A bitmap with a full tonal range should have an even number of pixels in all areas. The Levels feature corrects bitmaps with a high concentration of pixels in the highlights, midtones, or shadows.

Highlights corrects an excess of light pixels, which makes the image look washed out.

Midtones corrects an excess of pixels in the midtones, which makes the image bland.

Shadows corrects an excess of dark pixels, which hides much of the detail.

The Levels feature sets the darkest pixels as black and the lightest pixels as white, then redistributes the midtones proportionally. This produces an image with the sharpest detail in all of its pixels.

This is a picture of the feature being described.

Original with pixels concentrated in the highlights; after adjusting with Levels

You can use the Histogram in the Levels dialog box to view the pixel distribution of a bitmap. The Histogram is a graphical representation of the distribution of pixels in the highlights, midtones, and shadows.

The Histogram helps you determine the best method of correcting an image's tonal range. A high concentration of pixels in the shadows or highlights indicates that you could improve the image by applying the Levels or Curves feature.

The horizontal axis represents color values from darkest (0) to brightest (255). Read the horizontal axis from left to right: the darker pixels are on the left, the midtone pixels are in the center, and the brighter pixels are on the right.

The vertical axis represents the number of pixels at each brightness level. Typically, you should adjust the highlights and shadows first. Adjusting the midtones second lets you improve their brightness value without affecting the highlights and shadows.

To adjust highlights, midtones, and shadows:

  1. Select the bitmap image.
  2. Do one of the following to open the Levels dialog box:
    • In the Property inspector, click the Add Live Filters button, and then select Adjust Color > Levels from the Filters pop-up menu.
    • Select Filters > Adjust Color > Levels.

    NOTE

    Applying a filter from the Filters menu is destructive; that is, it cannot be undone except when Edit > Undo is an option. To maintain the ability to adjust, turn off, or remove this filter, apply it as a Live Filter, as described in the first bulleted option in this step. For more information, see Using Live Filters.

    This is a picture of the feature being described.

    Levels dialog box

    TIP

    To view your changes in the workspace, select Preview in the dialog box. As you make changes, the image updates automatically.

  3. In the Channel pop-up menu, select whether you want to apply changes to individual color channels (Red, Blue, or Green) or to all color channels (RGB).
  4. Drag the Input Levels sliders under the Histogram to adjust the highlights, midtones, and shadows:
    • The right slider adjusts the highlights using values from 255 to 0.
    • The center slider adjusts the midtones using values from 10 to 0.
    • The left slider adjusts the shadows using values from 0 to 255.

    As you move the sliders, the values are automatically entered in the Input Levels boxes.

    NOTE

    The shadow value cannot be higher than the highlight value; the highlight value cannot be lower than the shadow value; and the midtones must fall between the shadow and highlight settings.

  5. Drag the Output Levels sliders to adjust the contrast values in the image:
    • The right slider adjusts the highlights using values from 255 to 0.
    • The left slider adjusts the shadows using values from 0 to 255.

    As you move the sliders, the values are automatically entered in the Output Levels boxes.