313
ADOBE PHOTOSHOP CS2
User Guide
To convert images to black and white
The Threshold command converts grayscale or color images to high-contrast, black-and-white images. You can
specify a certain level as a threshold. All pixels lighter than the threshold are converted to white; all pixels darker are
converted to black.
1
Do one of the following:
•
Choose Image > Adjustments > Threshold.
•
Chose Layer > New Adjustment Layer > Threshold. Click OK in the New Layer dialog box. The Threshold dialog
box displays a histogram of the luminance levels of the pixels in the current selection.
2
Drag the slider below the histogram until the threshold level you want appears at the top of the dialog box, and
click OK. As you drag, the image changes to reflect the new threshold setting.
To posterize an image
The Posterize command lets you specify the number of tonal levels (or brightness values) for each channel in an
image and then maps pixels to the closest matching level. For example, choosing two tonal levels in an RGB image
gives six colors: two for red, two for green, and two for blue.
This command is useful for creating special effects, such as large, flat areas in a photograph. Its effects are most
evident when you reduce the number of gray levels in a grayscale image, but it also produces interesting effects in
color images.
If you want a specific number of colors in your image, convert the image to grayscale and specify the number of levels
you want. Then convert the image back to the previous color mode, and replace the various gray tones with the colors
you want.
1
Choose Image > Adjustments > Posterize.
2
Enter the number of tonal levels you want, and click OK.
To apply a gradient map to an image
The Gradient Map command maps the equivalent grayscale range of an image to the colors of a specified gradient
fill. If you specify a two-color gradient fill, for example, shadows in the image are mapped to one of the endpoint
colors of the gradient fill, highlights are mapped to the other endpoint color, and midtones are mapped to the grada
tions in between.
1
Do one of the following:
•
Choose Image > Adjustments > Gradient Map.
•
Choose Layer > New Adjustment Layer > Gradient Map. Click OK in the New Layer dialog box.
2
Specify the gradient fill you want to use:
•
To choose from a list of gradient fills, click the triangle to the right of the gradient fill displayed in the Gradient
Map dialog box. Click to select the desired gradient fill, and then click in a blank area of the dialog box to dismiss
the list. For information on customizing the gradient fill list, see “About the Preset Manager” on page 67.
•
To edit the gradient fill currently displayed in the Gradient Map dialog box, click the gradient fill. Then modify
the existing gradient fill or create a new gradient fill using the Gradient Editor. (See “To create a smooth gradient”
on page 494.)
Содержание PHOTOSHOP CS2
Страница 1: ...Chapter 1 Copyright User Guide ...
