The response/spatial frequency relation required to obtain an image sharpness enough for pictorial color hard copy is discussed at first, which is followed by an estimate of the level of sharpness achievable in color diffusion transfer process, using a computer simulation technique. The results are summarized below. 1. In a photothermographic system, such as Fujix Pictrography, an outstanding image sharpness is attained because of the shortened diffusion pathway. 2. Two substantial contributing factors on the image sharpness are the rate of dye adsorption to the mordant at the image-receiving layer and the diffusion length of the pathway from dye-releasing site to dye-trapping site. These computed predictions have been confirmed experimentally in the actual imaging.