Micro-columnar CsI(Tl) is the most popular scintillator material which is used for many indirect digital X-ray imaging
detectors. The light scattering at the surface of micro-columnar CsI(Tl) scintillator was studied to find the correlation
between the surface roughness and the resultant image resolution of indirect X-ray imaging detectors. Using a commercially
available optical simulation program, Light Tools, MTF (Modulation Transfer Function) curves of the CsI(Tl) film thermally
evaporated on glass substrate with different thickness were calculated and compared with the experimental estimation of
MTF values by the edge X-ray image method and CCD camera. It was found that the standard deviation value of Gaussian
scattering model which is determined by the surface roughness of micro-columns could certainly change the MTF value
of image sensors. This model and calculation methodology will be beneficial to estimate the overall performance of
indirect X-ray imaging system with CsI(Tl) scintillator film for optimum design depending on its application.