Comparitive study on photometric normalization algorithms for an innovative, robust and real-time eye gaze tracker

Eye gaze trackers (EGTs) are generally developed for scientific exploration in controlled environments or laboratories and data have been used in ophthalmology, neurology, psychology, and related areas to study oculomotor characteristics and abnormalities, and their relation to cognition and mental states. The illumination is one of the most restrictive limitation of the EGTs, due to a problem of pupil center estimation during illumination changes. Most of the current systems, indeed, work under controlled illumination conditions either in dark or indoor environments, e.g. using infrared sources or conforming the sources of light to fixed levels or pointing directions. This work is focused on exploring and comparing several photometric normalization techniques to improve EGT systems during light changes. In particular, a new wearable and wireless eye tracking system (HATCAM) is used for testing the different techniques in terms of real-time capability, eye tracking and pupil area detection. Embedding real-time image enhancement into the HATCAM can make it an innovative and robust system for eye tracking in different lighting conditions, i.e. darkness, sunlight, indoor and outdoor environments.     

All fiber-optic sensing of light using side-polished fiber overlaid with photoresponsive liquid crystals

This study presents a highly sensitive, all-fiber sensor for in situ detecting light. A fiber-optic light sensing platform was created by overlaying an in-line side-polished fiber (SPF) with a photoresponsive liquid crystal (P-LC) consisting of an azobenzene dye, a chiral dopant, and a nematic LC. The resulting P-LC overlaid SPF light sensor is sensitive to three different light sources, including 380 nm light emitting diode (LED), mercury lamp, and office ceiling lights. Under the light illumination, the energy of irradiation from short wavelengths of light (<450 nm) initiates the trans-to-cis photoisomerization of azobenzene. The photochemical LC-phase transition induced by the generated cis-moiety of azobenzene changes the refractive index of LC-overlaid side-polished area. Light illumination increased the attenuation of the input laser signal. After turning off the illumination, the attenuation returned to its original value, allowing the fiber-optic light sensor to be reused. The sensitivity of the resulting fiber-optic light sensor was 0.16 dB/(μW/cm²) with a detection limit of 5 μW/cm² and 0.06 dB/lx with a detection limit of 45 lx when a 380 nm LED and office ceiling lights were used as illumination sources, respectively. The detection limit increased from 45 to 12 lx when P-LC containing 20 wt% azobenzene was used as light sensing material. The proposed fiber-based light sensor has potential use in harsh environments, such as severely humid and corrosive environments, which could damage mechanical and electronic light sensors.     

基于梯度图的微结构表面全局光照实时绘制

针对带有微结构表面的几何模型全局光照计算复杂、难以达到实时性要求的问题,提出一种基于高度梯度图分析的全局光照实时绘制方法.首先,定义微结构高度梯度图,并据此构建可见点的局部最高点集合.其次,给出面向微结构表面对象实时绘制的全局光照计算模型,将光照计算近似分解为环境光入射、光源直接光照和一次交互漫反射这3种分量的计算.在环境光计算过程中,提出一种自适应环境光遮挡计算,借助局部最高点集合计算遮挡角.在直接光照中,给出一种微结构阴影的修正方法,搜索入射光方向的最近局部最高点剖面;通过比较剖面内光线投影与局部最高点的遮挡角,近似确定由微结构造成的阴影区域.最后,根据可见点的局部最高点集合确定一次交互漫反射的采样范围,进行渗色处理.整个全局光照计算方法在图像空间完成,较好地利用了延迟着色的思想和GPU并行计算的特点.算法可以在使用低精度几何模型时表现出带有微结构表面的高精度模型的全局光照效果,且适用于动态场景和可变形物体的全局光照计算.     

采用重要性面片采样的实时全局光照

提出了一种实时全局光照的计算方法。该方法支持任意视点下动态光源的一次间接光照计算,并且物体表面材质可实时编辑,该算法预计算了各面片上的形状因子来解决遮挡问题,并记录形状因子较大的重要性面片作为间接光源。渲染时先从光源方向对场景记录了一个扩展的阴影图,包含了光源照射到的面片ID和其光通量,再根据采样好的间接光源来计算间接光照。使用CUDA,整个光照计算过程在GPU中完成,可以对静态场景进行实时渲染,并能达到逼真的渲染效果。     

An Efficient Radiosity Approach for Realistic Image Synthesis

The radiosity method models the interaction of light between diffusely reflecting surfaces and accurately predicts the global illumination effects. Procedures are now available to simulate complex environments including occluded and textured surfaces. For accurate rendering, the environment must be discretized into a fine mesh, particularly in areas of high intensity gradients. The interdependence between surfaces implies solution techniques which are computationally intractable. This article describes new procedures to predict the global illumination function without excessive computational expense. Statistics indicate the enormous potential of this approach for realistic image synthesis, particularly for dynamic images of static environments.     

The back-buffer algorithm: An extension of the radiosity method to dynamic environments

An efficient algorithm is introduced for the production of realistic image sequences of dynamic environments. The practicality of the radiosity method, which computes the interreflection of light within complex diffuse environments independent of viewpoint, is extended to dynamic environments where the paths of moving objects have been predefined. The algorithm takes advantage of the object coherence between static portions of an environment. A preprocessing stage executes once for a given image sequence and precalculates constant geometrical relationships in the environment. When the environment geometry changes, an update stage determines the global illumination using information provided by the preprocessor and the current positions of all moving objects. Test environments show speedups of at least twenty-five times over previous radiosity methods.     

Inverse lighting design using a coverage optimization strategy

Lighting design is an essential process in computer cinematography, games, architectural design and various other applications for correctly illuminating or highlighting parts of a scene and enhancing storytelling. When targeting specific illumination goals and constraints, this process can be tedious and counter-intuitive even for experienced users and thus automatic, goal-driven methods have emerged for the estimation of a lighting configuration to match the desired result. We present a general automatic approach to such an inverse lighting design problem, where the number of light sources along with their position and emittance are computed given a set of user-specified lighting goals. To this end, we employ a special hierarchical light clustering that operates in the lighting goal coverage domain and overcomes limitations of previous approaches in environments with high occlusion or structural complexity. Our approach is independent of the underlying light transport model and can quickly converge to usable solutions. We validate our results and provide comparative evaluation with the current state of the art.     

Inverse lighting design for interior buildings integrating natural and artificial sources

In this paper we propose a new method for solving inverse lighting design problems that can include diverse sources such as diffuse roof skylights or artificial light sources. Given a user specification of illumination requirements, our approach provides optimal light source positions as well as optimal shapes for skylight installations in interior architectural models. The well known huge computational effort that involves searching for an optimal solution is tackled by combining two concepts: exploiting the scene coherence to compute global illumination and using a metaheuristic technique for optimization.Results and analysis show that our method provides both fast and accurate results, making it suitable for lighting design in indoor environments while supporting interactive visualization of global illumination.     

Free Form Incident Light Fields

This paper presents methods for photo‐realistic rendering using strongly spatially variant illumination captured from real scenes. The illumination is captured along arbitrary paths in space using a high dynamic range, HDR, video camera system with position tracking. Light samples are rearranged into 4‐D incident light fields (ILF) suitable for direct use as illumination in renderings. Analysis of the captured data allows for estimation of the shape, position and spatial and angular properties of light sources in the scene. The estimated light sources can be extracted from the large 4D data set and handled separately to render scenes more efficiently and with higher quality. The ILF lighting can also be edited for detailed artistic control.     

Illumination-Guided Furniture Layout Optimization

Lighting plays a very important role in interior design. However, in the specific problem of furniture layout recommendation, illumination has been either neglected or addressed with empirical or very simplified solutions. The effectiveness of a particular layout in its expected task performance can be greatly affected by daylighting and artificial illumination in a non-trivial manner. In this paper, we introduce a robust method for furniture layout optimization guided by illumination constraints. The method takes into account all dominant light sources, such as sun light, skylighting and fixtures, while also being able to handle movable light emitters. For this task, the method introduces multiple generic illumination constraints and physically-based light transport estimators, operating alongside typical geometric design guidelines, in a unified manner. We demonstrate how to produce furniture arrangements that comply with important safety, comfort and efficiency illumination criteria, such as glare suppression, under complex light-environment interactions, which are very hard to handle using empirical or simplified models.     

Approximating global illumination on mesostructure surfaces with height gradient maps

Rendering global illumination for objects with mesostructure surfaces is a time-consuming task, and cannot presently be applied to interactive graphics. This paper presents a real-time rendering method based on a mesostructure height gradient map (MHGM) to exhibit lighting effects on meso-scale details in dynamic environments. We approximate global illumination using a lighting model including three components: incident ambient light, direct light and single bounce indirect light. MHGM is introduced to create local apex sets, which would help us to compute the three components adaptively. Our approach runs entirely on the graphics hardware, and uses deferred shading and the graphics pipeline to accelerate computation. We achieve high quality results which can render meso-scale details with approximate global illumination even for low-resolution geometric models. Moreover, our approach fully supports dynamic scenes and deformable objects.     

Real-time Light Animation

Light source animation is a particularly hard field of real‐time global illumination algorithms since moving light sources result in drastic illumination changes and make coherence techniques less effective. However, the animation of small (point‐like) light sources represents a special but practically very important case, for which the reuse of the results of other frames is possible. This paper presents a fast light source animation algorithm based on the virtual light sources illumination method. The speed up is close to the length of the animation, and is due to reusing paths in all frames and not only in the frame where they were obtained. The possible applications of this algorithm are the lighting design and systems to convey shape and features with relighting.     

Photon streaming for interactive global illumination in dynamic scenes

While many methods exist for simulating diffuse light inter-reflections, relatively few of them are adapted to dynamic scenes. Despite approximations made on the formal rendering equation, managing dynamic environments at interactive or real-time frame rates still remains one of the most challenging problems. This paper presents a lighting simulation system based on photon streaming, performed continuously on the central processor unit. The power corresponding to each photon impact is accumulated onto predefined points, called virtual light accumulators (or VLA). VLA are used during the rendering phase as virtual light sources. We also introduce a priority management system that automatically adapts to brutal changes during lighting simulation (for instance due to visibility changes or fast object motion). Our system naturally benefits from multi-core architecture. The rendering process is performed in real time using a graphics processor unit, independently from the lighting simulation process. As shown in the results, our method provides high framerates for dynamic scenes, with moving viewpoint, objects and light sources.     

Efficient region tracking with parametric models of geometry andillumination

As an object moves through the field of view of a camera, the images of the object may change dramatically. This is not simply due to the translation of the object across the image plane; complications arise due to the fact that the object undergoes changes in pose relative to the viewing camera, in illumination relative to light sources, and may even become partially or fully occluded. We develop an efficient general framework for object tracking, which addresses each of these complications. We first develop a computationally efficient method for handling the geometric distortions produced by changes in pose. We then combine geometry and illumination into an algorithm that tracks large image regions using no more computation than would be required to track with no accommodation for illumination changes. Finally, we augment these methods with techniques from robust statistics and treat occluded regions on the object as statistical outliers. Experimental results are given to demonstrate the effectiveness of our methods     

一个高效的动态场景算法

为了实现动态场景下的局部光源照明,本文提出一种叫做软阴影的技术.这种技术的主要思想是预先计算每一个场景实体的阴影区域,描述实体在某点处的阴影效果.光源的阴影域称为源辐射度域,它记录了一个光源采用立方体采样向外发射的辐射图.本文提供的技术与其它软阴影生成技术有一个根本的区别:预先计算与场景结构完全独立开来.本文所提供的技术可以使实时的动态场景中产生低频的阴影效果,也能产生全频阴影.     

A compensation-based approach for view maintenance in distributed environments

Data integration over multiple heterogeneous data sources has become increasingly important for modern applications. The integrated data is usually stored as materialized views to allow better access, performance, and high availability. In loosely coupled environments, such as the data grid, the data sources are autonomous. Hence, tie source updates can be concurrent and cause erroneous results during view maintenance. State-of-the-art maintenance strategies apply compensating queries to correct such errors, making the restricting assumption that all source schemata remain static over time. However, in such dynamic environments, the data sources may change not only their data but also their schema. Consequently, either the maintenance queres or the compensating queries may fail. In this paper, we propose a novel framework called DyDa that overcomes these limitations and handles both source data updates and schema changes. We identify three types of maintenance anomalies, caused by either source data updates, data-preserving schema changes, or non-data-preserving schema changes. We propose a compensation algorithm to solve the first two types of anomalies. We show that the third type of anomaly is caused by the violation of dependencies between maintenance processes. Then, we propose dependency detection and correction algorithms to identify and resolve the violations. Put together, DyDa extends prior maintenance solutions to solve all types of view maintenance anomalies. The experimental results show that DyDa imposes a minimal overhead on data update processing while allowing for the extended functionality to handle concurrent schema changes.     

Radiosity redistribution for dynamic environments

The radiosity algorithm is extended to dynamic environments, providing global-illumination simulations to scenes that are modified interactively. The illumination effects introduced by a change in position, shape, or attributes of any object in the scene are computed very rapidly by redistributing the energy already exchanged between objects. Corrections are made by shooting positive and negative energy, accounting for increased illumination and the creation of shadows. Object coherence is used to minimize computation, and progressive-refinement techniques are used to accelerate convergence. The extended algorithm yields excellent approximations to the exact solutions at interactive speeds     

Lighting-driven voxels for memory-efficient computation of indirect illumination

Several recently proposed voxel-based global illumination algorithms rely on the use of reflective shadow maps (RSMs) to interactively compute indirect illumination. However, RSMs do not scale well with the number of light sources because of their high memory consumption when rendering. Observing that, in most cases only a fraction of the voxels really contribute to single-bounce indirect illumination, in this paper we propose the use of lighting-driven voxels (LDVs), which are constructed from a subset of voxels, to reduce the memory burden. They are used in conjunction with a voxel-based global illumination algorithm that enables the interactive indirect illumination of dynamic scenes. We evaluate the memory usage, query performance, and construction speed for various voxel resolutions. Empirically, rendering with LDVs consumes an order of magnitude less memory than rendering with RSMs. Further, it achieves a higher performance for radiance queries when multiple light sources are used. Moreover, we integrated our method into voxel ray tracing and voxel cone tracing. For each of algorithm, we achieve an interactive performance that significantly reduces memory with respect to the reference solution.     

人造光照下的单幅雾天图像复原

当前基于单幅雾天图像复原算法的研究都是在光照充足的情形下（白天）,这种情形下的光照主要来自天空光。然而,对于在光照主要来自人造光（夜间）的雾天图像复原算法的研究屈指可数。因此提出了新的基于人造光照下的雾天成像模型,并同时考虑了不均匀的环境光和对图像的光照补偿。检测出光源位置,根据光源的发光特性求出环境光和光照补偿系数,利用提出的新模型求出清晰的图像,使用基于边缘颜色恒常性（EBCC）来对颜色进行校正。实验结果表明,该算法优于其他算法。     

Appearance Sampling of Real Objects for Variable Illumination

The appearance of an object greatly changes under different lighting conditions. Even so, previous studies have demonstrated that the appearance of an object under varying illumination conditions can be represented by a linear subspace. A set of basis images spanning such a linear subspace can be obtained by applying the principal component analysis (PCA) for a large number of images taken under different lighting conditions. Since little is known about how to sample the appearance of an object in order to correctly obtain its basis images, it was a common practice to use as many input images as possible. In this study, we present a novel method for analytically obtaining a set of basis images of an object for varying illumination from input images of the object taken properly under a set of light sources, such as point light sources or extended light sources. Our proposed method incorporates the sampling theorem of spherical harmonics for determining a set of lighting directions to efficiently sample the appearance of an object. We further consider the issue of aliasing caused by insufficient sampling of the object's appearance. In particular, we investigate the effectiveness of using extended light sources for modeling the appearance of an object under varying illumination without suffering the aliasing caused by insufficient sampling of its appearance.