Low Light Level Imaging Research Articles

Off-axis compressed holographic microscopy in low-light conditions

This Letter reports a demonstration of off-axis compressed holography in low-light level imaging conditions. An acquisition protocol relying on a single exposure of a randomly undersampled diffraction map of the optical field, recorded in the high heterodyne gain regime, is proposed. The image acquisition scheme is based on compressed sensing, a theory establishing that near-exact recovery of an unknown sparse signal is possible from a small number of nonstructured measurements. Image reconstruction is further enhanced by introducing an off-axis spatial support constraint to the image estimation algorithm. We report accurate experimental recovering of holographic images of a resolution target in low-light conditions with a frame exposure of 5 μs, scaling down measurements to 9% of random pixels within the array detector.

A Method of Vehicle License Plate De-noising and Location in Low Light Level

License plate recognition system (LPRS) is one of the most important parts of the intelligent transportation system (ITS), and the license plate location is the key part of the LPRS, it affects the latter phase of the character segmentation and recognition directly. According to the characteristics of the vehicle license plate which contain the slat and pepper noise in low light level, wavelet transform is adopted to recognize the vehicle license plate in low light level, then the high frequency coefficient based on characteristic of noise is reconstructed, and the softthreshold method is used to do threshold processing of the reconstructed image and obtain the effect of image denoising. Finally, the method of edge detection and projection is used to locate the vehicle license plate area for de-noising vehicle license plate image. The simulation results indicate that the wavelet soft-threshold method can de-noise the low light level image greatly and the method of edge detection with projection can locate the vehicle license plate area fast and accurately. 

An opto-electro-mechanical infrared photon detector with high internal gain at room temperature

Many applications require detectors with both high sensitivity and linearity, such as low light level imaging and quantum computing. Here we present an opto-electro-mechanical detector based on nano-injection and lateral charge compression that operates at the short infrared (SWIR) range. Electrical signal is generated by photo-induced changes in a nano-injector gap, and subsequent change of tunneling current. We present a theoretical model developed for the OEM detector, and it shows good agreement with the measured experimental results for both the mechanical and electrical properties of the device. The device shows a measured responsivity of 276 A/W, equivalent to 220 electrons per incoming photon, and an NEP of 3.53 x 10(-14) W/Hz(0.5) at room temperature. Although these results are already competing with common APDs in linear mode, we believe replacing the AFM tip with a dedicated nano-injector can improve the sensitivity significantly.

Image fusion algorithm based on fuzzy integral

A novel image fusion algorithm was proposed,which was based on choquet fuzzy integral.The main idea was to obtain belief function using the wavelet coefficient of infrared images and low light level images,then construct fuzzy density using the fuzzy edge evaluation function of local area,finally get fused wavelet coefficient by fuzzy integral and reconstruct fused image by inverse wavelet transform.The experimental results show that the method not only keeps spectral quality of fused image,but also enhances the spatial detail quality of fused image.

Method of fusing dual-spectrum low light Level images based on gray-scale spatial correlation

Gray-scale spatial correlation reflects the definition of images, and the main purpose of fusing images is to improve the definition of images. Based on the spectrum characteristics of low light level (LLL) whole-wave image and LLL short-wave image and the analysis of the one-dimension at gray-scale histograms and the two-dimensional gray-scale spatial correlation charts of LLL whole-wave image and LLL short-wave image, the new method of fusing dual-spectrum LLL images based on gray-scale spatial correlation is proposed. The method is realized by gray-scale selection based standard deviation and gray-scale statistics balance, and the method can effectively improve the definition of images and is easy to execute on hardware compared with gray-scale modulation method and spectrum-field method. The theorefical expressions of the fusion method are expatiated particularly, and the experiment results with different scenes are analyzed.

Noise-adaptive spatio-temporal filter for real-time noise removal in low light level images

Noise reduction gradually becomes one of the most important features in consumer cameras. The video signal is easily interfered by noise during acquisition process especially in low light environment. Many of the state-of-the-art filters for noise reduction perform-well for high contrast images. However, for low light images, the filter performance degrades seriously. In this paper, we propose a noise-adaptive spatio-temporal (NAST) filtering for removal of noise in low light level images. The proposed algorithm consists of a statistical domain temporal filter (SDTF) for moving area and a spatial hybrid filter (SHF) for stationary area. By minimizing required resources for implementation, we present a high quality, low-cost noise reduction filter for low light images. Since the proposed algorithm is designed for real-time implementation, it can be used as a pre-filter for a DCT-based encoder to enhance the coding efficiency of many commercial applications such as low cost camcorders, digital cameras, CCTV, and surveillance video systems.

Design of a multi-anode microchannel array detector system

The Multi-Anode Microchannel Array (MAMA) is a photon counting detector which utilizes a photocathode for photon to electron conversion, a microchannel plate for signal amplification and a proximity focused anode array for position sensitivity. The detector electronics decode the position of an event through coincidence discrimination. These detectors are designed to provide high spatial and temporal resolution for applications in low-light level imaging and spectroscopy at ultraviolet, FUV and EUV wavelengths. Many space ultraviolet astrophysics missions such as STIS are using MAMA detector systems. Several MAMA detectors have been produced by Nanjing Electronic Devices Institute (Nanjing, China). The development of the MAMA systems based on these detectors is performed by Northwest Institute of Nuclear Technology. In this paper, both the design of the MAMA detector system and the progress of the project are presented.

Design of a multi-anode microchannel array detector system

The Multi-Anode Microchannel Array (MAMA) is a photon counting detector which utilizes a photocathode for photon to electron conversion, a microchannel plate for signal amplification and a proximity focused anode array for position sensitivity. The detector electronics decode the position of an event through coincidence discrimination. These detectors are designed to provide high spatial and temporal resolution for applications in low-light level imaging and spectroscopy at ultraviolet, FUV and EUV wavelengths. Many space ultraviolet astrophysics missions such as STIS are using MAMA detector systems. Several MAMA detectors have been produced by Nanjing Electronic Devices Institute (Nanjing, China). The development of the MAMA systems based on these detectors is performed by Northwest Institute of Nuclear Technology. In this paper, both the design of the MAMA detector system and the progress of the project are presented.

The noise performance of electron multiplying charge-coupled devices

Electron multiplying charge-coupled devices (EMCCDs) enable imaging with subelectron noise up to video frame rates and beyond, providing the multiplication gain is sufficiently high. The ultra-low noise, high resolution, high-quantum efficiency, and robustness to over exposure make these sensors ideally suited to applications traditionally served by image intensifiers. One important performance parameter of such low-light imaging systems is the noise introduced by the gain process. This work investigates the noise introduced by the electron multiplication within the EMCCD. The theory and measurements of the excess noise factor are presented. The measurement technique for determining the excess noise factor is described in detail. The results show that the noise performance matches that of the ideal staircase avalanche photodiode. A Monte Carlo method for simulating the low-light level images is demonstrated and the results compared with practical experience.

Excess noise and other important characteristics of low light level imaging using charge multiplying CCDs

This paper describes recent progress in technology of low light level image sensing using CCD sensors that multiply charge by impact ionization before its conversion into a voltage. The paper presents a brief description of the concept, the outline of a typical sensor design with some important details related to prevention of serial register blooming and achieving high dynamic range (DR), and then focuses primarily on the measurement and analysis of noise components that are important in these devices. The paper describes the theory of excess noise, shows the computation of the output signal probability distribution function (PDF), and the derivation of formula for the excess noise factor (ENF). Finally, it is concluded that under suitable conditions it is possible to achieve a single photon (electron) detection (SPD) performance.

TFA Image Sensors for Low Light Level Detection

AbstractTFA technology, using ASICs coated with amorphous silicon based photo detectors, opens new applications for CMOS image sensors. One particular field of interest is the detection of low light level images with pixel photocurrents in the femtoampere range and below. In this paper we describe the effects of the capacitances on the pixel amplifier, we derive noise values for the detector and the amplifier, and we estimate the gain fixed pattern noise level. An inverter circuit providing a 40-fold increase of the charge conversion gain is presented.

Impactron-a new solid state image intensifier

This paper describes the theory of operation and up to date achieved performance of a new image sensor concept that is using Impact Ionization to multiply photo-generated charge before sensing. It is shown that the charge multiplication based on a single carrier impact ionization is almost noiseless. This allows detected signal charge to be amplified directly in the charge domain and be always kept above the charge detector amplifier noise floor. Charge is repeatedly transferred in a CCD fashion through high field regions where the impact ionization occurs. Even though the impact ionization has a low probability and the high field regions are short the number of transfers is large and significant charge gains are obtained. The developed charge multiplication structure can be easily incorporated into pixels of any standard CCD image sensor and included in the image sensing area, the memory area, or any other vertical or horizontal CCD register with a minimum area penalty. This feature thus provides high flexibility in designing new sensors with various performance characteristics suitable for an extreme low light level imaging. The paper describes in detail the theory of charge multiplication and excess noise generation that is supported by the measured data obtained form the test image sensors. The measurement methods that are used to characterize the charge multiplication gain and noise are also described in detail.

Chemiluminescence Western blot assay for the detection of immunity against parvovirus B19 VP1 and VP2 linear epitopes using a videocamera based luminograph

A chemiluminescent Western blot (WB) assay was developed to detect the immune status against linear epitopes of parvovirus B19 structural proteins VP1 and VP2. The chemiluminescent WB assay combined the sensitivity of chemiluminescent substrates and the objective evaluation of the luminescent signal obtained with a new system which consists of a videocamera-based, high-performance, low light level imaging luminograph connected to a personal computer for image analysis. The potential for diagnostic purposes was evaluated using reference serum samples and 75 clinical samples from patients with different clinical conditions and laboratory evaluations regarding B19 infection. The chemiluminescent Western blot assay provided reproducible results, an objective evaluation of the results and a semi-quantitative analysis of the presence of antibodies against VP1 and VP2 in human sera. The chemiluminescent Western blot assay proved more sensitive than the classic colourimetric Western blot assay.

Prospects of uncooled HgCdTe detector technology

Over the last several years cooled applications of HgCdTe at low temperatures have proliferated. Having low fundamental dark current at any given wavelength and temperature makes HgCdTe attractive for high temperature applications as well. We are exploring detectors with cut off wavelengths from the near to middle infrared region (∼1.5 to ∼4 µm). Theory allows applications from low light level imaging in starlight and “nightglow” to thermal imaging, both with useful sensitivities at room temperature. The demonstrated possibility of reducing or eliminating traditional recombination processes (radiative and Auger) further increase the attractiveness of HgCdTe. Current materials technology shows some evidence that these sensitivities can be attained. Current detector technology, being limited by SRH traps, appears to require modest cooling (to about 250K). Improved materials and processes should eliminate the need for even this cooling.

Spatial Fourier transform of binary images using hardware operations: applications to object movement characterization

In a previous paper it was shown that when the Fourier transform technique is applied to binary images (low light level images where the photocurrent distribution is clipped to be binary or one-bit digital images), the processing time necessary for the spectrum estimate is considerably reduced.

Theory and Application of Fluorescence Microscopy

The growing importance in biology and especially in neurobiology of fluorescence microscopy is due to (1) the extraordinary development of new fluorescent molecular probes and (2) the development of improved low light level imaging systems and confocal microscopy techniques. This overview covers fluorescent molecular probes, filters and filter sets, multiband filters and multidye fluorescence, light sources, microscope objectives, image resolution and the point-spread function, and general steps for immunolabeling.

A fast, robust pattern recognition asystem for low light level image registration and its application to retinal imaging

We describe an image processing system which we have developed to align autofluorescence and high-magnification images taken with a laser scanning ophthalmoscope. The low signal to noise ratio of these images makes pattern recognition a non-trivial task. However, once n images are aligned and averaged, the noise levels drop by a factor of n and the image quality is improved. We include examples of autofluorescence images and images of the cone photoreceptor mosaic obtained using this system.

Sensitive chemiluminescence in situ hybridization for the detection of human papillomavirus genomes in biopsy specimens.

We developed a sensitive chemiluminescence in situ hybridization assay for detection of human papillomavirus (HPV) DNA for objective and semiquantitative evaluation of the results. The hybridization reaction was performed using either digoxigenin-, biotin-, or fluorescein-labeled probes, visualized with alkaline phosphatase as the revealing enzyme and a highly sensitive 1,2 dioxetane phosphate as chemiluminescent substrate. The light emitted from the hybridized probes was detected, analyzed, and measured using a high-performance, low light-level imaging luminograph connected to an optical microscope and to a personal computer for quantification of the photon fluxes and for image analysis. The system operated in consecutive steps: First, hybridized specimens were recorded in transmitted light. Then the net luminescent signal was recorded, and then an overlay of the two images provided by the transmitted light and by the luminescent signal allowed the spatial distribution of the target DNA to be localized, measured, and evaluated. Biopsy specimens from different pathological conditions associated with HPV, which had previously been proved positive for HPV DNA with the polymerase chain reaction (PCR), were analysed. The chemiluminescence in situ hybridization proved sensitive and specific with digoxigenin-, biotin-, or fluorescein-labeled probes, and provided an objective evaluation of the results. The results obtained with chemiluminescence in situ hybridization were also compared with results obtained with in situ hybridization with colorimetric detection, with good concordance of the data. Chemiluminescence in situ hybridization therefore offers the possibility of detecting HPV DNA with great sensitivity in biopsy specimens. Moreover, the images of the samples, stored in the computer, are a permanent record of the reaction and can also be sent for evaluation or comparison to other laboratories using computer networks.

Chemiluminescent Determination of Xanthine Oxidase Activity Using A Sensitive Low-Light Detection System

Abstract A highly sensitive and rapid chemiluminescent assay for the determination of the activity of xanthine oxidase (XOD) was developed. The chemiluminescent signal was obtained from the catalyzed oxidation of hypoxanthine, accelerated and amplified using a Fe-EDTA complex and perborate, which acts on luminol. The same luminescent mixture was previously used as detection system for immunoassays. Two different mixtures were used, which differ in their luminol and perborate content, with (CLMrho) or without (CLMb) addition of 0.1 μM rhodamine fluorophor. The response obtained from XOD standard solutions in buffer was linear from 5 to 500 U L−1 and from 0.7 to 250 U L−1 for CLMrho and CLMb respectively, at 25°C. 5 and 0.7 U L−1 were the detection limits at 1 standard deviation level. The intra- and inter-assay relative standard deviations ranged from 6 to 12 % for both CLM. Measurements were made using the high performance, low-light level imaging Berthold luminograph LB-980 which allows simultaneous dete...

Velocity and Acceleration Measurement from the Spatio-Temporal Fourier Transform of Low Light Level Images

The spatio-temporal Fourier transform is usually applied to determine the velocity of an object from a series of standard light intensity frames. In this paper the technique has been extended to determine the object acceleration. The techniques for velocity and acceleration determination based on the spatio-temporal Fourier transform have been applied to experimental low light level images. Under these conditions, the processing time is reduced so that, in those cases in which it is necessary to quickly obtain the object velocity or acceleration, low light level conditions would be advantageous, using intensity filters if necessary.