Photoshop’s Auto Levels, Auto Contrast, and Auto Color are smart commands which changes every images slightly differently.
Enhance Per Channel Contrast(Auto Levels) – Automatically fixes the brightness/contrast. A lot of good brightness/contrast, and removes any color cast. This command affects the image in a channel by channel basis. Make the darkest color black, while lightest color white.
Enhance Monochromatic Contrast(Auto Contrast) – Same with Auto Level which boost brightness/contrast and keeps the color cast. Instead of a channel by channel basis, Auto Contrast looks on the composite image or the RGB as a whole and makes the darkest composite color black and the lightest composite color white. As a result, it avoids changing the color cast of the image.
