Making tonal adjustments

The Adjust tab in the Camera Raw dialog box has five sliders for making tonal adjustments to your image.
Exposure
Adjusts the brightness or darkness of the image. Moving the slider to the left darkens the image, while moving the slider to the right brightens the image. The values are in increments equivalent to f-stops. A +1.50 adjustment is similar to increasing the aperture 1 1/2 stops wider. Likewise, a -1.50 adjustment is like reducing the aperture 1 1/2 stops.
Holding down the Alt (Windows) or Option (Mac OS) key while moving the Exposure slider lets you preview where the highlights become completely white with no detail (clipped). One way to use this feature is to adjust the slider until the highlights (not specular highlights) are completely clipped, and then back off slightly on the adjustment. Black indicates areas that are not clipped, and color indicates areas that are being clipped in only one or two channels.
Holding the Alt (Windows) or Option (Mac OS) key down while moving the Exposure slider shows the highlights being clipped.
Note: Clipping is the shifting of pixel values to either the highest highlight value (255) or the lowest shadow value (0). Areas of a photo that are clipped are either completely white or completely black and have no image detail.
Shadows
Controls what input levels will be mapped to black in the final image. Moving the slider to the right increases the areas that are mapped to black. This sometimes creates the impression of increased contrast in the image. Using the Shadows slider is similar to using the black point slider for the input levels in the Photoshop Levels command. For more information on levels, see Using the Levels dialog box.
Note: Holding down the Alt (Windows) or Option (Mac OS) key while moving the Shadow slider lets you preview where the shadows become completely black with no detail (clipped). One way to use this feature is to move the slider until the shadows begin to get clipped, and then back off slightly on the adjustment. Color indicates areas that are being clipped in one or two channels, and white indicates areas that aren't clipped.
Brightness
Adjusts the brightness or darkness of the image, similar to the Exposure slider. However, instead of clipping the image in the highlights (areas that are completely white, no detail) or shadows (areas that are completely black, no detail), Brightness compresses the shadows and expands the highlights when the slider is moved to the left. Generally, you use the Brightness slider to adjust the overall brightness or darkness after you set the white and black clipping points with the Exposure and Shadow sliders.
Contrast
Adjusts the midtones in an image. Higher values increase the midtone contrast, while lower values produce an image with less contrast. Generally, you use the Contrast slider to adjust the contrast of the midtones after setting the Exposure, Shadow, and Brightness values.
Saturation
Adjusts the color saturation of the image from -100 (pure monochrome) to +100 (double the saturation).