One of the arguments from manufacturers in the great megapixel wars is that to get a larger-than-life print, you need a ton of sensor resolution. While it’s true that the pixel count of the sensor largely will determine the acceptable image and print size, it’s not true that the more pixels you have, the bigger and better prints you’ll get. The quality of an enlarged print is largely subjective, and it’s important to point out that there are a number of factors determining optimum print quality. Remember, when you print big, everything is magnified, so there’s no hiding behind compressed details.
All that aside, more megapixels, as most photographers know, doesn’t actually mean an image with higher resolution. While resolution has come to be accepted generally as a term for the active pixel count on a sensor, too many photodiodes actually can be a bad thing when squashed onto a sensor just to boost a megapixel count for promotional purposes. Smaller light-sensitive areas can mean photodiodes that collect less information, as well as increased gaps in between the photodiodes for increased loss of light.
Myth: The larger the print, the bigger the sensor resolution needed
Secondly more megapixels doesn’t always equal a bigger and better print. It’s possible to achieve a better image through know-how, and a good, clean image, even one taken at a smaller resolution, always trumps a low-quality image taken at a higher resolution.
This isn’t to say that a 6-megapixel point-and-shoot will provide you with better or even the same results as a pro level D-SLR. There’s an acceptable maximum to every file size. (The graph provides a good estimation of file size capabilities.) For photographers who are most interested in making quality prints that will hold up to close inspection, a good rule of thumb for determining how big you can go is to multiply the pixel resolution by the horizontal and vertical inches of the final print size that you’d like and multiply those numbers together, finally dividing by one million for the megapixel size. For a 13×19-inch print at 200 ppi, the formula would look like this: 13 x 19 x 200, which equals 2600 x 3800, which equals 9,880,000 pixels. Divided by 1,000,000, the number becomes 9.8 megapixels, which means you need more or less a 10-megapixel camera to produce a 13×19-inch print at an acceptable 200 ppi.
By cheating ppi (or dpi when outputting to a print), or in other words, manipulating the pixels (or dots) per inch in an image, you have another good way to get a size boost in exchange for losing a little detail. The Nikon D3X and Sony A900 at 24.5 and 24.6 megapixels, respectively, for instance, can produce a high-quality, 300 dpi print at about 20×13 inches, but when you reduce to 200 dpi, you gain approximately a 50% increase in output size to 30×20.5 inches. Rarely will you want to go below 300 ppi when making a high-quality print, but many photographers realize that some loss in resolution, provided they have a great initial capture and meticulously edited final image, will be worth the gained size. Billboard and super-graphics manufacturers bank on the fact that most viewers won’t be closer than 50 yards or so, and they make use of large grain that looks perfectly acceptable from far away.
Available software is doing its best to increase these sizes, too, with exceptional up-rezzing ability from Photoshop and onOne Software’s Genuine Fractals 6 and sophisticated noise-reduction software like Nik Sharpener Pro 3.0 and Noise Ninja from PictureCode. If you have a firm understanding of all of these properties, you can produce some great results. What’s more, if you also have great lenses, an amazing camera with a large sensor and ample resolution, you can perform the same tasks with top-of-the-line imagery for truly larger-than-life results.