In this paper, we present the imaging parameters and compare both mercuric iodide (HgI2) and amorphous selenium (a-Se) films. Using MCNPX code, we designed the film structure and its thickness for the optimized detector in the diagnostic x-ray range. The mercuric iodide film was formed by a wet binder process, while the amorphous selenium film was deposited by physical vapor deposition (PVD). These deposition methods are capable of being scaled up to sizes required in diagnostic imaging applications. The electronic properties are investigated using dark current, x-ray sensitivity and signal to noise ratio (SNR). From our results, the developed HgI2 film as an alternative to a-Se photoconductor, which is in practical use in flat panel x-ray imaging detector, will prove its usefulness in the future design and the optimization for various diagnostic modalities.