Barycentric Filtering for BSDF Interpolation Artifacts

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Solution Overview

Problem

Conventional rendering techniques using bidirectional scattering distribution functions (BSDF) for 3D scenes suffer from artifacts like ripples when interpolating along diagonals of specular materials, due to the discrete nature of measured BSDF data and the use of linear interpolation.

Innovation Solution

Employing barycentric interpolation instead of linear interpolation for interpolating reflectance properties in the measured BSDF, particularly along diagonals, to determine reflected irradiance for surface points, using a renderer with a barycentric filter to select appropriate triangles and calculate barycentric coordinates for accurate rendering.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If linear interpolation is used for measured BSDF data, then the rendering process is simple and fast, but artifacts like ripples appear along diagonals of specular materials

Engineering Contradiction:

Improverendering speedVSAvoidrendering accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent changes the interpolation parameters by switching from linear interpolation to barycentric interpolation. This parameter change in the mathematical approach allows for more accurate rendering along diagonals of specular materials while maintaining computational efficiency through the use of pre-defined triangular patches in the BSDF data structure.

Inventive Principle:

Principle #35Parameter changes

2Quantity of substance

If measured BSDF data is stored as discrete 3D texture, then memory usage is reduced, but interpolation accuracy deteriorates due to discrete sampling

Engineering Contradiction:

Improvedata storage efficiencyVSAvoidinterpolation accuracy

Core Design Contradiction:

Quantity of substanceVSMeasurement precision

Solution Approach 1:

The patent segments the BSDF data into triangular patches within the 3D texture structure. By organizing the discrete data points into triangular segments, the system enables barycentric interpolation that accurately reconstructs continuous reflectance properties from the discrete samples, improving interpolation accuracy without increasing memory usage.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent utilizes the third dimension (w-coordinate) of the 3D texture to store additional angular information (θo). This dimensional organization allows the system to maintain compact data storage while enabling accurate barycentric interpolation across all three angular dimensions (Φo, θi, θo), resolving the trade-off between discrete sampling and interpolation accuracy.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Data Source

PatentUS9773342B2Barycentric filtering for measured biderectional scattering distribution function

Publication Date: 2017.09.26 NVIDIA CORP

AI summary

The disclosure provides a method of determining reflected irradiance for a surface point on a surface whose reflectance properties are represented by a measured BSDF. Additionally, the disclosure provides a renderer and a computer program product. In one embodiment, the method includes: (1) determining u, v and w coordinates in the measured BSDF for the surface point based on an incoming and an outgoing ray direction, (2) selecting a triangle for barycentric interpolation based on values of the v and the w coordinates at the surface point and (3) performing the barycentric interpolation for evaluating the measured BSDF for the surface point.