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commonly use an 85-line screen. Magazines use higher resolution screens, such as 133-lpi and 150-lpi. Check with your print shop for
correct screen frequencies.
Enter a value for the screen angle in degrees from -180 to +180. The screen angle refers to the orientation of the screen. Continuous-
tone and black-and-white halftone screens commonly use a 45° angle.
For Shape, choose the dot shape you want.
Important: The halftone screen becomes part of the image. If you print the image on a halftone printer, the printer will use its own halftone
screen as well as the halftone screen that is part of the image. On some printers, the result is a moiré pattern.
Custom Pattern Simulates the appearance of a custom halftone screen in the converted image. Choose a pattern that lends itself to
thickness variations, typically one with a variety of gray shades.
To use this option, you first define a pattern and then screen the grayscale image to apply the texture. To cover the entire image, the pattern
must be as large as the image. Otherwise, the pattern is tiled. Photoshop comes with several self-tiling patterns that can be used as halftone
screen patterns.
To prepare a black-and-white pattern for conversion, first convert the image to grayscale and then apply the Blur More filter several
times. This blurring technique creates thick lines tapering from dark gray to white.
Original grayscale image, and 50% Threshold conversion method
Pattern Dither conversion method, and Diffusion Dither conversion method
Convert a color photo to Grayscale mode
1. Open the photo you want to convert to black-and-white.
2. Choose Image > Mode > Grayscale.
3. Click Discard. Photoshop converts the colors in the image to black, white, and shades of gray.
Note: The technique above minimizes file size but discards color information and can convert adjacent colors to the exact same shade of
gray. Using a Black & White adjustment layer increases file size but retains color information, letting you map colors to shades of gray.
Convert a Bitmap mode image to Grayscale mode
You can convert a Bitmap mode image to Grayscale mode in order to edit it. Keep in mind that a Bitmap mode image edited in Grayscale mode
may not look the same when you convert it back to Bitmap mode. For example, suppose a pixel that is black in Bitmap mode is edited to a shade
of gray in Grayscale mode. When the image is converted back to Bitmap mode, that pixel is rendered as white if its gray value is above the middle
gray value of 128.
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.
Convert a grayscale or RGB image to indexed color
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