After writing two articles on the Nature of Light and its relevance to digital photography, I found that the subject of noise still fascinated me and decided that I had to make some measurements. Looking at the wiggly waveforms of my previous article might indicate that camera A is noisier than camera B but can we measure the noise in a rigorous way? This present article explains how to do that using free software. As well as presenting graphs of the measurements I have attempted to explain the results from physical principles – and evidently the noise is predominantly photon noise (aka shot noise).
In the second of two articles I look at another natural phenomenon, photon noise (also known as Shot noise). As with diffraction blur, the problem becomes more serious as the physical size of the sensor is reduced.
Whilst this is not the only source of noise, it is now the dominant one in the darker areas of an image where only a relatively small number of photons are incident on the sensor. It is the counting of photons, which is subject to Poisson statistics, which produces the noise.
I have devised a method of measuring gamma without the need for special equipment – a way of setting up a display which is independent of the operating system. Commercial profiling systems don’t seem to provide software for Ubuntu (Linux).
There are several charts and applets on the web which rely on subjectively matching stripes and grey patches but whilst my method uses the same principle the match is based on measured luminance rather than on human judgement.
The method uses test targets displayed in Photoshop (or other image/graphics processing application) – which has the advantage of predictable colour management – and hardware costing about £10 (US $16) including the meter!
I have just added a page describing the system. Have a look and feel free to comment.