Frank Forster

An endoscopic 3D scanner based on structured light

We present a new endoscopic 3D scanning system based on Single Shot Structured Light. The proposed design makes it possible to build an extremely small scanner. The sensor head contains a catadioptric camera and a pattern projection unit. The paper describes the working principle and calibration procedure of the sensor. The prototype sensor head has a diameter of only 3.6mm and a length of 14mm. It is mounted on a flexible shaft. The scanner is designed for tubular cavities and has a cylindrical working volume of about 30mm length and 30mm diameter. It acquires 3D video at 30 frames per second and typically generates approximately 5000 3D points per frame. By design, the resolution varies over the working volume, but is generally better than 200μm. A prototype scanner has been built and is evaluated in experiments with phantoms and biological samples. The recorded average error on a known test object was 92μm.

Real-time acquisition of depth and color images using structured light and its application to 3D face recognition

In this paper, a novel real-time 3D and color sensor for the mid-distance range (0.1-3m) based on color-encoded structured light is presented. The sensor is integrated using low-cost of-the-shelf components and allows the combination of 2D and 3D image processing algorithms, since it provides a 2D color image of the scene in addition to the range data. Its design is focused on enabling the system to operate reliably in real-world scenarios, i.e. in uncontrolled environments and with arbitrary scenes. To that end, novel approaches for encoding and recognizing the projected light are used, which make the system practically independent of intrinsic object colors and minimize the influence of the ambient light conditions. The system was designed to assist and complement a face authentication system integrating both 2D and 3D images. Depth information is used for robust face detection, localization and 3D pose estimation. To cope with illumination and pose variations, 3D information is used for the normalization of the input images. The performance and robustness of the proposed system is tested on a face database recorded in conditions similar to those encountered in real-world applications.

A High-Resolution and High Accuracy Real-Time 3D Sensor Based on Structured Light

A new real-time 3D sensor is presented that is capable of delivering 25 high-resolution depth maps per second with a representative measurement error of 0.2 mm. The sensor is well suited for real-world application as it imposes no major scene constraints, i.e. it copes well with colored objects, moving scenes and background illumination. The acquisition technique, which is a form of structured light with a single projection pattern, is introduced, where the focus is on two aspects: Firstly, a new type of projection pattern that employs local color edge patterns for encoding so that it is possible to decode them even under noisy real- world conditions. Secondly, an algorithm that exploits the pattern properties to recognize the projected color edge patterns reliably. It then describes a 3D sensor based on this technique and presents experimental results obtained with it. It furthermore discusses an exemplary commercial application of the 3D sensor to the task of wheel alignment.

Fast and Accurate 3D Scanning Using Coded Phase Shifting and High Speed Pattern Projection

We describe a structured light phase measuring triangulation technique extending the conventional four-step phase shift sequence with embedded information suited to assist the phase unwrapping process. Using the embedded information, we perform automatic phase unwrapping in the presence of discontinuous or isolated surfaces without extending the length of the phase shift sequence or requiring stereo cameras. We demonstrate the application of the proposed method using a novel structured light projector capable of extraordinarily high projection frequencies and pattern resolution, as well as grayscale quantization. Using high speed cameras, we demonstrate 3D measurements at 20ms total acquisition time for both mono- and stereoscopic camera configurations.

The HISCORE camera a real time three dimensional and color camera

A new real time 3D-data and color acquisition system for the mid-distance range (0.5-3 m) employing color-encoded structured light is presented. The system is integrated using low-cost components and allows the combination of 2D and 3D image processing algorithms since it provides a 2D-color image of the scene in addition to the range data. Its design is focused on enabling the system to operate reliably in real-world scenarios, i.e. in uncontrolled environments and with arbitrary scenes. To that end novel approaches for encoding and recognizing the projected light are used which make the system practically independent of intrinsic object colors and minimize the influence of the ambient light conditions. Experimental results obtained for the first applications of the system, 3D face and gesture recognition tasks, are presented.

Fast and low-cost structured light pattern sequence projection

We present a high-speed and low-cost approach for structured light pattern sequence projection. Using a fast rotating binary spatial light modulator, our method is potentially capable of projection frequencies in the kHz domain, while enabling pattern rasterization as low as 2 μm pixel size and inherently linear grayscale reproduction quantized at 12 bits/pixel or better. Due to the circular arrangement of the projected fringe patterns, we extend the widely used ray-plane triangulation method to ray-cone triangulation and provide a detailed description of the optical calibration procedure. Using the proposed projection concept in conjunction with the recently published coded phase shift (CPS) pattern sequence, we demonstrate high accuracy 3-D measurement at 200 Hz projection frequency and 20 Hz 3-D reconstruction rate.

Real-time range imaging for dynamic scenes using colour-edge based structured light

A novel real time 3D-data acquisition system for highly dynamic scenes is presented. It is based on colour coded structured light using a single projection pattern. Existing systems utilising this approach are usually limited to scenes with neutral surfaces or not very robust. The presented system overcomes these shortcomings by using an innovative approach for recognising the projected pattern based on colour edges. The low-cost system is integrated using off-the-shelf components only. Experimental results are presented including a report on the successful use of the system with a 3D gesture recognition application.