Igor S. Potemin

Spectral ray tracing in problems of photorealistic imagery construction

This paper analyzes color rendering problems arising in computer imaging of scenes with complex optical properties. The sources of these errors for imagery constructed on the basis of the RGB space are analyzed and an efficient and correct algorithm is proposed for spectral imagery. These solutions are applied to problems of direct stochastic and inverse deterministic ray tracing. In addition, complex scenes with mixed optical properties defined in different (including RGB) models are proposed to be treated by an efficient and correct algorithm for reducing all optical properties into a single spectral model.

Photorealistic volume scattering model in the bidirectional stochastic ray tracing problem

This paper is devoted to the development of physically correct rendering model of scenes containing volume scattering objects. The solution of the rendering equation is based on the Monte-Carlo bidirectional ray tracing. Two efficient approaches to the solution of the rendering equation for different parameters of the volume scattering medium (typically, concentration of scattering particles) are developed. Examples illustrate how the proposed models can be used for photorealistic visualization of scenes containing volume scattering objects and for the simulation of illuminators based on the volume scattering effect. Possible limitations of the application field of the proposed models are considered.

Indeterminate ray tracing in problems of the analysis of light scattering and the design of illuminating systems

This paper proposes using the Monte Carlo method to design optical systems with an indeterminate ray path. The main algorithms for direct stochastic ray tracing and programmed implementation of the given algorithms are considered. The work is illustrated with examples in which the scattered light is calculated in lens-based optical systems.

Aberration vignetting phenomena and its visualization in wide angular objectives

Aberration vignetting phenomena changes light distribution in the image plane. A method of physically accurate simulation of this effect in optical devices is presented. We modified a stochastic ray tracing technique to use it for the analysis and visualization of the aberration vignetting. Some useful illustrations with a number of visual examples of these phenomena for different optical systems are given: bi-concentric lens, wide-angle lens, fish-eye lenses, etc.

Photorealistic Rendering of Images Formed by Augmented Reality Optical Systems

Stochastic ray tracing is used for rendering photorealistic images formed by augmented reality optical systems that combine the image generated by an optoelectronic device with the image of the environment. Methods for improving the efficiency of stochastic ray tracing that preserve the physical correctness of the simulation are proposed. Using a head-up display (HUD) as an example, it is shown that the forward stochastic ray tracing methods are sometimes more efficient than backward stochastic ray tracing methods for the visual simulation of augmented reality images. Approaches making it possible to combine the forward, backward, and bidirectional ray tracing in a unified simulation procedure are proposed. The results are illustrated by synthesized images produced by the optical system of head-up display.

Virtual prototyping as an approach to optimizing starting point selection in a mass production of camera lenses

Mass-production of optical and opto-electronic devices is very critical to the number of the elements, their shape and type. Physical prototyping for this optical system depends not only on the lens quality and quantity, but also on the camera housing and the sensor. In our research we’ve studied the reasons of optical systems’ complexity and found out that it depends on optical system structure. After that a lens is optimized, tolerances are calculated and physical prototyping is implemented. In our case physical prototyping means a trial lot production. It was found, that virtual prototyping for different starting points can help to find the solution for mass-production, which will be then used for its manufacturing. This approach includes calculation of all elements of the camera lens from the first surface of a lens to the sensor, including 3D environment model. Depending on the type of the designed optical system, the virtual prototype modeling is included into a merit function for further optimization in the automatic lens design software. We can estimate a reduction of visual contrast of the image of the camera lens in the conditions similar to the conditions of the real device operation or show dependence of the contrast reduction in time of the operation. We implemented such an approach as a virtual parametric model of the lens camera device. We show a plot of the dependence on the cost of mass production of the mobile phone camera from the number of components. The cost information is valid for China.

Use of computer graphics methods for efficient stray light analysis in optical design

The problems of using stray light visualization for the effective analysis and design of complex optical systems are considered. Examples of real applications are given where the use of the light propagation criterion in conjunction with the visual representation of the ray path makes it possible to effectively analyze complex optical design problems. The suggested solution allows not only to visualize source of the stray light in the optical system but alto to render the image on the detector taking into account diffuse scattering on all illuminated surfaces.

Hybrid ray tracing method for photorealistic image synthesis in head-up displays

The paper describes the use of stochastic ray tracing methods for synthesizing of photorealistic images, formed by optical systems of augmented reality devices, that combines image synthesized by the optoelectronic device with the surrounding environment. As the result of the research, new methods are proposed that make it possible to increase the efficiency and preserve the physical correctness of stochastic ray tracing methods in the task of the photorealistic images synthesis formed by optical systems. The authors show that in such cases the methods of direct stochastic ray tracing are more effective for visual modeling of the augmented reality picture on an example of the head-up display (HUD) optical system. The proposed approaches allow to combine direct, inverse and bi-directional stochastic ray tracing methods in one calculation. The work is illustrated by examples of the synthesized images observed in HUD optical systems.

Optimization based on reconstruction of volume scattering medium parameters

Lighting design or stray light simulation of imaging or non-imaging optical systems requires a precise specification of the optical properties of the scattering materials and one of the ways of the proper specification is the Bidirectional Scattering Distribution Function (BSDF). Although, it is possible to obtain data about the optical properties of the sample for example by measurement of the BSDF, but it is difficult to extract the properties of the sample components (BSDF of the sample boundary, parameters of volume scattering, etc.). In such cases, it is required to reconstruct these properties. For this operation, there are many methods, like the reconstruction of the BSDF of the microrelief, but they not applicable in cases when the volume scattering is used. Authors have developed a method for optimization of the volume scattering media parameters, which shows good agreement with the measurements of the sample BSDF.

Efficient methods of BSDF reconstruction from the micro-relief dataset for the lighting simulation tasks

A physically accurate description of the optical properties of surfaces is the one of the most important requirements in optical simulation for both imaging and non-imaging optics. Uncertainty in the specification of the optical properties might influence the simulation image or the spatial distribution of radiation in optical system. One of the ways of describing the optical properties is using the Bidirectional Scattering Distribution Function (BSDF). As a rule, BSDF is measured by goniospectrophotometers, but sometimes it is not possible to perform such measurements. In some cases, the measurement should be done inside the material, but it is impossible to measure BSDF of the boundary there. One of the possible solutions is to measure the microrelief heights distribution by profile measurement machine or atomic force microscope and assign measured data for given model. But, not every optical design software solution has the ability to specify microrelief directly, while majority of them just have the ability to specify BSDF. In this article, authors show methods of BSDFs generation from measurements of the real microrelief in the form of spatial distribution of heights.