August 22, 2009

What's a Megapixel?

A while back, I sent out a survey for people to contribute their top three burning questions about digital photography. Many people asked questions related to “megapixels,” so here goes.

Most of you know what a mosaic looks like: a picture created with lots of small tiles of different colors. If you stand very close to a mosaic, all you see are the individual tiles. But if you back away, your vision causes the tiles to blend together and you can see the image.

A floor mosaic

Your digital camera contains a sensor (computer chip) with a grid of photo cells which collect the light coming in through the camera’s lens. The computer inside your camera processes this light and turns it into a grid of tiny colored squares called pixels (short for “picture elements”). So a digital image is really a grid made up of lots of little squares of color. If you greatly enlarge a digital photo on your computer screen, you can see the pixels themselves (like the tiles in a mosaic). But usually you just see the picture.

Individual pixels visible at high magnification in sunflower image

Every digital camera has a maximum number of pixels it can create, based on the grid of photo cells on the sensor. For example, a camera sensor might contain 3000 pixels across and 2000 pixels up and down. We can describe the size of the digital picture this sensor makes by saying the image is 3000 pixels x 2000 pixels. (Here “pixel” is a unit of measure like an inch or a foot.)

If we actually multiply the two numbers, we end up with the total number of pixels in the image (like the total area of a rectangle): 3000 pixels X 2000 pixels = 6,000,000 pixels. Six million pixels is the maximum number of pixels the camera can create. Another way to say the same thing is 6 megapixels. “Mega” means “million”.

(not to scale)
3000 pixels x 2000 pixels = 6,000,000 pixels
6,000,000 pixels = 6 megapixels

You can find out the maximum number of megapixels your camera creates in one of two ways. If you have a compact (point & shoot) digital camera, sometimes the number of megapixels is printed right on the camera body. The other way is to look in your camera's manual in the section usually called "Specifications". (Check the table of contents or index for the exact page.) In the Specifications section you are looking for an entry called "effective pixels". This number tells you the maximum number of megapixels the camera can create.

Compact camera displaying 7.1 megapixels

Now you can impress all your friends at your next cocktail party with what a megapixel is!