Monday, September 1, 2003

What the heck is a megapixel?


By David Gewirtz

Last week, I wrote a quick piece about getting started with digital photography. The response from readers was absolutely astounding. In fact, I believe we've gotten more letters about that short article than any other we've ever published (except, perhaps, my political commentaries, which managed to piss off 49.9% of the U.S. population).

There were so many questions, comments, and great ideas that we've probably got material for a year's worth of tips. In fact, we've started talking about spinning out a digital camera publication just because of that response. If that's something you're interested in, send me a note at and let me know.

Needless to say, I can't answer every question this week. Next week, we're going to flip back to PDA coverage for a review of some new, hush-hush devices that are pretty exciting. We're also going to continue our discussion of megapixels and camera choice. That said, I suspect we'll be adding more and more digital camera coverage, because it's clearly a topic that's got you interested.

Sifting through the letters, the biggest theme was one of confusion. Many of you asked what camera should you buy and many others told me you were confused by all the specs. Rather than going through individual cameras and recommending them (they change each week), I'm going to help you understand what makes these cameras tick.

The place to start is megapixels.

Since the megapixel count is a simple number, and that number seems to correlate to price, it seems easiest to choose based on this measure. In reality, you'll also want to choose a camera based on its optics, menu system, available storage, responsiveness, and picture quality.

Today, however, we're going to talk megapixels.

Understanding pixels

Let's start off by defining a pixel. The word "pixel" is actually a shortened form of the phrase "picture element." A picture element is, in the computer world, basically a dot. As you know, computer screens (and digital camera images) are made up of grids of dots. Today, a typical computer screen has 1024 dots across by 768 dots down, although older screens have less and gamers often punch their screens up to higher resolution.

Each dot, or each pixel, contains color information. Let's take a look at a simple picture, shown in Figure A.


Here's an example of how pixels contain color information. (click for larger image)

You can see the original image in the upper left side of the figure. When the image is enlarged, you can see each individual pixel, and you can see that each pixel is basically a square (some devices use slightly different shapes) containing color information.