The Levels adjustment is used for correcting the tonal range and color balance of an image by adjusting the brightness of its shadows, midtones, and highlights. Watch our video tutorial to learn more about the Levels adjustment.
The parameters of the Levels adjustment are displayed in the Settings Panel when selecting Image -> Adjustments -> Levels...
You can also use the Levels adjustment layer (Layers -> New -> Adjustment Layer -> Levels...) which will affect the underlying layers without changing their content.
Settings and Controls:
The left side of the histogram indicates the point of minimum brightness (black). This point corresponds to the black slider. If the histogram does not start at the left end, the image does not have any black pixels (brightness = 0). When you move the black slider to the right, the point against which the slider is located will assume the minimum brightness value. As a result this tone will become black, while other pixels will be re-calculated accordingly. The image will get darker.
The middle slider defines the tone of the image that will have the brightness of 128 (middle-gray tones). If you move the slider to the left, the mid-gray tones become lighter; if you move the slider to the right, the mid-gray tones become darker.
Using , , and you can select the white, black, and middle-gray points directly from the image, respectively. The values will vary for each color channel, so choose a neutral gray image area as a sample. Otherwise, the image will be tinted.
If the range of output levels is less than the range of input levels, the image becomes softer. Otherwise, the contrast will be increased.
Click on the Options button to open the Auto Color Correction Options dialog box.
Enhance Monochromatic Contrast clips all color channels using the same settings for each channel. As a result, the shadows become darker and highlights become lighter. This algorithm is applied when using the Auto Contrast command.
Enhance Per Channel Contrast adjusts the color channels individually. The values of black and white pixels for each color channel are changed by different amounts. The resulting image can be tinted. This algorithm is applied when using the Auto Levels command.
The Target Colors & Clipping section displays the percentages of white and black pixels which will be removed from each end of the range.
Save as Defaults check-box. If the check-box is enabled, the specified parameter values will be used as default when using the Auto command.
Click on Default to restore the default values.
Click on OK to apply all changes and close the dialog box.
Click on Cancel to close the dialog box without applying any changes.