Polychromatic imaging with extended depth of field using phase masks exhibiting constant phase over broad wavelength band.

A recent publication [Opt. Express16, 20540-20561 (2008)] presented a way for extending the depth of field (DOF) of imaging systems using a binary phase mask made of annular rings delivering a π-phase shift. Usually, such masks are designed with respect to some central wavelength; they will thus deliver a different phase shift for other wavelengths. This issue is reexamined in this paper, where it is shown that polychromatic masks that deliver the same phase shift over a wide range of wavelengths provide improved imaging over an extended DOF. The simulation results demonstrate the improved performance of imaging systems using such masks.

Performance of imaging systems analyzed with two-dimensional target.

We have recently shown [Appl. Opt.51, 2739 (2012)] that performance analysis of optical imaging systems based on results obtained with classic one-dimensional (1D) resolution targets (such as the U.S. Air Force resolution target) are significantly different than those obtained with a newly proposed two-dimensional (2D) target. We hereby provide experimental evidence and show how the new 2D template can be used to correctly characterize optical imaging systems in terms of resolution and contrast. In particular, we apply the consequences of these observations to the optimal design of some 2D barcode structures.

Optical imaging systems analyzed with a 2D template.

Present determination of optical imaging systems specifications are based on performance values and modulation transfer function results carried with a 1D resolution template (such as the USAF resolution target or spoke templates). Such a template allows determining image quality, resolution limit, and contrast. Nevertheless, the conventional 1D template does not provide satisfactory results, since most optical imaging systems handle 2D objects for which imaging system response may be different by virtue of some not readily observable spatial frequencies. In this paper we derive and analyze contrast transfer function results obtained with 1D as well as 2D templates.

Two-dimensional modulation transfer function: a new perspective.

One-dimensional templates, such as the U.S. Air Force resolution target or the circular spoke target, are commonly used for the characterization of imaging systems via the modulation transfer function response. It is shown in this paper that one needs a new family of templates for a true characterization of imaging systems that acquire two-dimensional (2D) high-density images or handle 2D information, such as 2D bar code detection and identification. The contrast provided by the newly defined 2D templates is the "true" contrast of the acquired image that the electronic processors are challenged with.

Pupil coding masks for imaging polychromatic scenes with high resolution and extended depth of field.

An algorithm for the design of imaging systems with circular symmetry that exhibit high resolution as well as extended depth of field for polychromatic incoherent illumination is presented. The approach provides a significant improvement over a publication [1] where the design was carried for a single wavelength. The approach is based on searching for a binary phase pupil mask that provides imaging with the highest cut-off spatial frequency, while assuring a desired contrast value over a given depth of field. Simulations followed by experimental results are provided.

Novel approach for extending the depth of field of Barcode decoders by using RGB channels of information.

A specially designed phase mask embedded in the lens assembly of an imaging system is shown to provide different response in the three major color bands, R, G and B of a detector array. Each channel provides optimal performance for different depth of field regions, such that the three channels jointly provide an imaging system with wide depth of field. The approach is useful in particular for Barcode imagers.

An optimal binary amplitude-phase mask for hybrid imaging systems that exhibit high resolution and extended depth of field.

The design of a circularly symmetric hybrid imaging system that exhibits high resolution as well as extended depth of field is presented. The design, which assumes spatially incoherent illumination, searches for an optimal "binary amplitude and phase" pupil mask, which for a certain desired depth of field, provides the largest spatial frequency band that assures a certain desired contrast value. The captured images are electronically processed by an off-line Wiener filter, to finally obtain high quality output images. Simulations as well as experimental results are provided.

Super resolution imaging with noise reduction and aberration elimination via random structured illumination and processing.

Hereby we describe an improved aberration-free super resolution imaging system that uses binary speckle patterns (BSP) for encoding and decoding. According to the scheme, the object is multiplied by a fine random speckle pattern and subsequently the poorly resolved acquired image is multiplied by the same pattern, stored digitally. Summing many samples of similar operations restores a high quality image. In this paper we define encoding and decoding BSP that form complementary sets. Contrary to using totally random BSP, the use of complementary sets reduces the noise of the resulting image significantly. Moreover, they allow reducing the number of operations necessary to restore the image. We found out that using sparse BSP followed by a stochastic noise reduction algorithm, fitted for the decoding process, reduces the noise significantly and allows use of even a single set of complementary BSP for obtaining excellent results. Simulation results are presented both for binary images as well as for gray level objects.

Radial mask for imaging systems that exhibit high resolution and extended depths of field.

A novel algorithm for the design of an imaging system that exhibits high resolution as well as extended depth of field is presented. This novel approach searches for an optimal pupil mask that minimizes the value of the mean-square error when performed over the intensity rather than in the field distribution of the acquired image. The captured images in such system do not require any postprocessing, and thus utilization of such a system is simplified. Simulations as well as experimental results are provided.

Experimental realization of an imaging system with an extended depth of field.

We describe the experimental realization of an all-optical imaging system with an extended depth of field (DOF). The core of the system is a phase mask consisting of 16 Fresnel lenses (FLs) that are spatially multiplexed and mutually exclusive. Because each FL, in tandem with the primary lens, is designed to produce a sharp image for a specific object plane location, jointly the FLs achieve a wide DOF. However, the resultant image exhibits reduced resolution. The acquired image, onto which we did not apply any postprocessing, clearly is sharper than that acquired with a clear-aperture imaging system with the same pupil size.

Time multiplexing superresolution based on interference grating projection.

In a previous work done by the authors, it was shown that the superresolution concept based on two moving gratings could be effected by a physical grating attached to the object and a virtual grating. This concept was shown to be very efficient and exhibited features that are helpful in removing some artifacts caused when coherent illumination is used. Furthermore, it simplifies the optical and mechanical modules of the super-resolving system by removing the need for mechanical movement of one grating. However, the system still required the need for moving the first (encoding) grating attached to the input. In this study the encoding grating is replaced by use of a projected grating. This approach simplifies the need for attaching the grating to the input object and thus new applications, such as remote sensing can be considered. The theoretical concept is demonstrated and experimental results are shown.