Effective dynamic range measurement for a CCD in full-field industrial X-ray imaging applications

CCD cameras are widely used for different applications. Recently they are employed for imaging in industrial X-ray digital radiography or computed tomography inspections. Scientific grade CCD sensors are usually characterized for what concern defects (bad pixels), resolution capability, spectral sensitivity, dark current, pixel full well capacity and so on. In former times CCDs were mostly used in astronomy and dark current was one of the most important parameters to evaluate in this kind of applications because of the long exposure time needed to obtain a good image. Thus, most manufacturers still refer to noise of a CCD as the background (or dark current) noise. This might be in some cases misleading. When one wants to compute the effective dynamic range on the full scale of greylevels, in order to match with the correct number of bit required to quantize the information, and, most of all, to evaluate if the dynamics is adequate, a different analysis of noise is required. It is possible to find an experimental method to measure noise and to derive the effective intrinsic dynamic range of a CCD. A case study, carried out on a commercial CCD camera used in a prototype industrial CT system, is reported in this work and the experimental results are discussed.