Setting Auto Color Correction Options in Photoshop

The options available in the Auto Color Correction dialog box are on the advanced side, and this set of tools is best used if you already understand manual color and contrast corrections. You can use the Auto Color Correction Options dialog box to tweak exactly how Photoshop applies its Auto Levels, Auto Color, and Auto Contrast controls, as well as for the manually operated Levels and Curves commands.

Understanding your Auto Correction options
Photoshop uses algorithms to make adjustments to images. When you use the Auto Correction Options dialog box, you have to decide which algorithms to use. Here are your options:
- Enhance Monochromatic Contrast: This option applies the same changes to the red, green, and blue channels, making brighter areas appear lighter, and shadow areas appear darker, with no changes made to the colors. (This is the method used by the Auto Contrast command.)
- Enhance Per Channel Contrast: This option individually adjusts the red, green, and blue colors so that each has its own best balance of light and dark tones, even if the color balance changes a bit. (This is the algorithm used by the Auto Levels command.)
- Find Dark & Light Colors: This option locates the average lightest and darkest pixels, and uses their values to maximize the contrast of the image. (This is the algorithm used by the Auto Color command.)

When you understand these commands, feel free to customize the automatic options, following these steps. You can apply the settings only to a particular image-editing session, or save the settings as defaults for all your Photoshop work.
1. Open an image and choose Image-->Adjustments-->Levels or Ctrl+L (or Ô+L on the Mac).
You can also use the Curves command by pressing Ctrl+M (or Ô+M on the Mac).
2. Click the Options button in the dialog box to access the Auto Color Correction Options dialog box.
3. In the algorithm area, click the method you want Photoshop to use to adjust the tones. Your choices include
- Enhance Monochromatic Contrast
- Enhance Per Channel Contrast
- Find Dark & Light Colors
4. Click to add a check mark in the Snap Neutral Midtones if you want Photoshop to base its gamma correction values around a neutral color located in the image.
The Auto Color command uses this option.
5. In the Target Colors & Clipping area, enter a value in each of the clip text entry boxes.
Setting clipping values between 0.5 and 1% eliminates the too-dark and too-light pixels. These values adjust the amount of black and white pixels that Photoshop removes from the darkest and lightest areas of the image. This option is useful because every image includes some very dark pixels that contain no real image information, as well as some very light pixels that are completely washed out. Factoring in these two kinds of pixels when you adjust tonal values is a waste.
6. Click the Shadows, Midtones, or Highlights patch.
The Color Picker appears, allowing you to set a preferred value for the darkest, medium, and lightest areas. You can click one, two, or all three of the patches.
7. Select the Eyedropper tool from the Tools palette and choose 3 x 3 Sample in the Options bar.
8. Move your mouse over the image and locate the dark, middle, or light tone you want to use. Click it when you find it.
9. Click OK to exit the Color Picker. Repeat Steps 6 through 8 for each of the three colors you want to change.
As you move the mouse over the image, the values in the Info palette change, helping you pick the shadow, midtone, or highlight area you want.
10. Back in the Auto Color Corrections dialog box, select the Save As Defaults option to store the settings you just made for subsequent use in any Photoshop session.
If you don’t select the option, Photoshop applies the changes you made only to the current session.
11. Click OK to exit the Auto Color Correction Options dialog box.
Your options are now customized.