If you've ever discussed digital cameras, inevitably you've heard someone ask "How many megapixels does that camera have?"
There seems to be a perception in digital photography that more megapixels equate to a better camera. While a camera's megapixel count can have a significant impact on image quality, a simple More-Is-Better approach is inadequate. In this article we'll try to understand megapixels, examine why you might want more, and, believe it or not, look at why you might not want more.
Let's begin by defining what a "megapixel" is.
Pixels: Digital Building Blocks
Digital images are made up of a series of dots or squares. If you put enough of the squares together in a small space, then your eye will see a continuous image, not the individual squares. For example, here's a picture of a tortoise from the San Diego Zoo. I've zoomed in on a corner of his shell to reveal the individual squares that make up the image.
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Each of the squares that make up this picture can be considered a "pixel". A megapixel is simply one million pixels. The tortoise picture was shot with a camera that has a 6 megapixel sensor, so the picture contains roughly 6 million of those pixel squares. Understanding megapixels in your digital camera is as simple as that.
Why Is Having More Megapixels a Good Thing?
More megapixels does not mean a better picture. Having more megapixels does two, and only two, things for you. It gives you the ability to make large prints and it gives you more flexibility in cropping pictures. That's it. Let's look at these two benefits individually.
Large Prints
More megapixels means that you'll be able to make large prints of your photos without seeing any pixels. For example, if you were to make a large 11x14 inch print taken from a 6 megapixel camera, you'd get a nice smooth print. If, however, you tried to make an 11x14 inch print from a 3 megapixel camera, the print would look rough. You'd be able to see individual dots in the 3 megapixel print which would seriously degrade the quality of your picture.
If, however, you were making smaller 4x6 inch prints, the 3 megapixel and 6 megapixel pictures would look just as good, assuming the two cameras were otherwise comparable. For regular 4x6 prints, anything more than 3 megapixels is just overkill and adds nothing to the image quality.
Cropping
If you’ve ever edited your digital pictures on a computer, then you've probably used cropping before. Cropping lets you draw a box around the area of the photo that you'd like to keep. Anything outside the box gets tossed away. This is very useful if you want to eliminate areas of the photo that are distracting - the strange, purple-haired guy who wandered through the background of your family photo, for example.
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When you crop, you are throwing away parts of the photo. This means that you're left with fewer pixels than you started with. If, for example, you started with a 6 megapixel image and cropped away 50% of the image, you'd be left with a 3 megapixel image. As we discussed, those 3 megapixels remaining would be plenty to make a good 4x6 inch print. If, however, you'd started with only a 3 megapixel image before you made your 50% crop, then you'd be left with only a 1.5 megapixel image which would not make a good quality 4x6 print.
Can You Have Too Many Megapixels?
So we've established that high megapixel cameras are useful for large prints and big crops. We've also established that having more megapixels won't be of any benefit beyond certain print sizes. But shouldn't you still try to get the most megapixels for your money? Can you have too many megapixels? Unfortunately, there are some drawbacks to having more megapixels.
First, a higher megapixel count means that the camera is trying to record a larger amount of data for each picture. The camera may take longer to write the data to your memory card, slowing your ability to take consecutive shots. More data also means larger files. With larger files, you won't be able to fit as many pictures on your memory card before you have to offload the pictures to a computer. Transferring those pictures to your computer will also take longer with bigger files.
The other concern with high megapixel counts is the introduction of noise into pictures. Manufacturers' marketing departments understand that most people equate more megapixels with better cameras. They push hard to get higher and higher megapixel cameras out the door to keep pace with their competitors. Unfortunately, technological development can't always keep up with marketing zeal.
As manufacturers cram more and more photosites onto their tiny sensor chips, some of those photosites interfere with adjacent sites. The result is noise. Noise shows up in your pictures as little off-color dots. I've included a rather extreme example of image noise below.
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Notice all the off-color red, blue, and green pixels? The speckled, grainy look absolutely kills the image quality of this picture. Some high megapixel cameras struggle more with noise than others, so be sure to examine sample pictures from any camera you're considering purchasing.
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How Many Megapixels Do I Need?
Since megapixels really only determine your biggest print size and crop capability, you can easily determine the minimum number of megapixels you'll need in a digital camera. Decide what your maximum print size will be and then get a digital camera with at least the minimum megapixel count indicated below.
| Maximum Print Size | Megapixels Needed |
| 5x7" | 3 megapixels |
| 8x10" | 4 megapixels |
| 11x14" | 5 megapixels |
| 13x19" | 6 megapixels |
| 16x20" | 8 megapixels |
| 24x36" | 10+ megapixels |
If you don't exceed the maximum print size indicated here for your camera's megapixels (or the megapixels remaining after a crop), then you'll get smooth prints with no visible pixels.
Once you understand your minimum megapixel needs, then forget about megapixels and focus on other features of a prospective camera purchase. What's the price? How big is the camera? Do you need it to fit in a pocket? How comfortable does it feel in your hand? Does it have enough optical zoom for you? Does it have the various bells and whistles that may be important to you (self timer, macro capability, video capability, good LCD screen, different exposure modes, image stabilizer, etc).
Finally, it all boils down to the quality of the pictures coming out of the camera. Be sure to examine sample photos from the camera, preferably photos you have taken with a display model. Don't rely on the camera's LCD screen to examine the samples: all pictures look good on a 2-inch screen. Ask the store if they'll print one of the sample pictures you've just taken. If the store is willing to print a sample for you, ask if they'll make a large print for you. If they won't print them for you, then load sample pictures onto their computer and examine them on the computer's monitor.
Understanding what megapixels do and, more importantly, what they don't do will help you get past the camera manufacturers' marketing hype and will make you a smarter camera consumer.
