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MegaPixels and Inches Explained

Digital cameras are becoming very popular, but there is still a lot of confusion about how megapixels relate to the size of the final printed photograph. I hope this this article will help you understand what mega pixels are in practical terms. (This article is aimed at the amateur and occasional photographer, not the professional. The professional photographer should really know all this stuff by now!)

So, how big, in inches, is a 3.2 MegaPixel image? For those of you who took photos with old non digital cameras here is a quick scene which may be enlightening:

You are taking a photograph of your grandmother, say.

Your grandmother: "That camera looks small. How big will this photo be?"
You, smiling: "Well, it depends how big it gets printed of course!"

And it is exactly the same for modern digital cameras. You can print your photos as large as you want, it does not matter how many mega pixels you have!

What more mega pixels give you are more details. So a camera with 6 Megapixels can take a more detailed picture than a camera with 2 Megapixels. You can print both at any size you want, but you may see better quality with the 6 MP (MP=MegaPixel) camera than with the 2 MP camera.

Imagine that this is what you see with your very own eyes:

Now, exagerating the effect of pixelization, using a 2 MP digital camera you would get an image like this:

And with a 6 MP digital camera:

So it seems that the 6 MP camera wins hands down. But it doesn't. Not always. Because if you have a shakey hand (or a dirty lens or bad focussing) a 2 MP camera and a 6 MP camera could give you equally bad results!

(Back to printing for a second. Notice that you could print both of the above images at the same size in inches. Pixels are not related to inches until you print. Only looking at a printed photograph can you say "this photo has 300 pixels per inch" for example.)

In the wrong hands a 6 Mega Pixel camera will give worse results than a 2 Mega Pixel camera in competent hands. Here is what a blurry 6 MP image can look like:

Another problem with higher resolution cameras is that the photographs occupy more memory. So you will need to spend more on memory for the camera, especially if you go on long trips away from a convenient computer.

So, in practice, what resolution level should you use? Here is my story:

I have kept photo albums since I was 17 years old. I have been using a digital camera for 3 years and still keep albums. I arrange my photos on an A4 page for printing, and then store the prints in transparent plastic envelopes in a binder.

Arranging 3 or 4 photos on an A4 page you get something like this:

1 of 40 days in Katmandu

The photographs were taken at less than 1 Mega Pixel! And I guarantee that printed 4 to an A4 page you cannot see any pixels (there is no "pixellation"). I set the resolution of my aging Sony. . .

Aging Sony Digicam

... to 1024 pixels wide. I used this resolution because I stayed for 40 days in Katmandu, Nepal, last year and was not able to easily save the photographs in a computer. I had 4 memory sticks, each of 32 MBytes. ("Memory stick" is Sony language "memory card")

Digital cameras allow you to choose the resolution (pixel size) of the photos you are taking. So even if you have a 6 MP camera you can set it to a lower resolution in order to get more images per memory card.

When is it reasonable to use very high resolution? If you have a very very steady hand or a tripod. If you have huge amounts of memory on hand. If you are taking photos close to your home or office, so that you can unload the photos to a nearby computer.

Another advantage of using a higher resolution is that you can extract interesting parts of the image without losing much quality. Maybe in this image...

...I am only interested in the group of people on the right...

With low resolution it is difficult to extract parts of the image without getting a pixelated or blurry image. I was lucky this time!

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