Adobe Photoshop CC 2014 v.14.xx - Manual (Page 174)

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Note:
A 620- by 400-pixel image displayed on monitors of various sizes and resolutions.
When preparing images for viewing on-screen, you should consider the lowest monitor resolution that your photo is likely to be viewed on.
About printer resolution
Printer resolution is measured in ink dots per inch, also known as dpi. Generally, the more dots per inch, the finer the printed output you’ll get.
Most inkjet printers have a resolution of approximately 720 to 2880 dpi. (Technically, inkjet printers produce a microscopic spray of ink, not actual
dots like imagesetters or laser printers.)
Printer resolution is different from, but related to image resolution. To print a high quality photo on an inkjet printer, an image resolution of at least
220 ppi should provide good results.
Screen frequency is 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 higher the
resolution of the output device, the finer (higher) a screen ruling you can use.
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.
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.
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
Determine a suggested resolution for an image
If you plan to print your image using a halftone screen, the range of suitable image resolutions depends on the screen frequency of your output
device. Photoshop can determine a recommended image resolution based on the screen frequency of your output device.
If your image resolution is more than 2.5 times the screen ruling, an alert message appears when you try to print the image. This means
that the image resolution is higher than necessary for the printer. Save a copy of the file, and then reduce the resolution.
1. Choose Image > Image Size.
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