No 3 (2023)

The importance of detecting and reducing the visibility of precipitation in video images obtained by fixed cameras is shown. A statistical analysis of the geometric (area, shape factor, and orientation deviation from the frame average), and color–brightness (intensity and color saturation) characteristics of rain and snow particles is performed in order to substantiate decision rules for detecting pixels corresponding to precipitation particles. This analysis consists in obtaining distributions of the particle parameters and approximating them by known distribution laws using the family of Pearson’s curves, the Kolmogorov criterion, and the Nelder–Mead simplex algorithm. An algorithm for detecting raindrops and snowflakes in video sequences is developed, which is supposed to be used as part of an algorithm for reducing the visibility of precipitation. The proposed approach is presented in the form of a multistage classification of frame pixels into zones with moving objects and regions of a stationary background distorted and undistorted by precipitation particles in accumulated frames. Depending on the region to which the processed pixel belongs, the final decision to assign it to the class of precipitation is made using the proposed decision rules or the developed thresholding procedure with automatic determination of local threshold values. The proposed algorithm is experimentally investigated and, using a two-criteria approach, the optimal values for the number of accumulated frames for the correct operation of the algorithm are determined—100 frames for video images with rain and 140 frames for video with snow. The gain of the developed approach in comparison with the known estimates of the probabilities of false positives and false negatives is up to 1.7% and 9.1%, respectively.

In this paper, we analyze realistic rendering methods in terms of their efficiency in calculating caustic and indirect illumination. As the basic approach to realistic rendering, we choose bidirectional progressive ray tracing with backward photon maps. The main factors that reduce the efficiency of this method are analyzed. It is shown that the main factor that affects its performance is slow access to photon map data. Different techniques for construction of spatial acceleration structures are considered, their advantages and disadvantages are investigated. As the main approaches, we select the regular spatial grid and binary kd tree. The spatial grid provides high-speed access to photon data at low adaptability of photon map partitioning. The kd tree is characterized by high spatial adaptability of photon map partitioning but slow access to photon data. We propose a combined solution that takes advantage of the adaptability of the kd tree and the fast data access of the spatial grid. For this purpose, the regular grid is superimposed on the kd tree constructed based on the principle of space partitioning of a photon region into geometrically identical halves. To reduce memory consumption, we propose, first, to use multilevel spatial grids superimposed on the selected nodes of the kd tree and, second, to store spatial grids in the form of hash tables in order to reduce the size of the acceleration structure. Thus, a spatial acceleration structure of a new type—a tree of hash tables—is proposed and implemented. For the spatial structure developed, we implement methods for finding the nearest photons the integration spheres of which cover the illumination point, as well as methods for finding the intersection between a ray segment and photon integration spheres. The proposed software solutions are implemented in the Lumicept software package; for some scenes, the proposed method is compared with the Lumicept method based on the binary tree. The comparison shows that our method can increase the overall speed of the rendering process by more than 40%.

In this paper, based on height field surface example, an efficient technology of real-time modeling of complex procedural objects on the ray tracing pipeline (RT-pipeline) is proposed. The proposed technology doesn’t overload the I-shader stage (intersection shader), but distributes the computational load between the I-shader and the AH-shader (any-hit shader). The key innovations of the technology are the early rejection at the I-shader stage of the bounding boxes (AABBs) extracted by the RT-pipeline hardware unit, and the “transparent AABB” concept which allows transferring costly computing of the “ray-procedural object” intersection to a later AH-shader stage. The paper also describes a number of modifications that reduce the amount of such calculations. The proposed technology was implemented in a software complex in C++, GLSL and using the Vulkan API. The performance of the developed solution was studied under various ray tracing conditions on the task of modeling the surface of a detailed Puget Sound height field. The obtained results confirmed high efficiency of the developed technology and the possibility of its application in virtual environment systems, simulators, scientific visualization, etc.