Most users will either use Curves a lot or they won’t use it at all. The Curves interface is more complex than Levels, which scares away many users. While Levels gives you three control points (highlights, midtones, and shadows), the Curves adjustment allows for up to 16 control points. This can significantly open up more options when adjusting color and exposure.
Lets try the Curves command on a practice image:
Step 1. Open the file Curves_Practice.jpg.
Step 2. Add a Curves adjustment layer by clicking the Curves button in the Adjustments panel. When you first open the Curves interface, there are two points (one for white and one for black).
Step 3. Add a single control point in the middle of the line (click at an Input Value of 50%).
Step 4. Pull this new control point down to lighten the image (toward the lighter area on the Y axis). You can pull the point up to darken the image. Notice that the Input and Output values update as you drag.
Step 5. The adjustment is applied gradually throughout the entire image. Multiple points can be employed for contrast adjustments based on tonal range.
The primary advantage of Curves is that you have precise control over which points get mapped (whereas in Levels you do not). Another benefit is that Curves adjustments can use several points connected by a curved line (as opposed to Levels, which uses only three control points) to make adjustments. So, color correction can be applied in a more gradual manner (without the hard clipping that can be associated with Levels).
Step 1. Open the image Curves.jpg (provided for educational use only).
Step 2. Add a Curves adjustment layer by clicking the Curves icon in the Adjustments panel. The curve has only two points on itone representing the black point; the other, the white point.
TIP: Pay Attention to Your Axes When working with a grayscale or CMYK file, the axes go from light to dark. When working with RGB images, the scales are reversed. This means that pulling a control point up or down may have a different effect depending on your image mode.
Step 3. Its now time to add more control points to refine the curve. To do this, you’ll use a Curves preset. Click the menu to select a Curves preset in the Adjustments panel. Choose the Strong Contrast (RGB) preset. Notice that the image now has more contrast in the shadows and highlights, and more visual pop.
Step 4. Experiment by adjusting the five control points. Try to further emphasize the shadows in the image. Continue to experiment by moving the control points (you can use the up and down arrow keys for precise control).
TIP: Make Curves Easier When the Curves Editor is open, you can easily add control points. Click the icon that looks like a pointing finger, and then just click and drag in the image to modify the curve. The control points will appear in the editor. These can be moved to lighten or darken the image.