Graham K. Lang

An all-solid-state optical range camera for 3D real-time imaging with sub-centimeter depth resolution (SwissRanger)

A new miniaturized camera system that is capable of 3-dimensional imaging in real-time is presented. The compact imaging device is able to entirely capture its environment in all three spatial dimensions. It reliably and simultaneously delivers intensity data as well as range information on the objects and persons in the scene. The depth measurement is based on the time-of-flight (TOF) principle. A custom solid-state image sensor allows the parallel measurement of the phase, offset and amplitude of a radio frequency (RF) modulated light field that is emitted by the system and reflected back by the camera surroundings without requiring any mechanical scanning parts. In this paper, the theoretical background of the implemented TOF principle is presented, together with the technological requirements and detailed practical implementation issues of such a distance measuring system. Furthermore, the schematic overview of the complete 3D-camera system is provided. The experimental test results are presented and discussed. The present camera system can achieve sub-centimeter depth resolution for a wide range of operating conditions. A miniaturized version of such a 3D-solid-state camera, the SwissRanger 2, is presented as an example, illustrating the possibility of manufacturing compact, robust and cost effective ranging camera products for 3D imaging in real-time.

Fabrication of kinoform structures for optical computing

The fabrication of kinoform micro-optical elements for applications in optical computing is described. The elements are recorded as continuous microrelief structures by programmable laser beam writing in photoresist with a computer-controlled precision xy stage and a modulated, focused laser beam. Kinoform structures can be programmed to any desired profile that is required for reproducing complex, optimized structures that are found by computer design techniques.

The Robust Recognition of Traffic Signs from a Moving Car

The robust and reliable recognition of traffic signs from a moving car is investigated as a specific example of the general ambitious goal of object recognition in natural surroundings. The newly proposed method of hierarchical spatial feature matching is employed, based on a pyramid representation of the scene and its local orientations. The worked example of designing a suitable template for “right-of-way” -signs (diamonds, rotated squares) illustrates some general principles of hierarchical feature matching. Hardware considerations indicate that the problem can be solved in real-time with a data-flow architecture using commercially available matching ICs. The performance with video imagery taken from a moving car (day and night, city and country scenes) is reported and some practical problems encountered are discussed. It is concluded that this non-AI based approach to traffic sign recognition is reliable, simple, fast and performs very well in real-life situations.

Fabrication of micro-optical components by laser beam writing in photoresist

A laser beam writing system for the fabrication of micro-optical elements as relief structures in photoresist is described. Using a computer controlled precision xy stage and a modulated, focused laser beam, a wide range of surface relief microstructures has been produced, with typical periods of 10 - 100 micrometers and a maximum relief amplitude of about 5 micrometers . Examples include microlens arrays, kinoforms and other phase structures for applications in optical computing, optical interconnects and micro-optical systems in general.

A time-of-flight line sensor: development and application

A new miniaturised 256 pixel silicon line sensor, which allows for the acquisition of depth-resolved images in real-time, is presented. It reliably and simultaneously delivers intensity data as well as distance information on the objects in the scene. The depth measurement is based on the time-of-flight (TOF) principle. The device allows the simultaneous measurement of the phase, offset and amplitude of a radio frequency modulated light field that is emitted by the system and reflected back by the camera surroundings, without requiring any mechanical scanning parts. The 3D line sensor will be used on a mobile robot platform to substitute the laser range scanners traditionally used for navigation in dynamic and/or unknown environments.

Robust classification of arbitrary object classes based on hierarchical spatial feature-matching

Abstract. We present a novel approach to the robust classification of arbitrary object classes in complex, natural scenes. Starting from a re-appraisal of Marrs ‘primal sketch’, we develop an algorithm that (1) employs local orientations as the fundamental picture primitives, rather than the more usual edge locations, (2) retains and exploits the local spatial arrangement of features of different complexity in an image and (3) is hierarchically arranged so that the level of feature abstraction increases at each processing stage. The resulting, simple technique is based on the accumulation of evidence in binary channels, followed by a weighted, non-linear sum of the evidence accumulators. The steps involved in designing a template for recognizing a simple object are explained. The practical application of the algorithm is illustrated, with examples taken from a broad range of object classification problems. We discuss the performance of the algorithm and describe a hardware implementation. First successful attempts to train the algorithm, automatically, are presented. Finally, we compare our algorithm with other object classification algorithms described in the literature.

A practical adaptive image compression technique using visual criteria for still-picture transmission with electronic mail

An efficient image compression/decompression technique for complex scenes is presented. An image is first decorrelated by a full two-dimensional DCT (discrete cosine transform). The resulting coefficient map is weighted using properties of the human visual system and finally encoded with a novel multiresolution encoder. The result is converted into printable ASCII for transmission by electronic mail. >

Using local orientation and hierarchical spatial feature matching for the robust recognition of objects

A new approach to the robust recognition of objects is presented. The fundamental picture primitives employed are local orientations, rather than the more traditionally used edge positions. A simple technique of feature-matching is used, based on the accumulation of evidence in binary channels (similar to the Hough transform) followed by a weighted non- linear sum of the evidence accumulators (matched filters, similar to those used in neural networks). By layering this simple feature-matcher, a hierarchical scheme is produced whose base is a binary representation of local orientations. The individual layers represent increasing levels of abstraction in the search for an object, so that the object can be arbitrarily complex. The universal algorithm presented can be implemented in less than 100 lines of a high-level programming language (e.g., Pascal). As evidenced by practical examples of various complexities, objects can be reliably and robustly identified in a wide variety of surroundings.