Bidirectional reflectance distribution functions (BRDFs) describe how light interacts with a point on a surface. To propose a new BRDF formulation or to compare different reflectance representations, it is necessary to confront the results obtained with those functions against previous work or measured data. Despite the importance of using reliable techniques to evaluate a BRDF, there is a lack of works in the literature that gathers and compares those. This paper proposes a compilation of techniques used to evaluate BRDF representations along with their formal definitions. Those techniques were classified into three different groups—comparison functions, rendered images, and plots—and, to illustrate their use, three classical and widely adopted models and one state-of-the-art BRDF representation were evaluated regarding their capacity to preserve the appearance of measured materials. Based on our research regarding comparison functions, a stable and robust BRDF evaluation technique is proposed. It has been observed during both literature review and experiments that each group of techniques provides complementary information about the evaluated BRDFs, which suggests that at least one model from each category should be adopted during the choice of criteria to evaluate a BRDF.

双向反射率分布函数（BRDF）描述了光如何与表面上的点相互作用。要提出新的BRDF公式或比较不同的反射率表示形式，必须将使用这些功能获得的结果与以前的工作或测量数据进行比较。尽管使用可靠的技术评估BRDF的重要性，但文献中缺乏收集和比较这些文献的著作。本文提出了用于评估BRDF表示形式及其正式定义的技术的汇编。这些技术被分为三个不同的组-比较函数，渲染的图像和曲线图-为了说明其用途，评估了三种经典且被广泛采用的模型和一种最先进的BRDF表示形式，以保持被测材料的外观。基于我们对比较函数的研究，提出了一种稳定而强大的BRDF评估技术。在文献综述和实验过程中都观察到，每组技术都提供了有关被评估的BRDF的补充信息，这表明在选择标准以评估BRDF时，应至少使用每个类别的一个模型。