Uniformity image

In the MRM model, the initial memory matrix is a tabula rasa, a white page that is gradually filled during the reconstruction process, while the reconstructed picture starts with a uniform image, and becomes progressively differentiated in the course of time. A reconstruction with the MRM model, in other words, is a set of two distinct reconstructions that are performed in parallel. The point is that this double reconstruction is necessary for reasons that are absolutely general. 

The flat fielding procedure described above essentially removes all spatial variation in what is assumed to be a uniform imaging field. Nonuniformities in signal that are not due to the detector, but are caused by such phenomena as heel effect of the X-ray tube, variation in X-ray path length through air (inverse square law), the beam filter, compression plate, and... 

The reconstruction filters (kernels) are the same for all four-scan modes, leading to a uniform image appearance when different modes are combined. AU image data can be automatically or retrospectively sent to different network nodes (PCs, workstations, archives) in the conventional DICOM format the new enhanced-... 

Homogeneity of data. Homogeneous data will be uniform in structure and composition, usually possible to describe with a fixed number of parameters. Homogeneous data is encountered in simple NDT inspection, e.g. quality control in production. Inhomogeneous data will contain various combinations of indications from construction elements, defects and noise sources. An example of inhomogenous data are ultrasonic B-scan images as described in [Hopgood, 1993] or as encountered in the ultrasonic rail-inspection system described later in this paper. 

Simulations of the adaptive reconstruction have been performed for a single slice of a porosity in ferritic weld as shown in Fig. 2a [11]. The image matrix has the dimensions 230x120 pixels. The number of beams in each projection is M=131. The total number of projections K was chosen to be 50. For the projections the usual CT setup was used restricted to angels between 0° and 180° with the uniform step size of about 3.7°. The diagonal form of the quadratic criteria F(a,a) and f(a,a) were used for the reconstruction algorithms (5) and (6). 

When the grey level dynamic range in the image processed is small, usually because of a poor illumination or a non uniform lighting, it s possible to increase this dynamic range by a histogram transformation. This transformation affect the intensity distributions and increase the contrast. 

Physical testing appHcations and methods for fibrous materials are reviewed in the Hterature (101—103) and are generally appHcable to polyester fibers. Microscopic analyses by optical or scanning electron microscopy are useful for evaluating fiber parameters including size, shape, uniformity, and surface characteristics. Computerized image analysis is often used to quantify and evaluate these parameters for quaUty control. 

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