In a converting method relating to picture luminance according to one aspect of the present disclosure, the picture luminance is formed by luminance values in a first luminance range. In this method, a first luminance signal that indicates code values obtained by quantizing the luminance value of the picture is obtained, code values, which are associated with the code values indicated by the obtained first luminance signal by quantization for a second luminance range different in a maximum value from the first luminance range are determined as converted code values, and the first luminance signal is converted into a second luminance signal indicating the converted code values. As a result, the converting method is further improved.