Showing papers on "Histogram equalization published in 1983"

Histogram concavity analysis as an aid in threshold selection

Abstract: A well-known heuristic for segmenting an image into gray level subpopulations is to select thresholds at the bottoms of valleys on the image's histogram. When the subpopulations overlap, valleys may not exist, but it is often still possible to define good thresholds at the `shoulders' of histogram peaks. Both valleys and shoulders correspond to concavities on the histogram, and this suggests that it should be possible to find good candidate thresholds by analyzing the histogram's concavity structure. Histogram concavity analysis as an approach to threshold selection is investigated and its performance on a set of histograms of infrared images of tanks is illustrated.

Smoothed histogram modification for image processing

Abstract: The technique of constructing a transformation, or regrading, of a discrete data set such that the histogram of the transformed data matches a given reference histogram is commonly known as histogram modification. The technique is widely used for image enhancement and normalization. A method which has been previously derived for producing such a regrading is shown to be “best” in the sense that it minimizes the error between the cumulative histogram of the transformed data and that of the given reference function, over all single-valued, monotone, discrete transformations of the data. Techniques for smoothed regrading, which provide a means of balancing the error in matching a given reference histogram against the information lost with respect to a linear transformation are also examined. The smoothed regradings are shown to optimize certain cost functionals. Numerical algorithms for generating the smoothed regradings, which are simple and efficient to implement, are described, and practical applications to the processing of LANDSAT image data are discussed.

An Investigation of Digital Mammographic Imaging

Abstract: Measurements and theoretical calculations of the limitations of film-screen mammography have been made. The results show that the use of mammographic film-screen systems to image the breast has three major drawbacks: 1) insufficient contrast enhancement for the visualization of subtle tumours and microcalcificatons; 2) limited latitude, i.e. in some patients, structures in thin and thick or dense regions of the breast are not clearly visible on the same film; and 3) dose inefficiency, since most mammograms are not quantum-limited. Digital techniques may overcome these problems by decoupling the image recording and display processes, allowing for contrast enhancement without loss of dynamic range. Using digitized film mammograms and phantom images, we have made a preliminary study of whether image processing can improve visualization of breast lesions. Contrast enhancement by histogram equalization and linear scaling with clipping, and edge enhancement by unsharp masking allowed the extraction of more information than was originally perceived on the film. In these images, however, film grain noise accounts for at least one-third of the total image noise, and thus limits the degree to which the images can be enhanced. To investigate the feasibility of recording digital mammographic images directly, an x-ray image intensifier (XRII) was evaluated. With the use of geometric magnification and small focal spot x-ray tubes, the XRII can produce images with sufficient resolution for mammography. Noise power spectra of both XRII and film-screen images were measured. The XRII was found to have better sensitivity and, if structural mottle can be removed, a higher signal-to-noise ratio than mammographic film-screen systems; however, it is limited by the high attenuation of the front input window at mammographic energies.

Interactive X-Ray And Particle Image Processings (Ixpip) In The Inertial Confinement Fusion Experiments

Abstract: Two-dimensional images by X-rays or particles in the inertial confinement fusion (ICF) experiments are digitally processed in a short period of time. Using a minicomputer image processing system, we find that such digital image processings as local average, gray scale transformation, level slice, two-dimensional intensity profile display, histogram equalization and pseudo-color display are useful for those ICF images. And, tomographic features of URA (uniformly redundant arrays) camera are investigated by computer simulation. According to calculation, URA camera will be useful for plane-like or small targets because of its brightness and high S/N.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Dual Image Processing For Stereoscopic Display

Abstract: For an in-depth study of features of the celestial surface, stereoscopic imaging technique serves as a powerful and efficient tool as it brings in depth information onto the images displayed. A system registering the stereo pair of satallite images, processing the dual images for enhancement and restoration and displaying them in twin picture tubes for stereo visualization is described. As an example, edge enhancement, median filtering and histogram equalization techniques are applied to the experimental stereo pair of images to show a considerable improvement in the quality of the 3D image visualized. Bicircularly polarized viewing system is used in the stereoscopic display system enabling the display for mass viewing. A method of generating the range image and stereoscopic image pair is also indicated.

Interactive image processing for observer performance enhancement

Abstract: Image processing techniques may be applied to assist a human observer in TV-reconnaissance tasks. Various enhancement methods have been investigated experimentally with regard to their measurable influence on observer performance. Global contrast enhancement by means of linear histogram stretching proved to be most suitable in target detection, in comparison with histogram equalization or histogram hyperbolization. In case of target classification local enhancement techniques and zoom operations resulted in an essential increase of observer performance. When implementing interactive image processing techniques in observation tasks the design of a convenient man-machine interface is a focal point. An operator station is put forward, whereby an observer may specify procedures and parameters by means of interactive tools (joystick, lightpen, function keys) using a user-guiding menu technique.