This paper presents a new reflectance model for rendering computer synthesized images. The model accounts for the relative brightness of different materials and light sources in the same scene. It describes the directional distribution of the reflected light and a color shift that occurs as the reflectance changes with incidence angle. The paper presents a method for obtaining the spectral energy distribution of the light reflected from an object made of a specific real material and discusses a procedure for accurately reproducing the color associated with the spectral energy distribution. The model is applied to the simulation of a metal and a plastic.

A reflectance model for computer graphics

Colour imaging technology has become almost ubiquitous in modern life in the form of monitors, liquid crystal screens, colour printers, scanners, and digital cameras. This book is a comprehensive guide to the scientific and engineering principles of colour imaging. It covers the physics of light and colour, how the eye and physical devices capture colour images, how colour is measured and calibrated, and how images are processed. It stresses physical principles and includes a wealth of real-world examples. The book will be of value to scientists and engineers in the colour imaging industry and, with homework problems, can also be used as a text for graduate courses on colour imaging.

Introduction to Color Imaging Science

The past, present, and future industry prospects of virtual reality (VR) and augmented reality (AR) are presented. The future of VR/AR technology based on holographic display is predicted by analogy with the VR/AR based on binocular vision display and light field display. The investigations on holographic display that can be used in VR/AR are reviewed. The breakthroughs of holographic display are promising in VR/AR with high resolution. The challenges faced by VR/AR based on holographic display are analyzed.

Progress in virtual reality and augmented reality based on holographic display.

Holographic three-dimensional display is an important display technique because it can provide all depth information of a real or virtual scene without any special eyewear. In recent years, with the development of computer and optoelectronic technology, computer-generated holograms have attracted extensive attention and developed as the most promising method to realize holographic display. However, some bottlenecks still restrict the development of computer-generated holograms, such as heavy computation burden, low image quality, and the complicated system of color holographic display. To overcome these problems, numerous algorithms have been investigated with the aim of color dynamic holographic three-dimensional display. In this review, we will explain the essence of various computer-generated hologram algorithms and provide some insights for future research. 

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Review of computer-generated hologram algorithms for color dynamic holographic three-dimensional display

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Mobile phone cameras are often significantly more useful than professional digital single-lens reflex (DSLR) cameras. Knowledge of the camera spectral sensitivity function is important in many fields that make use of images. In this study, methods for measuring and estimating spectral sensitivity functions for mobile phone cameras are developed. In the direct measurement method, the spectral sensitivity at each wavelength is measured using monochromatic light. Although accurate, this method is time-consuming and expensive. The indirect estimation method is based on color samples, in which the spectral sensitivities are estimated from the input data of color samples and the corresponding output RGB values from the camera. We first present an imaging system for direct measurements. A variety of mobile phone cameras are measured using the system to create a database of spectral sensitivity functions. The features of the measured spectral sensitivity functions are then studied using principal component analysis (PCA) and the statistical features of the spectral functions extracted. We next describe a normal method to estimate the spectral sensitivity functions using color samples and point out some drawbacks of the method. A method to solve the estimation problem using the spectral features of the sensitivity functions in addition to the color samples is then proposed. The estimation is stable even when only a small number of spectral features are selected. Finally, the results of the experiments to confirm the feasibility of the proposed method are presented. We establish that our method is excellent in terms of both the data volume of color samples required and the estimation accuracy of the spectral sensitivity functions.

Measurement and Estimation of Spectral Sensitivity Functions for Mobile Phone Cameras.

Fresnel CGH for a three-dimensional (3-D) object is generated by calculating the Fresnel diffraction, but it requires a huge amount of calculation. This is one reason for the difficulty in realizing real-time holography. We propose fast calculation method of computer-generated Fresnel hologram (Fresnel CGH) utilizing distributed parallel processing and array operation. In our method, a projected image with depth information of the 3-D object is prepared to calculate the Fresnel diffraction. The Fresnel diffraction of the projected image is then calculated with depth information by array operation and distributed parallel processing. Parallel processing is realized using JavaSpaces and many standard computers. In our array operation, calculation error in phase distribution on a hologram occurs more than the strict Fresnel diffraction. However, it was confirmed by experiments that the influence of an error can be controlled and ignored. In this paper, our proposed method and some experimental results are shown.

Fast Calculation of Computer-Generated Fresnel Hologram Utilizing Distributed Parallel Processing and Array Operation

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.

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

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.

Surface reflection properties of oil paints under various conditions

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.

Shogo Nishi

Papers

Measurement and Estimation of Spectral Sensitivity Functions for Mobile Phone Cameras.

Fast Calculation of Computer-Generated Fresnel Hologram Utilizing Distributed Parallel Processing and Array Operation

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

Surface reflection properties of oil paints under various conditions

Spectral matching imager with three-phase quadrature detection