We modeled discrimination thresholds for object colors under different lighting environments [J. Opt. Soc. Am. 35, B244 (2018)]. First, we built models based on chromatic statistics, testing 60 models in total. Second, we trained convolutional neural networks (CNNs), using 160,280 images labeled by either the ground-truth or human responses. No single chromatic statistics model was sufficient to describe human discrimination thresholds across conditions, while human-response-trained CNNs nearly perfectly predicted human thresholds. Guided by region-of-interest analysis of the network, we modified the chromatic statistics models to use only the lower regions of the objects, which substantially improved performance.
We reported on stereovisual localization of a labeled target versus three-dimensional (3D) position and orientation with a resolution of a few micrometers [Opt. Express 18, 24152 (2010)]. A pseudo-periodic pattern (PPP) is fixed on the target, whose center is identified with subpixel accuracy in both stereo images. This subpixel position definition is fed into the geometrical model of the stereovision system and, thus, leads to subvoxel resolution in the 3D target positioning. This paper reports on improvements and specialization of the method for addressing the measurement of 3D translations: (a) The use of an encrypted PPP wider than the field of observation of the cameras has two beneficial effects. First, the allowed lateral target displacements are wider than the field of view of each camera, thus extending the workspace volume. Second, the 3D position is always derived from the same zone located at the center of the camera sensor chip. A simplified geometrical model is thus sufficient, and the effects of the lens distortions lead to a different kind of calibration issues. (b) By considering only translations, the pattern directions remain stationary in the recorded images. Two-dimensional Fourier transforms are then replaced by single dimension ones, thus reducing the computation time. (c) The choice of a higher magnification lens allows the achievement of submicrometer resolution in target position determination. This level of performance makes the method attractive in various automated applications requiring microstage position control and sensing. This approach may, for instance, fulfill the requirements for the coarse positioning of specimens in front of nanotechnology instruments that are equipped with their own high-accuracy but short-excursion-range translation stages.
Intensity fluctuations of partially polarized light with Gaussian statistics are investigated using a field decomposition approach. These developments provide an enlightening interpretation of the Hanbury Brown-Twiss effect of partially polarized Gaussian light. In particular, the behavior of the intensity fluctuation correlations can be interpreted as resulting from the mixing of two incoherent lights between themselves.
An angular spectrum representation is applied for a description of statistical properties of arbitrary beamlike fields propagating through atmospheric turbulence. The Rytov theory is used for the characterization of the perturbation of the field by the atmosphere. In particular, we derive expressions for the cross-spectral density of a coherent and a partially coherent beam of arbitrary type in the case when the power spectrum of atmospheric fluctuations is described by the von Karman model. We illustrate the method by applying it to the propagation of several model beams through the atmosphere.
Scalar diffraction theory is frequently considered inadequate for predicting diffraction efficiencies for grating applications where lambda/d>0.1. It has also been stated that scalar theory imposes energy upon the evanescent diffracted orders. These notions, as well as several other common misconceptions, are driven more by an unnecessary paraxial approximation in the traditional Fourier treatment of scalar diffraction theory than by the scalar limitation. By scaling the spatial variables by the wavelength, we have previously shown that diffracted radiance is shift invariant in direction cosine space. Thus simple Fourier techniques can now be used to predict a variety of wide-angle (nonparaxial) diffraction grating effects. These include (1) the redistribution of energy from the evanescent orders to the propagating ones, (2) the angular broadening (and apparent shifting) of wide-angle diffracted orders, and (3) nonparaxial diffraction efficiencies predicted with an accuracy usually thought to require rigorous electromagnetic theory.
