The Generation Method Of 3D Sunken-relief Of Human Faces

Relief is a combination of sculpture and painting.As an art form that connects two-dimensional painting and three-dimensional sculpture,it has been active in the industry design since ancient times.Relief has been widely used in architectural decoration and daily necessities,bringing colorful artistic expressions to all occupations.With the improvement of the artisanship and the rapid development of computer technology,the form of relief has constantly updated.The contents,materials and forms of relief are rich and varied.The content of reliefs includes characters,animals,etc.The materials of reliefs include stone,wood,ivory,metal,etc.According to the different degrees of the depth of the carving object,the reliefs can be divided into four categories:high-relief,medium-relief,bas-relief and sunken-relief.The use of lines to express and enhance the shape of three-dimensional objects is one of the important research directions in the field of relief.As an important part of the sunken-relief,lines are used to depict the outl:ine and characteristic details of the relief,which plays a very important role in the formation of the relief.In the past few years,line-based shape depiction has been a hot topic in the field of non-photorealistic rendering(NPR).Researchers have made great progress in the definition of line and stroke style,which provides theoretical and technical support for computer-aided generation of sunken-reliefs and lays a solid foundation[1].However,the current processing of NPR line drawing and the use of computer-aided manufacturing techniques for 3D relief modeling are mainly focused on the generation of bas-relief[2].The algorithms in the field of sunken-relief are less and mainly focus on the use of a single line to express sunken-relief without considering the illumination information.This limitation makes the sunken-relief tedious and cannot present a more realistic sense of the original model.Therefore,in order to solve these problems,in this paper,we propose a line-based 3D sunken-relief generation method that considers the influence of light direction on the width and depth of the engraved lines.The main works of this paper are summarized as follows:1.Combining the knowledge of face field and considering the characteristics of different types of feature lines such as silhouettes(S),suggestive contour(SC),and apparent ridge(AR)and so on,we establish appropriate type of feature lines for the depiction of human faces',characteristics.Specifically,through comparative calculation and analysis,several feature lines that are suitable for facial feature expression are initially extracted.After being eliminated and processed,the feature lines of the sunken-relief are formed.2.In view of the limitation that the current engraving line of sunken relief doesn't consider the influence of illumination,line orientation and other factors on the width and depth of the engraved line,we comprehensively consider the normal,curvature,illumination information on the three-dimensional feature lines to establish a reasonable expression of the depth and width of engraving line.Specifically,the width of the engraving line is generated according to the line direction and the illumination direction,and the depth image of feature line is generated in combination with the stroke form of sunken-relief.3.Aiming at the engraving characteristics of decorative lines and contour shadows of sunken-relief,and combining the expressions of facial feature lines,we propose an algorithm for generating sunken-relief.Firstly,the height field of the 3D face model is compressed,and a concave embossed base mesh which maintains the height hierarchy of the original model is generated.Then,the information of the engraved line is added to base mesh,thereby generating the sunken-relief quickly and accurately.4.Based on GPU,we propose a fast sunken-relief generation algorithm based on image space.Experimental results show that the sunken-relief generated by our method can better express the facial features and reflect the illumination changes under different light direction,resulting in a more visually pleasing piece of art.