1. Automatic exposure method for use especially in a film-based mammograpmic apparatus, in which the object to be imaged is positioned in an imaging area, in which radiation source is. used to produce radiation for use in the imaging process, in which the radiation containing image information is dated by an image data receiving means and in which at least one imaging parameter is controlled during exposure, wherein the method comprises at least the following actions: modeling the radiation spectrum obtained from the radiation source of the imaging apparatus as a function of at least the essential operating parameters and production of radiation quanta, modeling in respect of attenuation of radiation at least some of the components of the imaging apparatus that may lie between the radiation source and the image data receiving means, and further of the possible other components that may lie in front of the exposure detector, modeling darkening of the image being detected by the image data receiving means as a function of radiation incident on it, determining thickness of the object to be imaged in the direction of the beam within the imaging area, beginning the exposure, measuring the signal obtained from the exposure detector and determining what object density relative to the modeled attenuation of radiation this signal corresponds to, and determining on the basis of the aforesaid modelings those changes in the imaging parameter values used for exposure, especially in exposure time, that are needed in order to reach the desired degree of darkening of the image with the object thickness and density in question, and adjusting said values accordingly.