All of the methods used so far have been manual. The following method is an auto routine. Once a few settings are input, the shadow and highlight values are automatically established.
The procedure starts off by launching Curves. The options for Auto Curves are set by clicking on the Options button in the lower right hand corner of the palette (see Figure 1).
The Auto Color Correction Options dialog box appears as shown in Figure 2. The dialog box allows the choice of three algorithms:
The Snap Neutral Midtones identifies a near neutral color in the image and adjusts the gamma to make the color neutral. In most cases, it is best to leave this unchecked as this option can cause color shifts in an image. The Shadows/Clip box sets the percent of the shadow values that are clipped. This value should be very low (less than one percent). The Highlights/Clip box sets the percent of the highlight values that are clipped. This value should also be very low (less than one percent). Once these values are set, clicking the OK button closes the Auto Color Correction Options dialog box. Clicking the OK button on the Curves dialog box closes Curves.
Figure 3 shows an original image. Figures 4 -- 9 show the image (and the associated histogram) after adjustment with the three Auto Color Correction options.
The last step is to adjust the contrast. The contrast adjustments are made in the same manner as the contrast adjustments with the Info palette approach used in Part II of this series (see Shadow Values, Highlight Values, and Contrast: Info Palette Approach).
Figures 11 -- 14 show the images with the contrast adjustment.
The answer is: It depends.
The fact that Curves allows independent adjustment to the three color channels makes it a tool that can be used for color correction. Figure 15 shows an image with a serious color cast. This shot is of a morgue in an old ghost town. The casket to the left of the door is a child's casket. The cold blue color cast totally ruins the old, worn feeling that one gets when they look into the building. The tone of the image needs to be warmed up.