: The field of picture processing by computer is reviewed from a technique-oriented standpoint. Only the processing of given pictures (as opposed to computer-synthesized pictures) is considered. Specific areas covered include: (a) Pictures as information sources and their efficient encoding; (b) Approximation of pictures - sampling and quantization techniques; (c) Position-invariant operations on pictures and their implementation (digital, electro-optical, optical); applications to matched filtering (template matching), spatial frequency filtering and image restoration, measurement of image quality, and image enhancement ('smoothing' and 'sharpening'); (d) Picture properties (linear; local and 'textural'; random) useful for pictorial pattern recognition; (e) 'Figure extraction' from pictures; figure properties (topology, size, shape); (f) Picture description and 'picture languages.' (Author)

Picture processing by computer

Structured light refers to the generation and application of custom light fields. As the tools and technology to create and detect structured light have evolved, steadily the applications have begun to emerge. This roadmap touches on the key fields within structured light from the perspective of experts in those areas, providing insight into the current state and the challenges their respective fields face. Collectively the roadmap outlines the venerable nature of structured light research and the exciting prospects for the future that are yet to be realized.

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Roadmap on structured light

Publisher Summary This chapter describes the self-imaging phenomenon and its applications. The self-imaging phenomenon requires a highly spatially coherent illumination. It disappears when the lateral dimensions of the light source are increased. When the source is made spatially periodic and is placed at the proper distance in front of the periodic structure, a fringe pattern is formed in the space behind the structure. The chapter discusses the theoretical and applicational aspects of the self-imaging phenomenon—that is, the property of the Fresnel diffraction field of some objects illuminated by a spatially coherent light beam. The applications of self-imaging are summarized in four main groups—namely, (1) image processing and synthesis, (2) technology of optical elements, (3) optical testing, and (4) optical metrology. The chapter describes the double diffraction systems using spatially incoherent illumination. The first periodic structure plays the role of a periodic source composed of a multiple of mutually incoherent slits. Depending on whether the periods of two periodic structures are equal, the Lau or the generalized Lau effect is discussed. Various applications of incoherent double-grating systems are described in the fields of optical testing, image processing, and optical metrology. After examining some cases of coherent and incoherent illumination, the general issue of spatial periodicities of optical fields and its relevance to the replication of partially coherent fields in space is discussed.

I The Self-Imaging Phenomenon and its Applications

As nanofabrication technology progresses, the emerging metasurface has offered unique opportunities for holography, such as an increased data capacity and the realization of polarization-sensitive functionality. Multicolor three-dimensional (3D) meta-hologram imaging is one of the most pursued applications for meta-hologram not yet realized. How to reduce the cross-talk among different colors in broad bandwidth designs is a critical question. On the basis of the off-axis illumination method, we develop a novel way to overcome the cross-talk limitation and achieve multicolor meta-holography with a single type of plasmonic pixel. With this method, the usable data capacity can also be improved. It not only leads to a remarkable image quality, with a signal-to-noise ratio (SNR) five times better than that of the previous meta-hologram designs, but also paves the way to new meta-hologram devices, which mark an advance in the field of meta-holography. For example, a seven-color meta-hologram can be fabricated with a color gamut 1.39 times larger than that of the red, green, and blue (RGB) design. For the first time, a full-color meta-holographic image in the 3D space is also experimentally demonstrated. Our approach to expanding the information capacity of the meta-hologram is unique, which extends broad applications in data storage, security, and authentication.

Multicolor 3D meta-holography by broadband plasmonic modulation

The basic techniques in generating and reconstructing holograms on a digital computer are described. Some applications of computer holography, including optical spatial filtering and the testing of optical surfaces, are discussed. Finally, the results on the effects of sampling and quantizing holograms are reviewed.

Digital holography

When a hologram is desired from an object which does not exist physically but is known in mathematical terms, one can compute the hologram. An automatic plotter will make a drawing at a large scale which is then reduced photographically. Since the drawing can contain only black and white areas, we have developed a theory for binary holograms. They are equivalent in terms of image reconstruction with ordinary holograms. This has been proven theoretically and verified experimentally.

Binary Fraunhofer Holograms, Generated by Computer

The setup used in many optical data processing schemes is a coherent optical image forming system. The most important lement in this setup is the complex spatial filter. It can perform a large variety of linear operations upon the object or input. In general, it is difficult to produce complex filters, since both amplitude transmission and phase delay may vary across the filter plane in a complicated manner. Our own filters which are very similar to binary holograms, consist of many little transparent rectangles on opaque background. They can easily be drawn on a large scale by a computer-guided plotter, and then photographically reduced in size. We show that our filters, despite containing only amplitude values zero and one, can perform any data processing operation which could be performed by any complex filter. After explaining the principle, we present three groups of applications. First, we describe new versions of some classical methods: schlieren observation and phase contrast. Next, we report on spatial which perform differential operations upon the object in order to enhance gradients or corners. Finally, we use our binary filters for signal detection.

Computer generated spatial filters for coherent optical data processiing.

Among the conceivable uses of Fresnel Zone Plates (FZP) are image formation, synthesis of holograms, coherence measurements, spectrometry, optical analog computation, and optical testing. Sometimes it is desirable to change the scale of the FZP continuously, for example to give a zoom lens effect when the FZP is used for image formation. Here we describe four ways of creating a FZP pattern as a moire effect by superposing pairs of suitable masks. The relative position of the two masks determines the FZP scale. The theory presented here is sufficiently general to allow the synthesis of patterns other than the FZP by means of a variable moire effect.

Variable Fresnel Zone pattern.

The theory of a superresolution experiment is developed. To achieve superresolution one must know in advance some properties of the objects, e.g., nonbirefringence, time independence, or wavelength independence. Assuming that the objects are nonbirefringent, it would be wasteful to use the two possible states of independent linear polarization of the light for simultaneously carrying the same information twice through the image-forming system. One can avoid this waste by inserting polarizers and certain double-refracting components into the system, so that the two states of polarization instead carry different information through the conventional image-forming system. The transfer function of such a superresolution system is derived for coherent and incoherent object illumination. It confirms qualitatively the results of previously reported experiments. A modification of the system is then proposed so that the one-dimensional restriction of the original concept is eliminated. The transfer function for the modified system is derived and numerical examples are presented. The modification imposes a further constraint on the class of allowed objects: the objects must be time-independent or only slowly time-varying.

D. P. Paris

Papers

Binary Fraunhofer Holograms, Generated by Computer

Computer generated spatial filters for coherent optical data processiing.

Variable Fresnel Zone pattern.

Superresolution for Nonbirefringent Objects

A Computer Generated Spatial Filter, Applied to Code Translation