J. Paul Owain Evans

Morphological corner detector using paired triangular structuring elements

This paper describes corner detection from segmented areas using mathematical morphology employing paired triangular structuring elements. The algorithm identified as TriSE02 detects the inner corners of a segmented area and stores information regarding each corners angular orientation and position. The theoretical development of this detector together with its empirical performance is established in a test utilising standard template images. Seven other established corner detectors were also tested to provide comparative performance information. This work was originally developed to identify conjugate corners in stereoscopic dual-energy X-ray images produced by an experimental system for aviation security screening. The oversensitivity exhibited by the established detectors when applied to the dual-energy X-ray images has been significantly improved upon by the new detector. Also, the careful development of the default parameterisation has resulted in a flexible approach, which is suitable for different image types and formats.

Line-scan system for all-round inspection of objects

Sensor choice is critical in all object inspection imaging systems and the suitability of different types of sensor must be thoroughly assessed before a decision is made. Despite its wide use, a television type camera may not represent the best choice for certain object inspection applications. Specifically, when inspection of an object that has a degree of cylindrical symmetry is required, a line-scan camera is a viable alternative to the television type and, in general, any matrix camera, offering a number of unique advantages. By applying rotational motion to the object of interest and using a line-scan device, an 360 degree(s) view of the object is obtained. The cylindrical surface of the object is effectively unfolded into a planar 2D one, allowing for the efficient inspection of the entire surface of the object from a single, continuous image. To allow accurate object space co-ordinate measurement, a line-scan camera calibration technique has been developed, catering for both interior and exterior parameter calibration. The former accounts for the lens effective focal length, the pierce-pixel value and the timing of the line-scan camera, while the latter yields the relative position and orientation of the camera with respect to a reference object space co-ordinate system.

Line-scan sensor: an alternative sensor modality for the extraction of three-dimensional coordinate information

We describe research carried out to investigate a stereoscopic line-scan system for the extraction of 3-D coordinate information from a scene of interest. Initial work involved analyzing the operating characteristics of a line-scan device for the production of 2-D images. Following this, a theoretical appraisal was undertaken of a sensor in a stereoscopic arrangement, and a mathematical model was derived for the calibration of a novel camera system. Algorithms to determine the 3-D relationship of points in the object space were developed using this model. To test the suitability of the model, a complete stereoscopic line-scan system was constructed. Experiments were conducted with the stereo camera to establish the accuracy that is achieved with such a system using the developed algorithms. The results indicate that the relative position of points in the object space could be determined to an accuracy of less than 1 mm at a range of 1.5 m.

Panoramic line-scan imaging system for teleoperator control

It is the intention of this paper to give details of the continuing research into obtaining 3-D coordinate information from an object space using non-standard video sources. Details are given on producing images with the line-scan sensor by rotating the device relative to an object space. Theoretically, this could provide picture information from a potential 360 degree panoramic view. However, initial results have demonstrated that such images are difficult for humans to interpret. Details are given in this paper on the limitations of the line-scan images produced from camera rotation for presentation to human observers.

Numerical classification of curvilinear structures for the identification of pistol barrels

This paper demonstrates a numerical pattern recognition method applied to curvilinear image structures. These structures are extracted from physical cross-sections of cast internal pistol barrel surfaces. Variations in structure arise from gun design and manufacturing method providing a basis for discrimination and identification. Binarised curvilinear land transition images are processed with fast Fourier transform on which principal component analysis is performed. One-way analysis of variance (95% confidence interval) concludes significant differentiation between 11 barrel manufacturers when calculating weighted Euclidean distance between any trio of land transitions and an average land transition for each barrel in the database. The proposed methodology is therefore a promising novel approach for the classification and identification of firearms.

Multiple-view stereoscopic line-scan imaging

A novel multiple view line-scan imaging technique that can be applied to transmission x-ray imaging as well as reflected light cameras is presented. In either case an area array image sensor is treated as a contiguous set of precisely arranged line-scan devices utilizing a single perspective center. IN the case of reflected light the perspective center is the nodal point of a lens whilst in the x-ray case it is the focal spot of an x-ray source. The line-scan images are accumulated in digital memory whilst the object under inspection is linearly translated through the field of view of the camera. In this way a number of perspective images, typically 6 to 16 are produced. The 3D information inherent in the perspective views can be visualized as a smooth object rotation or as a dynamic binocular stereoscopic sequence of views.

Motion-induced depth effect using a multiple-view dual-energy x-ray camera

A novel 3D X-ray imaging technique to enhance the visual interpretation of complex X-ray images routinely encountered in aviation security applications has been developed. The 3D information is visualised as a smooth object rotation on a video display monitor. Further work enabled motion parallax to be combined with binocular parallax to produce a dynamic stereoscopic display. This imaging technique is equally applicable to both standard monochrome X-ray imaging and dual-energy X-ray imaging. The latter exploits the difference in magnitude between a high energy X-ray signal and a low energy X-ray signal to compute materials discrimination information made available to the human observer by colour encoding the resultant images. To produce the required image data an integrated dual-energy X-ray camera incorporating a novel castellated dual-energy scintillator arrangement has been developed.

Derivation of 2.5D image models from one-dimensional x-ray image sensors

This paper describes on-going research into the development of a 21/2D image modeling technique based on the extraction of relative depth information from stereoscopic x-ray images. This research was initiated in order to aid operators of security x-ray screening equipment in the interpretation of complex radiographic images. It can be shown that a stereoscopic x-ray image can be thought of as a series of depth planes or slice images which are similar in some respects to tomograms produced by computed tomography systems. Thus, if the slice images can be isolated the resulting 3D data set can be used for image reconstruction. Conceptually, the production of a 21/2D image from a stereoscopic image can be thought of as the process of replacing the physiological depth cue of binocular parallax, inherent in a stereoscopic image, with the psychological depth cues such as occlusion and rotation. Once the data is represented in this form it is envisaged that, for instance in the case of a security imaging scenario a suspicious object could be electronically unpacked. The work presented in this paper is based on images obtained from a stereoscopic folded array dual energy x-ray screening system, designed and developed by the Nottingham Trent University group.

Three-dimensional line-scan imaging system for robotic measurement

This paper describes continuing work with three-dimensional (3-D) rotating line-scan vision systems in robotics and measurement. Mathematical algorithms have been developed for use with the line-scan arrangement allowing the extraction of three-dimensional co-ordinate information from an observed object workspace. To determine the measurement capability of the stereoscopic system, comparison is made between the system output data (calculated from image space values) and a calibrated volume in object space containing a distribution of target points. This paper describes the mathematical model and results pertaining to the current research demonstrate the use of the rotating line-scan scenario to the solution of specific applications where conventional sensor modalities may not be appropriate.

From stereoscopic x-ray images to 2.5-D volume visualization

The interpretation of standard 2D X-ray images by humans is often very difficult due to the lack of visual cues to depth in an image produced by transmitted radiation. The 3D Imaging Group has previously developed stereoscopic X-ray systems providing binocular parallax as a depth cue to aid images interpretation. The stereoscopic images produced have proven suitable for human viewing and allow the observer to determine the relative position of objects within the scene under consideration. Such additional information is useful for scene interpretation and understanding. The binocular parallax introduced into X-ray images can be utilized in a similar way to television type stereoscopic systems where the disparity is used to determine the range of objects within the scene. This range information can be used in a number of ways, for instance co-ordinate measurement. Current research at Nottingham has concentrated on grouping object points of similar depth and producing a series of contiguous slices through the scene of interest. The purpose of producing this new data base is to combine this and existing reconstruction software used in CAT scanning techniques to provide a 21/2D visualization of the observed scene or object. This representation of the scene is intended to introduce an alternative view to the observer, further enhancing their interpretation ability.