This paper describes the extended development process (extended process) that compensates for the image quality of mammographic film exposed at a lower radiation dose. First, we developed films exposed to a phantom with several small particles that simulated micro-calcifications at high and lower radiation doses, respectively. Next, we evaluated the image quality of those films developed for the standard development time of 90 seconds, and for the extended development times of 150 seconds and 210 seconds. Then we extracted micro-calcification regions and calculated the areas, perimeters, and normalized areas of micro-calcifications by using image analysis. There was no significant difference in areas or shape measurements between the development times of 90 seconds and 150 seconds in obtaining the same high-quality images as the standard process. Therefore, we determined that the development time of 150 seconds was the most appropriate time. As a result, we achieved a 20% reduction in radiation dose by using the extended process for mammographic film.