Adobe Photoshop CS4 - Manual (Page 196)

189 USING PHOTOSHOP CS4
Color and tonal adjustments
Last updated 1/10/2010
3 In the Adjustments panel, select Shadows, Midtones, or Highlights to select the tonal range in which you want to
focus the changes.
4 (Optional) Select Preserve Luminosity to prevent changing the luminosity values in the image while changing the
color. This option maintains the tonal balance in the image.
5 Drag a slider toward a color that you want to increase in the image; drag a slider away from a color that you want
to decrease in the image.
The values above the color bars show the color changes for the red, green, and blue channels. (For Lab images, the
values are for the A and B channels.) Values can range from -100 to +100.
Apply the Brightness/Contrast adjustment
The Brightness/Contrast adjustment lets you make simple adjustments to the tonal range of an image. Moving the
brightness slider to the right increases tonal values and expands image highlights, to the left decreases values and
expands shadows. The contrast slider expands or shrinks the overall range of tonal values in the image.
In normal mode, Brightness/Contrast applies proportionate (nonlinear) adjustments to image layer, as with Levels and
Curves adjustments. When Use Legacy is selected, Brightness/Contrast simply shifts all pixel values higher or lower
when adjusting brightness. Since this can cause clipping or loss of image detail in highlight or shadow areas, using
Brightness/Contrast in Legacy mode is not recommended for photographic images (but can be useful for editing
masks or scientific imagery).
Note: Use Legacy is automatically selected when editing Brightness/Contrast adjustment layers created with previous
versions of Photoshop.
1 Do one of the following:
• Click the Brightness/Contrast icon in the Adjustments panel.
• Choose Layer > New Adjustment Layer > Brightness/Contrast. Click OK in the New Layer dialog box.
Note: You can also choose Image > Adjustments > Brightness/Contrast. But keep in mind that this method makes direct
adjustments to the image layer and discards image information.
2 In the Adjustments panel, drag the sliders to adjust the brightness and contrast.
Dragging to the left decreases the level, and dragging to the right increases it. The number at the right of each slider
reflects the brightness or contrast value. Values can range from -150 to +150 for Brightness, -50 to +100 for Contrast.
Adjust black and white points with the Auto option
The Auto option for Levels and Curves and the Auto Tone command automatically adjust the black point and white
point in an image. This clips a portion of the shadows and highlights in each channel and maps the lightest and darkest
pixels in each color channel to pure white (level 255) and pure black (level 0). The intermediate pixel values are
redistributed proportionately. As a result, using the Auto option or Auto Tone increases the contrast in an image
because the pixel values are expanded. Because the Auto option and Auto Tone adjust each color channel individually,
it may remove color or introduce color casts.
The Auto option and Auto Tone give good results in certain images with an average distribution of pixel values that
need a simple increase in contrast.