Trine Kirkhus

Modelling and Compensating Measurement Errors Caused by Scattering in Time-Of-Flight Cameras

Recently, Range Imaging (RIM) cameras have become available that capture high resolution range images at video rate. Such cameras measure the distance from the scene for each pixel independently based upon a measured time of flight (TOF). Some cameras, such as the SwissRanger(tm) SR-3000, measure the TOF based on the phase shift of reflected light from a modulated light source. Such cameras are shown to be susceptible to severe distortions in the measured range due to light scattering within the lens and camera. Earlier work induced using a simplified Gaussian point spread function and inverse filtering to compensate for such distortions. In this work a method is proposed for how to identify and use generally shaped empirical models for the point spread function to get a more accurate compensation. The otherwise difficult inverse problem is solved by using the forward model iteratively, according to well established procedures from image restoration. Each iteration is done as a sequential process, starting with the brightest parts of the image and then moving sequentially to the least bright parts, with each step subtracting the estimated effects from the measurements. This approach gives a faster and more reliable compensation convergence. An average reduction of the error by more than 60% is demonstrated on real images. The computation load corresponds to one or two convolutions of the measured complex image with a real filter of the same size as the image.

System for estimation of pin bone positions in pre-rigor salmon

Current systems for automatic processing of salmon are not able to remove all bones from freshly slaughtered salmon. This is because some of the bones are attached to the flesh by tendons, and the fillet is damaged or the bones broken if the bones are pulled out. This paper describes a camera based system for determining the tendon positions in the tissue, so that the tendon can be cut with a knife and the bones removed. The location of the tendons deep in the tissue is estimated based on the position of a texture pattern on the fillet surface. Algorithms for locating this line-looking pattern, in the presence of several other similar-looking lines and significant other texture are described. The algorithm uses a model of the patterns location to achieve precision and speed, followed by a RANSAC/MLESAC inspired line fitting procedure. Close to the neck the pattern is barely visible; this is handled through a greedy search algorithm. We achieve a precision better than 3 mm for 78% of the fish using maximum 2 seconds processing time.

Adaptive image content-based exposure control for scanning applications in radiography

I-ImaS (Intelligent Imaging Sensors) is a European project which has designed and developed a new adaptive X-ray imaging system using on-line exposure control, to create locally optimized images. The I-ImaS system allows for real-time image analysis during acquisition, thus enabling real-time exposure adjustment. This adaptive imaging system has the potential of creating images with optimal information within a given dose constraint and to acquire optimally exposed images of objects with variable density during one scan. In this paper we present the control system and results from initial tests on mammographic and encephalographic images. Furthermore, algorithms for visualization of the resulting images, consisting of unevenly exposed image regions, are developed and tested. The preliminary results show that the same image quality can be achieved at 30-70% lower dose using the I-ImaS system compared to conventional mammography systems.

A motion based real-time foveation control loop for rapid and relevant 3D laser scanning

We present an implementation of a novel foveating 3D sensor concept, inspired by the human eye, which intends to allow future robots to better interact with their surroundings. The sensor is based on a time-of-flight laser scanning technology, where each range distance measurement is performed individually for increased quality. Micro-mirrors enable detailed control on where and when each sample point is acquired in the scene. By finding regions-of-interest (ROIs) and mainly concentrating the data acquisition here, the spatial resolution or frame rate of these ROIs can be significantly increased compared to a non-foveating system. Foveation is enabled through a real-time implementation of a feed-back control loop for the sensor hardware, based on vision algorithms for 3D scene analysis. In this paper, we describe and apply an algorithm for detecting ROIs based on motion detection in range data using background modeling. Heuristics are incorporated to cope with camera motion. We report first results applying this algorithm to scenes with moving objects, and show that the foveation capability allows the frame rate to be increased by up to 8.2 compared to a non-foveating sensor, utilizing up to 99% of the potential frame rate increase. The incorporated heuristics significantly improves the foveations performance for moving camera scenes.

Fast high resolution 3D laser scanning by real-time object tracking and segmentation

This paper presents a real-time contour tracking and object segmentation algorithm for 3D range images. The algorithm is used to control a novel micro-mirror based imaging laser scanner, which provides a dynamic trade-off between resolution and frame rate. The micro-mirrors are controllable, enabling us to speed up acquisition significantly by only sampling on the object that is tracked and of interest. As the hardware is under development, we benchmark our algorithms on data from a SICK LMS100-10000 laser scanner mounted on a tilting platform. We find that objects are tracked and segmented well on pixel-level; that frame rate/resolution can be increased 3-4 times through our approach compared to scanners having static scan trajectories, and that the algorithm runs in 30 ms/image on a Intel Core i7 CPU using a single core.

System for reading braille embossed on beverage can lids for authentication

The paper describes a system for reading embossed Braille patterns on used aluminum beverage container lids. The intent of the system is to check whether the used containers are entitled to a refund. The lids have strong specular reflections. The reflections are avoided by a novel method that illuminates the lid alternating from two angles, and acquires two separate images. This illumination method is more compact than existing methods. We use the extended maxima algorithm to detect the Braille dots, and a cluster-based pattern point matching algorithm to recognize a pre-defined Braille pattern. The algorithms are customized to increase speed using a priori information. The system was evaluated on a test set containing 225 images. The median time used for analyzing one beverage can was 1 second, and the recognition rate was 94 percent.

Quasi-imaging spectrometer with programmable field of view and field of illumination

8 Introduction t his article details the development of a robust, quasi-imaging spectrometer that reduces the effects of stray light from the background and nearby objects. In an industrial setting, samples are seldom well-ordered, making accurate spectral measurements more challenging than in a controlled, laboratory setting. objects may vary in size, shape and reflectance properties. Furthermore, background levels can fluctuate when, for example, measuring unordered objects in a bin or objects with unknown positions in a scene. thorough analysis of the measurement situation requires knowledge of spatial resolution, spectral resolution, wavelength band of interest and so forth. the solution to such problems may be a scanning point measurement or some kind of imaging spectrometer, often including a dispersive element, a camera and a scanning action; this latter may be achieved by either using a mirror device, such as a Digital Micro-mirror Device (DMD), or by moving the sample itself (the latter being more time-consuming). the system described here includes two digital micro-mirror devices (DMD) to dynamically select both the field of illumination (FoI) and the field of view (FoV) in a scene as shown in Figure 1. A DMD is an array of micro mirrors with two angle positions. the illumination DMD selects the illumination pattern, which can consist of sub-millimetre areas. the detection DMD selects the detector type; here a camera or spectrometer. the system can be programmed to operate in both reflection and remote interactance modes for increased flexibility. In Figure 1, the system is looking at an apple on a reflective surface. the entire image is illuminated in order to locate the region of interest, in this case the apple, and this image is sent to the camera (light path represented by dashed arrows). After this, the field of illumination is reprogrammed to illuminate only the apple (solid arrows), avoiding stray light from both the reflective surface and the apple’s green leaf. the detected light can again be sent to either the camera or spectrometer (in this case the spectrometer). Some preliminary results were conducted in three areas that could be considered advantageous as a result of the use of DMDs in an imaging/spectrometry system: 1) reference banking—to correct for variation across the image; 2) 3-D measurements for improved region-of-interest location and reference-bank selection; and 3) remote interactance measurements—for increased absorption information.