Image Processing & Applications

This paper is concerned with small strain measurement utilizing the numerical processing of digital images. The proposed method has its theoretical basis in digital signal analysis and, from a methodological point of view, it can be considered as an extension to digital images of the well-known white light speckle photography technique. That conventional method is based on the analysis of photographic plates that are exposed twice (before and after the specimen deformation) with the image of a random speckle pattern that has been previously printed on the test piece surface. The digital speckle correlation advantages consist of requiring a very simple specimen preparation and, mainly, of allowing the strain field computation just by numerical elaboration of the acquired images. In this paper, the theoretical basis of the technique and some valuable improvements to the known analogous methodologies are presented. Finally, test results for an application of digital speckle correlation are shown and advantages and disadvantages of the technique are elaborated. In addition, further developments in this area are discussed.

Keywords: Image processing , Speckle correlation , Speckle methods , Speckle photography , Strain analysis

This work presents a procedure aimed at automatically extracting the medulla duct outlines from a human femur radiographic image. The outlines are retrieved by referring to a suitable geometric model of the generic femoral cross section; the projection function deriving from such a model is fitted on the grey level values corresponding to the rows of the digitised radiographic image by means of a least square algorithm. The resulting outlines are used in a software system performing the hip prosthesis pre-operational planning.

An experimental study was carried out to analyze the temporal and spatial evolutions of a high pressure swirled spray from an electronically controlled single-hole injector for Direct Injection of fuel in Spark Ignition engines. As such, the experimental set up and the image processing technique have proven to be effective in describing the time- and space-evolution of the spray and they can be easily adapted to further application for different injection systems. The results have provided useful information for a better understanding of the phenomena related to the high-pressure swirled-injector sprays.

A computational model and an experimental analysis have been performed to study the atomisation processes of hollow cone fuel sprays from a high pressure swirl injector for gasoline direct injection (GDI) engines. The objective has been to obtain reliable simulations and better understood structure and evolution of the spray and its interaction with air the flow field. The 3D computations are based on the KIVA 3 code in which basic spray sub models have been modified to simulate break-up phenomena and evaporation process. Spray characteristics have been measured using a system, able to gather and to process spray images, including a CCD camera, a frame grabber and a pulsed sheet obtained by the second harmonic of Nd-YAG laser (wavelength 532 nm, width 12 ns, thickness 80 μm). The readout system has been triggered by a TTL signal synchronized with the start of injection. A digital image processing software has been used to analyse the collected pictures. Computed and measured spray characteristics, such pre-spray and main-spray structure, tip penetration and break-up phenomena, have been compared, achieving good levels of agreement. Copyright © 2002 Society of Automotive Engineers, Inc.

The main aims of this paper are to describe the thermographic methodologies currently used in Italy for the rapid evaluation of the fatigue limit and to describe the local energy approach actually under development by the authors. Thermographic methodologies currently used in Italy for the rapid evaluation of the fatigue limit were applied to two stainless steels (AISI 304 atad AISI 409). All the experimental results here obtained are in good agreement with the respective values reported in literature. An experimental programme for the local energy approach is under development: its main characteristic consists in doing, besides the usual thermal measurements made by thermography, mechanical measurements in order to evaluate the mechanical energy locally dissipated inside the material. This experimental research is part of an interuniversity research programme and it is made on stainless steel (AISI 304) notched specimens. © 2002 SPIE · 0277-786X/02/$15.00.

Keywords: Fatigue limit evaluation , Local energy approach , Thermographic methodologies

An extensive experimental work has been made in order to analyze the structure of the spray of a large-angle single-hole high-pressure swirl injector for direct-injection spark-ignited (DISI) gasoline engines. Spatial and temporal evolution measurements of the spray have been carried out in an optically accessible vessel. The spray has been lighted by an 80 mm thickness and 12 ns duration pulsed laser sheet, generated by a 532 nm Nd-YAG laser, both along the spray axis and in cross sections perpendicularly to it. The scattered light has been collected at 90° from the laser sheet direction by a digital CCD camera with a frame grabber synchronized to the single-shot injection command and the laser start pulse. A digital image processing system has allowed analyzing the images collected by the CCD camera. It has been possible to visualize the formation and the spatial and temporal evolution of the initial liquid slug (pre-spray) and of the hollow-cone and solid-cone stray structure. Many changes in the internal spray structure at different distances from the nozzle have been observed.

This work illustrates a computer program designed to aid surgeons in selecting the hip prosthesis femoral component during the preoperation planning stage of hip replacement surgery. Starting from the processing of the patient's coxo-femoral region X-ray image, the program, called Hippin, interacts with the user to outline the femoral region, including the head and the inner contour of the proximal femur. It automatically examines all possible couplings with the patient's femur outlines from a database containing the outlines of the available prostheses created by digitizing the templates normally used in preoperation planning. The resulting images enable the surgeon to visually compare all the alternatives. In addition, the program provides numerical values for the distances between the physiological rotation and prosthesis centers, helping the surgeon in selecting from among the possibilities. The program has been validated by comparing the computer results with actual surgeon selections. (C) 2000 Elsevier Science Ireland Ltd.

Keywords: Hip prosthesis , Image processing , Preoperation planning

The phase stepping technique has recently been applied to the automated analysis of photoelastic fringes to determine the isoclinic parameter and the relative retardation. Generally, in these methods the error of quarter-wave plates, due to common manufacturing tolerances, influences the determination of the isoclinic parameter and the fringe order. In this paper a new phase stepping method in which the influence of quarter-wave plate error is null on the isoclinic parameter and negligible on the fringe order is proposed. The theoretical results have been confirmed by experimental tests.

Keywords: Image processing , Phase stepping , Photoelasticity

The analysis of bone-remodelling processes by means of the relative radiographic follow-up has been proven to be a useful clinical diagnostic tool. A previous study has introduced a computerized, automatic, video-densitometric analysis. The main point of this procedure is that it potentially allows an objective, quantitative analysis of bone remodelling processes. This assertion is addressed by the present study. In particular, this study attempts to assess the repeatability of this procedure and to identify the main sources of noise.

Keywords: Bone-remodelling , Design of experiments , Diagnostics , Digital radiography , Factorial plane , Hip prosthesis , Image processing , Robustness , Video-densitometric analysis

Video-densitometric analysis has proved useful in the study of bone remodelling, however, for more efficient results, an investigation procedure that enables the comparison of X-rays is needed. In the present research an automated method has been developed which considerably speeds up the entire procedure through the implementation of specially designed C++ software. At present, a sequence of six X-rays can be analysed in about 1 h irrespective of the number of areas to be investigated, which can be arbitrarily increased (200 or more). Analysis is fast as well as more reliable and accurate. In clinical practice, the results offer an effective support to observations on the biomechanical behaviour of bone implant systems.

Keywords: arthroprosthesis implants , Bone remodelling , follow-up assessment , video-densitometric analysis , X-ray analysis