Brightness and Color Cast
Step 4: Move the Input Brightness slider in the RGB channel until the overall brightness of the image looks correct. I moved it to the left to 1.15 to bring out a little more shadow detail in the foreground wheat and in the dark trees around the house. You can't bring out more detail in an area that is totally black, so don't go too far on this shadow detail thing.
Figure 20.5 Step 4: After setting highlight and shadow, set overall brightness. Move the middle slider to the left in RGB.
Step 5: Now we need to go into each channel and correct for color casts, which is easiest to do if you try to fix the most annoying cast first, and then fine-tune the other colors and casts that appear along the way. The wheat in the foreground seems to have a greenish cast. I often have a hard time with these greenish casts because they're sometimes both green and cyan. This one looks greener, so go to the Green channel (Command-2) and move the middle slider to the right to add magenta; that should improve the situation and make the wheat look more golden. Move the slider until the wheat looks too magenta, move it back until you start to see the green again, and then add just a little magenta. If the image still has a greenish tinge, it might be that there is a cyan problem too, so move to the Red channel (Command-1) and add a little red by moving the middle slider to the left. Finally, add a little yellow by moving the middle slider in the Blue channel a little to the right. The color choices you make may be different than mine depending on your taste. That is certainly fine! When your color appears correct, look at the RGB values of your Color Sampler for the shadow in the Info palette. If they are no longer neutral, you can go back into each color channel and move them back where you want them using the Input Shadow slider for that channel. When you're happy with the color, you should click OK to complete your Levels changes. Because you have your Levels changes in a Levels adjustment layer, you can turn these changes on and off using the Eye icon for that layer, which is above the Background layer in the Layers palette. Choose File/Save to save your changes. Now you have done the initial Levels adjustment on this difficult image.
Figure 20.6 Step 5: Here are the adjustments I made to the middle sliders of the Red, Green, and Blue channels to adjust for color casts in this image. Because the wheat is the major component here, getting that to look good was the main goal. Other parts of the image can be fine-tuned later.
Figure 20.7 Step 5: Kansas, after all the Levels adjustments.
Figure 20.8 Step 5: Here we see the Histogram after the Levels adjustments. Choose All Channels View from the Histogram pop-up menu. Notice the white gaps in the R,G, & B channels.