AppGen: Interactive Material Modeling from a Single Image

晃晃

AppGen: Interactive Material Modeling from a Single Image

Yue Dong Xin Tong  Fabio Pellacini    Baining Guo

Tsinghua University  Microsoft Research Asia  Dartmouth College  Sapienza University of Rome





Abstract

We present AppGen, an interactive system for modeling materi-

als from a single image. Given a texture image of a nearly pla-

nar surface lit with directional lighting, our system models the de-

tailed spatially-varying reflectance properties (diffuse, specular and

roughness) and surface normal variations with minimal user inter-

action. We ask users to indicate global shading and reflectance in-

formation by roughly marking the image with a few user strokes,

while our system assigns reflectance properties and normals to each

pixel. We first interactively decompose the input image into the

product of a diffuse albedo map and a shading map. A two-scale

normal reconstruction algorithm is then introduced to recover the

normal variations from the shading map and preserve the geometric

features at different scales. We finally assign the specular param-

eters to each pixel guided by user strokes and the diffuse albedo.

Our system generates convincing results within minutes of interac-

tion and works well for a variety of material types that exhibit dif-

ferent reflectance and normal variations, including natural surfaces

and man-made ones.

CR Categories: I.3.7 [Computer Graphics]: Three-Dimensional

Graphics and Realism—Color, shading, shadowing, and texture;

Keywords: appearance modeling, user interaction

1 Introduction

Modeling Realistic Materials. The use of realistic materials is

necessary when rendering high-quality images. Measured materi-

als provide the highest quality datasets, but are cumbersome to use

in practice due to complex acquisition setups, lengthy measurement

times and the size of the generated data [Weyrich et al. 2009]. To-

day, the vast majority of applications use materials painstakingly

modeled by artists. Typically, artists start from a single texture

image, and use that to generate spatially-varying diffuse, specular

and roughness coefficients of an analytic reflectance model together

with a bump map to enrich the surface details. For many materials,

this process takes hours to perform, involving the use of image ma-

nipulation programs (e.g. photoshop), inverse shading tools (e.g.

CrazyBump), and shading networks in 3D software (e.g. maya).

Not only is this process cumbersome, but it often does not lead to

the highest quality materials since no robust method can be used to

easily derive detailed reflectance and normal maps from the image.

Fig. 3 shows two example materials generated by an experienced

artist in roughly one hour each, using the standard toolset that in-

cludes Photoshop and CrazyBump.

AppGen. In this paper, we present AppGen, an interactive system

for modeling material from a single image. We focus on modeling

spatially-varying reflectance (i.e. diffuse, specular and roughness

parameters) and normal variations from a texture image that is cap-

tured from a nearly planar surface lit by directional lighting. Such

images are easily found in texture collections since they are widely

used by artists when manually modeling materials. Our goal is not

to determine the exact reflectance and normals from such single

images, which is a well-known ill-posed problem. Instead, we are

interested in significantly speeding up the workflow of artists when

modeling such materials. Our key idea is that we can keep user

interaction minimal by asking the user to specify shading or re-

flectance information on a few pixels with sparse strokes, while our

algorithm efficiently infers the reflectance and normal details for

all pixels in the image. Fig. 1 shows one example of a material

modeled using our system with just a few user strokes. Note the

highly detailed, realistic look of the output material. Our experi-

enced artist was able to regenerate the example materials in Fig. 3

in a few minutes using AppGen.







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