An image rendering apparatus includes processing circuitry to obtain a volumetric medical imaging data set representative of a region of a material； associate one particular extinction color with the material； determine, based on the particular extinction color, a chromatic attenuation profile representative of color value as a function of intensity and as a function of depth in the material, the chromatic attenuation profile showing how the material having the particular extinction color changes in appearance with changes in the depth； obtain, from a user, a color value； determine a modified extinction color for the material based on the color value obtained from the user； and render a global illumination image from the volumetric medical imaging data set using the modified extinction color.
