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Mar 182014
 
The more pixels, the bigger the image, of course.  But how many pixels do you actually need?

The more pixels, the bigger the image, of course. But how many pixels do you actually need?

If you’re considering a new camera, the two measurements you are most likely to fixate on are the number of megapixels the camera’s sensor contains, and the zoom range of the lens.

Neither of these two issues are quite as important as they might seem, and both are misunderstood and conceal other underlying complexities.  Unlike what most people assume, in both cases, a higher number can sometimes be worse than a lower number.

As regards the megapixel count of a camera, how many do you need?  Is there such a thing as too many (or too few) megapixels?

Certainly, in the early days of digital cameras (think mid/late 1990s) it is true that the cameras then were woefully inadequate with their megapixel count, and so for a while it made sense to consider this measurement, because more megapixels always related to better picture quality.

But nowadays, with all cameras offering in excess of 10 MP, and some offering over 20 MP, this is no longer a concern or constraint for most people, most of the time.

How many megapixels do you actually need in a camera?

That depends on what you will do with the images.  If you want to display your pictures on a computer screen, or a television, or a tablet, then to show an image full screen, you probably want each picture to be in the order of about 2000 pixels by 1000 pixels – in other words (multiply the two numbers together) about two megapixels.

If you want to print out standard 4 x 6 pictures, then you want to have ideally 250 or more pixels per inch, making for 1000 x 1500 pixels, which is still only 1.5 MP.

There might be a slightly improvement in quality if you pushed this up to 300 ppi (this is sort of a ‘magic number’ that more or less matches the resolution of your eyes at typical reading distances, which is why Apple came out with its ‘retina’ screens on iPhones and tablets having this type of pixel resolution), but there’s unlikely to be any improvement at all beyond that, even if you are using a printer that promises 600 or 1200 or some other ridiculous number of pixels per inch of printing ability.  On the other hand, you can still print good looking pictures at 200 ppi and it would only be if you were closely studying the picture under a magnifying glass that you’d notice the individual pixels.  So 250 ppi is a reasonable midway point.

If you were to print out large 8 x 10 pictures, you’d hope for 2000 x 2500 pixels, or 5 MP.  And that’s a very big sized photo, while still requiring only a surprisingly small number of pixels.

It is rare for anyone to print out larger images, but you know your requirements, and if you must have a camera capable of printing out 11 x 14 pictures (ie 9.6 MP) or even larger, then do the sums to find the pixel count you need.

So, looking at the above, is 10 MP all you really need for just about anything, ever?

Yes and no.

There’s another issue to consider.  That is cropping and framing your pictures.  Maybe, after you took the picture, when you actually look at it, you realize there is too much background and other stuff, and you just want to focus on the bit of greatest interest, which might only be a half or a quarter of the total picture size.  Or maybe you took a picture with one aspect ratio (perhaps 2:3) and now want to display it at a different aspect ratio (perhaps 9:16) and so you need to crop off part of the image that won’t fit in the new aspect ratio.

That means you need a larger image so that when you crop off the unwanted bits, the part that remains is still ‘big enough’ to give you good images when viewing on screen or printing out.

Again, you probably have a feeling for how much extra resolution you need to allow for these types of contingencies.  If you’re a good photographer, you’ll do a lot of the cropping and composing prior to taking the picture, but if you want to spend less time taking the shot and have more options later when editing the photo, you will find more pixels useful.

Come back to the first numbers above – you need 1.5 MP to print out a good quality 4 x 6 print, and 2 MP to fill most computer/phone/tablet screens.  If you double the pixel count in both dimensions so as to give you lots of cropping and other options, you quadruple the total pixels you need.  So, for most purposes, most of the time, 8 MP is going to be massively more than you need.

If you’re a semi-professional, and either want to be able to significantly crop your images or print them out in very large poster sizes, then you’ll find value in having more than 8 MP resolution.  But, for most of us, most of the time, even 8 MP is overkill.

That might surprise you, and you might wonder why, if even 8 MP is massive overkill, it seems that each year brings new cameras with still more megapixels.

Why is this?  Probably the same reason that cars add extra horsepower and higher top speeds.  Maybe your car is rated at 0-60 in 6 seconds and 130 mph maximum speed – and, indeed, maybe when you bought your car you paid extra for a more powerful than standard engine option.  But, as you drive it around town every day (and even when you occasionally go for longer freeway drives), how often do you ever use full throttle acceleration, and how often do you reach 100 mph, let alone continue up to 130 mph?  For that matter, when you are stomping on the gas pedal, would it really make a difference if it took six or seven seconds to go from zero to sixty?

Another interesting indicator is to find and read an older review of an older digital camera.  If you look around a bit, you’ll find breathless excitement being expressed at 3 MP and 5 MP cameras, and statements suggesting they can be used for printing out enormous sized prints.  Now, you’ll find similar breathless excitement for 20+ MP cameras, and similar statements about printing out similar sized prints, and of course, implied scorn for earlier lower resolution cameras.  The whole thing about megapixels, and how many you ‘need’, is mainly hype.  Don’t be fooled.

Our point is simply this :  As long as your camera can give you at least 8 MP of picture, you are well taken care of.  Don’t allow the fact that one camera has 20 MP and the other camera ‘only’ has 15 MP to unduly influence your buying decision.  There are much more important issues  – and, perhaps surprisingly, the 15 MP camera might actually give you appreciably better quality images (and capture them faster and use up less of your memory cards in the process).

In other words, there actually is such a thing as ‘too many megapixels’.  And there are other picture quality parameters that are much more important than a simple megapixel count.  But the camera manufacturers don’t like to talk about these other issues.  We’ll tell you more about this in a follow-up article, next week.

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  One Response to “How Many Megapixels Should Your Camera Have?”

  1. […] it is such an important issue that we wrote a separate article about megapixel misunderstanding last week.  If you haven’t already done so, you should read that […]

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