place anchors somewhere in Zones III and VIII. Raise Zone VII anchor,
lower Zone III anchor. This is known as the S curve.
|Increases contrast in mid tone areas because in these areas the
curve is getting steeper.
Lightens highlights and darkens shadows. However, contrast is decreased
in these areas because the curve is getting flatter.
|Move the Input Levels white and black slider inward. Also move the
Output Levels white and black sliders inward but not as much. If we move
the Output Levels sliders the same as the Input Levels sliders the two
adjustments will cancel each other out.
Move black point both horizontally and vertically. Move white point
both horizontally and vertically.
|Slight decrease in contrast. Blacks and very dark shadows are
converted to a single tone, which will be slightly lighter than
originally. Whites and very light shadows are converted to a single
tone, which will be slightly darker than originally. Middle tones are
||Moving both Output Levels black and white sliders toward the center
will approximate this adjustment. See Example 3.
For Input value 0, change it to 255. For Input value 255, change it to
|Reverses tones and colors.
In graphing terminology, the default red curve has a positive slope
while the adjusted curve has a negative slope.
|Move Output Levels black slider to the far right. Move Output Levels
white slider to the far left.
This is an example of using the freeform mode and drawing a curve using
|This particular curve will create distinct bands of tonality in the
image, often called
This is an extreme example of how anchors can be used to reshape the
|The parts of the curve that have a negative slope will cause reverse
colors and tones in the image.
The parts of the curve that have a positive slope will increase contrast
because the slope is steeper than the default curve.
The default curve in red has a positive slope of 1:1.
|Create color sampler target
in the image
||Up to four color sampler targets can be added to an image. To add a
target while the Curves dialog box is open, turn Caps Lock on, mouse to
the desired location in the image, and Shift + click. Caps Lock changes
the cursor from an eyedropper cursor to a crosshair
which gives a little more precision in creating a target. Turning on
Caps Lock is not mandatory.
||Color Sampler targets do not affect the image. They place
information in the Info panel that can be used to monitor changes to
|Delete a color sampler target
||To delete a target while the Curves dialog box is open, mouse to the
target, hold down Alt + Shift (Option + Shift) until the cursor turns
into a pair of scissors
and then click to delete.
|Move a color sampler target
||To move a target while the Curves dialog box is open, mouse to the
target, hold down the Shift key until it becomes a black arrowhead, then
drag the target to the new location.