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A uniform distribution of illumination radiance across the surface of objects of interest is desired for most scene analysis approaches, including that of photometric stereo. Either specially designed parallel illumination or distant point light sources have been used to fulfil this requirement. However, there can be significant practical difficulties in achieving such idealised parallel light sources in real world applications, where setup space may be constrained and only generally available lights and lighting condition are provided. To solve this important but often overlooked problem, a flat reference object is proposed to sample the uneven incident lighting condition in order to allow the illumination radiance factor at every individual pixel to be cancelled out for the given scene analysis task. Experiments show that the proposed strategy can improve the accuracy of the photometric stereo method for reconstructing nominally planar surfaces containing topographic relief, even when normal low-cost commercial light sources are used.