[nextpage title=”Introduction”]

At the beginning of the age of digital cameras, it was all about the number of megapixels. A 2-megapixel camera was better than a 1-megapixel camera and a 3-megapixel camera was better than a 2-megapixel camera. If you wanted a better digital camera, you simply purchased the one with the highest megapixel count. This method of determining the quality of a digital camera became ingrained in the minds of consumers and has been sustained by the camera manufacturers.

The number of megapixels was very important when the cameras only had one, two, or three-megapixels. There was a big difference between a 1-megapixel camera and a 3-megapixel camera. Now, however, most digital cameras have at least 5-megapixels and the resolution that the megapixels offer is quite good. So as megapixel counts have increased, their importance has actually decreased.

Yet megapixels are one of the things that determine the quality of a digital camera and of a digital photograph, so today we’ll investigate what megapixels are and how much they really matter.

[nextpage title=”What is a Megapixel?”]

A digital camera’s resolution, which is a gauge of how much information and detail a camera can capture, is measured in megapixels. A megapixel if comprised of 2^20 (1,048,576) pixels. This number seems "broken" but in fact it is "rounded" because digital systems are based on binary numbers, which uses base 2 numbers (i.e., 0’s and 1’s) not base 10 (the numbers that we humans use). Some people round 1 megapixel to 1 million pixels, but the result will be technically wrong. In fact, some manufacturers lie about the true resolution of their digital cameras by assuming that 1 megapixel is 1 million pixels and not 1,048,576 pixels.

In digital imaging, a pixel (picture element) is the basic unit of an image. Pixels are also used to express the resolution of digital displays and pages printed by digital printers. You can think of pixels as a cluster of colored dots that combine to form images in a digital camera, on the computer screen or on a printed page.

A digital camera captures the image with its image sensor and records it on internal storage or, more commonly, on media cards. This image is essentially made up of digital pixels. Pixels are arranged in a grid. They are counted horizontally and vertically. There are more pixels horizontally because the images are wider than they are tall. For example, a 3 MP picture is a 2,048 x 1,536 image. 

So there are two ways for you to represent the resolution of an image. You can say the number of pixels it has on its horizontal axis and on its vertical axis (e.g., 2,048 x 1,536) or you can say the total number of pixels the image has (e.g. 3 megapixels). In summary the number of megapixel of an image is the number of pixels ("colored dots") it has.

The more megapixels a camera can handle, the greater the amount of information it records. Theoretically, the more pixels that the camera has, the greater the image resolution and therefore the higher the image quality and the sharper the pictures. This is why everyone thinks that the number of megapixels is so important. Yet, as we will see further in this article, this is not always true.

[nextpage title=”Print Sizes and Resolution”]

Megapixels are important because the greater the number of megapixels, the larger the photograph can be printed with good results.

Most ink jet printers can print good images at 200 or 300 ppi (pixels per inch) which is the rough equivalent of 100 to 150 dpi (dots per inch). There are more pixels per inch because there is no space between the pixels. (On a printed page, however, there is space between the dots, so the number of dots per inch is lower than the number of pixels per inch).

Many digital cameras today have at least six megapixels. That means that you can get close to perfect resolution when printing an 8" by 10" photograph at 300 ppi or 150 dpi. The same 6-megapixel photograph will give you excellent results when printed as large as 10” by 15” print at 200 ppi or 100 dpi.

Often perfect resolution is not even necessary because to the average eye a large 4-megapixel print will look as good as a similar-sized 6-megapixel print.

Most photographs are printed at 3” by 5” or 4” by 6” and most ink jet printers can only accept paper as large as 8 ½” by 11.” So a 6-megapixel camera will be more than adequate for most average computer users.

This chart will give you an idea of how many megapixels are needed for a good quality print, printing at 200 ppi. The pixel image size for the listed megapixels will differ slightly with different cameras.

Megapixels Image Size Print Size at 200 ppi
3 2048 x 1536 10.2" x 7.7" (25.9 x 19.6 cm)
4 2464 x 1632 12.32" x 8.16" (31.2 x 20.7 cm)
5 2592 x 1944 13" x 9.7" (33 x 24.6 cm)
6 3008 x 2000 15.04" x 10" (38.2 x 25.4 cm)
8 3504 x 2236 17.5" x 11.2" (44.4 x 28.4 cm)
10 3872 x 2592 19.36" x 12.96" (49.2 x 32.9 cm)
12 4290 x 2800 21.45" x 14" (54.5 x 35.6 cm)

If you print at 150 ppi, you will get a lesser quality, but often acceptable prints in larger sizes. True photo quality prints will be printed at 300 ppi.

To determine exactly the size prints that the megapixels will support, find the pixel resolution image size and divide each dimension by the number of pixels per inch for the print. For example, the 6-megapixel image size from the above table is listed at 3008 x 2000. To get the largest print size of good quality (200 ppi) divide each dimension by 200 which will give you 15.04” x 10.” If you will print at 150 ppi, divide each dimension by 150 which will give you a maximum print size of 20.05” x13.34.” If you want photo quality prints printed at 300 ppi, divide each dimension by 300 which results in 10.03” x 6.67.”

If you only want to print photographs up to 4” by 6,” a 3-megapixel camera would suffice. Yet, there may be times when you may want to blow up a portion of the photo to print it. In that case you will need a camera with a higher resolution so that when you blow up that area, it will still have enough resolution to print well.

If you want to get a detail from a picture, you need to get a picture in high resolution to be able to crop the detail out of the picture (I hope you get the idea by just reading this).

Also be aware that you don’t need a high megapixel count to show pictures on a computer monitor. Most monitors have resolution of 1024 x 768" or 1280 x 900. As you can see from the chart above, a 3-megapixel image will look fine on a computer monitor with these resolutions. So you don’t need a high-megapixel count for putting images on the Web or on a computer screen.

One more thing to be aware of, the higher the resolution of the picture, the larger the file and the more space it will take up on the media card. Most cameras allow you to take images of different quality. The adjustments usually say something like low, medium, or high quality. Some people use the lower quality to save space on the memory card. Then they find that when they decide to print a large photo, it is grainy or blurry. If you don’t know how large you will want to print your pictures, it is best to get a media card with a large capacity and to take your photos at a high quality.

[nextpage title=”Megapixels, the Caveat”]

As stated earlier, you would think that a higher number of megapixels would always produce a better image, but there is one c
aveat. All of the megapixels must fit on the camera’s sensor. Higher-end SLR (Single Len Reflex) cameras generally have larger sensors than smaller point-and-shoot cameras that fit in your pocket.

Since camera manufacturers still think that consumers buy cameras on the basis of the number of megapixels, they keep adding more and more megapixels to make the cameras appealing. But if the sensor is too small, the pixels must be smaller so that they can fit onto the sensor. Smaller pixels decrease the amount of light collected by each pixel and result in more noise in the image. Noise is the presence of specks of color that don’t belong in the photograph. So high megapixel counts on a small sensor may actually result in a degradation of the quality of the photos, making the image worse instead of better.

Although megapixels are important, it is obvious that other things also contribute to the quality of photographs. The size and quality of the sensor and the quality of the lens makes a big difference. An 8-megapixel camera with a large sensor and a better quality lens will produce better quality photos than an 8-megapixel camera with a small sensor and an inexpensive lens.

So don’t judge the quality of a digital camera only on the number of megapixels. You should also look at the sensor, lens, general hardware quality, the interface, and the controls. When looking for good quality prints, check out the prints yourself and/or read the camera reviews by qualified reviewers.