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Using target values to set highlights and shadows (Photoshop)


    Professional color technicians typically set the highlights and shadows in an image by assigning their lightest and darkest CMYK ink values to the lightest and darkest areas of detail in the image.

    When identifying the lightest and darkest areas of an image, it's important to identify representative highlights and shadows. Otherwise the tonal range may be expanded unnecessarily to include extreme pixel values that don't give the image detail. A highlight area must be a printable highlight, not specular white. Specular white has no detail, and so no ink is printed on the paper. For example, a spot of glare is specular white, not a printable highlight.

    Note: You can do the following procedure in ImageReady in the Levels dialog box.

To use target values to set highlights and shadows:

  1. Select the eyedropper tool, and choose 3 by 3 Average from the Sample Size menu in the eyedropper tool options. This ensures a representative sample of an area rather than the value of a single screen pixel.
  2. Open the Levels or Curves dialog box. (See Making color adjustments.)
  3. When you open Levels or Curves, the eyedropper tool eyedropper tool is still active outside the dialog box. You still have access to the scroll controls and to the hand and zoom tools by using keyboard shortcuts.

  4. Do one of the following to identify areas of representative highlights and shadows in the image:
    • Move the pointer around the image, and look at the Info palette to find the lightest and darkest areas. (See Seeing the color values of pixels (Photoshop).)
    • Drag the pointer in the image, and look at the Curves dialog box to find the lightest and darkest points in the range of values. This method does not work if the Curves dialog box is set to the CMYK composite channel.

    TipYou can also use the Threshold command to identify representative highlights and shadows before opening Levels or Curves. (See Using the Threshold command (Photoshop).)

  5. Do one of the following to assign color values to the lightest area of the image:
    • Double-click the Set White Point eyedropper tool Set White Point eyedropper tool in the Levels or Curves dialog box to display the Color Picker. Enter the values you want to assign to the lightest area in the image, and click OK. Then click the highlight you identified in step 3.

    TipIf you accidentally click the wrong highlight, hold down Alt (Windows) or Option (Mac OS), and click Reset in the Levels or Curves dialog box.

    • Click Options in the Levels or Curves dialog box. Click the Highlights color swatch to display the Color Picker. Enter the values you want to assign to the lightest area in the image, and click OK.

    In most situations when you are printing on white paper, you can achieve a good highlight in an average-key image using CMYK values of 5, 3, 3, and 0, respectively. An approximate RGB equivalent is 244, 244, 244, and an approximate grayscale equivalent is a 4% dot. You can approximate these target values quickly by entering 96 in the Brightness (B) text box under the HSB section of the Color Picker.

    TipWith a low-key image, you might want to set the highlight to a lower value to avoid too much contrast. Experiment with Brightness values between 96 and 80.

    Original
    Original
    Highlight set using average-key target brightness values (B: 96); and highlight set using lower target brightness values (B: 80)
    Highlight set using average-key target brightness values (B: 96); and highlight set using lower target brightness values (B: 80)

    The pixel values throughout the image are adjusted proportionately to the new highlight values. Any pixels lighter than the area you clicked become specular white. The Info palette shows the values both before and after the color adjustment.

  6. Do one of the following to assign color values to the darkest area of the image:
    • Double-click the Set Black Point eyedropper tool Set Black Point eyedropper tool in the Levels or Curves dialog box to display the Color Picker. Enter the values you want to assign to the darkest area in the image, and click OK. Then click the shadow you identified in step 3.
    • Click Options in the Levels or Curves dialog box. Click the Shadows color swatch to display the Color Picker. Enter the values you want to assign to the darkest area in the image, and click OK.

    In most situations when you're printing on white paper, you can achieve a good shadow in an average-key image using CMYK values of 65, 53, 51, and 95. An approximate RGB equivalent is 10, 10, 10, and an approximate grayscale equivalent is a 96% dot.You can approximate these same values quickly by entering 4 in the Brightness (B) text box under the HSB section of the Color Picker.

    TipWith a high-key image, you might want to set the shadow to a higher value to maintain detail in the highlights. Experiment with Brightness values between 4 and 20.

    Original
    Original
    Shadow set using average-key target brightness values (B: 4); and shadow set using higher target brightness values (B: 20)
    Shadow set using average-key target brightness values (B: 4); and shadow set using higher target brightness values (B: 20)

To use Threshold mode to identify the lightest and darkest areas in an image:

  1. Open the Levels dialog box, and select Preview.
  2. Note: The Threshold mode in Levels is not available for CMYK images.

  3. Hold down Alt (Windows) or Option (Mac OS), and drag the white or black Input Levels triangle.
  4. The image changes to Threshold mode, and a high-contrast preview image appears. The visible areas of the image indicate the lightest parts of the image if you are dragging the white slider, and the darkest parts if you are dragging the black slider. If a color channel is selected in the Levels dialog box, the black area indicates where none of the given color component exists.

    Image preview in Threshold mode.
    Image preview in Threshold mode
  5. Slowly drag the slider to the center of the histogram to identify the light or dark areas in the image. Use these pixels for targeting the black point and white point in your image.