Photoshop

Adjust tonal range using Levels

The outer two Input Levels sliders map the black point and white point to the settings of the Output sliders. By default, the Output sliders are at level 0, where the pixels are completely black, and level 255, where the pixels are completely white. So, in the default position for the Output sliders, moving the black input slider maps the pixel value to level 0, and moving the white point slider maps the pixel value to level 255. The remaining levels are redistributed between levels 0 and 255. This redistribution increases the tonal range of the image, in effect increasing the overall contrast of the image.

Note: When shadows are clipped, the pixels are completely black, with no detail. When highlights are clipped, the pixels are completely white, with no detail.

The middle Input slider adjusts the gamma in the image. It moves the midtone (level 128) and changes the intensity values of the middle range of gray tones without dramatically altering the highlights and shadows.

  1. Do one of the following:

    • Choose Image > Adjustments > Levels.

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

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

    To edit a combination of color channels at the same time, Shift-select the channels in the Channels palette before choosing the Levels command. 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. You must edit spot channels and alpha channels individually. Keep in mind that this method does not work in a Levels adjustment layer.

  3. To adjust the shadows and highlights manually, drag the black and white Input Levels sliders to the edge of the first group of pixels on 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.

    Note: You can also enter values directly into the first and third Input Levels text boxes.
    Adjusting black and white points with Levels Input sliders

  4. 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.

    Note: You can also enter a gamma adjustment value directly in the middle Input Levels text box.
    Moving the middle slider adjusts the image gamma

  5. Click OK.

    You can view the adjusted histogram in the Histogram palette.