What is the difference between ToF, stereo vision and structured light?

How does time-of-flight (ToF) work?

Time-of-flight cameras operate on the principle of active distance measurement. The camera emits light and measures how long it takes for the light (usually from a laser) to reach the object and return to the sensor. The distance to the object can be calculated from this information.

In principle, a distinction is made between direct and indirect time-of-flight measurement. In direct time-of-flight measurement, the actual time required for the light to travel to the object and back is determined. However, industrial ToF cameras are often based on the so-called indirect time-of-flight (iToF). In this method, the distance is calculated from the phase shift between the emitted and received light signal.

A significant advantage of ToF systems is that the depth information for each pixel can be captured simultaneously. With iToF, high image resolutions with very high frame rates are possible. This makes ToF cameras particularly suitable for fast processes and moving objects.

Strengths of time-of-flight

• Fast 3D acquisition in real time
• Depth information for all pixels in one image
• Well suited for moving objects
• Comparatively simple system integration
• Robust distance measurement over larger working ranges
• Cost-effective solution for many industrial 3D applications

Limitations of time-of-flight

• Typically lower accuracy than high-resolution stereo or structured light systems
• Multipath effects can influence measurement results
• Reflective surfaces can reduce measurement quality
• Dependence on active lighting
• Measuring range is limited by sensor and lighting technology

How does stereo vision work?

Stereo Vision is based on human vision and uses at least two cameras that capture the same scene from different angles. The depth is calculated from the image differences using triangulation. The distance of an object is determined based on geometric relationships between the camera positions.

In passive stereo vision, depth determination is performed exclusively on the basis of existing image features. The method works particularly well when the surface of an object has sufficient structure or texture.

Active stereo vision systems are often used for low-texture, monochrome or reflective surfaces. A projector projects a random or defined point pattern onto the scene, so that the depth calculation works reliably even under difficult conditions.

Active stereo vision thus forms bridges the gap between traditional stereo vision and structured light. Modern industrial 3D cameras combine the advantages of triangulation with targeted texture projection.

Strengths of stereo vision

• High measurement accuracy, robustness
• Detailed point clouds
• Flexible adaptation to different measurement ranges
• Ideally suited for bin picking
• Active stereo also works on low-texture (smooth or monochrome) objects

Limitations of stereo vision

• Calibration is more complex than with ToF systems
• Higher computing load
• Passive stereo requires sufficient surface structure
• Hidden areas can cause data gaps
• Moving objects can influence the measurement quality
• More sensitive to ambient light

How does structured light work?

Structured light systems project defined light patterns onto an object. Typical patterns include stripes, lines or grid structures. A camera then detects the deformation of these patterns on the object surface.

As the shape and position of the projected pattern are known, the geometry of the object can be calculated with high precision. Structured Light is also based on triangulation, but additionally uses the active projection of a known pattern.

The controlled projection enables highly detailed surface reconstructions to be generated This is why structured light is often used for surveying and inspection tasks.

Strengths of structured light

• Very high measurement accuracy
• Detailed reconstruction of surfaces
• High resolution of 3D data
• Suitable for surveying and inspection tasks
• Excellent results with small to medium-sized objects

Limitations of structured light

• Sensitive to strong ambient light
• Moving objects make measurement difficult
• Mostly limited range
• Additional projector required
• Higher system complexity

Which 3D process should I choose?

When fast depth acquisition in real time is required and moving objects also need to be reliably detected, time-of-flight is often the first choice. The method provides depth data with just one capture, is often comparatively cost-effective to implement and is well-suitable for robotics, logistics and automation applications.

When high-resolution point clouds and precise 3D data are required, stereo vision often offers the best balance between accuracy and flexibility. Active stereo vision systems also enable the reliable detection of objects with low surface texture and have become well-established in bin picking.

Where maximum measurement accuracy and a particularly detailed reconstruction of surfaces are required, structured light is frequently used. The method is particularly suitable for surveying, testing and inspection tasks.

The choice of the appropriate 3D method depends on the requirements of the respective application. Decisive factors are such as accuracy, speed, range and environmental conditions.

Which IDS products supports these methods?

IDS offers both 3D cameras based on time-of-flight and active stereo vision systems, thereby enabling solutions for a wide spectrum of industrial 3D applications.

How does IDS cover structured light applications?

Many applications that are traditionally implemented with structured light systems can now also be realized with active stereo vision. By combining triangulation and texture projection, Ensenso systems cover a wide range of application such as bin picking, robotics and industrial 3D inspection.

Our team will be happy to assist you with any questions you may have about selecting the appropriate 3D process or implementing specific applications.