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What is a Megapixel?

Answering the question "What is a Megapixel" is really pretty simple because a megapixel is simply one million pixels. But then that leads to the next question where things get a little more interesting and that is "What is a Pixel"?

Understanding Pixels and Megapixels

Foveon Image SensorDigital cameras use an electronic image sensor to take pictures instead of film. These image sensors convert the optical image (picture) into an electric signal which is then processed and stored electronically in some type of external (a removable memory card such as a SD or Compact flash card) or internal memory (memory built into the camera). Each image sensor is made up of individual optical components known as pixels (picture elements). One million of these pixels is referred to as a megapixel.

An image sensor is made up of individual optical components known as pixels (picture elements). The term megapixels simply means one million pixels with a pixel being a single point or dot that makes up part of the picture or image.

Now that we have a basic idea of what a pixel is we know the simple answer to our question "What is a Megapixel" but we still need to understand why megapixels matter and how important they are to overall picture quality.

Why are Megapixels Important?

Megapixels are important because they are an indication of camera's image quality or resolution. Higher megapixel cameras will produce higher resolution images which generally equals better quality photographs.

Important Note: There are other factors that influence picture quality as well; especially the size of the image sensor so be wary of falling into the Megapixel Myth trap and automatically equate more megapixels with better pictures.

In film cameras the image resolution was determined by the size of the film however in today's digital cameras it determined by the size of the camera's image sensor and the number of megapixels it has. To determine the number of megapixels you multiply the number of pixels the camera's image sensor has vertically by the number of pixels horizontally. That gives you the total pixel count for the camera which is expressed in megapixels.

Avoiding the Megapixel Myth Trap

Now that we have a better understanding of "What is a Megapixel" we need to make sure that we avoid falling prey to the Megapixel Myth trap. The megapixel myth is the assumption that "more megapixels are better" when evaluating digital cameras.

The number of megapixels a camera has is important because it indicates the image resolution that camera can capture, but it is just one of many factors that play a role in the overall quality of the picture. There are simply too many other related factors such as the size of the image sensor that affect overall image quality to automatically assume that just because one camera has more megapixels you will get a higher quality image than another camera.

While the number of megapixels is important when it comes to how large of an image can be printed there are other factors that contribute to the overall picture quality. Therefore when considering a digital camera do not assume that a higher megapixel camera will always be the best choice.

How many megapixels are needed for different print sizes?

As we continue to learn about what is a megapixel we will look at the important relationship between the number of megapixels and maximum print size. The general rule is that the more megapixels you have the larger your print can be without noticeable distortion.

The number of megapixels needed for different print sizes is determined by the print resolution which is normally listed in dots per inch with 300 dpi being a common standard for typical prints. Therefore determining the maximum print size is as easy as dividing the number of horizontal and vertical pixels by 300. For example a 5 megapixel camera might have a resolution of 2580 pixels by 1944 pixels or 5,015,520 total pixels. This means you can easily print an image up to 8.53 inches by 5.4 inches with a 5 megapixel camera.

To determine the maximum print sizes for cameras with a different number of megapixels please see the table below.

Camera Resolution In Megapixels Maximum Print Size At 300 dpi
5MP (2,580 x 1,944) 9x7
6MP (3,008 x 2,000) 10x7
7MP (3,072 x 2,304) 10x8
8MP (3,264 x 2,488) 11x8
9MP (3,488 x 2,616) 11x9
10MP (3,648 x 2,736) 12x9
11MP (3,830 x 2,872) 13x10
12MP (4,000 x 3,000) 13x10
14.6 MP (4416 x 3312) 15x11
24.6 MP (6048 x 4032) 20x13

*Horizontal and vertical measurements can vary depending on the format of the image sensor, etc. These are general guidelines not absolute standards.

 

How many pictures can my memory card hold?

In this last part of our discussion of "What is a Megapixel" we will briefly cover the relationship of megapixels and file size. The more megapixels a camera has means the larger the size of the standard JPEG picture file. This means that to store the same number of photos you will need a larger memory card, an important fact to keep in mind when considering replacing your digital camera with one that has more megapixels.

Below is a chart that shows an average file size for different megapixel sizes and the number of standard JPEG images that can be stored on different sizes of memory cards.

Memory Card Capacity
CameraFile size2GB4GB8GB16 GB 32 GB
5 MP 1.5 MB 1200 2400 5000 10000 20300
6 MP 1.7 MB 1000 2000 4300 8700 17300
8 MP 2.3 MB 700 1500 3200 6400 12900
10 MP 2.9 MB 600 1200 2500 5000 10100
12 MP 3.4 MB 500 1000 2000 4300 8600
16 MP 4.6 MB 300 700 1600 3200 6400
21 MP 6.4 MB 200 550 1100 2300 4600

 

While many people associate a higher megapixel camera with better quality photos there are too many other related factors to make that type of sweeping generalization.

There are many other factors than just the amount of Megapixels a camera has that must be given careful consideration when purchasing a digital camera. For more information on the different types of digital cameras available checkout our digital camera comparison page. I hope you have found this page on what is a megapixel helpful.

Tags: Photography Info Digital Photography