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A severely defocused incoherent system has isolated zeros in its optical transfer function(OTF); therefore, an exact inverse filtering cannot be performed. It has been established that, by using an annular aperture in an optical system, the depth of focus can be extended. Isolated zeros in the OTF can therefore be avoided by choosing an annular aperture with a proper radius ratio. However, in the process of increasing the depth of focus of the system, this method results in a loss of image contrast. An annular pass filter can be used to restore this loss in contrast. A simple hybrid optical/digital image processing system in which a TV camera is coupled with an annular aperture is considered. The annular-pass filtering to compensate for the loss of contrast is performed by a digital computer. The experimental results are presented. / M.S.

The effect of spatial frequency manipulation of color images and its impact on subjective image quality were examined by measuring subjective image quality and the changes in several prominent image quality metrics. The Modulation Transfer Function Area (M1F A), the Square Root Integral (SQRI), the Integrated Contrast Sensitivity (ICS), the Subjective Quality Factor (SQF), and several other acutance-derived image quality metrics were evaluated for their ability to predict image quality. Five distinct spatial frequency filters were applied to each of four pictorial color scenes in the horizontal dimension, the vertical dimension, and in a combined two dimensional format. The same spatial frequency filters also were applied in a circular format. Thirty-two subjects, 24 college students and 8 Eastman Kodak employees, participated in a paired comparison method in which 21 stimuli for each of the four scenes were evaluated for their perceived image quality. Horizontal and vertical modulation transfer functions were acquired by photometric scans of a cross-hair one-pixel wide white line target as well as by luminance profile manipulation of square-waves of differing frequencies, both utilized as input signals. From the modulation transfer functions, values for the various image quality metrics were calculated and related to the subjective image quality data. In the evaluation of perceived image quality, several experimental procedures are available, such as magnitude estimation, rank ordering, rating-scale, categorical judgments, and the method of paired comparison. The method of paired comparison is frequently avoided for its time consuming nature. However, results indicate that with the use of computer automatization it is a powerful and reliable experimental procedure for testing subjective preferences between digital stimuli containing small perceptual differences. The highest correlation between perceived image quality and image quality metrics was obtained for the pictorial scene which contained a uniform and dense set of frequencies in the horizontal and vertical directions. The lowest R 2 values were reported from the pictorial scene that contained more scattered frequencies in both directions. Therefore, it is advised when performing perceived image quality evaluations of frequency-manipulated pictorial stimuli to use those stimuli that contain a broad range and uniform set of spatial frequencies. The impact of frequency manipulation is then more apparent and, in addition, it may provide for a more reliable transfer of results across experiments. Small increases in modulation produced perceived quality increases in the pictorial color images. Furthermore, improved image quality was obtained with low frequency (less than 9 c/deg) modulation enhancement. In addition, vertical filtering produced greater subjective image quality improvement than did horizontal filtering. For all scenes, the two-dimensional filtered images were perceived as possessing equal or better quality than the circular filtered images. Low-frequency enhancement, close to zero spatial frequency, and no high-frequency enhancement, only minutely (if at all), increased perceived image quality; however, continuing the enhancement process from the low frequencies to the higher frequencies significantly improved perceived image quality. The SQRI metric is not recommended for use in the evaluation of image quality when changes in the MTFs occur at spatial frequencies of 3 cycles per degree and higher. The ICS and MTFA behaved in an acceptable manner with changes in subjective image quality and should be considered for their computational accuracy and practicality. The SQF and the acutance metrics were highly recommended for predicting subjective image quality. In addition, the development of a standardized display measurement technique for color CRTs and a standardized verification process of display image quality are recommended. / Ph. D.

The focal plane power distribution due to a bright source is analyzed for an infrared imaging optical system. Irradiance from the bright source is spread throughout the focal plane according to the characteristics of the system. This effect is attributed to diffraction, reflection and scattering in the optical train. Expected focal plane power distributions due to diffraction and multiple reflections between dielectric surfaces are calculated and compared to measured data. The difference is attributed to scatter characteristics of the optical elements. A brief overview of the major sources of scatter lays groundwork for a further analysis of scattering characteristics in the optical system. / Master of Science

Rapid engineering developments in electronic imaging during the last decade have led to the widespread use of color CRT displays. misconvergence among the primary colors of a shadow-mask CRT is a principle human factors concern for applications of this technology. The major objectives of this research were: (1) to determine the effect of misconvergence on visual search performance (i.e., search time and error), (2) to examine the effects of misconvergence on subjective image quality estimates, and (3) to examine the interactions among target size, nontarget density, and misconvergence type and degree upon subjective and objective human performance indices. Ten participants performed a visual "search-and-select" task on a color CRT computer workstation. Following each trial in this procedure, participants subjectively rated the image quality of the display screen using a 9-point scale. Reducing target size increased selection errors and response times, while increasing nontarget density generally increased response times. Type and degree of shadow-mask CRT misconvergence had almost no effect on visual search performance, suggesting that low levels (1 to 2 arcmin) of misconvergence may be acceptable in effective color CRT applications. However, misconvergence adversely affected subjective image quality ratings, indicating that color CRT usage should be avoided where their use is not essential. / Master of Science

The multispectral scanners (MSS) of the LANDSAT satellites collect solar radiation of different wavelengths reflected from the earth's surface. While the different greytone values of a given band of a LANDSAT image of simple terrain are due almost entirely to the various reflectivity values of the features of the earth's surface (such as vegetation, mineral deposits, or bodies of water), the same is not true of areas of complex topography. In mountainous areas, the mixture of light and dark regions in a LANDSAT image may be due to shadow effects as well as the reflectivity values for those wavelengths of light of the various surface features. In this research, an illumination model is developed to help understand features observed in a LANDSAT scene of a mountainous area. The illumination model is defined and its implementation in the GIPSY (General Image Processing System) system is discussed. The application of the model to a particular LANDSAT scene is described including the development of an elevation model from the LANDSAT data. Finally, the illumination model image is compared with the LANDSAT scene and the results are discussed. / Master of Science

Just as image processing and image data bases have moved out of the lab and into the office environment, so has the need for image enhancement. Image scanners must to be able to capture and store a wide variety of information including faded documents, carbon copies, signatures, postmarks, etc. OCR systems put further demands on scanned image quality in terms of low noise, and unbroken disconnected characters. Straight thresholding techniques do not always meet the performance requirements, but by applying simple image processing techniques some of these problems can be solved. However, more burden is placed on the users to control the image enhancement techniques. The users, most of whom have little technical background, want no part in adjusting parameters. This paper proposes a method of examining small windows of the image to derive parameter settings autonomously. Histograms allow rudimentary measures to be used in setting parameters for edge detection, non-linear filters, and point operators such as non-linear gray scale mapping. Some examples of automatic parameter setting are given in chapter three. / Master of Science

This document describes the design and construction of a high performance Micro Channel interface. The interface collects image data from a color linescan camera and transfers this data into the Micro Channel system memory. A maximum data transfer rate of 20 Mbytes/sec can be achieved using the camera interface. Programmability is offered in features such as collected field-of-view, data format, collection method, and camera control. A DOS device driver is developed for the collection of camera images. The final design is constructed to collect images intended for real-time image processing by Micro Channel resident processor(s). / M.S.

Abstract not available