Megapixels and Sufficient Resolution
Dan Knight - 2003.04.16
There are lots of variables in digital photography, but the most important one is megapixels. Even a lowly 1 megapixel (MP) camera will give you just great 4 by 6 snapshots, assuming a good lens and exposure. I've printed pretty sharp 5 by 7s from my 1.3 MP Canon PowerShot A50 on my Epson Stylus Photo 870 inkjet printer.
How resolution correlates with print quality depends on how you're making your final print. If you're using a color inkjet printer, a resolution of 180-200 dots per inch in the original file is fine. Using the lower figure:
4" x 6" = 720 x 1080 = 0.78 MP 5" x 7" = 900 x 1260 = 1.13 MP 8" x 10" = 1440 x 1800 = 2.6 MP 11" x 17" = 1980 x 3060 = 6.0 MP 20" x 30" = 3600 x 5400 = 19.4 MP
In other words, just about anyone would be satisfied with an 8 by 10 from a 3 MP digicam. And 20 x 30 poster prints tend to be viewed from further away, so 150 dpi resolution would be fine, which requires 13.5 MP - exactly the rating of Kodak's incredible new digital SLR. If you're going to print out using a large inkjet system, you could easily pull off a 20 x 30 poster using this camera.
For other processes, such as dye sublimation or "wet" printing (producing the final print on photographic paper), you need higher resolution for the same perceived output quality. A local lab does top quality work when customer files are provided at 250 dpi....
4" x 6" = 1000 x 1500 = 1.5 MP 5" x 7" = 1250 x 1750 = 2.2 MP 8" x 10" = 2000 x 3000 = 6.0 MP 11" x 17" = 2750 x 4250 = 11.7 MP 16" x 20" = 4000 x 6000 = 24.0 MP
The difference is because of the way inkjet printers spurt tiny dots of ink onto the page while other processes are continuous tone. For the better quality output, you have to double the number of pixels. If you're having prints done in a digital minilab, these are the figures you want to use for the best possible results, although many users may find the earlier number satisfactory.
You can get excellent 8 by 10 dye-based prints from 5 MP cameras, and the few 3 MP Fujifilm models (such as the F601 and S602) that create 6 MP files within the camera. The same may apply to the Sigma SLR with the Foveon imager.
Still, for sharpest results a camera with a 6 MP or better imager will do the job.
There are some models available for as little as $500 than can produce 6 MP files (e.g., the FinePix 601), although their zoom range is somewhat limited.
If you want the ability to change lenses, you're looking at $1,500 minimum for a camera body, such as the just announced 6 MP Canon EOS 10D. Unless you're doing large art prints, 6 MP should be plenty of quality.
The step beyond that is Kodak's 14 MP beastie ($5,000 plus the cost of Nikon-mount lenses), which can easily create a gorgeous 12" x 18" miniposter using dye-based processes or a very nice 20" x 30" print using inkjet technology.
Unless you can justify the expense of a $1,500 camera body, serious photographers may do well to stick with film for the next year or two. Minolta has a wonderful new $300 film scanner that all the computer and photo magazines are raving about; with it you can create 11 MP files from your 35mm slides or negatives. (This is also a great way to get the best of your old images into your computer.)
Film vs. digital depends on your needs. For the average snapshooter, a 2 MP camera is all they'll ever need. For those who might make an 8 by 10 once in a while, a 3 MP camera will generally do the job.
But for demanding photographers, you really want 5 MP as a realistic minimum - and a lot more than that if you plan on going beyond the 8 by 10 level.
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