300ppi (or dpi) is the accepted standard in stock photography because it meets the needs of most high quality reproduction. Magazines, books and most other high quality publications are typically printed at a 133 or 150 Line Screen ( LPI for Lines Per Inch). The common rule of thumb for determining the dpi required for print is to double the LPI, so for a 150 Line Screen a 300 ppi image resolution would be appropriate. Newspapers typically use a lower 85 Line Screen so 170 ppi is all that would be needed. So an 8 inch by 10 inch image with a 300ppi resolution would have a pixel dimension of 2400 px (8x300=2400) by 3000 px ( 10 x 300=3000). That same image could be reproduced for a newspaper requiring ony 170ppi at up to 14 inches x 17.6 inches ( 2400/170 = 14 and 3000/170 = 17.6 ).
A digital image's size is really dependent on the number of pixels it contains.
|W x H in pixels||PPI ( or DPI)||Line Screen||Max. repro size in Inches||Example end uses|
|2610 x 3900||300||150||8.7" x 13"||magazine, book, calendar|
|2610 x 3900||266||133||9.8" x 14.6"||magazine, book, calendar|
|2610 x 3900||170||85||15.3" x 22.9"||newsprint|
|2610 x 3900||20||10*||261" x 390" (32.5 ft)||billboard|
|3930 x 6000||300||150||13.1" x 20"||magazine, book, calendar, poster|
|* Line Screen used for this example is common but actual LPI may vary depending on printing method and viewing distance|