A Physically‐Based Model for Rendering Realistic Scratches

Abstract

Individually visible scratches, also called isolated scratches, are very common in real world surfaces. Although their microgeometry is not visible, they are individually perceptible by the human eye, lying into a representation scale between BRDF and texture. In order to simulate this kind of scratches in synthetic images we need to know their position over the surface (texture scale), so we can determine where to use the specific scratch BRDF instead of the ordinary surface BRDF. Computing the BRDF of a scratch is difficult because it depends on the scratch's invisible microgeometry. In this paper, we propose a new physically based model to derive this microgeometry by simulating the formation process of scratches. We allow specifying intuitively the parameters involved in the process such as the scratching tool, the penetration forces, and the material properties of the object. From these parameters, we derive the microgeometries of the scratches by taking into account the real behaviour of the process. This behaviour has been determined by analysing existing models in the field of materials engineering and some "scratch tests" that we performed on metals. Our method has the advantages of easily simulating scratches with a wide range of microgeometries and taking into account the variability of their microgeometry along the scratch path. Another contribution is related to the location of the scratches over the surface. Instead of using an image of the paths as in previous work, we present a new representation based on curves defining the paths. This offers an independence on the image resolution or the distance from the observer and accurately provides the scratch direction in order to compute scratch BRDFs.

A method to create sculptures with Chinkin in the virtual space

“…Consideration of the tilt angle of a chisel in virtual Chinkin is one of the future works. To render more realistic images, the microgeometry of carved tracks should be considered [19]. In the real Chinkin, some different size of gold powder are used to change the style of works, and it is necessary to consider the difference of property of virtual gold powder for more realistic virtual Chinkin works.…”

Context-aware textures

“…-Mechanical processes involve the disintegration of a material into fragments or the transport and deposition of material, such as dirt and salts. Examples of mechanical stress and fracture include cracking and peeling [Hirota et al 1998[Hirota et al , 2000Chiba 2001a, 2001b;Aoki et al 2002;Paquette et al 2002], scratches [Mérillou et al 2001b;Bosch et al 2004], and impacts [Paquette et al 2001]. Examples of transport processes include dust accumulation [Hsu and Wong 1995] and flow ].…”

Real-time path-based surface detail

“…In our approach, details are modeled using a representation based on paths and cross-sections in texture space, similar to the one described by Bosch et al [BPMG04]. Such a representation is very compact and can be easily applied to any surface having a texture parametrization, without the need of reprojecting the paths between different surfaces.…”

“…The texture specifies the position and path of each feature over the surface, and is represented by an image with the features painted on it. Examples are the works by Mérillou et al [MDG01] and Bosch et al [BPMG04]. Bosch et al [BPMG08] propose a method to encode and render grooves similar to ours, but their method is much slower than the one presented here and not feasible to be used in real-time applications.…”