X-ray image intensifiers are applied where low dose X-ray images have to be observed. The modulation transfer function, the veiling glare figure and the noise power factor are important characteristics of the performance of X-ray image intensifiers. The relationship between noise and sharpness can fruitfully be used to measure the sharpness in terms of the spatial noise equivalent bandwidth. Methods are described for measuring MTF, spatial bandwidth, veiling glare and noise power factor of X-ray image intensifiers. Suggestions are made for the use of these imaging characteristics in the development of X-ray image intensifiers and X-ray image intensifying systems.