A multispectral imaging system enabling biological tissue identifying and differentiation is presented. The measurement
of β(λ) spectral radiance factor cube for four tissue types (beef muscle, pork muscle, turkey muscle and beef liver)
present in the same scene was carried out. Three methods for tissue identification are proposed and their relevance
evaluated. The first method correlates the scene spectral radiance factor with tissue database characteristics. This method
gives detection rates ranging from 63.5 % to 85 %. The second method correlates the scene spectral radiance factor
derivatives with a database of tissue β(λ) derivatives. This method is more efficient than the first one because it gives
detection rates ranging from 79 % to 89 % with over-detection rates smaller than 0.2 %. The third method uses the
biological tissue spectral signature. It enhances contrast in order to afford tissue differentiation and identification.
In order to build biological tissues spectral characteristics database to be used in a multispectral imaging system a tissues
optical characterization bench is developed and validated. Several biological tissue types have been characterized in vitro
and ex vivo with our device such as beef, turkey and pork muscle and beef liver. Multispectral images obtained have
been analyzed in order to study the dispersion of biological tissues spectral luminance factor. Tissue internal structure
inhomogeneity was identified as a phenomenon contributing to the dispersion of spectral luminance factor. This
dispersion of spectral luminance factor could be a characteristic of the tissue. A method based on envelope technique has
been developed to identify and differentiate biological tissues in the same scene. This method applied to pork tissues
containing muscle and fat gives detection rates of 59% for pork muscle and 14% for pork fat.
Many new proposals are continually published in the halftoning domain. Alas, the demonstration of the interest of the
proposed methods is often limited to a few favourable tests for the proposed methods, and images showing the defects of
the other halftoning methods.
The halftoning community needs to be able to compare a halftoning method with the innovations that appear in this
domain. A complete and measured evaluation of quality is necessary through to a well defined set of test images and
metrics to evaluate the algorithm.
This paper proposes a protocol for the quality assessment of digital halftoning algorithm that can be used to compare one
algorithm to another.
It discusses the assessment of halftoner quality. It analyzes the perceived image quality concepts and defines the
technical criteria that a good halftoner must match. A first sketch of a simple quality assessment protocol is proposed. It
is composed of test images and quality metrics.
This protocol could be used to provide new proposed halftoning algorithms with objective results.
There are two main families among the halftoning methods: halftoning by masking (i.e. blue noise masking) and error diffusion halftoning. The first family produces neither "worms" nor defects related to stationary regimes but has a limited spatial bandwidth. The error diffusion halftoning method is characterized by a very broad spatial bandwidth allowing good rendition of very thin lines and patterns but this method presents sometimes unpleasant worms or stationary regimes. These methods are complementary with respect to quality. In this paper we propose a halftoning algorithm in black and white, derived from the error diffusion of Floyd Steinberg. By using a new threshold modulation, our new method combines the advantages of both masking and error diffusion algorithms. In order to evaluate our algorithm we defined a set of test images allowing the evaluation of the critical points of quality for the technical imagery: graininess, patterning and spatial bandwidth. The rendering of the presented algorithm has low graininess, no unpleasant patterning and broad spatial bandwidth.
KEYWORDS: Sensors, Optoelectronics, Device simulation, RGB color model, CMOS sensors, Imaging systems, Diffusion, Systems modeling, Data modeling, Color imaging
Color imaging systems still use a combination of conventional photo-detectors and RGB optical filters for color measurement. This entails many limitations to the color sensor performances. We reported that buried junction color detectors give good alternatives to overcome these limitations. However, successful design of color sensors using these detectors requires an accurate knowledge of their behaviors. Unfortunately, circuit simulators do not provide models for these devices. In order to make the designer task more flexible, an optoelectronic library is developed under CADENCE design tool. It consists of some optoelectronic elements such as Buried Double pn Junction (BDJ) detector and a set of optical sources. This allows the designer to choose an optical stimulus with a specific spectral distribution and also to select the total power incident on the BDJ surface.
The library is obtained by implementing, in Spectre simulator, the behavioral models of the optoelectronic elements. The models are written using Verilog-A language. Simulations of the BDJ spectral response and dark currents give a good agreement with experimental data. We also note the absence of convergence errors or mathematical faults during DC and transient simulations of active pixel sensor architectures. These results confirm the robustness of the optoelectronic library.
We have recently developed in our laboratory a new integrated photodetector called BDJ. This detector allows determination of the wavelength of a monochromatic light. It was used to realize colorimetric applications. To develop such optoelectronic systems or microsystems we need simulations of their electronic behavior. Simulators like SPICE give in their libraries models for electrical components but not for optoelectronic components like photosensors or optic system. So we have developed a SPICE model to simulate the BDJ detector behavior and the optic source response. This model was implemented under SPICE and to illustrate its use, we have chosen to simulate two colorimetric applications developed in our laboratory; the first one allows determination of iron concentration and the second of the pH of solutions. In these applications, the optic system is composed of a light source (in practice Led's), and of a tube containing a liquid sensitive to the incident light wavelength; the transmission coefficient of the liquid depends on iron concentration in the first case and on reactive concentration and pH in the second case. Behavioral models of this optic system were included in the BDJ detector SPICE model. So we can obtain photocurrents ratio versus iron concentration or pH and reactive concentration. This system was simulated with an electronic associated circuit. This circuit is a classic analog circuit including several operational amplifiers. The optoelectronic system with associated circuit was described and simulated under SPICE and gives good results in comparison with measurements.
Two novel integrated optical detectors called BDJ detector and BTJ detector have been developed in our laboratory. These two detectors have different applications: the BDJ detector elaborated in CMOS process can be used for wavelength or light flux detection while the BTJ detector based on a bipolar structure gives the trichromatics components of a light. To develop microsystems, we need simulation tools as SPICE model. So, we have elaborated a physical mode, proposed a parameters extraction method and study influence of different parameters for BDJ detectors. Simulations and measurements have validated these models. More, we prose a design of BTJ detectors for developing new color imaging systems.
The integrated BDJ detector basically consists of two buried junctions for collection of photocarriers at different depths. It can operate not only as a photodetector, but also as a wavelength-sensitive detector, because the ratio of the deep junction photocurrent to the shallow junction photocurrent is wavelength-dependent. The BDJ detector can be implemented using a standard CMOS process. The optimum design for a particular application requires divers considerations, such as process parameters, detector sizing, on-chip interface electronics, temperature sensing and compensation, etc. In particular, some geometrical and electrical parameters have significant effects on the device behavior and performances, and detector size as well as on- chip circuitry should be properly defined to meet specifications. Also, temperature-dependence of characteristics may need to be compensated. Two examples concerning design of integrated BDJ detector for specific applications are shown. One is for detecting spectral changes of absorption, while the other is for building a self-calibrated microspectrophotometer.
Two color-sensitive detectors, based respectively on BDJ and BTJ structures, have recently been developed in standard VLSI processes. The BDJ structure implemented in a CMOS process can produce two photocurrents, and the photocurrent ratio is a monotone function of the wavelength. The BTJ structure realized in a BiCMOS process gives three band-pass spectral response, thus allowing trichromatic color detection. In order to obtain better insight into the behavior of these two structures, and to simulate their characteristics, we have established physical models for photocurrent calculations. The following approach has been adopted: i) calculating drift and diffusion photocurrent components which are produced in different depletion layers and neutral regions of silicon; ii) according to their contributions, determining photocurrents flowing through each buried junction. A computer program can be written for device simulations. The validity of these models has been verified through comparison between simulations and measurements. These models can also be used to study effects of parameters involved in the presented models.
A linear array of 64 BDJ cells has been designed and fabricated in a 1.2 micrometers CMOS process. It is aimed to build anew, self-calibrated micro-spectrophotometer. Each cell contains a BDJ detector which can operate as booth light intensity-sensitive and wavelength-sensitive device, and makes use of MOS transistors working in the weak inversion mode to perform logarithmic current-voltage conversion. Measurement of the fabricated chip has been carried out. A large detection light intensity dynamic range and a low fixed pattern noise have been obtained.
KEYWORDS: Sensors, Temperature metrology, Electronic filtering, Color difference, Standards development, Colorimetry, Signal processing, Information operations, Gadolinium, Reflectivity
Measurements of the spectral sensitivities of the Buried Triple p-n Junction color detector have been carried out in the -60 degrees C to 60 degrees C temperature range. Temperature behavior of the photo-currents are described. Variations in the BTJ CMFs have been calculated and a procedure for colorimetric characterization which consider the detector temperature is proposed. Using the proposed procedure, color differences between the detector specifications and the color coordinates in the CIE standard have been determined. The validity of this procedure is evaluated in terms of color shift between the detector specifications caused by a temperature change.
The operation and the colorimetric characterization of a buried triple p-n junction (BTJ) tristimulus detector are presented. A method defining a linear transformation between the detector color space and the C.I.E. standard is proposed. With the least squares fitting to the third order a mean color difference of 2.15 CIELAB units, between the detector response and the C.I.E. specification is predicted. The temperature effects on the detector and the linear transformation accuracy are studied between minus 60 degrees Celsius and 60 degrees Celsius. The color shifts in the detector specifications due to a temperature variations are smaller than 0.5.
A tristimulus color sensitive photo-detector consisting of three buried p-n junctions, implemented in a BiCMOS technology is presented. The three buried junctions give three band-pass- like spectral responses, which peak respectively in the blue, green and red areas. Simulated results obtained with a 1-D analytic model fit well the experimental curves obtained by measuring the sensing arrays in the test chip, designed and fabricated in a 1.2 micrometer BiCMOS process. The colorimetric characterization of the device is performed. A mean color difference of 2.15 is obtained.
Buried double p-n junction (BDJ) structure designed and fabricated in a standard CMOS process is presented. Under reverse-biasing conditions, it provides two measurable photo- generated junction currents I1 and I2, which have a linear dependence on the incident photon flux. Over the visible range, the ratio I2/I1 is a monotone- increasing function of the wavelength, which can serve as a reference curve for wavelength determination. The reference curve r((lambda) ) can be obtained by measurement or by calculation. A physically-based model is suggested for the simulation of photocurrents and the computation of the curve r((lambda) ). Two application examples of the BDJ detector are presented. For the development of microspectrophotometry, replacing photodiodes by BDJ detectors offers a solution to problems of wavelength calibration. In the case of colorimetric pH measurement, the BDJ detector is used to detect spectral changes of absorption.
The authors present a novel technique for color detection by using a buried double pn junction (B.D.J.) and a buried triple pn junction (B.T.J.) structure. For the B.D.J. wavelength-dependent photocurrents I1 and I2 can be measured. The wavelength of monochromatic incident light can be identified from the ratio I2/I1. In the case of the B.T.J. with wavelength dependent photocurrents the three colorimetric components of the incident light can be extracted. These structures can be implemented in standard CMOS and BiCMOS technology respectively.
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