Pablo Meza

Total variation approach for adaptive nonuniformity correction in focal-plane arrays

In this Letter we propose an adaptive scene-based nonuniformity correction method for fixed-pattern noise removal in imaging arrays. It is based on the minimization of the total variation of the estimated irradiance, and the resulting function is optimized by an isotropic total variation approach making use of an alternating minimization strategy. The proposed method provides enhanced results when applied to a diverse set of real IR imagery, accurately estimating the nonunifomity parameters of each detector in the focal-plane array at a fast convergence rate, while also forming fewer ghosting artifacts.

Characterization of Chromobacterium violaceum pigment through a hyperspectral imaging system

In this paper, a comprehensive spatio-spectral and temporal analysis for Chromobacterium violaceum colonies is reported. A hyperspectral imaging (HSI) system is used to recover the spectral signatures of pigment production in a non-homogeneous media with high spectral resolution and high sensitivity in vivo, without destructing the sample. This non-contact sensing technique opens avenues to study the temporal growing of a specific section in the bacterial colony. Further, from a 580 [nm] and 764 [nm] spatio-spectral time series, a wild-type and mutant Chromobacterium violaceum strains are characterized. Such study provides quantitative information about kinetic parameters of pigment production and bacterial growing.

Quaternion correlation filters for illumination invariant face recognition

Illumination variations is one of the factors that causes the degradation of face recognition systems performance. The representation of face image features using the structure of quaternion numbers is a novel way to alleviate the illumination effects on face images. In this paper a comparison of different quaternion representations, based on verification and identification experiments, is presented. Four different face features approaches are used to construct quaternion representations. A quaternion correlation filter is used as similarity measure, allowing to process together all the information encapsulated in quaternion components. The experiment results confirms that using quaternion algebra together with existing face recognition techniques permits to obtain more discriminative and illumination invariant methods.

A multidimensional approach for striping noise compensation in hyperspectral imaging devices

Algorithms for striping noise compensation (SNC) for push-broom hyperspectral cameras (PBHCs) are primarily based on image processing techniques. These algorithms rely on the spatial and temporal information available at the readout data; however, they disregard the large amount of spectral information also available at the data. In this paper such flaw has been tackled and a multidimensional approach for SNC is proposed. The main assumption of the proposed approach is the short-term stationary behavior of the spatial, spectral, and temporal input information. This assumption is justified after analyzing the optoelectronic sampling mechanism carried out by PBHCs. Namely, when the wavelength-resolution of hyperspectral cameras is high enough with respect to the target application, the spectral information at neighboring photodetectors in adjacent spectral bands can be regarded as a stationary input. Moreover, when the temporal scanning of hyperspectral information is fast enough, consecutive temporal and spectral data samples can also be regarded as a stationary input at a single photodetector. The strength and applicability of the multidimensional approach presented here is illustrated by compensating for stripping noise real hyperspectral images. To this end, a laboratory prototype, based on a Photonfocus Hurricane hyperspectral camera, has been implemented to acquire data in the range of 400-1000 [nm], at a wavelength resolution of 1.04 [nm]. A mobile platform has been also constructed to simulate and synchronize the scanning procedure of the camera. Finally, an image-processing-based SNC algorithm has been extended yielding an approach that employs all the multidimensional information collected by the camera.

Infrared focal plane array imaging system characterization by means of a blackbody radiator

Infrared (IR) Focal plane array (IRFPA) cameras are nowadays both, more accessible and with a broad variety in terms of detectors design. In many cases, the IRFPA characterization is not completely given by the manufacturer. In this paper a long wave 8-12 [μm] microbolometer IRFPA is characterized by means of calculating the Noise Equivalent Temperature Difference (NETD) and the Correctability performance parameters. The Correctability parameter has been evaluated by using a black body radiator and Two-Points calibration technique. Also, the Transfer Function of the microbolometer IR camera has been experimentally obtained as well as the NETD by the evaluation of radiometric data from a blackbody radiator. The obtained parameters are the key for any successful application of IR imaging pattern recognition.

Thermal characterization of a NIR hyperspectral camera

The accuracy achieved by applications employing hyperspectral data collected by hyperspectral cameras depends heavily on a proper estimation of the true spectral signal. Beyond question, a proper knowledge about the sensor response is key in this process. It is argued here that the common first order representation for hyperspectral NIR sensors does not represent accurately their thermal wavelength-dependent response, hence calling for more sophisticated and precise models. In this work, a wavelength-dependent, nonlinear model for a near infrared (NIR) hyperspectral camera is proposed based on its experimental characterization. Experiments have shown that when temperature is used as the input signal, the camera response is almost linear at low wavelengths, while as the wavelength increases the response becomes exponential. This wavelength-dependent behavior is attributed to the nonlinear responsivity of the sensors in the NIR spectrum. As a result, the proposed model considers different nonlinear input/output responses, at different wavelengths. To complete the representation, both the nonuniform response of neighboring detectors in the camera and the time varying behavior of the input temperature have also been modeled. The experimental characterization and the proposed model assessment have been conducted using a NIR hyperspectral camera in the range of 900 to 1700 [nm] and a black body radiator source. The proposed model was utilized to successfully compensate for both: (i) the nonuniformity noise inherent to the NIR camera, and (ii) the stripping noise induced by the nonuniformity and the scanning process of the camera while rendering hyperspectral images.

A quantitative evaluation of fixed-pattern noise reduction methods in imaging systems

Fixed-pattern noise is a common feature in several uncalibrated imaging systems, and it typically appears as striping and grid-like nonuniformity artifacts in hyperspectral and infrared cameras. In this work, we present a quantitative and comparative analysis of fixed-pattern noise reduction, or calibrating techniques, by using several image quality indexes. A special emphasis is made in demonstrating the correspondence between the reference-free (blind) image quality indexes and the typical reference-based metrics, specially when using online calibration procedures where reference data is not available. We evaluate the performance of several classic scene-based calibrating algorithms applied to: multispectral images with simulated striping noise; and infrared image sequences with simulated nonuniformity. The results show that most of the tested reference-free indexes are useful indicators for tracking some of the real degradation of the calibrated or even uncalibrated imagery, but they are far from perfect to match an error or similarity measure if the clean or reference data is available.

Controlled aberrations for snapshot compressive imaging

Snapshot compressive imaging aims to capture high resolution images using low resolution detectors. The challenge is the generation of simultaneous optical projections that fulfill the compressed sensing reconstruction requirements. We propose the use of controlled aberrations through wavefront coding to produce point spread functions that can simultaneously code and multiplex the scene in a variety of ways. Apart from light efficiency, we can analytically characterize the system matrix response. We explore combinations of Zernike modes and analyze the corresponding coherence parameter. Simulation results using natively sparse and natural scenes demonstrate the feasibility of using controlled aberrations for compressive imaging.

Non-contact measurement technique for enzymatic reaction of glucokinase

A non-contact infrared imaging-based measurement technique is applied to quantify the enzymatic reaction of glucokinase. The method is implemented by a long-wave (8-12 [μm]) infrared microbolometer imaging array and a germanium-based infrared optical vision system adjusted to the size of a small biological sample. The enzymatic reaction is carried out by the glucokinase enzyme, which is representative of the internal dynamics of the cell. Such reactions produce a spontaneous exothermal release of energy detected by the infrared imaging system as a non-contact measurement technique. It is shown by stoichiometry computations and infrared thermal resolution metrics that the infrared imaging system can detect the energy release at the [mK] range. This allows to quantify the spontaneity of the enzymatic reaction in a three dimensional (surface and time) single and noncontact real- time measurement. The camera is characterized for disclosing its sensibility, and the fixed pattern noise is compensated by a two point calibration method. On the other hand, the glucokinase enzyme is isolated from Pyrococcus furiosus. Therefore, the experiment is carried out by manual injection with graduated micropipettes using 40 [μl] of glucokinase at the surface of the substrate contained in an eppendorf tube. For recording, the infrared camera is adjusted in-focus at 25.4 [mm] from the superficial level of the substrate. The obtained values of energy release are 139 ± 22 [mK] at room temperature and 274 ± 22 [mK] for a bath temperature of 334 [K].

Wavelet-FFT Filter Applied to Non Uniformity Correction in Infrared Imaging System

In this paper, we use the recently presented wavelet-FFT filter [1] to reduce the nonuniformity noise that affect almost all infrared imaging systems. The wavelet-FFT filter was originally developed to compensate the one-dimensional noise known as stripping noise. We perform an extension of this methodology in order to compensate the two-dimensional noise that degrades infrared imagery. The principal hypothesis of this work is that the two-dimensional focal-plane array can be considered as the composition of vertical and horizontal one-dimensional array sensors. Under this assumption we use a specific design of the wavelet filter to synthesize a replica of the two-dimensional noise and then recover the real incident radiation. The method is evaluated using real mid- and long-wave infrared data from two cameras. The results show the promising performance of the wavelet-FFT filter when is applied in infrared imaging system such as self heating effect.