中口 俊哉

第一報では，デジタルカメラの RGB 画像から任意照明光下における 被写体の測色値を予測する手法を提案した． 第二報となる本稿では，提案手法の評価について述べる． シミュレーションによる評価では，提案手法の予測精度を，照明光，カメラの分光感度，被写体の種別，および色予測モデル構築に 使用する母集団データの複数の組み合わせについて検証した． その結果，精度，および母集団データの選択に対する安定性のいずれについても，従来手法に対する提案手法の優位性が確認された． また，デジタルカメラで撮影して得た画像を用いた実験により，提案手法は実際の画像に対しても有効であることが示された．

我々は製造段階での作業に対する質感の変化を視覚的にシミュレーションする質感再現システムを開発している.目標とするシステムには作業と連動する質感再現が重要で,実作業,特に手動作との連携が必要不可欠である.そこで本研究では机上作業における手の位置と動作をロバストに計測する手法を開発した.手の位置の検出には赤外線のみを発するプロジェクタで投影した構造パターンを用い,机上から一定高さ以内の手の位置のみを検出することで,作業時のみの手の位置を検出することができる.また手動作判定に必要な手の形状計測には空間コード化法を用いたが,計測範囲を計算で求めた手の周辺位置のみと限定することで計測及び形状再構築の処理時間を飛躍的に削減することができた.本報告ではこれら画像処理的な手法と,試作したプロトタイプシステムの性能について述べる.

In percutaneous puncture simulation, the finite element method is usually used to compute the needle bend and tissue deformation. This method, however, tends to be not suitable for real-time applications such as training systems due to its high computational cost. In this paper, we propose a novel deformable model with a low computational cost. The proposed model reproduces needle bend and tissue deformation in the direction perpendicular to the long axis of the needle. The proposed model consists of a soft tissue deformation model based on the Long Element Method (LEM) and a needle bending model which is designed to be consistent with the tissue model. The parameters for both models are put in the same simultaneous equation to be solved for the simulation. We verified that the proposed model shows a low computational cost by the computer simulation. The accuracy of the model was also evaluated by the experiment using needles and tissue phantoms. The experimental result using only needles showed that a bend could be estimated by the pre-optimized parameters. The optimized parameters were available even if different displacement was given to the manipulated point of the needle.

This paper proposes a practical measurement system for bidirectional reflectance distribution functions (BRDFs) of a three-dimensional (3D) object with a linear light source. Using the linear light source, the proposed system can reduce the number of image acquisitions which are necessary for an estimation of the spatially-varying BRDFs of the object. Furthermore, the size of the proposed system is much smaller than a conventional system which uses a parallel light. In this proposed system, the light field of the linear light source is previously measured to determine direction and radiance of incident rays to each point of the object, because the direction and radiance are not constant at each point. Using the proposed system, the BRDF of a point of flat objects was experimentally measured, and results showed validation of the estimation accuracy of the proposed system. Measurement efficiency of the proposed system was also evaluated by comparing reflectance model parameters estimated by the conventional and proposed systems. For the estimation, the reflectance function of a 3D object was measured by both systems. The estimation accuracy of the proposed method was also evaluated by comparing among a real image and rendered 3D objects of the conventional and proposed methods. (c) 2008 The Optical Society of Japan.

A simple regression-based model of skin diffuse reflectance is developed based on reflectance samples calculated by Monte Carlo simulation of light transport in a two-layered skin model. This reflectance model includes the values of spectral reflectance in the visible spectra for Japanese women. The modified Lambert Beer law holds in the proposed model with a modified mean free path length in non-linear density space. The averaged RMS and maximum errors of the proposed model were 1.1 and 3.1%, respectively, in the above range. (C) 2008 The Optical Society of Japan

In this article, a video-based analysis for facial skin appearance with an automatic face tracking technique is proposed. The change of skin appearance under various illuminations observed by illuminating the face from various light source positions, and the changes in facial appearance are recorded (is a video stream during this measurement. The recorded video stream is then analyzed to obtain the bidirectional reflectance distribution function (BRDF) (it each position of the facial skin. Automatic face tracking is necessary to compensate the facial movement in order to obtain an accurate BRDF measurement at each position. Since conventional face tracking techniques cannot be used for a face illuminated from various light source positions, a new face tracking technique that is robust to the various face shadings has been developed. Experimental studies show the effectiveness of both the proposed video-based analysis technique and the automatic face tracking technique. (c) 2008 Wiley Periodicals, Inc. Cot Res Appl, 33, 477-484, 2008: Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20440

我々は, 被写体の顔の位置, 向き, 口の動きを1台のカメラで実時間追跡することにより化粧シミュレーションを実現するバーチャルミラーシステムを構築した. バーチャルミラーとは, ハーフミラーとビデオカメラを用いることで, ディスプレイを被写体 (今回の場合は使用者の顔) への画像処理が可能な鏡として扱うシステムである. このシステムを顔追跡, 顔への付加処理と組み合わせることで, 簡便な化粧シミュレータを構築した. 顔追跡には, 顔の動きと表情を分離して確率的に推定する手法を提案した. また, 追跡に必要なデータは人体寸法のデータベースより取得した. これにより1台のカメラでも精度良く顔追跡を行うことが可能となった.

液晶ディスプレイ(LCD)やプラズマディスプレイ(PDP)等様々な種類の平面ディスプレイが急速に普及しており,それらの画質を評価・比較するために定量的評価法が盛んに研究されている.MPRT (Moving Picture Response Time)は平面ディスプレイの動きぼやけを定量化する方法の一つであり,応答時間に代わるLCDの動画表示性能を示す指標として注目されている.通常のMPRT評価法は水平方向の動きぼやけのみしか計測していないが,動きぼやけは水平方向に限らず様々な方向に独立して存在する.この論文では,ロボットアームを用いたMPRT計測システムを構築することで,水平方向を含む様々な方向に対して動きぼやけを計測することを可能にした.計測の際様々なデバイス間でMPRTを比較するために,PDPの表示特性を考慮した計測法の改良を行っている.また様々な方向に対して知覚される動きぼやけを評価する主観評価実験を行い,計測によって得られたMPRTと比較することで水平方向以外の動きぼやけ評価の必要性を論じる.

We examined the validity of perceived blur edge width (PBEW) by analyzing the correlation between observer rating values and physical properties that were extended blur edge width (EBEW) and PBEW. We also examined the correlation with changing contrast sensitivity function (CSF) models in the calculation of PBEW. In our results, PBEW correlated more with the observer's rating values than EBEW. It was also shown that Spatio-Velocity CSF model is significant for calculating PBEW.

Many methods have been proposed to restore the blurred images caused by motion blur, camera shake, out of focus and so on. However, little work has been done to restore the blurred images by multiple factors. In this paper, we propose a method for restoration of blurred image by camera shake and characteristics of system response.

An interactive animation method for viscoelastic materials builds on Rouse's spring-bead model. Particles are connected one-dimensionally by spring forces to represent single polymer chains. The method approximates the collision's force between particles through the particle density's gradient. This model lets the viscoelasticity be changed dynamically by severing the interconnection of polymer chains.

腹腔鏡下手術において、先端部に二つのカメラを配置した立体腹腔鏡を用いてステレオ視を行い、臓器の形状を計測する手法がStoyanovらにより提案されている。Stoyanovらの手法では、画像全体を同時に対応付け、臓器の形状を復元した。しかし、計算コストが高く、リアルタイム処理を実現できなかった。そこで本研究では、画像全体ではなく、画像の局所部毎に別々に対応付けを行うことで計算コストを削減し、よりリアルタイム処理に適した処理を実現する。形状が既知である物体を撮影した画像を用いて、計算コスト及び復元精度について、従来手法との比較を行った。その結果、提案手法が従来手法と同等の精度を維持しつつ、計算コストが大幅に削減されたことから、提案手法の有効性を確認した。(著者抄録)

We propose a technique for estimating gene expression values for duplicated data on cDNA microarrays. In the scatter plots, the distribution is constructed from a mixture of normal two-dimensional distributions, which represent fluctuations in gene expression values due to noise. An expectation-maximization (EM) algorithm is used for estimating the modeling parameters. The probability that duplicated data is shifted by noise is calculated using Bayesian estimation. Six data sets of rice cDNA microarray assays were used to test the proposed technique. Genes in the data sets were subjected to clustering based on probability of true value. Clustering successfully identified candidate genes regulated by circadian rhythms in rice. (c) 2007 The Optical Society of Japan

The authors have developed a multi-spectral scanner for accurately printing proofs that employs an LED array coupled witha photodiode array to measure the reflectance spectra. The system is composed of an LED array with five different spectral radiant distributions and 2048 silicon photodiodes with a Selfoc lens array (SLA) for imaging. Five types of LED were selected from among 40 types of commercially available LED with different spectral radiant distributions in order to minimize the average color difference Delta E-94 between the measured and estimate reflectance spectra of 81 typical color color charts. The multiple regression method based on the clustering and polynomial regression algorithm was introduced for highly accurate estimation of the spectral reflectance for printing. The results indicate that the average and maximum color differences Delta E-94 between the measured and estimated reflectance spectra of 928 color charts were 1.02 and 2.84, respectively. The scanner can measure the reflectance of prints having a 0.5 mm pitch resolution and a scanning speed of 100 mm/s. The field programmable gate array (FPGA) and digital signal processor (DSP) were introduced in order to accelerate the calculation of sensor calibration and the estimation of the reflectance spectra of printed proof for practical and commercial use. As a result, the developed scanner could measure the reflectance spectra of printed proof within 20 s. (c) 2007 Society for Imaging Science and Technology.

In this paper, we propose a method for improving image quality in order to match precisely the appearances of recorded video sequences with those of real scenes. Captured video and still images by cameras often have saturated and underexposed areas due to their limited dynamic range. Therefore, it is required to acquire images with a wide dynamic range and much tone data for the accurate reproduction of appearances. In addition, it is important to apply color reproduction processing based on human visual models to recorded videos because the appearances between the videos and real scenes differ due to the characteristics of human vision. In our method, a photometric high-dynamic-range (PHDR) video is generated by using a recorded video sequence and metadata of a camera such as the sensitivity (speed), aperture, and shutter speed. The PHDR video consists of the values of high-dynamic-range tone and absolute luminance. After the generation of a PHDR video, the video is processed by using color reproduction techniques based on spatiotemporal visual adaptation models for the accurate reproduction of appearances. Our results show that the proposed method reproduces fine appearance of videos which is the close appearance of real scenes. (C) 2007 Wiley Periodicals, Inc.

In recent years, many kinds of displays and recording systems for X-ray medical images have appeared. In this paper, sharpness of X-ray images displayed onto high-accuracy monochrome CRT and LCD monitors was analyzed and compared. Images recorded on the exclusive film and coated paper by inkjet printer and the wet-type and dry-type photo printers using a silver halide material were also analyzed and compared. The modified Gan's method was introduced to calculate the modulation transfer function (MTF) from the edge spread function (ESF). The results showed that the MTFs of the LCD, the inkjet image on the transparency, and the wet-type silver halide film image have fairly similar and good response in comparison with the inkjet image on the glossy paper and the dry-type silver halide film. It was also shown that the CRT has the worst response over the spatial frequency range. It was well correlated between the MTF and observer rating value. We thus consider the proposed method to be effective. (C) 2007 Wiley Periodicals, Inc.

腹腔鏡下手術において、先端部に2つのカメラを配置した立体腹腔鏡を用いてステレオ視を行い、臓器の形状を計測する手法がStoyanovらにより提案されている。Stoyanovらの手法では、画像全体を同時に対応付けて臓器の形状を復元するが、計算コストが高く、リアルタイム処理を実現できなかった。そこで本研究では、画像全体ではなく、画像の局所領域ごとに別々に対応付けを行うことで計算コストを削減し、よりリアルタイム処理に適したアルゴリズムを提案する。臓器模型を撮影した3種類の画像を用いて、計算コストおよび復元精度について、従来手法との比較を行った。その結果、対応付けの際に計算コストに強く依存する相関計算のテンプレートサイズを、従来手法の約16分の1とした場合でも、復元精度は4.68mm,7.18mm,7.44mmとなり、従来手法と同等の精度が得られた。(著者抄録)

In this paper, we propose a new projector-based display which can perform the color simulator for print industry. The proposed color simulator can change the color of print by projecting the image onto the print. A color of print can be matched to the desired color by projecting the image which is calculated to minimize the color difference between the colors of target print and current print. This current print is measured by digital camera or digital scanner. Ideally, spectral camera or scanner is expected to be used for accurate color simulation on the current print, but it costs a lot for practical application. Therefore, in this paper, we compared two methods for color matching, one is the tristimulus-based method with XYZ tristimulus values and the other is the spectral-based method with spectral values. As the result of computer simulation, the average color difference Delta E*(94) was 0.27 by the spectral-based method between the reflected radiance from the color of target print and the color of current print with projector, and the average color difference Delta E*(94) was 2.09 by the tristimulus-based method. The efficiency of the proposed system is verified by the subjective evaluation between the target and current print with appropriate image projection.

The purpose of this research is to propose an effective color metric which can predict the perceptual image quality for Retinex method. In this paper, we first give a brief introduction of three kinds of typical single Retinex methods to improve the color reproduction. And then, we state the process for obtaining the observer rating value from the subjective evaluation experiment performed under the sRGB illumination condition. Next, we introduce the S-CIELAB metric and propose a new metric on the basis of S-CIELAB metric that considers the gazing information. The average S-CIELAB color differences with and without the consideration of gazing information were calculated as the objective image quality measures. The correlations between the observer rating values and the objective image quality measures were calculated. The result shows that all of the average S-CIELAB color differences based on the gazing information are better correlated to the observer rating value than the average S-CIELAB color difference over the whole area. The average S-CIELAB color difference weighted by the gazing frequency over the gazing area shows the strong correlation with the observer rating value.

X線写真を用いた画像診断は古くから広く用いられてきた。近年では、ディジタルX線画像撮影システムが開発されたことにより、X線画像が銀塩写真のみならず、CRT、LCD、インクジェットプリンタといった様々な画像出力システムに表示・記録されるようになった。本論文では、画質を決める因子の中でも特に重要な鮮鋭度に注目し、湿式及び感熱式銀塩プリンタ、高精細モノクロCRT及びLCDモニタ、医用インクジェットプリンタのフィルム出力及び光沢紙出力の計6種類の医用画像出力システムの画質をそれぞれ解析評価し、画質比較を行った。Gans' methodを用いて、ナイフエッジ画像の出力応答を解析し、MTF(modulation transfer function)を算出することで鮮鋭度を評価した。Gans' methodにおけるシフトずれの問題について指摘し、独自に改良を加え測定精度を向上させた。評価の結果、インクジェットプリンタは銀塩プリンタに劣らない鮮鋭度を有しており、CRTは鮮鋭度において他のシステムより不利であることが分かった。また、主観評価実験を通して、本手法が鮮鋭度を評価する尺度として有効であることを示した。(著者抄録)

This paper presents a method of measuring a light field of a light source with high directional resolution using a mirrored ball and a pinhole camera. The light field describes a spatial and directional distribution of radiances from the light source. The directional distribution is expanded by a reflection on the mirrored ball, and the radiances are measured by a charge-coupled device (CCD) camera with a pinhole lens. The light source is laterally moved by a robot arm to measure the directionally expanded light field, and each pixel on a CCD can obtain the radiances from the light source through the pinhole lens with high directional resolution. The light field is estimated from the pixel value and the position of each pixel using a ray tracing technique. The light field of a krypton lamp was experimentally measured by the proposed method, and the accuracy of the measurement was evaluated against the irradiances measured by a spectro-radiometer at sample points. (c) 2006 The Optical Society of Japan

CT画像から再構築された上腕骨頭の三次元形状を左右間で比較し、欠損を定量的に評価する診断支援システムを構築した。三次元形状の再構成においては、新たに提案する判別基準法とヒストグラム解析を組み合わせた閾値決定法及び動的輪郭モデルにより、上腕骨の表面形状を抽出した。再構成した左右上腕骨の三次元形状を計算機上で重ね合わせ、直接比較することによって上腕骨頭の欠損部位を抽出できた。この際、両上腕骨頭の形状は鏡像対象であると仮定した。抽出された欠損部位の体積及び形状を解析したところ、本法の有効性を確認できた。

One of the most serious bottle-necks in fluid simulation occurs because the time step must be set to a small value to avoid numerical instability. To overcome this problem, this paper introduces a rigid core for the particles to maintain stability in particle-based fluid simulations. The fluid dynamics is calculated using the particle-based method with smoothed particle hydrodynamics (SPH) [Müller et al. 2003]. By using continuous collision detection (CCD) [Redon et al. 2001] among the rigid cores, unnatural compression and expansion can be prevented in large time step simulations. The calculation cost of CCD is negligible compared to that of small time step simulations, since CCD can be accelerated by a physics processing unit (PPU). Furthermore, this paper proposes a new real-time surface visualization technique that can also be assisted by a PPU. This technique generates large-scale high-resolution meshes compared to those generated by conventional lattice-based methods.

A spectral turn method is presented as a spectral based color correction method compatible with the standard RGB system by applying the idea of a multi-spectral method. The multi-spectral based color reproduction technique has been proposed for providing independent color of device and viewing conditions. However, it is difficult to replace the RGB devices with high cost multi-spectral devices since the latter have advanced only to the laboratory level. In the proposed method, the standard RGB values are converted into spectral information, then returned to RGB values for different viewing conditions. This process provides more accurate reproduction than the conventional forward process of the color reproduction. An experiment of psychophysical color matching was performed to evaluate the technique. The mixed chromatic adaptation model was applied to the method in the experiment, and the results showed the effectiveness of the proposed method. (c) 2006 The Optical Society of Japan.

We introduce a useful tool for controlling the skin melanin texture of facial photographs. Controlling the skin melanin texture is an important task in the reproduction of posters, TV commercials, movies, and so on. We used component maps of melanin, which were obtained by a previous method [J. Opt. Soc. Am. A 16, 2169 (1999)] as the first processing step. We propose to control the melanin texture continuously and physiologically, based on the analysis of 123 skin textures in our database. The physiological validity for the change of the melanin texture is confirmed by comparing the synthesized image with an ultraviolet image, which can be used to predict the change of melanin texture due to aging. The control processes are implemented on programmable graphics hardware, and real-time processing is achieved for a facial videostream. (c) 2006 Optical Society of America.

The system overlaying the stereoscopic images onto the haptic interface is proposed. In order to develop the tnaining systems based on virtual reality for medical doctors to experience medical treatments, it is important to improve the reality that visual and haptic information are synchronized. Our training system proposed in a previous paper for central venous injection uses the stereoscopic glasses and the haptic interface. This system has a palpation phase and an injection phase. During the injection phase, it is important that the user can see 3D injector images and the stylus of the haptic interface corresponding. In the proposed system, the user can look down the images projected from the display and reflected on the half mirror, and the haptic interface through the mirror. Using infrared LEDs wirelessly attached to the stereoscopic glasses and the infrared camera set under the display, the proposed system can show the 3D images considering with the face position in real-time. This system can achieve higher reality and more effectiveness than our conventional system. This system is evaluated by the experienced medical doctor as effective one.

人体切開手技トレーニングシステムを構築するため、切開時にメスに生じる力(切断力、粘性力、固定力)を再現する6自由度反力生成モデルを提案した。従来法は、反力計算においてメスの形状に制限がある、不均質な組織に対応していない、また3自由度の並進力のみの反力再現を行うため実際の操作感覚と差が大きいという問題が存在する。提案手法はこれらの問題を解決し、メスの形状と組織内部の粘性、硬性分布を考慮した反力計算モデルを用いた。本法は6自由度の力覚による反力提示が可能で、12名の非外科医による主観評価実験でも反力再現の有効性を確認できた。

腹腔鏡下手術の視野を通常の開腹手術の視野に近づけることによって、術者の負担を低減させることを最終的な目標とし、プロジェクターを用いた患者腹部への画像の投影による手術支援方式を提案した。まず腹腔鏡下手術の視野を通常の開腹手術の視野に近づける最初のステップとして、腹腔鏡画像を単純に患者の腹部に投影する方式(単純な投影方式)を提案した。腹部形状を取得することによって、投影による画像の歪みを補正し、術者の視点位置をリアルタイムで取得することによって、投影画像を術者の視点移動に対応させた。通常の手術方式との比較実験により鉗子挿入操作の有効性を確認した。