Do one of the following:

• Click the Levels icon  in the Adjustments panel, or choose Levels from the panel menu.

• Choose Layer > New Adjustment Layer > Levels. Click OK in the New Layer dialog box.

(Optional) To adjust tones for a specific color channel, choose an option from the Channel menu.

(Optional) To edit a combination of color channels at the same time, Shift-select the channels in the Channels panel before choosing the Image > Adjustments > Levels command. (This method does not work in a Levels adjustment layer.) The Channel menu then displays the abbreviations for the target channels—for example, CM for cyan and magenta. The menu also contains the individual channels for the selected combination. Edit spot channels and alpha channels individually.

To adjust the shadows and highlights manually, drag the black and white Input Levels sliders to the edge of the first group of pixels at either end of the histogram.

For example, if you move the black point slider to the right at level 5, Photoshop maps all the pixels at level 5 and lower to level 0. Similarly, if you move the white point slider to the left at level 243, Photoshop maps all pixels at level 243 and higher to level 255. The mapping affects the darkest and lightest pixels in each channel. The corresponding pixels in the other channels are adjusted proportionately to avoid altering the color balance.

(Optional) To identify areas in the image that are being clipped (completely black or completely white), do one of the following:

• Hold down Alt (Windows) or Option (Mac OS) as you drag the black point and white point sliders.

• Choose Show Clipping For Black/White Points from the panel menu.

To adjust midtones, use the middle Input slider to make a gamma adjustment.

Moving the middle Input slider to the left makes the overall image lighter. This slider adjustment maps a lower (darker) level up to the midpoint level between the Output sliders. If the Output sliders are in their default position (0 and 255), the midpoint is level 128. In this example, the shadows expand to fill the tonal range from 0 to 128, and the highlights are compressed. Moving the middle Input slider to the right has the opposite effect, making the image darker.

You can view the adjusted histogram in the Histogram panel.

In the Adjustments panel, click the Levels icon or choose Levels from the panel menu.

In the Properties panel, do one of the following to neutralize a color cast:

• Click the eyedropper tool to set the gray point . Then click in a part of the image that is neutral gray.

• Click Auto to apply the default automatic levels adjustment. To experiment with other automatic adjustment options, choose Auto Options from the Properties panel menu, then change Algorithms in the Auto Color Corrections Options dialog box.

In general, assign equal color component values to achieve a neutral gray. For example, assign equal red, green, and blue values to produce a neutral gray in an RGB image.