Proc. SPIE. 6057, Human Vision and Electronic Imaging XI
KEYWORDS: Statistical analysis, Human subjects, Visual process modeling, Visualization, Fourier transforms, Computer science, Human vision and color perception, Image classification, Computer graphics, Electronic imaging
This paper presents some insights into perceptual metrics for texture pattern categorization. An increasing number of researchers in the field of visualization are trying to exploit texture patterns to overcome the innate limitations of three dimensional color spaces. However, a comprehensive understanding of the most important features by which people group textures is essential for effective texture utilization in visualization. There have been a number of studies aiming at finding the perceptual dimensions of the texture. However, in order to use texture for multivariate visualization we need to first realize the circumstances under which each of these classification holds. In this paper we discuss the results of our three recent studies intended to gain greater insight into perceptual texture metrics. The first and second experiments investigate the role that orientation, scale and contrast play in characterizing a texture pattern. The third experiment is designed to understand the perceptual rules people utilize in arranging texture patterns based on the perceived directionality. Finally, in our last section we present our current effort in designing a computational method which orders the input textures based on directionality and explain its correlation with the human study.
Studies have shown that observers' judgment of surface orientation and curvature is affected by the presence of surface texture pattern. However, the question of designing a texture pattern that does not hide the surace information nor does convey a misrepresentation of the surface remains unsolved. The answer to this question has important potential imapct across a wide range of visualization application. Molecular modeling and radiation therapy are among the many fields that are in need of accurately visualizing their data and could benefit from such methods. Over the past several years we have carried out a series of experiments to investigate the impact of various texture pattern characteristics on shape perception. In this paper we report the result of our most recent study. The task in this study was adjusting surface attitude probes under three different texture conditions and a control condition in which no texture was present. We later compare the performances of the subjects. The three texture conditions were: a doubly oriented texture in which approximately evenly spaced lines followed both of the principal directions, a singly oriented texture in which lines followed only the first principal direction, and a singly oriented line integral convolution. Over a series of 200 trials (4 texture conditions, 10 surface probe locations * five repeated measures) a total of five naive participants were asked to adjust a circular probe. The probes were randomly located on an arbitrary curved surface and its perpendicular extension appeared to be oriented in the direction of the surface normal. An analysis of the results showed that the performance was best in the two directional texture condition. Performances were further decreased in one directional and no texture conditions (in that order). The paper is organized as follows. In Section 1 we briefly describe the motivation for our work. In Section 2 we describe our experimental methods, including a brief summary of the process of the stimuli preparation and a detailed presentation of statistic analysis of our experimental results. In Section 3 we discuss the implications of our findings and in the last section we will talk about our future plans.
If we could design the perfect texture pattern to apply to any smooth surface in order to enable observers to more accurately perceive the surface's shape in a static monocular image taken from an arbitrary generic viewpoint under standard lighting conditions, what would the characteristics of that texture pattern be? In order to gain insight into this question, our group has developed an efficient algorithm for synthesizing a high resolution texture pattern, derived from a provided 2D sample, over an arbitrary doubly curved surface in such a way that the orientation of the texture is constrained to follow a specified underlying vector field over the surface, at a per-pixel level, without evidence of seams or projective distortion artifacts. In this paper, we report the findings of a recent experiment in which we attempt to use this new texture synthesis method to assess the shape information carrying capacity of two different types of directional texture patterns (unidirectional and bi-directional) under three different orientation conditions (following the first principal direction, following a constant uniform direction, or swirling sinusoidally in the surface). In a four alternative forced choice task, we asked participants to identify the quadrant in which two B-spline surfaces, illuminated from different random directions and simultaneously and persistently displayed, differed in their shapes. We found, after all subjects had gained sufficient training in the task, that accuracy increased fairly consistently with increasing magnitude of surface shape disparity, but that the characteristics of this increase differed under the different texture orientation conditions. Subjects were able to more reliably perceive smaller shape differences when the surfaces were textured with a pattern whose orientation followed one of the principal directions than when the surfaces were textured with a pattern that either gradually swirled in the surface or followed a constant uniform direction in the tangent plane regardless of the surface shape characteristics. These findings appear to support our hypothesis that anisotropic textures aligned with the first principal direction may facilitate shape perception, for a generic view, by making more, reliable information about the extent of the surface curvature explicitly available to the observer than would be available if the texture pattern were oriented in any other way.