Kimiyoshi Miyata

Wiener estimation method in estimating of spectral reflectance from RGB images

Color is one of the most important features in digital images. The representation of color in digital form with a three-component image (RGB) is not very accurate, hence the use of a multiple-component spectral image is justified. At the moment, acquiring a spectral image is not as easy and as fast as acquiring a conventional three-component image. One answer to this problem is to use a regular digital RGB camera and estimate its RGB image into a spectral image by the Wiener estimation method, which is based on the use of a priori knowledge. In this paper, the Wiener estimation method is used to estimate the spectra of icons. The experimental results of the spectral estimation are presented.

Application of image quality metamerism to investigate gold color area in cultural property

Abstract. A concept of image quality metamerism as an expansion of conventional metamerism defined in color science is introduced, and it is applied to segment similar color areas in a cultural property. The image quality metamerism can unify different image quality attributes based on an index showing the degree of image quality metamerism proposed. As a basic research step, the index is consisted of color and texture information and examined to investigate a cultural property. The property investigated is a pair of folding screen paintings that depict the thriving city of Kyoto designated as a nationally important cultural property in Japan. Gold-colored areas painted by using high granularity colorants compared with other color areas are evaluated based on the image quality metamerism index locally, then the index is visualized as a map showing the possibility of the image quality metamer to the reference pixel set in the same image. This visualization means a segmentation of areas where color is similar but texture is different. The experimental result showed that the proposed method was effective to show areas of gold color areas in the property.

A Technique for Detecting Metameric Color Areas for the Investigation of Historical Materials

The spectral reflectance of icons is measured using a measurement system developed in our previous study, and it is applied to detect metameric color areas in the icons. In this paper, a technique for detecting metameric color areas is proposed and examined by using a test chart and ten icons painted on wooden plates. In the proposed technique, a coefficient showing the degree of metamerism is proposed; based on the definition of metamerism whereby two stimuli can match in color while having different spectral reflectance functions. The experimental results can then be used to consider which parts of the icons have previously been repainted as restoration treatments. Despite the necessity of further consideration using certain chemical analyses and so on to conclude whether or not the experimental results are reliable, they demonstrate that the proposed technique has the basic ability to detect metameric color areas.

Application of spectral information to investigate historical materials – detection of metameric color area in icon images -

The spectral reflectance of Icons is estimated from RGB digital images taken by a digital camera, and it is applied to detect metameric color areas in the Icons. In this paper, two detection methods are proposed and examined by using a test chart and ten Icons painted on wooden plates. The first method is based on the definition of metamerism that two stimuli can match in color while having a disparate spectral reflectance. The second method is based on a phenomenon that the variation of the color difference between two colors is changed by replacing the illuminant if the colors are metamers to each other. The experimental results can be used to consider which parts of the Icons have been repainted as restoration treatments. Despite the necessity of further consideration and improvement, the experimental results demonstrate that the proposed methods have the basic ability to detect metameric color areas.

Application of imaging technology for archaeology researches: framework design for connectivity analysis in pieces of Jomon pottery

Jomon pottery is one kind of earthenware produced in Jomon period in Japan. Potteries are found by the excavations in archaeological sites, however their original whole shapes have been dismissed because those are broken and separated into small pieces. In the archaeological investigation process, reproduction of the whole shape of the potteries is one of the important and difficult tasks because there are a lot of pieces and the number of combinations among the pieces is huge. In this paper, a framework for an application of the imaging technology is explained at first, then connectivity analysis among the pieces of Jomon potteries is focused on to reduce the number of trial and error to find connectable combinations in the pieces. The authentic pieces are chosen and taken by a digital camera, and each piece in the image is labeled to calculate the statistical information in the analysis of the connectivity. A coefficient showing the connectivity of the pieces is defined and calculated to indicate probability of connection among the pieces in the image. Experimental result showed that the correct pieces could be detected by using the coefficient.

Detection of image quality metamers based on the metric for unified image quality

In this paper, we introduce a concept of the image quality metamerism as an expanded version of the metamerism defined in the color science. The concept is used to unify different image quality attributes, and applied to introduce a metric showing the degree of image quality metamerism to analyze a cultural property. Our global goal is to build a metric to evaluate total quality of images acquired by different imaging systems and observed under different viewing conditions. As the basic step to the global goal, the metric is consisted of color, spectral and texture information in this research, and applied to detect image quality metamers to investigate the cultural property. The property investigated is the oldest extant version of folding screen paintings that depict the thriving city of Kyoto designated as a nationally important cultural property in Japan. Gold colored areas painted by using high granularity colorants compared with other color areas in the property are evaluated based on the metric, then the metric is visualized as a map showing the possibility of the image quality metamer to the reference pixel.

Development of Practical Investigation System for Cultural Properties Based on a Projector-Camera System

Huge number of historical materials and cultural properties in museums are investigated based on scientific and chemical analysis techniques, however these techniques require specific equipments with difficult operations. In this research, a practical investigation system is developed to provide convenient way for investigating color information in variety of materials as the first step of the investigation process. The system consists of a data projector and a digital camera, and the system is examined to detect metameric color area as an example of investigation purposes. In this research, the data projector has a role of illuminator to yield illuminant metamerism, and the camera takes sequential images under different illumination colors created by the projector. In the experiment, seven colors of illumination are created by the projector, then images are taken under each colored illumination. The Euclid distance in the RGB space between a predetermined reference pixel and test pixels is calculated in each of taken images. These distances are compared with thresholds determined by using a metamerism test chart. The proposed system was examined for the test charts and Japanese authentic wooden prints, and the experimental results showed that the system could offer convenience as the first investigation of the materials.

Designing flat-bed scanning system for spectral and glossiness recording

In this paper, we propose a flat-bed scanner system to record spectral and glossiness information for various sheets like objects. In the proposed system, five filters are used to acquire the multi-band images of the object. The spectral reflectance image can be estimated and be recorded from the multi-band images. The glossiness of the object is recorded as two images taken by the different geometries about illuminant which is from 45 degrees, and from 0+α degrees respectively when the averaged normal vector of the sheet like object is defined as 0 degree. We performed two types of computer simulation by using the two images to reproduce various appearance of recorded object. As the first simulation, the various appearances of image are reproduced through a weighted linear combination of the two images. As the second simulation, the normal vector distribution of the object is estimated from the image taken by 45 degree illuminant. By using this normal vector distribution, roughness of the object is estimated from the image taken by 0 + α degree illuminant. The normal vector and estimated roughness are used to reproduce the various appearance of the object under arbitrary illuminant.