Auto levels
From The Glossary of Digital Photography
A function in Photoshop used to improve the look of an image. It works by adjusting the black point and white point of an image and then readjusting all of the pixels in between by using a function to move them proportionally in the new image. This tends to increase contrast and improve flat and washed-out images. Since it actually works on each color (red, green, and blue) individually, auto levels can be fooled by images with a predominance of a single color. In those cases it is best to turn off auto levels, adjust the image manually using the levels function, and drag each end and the middle gray sliders separately until a more pleasing image results. See also levels
