Adobe 13101332 - Photoshop - Mac User Manual page 95

Adobe Photoshop Help
Using Help | Contents
Making Grayscale and Bitmap mode conversions
Refer to the following instructions for converting images between Grayscale and Bitmap
mode.
To convert an image to Bitmap mode:
1 Do one of the following:
If the image is in color, choose Image > Mode > Grayscale. Then choose Image > Mode >
•
Bitmap.
If the image is grayscale, choose Image > Mode > Bitmap.
•
2 For Output, enter a value for the output resolution of the Bitmap-mode image, and
choose a unit of measurement. By default, the current image resolution appears as both
the input and the output resolutions.
3 Select one of the following bitmap conversion methods:
50% Threshold, Pattern Dither, or Diffusion Dither to use a predefined conversion
•
method. (See "Specifying predefined Bitmap conversion methods" on page
Halftone Screen to simulate the appearance of halftone dots in the converted image.
•
(See "Specifying halftone screens for Bitmap-mode images" on page
Custom Pattern to simulate the appearance of a custom halftone screen in the
•
converted image. (See
on page 97.)
To convert a Bitmap-mode image to grayscale:
1 Choose Image > Mode > Grayscale.
2 Enter a value between 1 and 16 for the size ratio.
The size ratio is the factor for scaling down the image. For example, to reduce a grayscale
image by 50%, enter 2 for the size ratio. If you enter a number greater than 1, the program
averages multiple pixels in the Bitmap-mode image to produce a single pixel in the
grayscale image. This process lets you generate multiple shades of gray from an image
scanned on a 1-bit scanner.
Specifying predefined Bitmap conversion methods
The predefined conversion options in the Bitmap dialog box determine the quality of the
converted image.
50% Threshold Converts pixels with gray values above the middle gray level (128) to
white and below to black. The result is a very high-contrast, black-and-white represen-
tation of the image.
Pattern Dither Converts an image by organizing the gray levels into geometric configu-
rations of black and white dots.
Using Help | Contents
| Index
"Specifying custom halftone screens for Bitmap-mode images"
| Index
Working with Color
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95.)
96.)
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