Use the Levels command to make adjustments to the brightness, contrast, and gamma in the image. Adjusting the gamma changes the brightness values of middle grey tones.
Important: To apply this command to a selection, the image must be a 16 million (24-bit) color image (otherwise the command is applied to the entire image). To increase the color depth of an image, see Increasing the Color Depth of an Image.
To use the Levels command:
To limit the correction to a specific area, make a selection in the image. See Using the Selection Tools.
Do one of the following:
To modify the image pixels directly, choose Adjust > Brightness and Contrast > Levels.
To create a Levels adjustment layer, choose Layers > New Adjustment Layer > Levels. For information on adjustment layers, see Using Adjustment Layers.
In the Channel drop-down list, select a color channel to edit. Choose RGB to edit the red, green, and blue channels together. Choose Red, Green, or Blue to edit the individual color channels.
To increase the contrast of the image, drag the Input levels sliders, which show the image’s brightness values. To darken the darkest values, drag the black diamond to the right; all values below this value become zero (black). To lighten the lightest values, drag the clear diamond to the left; all values above this value become 255 (white). To change the value of medium grey, drag the grey Gamma diamond left or right; the range for of the gamma value is 0 to 7.99, with 1 being in the middle.
To decrease the contrast, drag the Output levels sliders. To lighten the darkest pixels, drag the black diamond to the right. To darken the lightest pixels, drag the clear diamond to the left.
Click OK.
Adjusting Individual Brightness Values
Adjusting the Brightness and Contrast in Unison
Adjusting the Brightness of the Highlights, Midtones, and Shadows
Correcting Images by Adjusting the Histogram
Manually Adjusting Brightness and Contrast