Mega-what?: Understanding Megapixels
This is the first entry in my weekly “Mega-what?” feature on phewse, so I figured the only way to start is with the term “megapixel,” of course! This is a word that is tossed around routinely, and most people have a basic idea of what it means. I’m here to tell you a little more about it, and also clear up some common misconceptions.
What exactly is a megapixel?
First, to understand megapixels, you have to understand how a digital camera captures a photo. I’m not going to go into all the details, as it would take far too much space. (If you’re interested in reading more about how a digital camera works, I’d recommend checking out HowStuffWorks.) Essentially, when you press the shutter button on a digital camera, light goes through the lens and hits a chip at the back of the camera. This “chip” consists of millions of little sensors, which interpret the light. Each of these little sensors is called a “pixel.” One million pixels equals one megapixel.
Millions of pixels? But I just want to take pictures!
Well, that’s exactly what these are doing. The camera takes down all the information these pixels record and puts them into a nice JPEG (or RAW, TIFF, whatever format your camera outputs) and writes them to the card. Then, when your computer reads the file, it puts this information on the screen! Cool, huh?
Wait a second here! I thought megapixels were all about quality, not little dots!
This is a common misconception—that more megapixels means more better quality. While this is partially true, it’s not the whole story. If you’re like most people, if you’re going to print a picture, you’re probably going to print a 4×6, right? Here’s a surprising fact—when a photo is printed as a 4×6 at 300 dots per inch (the standard resolution for printing) it results in 2.16 megapixels. So basically, If you have a camera that’s anything over 2.16MP, it’s overkill! Here’s a chart of standard print sizes and their respective megapixels (at 300DPI):
| Print Size | Megapixels |
|---|---|
| 3×5 | 1.35MP |
| 4×6 | 2.16MP |
| 5×7 | 3.15MP |
| 8×10 | 7.2MP |
| 16×20 | 28.8MP |
(I figured this out by multiplying the width x 300dpi x the height x 300dpi)
Another thing to consider is that megapixel counts are only one facet of image quality. There are many other factors that come into play, such as noise, lens quality, and sensor quality, but I’ll save all those for another day.
Alright, you proved your point…sort of—all I have is a 6MP camera, and I want to print an 8×10. Is there no hope?
Now, before everyone jumps down my throat, let me say this: the above table isn’t entirely true. You don’t really need a 7.2MP camera to print an 8×10, as there are many great programs out there that let you interpolate, or fill in, any missing pixels and you can get a pretty decent enlargement out of lower megapixel cameras. Also, unless you’re looking at prints under a microscope, you really won’t notice much of a difference as you enlarge your photos. I’d say you could probably get away with a 5MP camera and still get a decent 8×10, although you would most likely want something more in the range of 6MP.
If you want more reading on the “megapixel myth,” I highly recommend this article over at KenRockwell.com. Ken has some great information on those millions of dots, and it’s well worth checking out.
Hopefully, I helped you understand a bit more what cameras mean when they quote megapixel numbers. If you have any further questions or anything to add, feel free to leave a comment.
“Mega-what?” is a weekly feature of phewse where I clear up a different photographic term every Thursday. Want to view other entries? Check them all out on the category page.