Layer > New Adjustment Layer > Curves
Or, click the Create new adjustment layer icon
at the bottom of the Layers panel.
I like Curves. You will too.
The Curves and Levels controls do the same thing but in different ways.
The Levels control allows us to target three areas in an image's tonal range:
shadows, highlights and mid tone. Curves allows us to control up to 14
points of our choosing for a total of 16 points when we include the black and
white points that Adobe Photoshop automatically provides. In addition, the
Curves control allows us to custom draw our own tonal range if desired.
The adjusting of color balance using Curves is discussed on the
Curves Color Correction page.
The Levels dialog box shows us a histogram so we can clearly see where our
image's tones are when plotted against the digital tonal scale. In Levels,
we use the histogram as a reference. The Curves dialog box does not show
us a histogram. In fact, the Curves dialog box does not show us our
image's tones at all. The Curves dialog box shows us two gradients in the
form of a grid. One gradient represents the digital tonal range before the
adjustment and the other represents the digital tonal range after the
Figure 1. Curves Dialog Box
When we first create a Curves adjustment layer, the dialog box will look
similar to Figure 1. In the Curves dialog box, there are four ways to make
adjustments: the curve (A) in combination with anchor points (B, B1 and B2), the
Input and Output boxes (C), the freehand drawing tool
(D) and the eyedropper tools
The predominant feature of the Curves dialog box is a chart with a straight line
going from the bottom left to the upper right. The straight line is
labeled A in Figure 1 and it is the curve. This chart is an interactive
chart (in Photoshop, not on this web page). We reshape the line in the
chart to make our adjustments.
Like most charts, the Curves chart has a X and Y axis, which are labeled as such
in Figure 1. The X axis is the input or source tonal range. We can
think of it as the 'before' status. Like a histogram, it goes from solid
black on the left to solid white on the right. Also like the histogram,
black is represented by 0 and white by 255. The Y axis is the output or
destination tonal range. We can think of it as the 'after' status.
If we look closely at the X and Y axis, we can see there is a miniature tonal
scale gradient going from solid black to solid white.
The Curves chart is mapping all 256 input tones to output tones. When a
Curves adjustment layer is first created the curve is straight because Photoshop
defaults to mapping the input tones 1:1 to the output tones. When we
reshape the curve, we are changing what input tones get mapped to which output
tones. When manipulating the curve, we are required to account for all 256
input tones. However, we are not required to use all 256 output tones.
In fact, we can map all 256 input tones to a single output tone.
Below the grid are two numeric boxes called Input and Output. These boxes
are labeled C in Figure 1. Once we place an anchor point on the curve,
these two boxes become active and show the before (Input) tonal value and the
after (Output) tonal value. Once the Input and Output boxes are active, we
can click in these boxes and make changes by either typing new numeric values or
pressing the Up/Down arrow keys to change the existing value.
Clicking in the Input box allows us to change the placement of the anchor point
horizontally in the grid. This changes the Input tone being adjusted.
Clicking in the Output box allows us to change the placement of the anchor point
vertically in the grid. This changes what Output tone the Input tone
is being mapped to. The Input box specifies what tone is to be changed.
The Output box specifies what tone it is being changed to. As we
reposition the anchor point, it 'drags' the curve with it. It is the
repositioning of the anchor point(s) within the grid that forces the reshaping
of the curve, thus changing the tonal values in the image.
Figure 2. Reshape the
curve by moving anchor points
On the curve, Photoshop automatically places an anchor on solid black and
solid white. These anchor points are labeled B1 and B2 respectfully in
Figure 1. Solid black is in the lower left corner. Solid white is in
the upper right. The other anchor labeled B is an anchor I manually added
by clicking on the curve. This anchor represents tone 90. How do we
know it is 90? Because the Input box, labeled C in Figure 1, tells us the
tonal value of whatever anchor is active. We can click in the Input box
and change this value. When we do, the anchor will automatically
reposition itself on the curve. If we leave Input to 90 and click in the
Output box and change the output value to 115, this will cause the curve to
automatically reshape itself. Mouse over Figure 2 to see the reshaped
curve. By reshaping the curve, we are remapping input tones to new output
tones. In this specific example, we are remapping input tones to lighter
tones because tone 115 is lighter than tone 90. In fact, in this
example, we shifted this part of the image by one full f-stop.
The eyedropper controls, labeled F in Figure 1, are used to set the black, mid
and/or white points of the tonal scale to specific areas in the image.
Part D of Figure 1 shows two icons. The pencil icon
turns the Curves cursor into a pencil where we can free hand draw our own curve
in the grid. The curve icon takes us out of free form mode and back into
the default mode of reshaping the curve using anchors. The Smooth button
is only active when in free form mode. After hand drawing a curve, it can
be smoothed by clicking this button. The more we click the button, the
more the curve will be smoothed. Click it enough and the curve will become
Like Levels, we can save an adjustment. Curves adjustments are saved as a
Photoshop *.acv file using the Save button. The Load button is used to
load the adjustment.
There are a number of predefined Curves adjustments I
have created and make available on the
To reset the curve to the Photoshop default, hold down the Alt (Option) key
and the Cancel button becomes a Reset button. Click while still holding
down the Alt (Option) button to reset the curve to a straight line.
The Auto and Options buttons are used to set up and apply automatic settings,
which are not discussed on this web site.
The Channel drop down box at the top of the dialog box allows us to work on the
full image (RGB) or just individual
The preview check box allows us to see our changes in real time. When this
box is checked, the impact of our changes can be readily seen in the image.
When this box is not checked, we will not see the impact until we click OK.
This check box is most useful when we want to see a before/after affect while
the dialog box is open. This is accomplished by clicking the check box on
Clicking the scale button, which is labeled E in Figure 1, changes the size of
the dialog box between large and small. Which size of the dialog box to
use depends on whether or not there is enough space on your monitor for both the
document window and the large dialog box.
By Alt + clicking (Option + clicking) in the grid, the grid dimensions toggle
between 4x4 and 10x10. Figure 1 shows a 10x10 grid. Most
photographers find the 10x10 grid easier to work with.
The double headed arrow in the middle of the gradient on the X axis in Figure 1
changes both the orientation of the gradient and the unit of measure. For
RGB images, the default gradient for the X axis is black on the left and white
on the right. For the Y axis, it is black on the bottom and white on the
top. For RGB images, the default unit of measure is the numeric tonal
range with 0 for black and 255 for white. For CMYK images, the default
gradient for the X axis is white on the left and black on the right. For
the Y axis it is white on the bottom and black on the top. For CMYK
images, the default unit of measure is percent black with 0% for white and 100%
By clicking the double headed arrow, Curves will switch between these two
defaults. Rest assured that Photoshop will not convert the image
to/from RGB/CMYK while clicking the double headed arrow. The image will
remain in the
color model it was set to. Photoshop only changes how the Curves
dialog box displays information. Most photographers prefer the RGB default
of displaying numeric tonal values.