Adobe 13101332 - Photoshop - Mac User Manual page 64

Adobe Photoshop Help
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Understanding monitor resolution helps explain why the display size of an image on-
screen often differs from its printed size. Image pixels are translated directly into monitor
pixels. This means that when the image resolution is higher than the monitor resolution,
the image appears larger on-screen than its specified print dimensions. For example,
when you display a 1-by-1 inch, 144-ppi image on a 72-dpi monitor, it appears in a 2-by-2
inch area on-screen. Because the monitor can display only 72 pixels per inch, it needs
2 inches to display the 144 pixels that make up one edge of the image.
Printer resolution The number of ink dots per inch (dpi) produced by all laser printers,
including imagesetters. Most desktop laser printers have a resolution of 600 dpi, and
imagesetters have a resolution of 1200 dpi or higher. To determine the appropriate
resolution for your image when printing to any laser printer, but especially to image-
setters, see "screen frequency."
Ink jet printers produce a microscopic spray of ink, not actual dots; however, most ink jet
printers have an approximate resolution of 300 to 720 dpi. To determine your printer's
optimal resolution, check your printer documentation.
Screen frequency The number of printer dots or halftone cells per inch used to print
grayscale images or color separations. Also known as screen ruling or line screen, screen
frequency is measured in lines per inch (lpi)—or lines of cells per inch in a halftone screen.
The relationship between image resolution and screen frequency determines the quality
of detail in the printed image. To produce a halftone image of the highest quality, you
generally use an image resolution that is from 1.5 to at most 2 times the screen frequency.
But with some images and output devices, a lower resolution can produce good results. To
determine your printer's screen frequency, check your printer documentation or consult
your service provider.
Note: Some imagesetters and 600-dpi laser printers use screening technologies other than
halftoning. If you are printing an image on a nonhalftone printer, consult your service
provider or your printer documentation for the recommended image resolutions.
A
C
Screen frequency examples:
A. 65 lpi: Coarse screen typically used to print newsletters and grocery coupons B. 85 lpi: Average
screen typically used to print newspapers C. 133 lpi: High-quality screen typically used to print
four-color magazines D. 177 lpi: Very fine screen typically used for annual reports and images in
art books
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B
D
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