Imagine this scenario: you're going to purchase a camera, and you can't choose between a consumer pro DSLR with 20 megapixels or a more expensive model with 25 megapixels. If you're like me, you usually equate price with quality and assume the 25 megapixels would be the best bang for your buck.
And you'd be wrong. Well, sort of.
You see, most people believe the false assumption that more megapixels equals better photo quality. Megapixels are related to two things, roughly: cropping and printing.
When you crop an image, you remove megapixels from your image. It's simple subtraction. So when you have an image with a large amount of megapixels, you're not compromising the image when you crop. When you crop an image with a small amount of pixels, you create image degradation when you print the image at its original size.
For example, let's say you want a 5x7 print of your kids on the beach. You use the camera on your phone to snap the picture. You crop the photo down to tighten the focus on the kids (and away from the seagulls in the sky). Now, you go to print your image at a local drug store and see that your image is distorted.
More than likely, you cropped too much and there were not enough megapixels to keep the image sharp when you blew it up. It happens to the best of us.
Printing is arguably the strongest case for needing more megapixels. But it's overkill past a certain amount.
For the mathematicians out there, there's a pretty straightforward formula to calculating megapixels needed.
Determine the physical length and width of your print, multiply the dimensions by 300, and then divide the total by 1 million.
(Width in. x 300) x (Height in. x 300) / 1 million
Using this formula, an 8x10 print would require 7.2 megapixels, while a 12x14 print requires about 15.1 megapixels.
With that in mind, comparing a 20 megapixel camera to a 25 megapixel camera is pointless if you're not producing large prints. 20 megapixels is more than enough to produce quality prints, especially for the amateur who's printing mostly for keepsakes.
We've reached this point and you're saying, "Great. I know the purpose of megapixels. What I'm wondering is how I get really sharp, beautiful photos."
What you're gonna wanna focus on is the size of the image sensor and its resolution. Larger image sensors equal larger pixels (not to be confused with megapixels), which allow more light to be captured on the sensor. More light captured means a better photo.
This is why a 12MP smartphone camera versus a 12MP compact camera has a pretty significant image quality difference: the compact camera has a much larger sensor.
But as time progresses, smart phones are bridging that gap. Smart phones are becoming more capable of producing higher quality photos than ever before.
The reason I'm writing this is not to discourage you from purchasing higher megapixel cameras. Instead, be aware of the selling point of a camera being better quality than a competitor because of its higher megapixel count.
Know what your needs are. If you're preparing prints for a gallery showing, higher megapixels will allow sharp, large prints. If you're an amateur who wants to print pictures of your loved ones, a more modest camera will suit you just fine.
And if you're in the market to buy a camera that can shoot sharp pictures, focus on image sensor size and resolution.