A method for detecting human skin and identifying the surface condition of it using the three-phase spectral
matching imager (3PSMI) is proposed. The 3PSMI produces correlations pixel-wise between the spectrum of
an unknown object and an orthonormal pair of known reference spectra by use of the correlation image sensor
(CIS), and outputs the result as a complex image at an ordinary video frame rate, thus realizing both real-time
operation and high spectral resolution. In order to apply the 3PSMI to human skin, two tasks-discrimination
between skin and non-skin objects and evaluation of the degree of suntan and congestion on skin-are considered
and methods of generating an orthonormal pair of reference spectra for these tasks are proposed. Experiments
on these tasks are carried out on the developed 3PSMI with the reference spectra generated by the proposed
methods.
We propose a three-phase spectral matching imager (3PSMI) to realize a novel spectral matching method called quadrature spectral matching (QSM) in real time. The 3PSMI is comprised of the correlation image sensor (CIS) and wavelength-swept monochromatic illumination (WSMI) to perform QSM at each pixel on the CIS at a video frame rate. QSM consists of spectral correlation between an ac component of an object spectrum and an orthonormal pair of reference spectra, being equivalent to projecting the ac object spectrum onto a two-dimensional subspace spanned by the reference spectra. Similarity of the ac object spectrum to the reference spectra is evaluated in terms of the azimuth angle of the projection, independently of the norm of the ac object spectrum as well as spatial intensity distribution of the WSMI. A programable spectral light source is employed to implement the WSMI so that the spectral characteristics of the WSMI and CIS cancel each other and thus do not affect QSM on the 3PSMI. Experimental results confirm that the developed 3PSMI system can distinguish objects with smaller difference in spectral reflectance in real time than RGB imaging with off-the-shelf cameras.
A real-time method for heterodyne speckle pattern interferometry using the correlation image sensor (CIS) is
proposed. The CIS demodulates the interference phase of heterodyned speckle pattern waves from a singleframe
set of temporal correlation images between the beat signal of incident light and three-phase sinusoidal
reference signals at each pixel at an ordinary video frame rate. The proposed method does not suffer loss of
spatial resolution or decrease in signal-to-noise ratio that would happen for a high-speed image sensor. In-plane
and out-of-plane deformation measurement systems are developed with a 200 × 200-pixel CIS camera. The
experimental results obtained on these systems show good linearity of the change in speckle interference phase
to the voltage applied to a piezoelectric actuator that moves the object.
This paper proposes a spectral matching imager with a novel three-phase quadrature detection method. The
proposed imager consists of the time-domain correlation image sensor (CIS) and a high-speed programmable
spectral light source (PSLS) to produce the correlations between each of a quadrature pair of reference spectral
functions and spectral functions of objects. This is realized by modulating the object spectra into temporal
signals with the PSLS and then producing temporal correlations with reference signals at each pixel of the CIS.
The object that has the same spectral function as the target spectral function is detected as a vector with
an azimuthal angle of zero projected onto the two-dimensional (2-D) space spanned by the reference spectral
functions. The proposed method can estimate the correlation coefficient between the object and reference spectra
more reliably in a 2-D space than previous 1-D spectral matching methods, by factoring out the norm of the
object spectral function. Experimental results for a color chart confirm the effectiveness of the proposed method.
This paper proposes a method for compensating errors in the phase-stamp range finder (PSRF) proposed by the
author. The PSRF consists of the time-domain correlation image sensor (CIS), a sheet of light (SOL), and three-phase
sinusoidal reference signals supplied to the CIS. The PSRF produces a range image at the frame rate of the
CIS by recording the "phase stamp" of the reference signals at the time of incidence of the SOL over the object
during the frame period at each pixel. A problem with the previous PSRF system is that the reconstructed
range image suffers artifacts that appear as an undulation and a random noise pattern superimposed on the
original surface shape of the object. Experimental results confirm the effectiveness of the proposed method for
suppressing the errors in the CIS output images as well as the artifacts in the range images of the PSRF.
A simple and stable method is proposed for distinguishing dielectric and metal material surfaces from the polarization images captured by a vision system consisting of a linear polarizer and a digital camera. The polarization state is determined by the transmitted light intensity through the polarizer as a function of polarizing orientation. The degree of polarization (DOP) is estimated from the image intensities through the polarizer. The DOP map is quite effective for material classification around specular highlight on an object surface. We prove that the DOP map is convex for a dielectric surface and concave for a metal surface. The problem of material classification is then reduced to a simple judgment of the convexity of the DOP map obtained around the highlight peak. The proposed method is not a pixelwise local method based on thresholding the Fresnel ratio computed at each pixel but an area-based method based on the DOP map in a highlight area. The feasibility of the method is confirmed in experiments under a variety of conditions.
This paper proposes a real-time phase-stamp range finder (PSRF) using a three-phase correlation image sensor (3PCIS). The system onsists of the same components as in the conventional light-stripe ange finder except the 3PCIS and a three-phase reference signal enerator. During a single scan of the sheet beam, the 3PCIS "stamps" the phase of the reference signals at the moment the light stripe is imaged on each pixel. The three-dimensional shape of the object is obtained in real time by converting the detected phase to the angle of the projected sheet beam. Compared to time-stamp VLSI range finders, the proposed PSRF is not affected by spatial nonuniformity in surface reflectance of the object and background illumination. It can be realized with a simpler architecture than the modulation-type PSRF previously proposed by the authors. Experimental results on a developed PSRF system are demonstrated.
This paper describes application of the amplitude-modulation (AM)-coded spectral matching imager (SMI) to real-time detection of natural objects such as human beings, animals, vegetables, or geological objects or phenomena, which are much more liable to change with time than artificial products while often exhibiting characteristic spectral functions associated with some specific activity states. The AM-SMI produces correlation between spectral functions of the object and a reference at each pixel of the correlation image sensor (CIS) in every frame, based on orthogonal amplitude modulation (AM) of each spectral channel and simultaneous demodulation of all channels on the CIS. This principle makes the SMI suitable to monitoring dynamic behavior of natural objects in real-time by looking at a particular spectral reflectance or transmittance function. A twelve-channel multispectral light source was developed with improved spatial uniformity of spectral irradiance compared to a previous one. Experimental results of spectral matching imaging of human skin and vegetable leaves are demonstrated, as well as a preliminary feasibility test of imaging a reflective object using a test color chart.
We propose a spectral matching imager using light-emitting diodes (LEDs) of narrowband spectral power distributions. Each spectral channel of the LED illumination undergoes amplitude modulation (AM) with one of an orthonormal set of carrier signals. This imager, which employs the correlation image sensor (CIS) as its imaging device, performs spectral correlation pixelwise between a reference spectrum and that of the object in every frame by demodulating the orthonormal AM carriers via temporal correlation. This sensing principle enables a higher efficiency in the use of illumination power than the spectral matching imager we originally proposed. A twelve-channel AM-coded multispectral light source is developed by assembling commercial LEDs. Under this LED light source, experiments were carried out on pairs of glass pieces of a similar color, but with different spectral transmittance functions. The results confirmed that the proposed imager successfully performed spectral matching on each pair of glass pieces in real time.
In Electronic Imaging 2002 we proposed the spectral mathing imager, which detects an object having a particular spectral property out of a scene in real time using the correlation image sensor. This paper proposes another type of spectral matching imager that employs AM-coded multispectral illumination, instead of the variable wavelength monochrome illumination used previously, in order to increase power efficiency of the illumination. The AM-coded multispectral illumination consists of lights from LEDs with different illuminant spectra, which are also amplitude-modulated with orthogonal carrier signals. The reference signal to the correlation image sensor is created as a weighted sum of the AM signals with weights given by the values of a reference spectrum sampled at the peak wavelengths of the LED spectra. Owing to the orthogonality of the AM carrier signals,
the correlation image sensor outputs the pixelwise spectral correlation between the imaged object and a reference material in every frame. The theory and an implementation of the AM-coded spectral matching imager are described and preliminary experimental results on a set of oxide-doped colored glass pieces are given.
This paper proposes a spectrally selective imaging system called 'spectral matching imager,' which consists of the variable wavelength monochrome light source and the correlation image sensor. The variable wavelength monochrome light source illuminates the scene while sweeping its wavelength with time to expand the spectral reflectance/transmittance function of objects along the time axis. At each pixel, the correlation image sensor produces the correlation in the time domain between the expanded spectral function and a reference spectral function. Consequently, pixels that establish a good spectral match have large values in the output image. The spectral matching imager satisfies (1) high spectral resolution, (2) efficient data compression, and (3) tunability to arbitrary optical filter characteristics. Experimental results demonstrate successful detection of objects having detailed narrowband structures, such as glass pieces doped with rare-earth elements.
This paper proposes a 3D measurement principle for the correlation image sensor (CIS), which generates temporal correlation between light intensity and an external reference signal at each pixel. Another key of our system besides the CIS is amplitude-modulation of the scanning sheet beam, the phase of which relative to a reference signal is varied according to the scanning angle. After a scan within a frame, the phase is demodulated with a quadrature pair of reference signals and output by the CIS to compute the individual angle of the sheet bam at each pixel. By virtue of lock-in detection principle, the effects of background illumination and/or surface reflectance nonuniformity of the object are thoroughly removed. We implemented this system using our CMOS 64 by 64 pixel CIS, and successfully reconstructed a depth map under its frame rate.
We describe CMOS pixel design and fabrication results of the time-domain correlation image sensor, which has been proposed and studied in our laboratory. This sensor can essentially be regarded as an array of demodulators--it computes temporal correlation between incident light intensity and a global reference signal every frame. The correlation detection allows sensitivity to high frequency illumination, and makes various applications possible by using this sensor together with active sensing methods such as modulated illumination and camera motion. The prototype pixel, based on a transconductance multiplier with a photodiode current source and a pair of capacitive loads, is designed as a MOS pair with its common source and drains extended to form a photodiode and capacitors, respectively. Based on this design, 64 times 64-pixel sensors were fabricated with a 1.2-micron CMOS process. Experiments under sinusoidally modulated illumination confirmed temporal correlation performance of the fabricated sensors. Application examples such as lock-in photometry and vibrometry are also presented.
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