Showing papers on "Edge enhancement published in 1987"

Unsharp masking for image enhancement

Abstract: In an unsharp masking processing for sharpening images such as radiographic images, an emphasizing coefficient of an image and parameters for real-time change of picture quality are set interactively. The entire image is divided into a plurality of regional images and filtering optimized for each pixel image is effected using a standard deviation computed for each regional image and a density difference between pixel images.

Optical Information Processing With The Double Phase Conjugate Mirror

Abstract: The operation of the double phase conjugate mirror (DPCM) is described. It can be regarded as a bidirectional spatial light modulator and controllable filter. Two independent image-bearing beams that may be derived from different lasers exchange their spatial information as they are coupled into each other in a photorefractive crystal. The,DPCM is also shown to be an optical thresholder and spatial filtering device, displaying edge enhancement. We propose the use of a resonator with two facing DPCMs to implement iterative image processing algorithms.

Optical preprocessing using liquid crystal televisions.

Abstract: The suitability of a low-cost liquid crystal TV to function as a spatial light modulator in an optical preprocessor for an electronic pattern recognition system is investigated. The application presented is optical edge enhancement. The liquid crystal TV performs reasonably well where high-quality images are not required. Three optical edge enhancement methods are presented: spatial filtering; image cancellation; and phase cancellation. The phase cancellation method was discovered during the course of this research.

Multiple detector fog suppression and edge enhancement

Abstract: A proximity sensing system and signal processing method for detecting target objects from a movable vehicle (80) while protecting against false target detection due to the presence of fog, clouds, or other aerosols. One or more target detectors (202) are alternately disposed adjacent to one or more guard detectors (201; 203) so the edges of the fields of view are immediately adjacent. A collimated laser beam (B) is projected away from the vehicle by a transmitter (30) along an axis which intersects at an angle with the adjacent fields of view defining active areas in which the beam will be reflected from objects. Signals generated from any beam reflections to a target detector are made positive while signals generated by any beam reflections to a guard detector are made negative with respect to a threshold reference. The signals are summed in a differential amplifier and the resultant signal presented to a digital comparator.

Implementation Of Adaptive Filtration For Digital Chest Imaging

Abstract: Previous work has demonstrated the potential for adaptive filtration in processing digital chest images. The technique uses the histogram of the image to determine the pixels (and regions) in which edge enhancement is applied. This paper extends that work by investigating the choice of parameters used in selectively enhancing the mediastinum. The image is separated into its low and high frequency components by convolution with a square kernel. The effect of kernel size was studied with a choice of 17 x 17 mm, which was found to be sufficient to include the frequencies of interest. A serious deficiency in previous implementations of this technique is the existence of ringing artifacts at the juncture of the lung and mediastinum. These result in part from the use of a step function to specify the low frequency image intensity above which high frequencies are amplified. By replacing this step with a smoother (cosine) function, the artifact can be removed. Finally, the amplification constant was examined in light of its effect on both structure and noise in the image.

Applications of Digital Image Enhancement Techniques to the Ultrasonic NDE of Composite Materials

Abstract: Results of the applications of local and global digital image enhancement techniques to ultrasonic C-scan images of damaged graphite/epoxy composites are presented. The original unenhanced images were generated by using focused ultrasonic transducers with center frequencies between 3.5 and 25 MHz. Small defects were often difficult to detect in the unenhanced images because the relatively small signal amplitude changes resulting from the defects were obscured by the larger signal amplitude changes caused by variations in: (1) surface roughness, (2) material attenuation, and (3) material morphology. Results given in this paper indicate that those enhancement techniques which emphasize the higher spatial frequencies at the expense of the lower spatial frequencies and those techniques which operate on local pixel regions can often remove enough of the undesirable variations to make small defects visible in the enhanced images.

Data dependent filters for the edge enhancement of Landsat images

Abstract: Some 2D-filters that are very efficient in edge enhancement of Landsat imagery are presented. The filtered images are obtained as differences between the original images and some minimum mean square error predictions based on suitably chosen “predictor sets”. The filters are compared to other high pass filters as the Laplacian and Gaussian filters, and they compare very favorably.

Aspects of directional filtering and applications in image processing

Abstract: This paper gives a brief overview of an approach to several problems of image processing based on directional filtering. Definitions and possible implementation routes will be given. Direction filtering allows the extraction from an image of edge structures within a limited interval of directions. It is shown that a powerful edge detection scheme based on one implementation of this filtering may lead to very interesting solutions to various problems such as coding, restoration and texture discrimination.

Applications of Digital Image Enhancement Techniques for Improved Ultrasonic Imaging of Defects in Composite Materials

Abstract: Several standard digital image enhancement techniques have been applied to digitized ultrasonic C-scan images of defects in graphite/epoxy composites. Features in the computer enhanced images are much more distinct than those in the original images. In some cases, cracks which are too close together to be visually resolved in the original images are clearly resolved in the enhanced images. Noisy images have been improved by first smoothing the original data and then edge enhancing the smoothed data. The resulting sharpened edges improve the visualization of features in the images. The application of digital image enhancement techniques has allowed the imaging of defects in composite materials at frequencies as low as 3.5 MHz. This use of these lower frequencies permits better imaging of defects in thick composite materials.

Utilization Of Spatial Self-Similarity In Medical Image Processing

Abstract: Many current medical image processing algorithms utilize Fourier Transform techniques that represent images as sums of translationally invariant complex exponential basis functions. Selective removal or enhancement of these translationally invariant components can be used to effect a number of image processing operations such as edge enhancement or noise attenuation. An important characteristic of many natural phenomena, including the structures of interest in medical imaging is spatial self-similarity. In this work a filtering technique that represents images as sums of scale invariant self-similar basis functions will be presented. The decomposition of a signal or image into scale invariant components can be accomplished using the Mellin Transform, which diagonalizes changes of scale in a manner analogous to the way the Fourier Transform diagonalizes translation.

Color Optical Processing Using A Microchannel Spatial Light Modulator Under White Light

Abstract: The color characteristics of a microchannel spatial light modulator (MSLM) under white-light read out illumination is examined, and a system for performing color optical processing operations using an electro-optic crystal plate along with the MSLM is presented. Experimental results for edge enhancement and image subtraction operations are demonstrated.

A Digital Camera and Real-Time Image Correction for Use in Edge Location.

Abstract: The accuracy of a depth map acquired using triangulation or stereo techniques is limited by the resolution of the sensor, and by the accuracy with which distortions of the image can be calibrated. This paper lists the sources of error in an imaging system, and concludes that most of them can be removed by careful camera design and calibration, with the exception of the spatial quantisation (discrete sampling). The use of a high-fidelity camera in performing experiments to calculate the errors in a lens and CCD array is described, and the results are compared with a standard technique for camera calibration. A pipeline architecture for real-time calibration of the image is proposed.