Subsurface Scattering Calculation for Translucent Material Rendering
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Solution Overview
Problem
Current subsurface scattering calculation methods for translucent materials face challenges in accurately defining the maximum scattering distance, leading to over blurring or incorrect distribution of sample points, which affects the accuracy and efficiency of real-time rendering.
Innovation Solution
A novel subsurface scattering calculation model using a simple polynomial mathematical model to fit Monte Carlo photon tracking results, with a method to directly calculate the maximum scattering distance and an importance sampling solution for accurate rendering in screen space.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed maximum scattering distance is used to select sampling points, then the calculation process is simplified, but the calculation results become homogeneous and the low reflection region is over blurred
Solution Approach 1:
The patent applies dynamics by making the maximum scattering distance variable rather than fixed. The scattering distance is dynamically adjusted based on the single scattering rate, allowing the sampling range to adapt to different material properties and lighting conditions, thereby avoiding over-blurring while maintaining computational efficiency
Solution Approach 2:
The patent changes the parameter of maximum scattering distance from a fixed value to a calculated value based on single scattering rate. By introducing the relationship between scattering distance and single scattering rate, the system can adjust the sampling range dynamically, improving rendering accuracy without significantly increasing computational complexity
2Area of stationary object
If the maximum scattering distance is assumed to be infinite, then the sampling coverage is maximized, but the distance between sample points and surface points becomes extremely large resulting in calculation errors
Solution Approach 1:
The patent changes the parameter of maximum scattering distance from infinite to a finite value calculated based on single scattering rate. This provides an optimal balance between sampling coverage and calculation accuracy, ensuring that sample points are distributed over a sufficient area while maintaining reasonable distances from surface points
Solution Approach 2:
The patent uses Monte Carlo simulation to generate reference data for determining the relationship between single scattering rate and maximum scattering distance. This copied approach allows the system to learn optimal sampling parameters from simulated data and apply them in real-time rendering without performing expensive Monte Carlo calculations during actual rendering
3Manufacturing precision
If ray tracing is used to calculate outgoing radiation by accumulating photon paths, then the most accurate calculation result is obtained, but a lot of calculation time is required
Solution Approach 1:
The patent segments the subsurface scattering calculation into two parts: (1) pre-computation of the relationship between single scattering rate and maximum scattering distance using Monte Carlo ray tracing, and (2) real-time rendering using the pre-computed parameters with simplified sampling. This segmentation allows accurate parameter determination offline while achieving real-time performance during actual rendering
Solution Approach 2:
The patent performs preliminary action by pre-computing the scattering distance parameters using Monte Carlo simulation before real-time rendering. The relationship between single scattering rate and maximum scattering distance is established in advance, so that during real-time rendering, only simple sampling and compositing are needed, achieving both accuracy and speed
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The proposed method provides accurate rendering of translucent objects, especially in low reflectivity regions, by overcoming scattering range estimation errors and achieving real-time performance, with improved accuracy and efficiency compared to existing models.
Implementation Method 1
the rendering equation proposed by Kajiya, usually referred to as BRDF (Bidirectional Reflection Distribution Function) calculation model, can only consider the transmission behavior of light on the surface, and the solution introduced thereby is subsurface scattering
Data Source
AI summary
The embodiments of the present disclosure disclose subsurface scattering calculation method for translucent material rendering, which relates to the clipping and polynomial fitting of brute-force Monte Carlo photon tracking experimental results to accurately represent the energy attenuation of subsurface scattering in distance. On this basis, an average free path and a single scattering rate are used to determine the relationship of each term in the multinomial fitting formula so as to facilitate the calculation and adjustment of the reflection profile. In the end, through a new real-time importance sampling solution, the outgoing radiation from any point on the object surface is calculated by the Monte Carlo method. This importance sampling solution is also applicable to any other subsurface scattering calculation model. By combining this subsurface scattering calculation result with other results, such as highlight reflection, any translucent material object can be rendered accurately and efficiently.