How Digital Schlieren (BOS Method) Makes Density Gradients Visible—Without Complex Optical Setups
📑 Table of Contents
What is Schlieren?
What is Digital Schlieren (BOS Method)?
Measurement Flow
Key Advantages of Digital Schlieren
Applications
🔍 What is Schlieren?
Schlieren is an optical visualization technique developed in the 19th century to observe changes in transparent media—such as air or gas—that are invisible to the naked eye. When a gas is released into the atmosphere, the gas itself may not be seen directly, but if it differs in density from the surrounding air, it refracts light as it passes through. This causes visible brightness variations that can be captured using optical systems.
This effect explains natural phenomena like heat haze, where hot air rising from a surface causes visible shimmering. The word "Schlieren" originates from the German term for "streaks" or "mottled patterns," which describes the visual artifacts produced by density variations.
Conventional Schlieren Systems
Traditional Schlieren systems use:
High-precision lenses and concave mirrors
A collimated light source
A knife-edge or optical filter to detect refraction-induced distortions
While powerful, these systems are:
Expensive
Sensitive to alignment
Difficult to scale to large areas
Time-consuming to set up and operate
Generally restricted to laboratory environments
💡 What is Digital Schlieren (BOS Method)?
Digital Schlieren—also known as Background Oriented Schlieren (BOS)—is a modern, simplified approach to Schlieren imaging. It eliminates the need for complex optical assemblies and instead relies on digital imaging and pattern analysis.
The Digital Schlieren System developed by Seika Digital Image uses:
A high-resolution or high-speed camera
A background with a printed or projected pattern
Specialized analysis software (Koncerto DSS)
How It Works:
A background pattern (such as a dot grid or speckle pattern) is positioned behind the measurement area.
A base image is taken when no phenomenon is occurring (i.e., no density gradient).
During the event (e.g., airflow, gas leak, heat transfer), the camera records changes in the pattern caused by light refraction.
Using the Koncerto DSS software, Schlieren images are generated by analyzing differences between the base image and the affected images.
This method allows visualization of minute changes in air or gas density in real time, even in wide-area setups or microscopic environments.
📸 Measurement Flow
The measurement process is straightforward and user-friendly:
Setup: Place the camera facing the test subject and align the patterned background behind it.
Capture Base Image: Record a reference image before any density change occurs.
Capture Event: Record images or video while the event takes place (e.g., heat rising, gas dispersing).
Analysis: Compare the reference image to the recorded images using the Koncerto DSS software to visualize refractive index changes.
✅ Key Advantages of Digital Schlieren
| Feature | Digital Schlieren (BOS) |
|---|---|
| Setup Time | Minutes |
| Required Components | Camera, Background, Software |
| Optical Adjustment | None |
| Scalability | Microscopic to meter-scale |
| Ease of Use | Simple, repeatable, low training required |
| Cost Efficiency | Lower cost than traditional Schlieren setups |
| Compatibility | Works with existing high-speed or high-res cameras |
This system is so sensitive that it can detect the heat rising from a human hand or visualize gas escaping from a carbonated beverage—all without lasers, mirrors, or knife-edges.
🔬 Applications
Digital Schlieren is useful across R&D, industrial, and educational environments. Common use cases include:
Thermal Convection Studies (battery heat, component cooling)
Gas Leak Detection (e.g., hydrogen, methane)
Airflow Visualization (HVAC vents, combustion flows)
Foreign Body Detection (in transparent films or packaging)
Medical Research (visualization of human breath or airflow)
Engineering Education & Demonstration
📦 Build Your Own System
The Digital Schlieren System includes:
Camera (high-speed or high-resolution)
Display-based or printed background
Koncerto DSS analysis software
Optional background pattern generation tool
Compatible workstation (laptop or desktop)
Existing imaging equipment can be integrated, minimizing cost and accelerating deployment.