Camera Calibration Technical Report:
Glare

Glare

It should be noted that the calibration method described is concerned with the calibration of the camera and digitisation devices only, and takes no account of optical characteristics of the microscope, such as the glare.

A widely accepted model [6] characterises glare by a parameter F defined as the intensity of additive glare as a fraction of the illuminating intensity. For many applications this model is appropriate and for completeness we include the appropriate formulae here. The parameter depends on the proportion of background illumination in the microscope field and nature of the sample to be measured. In many applications it is a reasonable approximation to assume that the sample occupies a negligible proportion of the field and the glare parameter can then be obtained for a particular microscope setup by measuring the apparent OD of a microscopic slide object (eg soot particle) which can be assumed to be black. Writing the apparent OD of the black object as $\rho_b$ we have:

$$F = 10^{-\rho_b}$$

and the true OD, $\rho_t$ of an object having an apparent OD $\rho_a$ is given by

$$\rho_t = \log_{10} \left( \frac{1-F}{10^{-\rho_a} - F} \right).$$

This glare correction may be applied after the OD correction if required.