An Evaluation Framework for the Accuracy of Camera Transfer Functions Estimated from Differently Exposed Images

Abstract

Intensity values read from CCD- or CMOS-cameras are usually not proportional to the irradiance acquired by the sensor, but are mapped by a mostly nonlinear camera transfer function (CTF). This CTF can be measured using a test chart. This, however, is afflicted with the difficulty of ensuring uniform illumination of the chart. An alternative to chart-based measurements of the CTF is to use differently exposed images of the same scene. In this paper, we describe a radiometry-based experimental setup to directly measure the CTF. We furthermore show how to obtain image pairs of known exposure ratios from the same experiment, i.e., under identical environmental circumstances (light, temperature, camera settings). We use these images to estimate the CTF on differently exposed images, thus enabling a quantitative comparison of estimated and measured CTF