Apply the auto contrast adjustment – Adobe Photoshop CS4 User Manual
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USING PHOTOSHOP CS4
Color and tonal adjustments
Last updated 1/10/2010
By default, the Auto option and the Auto Tone command clip the white and black pixels by 0.1%—that is, it ignores
the first 0.1% of either extreme when identifying the lightest and darkest pixels in the image. The default settings for
the Auto option can be changed in the Auto Color Correction Options dialog box.
1
Do one of the following:
•
Click the Levels or Curves icon in the Adjustments panel.
•
Choose Layer
> New Adjustment Layer and choose either Levels or Curves. Click
OK in the New Layer dialog box.
Note: You can choose Image > Auto Tone to apply the adjustment directly to the image layer. Keep in mind that this
method discards image information and is automatic. You cannot adjust any of the options in the following steps.
2
In the Adjustments panel, Alt-click (Windows) or Option-click (Mac OS) the Auto button.
3
Under Algorithms in the Auto Color Correction Options dialog box, select Enhance Per Channel Contrast.
4
Adjust the amount of shadow and highlight values that are clipped, and adjust the target color for the midtones.
5
Click OK to apply the Auto option settings.
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Apply the Auto Contrast adjustment
The Auto Contrast command adjusts image contrast automatically. Because Auto Contrast does not adjust channels
individually, it does not introduce or remove color casts. It clips the shadow and highlight values in an image and then
maps the remaining lightest and darkest pixels in the image to pure white (level 255) and pure black (level 0). This
makes the highlights appear lighter and shadows appear darker.
By default, when identifying the lightest and darkest pixels in an image, Auto Contrast clips the white and black pixels
by 0.5%—that is, it ignores the first 0.5% of either extreme. You can change this default using the Auto Color
Correction Options found in the Levels and the Curves dialog boxes.
Auto Contrast can improve the appearance of many photographic or continuous-tone images. It does not improve
flat-color images.
1
Do one of the following:
•
Click the Levels or Curves icon in the Adjustments panel.
•
Choose Layer
> New Adjustment Layer and choose either Levels or Curves. Click
OK in the New Layer dialog box.
Note: You can also choose Image > Auto Contrast to apply the adjustment directly to the image layer. Keep in mind that
this method discards image information and its application is automatic. You cannot adjust any of the options in the
following steps.
2
In the Adjustments panel, Alt-click (Windows) or Option-click (Mac OS) the Auto button.
3
Under Algorithms in the Auto Color Correction Options dialog box, select the Enhance Monochromatic Contrast
option.
4
Specify the shadows and highlights that are clipped, and adjust the target color for the midtones.
5
Click OK to apply Auto Contrast.
More Help topics