Shading method for volumetric imaging

A medical image processing apparatus comprises processing circuitry configured to: obtain volumetric data corresponding to a three dimensional region of a subject; perform a sampling process that comprises sampling the volumetric data at a plurality of sampling points along a plurality of sampling paths; for each of a plurality of intervals between sampling points on sampling paths, determine a position of a shading evaluation point in the interval based on intensity values and/or opacity values for a front sampling point and back sampling point of the interval; and determine a value for a shading parameter at the determined shading evaluation point; and perform a rendering process using the determined values for the shading parameter.