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Physics Faculty Publications and Presentations

Image processing -- Digital techniques

Articles 1 - 14 of 14

Full-Text Articles in Physics

Dynamic Ccd Pixel Depletion Edge Model And The Effects On Dark Current Production, Justin Charles Dunlap, Morley M. Blouke, Erik Bodegom, Ralf Widenhorn Jan 2012

Dynamic Ccd Pixel Depletion Edge Model And The Effects On Dark Current Production, Justin Charles Dunlap, Morley M. Blouke, Erik Bodegom, Ralf Widenhorn

Physics Faculty Publications and Presentations

The depletion edge in Charge-Coupled Devices (CCD) pixels is dependent upon the amount of signal charge located within the depletion region. A model is presented that describes the movement of the depletion edge with increasing signal charge. This dynamic depletion edge is shown to have an effect on the amount of dark current produced by some pixels. Modeling the dark current behavior of pixels both with and without impurities over an entire imager demonstrates that this moving depletion edge has a significant effect on a subset of the pixels. Dark current collected by these pixels is shown to behave nonlinearly ...


Nonlinear Time Dependence Of Dark Current In Charge-Coupled Devices, Justin Charles Dunlap, Erik Bodegom, Ralf Widenhorn Jan 2011

Nonlinear Time Dependence Of Dark Current In Charge-Coupled Devices, Justin Charles Dunlap, Erik Bodegom, Ralf Widenhorn

Physics Faculty Publications and Presentations

It is generally assumed that charge-coupled device (CCD) imagers produce a linear response of dark current versus exposure time except near saturation. We found a large number of pixels with nonlinear dark current response to exposure time to be present in two scientific CCD imagers. These pixels are found to exhibit distinguishable behavior with other analogous pixels and therefore can be characterized in groupings. Data from two Kodak CCD sensors are presented for exposure times from a few seconds up to two hours. Linear behavior is traditionally taken for granted when carrying out dark current correction and as a result ...


Study Of The Numerical Modeling Of The Temperature Dependence Of The Dark Current In Charge Coupled Devices, Ralf Widenhorn, Ionel Tunaru, Erik Bodegom, Dan A. Iordache Jan 2010

Study Of The Numerical Modeling Of The Temperature Dependence Of The Dark Current In Charge Coupled Devices, Ralf Widenhorn, Ionel Tunaru, Erik Bodegom, Dan A. Iordache

Physics Faculty Publications and Presentations

As it is well known, the classical works of the Dark Current Spectroscopy method allow - using some not too accurate theoretical relations, but huge numbers of dark current values for thousands of pixels - the evaluation of a reduced number of basic impurities parameters. Unlike these works, this paper tries to obtain--by means of some better approximations of the Shockley-Read-Hall (SRH) model--more information about the studied impurities, as well as the study of the compatibility of the used theoretical model SRH relative to the experimental data. In this manner, both the compatibility SRH model with the studied experimental data was checked ...


Characterization And Correction Of Dark Current In Compact Consumer Cameras, Justin Charles Dunlap, Erik Bodegom, Ralf Widenhorn Jan 2010

Characterization And Correction Of Dark Current In Compact Consumer Cameras, Justin Charles Dunlap, Erik Bodegom, Ralf Widenhorn

Physics Faculty Publications and Presentations

A study of dark current in digital imagers within consumer grade digital cameras is presented. Dark current is shown to vary with temperature, exposure time, and ISO setting. Further, dark current is shown to increase in successive images during a series of images. Consumer cameras are often designed to be as compact as possible and therefore the digital imagers within the camera frame are prone to heat generated by nearby elements within the camera body. It is the scope of this work to characterize the dark current in such cameras and to show that the dark current, in part due ...


Influence Of Illumination On Dark Current In Charge-Coupled Device Imagers, Ralf Widenhorn, Ines Hartwig, Justin Charles Dunlap, Erik Bodegom Sep 2009

Influence Of Illumination On Dark Current In Charge-Coupled Device Imagers, Ralf Widenhorn, Ines Hartwig, Justin Charles Dunlap, Erik Bodegom

Physics Faculty Publications and Presentations

Thermal excitation of electrons is a major source of noise in charge-coupled-device (CCD) imagers. Those electrons are generated even in the absence of light, hence, the name dark current. Dark current is particularly important for long exposure times and elevated temperatures. The standard procedure to correct for dark current is to take several pictures under the same condition as the real image, except with the shutter closed. The resulting dark frame is later subtracted from the exposed image. We address the question of whether the dark current produced in an image taken with a closed shutter is identical to the ...


Dark Current Behavior In Dslr Cameras, Justin Charles Dunlap, Oleg Sostin, Ralf Widenhorn, Erik Bodegom Jan 2009

Dark Current Behavior In Dslr Cameras, Justin Charles Dunlap, Oleg Sostin, Ralf Widenhorn, Erik Bodegom

Physics Faculty Publications and Presentations

Digital single-lens reflex (DSLR) cameras are examined and their dark current behavior is presented. We examine the influence of varying temperature, exposure time, and gain setting on dark current. Dark current behavior unique to sensors within such cameras is observed. In particular, heat is trapped within the camera body resulting in higher internal temperatures and an increase in dark current after successive images. We look at the possibility of correcting for the dark current, based on previous work done for scientific grade imagers, where hot pixels are used as indicators for the entire chip?s dark current behavior. Standard methods ...


Dark Current Measurements In A Cmos Imager, William C. Porter, Bradley Kopp, Justin Charles Dunlap, Ralf Widenhorn, Erik Bodegom Feb 2008

Dark Current Measurements In A Cmos Imager, William C. Porter, Bradley Kopp, Justin Charles Dunlap, Ralf Widenhorn, Erik Bodegom

Physics Faculty Publications and Presentations

We present data for the dark current of a commercially available CMOS image sensor for different gain settings and bias offsets over the temperature range of 295 to 340 K and exposure times of 0 to 500 ms. The analysis of hot pixels shows two different sources of dark current. One source results in hot pixels with high but constant count for exposure times smaller than the frame time. Other hot pixels exhibit a linear increase with exposure time. We discuss how these hot pixels can be used to calculate the dark current for all pixels. Finally, we show that ...


Measurements Of Dark Current In A Ccd Imager During Light Exposures, Ralf Widenhorn, Ines Hartwig, Justin Charles Dunlap, Erik Bodegom Feb 2008

Measurements Of Dark Current In A Ccd Imager During Light Exposures, Ralf Widenhorn, Ines Hartwig, Justin Charles Dunlap, Erik Bodegom

Physics Faculty Publications and Presentations

Thermal excitation of electrons is a major source of noise in Charge-Coupled Device (CCD) imagers. Those electrons are generated even in the absence of light, hence the name dark current. Dark current is particularly important for long exposure times and elevated temperatures. The standard procedure to correct for dark current is to take several pictures under the same condition as the real image, except with the shutter closed. The resulting dark frame is later subtracted from the exposed image. We address the question of whether the dark current produced in an image taken with a closed shutter is identical to ...


Computation Of Dark Frames In Digital Imagers, Ralf Widenhorn, Armin Rest, Morley M. Blouke, Richard L. Berry, Erik Bodegom Feb 2007

Computation Of Dark Frames In Digital Imagers, Ralf Widenhorn, Armin Rest, Morley M. Blouke, Richard L. Berry, Erik Bodegom

Physics Faculty Publications and Presentations

Dark current is caused by electrons that are thermally exited into the conduction band. These electrons are collected by the well of the CCD and add a false signal to the chip. We will present an algorithm that automatically corrects for dark current. It uses a calibration protocol to characterize the image sensor for different temperatures. For a given exposure time, the dark current of every pixel is characteristic of a specific temperature. The dark current of every pixel can therefore be used as an indicator of the temperature. Hot pixels have the highest signal-to-noise ratio and are the best ...


Infrared Response Of Charge-Coupled Devices, Matthias Loch, Ralf Widenhorn, Erik Bodegom Jan 2005

Infrared Response Of Charge-Coupled Devices, Matthias Loch, Ralf Widenhorn, Erik Bodegom

Physics Faculty Publications and Presentations

With a band gap of silicon of 1.1eV, the largest wavelength that can excite electrons from the valence to the conduction band is roughly 1100nm. As a consequence, in, for instance, a charge-coupled device, the quantum efficiency (QE) for wavelengths larger than 1100nm is assumed to be zero. We found that there is a response at those longer wavelengths and that the response decreases with increasing wavelength. The QE increases with increasing chip temperature which suggests a thermally activated process. Impurities in the silicon provide the energy levels in the band gap, from which electrons can be excited either ...


Psf Measurements On Back-Illuminated Ccds, Ralf Widenhorn, Alexander Weber, Morley M. Blouke, Albert J. Bae, Erik Bodegom May 2003

Psf Measurements On Back-Illuminated Ccds, Ralf Widenhorn, Alexander Weber, Morley M. Blouke, Albert J. Bae, Erik Bodegom

Physics Faculty Publications and Presentations

The spatial resolution of an optical device is generally characterized by either the Point Spread Function (PSF) or the Modulation Transfer Function (MTF). To directly obtain the PSF one needs to measure the response of an optical system to a point light source. We present data that show the response of a back-illuminated CCD to light emitted from a sub-micron diameter glass fiber tip. The potential well in back-illuminated CCD"s does not reach all the way to the back surface. Hence, light that is absorbed in the field-free region generates electrons that can diffuse into other pixels. We analyzed ...


Residual Images In Charged-Coupled Device Detectors, Armin Rest, Lars Mündermann, Ralf Widenhorn, Erik Bodegom, T. C. Mcglinn May 2002

Residual Images In Charged-Coupled Device Detectors, Armin Rest, Lars Mündermann, Ralf Widenhorn, Erik Bodegom, T. C. Mcglinn

Physics Faculty Publications and Presentations

We present results of a systematic study of persistent, or residual, images that occur in charged-coupled device (CCD) detectors. A phenomenological model for these residual images, also known as "ghosting," is introduced. This model relates the excess dark current in a CCD after exposure to the number of filled impurity sites which is tested for various temperatures and exposure times. We experimentally derive values for the cross section, density, and characteristic energy of the impurity sites responsible for the residual images.


Temperature Dependence Of Dark Current In A Ccd, Ralf Widenhorn, Morley M. Blouke, Alexander Weber, Armin Rest, Erik Bodegom Apr 2002

Temperature Dependence Of Dark Current In A Ccd, Ralf Widenhorn, Morley M. Blouke, Alexander Weber, Armin Rest, Erik Bodegom

Physics Faculty Publications and Presentations

We present data for dark current of a back-illuminated CCD over the temperature range of 222 to 291 K. Using an Arrhenius law, we found that the analysis of the data leads to the relation between the prefactor and the apparent activation energy as described by the Meyer-Neldel rule. However, a more detailed analysis shows that the activation energy for the dark current changes in the temperature range investigated. This transition can be explained by the larger relative importance at high temperatures of the diffusion dark current and at low temperatures by the depletion dark current. The diffusion dark current ...


Meyer-Neldel Rule For Dark Current In Charge-Coupled Devices, Ralf Widenhorn, Lars Mündermann, Armin Rest, Erik Bodegom Jun 2001

Meyer-Neldel Rule For Dark Current In Charge-Coupled Devices, Ralf Widenhorn, Lars Mündermann, Armin Rest, Erik Bodegom

Physics Faculty Publications and Presentations

We present the results of a systematic study of the dark current in each pixel of a charged-coupled device chip. It was found that the Arrhenius plot, at temperatures between 222 and 291 K, deviated from a linear behavior in the form of continuous bending. However, as a first approximation, the dark current, D, can be expressed as: D=Dₒ exp(−ΔE/kT),where ΔE is the activation energy, k is Boltzmann’s constant, and T the absolute temperature. It was found that ΔE and the exponential prefactor Dₒ follow the Meyer–Neldel rule (MNR) for all of the more ...