Guidelines for Photo Resolution for Print

Our professional photographers supply photos at a high resolution appropriate for print, but when we obtain photos from other sources, they may be too “low res” to use. For example, photos that look just fine on the web are almost always too low res to use in print. Photos sent by email may have been reduced in file size for easy transmission.
It is important to know whether a photo is usable before Kim or her student designers sit down to design a project. How can you tell? Here are two ways of checking:

By pixels

• This is the preferred test of resolution.
• To determine resolution from pixel dimensions, divide pixel width and height by 300 to determine the maximum size at which you will be able to use the image.
• If a photo is 1200 pixels x 1600 pixels,
• 1200 ÷ 300 = 4 and 1600 ÷ 300 = 5.33
• The photo could be used at 4” x 5.33” or smaller.

How do I determine how many pixels there are?

Windows

• Pixel count will show up if you go to "View,” then “Choose Details,” and check “Dimensions.”
• Then you can just roll over a given photo and it will tell you the dimensions, e.g. “2592 x 1944” pixels. This should work if you use Microsoft Office Picture Manager (on all PCs at Macalester) or Picasa (free download from Google.)

Mac

• Open image in “Preview,” then select “Tools,” then “Show Inspector.”

By DPI

• Images should be 300 dpi (dots per inch) at the size in which they will be used. Be aware that if you enlarge a photo, the dpi goes down.
• For example, an image that is 300 dpi at 2” x 2”, will be only 150 dpi at 4” x 4”. So you could use the image at 2” x 2” with satisfactory results, but not at the larger size.
• By the same token, an image that is only 72 dpi at 17” x 13” will be sharper at a smaller size and would be 300 dpi at 4” x 3”. When “shrunk,” the dots are closer together, so you have more dpi, dots per inch.

How do I determine DPI?
Windows

• Right click on the image file and select “Properties,” the “Summary” tab, then “Advanced Option.” This will also give you pixels.

Mac

• As when finding pixels, open image in "Preview," then select “Tools,” then “Show Inspector.”

“Up-Resing” Images
Sometimes images can be enlarged and sharpened with Photoshop, allowing use at a larger size than the above guidelines would suggest. See www.creativepro.com/files/story_images/101504_PSimageres.pdf . However, it is not a simple process and would require some familiarity with Photoshop, so it is probably not efficient to frequently manipulate photos in this way.

Thanks to the following resources:
H. Jay Burns, Editor, Bates magazine, Bates College
Susan Woolley, Director of Publications, Moravian College
http://www.printingforless.com/images.html
http://www.articlesbase.com/prepress-articles/photo-enlargement-understanding-dots-per-inch-dpi-721170.html

12-14-09