This paper analyses the image homogeneity realized by recording the spatial distribution of the gas discharge light emission in an ionization-type infrared (IR) image converter with a gallium arsenide semiconductor photodetector. The image of the photodetector material which contains the internal inhomogeneities is studied thoroughly at the optimum converter condition in order to image the large-diameter photodetector plates (100 mm) for non-destructive analysis. The analysis of the image homogeneity is determined by the fractal dimension of the gas discharge light emission when a current is passed through a converter cell. The images are analysed using both the profile and spatial distribution light emission intensity data showing the internal inhomogeneity in the photodetector plate. Thus, by using the fractal concept, the image quality of the high-resistivity photodetector plate can be assessed exactly and the size and location of the internal inhomogeneities in the photodetector plate can be ascertained.