What’s a Megapixel?

Megapixel, Megapixel, What For Art Thou, Megapixel?

All digital cameras have an imaging sensor that uses very tiny light-gathering points called pixels—an abbreviation of “picture-elements” (pix-els). There are millions of these tiny light-gathering pixels on the imaging sensor. Each pixel captures a tiny part of the image of your subject. All the pixels working together capture the full image.

You have heard the word megapixels if you have been doing digital photography for very long. The word megapixels simply means millions of pixels. Camera companies use the megapixel rating of their cameras as a major sales point. Most people think that the more megapixels, the better the image; however, that may not always be true, as we’ll discuss in a moment.

The letters MP are used to represent megapixels. If your camera has 18 megapixels, it will be called an 18 MP camera. Some common megapixel sizes over the last few years have been 6 MP, 8 MP, 10 MP, 12 MP, 16 MP, 14 MP, 18 MP, and 24 MP. If things continue as before, expect the MP rating to keep on increasing as camera companies try to outdo one another.

The size of the imaging sensor, and the number of megapixels on it, determine the maximum resolution (size) of the images you can create with the camera. However, there is a tradeoff in quality when too many pixels are added to a sensor. The problem with a point-and-shoot camera is that the sensor is very small and the millions of pixels are very, very tiny. That can cause some problems, as discussed in the next section.

What about Imaging Sensor Size?

To make a comparison, a point-and-shoot camera has an imaging sensor about the size of your little fingernail. Imagine cramming millions of pixels into a space the size of your little fingernail. Those pixels are so small that they are not very light sensitive. The gain (sensitivity) of the pixels is increased in lower light levels so that a point-and-shoot camera can make a good picture. That degrades the image by introducing random, meaningless color-flecked graininess in the image, called noise.

You know how static sounds when you turn up a radio to hear a station that is slightly out of range. The static is a noisy sound that degrades your radio-listening experience.

Digital image noise is similar to static on a radio, except it is visual. Noise is random specks of grainy-looking dark or light color specks that were not in the scene you photographed. Noise is one of the reasons people realize they need better cameras and move into the DSLR or ILC world.

You may remember what noise looks like in images you’ve taken with your old point-and-shoot camera in low ambient light conditions. The grainy look of the images was not pleasant, was it? A point-and-shoot camera has a much harder time making high quality images because there are too many pixels crammed into too small an imaging sensor size. If you have a point-and-shoot camera with 14 MP, that means the camera manufacturer packed 14 million pixels onto a tiny little imaging sensor. Noisy images are the result!

On the other hand, a DSLR or ILC has an imaging sensor nearer the size of a postage stamp. That’s quite a difference! The same number of pixels put into a larger sensor area means the pixels can be much larger and can gather light much more efficiently. The images can be sharper and have better color, contrast, and dynamic range (how much light range from dark to light its sensor can capture).

The DSLR/ILC’s photos can be enlarged (made bigger) more efficiently and with higher quality. You’ll be amazed at the difference and so will your friends and family.

Pixel size is a strong determining factor in image clarity and lack of noise. As discussed previously, the larger the pixel, the better it can gather light. Sometimes more megapixels is not the best thing for your photography. If a camera manufacturer comes out with a new model with “even more megapixels” and they haven’t increased the size of the imaging sensor—beware!

When there are millions of extra pixels jam-packed into even a larger DSLR/ILC sensor, the pixels must be smaller in order to fit the available space on the sensor. When the pixel size is reduced to the size of a point-and-shoot camera’s pixels, image degradation can result.

Thankfully, camera manufacturers are usually balanced about this and don’t push the pixel sizes down too far. They know noise will result and people will be unhappy. There was one major camera manufacturer who recently reduced the number of pixels in one of its cameras, from the previous one, because people were complaining about noise.

Don’t be fooled by the hype in advertising. The number of pixels is an important factor in maximum image size, and the size of the pixels is an important factor in maximum image quality. Just be aware of the trade off between the size and the number of pixels. More megapixels can sometimes make for a lesser quality image. Interesting, huh?

This has been an excerpt from my book: Beyond Point-and-Shoot

Keep on capturing time…

Darrell Young

Dancing clouds on Blue Ridge Parkway

Darrell Young is an active member of the Nikonians User Community and author of 12 photography books from NikoniansPress through Rocky Nook, including Beyond Point-and-ShootMastering the Nikon D600Mastering the Nikon D800Mastering the Nikon D7000, and the upcoming Mastering the Nikon D7100, to name a few. He’s been an avid photographer since 1968 when his mother gave him a Brownie Hawkeye camera.

His website, www.PictureAndPen.com, was created to support the readers of his educational books, photography students, and clients. Visitors to his website “will find articles and reviews designed to inform, teach, and help you enjoy your photographic journey.”

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