Computer and Robot Vision Vol. 1, by R.M. Haralick and Linda G. Shapiro, Addison-Wesley, 1992, ISBN 0-201-10887-1.

Computer and Robot Vision

Dielectric microspheres with appropriate refractive index can image objects with super-resolution, that is, with a precision well beyond the classical diffraction limit. A microsphere is also known to generate upon illumination a photonic nanojet, which is a scattered beam of light with a high-intensity main lobe and very narrow waist. Here, we report a systematic study of the imaging of water-immersed nanostructures by barium titanate glass microspheres of different size. A numerical study of the light propagation through a microsphere points out the light focusing capability of microspheres of different size and the waist of their photonic nanojet. The former correlates to the magnification factor of the virtual images obtained from linear test nanostructures, the biggest magnification being obtained with microspheres of ∼6-7 μm in size. Analyzing the light intensity distribution of microscopy images allows determining analytically the point spread function of the optical system and thereby quantifies its resolution. We find that the super-resolution imaging of a microsphere is dependent on the waist of its photonic nanojet, the best resolution being obtained with a 6 μm O microsphere, which generates the nanojet with the minimum waist. This comparison allows elucidating the super-resolution imaging mechanism.

Super-Resolution Imaging of a Dielectric Microsphere Is Governed by the Waist of Its Photonic Nanojet

The spatial resolution of an optical system is limited by diffraction. Various schemes have been proposed to achieve resolution enhancement by employing either a scanning source/detector configuration or a two-photon response of the object. Here, we experimentally demonstrate a full-field resolution-enhancing scheme, based on the centroid estimation of spatially quantum-correlated biphotons. Our standard-quantum-limited scheme is able to image a general non-fluorescing object, using low-energy and low-intensity infrared illumination (i.e., with <0.001 photon per pixel per frame at 710 nm), achieving 41% of the theoretically available resolution enhancement. Images of real-world objects are shown for visual comparison, in which the classically bound resolution is surpassed using our technically straightforward quantum-imaging scheme.

Resolution-enhanced quantum imaging by centroid estimation of biphotons

An organic lateral resolution test device has been developed to measure the performance of imaging mass spectrometry (IMS) systems. The device contains periodic gratings of polyethylene glycol (PEG) and lipid bars covering a wide range of spatial frequencies. Microfabrication technologies were employed to produce well-defined chemical interfaces, which allow lateral resolution to be assessed using the edge-spread function (ESF). In addition, the design of the device allows for the direct measurement of the modulation transfer function (MTF) to assess image quality. Scanning electron microscopy (SEM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) were used to characterize the device. TOF-SIMS imaging was used to measure the chemical displacement of biomolecules in matrix-assisted laser desorption/ionization (MALDI) matrix crystals. In a proof-of-concept experiment, the platform was also used to evaluate MALDI matrix application methods, specifically aerosol spray and sublimation methods.

https://pubs.acs.org/doi/pdf/10.1021/ac501228x

Development of an Organic Lateral Resolution Test Device for Imaging Mass Spectrometry

The acousto-optic tunable filter (AOTF) is one of the most used techniques for hyperspectral imaging (HSI), and is capable of fast and random wavelength access, high diffraction efficiency, and good spectral resolution. Typical AOTF-HSI works with linearly polarized light; hence, its throughput is limited for randomly polarized applications such as fluorescence imaging. We report an AOTF-based imager design using both polarized components of the input light. The imager is designed to operate in the 450 to 800 nm region with resolutions in the range of 1.5–4 nm. The performance characterization results show that this design leads to 68% improvement in throughput for randomly polarized light. We also compared its performance against a liquid crystal tunable filter (LCTF)-based imager.

High Throughput AOTF Hyperspectral Imager for Randomly Polarized Light

The modulation transfer function (MTF) is a fundamental tool for assessing the performance of imaging systems.
It has been applied to a range of capture and output devices, including printers and even the media itself. In this
paper, we consider the problem of measuring the MTF of image capture devices. We analyze the factors that
limit the MTF of a capture device. Then, we examine three different approaches to this task based, respectively,
on a slant-edge target, a sinewave target, and a grill pattern. We review the mathematical relationship between
the three different methods, and discuss their comparative advantages and disadvantages. Finally, we present
experimental results for MTF measurement with a number of different commercially available image capture devices
that are specifically designed for capture of 2D reflection or transmission copy. These include camera-based
systems, flat-bed scanners, and a drum scanner.

Measuring the modulation transfer function of image capture devices: what do the numbers really mean?

A system includes a structure module, graininess module, mottle module, and standard deviation (STD) module. The structure module is to identify a structure metric based on an input digital image, and remove a structured nonuniformity from the input digital image to produce a second input digital image. The graininess module is to identify a graininess metric based on the second input digital image. The mottle module is to identify a mottle metric based on the second input digital image. The STD module is to identify a STD metric that is to correspond to overall smoothness of the input digital image.

Metrics to identify image smoothness

With the emergence of high-end digital printing technologies, it is of interest to analyze the nature and causes of image graininess in order to understand the factors that prevent high-end digital presses from achieving the same print quality as commercial offset presses. In this paper, we report on a study to understand the relationship between image graininess and halftone technology. With high-end digital printing technology, irregular screens can be considered since they can achieve a better approximation to the screen sets used for commercial offset presses. This is due to the fact that the elements of the periodicity matrix of an irregular screen are rational numbers, rather than integers, which would be the case for a regular screen. To understand how image graininess relates to the halftoning technology, we recently performed a Fourier-based analysis of regular and irregular periodic, clustered-dot halftone textures. From the analytical results, we showed that irregular halftone textures generate new frequency components near the spectrum origin; and that these frequency components are low enough to be visible to the human viewer, and to be perceived as a lack of smoothness. In this paper, given a set of target irrational screen periodicity matrices, we describe a process, based on this Fourier analysis, for finding the best realizable screen set. We demonstrate the efficacy of our method with a number of experimental results.

Design of irregular screen sets that generate maximally smooth halftone patterns

Digital halftoning is an essential part of the process for printing color, continuous-tone content. Traditionally, the highest quality has been achieved with analog, offset lithographic presses, using color screen sets that yield periodic, clustered-dot halftone patterns. Increasingly, these systems are being supplanted by digital presses that are based on either electrophotographic or inkjet marking processes. Due to the inherent instability of the electrophotographic marking process, periodic, clustered-dot halftone patterns are also widely used with such presses. However, digital presses have much lower resolution than their analog counterparts. Simply mimicking the traditional screen designs used with commercial, offset presses will result in halftone patterns that are more susceptible to moire due to the interaction between the periodic patterns used to render the different color channels. This causes instability in the printed colors. The moire can be reduced by increasing the frequency of the halftone patterns. But this may make the print appear grainier than its analog counterpart. In this paper, we introduce a principled design procedure that allows one to design color screen sets that generate periodic, clustered-dot halftone patterns that improve color stability without increasing graininess. We present experimental results to support the benefits of our new color screen set design framework.

Tal Frank

Papers

Measuring the modulation transfer function of image capture devices: what do the numbers really mean?

Metrics to identify image smoothness

Design of irregular screen sets that generate maximally smooth halftone patterns

New Design for Compact Color Screen Sets for High-End Digital Color Press

Color Halftoning Based on Multi-Stage, Multi-Pass, Clustered-DBS