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We all like numbers. It lowers the bar for understanding, and digits are powerfully symbolic, rather than an idea, which is vague and subjective. A number, even if it’s a decimal, is decisive. A five is always a five, and if you add a one it becomes a six. But one man’s art is another man’s elevator music, and that’s why we love points, even if they’re marks at art school. We loved the .44 Magnum, shoot 35mm, applaud the eight gears in the latest Lexus and want to be six feet tall.

But worst of all, we buy cameras by the only thing we can really grasp about them: their pixel count. Thrown out of the window are things like colour reproduction, light sensitivity, noise reduction, sensor size, maximum aperture and generally everything that will help you make a better picture.

So now you’ve dumped your ancient one year old five megapixel wonder of yesteryear, and bought the latest 10MP replacement. It’s worth it because, as everyone knows, double the pixels means double the size of the print, double the quality of the image, double the number of people who can say ‘cheese’ at the same time and double the number of teeth they can cram into double the size of the viewfinder. That’s also double the number of lies you need to swallow before you make your next big mistake.

The question is, do you think you can look at an image by a 6.1 megapixel camera and differentiate it from the identical shot by its 10.2MP successor? Do you think you can look at a print and make out the difference, even if you leant in so close your nose was smudging the ink and you crossed your DPIs with your PPIs?

David Pogue of The New York Times decided to find out: he created three versions of the same photograph, showing a cute baby with spiky hair in a rowboat. One was a five megapixel shot, one was eight megapixels and one was 13.

He mounted the three prints on a wall in a public square and asked passers-by if they could see any difference. A small crowd gathered, and several dozen people volunteered to take the test. They were allowed to mash their faces up against the print, step back and squint, whatever they liked.

Only one person correctly identified which were the low, medium and high-resolution prints. Everybody else either guessed wrong or gave up, conceding that there was absolutely no difference. In another trial, out of about 50 test subjects only three could say which photo was which.

Critics of such tests typically say, of course more pixels make a difference, you just can’t see them. But that’s really quite ridiculous, since photography is all about seeing anyway. And if you can’t see it then why buy it?

As Pogue himself points out, a megapixel is one million tiny colour dots in a photo. It seems logical that more megapixels would mean a sharper photo. In truth, though, it could just mean a terrible photo made of more dots. A camera’s lens, circuitry and sensor – not to mention your mastery of lighting, composition and the camera’s controls – are far more important factors.

There could even be enlargements from a 4MP camera that look much sharper and better than ones from an 8MP model. Meanwhile, a camera with more megapixels usually costs more and its photos fill up your memory card and hard drive much faster. And more densely packed pixels on a sensor chip means more heat, which can introduce speckles into low-light shots.

Of course, this does in no way mean that pixels are irrelevant. But they’re just part of the larger picture, and if you go by this one magic number your photos aren’t going to improve. Technology might be cramming our sensors with an increasing number of dots, but photography hasn’t changed at all: it is still about exploring and expressing, and, above all else, seeing.

The technicalities
Ken Rockwell, an old hand at digital imaging and now a keen reviewer, had been talking of his own megapixel myth before Pogue’s article caught the attention of everyone who loved the numbers. His explanation for the whole issue starts with the basics of how pixels build up an image:

Images are made up of little dots called pixels. Pixel stands for PICture ELement. Put enough of them together and you have a picture. They are arranged horizontally and vertically.

Resolution is how many pixels you have counted horizontally or vertically when used to describe a stored image. Digital cameras today have between 2,048 and 4,500 pixels horizontally. 3MP cameras have 2,048 pixels horizontally and 14 MP cameras have 4,500 pixels. They have fewer pixels vertically since the images aren’t as tall as they are wide. That’s not much of a difference, is it?

Pixel count, expressed as megapixels, is simply multiplying

the number of horizontal pixels by the number of vertical pixels. It’s exactly like calculating area. A three megapixel camera has 2,048 (horizontal) x 1,536 (vertical) pixels, or 3,145,728 pixels. We simply call this 3MP.

Small differences in pixel count, between say 5MP and 8MP, are unimportant because pixel counts are a square function. It’s exactly like calculating area or square footage. It only takes a 40 per cent increase in linear dimensions to double the pixel count. Doubling pixel count only increases the real, linear resolution by 40 per cent, which is pretty much invisible.

One needs about a doubling of linear resolution or film size to make an obvious improvement. This is the same as a quadrupling of megapixels. A simple doubling of megapixels, even if all else remained the same, is very subtle. The factors that matter, like colour and sharpening algorithms, are far more significant. The number of megapixels a camera sports has very little to do with how the image looks.