In the world of marketing digital cameras, megapixels seem to be the beginning and end of a camera’s power. Like a computer’s RAM and hard drive, “the more, the better,” and all of the other features of a camera fall by the roadside. But there’s more to a photo than the megapixels.
The quality of the lens, for a prime example, is a much more important feature than the pixels. A poorly built lens will take all the power out of the camera, because a fuzzy picture is still fuzzy, even at ten megapixels.
Once they’re out of the camera, megapixels are a reasonably good guide to how large a print you can get out of them. Since pixels are actually “dots,” if you enlarge the picture enough, the illusion will be broken–and the individual dots will become obvious. The more pixels, the larger you can expand the picture before the dots become visible.
As a general rule of thumb, four megapixels is perfect for 5×7 prints, but generally not much larger. There are exceptions, but they depend mostly on the subject of the picture, and not the megapixels of the camera. While a three megapixel image will look great on the computer screen, printed at 3×5, or maybe even printed at 5×7, the dots will be really obvious if the picture is blown up onto a highway billboard. Five megapixels will make for a great 8×10 print.
When it comes to enlarging pictures, photo editing programs do not have a very good track record. Shrinking a picture works very well, but enlarging is a lot more difficult–because you can’t just make the dots bigger. The program has to Interpolate–that is, it has to guess at what color the new pixels have to be. There are programs specifically designed for enlarging digital images, but it’s still a fairly new technique.