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In the Curves adjustment, you adjust points throughout an image’s tonal range. Initially, the image’s tonality is represented as a straight diagonal line on a graph. When adjusting an RGB image, the upper-right area of the graph represents the highlights and the lower-left area represents the shadows. The horizontal axis of the graph represents the input levels (original image values) and the vertical axis represents the output levels (new adjusted values). As you add control points to the line and move them, the shape of the curve changes, reflecting your image adjustments. The steeper sections of the curve represent areas of higher contrast while flatter sections represent areas of lower contrast.
You can save Curves adjustment settings as presets. See Save adjustment settings and Reapply adjustment settings.
Note:
The Curves adjustment can also be applied to CMYK, LAB, or Grayscale images. For CMYK images, the graph displays percentages of ink/pigment. For LAB and Grayscale images, the graph displays light values.
A. On-image adjustment tool B. Sample in image to set black point. C. Sample in image to set gray point. D. Sample in image to set white point. E. Edit points to modify the curve. F. Draw to modify the curve. G. Curves presets menu H. Set black point. I. Set gray point. J. Set white point. K. Show clipping.
Moving a point in the top portion of the curve adjusts the highlights. Moving a point in the center of the curve adjusts the midtones, and moving a point in the bottom section of the curve adjusts the shadows. To darken highlights, move a point near the top of the curve downward. Moving a point either down or to the right maps the Input value to a lower Output value, and the image darkens. To lighten the shadows, move a point near the bottom of the curve upward. Moving a point either up or to the left maps a lower Input value to a higher Output value, and the image lightens.
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In the Properties panel, do any of the following:
- Click directly on the curve line and then drag the control point to adjust a tonal area.
- Select the On-image adjustment tool and then drag in the area of the image you want to adjust.
- Select the On-image adjustment tool and click the tonal areas in the image that you want to adjust. This places control points along the curve line.
- Choose a preset from the Preset menu.
Dragging a control point up or down lightens or darkens the tonal area you’re adjusting. Dragging a control point left or right increases or decreases the contrast. You can add up to 14 control points to the curve. To remove a control point, drag it off the graph. As you adjust the tonality, the graph continues displaying the original diagonal baseline and image histogram as references. These options can be turned off, see Set Curves Display Options.
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(Optional) Do any of the following to modify the adjustment:
- Add more points directly to the curve to adjust different tonal areas.
- Click the On-image adjustment tool in other areas of the image, and drag up or down.
- Move the Set Black and White Point sliders or use the Eyedropper tools to specify the darkest and lightest values in the image.
- Click a point on the curve, and enter values in the Input and Output text boxes.
- Select the pencil icon and draw a new curve over the existing one. When you have finished, click the Smooth the Curve Values icon or to smooth the curve you drew. Clicking more than once continues to smooth the curve further.
To remove a control point, do any of the following:
- Drag the control point off the graph.
- Select the control point and press Delete.
- Ctrl-click (Windows) or Command-click (Mac OS) the control point.
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Light (0-255) Displays the intensity values for RGB images in a range from 0 to 255, with black (0) at the lower-left corner.
Pigment/Ink % Displays the percentages for CMYK images are displayed in a range from 0 to 100, with highlights (0%) at the lower-left corner.
Simple Grid Displays gridlines in 25% increments.
Detailed Grid Displays gridlines in 10% increments.
Show Channel Overlays Displays color channel curves superimposed on the composite curve.
Histogram Displays a histogram of the original image tonal values behind the graph.
Baseline Displays the original image color and tonality as a 45-degree angle line for reference,
Intersection Line Displays horizontal and vertical lines to help you align control points as your drag them relative to the histogram or grid.Note:
To change the gridline increment, Alt-click (Windows) or Option-click (Mac OS) the grid.
Auto applies an automatic color correction using the current default setting. To change the default setting, choose Auto Options from the Properties panel menu and set the options in the Auto Color Correction Options dialog box. You can apply an Auto Color, Auto Contrast, or Auto Tone correction to an image. For more information on these options, see Set Auto adjustment options.
When applying a Curves adjustment, use the black and white sliders to quickly set the black and white points (pure black and pure white values) in the image.
If
the image uses the full tonal range, but needs midtone contrast,
Click the Curves icon 
in
the Adjustments panel. Drag the curve into an S shape.
- To set a point on the curve for the selected color in each color component channel (but not in the composite channel), Shift+Ctrl-click (Windows) or Shift+Command-click (Mac OS) in the image.
- To deselect all points on the curve, click in the grid, or press Ctrl‑D (Windows) or Command-D (Mac OS).
- To select the next higher point on the curve, press the plus key; to select the next lowest, press the minus key.
(Curves dialog box) To set a point on the curve for the current channel, Ctrl-click (Windows) or Command-click (Mac OS) in the image.
Note:
If you’re instead using the Curves adjustment, simply click in the image with the On-image adjustment tool 
.