A ray tracing kernel calibration procedure for the film simulation mode of digitized tomosynthesis in which the coordinate of the source position with respect to an energy source, e. This titanium alloy can be used in a variety of products, which are required to exhibit a low Young’s modulus, a high elastic deformability and a high strength, in a variety of fields. 5:1 relative to the upper layer. When the last developing operation is executed at an ordinary speed, whereafter next developing operation is executed at a low speed, a toner image of predetermined density is formed, and the density of this toner image is detected by an image density sensor.