As each new camera model is introduced one thing that you can be certain of is that the Megapixel rating of the new camera will have been increased, the latest compact cameras have ratings of around 14Mp and D-SLR's have now broken the 20Mp barrier.

With ever increasing Megapixel (Mp) ratings it is all to easy to get caught up in the technology race thinking that more Megapixels must equal better image quality.  To find out if this is the case we need to look at what Megapixels are and how they effect the quality of our images.

All digital cameras have a Sensor that captures your image, they achieve this by having a surface covered in microscopic light sensitve photosites that each produce one element of your picture refered to as a Pixel, one million of these Pixels are known as a Megapixel. If you have a camera that is rated at 6 Megapixels, all this actually means is that the sensor within the camera has 6 million light sensitive Photosites on it, which will give you 6 Megapixels of picture information often known as the cameras resolution.

If you look at the two images below you will see one is at normal size and the other an enlarged  (x 1000) section of the same image, at this magnification each individual pixel is clearly visible.  A good way of thinking of a digital image is as a mosaic of pixels and the more pixels in the mosaic the finer the image will be.

Now still with me haven't lost the will to live yet?  Then it's at about this point that you may well be thinking, all right I now know what Meagapixels are, but I still don't know how they actually effect image quality and exactly how many do I need in my camera?  

Image quality is partly determined by how many pixels you have in your print, so to achieve true photo quality you will need a maximum of 300 pixels in every inch of your print (300 ppi) both horizontally and vertically, any more pixels than this will be wasted as the human eye can  not detect a visual difference in image quality above this level.

Don't worry to much about the mathematics required to work out how many Megapixels you will need as we have produced this simple chart for you to show you how many Megapixels are required to give true photo quality at various print sizes:-

You will have noticed that we have used print sizes at 200ppi as well as 300ppi, the reason for this is that 300ppi is the ideal option for standard print sizes, but 200ppi will be acceptable for very large prints, this is because you view these from a greater distance making it very hard to detect any loss in image quality.

To use the chart first decide on what print size you want at either 200ppi or 300ppi then follow the "Blue" bar up untill it stops, then read off from the "Blue" scale on the left hand side of the chart how many Megapixels you will need.  For example to print all sizes up to 8"x6" at 300ppi you will need a camera rated at 4 Megapixels for true photo quality.

So that's the theory behind Megapixels and getting great print quality, but what happens in actual practice. Have a look these three images shown below they are all small sections taken from 12"x 8" prints using three different digital cameras rated at 3Mp, 6Mp & 10Mp, all of the images were sized in exactly the same way in Adobe Photoshop (lowering the ppi until a print size of 12"x 8" was achieved). 

If you are having problems deciding which one is which, then you are in very good company as most people will find it very difficult to spot a difference between good quality cameras (rated over 3Mp) at standard print sizes.  I think it is fair to say that our little comparison test has demonstrated that generally an increase in Megapixels alone does not guarantee you better image quality up to a print size of A4 (approx 12"x 8"). 

So what are the advantages of owning a high Megapixel rated camera, well the answer is that they come into their own in producing very high quality poster sized prints, the more Megapixels you have the greater you can enlarge your image, another plus point is that if you need to greatly crop your images you will still be able to do so and retain high image quality (e.g. crop an image from a 12Mp camera by half and you will still have a 6Mp image).

To sum up, in practical terms you are unlikely to see a vast difference in image quality by just increasing the cameras Megapixel count at standard print sizes, for prints at this size a camera with a rating of around 6 megapixels will be all most of us will ever need.   

But if you often produce large poster sized prints (above A4) that are to be of the highest quality, or regularly need to crop your images drastically then you will certainly need all of those extra pixels that a high rated Megapixel camera will give you

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