Printing > Setting PostScript prepress options > About screen ruling

 

About screen ruling

Screen ruling, measured in lines per inch (lpi), is the number of lines or rows of halftone dots printed per inch on the page. A high screen ruling prints the dots close together, creating sharp, distinct colors and images. A low screen ruling prints the dots farther apart, creating a coarser effect.

Image resolution, measured in pixels or dots per inch (dpi), is the number of pixels displayed per inch of printed length of an image. An image with a high resolution contains more pixels per inch and therefore has more detail.

The relationship between image resolution and screen ruling determines the appearance of detail in a printed document. In general, the higher the image resolution is, the higher the screen frequency you should use for printing.

In addition, because different types of paper absorb inks in different ways, the characteristics of your paper and the press also determine the screen ruling you should use.

When setting the screen ruling for grayscale images, the maximum number of grays possible in an image is 256. Increasing the screen ruling decreases the number of grays available. The maximum number of grays that can be used in Gradient fills or blends depends on the capability of your final output device and the maximum steps value.

For color images, follow the guidelines in the table for specifying a screen ruling:

Screen Ruling (lpi)

Type of Printing

65 to 85

Newspapers or point of purchase displays on absorbent, uncoated stock

90 to 133

Business publications, freestanding inserts, or newspaper coupons on coated stock

133 to 150

Menus, travel publications, or yearbooks on medium- to high-quality coated stocks

Above 150

Coffee table books, museum-quality prints, fine art reproductions, automobile promotional brochures, or annual reports on high-quality coated stock running on highly accurate presses


For grayscale images, follow the guidelines in the following table:

Resolution (dpi)

Screen Ruling (lpi)

Number of Grays Printed

300

53 to 60

26 to 33

600

71 to 85

51 to 72

1200 or 1270

65 to 128

89 to 256

2400 or 2540

90 to 150

256

3386 or 3600

150 to 300

128 to 256