This paper proposes an improved six-color separation method that reduces the graininess in middle tone regions based on the standard deviation of lightness and chrominance in SCIELAB space. Graininess is regarded as the visual perception of the fluctuation of the lightness of light cyan and cyan or light magenta and magenta. In conventional methods, granularity is extremely heuristic and inaccurate due to the use of a visual examination score. Accordingly, this paper proposes an objective method for calculating granularity for six-color separation. First, the lightness, redness-greenness,
and yellowness-blueness of SCIELAB space is calculated, reflecting the spatial-color sensitivity of the human eye and the sum of the three standard deviations normalized. Finally, after assigning the proposed granularity to a lookup table, the objective granularity is applied to six-color separation , thereby reducing the graininess in middle tone regions.