1. A polychromatic reproduction procedure for obtaining a reproduction having a plurality of shading degrees for each primary color in the polychromatic system characterized by the fact that only one mask capable of being stripped is required to reproduce all the shading degrees for each primary color, said mask having recorded thereon areas to be shaded a plurality of shading degrees and serving sequentially as the mask for the areas to be most densely shaded and upon stripping as the mask for the areas to be shaded the remaining shading degrees, said procedure comprising: stripping said mask of the areas to be most densely shaded, placing said mask on said light-sensitive film and underexposing said film to light to form underexposed areas corresponding to the areas to be most densely shaded; subsequently stripping said mask of the next densest area, replacing said mask on said film and again underexposing said film to light such that the areas to be most densely shaded are again exposed and in addition underexposed areas are formed on said film corresponding to the next densest areas in said mask; repeating said stripping and underexposing for each of the plurality of shading degrees, each time reexposing the denser areas and forming underexposed areas corresponding to the newly stripped dense area in said mask.