Monday 29 June 2009

Digitising is NOT measuring

Measurement is an operationally defined process. It requires a well defined protocol that describes what is being measured by what means and with what level of reproducibility and an understanding of the error structure of the problem.

Digitising is the capture of digital data from a sensor. It is a new and low cost way of generating petabytes of data. However, simply taking an analogue input and transforming it to a digital image or signal does not mean it is a measurement.

There are millions and millions of digital images captured every day (perhaps billions). The vast majority of these are NOT measurements they are 'snapshots'. In order to use digital imagery as a measurement modality for science one needs to take care of magnification issues (not always equal in X-Y), linearity of grey scale response and/or colour response, bit depth, illumination set up to highlight features of interest, effect of image compression, frequency response of lenses used etc etc.