Diffuse-Specular Separation Using Binary Spherical Gradient Illumination
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Solution Overview
Problem
Current methods for acquiring separate mappings of specular and diffuse reflectance and photometric normals of an imaged object are complex, often requiring polarized light sources, multiple cameras, and restrictive acquisition viewpoints, limiting their applicability and efficiency.
Innovation Solution
A method using binary spherical gradient illumination and its complements, provided by an LED sphere, to acquire images without polarizing filters, allowing for diffuse-specular separation and photometric normal estimation without the need for polarized light or restrictive viewpoints, utilizing a simpler setup and fewer images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If polarized spherical gradient illumination with polarized LED sphere and multiple polarized cameras is used, then separate mappings of specular and diffuse reflectance can be acquired, but device complexity increases and acquisition viewpoint becomes restrictive
Solution Approach 1:
The illumination sphere is divided into two independent components: an unpolarized LED sphere for providing gradient illumination and a separate rotating polarizer for controlling polarization state. This segmentation allows the system to achieve polarized spherical gradient illumination without requiring multiple polarized cameras or a complex polarized LED sphere, thereby reducing device complexity while maintaining measurement precision
Solution Approach 2:
A single camera system is designed to perform multiple functions: capturing images under different illumination gradients and polarization states by rotating the polarizer. This multi-functional approach eliminates the need for multiple specialized cameras, reducing device complexity while maintaining the capability to acquire separate specular and diffuse reflectance mappings
2Measurement precision
If polarized spherical gradient illumination is used, then diffuse-specular separation can be achieved, but the acquisition setup becomes more complex and time-consuming
Solution Approach 1:
The polarizer is rotated periodically to capture images at different polarization angles (0°, 45°, 90°, 135°) during a single continuous acquisition sequence. This periodic rotation allows the system to gather all necessary polarized information in one go, achieving diffuse-specular separation without requiring multiple separate acquisition sessions, thereby reducing total acquisition time
Solution Approach 2:
The illumination and imaging process continues uninterrupted during polarizer rotation, with the camera continuously capturing images under varying polarization states. This continuous acquisition approach eliminates idle time between captures and ensures that the entire diffuse-specular separation process is completed in a single efficient operation
3Measurement precision
If multiple images with different polarization states are captured, then accurate diffuse-specular separation is achieved, but the number of images and processing complexity increase
Solution Approach 1:
The system varies the polarization angle parameter by rotating the polarizer to capture images at four distinct angles (0°, 45°, 90°, 135°). By systematically changing this single parameter, the system obtains sufficient information for accurate diffuse-specular separation without requiring changes to the overall system configuration or capturing excessive images, thereby managing processing complexity effectively
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
Enables efficient and robust separation of diffuse and specular reflectance and photometric normals, suitable for dynamic capture applications, with improved signal-to-noise ratio and reduced complexity compared to existing techniques.
Implementation Method 1
A computer is provided with means for providing binary spherical gradient illumination along first, second and third mutually orthogonal axes to an object
Data Source
AI summary
A method of image processing includes receiving a set of images of an object, the set of images including images corresponding to binary spherical gradient illumination along first, second and third mutually orthogonal axes and images corresponding to complementary binary spherical gradient illumination along the first, second and third axes. The method also includes determining a specular reflectance map of the object and a diffuse reflectance map of the object based on the set of images, and/or determining a diffuse photometric normal map and a specular photometric normal map of the object based on the set of images.