Shape-from-Shading – Illuminating 3D Surface Inspection with Integrated Multi-Light Control
Shape-from-shading (SFS) is a computer vision technique that draws upon light and shadow patterns to reconstruct an object’s 3D shape from a single 2D image. As an inspection tool, SFS can be highly effective at identifying and measuring surface defects on an object such as scratches, dents, pores, and grinding marks that are often invisible in typical machine vision setups. While SFS is not as widely used as other 3D reconstruction techniques, it is seeing renewed interest with recent advances in Deep Learning applications leveraging large datasets and learned priors.
As a technology leader in machine vision, SVS-Vistek offers multiple camera models supporting SFS through an integrated multichannel LED strobe controller dubbed the 4I0 Strobe Control. This feature enables up to four LED lights to be controlled via the camera’s SDK, paving the way for construction of economical SFS systems.
Algorithms Infer Surface Shape
Multiple light sources provide supplemental shading information, which helps SFS algorithms resolve ambiguities and improve reconstruction accuracy. Each light source comes from a different direction towards the object, therefore creating a unique perspective by the way light is reflected. For instance, a surface facing the light appears brighter, while one angled away appears darker. By modeling how light interacts with the surface, SFS algorithms infer the surface’s shape, typically represented as a depth map or a field of surface normals, thus enabling reliable detection of faults the size of just a few micrometers.
Quality-Control of Complex Aerodynamic Shapes
This high level of precision makes SFS particularly suitable for quality-control of complex aerodynamic shapes such as turbine blades designed for energy generation or aircraft engines. Examining raised or recessed letters on surfaces—such as laser-cut codes and embossed text on metal components—is another application. Because SFS algorithms may be modified to be independent of color and reflectivity differences, it is possible to precisely evaluate shiny or dark metals and plstics. Beyond industry, SFS is a proven method for detecting Braille on colored backgrounds, and reconstructing 3D shapes in fields as diverse as medical imaging, archaeology, or planetary sciences.
One of the challenges of SFS is that reconstructing 3D geometry of an object or surface requires precise timing between multiple light sources and the camera. This usually requires the addition of a separate LED driver lighting controller, which raises costs, complicates operations, and introduces another point of failure.
SVS-Vistek simplifies SFS timing with 4IO Strobe Control, an integrated 4-channel PWM strobe controller for LED lighting. SVS-Vistek 4IO Strobe Control supports up to 3 amps across channels with precise timing in 15 nanosecond steps. Integrated into more than 200 SVS-Vistek camera models, the strobe controller eliminates the need for external LED drivers, saving valuable space, field wiring, application complexity, and costs. SVS-Vistek cameras equipped with 4I0 Strobe Controls have an SDK that provides direct access to all its parameters, including light duration, current, and delays.
For more information: www.svs-vistek.com
