Megapixels. How did such a simple concept become so wrapped up in hyperbole, controversy and confusion? Compact camera manufacturers act like everyone needs more of them. Photography pundits generally wish there were less. Smartphone manufacturers are completely unable to agree where they stand on the issue. The current generation of premium smartphones includes a 4MP model from HTC, 8MP from both Apple and Google, 13MP from Samsung and LG, 20.7MP Sony and 41MP from Nokia. Surely they can’t all be right?
So how many megapixels do you really need? It’s a simple question without a simple answer, but let’s start by breaking it down into two parts. If we take the assumption that more detail is generally welcome, at what point is there no practical benefit to the user? Then there’s the issue of technical limitations. How many megapixels can a smartphone deliver before the drawbacks outweigh the benefits?
Before we tackle these questions, let’s make sure we’re talking about the same thing. A megapixel rating tells you how many pixels there are in a photo. If it measures 4,000 by 3,000 pixels, multiply the two numbers to get 12 million, so it’s a 12-megapixel photo.
It’s worth noting that a 24MP photo isn’t twice as wide as a 12MP photo. It’ll have twice as many pixels, but that means it’ll only be 41% wider and 41% taller – in this case, that’s 5,656 x 4,242. Similarly, if you halve the width of a 12MP photo, to 2,000 x 1,500, the megapixel rating drops to a quarter, or 3MP. As such, the differences between a 4MP, 8MP, 13MP and 41MP photo perhaps aren’t as big as the numbers might suggest.
How many megapixels are sufficient for the average smartphone user?
These days, most photos are shared on social media services and viewed on computers, TVs, tablets and phones. The resolution of these screens varies from around 1MP for a typical smartphone to just over 3MP for the Retina Display on an iPad. A large number of TVs are Full HD (also known as 1080p), which works out at 2MP. A lot of computer monitors and an increasing number of phones and tablets use this resolution, too. The biggest screens around are 4K TVs, which equate to 8MP. They’re ridiculously expensive at the moment, but they’re bound to become more affordable and commonplace over the next decade.
On this basis, the most megapixels you’re likely to need to show your photos at their best on today’s electronic displays is 3MP. If you want them to look great for decades to come, you might want to shoot them at 8MP.
If you print photos out, the demands are similar: 300 pixels per inch (ppi) is widely accepted to be as sharp as the eye can see for photo prints. A 5×7-inch photo at 300 ppi weighs in at 3MP, while for an A4 print it jumps to 9MP. Even an A2 poster print at 300 ppi is only 35MP – still less than the 38MP photos from the Lumia 1020.
The graphic below shows how these sizes stack up – red for displays, blue for print sizes and green for the photo resolutions of the four smartphones that we’re concentrating on in this feature. The figures are included below for reference, too. A 4MP image can contain enough detail to fill an iPad screen or produce sharp 5×7-inch prints. It’s only when you get to A4 enlargements or 4K TVs that higher resolutions become necessary. Even then, 8MP is perfectly sufficient.
The bottom line
So how many megapixels do you need? Here’s the shortest answer we can muster: for most purposes 3MP is plenty, but you might want to shoot at around 8MP for the crispest possible details. 8MP is a sensible minimum for big prints and 4K TVs, and even higher resolutions allow you to crop photos without sacrificing quality too much. However, make sure that very high resolutions are matched by an equivalent increase in sensor size.
Of course, image quality is also defined by the design of the sensor, the quality of the lens, the intelligence of the metering and automatic exposure system … the list goes on. It’s a good job, because if you could tell a camera’s quality just by its megapixel rating, we’d be out of a job.