Towards fully automated precise measurement of camera transfer functions

The mapping of incident irradiance to sensor output value, the so-called camera transfer function (CTF), of CCD or CMOS imaging devices is in general a non-linear function. Applications that utilize the camera as a measurement device for the incident irradiance, e.g DNA image cytometry for early cancer detection or HDR imaging, require a linear CTF. Thus, this non-linearity has to be corrected. This, in turn, requires the non-linear CTF to be estimated or measured. In this paper we present a radiometric measurement setup. We point out a particular problem, i.e., the calibration of the distance offset between sensor and light source. We then show a solution which integrates this calibration into the measurement process, enabling a fully automated measurement of the CTF.