Underwater stereo-video measurement systems are used widely for counting and measuring fish in aquaculture, fisheries and conservation management. To determine population counts, spatial or temporal frequencies, and age or weight distributions, snout to fork length measurements are captured from the video sequences, most commonly using a point and click process by a human operator. Current research aims to automate the measurement and counting task in order to improve the efficiency of the process and expand the use of stereo-video systems within marine science. A fully automated process will require the detection and identification of candidates for measurement, followed by the snout to fork length measurement, as well as the counting and tracking of fish. This paper presents a review of the techniques used for the detection, identification, measurement, counting and tracking of fish in underwater stereo-video image sequences, including consideration of the changing body shape. The review will analyse the most commonly used approaches, leading to an evaluation of the techniques most likely to be a general solution to the complete process of detection, identification, measurement, counting and tracking.
The paper presents a metric investigation of the Fuji FinePix Real 3D W1 stereo photo-camera. The stereo-camera uses a synchronized Twin Lens-CCD System to acquire simultaneously two images using two Fujinon 3x optical zoom lenses arranged in an aluminum die-cast frame integrated in a very compact body. The nominal baseline is 77 mm and the resolution of the each CCD is 10 megapixels. Given the short baseline and the presence of two optical paths, the investigation aims to evaluate the accuracy of the 3D data that can be produced and the stability of the camera. From a photogrammetric point of view, the interest in this camera is its capability to acquire synchronized image pairs that contain important 3D metric information for many close-range applications (human body parts measurement, rapid prototyping, surveying of archeological artifacts, etc.). Calibration values - for the left and right cameras - at different focal lengths, derived with an in-house software application, are reported together with accuracy analyses. The object coordinates obtained from the bundle adjustment computation for each focal length were compared to reference coordinates of a test range by means of a similarity transformation. Additionally, the article reports on the investigation of the asymmetrical relative orientation between the left and right camera.
Multi-View Stereo (MVS) as a low cost technique for precise 3D reconstruction can be a rival for laser scanners if the scale of the model is resolved. A fusion of stereo imaging equipment with photogrammetric bundle adjustment and MVS methods, known as photogrammetric MVS, can generate correctly scaled 3D models without using any known object distances. Although a huge number of stereo images (e.g. 200 high resolution images from a small object) captured of the object contains redundant data that allows detailed and accurate 3D reconstruction, the capture and processing time is increased when a vast amount of high resolution images are employed. Moreover, some parts of the object are often missing due to the lack of coverage of all areas. These problems demand a logical selection of the most suitable stereo camera views from the large image dataset. This paper presents a method for clustering and choosing optimal stereo or optionally single images from a large image dataset. The approach focusses on the two key steps of image clustering and iterative image selection. The method is developed within a software application called Imaging Network Designer (IND) and tested by the 3D recording of a gearbox and three metric reference objects. A comparison is made between IND and CMVS, which is a free package for selecting vantage images. The final 3D models obtained from the IND and CMVS approaches are compared with datasets generated with an MMDx Nikon Laser scanner. Results demonstrate that IND can provide a better image selection for MVS than CMVS in terms of surface coordinate uncertainty and completeness.
Parachute systems play a critical role in many science and military missions. Currently, NASA and the U.S. Army air
delivery systems programs are evaluating measurement technologies to support experimental and qualification testing of
new and modified parachute concepts. Experiments to validate the concept of parachute shape measurement have been
conducted in a controlled, indoor environment using both fixed and payload cameras. The paper will provide further
detail on the rationale for the experiments, the design of the payload systems, the indoor and outdoor testing, and the
subsequent data analysis to track and visualise the shape of the parachute.
Bayer colour filter arrays (CFA) are commonly used to obtain digital colour imagery from a single-chip CCD or CMOS camera. Colour information is captured via a regular array of colour filters placed over the image sensor, and the full colour image is reconstructed in a demosaicing process. Colour imagery derived in such a way is prone to visual artefacts including false colours, poor edge definition and a loss of image and colour sharpness. Such artefacts are suspected of degrading the quality of photogrammetric measurements made from demosaiced images. An approach to demosaicing based on the use of tuneable Gaussian filters is proposed. The new approach is designed to minimise image artefacts and is specifically aimed at improving the quality of photogrammetric measurements made with the demosaiced imagery. Results are given for a specific application of Bayer CFA cameras to underwater stereo length measurement of fish. The results show a reduction in visual artefacts and an improvement in the quality of stereo measurements.
This paper will present details of a coded target system that employs a Hough transform and segment matching to automatically recognise and identify the targets in digital images. The code system is based on a square surrounding the central circular target and will be described at a level of detail that would allow the system to be readily duplicated. Pre-detection processes, developed to improve the success rate under unfavourable conditions, and the tests conducted to validate a correct target match will also be described. Finally, the paper will include some examples of the use of the coded targets, drawn from calibrations of digital still cameras and underwater stereo-video systems.
This paper reports on initial investigations into appropriate calibration models for and the reliability and stability of the calibration of the Kodak DC200 series cameras. Results of test of different types of digital still cameras are compared, in general, to the DC200 series and then various calibration test of a DC265 camera are presented and analyzed. Block- and photo-invariant camera calibration models are compared to ascertain their suitability for the physical variability of the cameras. In conclusion, this paper makes some recommendations on the potential reliability and stability of the Kodak DC265 camera.
Photogrammetrists have generally made use of wide or super wide angle rectilinear lenses that are designed to reproduce straight lines in the object space as straight lines in the image space. This paper investigates the use of fish-eye optics as an alternative to the conventional super wide-angle lens for vision metrology. The fish-eye design, whilst still retro-focus in construction, rejects the design constraints of rectilinear imaging in exchange for more even illumination across the image format and the expectation of reduced lens aberration effects. By means of a series of practical comparisons, this paper will investigate the target image performance and practical usage of two off-the-shelf 35 mm camera mount lenses, namely an 18 mm focal length super wide- angle rectilinear lens and a 16 mm quasi fish-eye lens. Investigations include: an image quality assessment of retro- target images of differing sizes; an analysis of the variation in retro-target image quality with lens aperture; the influence of the different lenses on the internal consistency of highly over-determined self-calibrating multi-station photogrammetric networks and; an accuracy test between networks obtained with each lens type against measurement of the same targets using an industrial theodolite system.
Portable digital image cameras such as the Kodak DCS420 and 460 are widely used for metric applications of close-range photogrammetry. The use of these cameras is typically in one of two forms, either as a mobile single camera for offline industrial measurement applications, or in a multi-camera system for online operation in a `work-cell' environment. In common with any metric system, the calibration of the cameras is of paramount importance to maintain the fidelity of the collinearity solution, and therefore the maximum possible accuracy. Any variation in the calibration during image capture for an offline or an online system will inevitably have a deleterious effect on the measurement accuracy. This paper describes a series of experiments concerning the calibration stability of DCS420 and 460 cameras in offline and online configurations. The calibration strategy is described and the effect of a minor modification to the CCD sensor mounting is presented. The variations in RMS image residuals and calibration parameters are quantified in terms of magnitude and significance for the different modes of operation.
Small format, medium resolution CCD cameras are at present widely used for industrial metrology applications because they are readily available and relatively inexpensive. The calibration of CCD cameras is necessary in order to characterize the geometry of the sensors and lenses. In cases where a static or slowly moving object is to be imaged, frame capture mode is most often used to maximize the resolution of the CCD sensor. In cases where the object to be imaged is in rapid motion, field mode capture is frequently adopted to avoid discontinuities caused by the interlaced scanning process used by the sensors. A strategy for the computation of calibration parameters for field modes, based on a frame mode calibration, is proposed. The strategy is then verified by testing using real data from test range calibrations of three different types of CCD camera. The results of these calibration tests are described, with particular emphasis on the changes required to adjust between frame and field capture modes.
Close range photogrammetry and vision metrology often use signalized points in the form of active or passive targets. Many theoretical and some practical tests of different target image centering algorithms have been carried out. This paper will describe the empirical testing of several such algorithms using real data acquired for industrial measurement projects and camera calibrations. The precision and accuracy of the centering algorithms will be characterized by analysis of self calibrating network solutions using multiple camera stations and a target array. Particular emphasis will be placed on the comparison between centroiding and ellipse fitting to locate target image center.
This paper will address the topic of multisensor self-calibration in vision metrology systems employing still-video imagery. Under this approach greater fidelity is afforded in the recovery of sensor interior orientation and distortion parameters. Moreover, a combination of wide- and narrow-angle imaging sensors affords a better insight into the problems of in-plane image distortion and out-of-plane sensor surface deformation, which are often overlooked sources of error in metric applications of CCD cameras. This on-site calibration approach is demonstrated in the measurement, to better than 1 to 100,000 accuracy, of a 5m X 2.5m bond tool used in aircraft manufacturing.
Photogrammetry affords the only noncontact means of providing unambiguous six-degree-of- freedom estimates for rigid body motion analysis. Video technology enables convenient off- the-shelf capability for obtaining and storing image data at frame (30 Hz) or field (60 Hz) rates. Videometry combines these technologies with frame capture capability accessible to PCs to allow unavailable measurements critical to the study of rigid body dynamics. To effectively utilize this capability, however, some means of editing, post processing, and sorting substantial amounts of time coded video data is required. This paper discusses a prototype motion analysis system built around PC and video disk technology, which is proving useful in exploring applications of these concepts to rigid body tracking and deformation analysis. Calibration issues and user interactive software development associated with this project will be discussed, as will examples of measurement projects and data reduction.
A stereo vision system has been designed to locate and track a dynamic object in real time. The system consists of two CCD cameras, a frame grabber and digital image processing software. The algorithm is based on the priciple of constructing a mathematical stereo model from two overlapping images while a dynamic object is passing through the scene. The stereo models are constructed at finite time intervals to provide a sequence of locations for the dynamic object. The size, shape, and behavior of the object in the scene, the precise position of CCD cameras and the performance of the system are fundamental parameters which should be carefully considered to achieve an appropriate precision and reliability. The system has two advantages. Firstly, the system is quickly able to recognize, detect, and track and object. Secondly, because fundamental photogrammetric equations (collinearity equations) have been used in this system, the points will be located precisely. This paper will explain the methodolgoy of the system, the problems and issues involved, and outline the results of experimentation with the system.
Signalizing points of interest on the object to be measured is a reliable and common method of achieving optimum target location accuracy for many high precision measurement tasks. In photogrammetric metrology, images of the targets originate from photographs and CCD cameras. Regardless of whether the photographs are scanned or the digital images are captured directly, the overall accuracy of the technique is partly dependent on the precise and accurate location of the target images. However, it is often not clear which technique to choose for a particular task, or what are the significant sources of error. The research described in this paper describes aspects of target recognition, thresholding, and location. The results of a series of simulation experiments are used to analyze the performance of subpixel target location techniques such as: centroiding; Gaussian shape fitting; and ellipse fitting, under varying conditions.
Developers of videometric systems must attend to the problems of image storage, retrieval and, for multi-station triangulation, the unambiguous correlation of images with appropriate epochs. For dynamic testing with multiple cameras, this problem is manifest. An `off-the- shelf' component two camera system was recently developed for measuring the six degree-of- freedom time histories of a free flight wind tunnel model. Vertical interval time codes (VITC) were used to correlate fields from each camera station which had been stored onto video cassette recorders (VCR). Subsequent use and development has emphasized the practicality of this approach. This paper discusses the image management technique used along with some details of the particular wind tunnel application. The utility of post-test processing of long sequences of VITC encoded imagery stored to VCR is established.
KEYWORDS: Video, Analog electronics, Calibration, CCD cameras, Image processing, Video processing, Digital video recorders, Cameras, Frame grabbers, Charge-coupled devices
A clear advantage of digital photogrammetric measurement over other, more conventional techniques in the fast sample rate of the data acquisition. CCD cameras and video systems can be used very effectively to analyze dynamic objects or cases of rapid deformation. However, long sequences of images can introduce the penalty of large volumes of digital data, which may not be able or appropriate to be processed in real time. The images are typically stored in analog form, using media such as video tape or video disk, for off line processing subsequent to the image capture. This paper investigates the degradation in accuracy and repeatability caused by the influence of the analog recording. A number of experiments using a Hitachi medium resolution CCD camera, a three dimensional test range and a self calibrating bundle adjustment are described. For cases of near real time monitoring, the ability of frame averaging to reduce the degradation caused by the analog recording is also investigated. The results of the experiments are presented in summary to provide some guidelines as to the degree of degradation which can be expected under similar circumstances.
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