A Wider Angle:  June 2012, by Geoff Dickinson

You may or may not know that the image sensor at the heart of your digital camera is totally colour-blind.  All that the tiny photo-sensitive elements on the sensor measure, is just the intensity of the incoming light, not its wavelength which is what produces colour.  To produce the colours, an array of red, blue and green filters is placed in front of the elements. Software inside the camera then reconstructs the original scene through a process known as demosaicing.  In effect, the software takes a guess at the colour of each pixel based upon that of its neighbours to produce your final image.

This procedure can be problematic, however.  Fine details in the original are inevitably lost, especially at shapes’ edges, robbing the final image of sharpness.  False colours can pop up, ugly interference patterns emerge, caused by a clash between the repeated structure of the filter and patterns in the scene being captured.  Noise (random speckling caused by electronic fluctuations in the sensor’s circuitry) is also accentuated, especially under low light.  Crucially, all this number crunching takes time, causing a delay before the camera is ready to shoot again.  It’s a wonder we get any images at all.

Interesting but do we really need to know this stuff to take good photos?  Yes, is the answer for a couple of reasons.  First, if you are about to part with a sizeable wad of cash for your next camera, it helps if you can understand what you are actually looking at in the shop and reach a properly informed buying decision for the intended use.  That way you don’t end up with a lemon that frustrates the heck out of you when you come to take that once in a lifetime action shot and find you miss it because of shutter lag.  Eh? What’s that mean?  I’m not telling you.  Go and research it for yourself.

Secondly, if you know your digital camera’s technical limitations, you can then work round them.  For example?  Well, your camera is essentially a computer with a lens attached and you probably know that a computer works by flipping binary digits on and off.  You might say that everything is either black or white.  In practical terms, it means that compared to film, at its extremes, digital can have all the subtlety of a sledgehammer when you suddenly hit the tipping points and we lose all detail in whites and blacks.  Knowing the gap between these tipping points (the geeky expression is “dynamic range”) and exposing properly means you don’t end up with horrible blown highlights or speckly dark patches.

 See you around.  Geoff