Too many pixels

If I were to tell you that manufacturers of certain very popular electronic devices had a policy of producing newer, higher technology versions of their products at frequent intervals, you would, I am sure, be unsurprised. However, if I could show that some of these newer, “better” devices were actually inferior to their predecessors in some key respects, that might be news.

The technology, to which I am referring, is close to my heart: digital cameras …

How do you select a digital camera? Of course, there are many parameters that might drive you to choose a specific model, but I am sure that one thing you might consider is what is confusingly called the resolution – the number of megapixels used to capture an image. It might seem reasonable to assume that the more megapixels [i.e. the higher the resolution], the better the quality of the images would be. This is certainly what the camera manufacturers want you to believe. This means that, each time they “upgrade” a model by increasing the pixel count, customers are keen to part with their money. Sadly, this is not the way it is.

The first thing to do is think about how many megapixels do you need. If all you are doing is looking at images on the screen or projecting them using digital projector, one megapixel is quite satisfactory. However, maybe you want to crop out part of a captured image and just use that, so some extra pixels might come in handy, but I guess 4 megapixels would do the job. You might want to make prints. The size of most prints is 6″x4″. How many pixels do you want for that? It is generally agreed that you need about 300 pixels per linear inch, so this print would need 6x300x4x300 = about 2 megapixels. Perhaps a good compromise would be an 8 megapixel camera to cover all possibilities.

If you look at cameras on the market today, you would be hard pressed to find anything less than 16 megapixels. There is even a phone available with 24mpx, which seems like madness to me. It might not seem a problem having more pixels than you strictly need, but there are a number of reasons why too many pixels might be problem:

• The size of files grows drastically. Although memory cards are fantastically cheap nowadays, it still takes time to move large chunks of data around, so uploading to a computer is very slow. This becomes more of a problem if the data transfer is using up your allocation on your mobile data plan.
• Many cameras have tiny lenses, which just do not have the intrinsic resolution to render an image well enough for a high resolution camera sensor. The effect is to store the fuzziness of the image in faithful detail, which is no use to anyone.
• Last, if a very high resolution camera sensor is physically larger than its lower resolution predecessor, then it can indeed capture more image detail. However, it is quite common for the sensor to be no physically bigger, which means the pixels themselves are smaller. In electronic devices, the smaller the architecture of a component feature, the higher its propensity to “noise” – i.e. unwanted background signal. This manifests itself as “graininess” [i.e. uneven texture] and/or speckles of color in a digital image. The net result is extra pixels do not necessarily mean extra usable image resolution.

I am not belittling the fantastic achievements of the designers of modern digital cameras. They have come a long way in a very short time. I just wanted to bust the myth that more megapixels is always better. I do suspect that the camera manufacturers are exploiting that fact that most people regard a bigger number as an indication that something is better.

On another occasion, I will explain why the top of the range type of camera – digital single lens reflexes [DSLRs] – are not necessarily the best, just the most expensive.