Generally, you shouldn’t trust any correction tool with the word Auto in its name. Although the quality of Adobe’s Auto tools is constantly improving, your own eyesight and judgement will usually produce better results. There are exceptions to this rule, and one of them involves using Auto Color Correction on a layer to improve image contrast. The process consists of five separate steps that we will demonstrate using the unsharpened image detail in Figure 7-62:
Create a new Levels adjustment layer. The dialog in Figure 7-63 then appears.
Select Auto Options in the dialog menu
. The dialog in Figure 7-64 pops up. Adjust the default settings as follows:Check the Enhance Per Channel Contrast option
Set Shadows and Highlights clipping values to 0.20%
The default values are often unsuitable, so you will have to experiment to find out which settings suit your particular image. You can save your settings as the new defaults by checking the Save as defaults option.
Click OK and then click on Auto in the panel dialog.
Clipping tonal values generally has a negative effect on an image but, as shown here, you can achieve useful results with appropriate settings. Don’t be put off at this stage by the colors in Figure 7-66.
These settings clip the shadows and highlights by 0.2% for all channels. The automatic function settings tend to clip each channel slightly differently, resulting in visible color shifts.
The histogram in Figure 7-65 shows only the red channel, so take the time to look at the blue and green channels as well. Our result (Figure 7-66) looks pretty awful to begin with.
The following steps will help to sort things out.
We select Luminosity blending mode (Figure 7-67). This starts to shift the colors back to normal levels (Figure 7-68).
Luminosity mode is designed for use with layers on which detail contrast is adjusted, but where colors remain largely unchanged.
The contrast visible in Figure 7-68 is still a little high due to the tonal value clipping. What do we do if a layer effect is too strong? We reduce that layer’s opacity! 30% opacity produces the desired effect in our example (Figure 7-69).
A little sharpening then completes our processing, producing the result shown in Figure 7-70.
The image in Figure 7-70 could be further improved by applying local contrast adjustment as described in Enhancing Local Contrast.
