"How To" Guides > Printing Images

Printing Quality Photo and Document Digital Images

By R. Anderson - 2/2009

Online Printer Resolution Recommendations (continued)

Shutterfly's recommendation for minimum pixel dimensions start with the assumption that most images will have the 1.33 aspect ratio associated with a compact digital camera. The third column is the megapixels reflected in the pixel dimensions. You can see that Shutterfly.comsuggests a minimum of roughly 2 megapixels for an 8 x 10 print and 3 plus megapixels for enlargements over 8 x 10. The fourth column is simply the pixel dimensions divided by the print size inches to calculate how many uncropped pixels there are for each printed inch. As the aspect ratio is different for each print size from the starting image's 1.33 aspect ratio, some default cropping will take place to "fit" the image to the specified print size. The last column indicates the resulting minimum default cropped PPI resolution recommended by Shutterfly.comfor common print sizes.

Print Size	Minimum Recommended Pixel Dimensions	Megapixels	Available Pixels Per Inch	Fit to Size Default Cropped PPI Resolution
4 x 6	1024 x 768	0.79	171 x 192	171
5 x 7	1152 x 864	0.99	165 x 173	165
8 x 10	1600 x 1200	1.92	160 x 150	150
11 x 14	2048 x 1536	3.15	146 x 140	140
16 x 20	2048 x 1536	3.15	102 x 96	96
20 x 30	2048 x 1536	3.15	68 x 77	68

Snapfish's recommendation for minimum pixel dimensions start with the assumption that image pixel dimensions have already been cropped to the aspect ratio of the print size. You can also see that Snapfish.com by HP has taken a very different approach by suggesting that 90 pixels per inch is likely to be an acceptable level of pixel resolution across the range of print sizes.

Print Size	Minimum Recommended Pixel Dimensions	Megapixels	Pixels Per Inch	Pre-Cropped PPI Resolution
4 x 6	540 x 360	0.19	90 x 90	90
5 x 7	630 x 450	0.28	90 x 90	90
8 x 10	900 x 720	0.65	90 x 90	90
11 x 14	1260 x 990	1.25	90 x 90	90
16 x 20	1800 x 1440	2.59	90 x 90	90
20 x 30	2700 x 1800	4.86	90 x 90	90

Clearly, online printers prefer that pixel resolutions exceed these levels for better results. The comparisons above illustrate that determining acceptable image quality is not an exact science. Therefore, particularly when printing more expensive enlargements at lower PPI resolutions, it is a good idea to test a few images to make sure that they are satisfactory to your purposes.

Recall that in the scanning guide, it was suggested that you scan and photograph to specific needs when known. For general purpose scanning, we suggested that you scan at 600 PPI. In the table below, we see what this means to our printed PPI density, for various print sizes, when we scan a 4x6 original.

Print Size	4 x 6 Original 600 PPI Scan Pixel Dimensions	Megapixels	Maximum Print Pixels Per Inch Available	Fit to Size Default Cropped PPI Resolution
4 x 6	3600 x 2400	8.64	600 x 600	600
5 x 7	3600 x 2400	8.64	480 x 514	480
8 x 10	3600 x 2400	8.64	300 x 360	300
11 x 14	3600 x 2400	8.64	218 x 257	218
16 x 20	3600 x 2400	8.64	150 x 120	120
20 x 30	3600 x 2400	8.64	120 x 120	120

You can see that the 600 PPI scan provides print resolution pixels across the range of print sizes that meets Shutterfly.com and Snapfish.com by HP minimums. In fact, the number of pixels provide cushion for moderate cropping, and the likelihood that you may scan some images smaller than 4" x 6".

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