The relationship between signals and graininess on radiographs is discussed. It has been reported that the signals are reproduced by Fourier inverse transform even though the spectra of signals are cut off. For this reason, it is considered that the intensity of light which is transmitted through films produces the products of the signals and the radiographic mottles. However, the following could be obtained experimentally: those products which are produced by the signals are the grains of films from the radiographic mottles, and the brightness of reproduced images is related to the size of grains.