The search for more realism in renderings led to increased interest in tabular bidirectional reflectance distribution function (BRDF) samples captured from real-world materials. This representation provides a high degree of realism at the cost of a long acquisition time and high storage space. Because of those drawbacks, the literature presents few BRDF databases captured from real materials, and the available ones present a limited number of samples. Aiming to create new and realistic-looking materials, this work proposes an approach to generate new BRDFs from a tabular BRDF database. Our goal is to provide a pipeline where the user expresses appearance necessities by selecting materials from a BRDF database. We generate an appearance-driven space shaped by the user’s interests, in which it is feasible to navigate and retrieve new tabular BRDFs. This new space should enable smooth navigation and, to provide visual richness and realism, not rely only on the materials selected by the user. To this end, we first preprocess a tabular BRDF database by keeping BRDF samples with relevant reflectance features. A low-dimensional representation of this preprocessed database is obtained by applying a dimensionality reduction method, and a clustering algorithm is applied to obtain clusters of materials with similar features. Based on the materials selected by the user, we define one or more clusters of materials to build the appearance-driven space. Any point in this lower-dimensional space can be mapped to the original BRDFs space. Therefore, new BRDFs that present similar properties to the ones which the user selected are created. We compare the performance of linear (Multidimensional Scaling - MDS) and nonlinear (Isometric Feature Mapping - ISOMAP) dimensionality reduction methods in this task and analyze the obtained materials.

在渲染中寻求更逼真的效果导致人们对从真实世界材料中捕获的表格双向反射分布函数 (BRDF) 样本的兴趣增加。这种表示以较长的采集时间和较高的存储空间为代价提供了高度的真实感。由于这些缺点，文献中几乎没有从真实材料中捕获的 BRDF 数据库，可用的数据库提供的样本数量有限。为了创建新的和逼真的材料，这项工作提出了一种从表格 BRDF 数据库生成新 BRDF 的方法。我们的目标是提供一个管道，用户可以通过从 BRDF 数据库中选择材料来表达外观需求。我们生成了一个由用户兴趣塑造的外观驱动空间，在其中导航和检索新的表格 BRDF 是可行的。这个新空间应该能够实现流畅的导航，并提供丰富的视觉效果和真实感，而不仅仅依赖于用户选择的材料。为此，我们首先通过保留具有相关反射特征的 BRDF 样本来预处理表格 BRDF 数据库。通过应用降维方法获得该预处理数据库的低维表示，并应用聚类算法获得具有相似特征的材料簇。根据用户选择的材料，我们定义一个或多个材料集群来构建外观驱动的空间。这个低维空间中的任何点都可以映射到原始 BRDF 空间。因此，创建了与用户选择的那些具有相似属性的新 BRDF。