Learn the Terms > Megapixels

Megapixels

How many megapixels you need to print your favorite photographs

When you hear the term megapixel, what comes to mind?

  1. A very large pixel
  2. The superhero of pixel land
  3. The total number of pixels captured by an image sensor

If you answered number three, then you are already well on your way toward understanding why megapixels are important when it comes to digital cameras.

Unfortunately, there is a lot of hype surrounding megapixels, which makes it hard to determine what you really need. One person will say you only need 4.0 megapixels, and the next will assure you that only 8.0 megapixels will do.

How do you sort through the hype and figure out how many megapixels is right for you?
Read on...

What are these megapixels really all about?

A photograph produced by a digital camera is a collection of tiny dots. Each dot is called a pixel. The image that you see is created out of millions of pixels: hence, megapixels.

Problems emerge when you increase the size of a digital photograph. The more you increase the size, the more you begin to notice all of the tiny dots. The digital image is revealed for what it really is.

This is especially true when you want to print your digital photo. While you may not be able to see the individual pixels on your computer monitor, you will definitely notice them when the image is printed. Printers require a LOT of pixels to create a decent photographic print.

Interpolated megapixels

You might have heard about some cameras that say their "interpolated" megapixels allow you capture double the number of megapixels. How does this work?

In cameras with interpolated megapixels, an additional pixel of information is created by the camera for every actual pixel captured by the camera's sensor.

A camera that only captures 4 megapixels (2 pixels for each square) per photograph can interpolate the image up to 8 megapixels (since the number of pixels are doubled). What do you get? An 8 megapixel camera for the price of a 4 megapixel camera! What a great deal!

But maybe too good to be true...

There is a limitation here. The camera is not actually capturing the extra pixels, but it is "guessing" about how they should look. This artificial enhancement of the image creates artificial results. If you pay attention to detail, you can see that interpolated images are not as clear as non-interpolated ones.

Effective megapixels

Let's imagine for a moment that taking a photograph with your digital camera is like sitting down to a good meal. You start out with a full plate of food and eat what you can, but wind up with leftovers. A similar thing happens with your camera's total and effective megapixels.

Total Megapixels

This is like the full plate of food. It is the total number of pixels that are included on your camera's CCD or CMOS sensor. All of these pixels are available to be used any time you take a photograph and expose the sensor to light.

Effective Megapixels

This is the amount that you eat. Some cameras use all the pixels on the sensor (and wind up with a clean plate) and others only use a portion of the pixels for the photograph. A camera's effective megapixel number is the number of pixels on the sensor that are actually used to capture the photographic image.

Example

Here's an example to help clarify this. Let's say that you are looking at a digital camera with 5.3 total megapixels, but 5.0 effective megapixels. This means that even though the sensor includes 5.3 million pixels, only 5 million pixels are used when you take a photo. The other .3 (o 300,000) are leftovers.

What Leftover Pixels Are Used For

So now you're wondering why in the world anyone would make a camera sensor that doesn't use all of it's pixels. Where's the sense in that?

The pixels are used, just not to capture the photographic image. How the extra pixels are used depends on the camera manufacturer. In many cases they exist to make the digital photograph look clean, covering up artifacts and other problems that may exist in the photo. They don't go unused, but play more of a supporting role to the other pixels doing the real work.

When you need more megapixels

You will need a camera with a lot of megapixels in the following cases:

Magazines and other print media have higher print requirements than a home printer used for snapshots of your latest vacation.

This table shows the relationship between megapixels and print size:

MegapixelsPrint Size (inches)
2.04 x 6 [standard]
3.05 x 7
4.08 x 10
5.09 x 12
6.011 x 14
8.012 x 16

Notice something interesting here? A digital camera that creates images with 2.0 megapixels is going to be enough to produce decent quality prints at 4 x 6, the most common print size for most photographs.

However, if you try to print a 2.0 megapixel image at 8 x 10, you will probably not be happy with the result. The image will look blurry and fuzzy, and you will be able to see the actual pixels in the photo.

When you need less megapixels

You may be wondering, "If more megapixels creates better images, why not just get the one with the most?" There are two reasons why this might not be a good idea for you.

COST

If you take two digital cameras that are essentially identical to each other with the exception of the number of megapixels (and they do exist) the camera with more megapixels will always cost more. Sometimes up to $100 more. Make sure that you need the extra megapixels before paying the extra expense.

FILE SIZE

When you take a photo with a digital camera, the image is saved onto a removable memory card. These removable memory cards come in a variety of different storage capacities.

More megapixels is equivalent to more information in the digital photograph. This means that digital photo files created by cameras with more megapixels are larger. You can easily fill up a small memory card in a few minutes with an 8.0 megapixel camera.

Let's assume that you are going to use the memory card that ships with most digital cameras and that it is not your intention to buy another one. The standard memory card has a capacity of 16MB (MegaBytes).

Back to the megapixel table to see how many photos you can store on a 16 MB card:

MegapixelsNumber of Photos *
2.0About 22
3.0About 10
4.0About 8
5.0About 6
6.0About 4
8.01 to 2

* These numbers are approximate, and will vary between different cameras models. This is also assuming that the photos are being taken at the higest quality setting.

Every digital camera with a lot of megapixels allows you to take photographs at a lower setting. With a 6.0 megapixel camera, you will also be able to take photos at 2.0 megapixels if you want to e-mail them to friends. But if you don't need the 6.0 megapixels in the first place, does it really make sense to spend the extra 300 to 500 dollars?

The Basic Rule of Thumb

If you think that at some point you will want to print one of your photographs at 8 x 10 (which can be nice if you get a real winner), then you just need a 4.0 megapixel camera. Don't let a salesperson tell you that you need more.

The Real Truth

I have printed images from a 3.0 megapixel camera at 20 x 30. If you're getting ready to break out a measuring tape, that is standard poster size - a pretty large print. Based upon what I have said so far, you might believe this didn't turn out very well.

The reality is that it printed just fine and I have the image hanging on my wall at home. Would it look better if I had used a 4.0 or 8.0 megapixel camera? Sure. Can I tell that it is 3.0 megapixels by looking at it? Not really.

In the end, the choice will be yours. If you have a discriminating eye and little imperfections bother you, get the camera with more megapixels. You will be happier in the end.

If you are less prone to notice every little flaw, get the camera that has all the features you want, but NOT the one that boasts the highest number of megapixels.

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