This paper considers the problem of high-dynamic-range (HDR) image capture using low-dynamic-range (LDR) cameras. We present three different minimal-bracketing algorithms for computing minimum-sized exposure sets bracketing of HDR scenes. Each algorithm is applicable to a different HDR-imaging scenario depending on the amount of target-scene-irradiance information and real-time image processing available at the time of image acquisition. We prove the optimality of each algorithm with respect to its ability to obtain a theoretically minimum-size bracketing set of exposures. We also provide closed-form expressions for computing minimal-bracketing exposure sets for two common types of HDR-imaging systems, those with geometrically varying and arithmetically varying exposure settings. We experimentally demonstrate the advantages of the proposed methods by capturing and processing multiple HDR scenes using minimal-bracketing and 1-stop bracketing methods. The results show that minimal-bracketing can be used to produce high-quality HDR images, while requiring only one third as many LDR images be acquired compared to 1-stop bracketing. We also perform a detailed SNR analysis that quantifies the tradeoff between signal-to-noise ratio and image-bracketing-set size.

No abstract

Arrayed hexagonal metal nanostructures are used to maximize the local current density while providing effective thermal management at the nanoscale, thereby allowing for increased emission from photoconductive terahertz (THz) sources. The THz emission field amplitude was increased by 60% above that of a commercial THz photoconductive antenna, even though the hexagonal nanostructured device had 75% of the bias voltage. The arrayed hexagonal outperforms our previously investigated strip array nanoplasmonic structure by providing stronger localization of the current density near the metal surface with an operating bandwidth of 2.6 THz. This approach is promising to achieve efficient THz sources.

Figure 3Shape of the pulse modulating the second harmonic of the photocurrent, as detected at three different distances from the reference coordinate z = 147.9 Km, which is one of the zeros of the second-harmonic amplitude in the no-modulation case. The values of IZ. m, and D are as in Figure 1. Note how the amplitude of the pulse decreases as the pulse approaches this point, and then increases again pulse broadening, but rather through harmonic and interharmonic distortions of the subcarriers.Using this approach to consider the interharmonic distortion of two or more subcarriers, though involving lengthier calculations, would present no formal difficulty. REFERENCES 1. R. Olshansky, V. Lanzisera, and P. M. Hill, "Subcarrier Multiplexed Lightwave Systems for Broad-Band Distribution," IEEE ABSTRACT This article describes a technique to reduce the poor conditioning of linear systems to be solved for numerical inverse-scattering solutions based on integral formulations and on the moment method. Some preliminary results are reported to show the improvemeni over a previously proposed approach. 0 1993 John Wiley & Sons. Inc. ABSTRACT A phase-encoded object has been modeled as the input to a joint transform correlator. The joint transform power spectrum is modeled as a binary phase object to calculate the correlation output. The results have been experimentally verified using a liquid-crystal television operating in the phase modulation mode. 0 1993 John Wiley & Sons, Inc.

We use plasmon enhancement to achieve terahertz (THz) photoconductive switches that combine the benefits of low-temperature grown GaAs with mature 1.5 μm femtosecond lasers operating below the bandgap. These below bandgap plasmon-enhanced photoconductive receivers and sources significantly outperform commercial devices based on InGaAs, both in terms of bandwidth and power, even though they operate well below saturation. This paves the way for high-performance low-cost portable systems to enable emerging THz applications in spectroscopy, security, medical imaging, and communication.