One question that often comes up when printing digital photos – how many megapixels do you need for a certain size print, such as an 8×10 inch print, an 11×14 inch print, or a larger poster size?
Part of this discussion rests on the quality of the image. If an image is slightly blurry, you may need to resample it to a lower number of megapixels to offset the blurriness, else the quality of the full-size printout may be less than expected.
Printout quality depends on the paper and printer as well. Make sure you are using quality photo paper and not just inkjet or laser paper. Plus, ensure that your printer is configured to use the high-quality paper.
The dpi (dots per inch) of a printout helps determine the image quality and how many megapixels you may need. Generally, the greater the dpi, the clearer and cripser the printout (up to a point). While you can print larger images from smaller digital photos by decreasing the dpi, the results may not be as impressive as if the original image were larger and printed with a larger dpi.
To factor how many pixels you need, multiple the dpi by the size of the photo. Thus an 11×14 image at 150 dpi will need 11*150 by 14*150 pixels, or 1,650 by 2,100 pixels (3.465 million pixels).
Now, with this size, you would think that a 3.5 megapixel camera would handle it. Not so fast! One 3.5 megapixel digital camera I found actually had an image resolution of 2144 x 1608. While 2144 is greater than 2100, 1608 is NOT greater than 1650! Thus this digital camera, which SHOULD be able to print 11×14 images at a 150 dpi, can’t muster enough detail. It’s close, but not enough, yet it might be satisfactory for you needs.
Digital camera megapixels and actual resolution (note these can differ depending on the camera):
2 megapixels: 1600 x 1200
3 megapixels: 2048 x 1536
4 megapixels: 2274 x 1704
5 megapixels: 2560 x 1920
6 megapixels: 2816 x 2112 – 3032 x 2008
7 megapixels: 3072 x 2304
8 megapixels: 3264 x 2,468
Pixels needed for a 150 DPI image (fair to good image quality)
8×10: 1,200 X 1,500 pixels – most 2-megapixel cameras
11×14: 1,650 X 2,100 pixels – most 4-megapixel cameras
16×20: 2,400 X 3,000 pixels – most 8-megapixel cameras, maybe some 7-megapixel cameras
Pixels needed for a 200 DPI (good image quality)
8×10: 1,600 X 2,000 pixels – most 4-megapixel cameras, maybe some 3-megapixel cameras
11×14: 2,200 X 2,800 pixels – 7-megapixel cameras, though most 6-megapixels cameras should be close enough
16×20: 3,200 X 4,000 pixels – although this is only 12.8 megapixels, most cameras won’t have the same aspect ratio (width versus height), thus you may need a camera with a greater number of megapixels
Again, these numbers are just provided as the results of mathematical formulas. You can resample the image to some degree to make it larger than normal, play around with the printer dpi, etc., and get acceptable larger prints from smaller photos. Just realize that the image quality may not be optimum, though it may be sufficient for your needs.