[Color Levels] allow you to modify the attributes of all the colors in your image. These controls are similar to the controls on a television set. They do not change the actual color, but they can shift the color from light to dark and dark to light.

• ContrastThe difference in tone between the darker and lighter parts of an image. -This option makes the dark colors darker and the light colors lighter.
• BrightnessA measure of the total amount of light emitted, transmitted, or reflected by an object or image. This is normally measured in CandelaInternational unit of measure for Luminance, approximately equal to one candlepower. In technical terms, a candela is 1/60th of the luminous intensity per square centimeter of a blackbody radiating at the temperature of solidification of platinum (2,046 K).. See also LuminanceThe lightness or Brightness of an image.. -This option controls the amount of K in all the colors of your image. The more K in your image, the less bright it will be. The less K in your image, the more bright it will be.
• SaturationTerm used to describe the strength, purity, or vividness of a hue. Saturation indicates how much color is present. When there is no saturation, there is no color; the more saturation, the more color there is of the given hue. - This option controls how much color there is in your image. Increasing saturation increases the amount of color. Decreasing saturation removes color. This tool does not affect the amount of K in your image.

[Gray Levels] allow you to modify the K level of an image in three different ranges: Highlights, MidtonesTones in an image that are in the middle the tonal range, halfway between the lightest and the darkest., and Shadows.

• Highlights -This option controls the amount of K in the lighter tones of an image.
• Mid-tones -This option controls the amount of K in the middle tones of an image.
• Shadows - This option controls the amount of K in the darker tones of an image.