Recently, spatially varying Bidirectional Reflectance Distribution Functions (svBRDF) is widely used as a model to characterize the appearance of materials with varying visual properties over the surface. One of the challenges in image-based svBRDF capture systems rises for surfaces with high specularity and sparkles, which require a dynamic range higher than the dynamic range of cameras. High Dynamic Range Imaging (HDRI) for svBRDF systems with multispectral camera has not been addressed properly in the literature. In HDRI, Camera Response Function (CRF) plays a crucial role in the precision of results specially when measuring metrological data such as spectral svBRDF. In this work, we investigate the effect of CRF assessment on the precision of measurement. Therefore, we have conducted two experiments to measure absolute CRF using reflective chart method as well as estimate relative CRF by Debevec and Malik’s method for a filter wheel multispectral camera to be used in a svBRDF setup. Results are evaluated on two levels: radiance map construction and reflectance calculation, by comparing to telespectroradiometer measurements as ground truth data. Results showed that although the HDRI with measured absolute CRF outputs radiance measurements with the same physical units and in the same scale as ground truth data, HDRI with estimated relative CRF outperformed in terms of the precision of reflectance measurement.
Translucency is an important appearance attribute. The caustic patterns that are cast by translucent objects onto another surface encapsulate information about subsurface light transport properties of a material. A previous study demonstrated that objects placed on a white surface are considered more translucent by human observers than identical objects placed on a black surface. The authors propose the lack of caustics as a potential explanation for these discrepancies — since a perfectly black surface, unlike its white counterpart, does not permit observation of the caustics. We hypothesize that caustics are salient image cues to perceived translucency, and they attract the visual attention of the human observers when assessing translucency of an object. To test this hypothesis, we replicated the experiment reported in the previous study, but in addition to collecting the observer responses, we also conducted eye tracking during the experiment. This study has revealed that although gaze fixation patterns differ between white and black floor images, the objects’ body still attract most of the fixations, while caustics might be a cue of only secondary importance.
With the proliferation of smartphones and social networking services, the opportunities for individuals to take photographs have increased exponentially. In a previous study, the perceived gloss of an object was reduced by representing as a digital image compared with a real object. It is also known that image editing, such as lossy image compression, can reduce the glossiness of an image. Therefore, the glossiness of real objects may be easily changed in digital images; thus, a method for appropriately editing the gloss in digital images is required for post-processing. In this study, we proposed a gloss appearance editing method for various material objects in a single digital image. The proposed method consists of three steps: color space conversion, gloss detection, and gloss editing. The relationship between the proposed method and the respective reflection models of inhomogeneous objects, metallic objects, and translucent objects was analyzed. Consequently, we determined that the gloss editing of the proposed method is equivalent to editing the specular reflection component of an inhomogeneous object, the grazing reflection component of a metallic object, and the specular reflection component of a translucent object. We applied the proposed method to test images including objects of various materials and confirmed its effectiveness through a subjective evaluation by visual inspection and an objective evaluation using image statistics.