To provide a composite image without a strange feeling by calculating an optimum resolution for attaining the theoretical limit of precision when the error of an image exists.

In the configuration grid pattern of a bluescreening back panel having an optimum grid pattern, an invariable compound ratio is used in camera see-through conversion which is calculated from four continuous points obtained by formulas I-IV in a progression consisting of a continuous dot string for generating the configuration grid pattern, the optimum progression is created in terms of establishment based on the establishment density with the condition of the compound ratio, which is decided by reducing an interval in proportion with an expectation error in a place with the large expectation error from a standard deviation which is obtained from a first approximation concerning the error of the compound ratio and, then, the bluescreening back panel is used, which is provided with the optimum grid pattern generated by two- dimensionally combining the optimum progression. Thus, in a process where a subject is photographed during a camera work in a studio camera, an optimum and stable camera parameter is estimated while analyzing the image.