The purpose of this paper is to improve the spatial resolution of scintillator X-ray image detectors. The spatial resolution of these detectors is lower than that of other direct conversion detectors because of the diffusion of visible light in the scintillator. This problem was solved by using a collimator manufactured from a silicon wafer. The silicon wafer was processed to make many small square holes in a grid pattern by a MEMS technique for the optical separation of visible light in the scintillator upon X-ray irradiation. Moreover, the structures of these grid holes were integrated with a silicon photodiode array to operate as a single detector. The properties of thallium-doped cesium iodide (CsI:Tl) depend on the Tl concentration. By optimizing the filling conditions of the scintillator for the silicon, collimator, the emission characteristics of CsI:Tl were adjusted to ensure their suitability for use with the Si photodiode, and the sealed state was observed by SEM and computed tomography (CT). CsI:Tl was encapsulated in a collimator under optimized conditions, and the improved spatial resolution was confirmed from the Modulation Transfer Function (MTF). The pixel-structured scintillator with a silicon collimator was successfully fabricated, and our method shows the high-spatial-resolution imaging performance of an indirect X-ray imaging detector.