Abstract: RMS-granularity is an important characteristic of photographic image quality.Measuring RMS-granularity by microdensitometer-computer system is the most advanced method nowaday.Auto-sampling and programmed calculation make the measuring to be fast and convenient.However,a completely wrong result may be occured if some points are not properly handled during processing.The relationships between the RMS-granularity and instrumental system noise,the ununi-formity of sample macrodensity,the sampling interval of image digitalization were studied.As a result,it indicates that various disturbances may be removed and a correct estimating value of RMS-granularity can be obtained if the appropriate parameters and program are selected.In the meantime,the RMS results were compared by using digital simulating optical aperture and real optical aperture,and got some results valuable in application.

Key words: RMS granlarity, system noise, digital filtration, sampling interval