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

Abstract

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.

Computer‐assisted Relief Modelling: A Comprehensive Survey

“…Current methods producing acceptable reliefs are developed according to their application scenarios, utilizing the characteristics of and constraints from the application domain, e.g. modelling of frontal human faces [WMR∗13] [WMR∗14], Chinese calligraphies [ZCL∗18], brush paintings [FYY∗18], and modelling from rubbing images [LWYM12]. Despite the strong binding with applications, interactive inputs from users are usually required as well to guide the modelling process.…”

“…Modelling reliefs from images has wider applications than object‐space modelling because of the ubiquitous availability and easy acquisition of 2D images. The reviewed works have demonstrated applications in coinage [WMR∗13] [WMR∗14], archaeology [KLST11] [LWYM12], arts [ZCL∗18] [FYY∗18], cartoons [SKJ∗14] [DNJ∗18] and sensory substitution [RMP11], [FGV∗14] where relief modelling provides a means for visual impaired people to appreciate photos and artworks in 2D. For the purpose of sensory substitution, the modelling method is required not only to create a 3D‐like model, but also to ensure the recovered depth can effectively convey visual information.…”

Normal‐Based Bas‐Relief Modelling via Near‐Lighting Photometric Stereo

“…Moreover, some techniques generate bas‐reliefs from natural images [AM10, LWYM12, WMR*13, WMR*14], because 2D images are much easier and less expensive to be captured. However, these algorithms often do not work for objects with complex materials.…”

“…phthisis caused by the inhalation of crystalline silica dust generated from stone, metal and wood carving). Subsequently, bas‐reliefs can be modelled digitally from images by human–computer interactions [AM10, LWYM12, WMR*13, WMR*14, GCF*14, YHJ*17]. However, these approaches could not handle objects with complex materials, due to the fact that colour, luminance and texture in an image could not properly reflect the geometric attributes of a 3D scene.…”

From 2D to 2.5D i.e. from painting to tactile model

“…Explicitly dealing with relief reconstruction from single images, some significant studies can be found in literature, especially dealing with coinage and commemorative medals (see for instance [10,11]). In most of the proposed approaches the input image, often representing human faces, stemmas, logos and figures standing out from the image background are translated into a flat bas-relief by adding volume to the represented subjects.…”