The content of processing of an input image signal varies depending upon the conditions of an apparatus. In view of the fact that this results in the variations of correlation between tone data and toner consumption, a coefficient by which an integration value of the tone data is defined according to the content of the signal processing. In an image forming apparatus which performs tone correction as the signal processing and which has a characteristic (2) of forming images of higher densities relative to tone levels, for example, a larger amount of toner is consumed. Therefore, the coefficient of the apparatus is defined to be a higher value than that of an apparatus having a substantially linear characteristic (1). Conversely, in the case of an apparatus having a characteristic (3) of forming images of lower densities, thus consuming less toner, the coefficient is defined to be a lower value.