Specular Highlights Research Articles

The perception and discrimination of global 3-D shape from the deformations of texture, shading, and specular highlights

The perception and discrimination of global 3-D shape from the deformations of texture, shading, and specular highlights

Automatic Segmentation and Inpainting of Specular Highlights for Endoscopic Imaging

Minimally invasive medical procedures have become increasingly common in today's healthcare practice. Images taken during such procedures largely show tissues of human organs, such as the mucosa of the gastrointestinal tract. These surfaces usually have a glossy appearance showing specular highlights. For many visual analysis algorithms, these distinct and bright visual features can become a significant source of error. In this article, we propose two methods to address this problem: (a) a segmentation method based on nonlinear filtering and colour image thresholding and (b) an efficient inpainting method. The inpainting algorithm eliminates the negative effect of specular highlights on other image analysis algorithms and also gives a visually pleasing result. The methods compare favourably to the existing approaches reported for endoscopic imaging. Furthermore, in contrast to the existing approaches, the proposed segmentation method is applicable to the widely used sequential RGB image acquisition systems.

On a Methodology for Robust Segmentation of Nonideal Iris Images

Iris biometric is one of the most reliable biometrics with respect to performance. However, this reliability is a function of the ideality of the data. One of the most important steps in processing nonideal data is reliable and precise segmentation of the iris pattern from remaining background. In this paper, a segmentation methodology that aims at compensating various nonidealities contained in iris images during segmentation is proposed. The virtue of this methodology lies in its capability to reliably segment nonideal imagery that is simultaneously affected with such factors as specular reflection, blur, lighting variation, occlusion, and off-angle images. We demonstrate the robustness of our segmentation methodology by evaluating ideal and nonideal data sets, namely, the Chinese Academy of Sciences iris data version 3 interval subdirectory, the iris challenge evaluation data, the West Virginia University (WVU) data, and the WVU off-angle data. Furthermore, we compare our performance to that of our implementation of Camus and Wildes's algorithm and Masek's algorithm. We demonstrate considerable improvement in segmentation performance over the formerly mentioned algorithms.

Specular Highlights as a Guide to Perceptual Content

This article is a contribution to a recent debate in the philosophy of perception between Alva Noë and Sean Kelly. Noë (2004) has argued that the perspectival part of perception is simultaneously represented along with the non-perspectival part of perception. Kelly (2004) argues that the two parts of perception are not always simultaneously experienced. Here I focus on specular highlights as an example of the perspectival part of perception. First I give a priori motivation to think that specular highlights are experienced at the same time as non-perspectival properties, which challenges Kelly's position. Then I discuss psychophysical work by Andrew Blake and Heinrich Bülthoff (1990) which seems to show that specular highlights are not represented in the way that Noë (2004) would suggest. In the third section I suggest a compromise between Noë and Kelly: specular highlights are not represented, but rather play an evidentiary role in the representation of perspective-independent properties, like gloss and shape. I conclude with some thoughts about how this study can generalize to other kinds of experience.

Writing impressions revealed by scanners.

Heavily impressed writing impressions in paper and impressions in glossy brochures are often difficult or impossible to develop using the electrostatic detection apparatus (ESDA, manufactured by Foster and Freeman). Oblique and specular reflectance lighting can be used but they are time-consuming techniques and not always very successful. This paper briefly describes a scanning and image-processing method for producing excellent images of such writing impressions.

The Reproduction of Specular Highlights on High Dynamic Range Displays

The Reproduction of Specular Highlights on High Dynamic Range Displays

Perception of three-dimensional shape from specular highlights, deformations of shading, and other types of visual information.

There have been numerous computational models developed in an effort to explain how the human visual system analyzes three-dimensional (3D) surface shape from patterns of image shading, but they all share some important limitations. Models that are applicable to individual static images cannot correctly interpret regions that contain specular highlights, and those that are applicable to moving images have difficulties when a surface moves relative to its sources of illumination. Here we describe a psychophysical experiment that measured the sensitivity of human observers to small differences of 3D shape over a wide variety of conditions. The results provide clear evidence that the presence of specular highlights or the motions of a surface relative to its light source do not pose an impediment to perception, but rather, provide powerful sources of information for the perceptual analysis of 3D shape.

Lightness constancy in the presence of specular highlights.

Visible surfaces in a natural environment often have multiple components of reflectance, including a diffuse component, by which light is scattered isotropically in all possible directions, and a specular component, by which light is reflected anisotropically within a limited range of directions. The research described in the present article was designed to investigate how these different components of reflectance influence the perception of lightness. Human observers were presented with shaded images of smoothly curved surfaces and asked to compare the relative lightness of different surface regions whose diffuse and specular components of luminance were independently manipulated. The results revealed that observers are able to discount the presence of specular highlights so that the relative lightness among different regions is determined almost entirely by the diffuse component of surface reflectance.

Interactive examination of surface quality on car bodies

The use of reflection lines and specular high lights for the quality control of car body surfaces is an important issue in the development process of a car. The interactive examination is based on standard graphics tools such as the SceneViewer of OpenInventor which simulates reflection lines by using striped environment maps. The interpolation of texturing and shading values is critical and requires high quality meshes. Thus, element shape and size are essential. In this paper we present a new technique for the tessellation of trimmed surfaces. The result of the algorithm is a 2-manifold mesh with a low triangle count and a triangulation pattern which is best suited for the visualization.

Robust Vergence with Concurrent Identification of Occlusion and Specular Highlights

The early detection, classification, and elimination of occlusion and specular highlights which occur frequently in real scenes are of utmost importance. However, most of vergence algorithms which have been proposed in recent years do not take into consideration the effect of occlusion and specular highlights present in real scenes. In this paper, we propose an active exploratory vergence method based on concurrent cross-correlation of multiscale stereo images and an adaptive feedback strategy using weighted normalized cross-correlation to detect and distinguish occlusion and specular highlights concurrently during the vergence process. It not only improves computational efficiency but also leads to the exploration of a better viewing direction and position that overcome the problem created by occlusion and specular highlights. The robustness of the proposed method against occlusion and specular highlights is demonstrated with real scenes.