Sunghwan Choi

Fast global image smoothing based on weighted least squares.

This paper presents an efficient technique for performing a spatially inhomogeneous edge-preserving image smoothing, called fast global smoother. Focusing on sparse Laplacian matrices consisting of a data term and a prior term (typically defined using four or eight neighbors for 2D image), our approach efficiently solves such global objective functions. In particular, we approximate the solution of the memory- and computation-intensive large linear system, defined over a d -dimensional spatial domain, by solving a sequence of 1D subsystems. Our separable implementation enables applying a linear-time tridiagonal matrix algorithm to solve d three-point Laplacian matrices iteratively. Our approach combines the best of two paradigms, i.e., efficient edge-preserving filters and optimization-based smoothing. Our method has a comparable runtime to the fast edge-preserving filters, but its global optimization formulation overcomes many limitations of the local filtering approaches. Our method also achieves high-quality results as the state-of-the-art optimization-based techniques, but runs ~10-30 times faster. Besides, considering the flexibility in defining an objective function, we further propose generalized fast algorithms that perform Lγ norm smoothing (0 <; γ <;2) and support an aggregated (robust) data term for handling imprecise data constraints. We demonstrate the effectiveness and efficiency of our techniques in a range of image processing and computer graphics applications.

Visual fatigue evaluation and enhancement for 2D-plus-depth video

A 3D video is expected to be a representative technique of realistic system but still has some problems such as visual fatigue and headache. In this paper, we propose a visual fatigue evaluation algorithm to predict the degree of visual fatigue from a 2D-plus-depth video. Spatial and temporal characteristics of the depth video are main factors of visual fatigue for autostereoscopic displays. Using depth image directly, we estimate spatial and temporal complexities, depth position and scene movement of the 3D video. Then, the overall visual fatigue of the 3D video is evaluated to have higher correlation with subjective fatigue evaluation by a linear regression. Moreover we control the pixel value of depth image from the 3D video which may induce severe fatigue to make more comfortable 3D video. The results of proposed algorithm show a considerable correlation with subjective visual fatigue.

Visual fatigue modeling and analysis for stereoscopic video

In this paper, we propose a visual fatigue prediction method for stereoscopic video. We select visual fatigue factor candidates and determine the equations for each. The candidates are then classified into their principal components, and the validity of each is confirmed using principal component analysis. Visual fatigue is predicted using multiple regression with subjective visual fatigue. In order to determine the best model, we select the visual fatigue factors that have sufficient significance in terms of subjective fatigue according to the stepwise method. The predicted visual fatigue score is presented as a linear combination of the selected visual fatigue factors. Consequently, the proposed algorithm provides more reliable performance in terms of correlation with the subjective test results compared with a conventional algorithm.

Stereoscopic visual fatigue measurement based on fusional response curve and eye-blinks

In this paper, we propose an experiment that assesses fusional response curve and eye-blink rate to measure visual fatigue induced by stereoscopic videos. A random dot stereogram was utilized to measure the reliable fusional limit and response curve acquired by determining the direction of Landolt C. The results were analyzed to discriminate the individual ability of 3D fusion and compared with the results of subjective evaluation and descriptive self-report. It shows that while watching 3D video, viewers who have slow fusional response and low fusional limits are more sensitive to visual fatigue. In addition, eye-blinks were measured using eye images captured by a camera. Eye-blinks were increased in the video with moderate visual fatigue than low visual fatigue and decreased more in the second half than the first half of the session.

Space-Time Hole Filling With Random Walks in View Extrapolation for 3D Video

In this paper, a space-time hole filling approach is presented to deal with a disocclusion when a view is synthesized for the 3D video. The problem becomes even more complicated when the view is extrapolated from a single view, since the hole is large and has no stereo depth cues. Although many techniques have been developed to address this problem, most of them focus only on view interpolation. We propose a space-time joint filling method for color and depth videos in view extrapolation. For proper texture and depth to be sampled in the following hole filling process, the background of a scene is automatically segmented by the random walker segmentation in conjunction with the hole formation process. Then, the patch candidate selection process is formulated as a labeling problem, which can be solved with random walks. The patch candidates that best describe the hole region are dynamically selected in the space-time domain, and the hole is filled with the optimal patch for ensuring both spatial and temporal coherence. The experimental results show that the proposed method is superior to state-of-the-art methods and provides both spatially and temporally consistent results with significantly reduced flicker artifacts.

Depth adjustment for stereoscopic images and subjective preference evaluation

Visual fatigue is a common problem when viewing stereoscopic images. We propose a depth adjustment method that controls the amount of disparity in stereoscopic images using visual fatigue prediction and conducted subjective preference evaluation based on individual fusional response characteristics. Visual fatigue level is predicted by examining the characteristics of horizontal disparity. Viewers are classified into two groups (those with normal susceptibility to visual fatigue and those with high susceptibility to visual fatigue) according to individual fusional limit and speed of fusion, which are determined using a random dot stereogram test. Subjective preferences for the amount of depth adjustment are investigated based on the degree of fusion ability. Our experimental results support the suitability of the proposed depth adjustment method for reducing visual fatigue.

Effect of Vergence–Accommodation Conflict and Parallax Difference on Binocular Fusion for Random Dot Stereogram

Recently, various studies of human factors have been conducted to reveal stereoscopic characteristics of the human visual system and visual fatigue. In this paper, we investigate the effect of vergence-accommodation conflict and parallax difference on binocular fusion for random dot stereograms. The aim of this paper is to provide a study on visual fatigue induced by the conflict. We measured the time required for fusion under various conditions that include foreground parallax, background parallax, focal distance, aperture size, and corrugation frequency. The results show that foreground parallax and parallax difference between foreground parallax and background parallax have significant influences on fusion time. In addition, we verify the relationship between fusion time and visual fatigue by conducting a subjective evaluation of stereoscopic images.

Visual Comfort Enhancement for Stereoscopic Video Based on Binocular Fusion Characteristics

A well-known problem in stereoscopic videos is visual fatigue. However, conventional depth adjustment methods provide little guidance in deciding the amount of depth control or determining the condition for depth control. We propose a depth adjustment method based on binocular fusion characteristics, where the fusion time is used as the parameter for adjustment. Visual comfort enhancement is implemented with the horizontal image shift approach for depth adjustment. The speeded-up robust feature is used to estimate maximum disparity and disparity distribution, while a face detection algorithm is used to estimate the viewing distance with a single web camera. Binocular fusion characteristics are acquired in advance by measuring the time required for fusion under various conditions, including foreground disparity, background disparity, and focal distance for random-dot stereograms. Finally, a subjective evaluation is conducted in fixed and free-to-move viewing conditions, and the results show that comfortable videos were generated based on the proposed depth adjustment method.

Visual fatigue monitoring system based on eye-movement and eye-blink detection

In this paper, we proposed a visual fatigue monitoring system based on eye-movement and eye-blink detection. It analyzes the eye-movement and number of blinks based on the assumption that saccade movement of the eye decreases and the number of eye blink increases when visual fatigue of viewer is accumulated. The proposed system has an infrared single camera and an infrared light source. Then, the pupil of the eye can be detected by applying binary threshold to Purkinje image. The threshold is automatically selected by two constraints which are the eccentricity of ellipse fitting and the size of the pupil. Finally, total amount of eye movement and the number of eye blinks are measured by using the positions of the pupil. The results were obtained while watching stereoscopic videos after personal calibration procedure. The results show that saccade movement of the eye decreases as the visual fatigue of the viewer is accumulated. However, the number of eye blinks shows large variance along the time axis which implies it is not proper for visual fatigue monitoring system.

Visual Fatigue Relaxation for Stereoscopic Video via Nonlinear Disparity Remapping

A nonlinear disparity remapping scheme is presented to enhance the visual comfort of stereoscopic videos. The stereoscopic video is analyzed for predicting a degree of fatigue with the viewpoint of three factors: 1) spatial frequency; 2) disparity magnitude; and 3) disparity motion. The degree of fatigue is then estimated in a local manner. It can be visualized as an index map so-called a “visual fatigue map,” and an overall fatigue score is obtained by pooling the visual fatigue map. Based on this information, a nonlinear remapping operator is generated in two phases: 1) disparity range adaptation and 2) operator nonlinearization. First, a disparity range is automatically adjusted according to the determined overall fatigue score. Second, rather than linearly adjusting the disparity range of an original video to the determined disparity range, a nonlinear remapping operator is constructed in a manner that the disparity range of inducible problematic region is compressed, while that of comfortable region is stretched. The proposed scheme is verified via subjective evaluations where visual fatigue and depth sensation are compared among original videos, linearly remapped videos, and nonlinearly remapped videos. Experimental results show that the nonlinearly remapped videos provide more comfort than the linearly remapped videos without losing depth sensation.