Jay Arre Toque

Pigment identification by analytical imaging using multispectral images

This study utilized multispectral images to analyze pigments on a painting. This was accomplished by capturing multispectral images using a high-resolution image scanning system equipped with a monochromatic line CCD. The images were used to reconstruct spectral reflectance by solving a linear transfer function model representing camera response and material response. The CCD sensor response was filtered using Akaike Information Criterion (AIC) to eliminate the effect of noisy data. The pigments on the painting were identified by comparing the reconstructed spectral reflectance to a database of widely used Japanese pigments. The first derivative of the spectral reflectance was calculated using the Savitzky-Golay method to further improve the matching. Experimental results have shown good agreement between the actual pigments and the estimated pigments. Further developments on the technique employed in this study may eventually provide a beneficial tool for the nondestructive and noninvasive investigation of artworks.

Analytical Imaging of Traditional Japanese Paintings Using Multispectral Images

In this study, the influence of lighting conditions on the reconstruction of spectral reflectance and image stitching was explored. Pigment estimation using the reconstructed spectral reflectance was also discussed. Spectral reflectance was estimated using pseudoinverse model from multispectral images of a traditional Japanese painting. It was observed that the accuracy of the estimation is greatly influenced by lighting conditions. High specular reflection on the target yielded large amount of estimation errors. On the other hand, it was observed that in addition to specular reflection, the distribution of light highly affects image stitching. Image stitching is important especially when acquiring images of large objects. Finally, pigments used on the painting were estimated using spectral curve matching of the reconstructed spectral reflectance compared to a pigment database. It was shown that multispectral images could be used for the analytical imaging of artworks.

Pigment identification based on spectral reflectance reconstructed from RGB images for cultural heritage investigations

Common analysis techniques for artworks, such as X-ray based techniques, usually employ high-energy radiation sources. It also oftentimes requires the removal of material from the sample making the analysis relatively destructive. This is unacceptable for samples with high cultural value. Therefore, there is a need to develop alternative nondestructive and noninvasive analysis methods. This paper presents an approach for pigment estimation of Japanese paintings. Reflectance spectra were reconstructed from the RGB values of digital images with the help of multiple linear regression analysis. A reference database with the measured reflectance spectra of the most common pigments used in Japanese artworks was developed and used for identification by comparison and matching. Results have shown that estimation can be successfully performed with only 2% error. The estimation results show some promise that the system could become a powerful tool for the analysis of cultural heritage.

A line scan camera based stereo method for high resolution 3D image reconstruction

A Line-scan camera based stereo method for high resolution 3D image reconstruction is proposed. The imaging model of a line scan camera is addressed in detail to describe the relationship between the coordinate of a physical object in space and the coordinate of its image captured by the scanner. Affine-SIFT feature detector is utilized for establishing dense stereo correspondence. Experimental result demonstrates the effectiveness and merit of this method to high resolution digitization of cultural heritages.

Non-destructive analytical imaging of metallic surfaces using spectral measurements and ultrahigh-resolution scanning for cultural heritage investigation

This paper presents a new approach for analyzing spectroscopic characteristic of metallic surfaces using spectroscopic and image analysis. This method is useful for contactless and non destructive analysis of cultural heritage. Spectral luminance, CIELAB, and CIEXYZ value of more than 80 metallic surfaces were measured with spectrometer and scanned to examine spectroscopic characteristics of foils by using multiband images. This analysis through imaging can improve the method for extracting difference related to types of metallic foils. Firstly, the spectral reflectance of each foil was measured ranging from 220 to 850 nm in steps of 1 nm. The images were captured with color and monochromatic camera using color filter in order to analyze the targets by multispectral approach. Then, principal component analysis (PCA) was conducted with image pixel value of each target. The results have shown that the spectral reflectance whose peak and change rate at a particular wavelength region differed from each foils, and that the multispectral images extracted the difference in spectral characteristics related to different types of metallic foils and Japanese papers. This could be useful in distinguishing among foils. This provides some promise that unknown metallic foils can be identified through the measurement of their spectroscopic features.

Investigation of the degradation mechanism and discoloration of traditional Japanese pigments by multispectral imaging

Pigment degradation has been a subject of interest among researchers in the field of cultural heritage studies. Knowing how pigments behave when subjected to different elements such as high temperature, humidity, electromagnetic radiation and many more others is of prime importance. In this study, the effects of subjecting Japanese pigments to high temperature were investigated. Focus was given on the effects in terms of pigment discoloration and the micromechanism of degradation. Multispectral images were used to track the changes in color and spectral reflectance by reconstructing colorimetric and spectral information from the images. The multispectral images were taken using a high-resolution flat-bed scanner equipped with a line-CMOS camera. In addition, the pigments were characterized using commercially available spectrometers, X-ray diffraction, X-ray fluorescence spectroscopy and X-ray absorption fine structure were used to ascertain the influence of high temperature exposure of the pigments. The high resolution multispectral scans gave the most valuable insights into the discoloration and micromechanism of pigment degradation since they provide both analytical and visual information.

Polarized light scanning for cultural heritage investigation

Numerous cultural heritage art works have shiny surfaces resulting form gold, silver, and other metallic pigments. In addition varnish overlayer on oil paintings makes it challenging to retrieve true color information. This is due to the great effect of lighting condition when images are acquired and viewed. The reflection of light from such surfaces is a combination of the surfaces specular and diffused light reflections. In this paper, this specific problems encountered when digitizing cultural heritage were discussed. Experimental results using the images acquired with a high-resolution large flat bed scanner, together with a mathematical method for processing the captured images were presented and discussed in detail. Focus was given in separating the diffused and specular components of the reflected light for the purpose of analytical imaging. The mathematical algorithm developed in this study enables imaging of cultural heritage with shiny and glossy surfaces effectively and efficiently.

High-Resolution Multispectral Scanning for Mesoscopic Investigation of Discoloration of Traditional Japanese Pigments

This study describes a non-invasive analytical imaging scanning technique utilizing multispectral images to study discoloration and degradation of pigments used in traditional Japanese artworks. The images have high spatial resolution which can achieve mesoscopic resolution (typically 0.1mm-10mm). Since the images are being scanned line by line instead of being recorded frame by frame, this enables accurate color and spectral recording of the material response from visible and near infrared irradiation. The multispectral images were used to reconstruct color information and spectral reflectance. The mathematical model is based on the Moore-Penrose pseuodoinverse. Using mesoscopically resolvable images, it is possible to measure the spectral reflectance of pigments ranging from μm-mm ROI unlike conventional spectrometers that requires big sampling area. The significance of mesoscopically-resolved analysis is demonstrated by investigating the discoloration and degradation of natural and artificial Japanese pigments. The pigments were heated in air at 300°C and sampled every 10 minutes. It was observed that the pigments discolored at seemingly random clusters. The reconstruction of the spectral reflectance at different sizes of ROI reveals strong correlation with background reflection. The size of the initial discoloration sites makes it impossible to measure using conventional spectrometers. It was observed that by using sub-mm ROI, it is possible to observe reflection and absorption patterns in the pigments which does not register with mm-scale ROI. The results have shown that mesoscopically resolvable multispectral images can be used effectively to study degradation and discoloration in pigments.

A High Speed Dynamic System for Scanning Reflective Surface with Rotating Polarized Filters

Shiny materials are commonly used in traditional Asian arts. Taking an image of such objects often poses serious challenges because the intensity of specular reflection component is usually much higher than that of the diffuse reflection which could lead to image saturation. Many methods for obtaining the specular component have been developed. But these methods do not satisfy the requirements of a final image with good reflection characteristics practical enough to be used onsite. It usually requires multiple images obtained at different light source or polarization filter angle. Using this method poses other practical problems like accuracy of image registration of different layers, long data acquisition time, and high computing requirements. This paper proposes a new method for acquiring specular information in high resolution for large cultural heritage objects from a single image using dynamic polarization direction control. The main idea is implemented by allowing the polarized filters placed in front of the camera to rotate at a fixed angular speed while the object is being scanned. This study discusses both the development of new equipment for acquiring the image and the image processing algorithm. The technique was used on the site on a large Japanese sliding door panel to show how it can be implemented for acquiring images with good quality and precise image registration taken at high resolution (>500dpi).

RECONSTRUCTION OF ELEMENTAL DISTRIBUTION IMAGES FROM SYNCHROTRON RADIATION X-RAY FLUORESCENCE SPECTRA

Synchrotron radiation X-ray fluorescence spectroscopy (SRXRF) is a powerful technique for studying trace elements in biological samples and other materials in general. Its features including capability to perform measurements in air and water, noncontact and nondestructive assay are superior to other elemental analysis techniques. In this study, a technique for reconstructing elemental distribution mapping of trace elements from spectral data was developed. The reconstruction was made possible by using the measured fluorescent signals to obtain local differences in elemental concentrations. The proposed technique features interpolation and background subtraction using matrix transformations of the spectral data to produce an enhanced distribution images. It is achieved by employing polychromatic or monochromatic color assignments proportional to the fluorescence intensities for displaying single-element or multiple-element distributions respectively. Some typical applications (i.e., macrophage and tissue ...