Use of non-photorealistic rendering and photometric stereo in making bas-reliefs from photographs

Automatic bas-relief generation from 2D photographs potentially has applications to coinage, commemorative medals and souvenirs. However current methods are not yet ready for real use in industry due to insufficient artistic effect, noticeable distortion, and unbalanced contrast. We previously proposed a shape-from-shading (SFS) based method to automatically generate bas-reliefs from single frontal photographs of human faces; however, suppression of unwanted details remained a problem. Here, our experimental results show how incorporating non-photorealistic rendering (NPR) into our previous framework enables us to both suppress unwanted detail, and yet also emphasise important detail. We have also experimented with an alternative approach to recovering relief shape, using photometric stereo instead of SFS for surface orientation estimation. This can effectively reduce the computational time.