Shogo Nishi

Three-phase quadrature spectral matching imager using correlation image sensor and wavelength-swept monochromatic illumination

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.

Surface reflection properties of oil paints under various conditions

This paper describes a method for measurement and analysis of surface reflection properties of oil paints under a variety of conditions. First, the radiance factor of a painting surface is measured at different incidence and viewing angles by using a gonio-spectro photometer. The samples are made from different oil paint materials on supporting boards with different paint thicknesses. Next, typical reflection models are examined for describing 3D reflection of the oil painting surfaces. The models are fitted to the observed radiance factors from the oil paint samples. The Cook- Torrance model describes well the reflection properties. The model parameters are estimated from the least-squared fitting to the genio-photometric measurements. Third, the reflection properties are analyzed on the basis of several material conditions such as pigment, supporting material, oil quantity, paint thickness, and support color.

Robust estimation of pigment distributions from multiband skin images and its application to realistic skin image synthesis

This paper describes a robust method for estimating pigment distributions on a skin surface from multiband images. The spatial distributions of the pigments such as melanin, oxy-hemoglobin and deoxy-hemoglobin give rise to a color texture. The distributions are estimated by using the Kubelka-Munk theory. The accuracy of estimating the pigment distributions is affected by a fine texture of sulcus cutis and a broad texture of shade caused by three-dimensional body shape. In order to separate these textures from the color texture, wavelet-based multi-resolution analysis (MRA) is applied to the multiband images before the pigment estimation, because the textures of sulcus cutis and shade predominantly have low and high spatial frequency components in the multiband skin images, respectively. Realistic skin image is synthesized from modified pigment distributions with additional features such as stain, inflammation and bruise by changing the concentrations of melanin, oxy-hemoglobin and deoxy-hemoglobin, respectively. The experimental results of skin image synthesis show good feasibility of the proposed method.

Spectral matching imager with three-phase quadrature detection

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.

Robust color object tracking method against illumination color Change

Color information is one of the most important keys in object tracking. Color appearance of objects depends on illumination color. Therefore, object tracking by color information does not work well in environments with illumination color changes. In some computer vision algorithms, illumination changes are compensated by brightness correction. However, the compensation is insufficient for tracking in recent indoor environments with some types of fluorescent lights and LEDs. The color changes by illumination should be considered in color object tracking. This paper presents an object tracking method based on the gray world assumption (GWA) that relates to the color constancy in human vision. The average color in the vision is regarded as neutral gray in the GWA. In this method, the object color is defined as relative values from the average color in the frame of the image sequence, based on the GWA. Particle filter is used for robust tracking against sudden situation changes. We applied the proposed method to person tracking. Several experiments were examined for evaluation of the proposed method. The experimental results showed good feasibility of the proposed method.

Scene Radiance Estimation from Human Corneal Reflections

A method is proposed for estimating spectral radiances of the surrounding scene from a reflected image on the corneal surface. A color camera and the human eyeball are used to develop a simple imaging system.

Enhancement of spectral matching imager output for discriminating multiple similar spectra by time-nonlinear wavelength sweeping

A method for enhancing the difference in the outputs of the spectral matching imager (SMI) for multiple similar spectra is proposed. A spectral weight function is introduced to the joint probability density of the target spectra for diagonalizing the covariance matrix by sweeping the peak wavelength in the SMI nonlinearly to time. The weight function, or equivalently a wavelength sweep function, is optimally obtained by minimizing a cost functional consisting of the sum of all the squared off-diagonal elements of the covariance matrix. The experimental results on a set of three similar spectral reflectances demonstrate that the proposed method effectively suppresses the off-diagonal elements of the covariance matrix with the estimated weight function to enhance the difference in SMI outputs.

Human skin imaging using three-phase spectral matching imager

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.

Human skin color simulator using active illumination

Skin color simulation is one of the most important topics. We propose a novel method to reproduce realistic skin color under different conditions by projecting active illumination to a real human skin surface. The active illumination is generated by a programmable light source, which can emit illuminant in high speed with any spectral distribution. The spectral reflectances of human skin with different concentrations of pigments in the skin are estimated based on the Kubelka-Munk theory. Then, the appearance of the skin surface under arbitrary illuminant is displayed by projecting the programmed light onto a real human skin surface. The experimental results show the feasibility of the proposed method.

Calibration of a multispectral camera system using interference filters

The present paper proposes a calibration method of a multispectral camera system using interference filters. A spectral image processing is effective to acquire an inherent information of an object in a general way. However, filter registration error often occurs when the interference filter is used. Therefore, a calibration method is presented for correcting observed images. Moreover, we describe a method for digital archiving of oil paintings based the present imaging system.