In the digital photography system, the tonal characteristics of the system is evaluated by Camera-Through Sensitometry as the traditional silver halide analog photography. During the camera-through sensitometry, the lightness data on the displayed image of lightness linear single color step chart on the CRT monitor showed linear relation to the input data level. The slope of that characteristics indicated the qualitative tone characteristics of digital still camera. It was also closely related to the tonal characteristics of reproduced object image on the photo-prints taken by DSC and printed by digital color printer.