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By Hoan K. Trinh

One photo was taken on a 7.1 megapixels camera while the other one was shot on a 6.1 megapixels camera, which one is which?


Camera companies have, since the beginning of the digital age, boasted about the amount of megapixels contained in their image sensors.  But what does it mean and how does it actually affect the quality of an image?

First, we need to understand the technical parameters on which an image sensor is judged.  The four parameters of which a sensor is judged on are: color depth (color accuracy), dynamic range (details in highlight and shadow) , digital noise (low light capability), and resolution .

Which one of these of parameters does megapixels count directly affect?  Resolution (not the one on New Year)

The higher the amount of megapixel means the higher the linear resolution (it’s not exactly a linear correlation, however).  The higher the megapixel for a particular size of image sensor will typically hurt the ISO performance making low light photography a challenge.   Color depth and dynamic range are typically not affected by the megapixel count.  Two cameras with the same amount of megapixel will have reasonably similar resolution, however, the color depth and dynamic range of the sensor can be totally diferent!!!  A DSLR with 6.1 megapixels will kill a point and shoot camera with 14 megapixels because the larger sensor in a DSLR with higher quality pixel will allow for better color depth and dynamic range as well as much lower digital noise in a photo.  There is no point in having high resolution when the color, noise, and dynamic range is less than stellar.

So to answer the question of whether or not megapixel really matter, you need to determine how much resolution you really need.  For Facebook photo, a couple of megapixel is plenty, if you want to print an 8×10 photo, I would said a 4 megapixel file would be adequate, 6-8 megapixels is plenty, and 20 megapixels is just a waste of memory space.   What truly matter are the color depth, dynamic range, and digital noise in low light.  Unfortunately, it is easier to market megapixels counts rather than all the other factors.  Camera companies have been focusing on waging their megapixel war for a while now and sometimes neglected the other factors.  If anyone has notice, the higher end and newer $5,000 Canon 1D Mark IV has 16 megapixels, 2 megapixels less than its older and quite cheaper $1800 Canon 7D as well as the entry level T2i (both are smaller sensors than the Mark IV too), the reason being that having the extra megapixel hurt the low light performance of the camera and Canon just had to call it quit on the megapixel war.  Nikon, until very recently, had kept their megapixels count at 12 megapixels for the last few years on most of their cameras to ensure great low light performance.  All in all, companies have been neglecting other aspects of an image sensor to bolster their megapixel claims and there is no need to follow their marketing tools.

Now, I am not saying that having extra megapixel is necessarily a bad thing, landscape and studio photographers will cherish it as the extra resolution will come in handy when making big photo prints and low light is just not an issue for them as they has much more control over their lightings compare to other photographers such as sport and wedding photographers.  However, for most of us who do not have a requirement to make big prints on a daily basis, then the extra high megapixels sensor could actually be quite a hindrance.

* The photo on the left was taken with a 7.1 megapixels Kodak Z710 point and shoot camera while photo on the right was taken with a 6.1 megapixels Nikon D40 DSLR with a 55-200mm F4-5.6 VR lens.  Noticed how the color rendition in the image on the right is much stronger even with less megapixel?


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