Optical noise reduction using partial coherence in spatial filtering for image detail enhancement

Coherent optical spatial filtering can be used to increase the contrast of fine detail in photographs. The images produced, however, contain optical noise blemishes that make the procedure seldom usable in practical photography. A promising method of reducing the optical noise by means of partial coherence in a projection printer has been investigated involving the use of a plurality of point sources. It has been demonstrated, using pictorial enlargements, that subjective sharpness levels may be obtained which are similar to those obtained by using specular illumination while greatly reducing the amount of coherent noise on the image. Enlargements of a sine wave negative have demonstrated the contrast enhancement produced by spatially filtering the zero-order diffraction pattern of the point source array

The parallax view: the military origins of holography

The title of this piece is meant to evoke at least three sources. The first – and perhaps the only obvious one – concerns the ability of holograms to display parallax, a shifting of visual viewpoint that allows a three-dimensional image to reveal background objects behind those in the foreground. This parallax view is a unique feature of holograms as visual media. A second allusion is to the American film The Parallax View (1974, director A. J. Pakula), a rather paranoid thriller focusing on conspiracy theories concerning government and corporations. To a casual observer, the bare details of the military origins of holography suggest just such cynical and centrally-directed development, although I hope to dispel such simplistic ideas here. And a third passing reference is to the book The Parallax View (2006) by Slavoj Zizek, a wide-ranging and deep exploration of duality in political views, ontological interpretations and scientific methods, among other topics. Zizek’s theme, as well as Pakula’s, is relevant to my approach, which focuses on a parallax of both practice and intent. During the first successful decade of holography, conflicting viewpoints developed between distinct communities: the militarily-guided engineers who invented practical holography, and the later imaging scientists and artisans who stressed three-dimensionality and other attributes instead of the original goal of optical image processing. I argue that distinct groups of users had different perceptions of what holography is and what it is for

Conceptual design of an on-board optical processor with components

The specification of components for a spacecraft on-board optical processor was investigated. A space oriented application of optical data processing and the investigation of certain aspects of optical correlators were examined. The investigation confirmed that real-time optical processing has made significant advances over the past few years, but that there are still critical components which will require further development for use in an on-board optical processor. The devices evaluated were the coherent light valve, the readout optical modulator, the liquid crystal modulator, and the image forming light modulator

Image Enhancement Techniques

This paper discusses the enhancement of images to restore detail that has been obscured by blurring. An optical analog method and several digital methods of performing this processing are discussed. Sample results from one of the digital methods are shown

High-performance real-world optical computing trained by in situ model-free optimization

Optical computing systems can provide high-speed and low-energy data processing but face deficiencies in computationally demanding training and simulation-to-reality gap. We propose a model-free solution for lightweight in situ optimization of optical computing systems based on the score gradient estimation algorithm. This approach treats the system as a black box and back-propagates loss directly to the optical weights' probabilistic distributions, hence circumventing the need for computation-heavy and biased system simulation. We demonstrate a superior classification accuracy on the MNIST and FMNIST datasets through experiments on a single-layer diffractive optical computing system. Furthermore, we show its potential for image-free and high-speed cell analysis. The inherent simplicity of our proposed method, combined with its low demand for computational resources, expedites the transition of optical computing from laboratory demonstrations to real-world applications

Image enhancement in a microfilm projection printer utilizing partial coherence and spatial filtering

An optical system was assembled for a study of spatial filtering and partial coherence. It was used to produce enlargements of microfilm images at a magnification of 12-X. Enhancement of fine-detail contrast was obtained by means of a spatial filter that transmitted most of the light diffracted by the microfilm negative and absorbed about 60$ of the undiffracted light. The filter increased the modulation transfer function (MTF) of the enlarging system by a factor of about 1.5 measured at spatial frequencies lying in the region where the eye is most sensitive. At higher frequencies, the enhancement became greater than was expected, possibly because of phase effects. The optical system was partially coherent and produced coherent-noise blemishes in the enlargements. Consequently, a study was made of the effect of decreasing the degree of coherence by increasing the angular size of the light-source aperture. The 0.8 mm aperture being used was replaced successively by larger ones ( 1 , 3 5, 10, and 20 mm) and by a completely diffuse system. The 10 mm aperture (0.04 radians), which gave a coherence interval of 14.3 \u3eum on the negative, reduced the optical noise greatly and produced as good a result in terms of the system MTF as compared to apertures of higher coherence intervals. For the frequency range that is visually important for a 12-X enlargement, it kept the MTF nearly equal to that of a coherent system and made it distinctly better than that obtained with the diffuse system. Spatial filtering with the 10 mm aperture is possible for enhancement at high frequencies that become important when enlargements much greater than 12-X are used

The response of an optical spatial filter system to photographic edges.

Thesis (M.A.)--Boston UniversityThe purpose of this thesis is the empirical determination of the response of an optical spatial filter system to photographic detail edges. Spatial filtering in an optical system refers to a process in which the performance of the system is modified in terms of object size and shape. In its essentials the optical system tested is well known, with spatial filtering experiments having been performed as early as 1906. A renewed interest in recent years has been the result of the application of communication theory to optics. Reference is made to recent publications concerning the analytical treatment of coherent imagery in general and spatial filtering in particular as well as to more recent experimental studies. Theoretical considerations and analytical treatment are included in this thesis to an extent sufficient for the scope of the investigation. [TRUNCATED] The thesis is concluded with the recommendation that further work with the filter system be undertaken from the point of view of producing an optimum filter for a certain practical application. Also the recommendation is made that the system be used for harmonic analysis as a research tool or a classroom demonstration device

Project Tech Top study of lunar, planetary and solar topography Final report

Data acquisition techniques for information on lunar, planetary, and solar topograph