Tone conversion characteristics of the digital still camera is not only one of the most important characteristics, but also used for a transformation from raw red, green and blue digital values to colorimetric values. Tone conversion characteristics are produced usually from measured digital values as a function of known luminance or reflectance of subject from the images including a gray scale. Instead, we developed a new method, which is based on working values of subject exposure calculated on the basis of the digital values of digital still camera of two images of the same subject formed at two different exposure levels whose ratio is known. Digital value between digital value pair, which are digital values for two image corresponding to same cumulative frequency, is calculated as a weighted average, and log relative exposure is integrated from digital value pair. Thus, log relative exposures and corresponding digital values are calculated, i.e. tone conversion characteristics are obtained without a gray scale. The calculated tone conversion characteristic by the new method was compared to a characteristic obtained conventionally from the gray scale. Again, a comparison of the two tone conversion characteristics demonstrates that they are almost identical except in the region of lower luminance where flare is effective and that the new method performed accurately. Using the tone conversion characteristic and a gray scale included in subject scene, influence of flare can be eliminated. Colorimetric values for color patches are calculated from the new process, in which the tone conversion characteristic determined by the new method was used and flare was eliminated, and the conventional process by using an analytical model. Average color difference for the new process was less than that for the other. From our studies, the new process has proven to be accurate and practical.