Mihir K. Ravel

Comparison of temporal pooling methods for estimating the quality of complex video sequences

Many models of image quality have been developed to predict the visibility of differences between pairs of still images. Various methods have been suggested for combining predictions generated for individual frames of a video sequence. To explore this issue, we have compared the objective quality predictions of three temporal pooling methods against viewer ratings of perceived video quality. The subjective data were obtained from a large group of viewers in an experiment performed by Cable Television Laboratories, Inc., that utilized extended-duration video sequences containing material of significant complexity. Objective quality measures obtained for each field of the sequences were pooled using three simple methods: histogram, Minkowski summation and exponentially-weighted Minkowski summation. The results demonstrated that, for sequence durations on the order of 1 min, the three pooling methods have similar ability to predict overall perceived video quality.

Vector characterization of photodetectors, photoreceivers, and optical pulse sources by time-domain pulse response measurements

Deconvolution of measurement system effects from pulse response measurements is demonstrated to yield reproducible, accurate characterization of the impulse response (and vector frequency response) of a photodetector or photoreceiver, as well as the intensity waveform of an optical pulse. Calibration is based on a 40 GHz and an optical pulse source to >30 GHz are demonstrated. Calibration and effects of noise are discussed. >

Backside-thinned CCDs for keV electron detection

This paper presents preliminary results on the performance of n-channel, backside-thinned charge-coupled devices (CCDs) as electron-bombarded-semiconductor (EBS) imagers for the detection of 1-10 keV electrons. The devices exhibit average EBS gains ranging from approximately 50 at 1 keV to 1600 at 10 keV. Device radiation tolerance has been investigated by exposing normally-clocked devices to 6 keV electron doses up to 0.01 Coulombs/cm2. Room temperature pre- and post-irradiation results are presented for these key device parameters: full well capacity, dark current, and charge transfer efficiency (CTE). At the maximum dose of 0.01 Coulombs/cm2, full well capacity decreases 9 from an initial value of 680,000 e-, and dark current increases from 2 to approximately 50 nA/cm2. There are no measurable changes in large signal CTE up to the maximum dose. Radiation damage at energies other than 6 keV is estimated by measurement of the x-ray generation efficiency of silicon as a function of electron energy. Device stability after temperature cycling has been studied by subjecting packaged devices to vacuum bakes of 24 hours at 300 degree(s)C. Full well, CTE, EBS gain, and output amplifier performance are unchanged after the extended temperature cycle, while dark current decreases slightly by 15. In summary, these initial results indicate that the CCD can function as both an efficient and robust electron imager.

Measuring ATM video quality of service using an objective picture quality model

End-to-end quality of service for real-time video delivery over ATM networks depends on both video coding and network performance. Historical measures of QoS for data services have involved packet delivery parameters such as cell loss and delay, but these are not directly representative of a users perception of the delivered video quality. To this end, this paper describes the use of a video quality measurement scheme that employs a human vision based picture quality model to objectively estimate end-user video quality. We present results to demonstrate that the video quality analysis based approach can be used to determine performance characteristics for distribution-quality video coding parameters over ATM networks.

Charge‐coupled‐device based time‐of‐flight charged particle analyzer

The time‐of‐flight technique is well suited for the analysis of electrons photoemitted from a surface by a pulsed laser. In this paper, a novel design for a time‐of‐flight charged particle analyzer is presented which incorporates a charge‐coupled device (CCD) for the direct detection of electrons photoemitted by an ultrashort laser. After traveling through a field‐free drift region, the electrons are accelerated, focused, and deflected onto a CCD. The positions at which the electrons strike the CCD determine their flight times through the drift region. The use of this analyzer is demonstrated by detecting electrons emitted from a Cu(111) surface by two‐photon photoemission. A computer simulation of the electron trajectories reveals that degradation in resolution and throughput at higher energies can be traced to the chromatic aberrations of the acceleration region just past the drift region.