All You Wanted to Know about Noise

Noise is probably the most dreaded word in digital photography! Manufacturers of cameras, doubtless devote considerable resources and time to reduce this unwanted guest. So do photographers like us. There are innumerable articles in print and on the Net on this topic, usually with the catchy title “Noise about Noise” or something like that. Most, unfortunately, do just that — add to the confusion. Recognising this problem, we at Smart Photography bring to you this concise article that deals with all the important aspects of this nettlesome subject. So read on!

What is noise? By the simplest definition it is something that alters and thus corrupts what you want. If you are talking to your friend at a busy street corner, then any sound other than from your conversation will disturb you and as you have guessed, this can be called noise. Those who study science are told that any ‘unwanted’ signal contributes to ‘noise’ as it corrupts the signal you want. As photographers, we want artefacts (things that are not originally in the scene that is being captured) to be absent in our captured image as these degrade the overall quality. Noise in images does just that — it adds something that is not there originally. In fact, noise has two components, called ‘chroma’ and ‘luminance’. The former causes pixels of uneven colour resulting in coloured blotches (mottling) (Picture 1). The latter gives rise to uneven brightness of pixels that cause grain (Picture 2) like features, when you were expecting a smooth result. Most popular editing packages like Photoshop or Lightroom have commands with very advanced algorithms to reduce both these types of noise. Most cameras too have in-built settings that do the same albeit with less sophistication. Another way to reduce noise is to take multiple images of the same scene and then process them together to reduce noise (refer to April ’18 issue). These topics have been discussed in detail in earlier. All deal with