中口 俊哉

画質の解析・評価を行うためには色彩を定量的に計測・解析する必要がある.本稿では色彩工学の基本となるデバイスインディペンデントな色再現手法としてXYZ表色系,CIE LAB均等位空間,そして色差の導出について解説する.また,色彩工学を評価に応用した例としてフラットパネルディスプレイの画質評価研究を紹介し,主観的評価と物理的測定の関係を述べる.最後に色彩工学の次のステップとして注目を浴びている「質感」を取り上げ,質感の測定手法として偏角分光イメージング法を紹介し,質感工学の今後の展望を述べる.

デジタルスチルカメラに匹敵する空間解像度を持つカラー動画撮像を民生機器で実現するために，解像度とフレームレートの異なる RGB3 チャネルの動画像を用いて高解像度高フレームレートのカラー動画像を生成する手法を提案する．色分解プリズムと解像度の異なる撮像素子の組み合わせで，色と解像度を同時に分解する．間欠的に取得される G の高解像度画像と R と B の低解像度画像のペアを事例学習して辞書に登録し，毎フレーム取得される R と B の低解像度画像から G の高解像画像を生成する． 1 台のカメラで低解像度と高解像度の事例データが取得でき，かつ，ビデオシーケンスの中から撮影シーンに依存した学習辞書を作成できる．This paper proposes an example-based super-resolution using two kinds of input-image sequences to get a high-resolution, high-frame-rate image sequence. One sequence consists of high-resolution images with low frame rate; the other sequence consists of low-resolution images with high frame rate. The combination of a color-separating prism and three multiple-resolution sensors simultaneously separated the color and spatio-temporal resolutions. The super-resolution of low-resolution red and blue images reconstructs high-resolution green images by referring to the training dictionary. The training dictionary is given as the pair of a high-resolution green image and low-resolution red-and-blue images.

デジタルスチルカメラに匹敵する空間解像度を持つカラー動画撮像を民生機器で実現するために,解像度とフレームレートの異なるRGB3チャネルの動画像を用いて高解像度高フレームレートのカラー動画像を生成する手法を提案する.色分解プリズムと解像度の異なる撮像素子の組み合わせで,色と解像度を同時に分解する.間欠的に取得されるGの高解像度画像とRとBの低解像度画像のペアを事例学習して辞書に登録し,毎フレーム取得されるRとBの低解像度画像からGの高解像画像を生成する.1台のカメラで低解像度と高解像度の事例データが取得でき,かつ,ビデオシーケンスの中から撮影シーンに依存した学習辞書を作成できる.

Many image processing methods have been developed for clearing up a blurred image. However, they cannot process an image that contains multiple kinds of blurs (e.g. camera shake, motion blur, out of focus, etc.), or what is called a combined blur image. Therefore, we propose a method for deblurring a combined blur image that contains two kinds of blurs, a system point spread function (PSF) and camera shakes. In addition, we take into account image enhancements, such as edge reinforcement and gamma correction, which is usually contained in images taken with consumer cameras, and that is not considered in conventional methods. The results show our method improved the deblurring performance for combined blur images.

E-cosmetic function for digital images is introduced based on physics and physiologically based image processing. A practical skin color and texture analysis/synthesis technique is developed for this E-cosmetic function. Shading on the face is removed by a simple color vector analysis in the optical density domain as an inverse lighting technique. The image without shading is analyzed by extracting hemoglobin and melanin components using independent component analysis. Based on the image processing for the extracted components, we synthesized the various appearances of facial images changed due to these extracted components. © 2008 Springer US.

We propose a deformable model for elastic organ based on structural mechanics under the consideration of multi-point-contact for medical training systems using Virtual Reality (VR) technology. In a previous paper, we proposed an organ deformation model which approximates a liver deformation by a single-beam deformation based on the structural mechanics. The calculation cost of the single-beam model is much less than that of the 3D Finite element method (FEM) since the beam consists of one-dimensional elements. In this paper, we propose a multi-beam model under the consideration of multi-point-contact by extending the single-beam model. A real-time deformation can be realized and the proposed model was implemented in the laparoscopic surgery training system.

We propose a fast stereo matching algorithm for 3D reconstruction of internal organs using a stereoscopic laparoscope. Stoyanov et al. have proposed a technique for recovering the 3D depth of internal organs from images taken by a stereoscopic laparoscope. In their technique, the dense stereo correspondence is solved by registration of the entire image. However, the computational cost is very high because registration of the entire image requires multidimensional optimization. In this paper, we propose a new algorithm based on a local area registration method that requires only low-dimensional optimization for reduction of computational cost. We evaluated the computational cost of the proposed algorithm using a stereoscopic laparoscope. We also evaluated the accuracy of the proposed algorithm using three types of images of abdominal models taken by a 3D laser scanner. In the matching step, the size of the template used to calculate the correlation coefficient, on which the computational cost is strongly dependent, was reduced by a factor of 16 as compared with the conventional algorithm. On the other hand, the average depth errors were 4.68 mm, 7.18 mm, and 7.44 mm respectively, and accuracy was approximately as same as the conventional algorithm.

We propose a new projector-based augmented reality (PBAR) system which can project the image of forceps and a surgical target simultaneously for support of laparoscopic surgery. A compensation method of an error arisen from motion of a body is also proposed to improve the quality of the projection images. It is shown that the system is significant for the forceps insertion by the experiments using the dry-box.

Humeral head (top of arm bone) defect has been diagnosed subjectively by physician. Therefore, it is required to develop a quantitative evaluation method of those defects. In this paper, we propose a quantitative diagnostic method for evaluating humeral head defects by comparing the shapes of the left and right humeral heads. The proposed method is composed of three steps. In the first step, the contour of humerus is extracted from a set of multi-slice CT images by using thresholding technique and active contour model. In the second step, the three-dimensional (3-D) surface model of humerus is reconstructed from extracted contours. In the third step, the reconstructed 3-D shape of left and right humerus is superimposed each other, and then the non-overlapped part is recognized as the defect part. This idea is based on the assumption that human bone structure is symmetrical each other. Finally, the shape of visualized defect part is analyzed by principal component analysis, and we consider that those obtained principal components and contributions represent the feature of the defect part. In this research, seven sets of shoulder multi-slice CT images are analyzed and evaluated.

Automatic segmentation of specific organ from CT image is one of the most important problems for computer aided diagnosis. Therefore, many automatic segmentation methods have been proposed. However, in these conventional methods, it is necessary to set some empirical parameters by users for supporting the automatic segmentation. It takes, however, much time to obtain the optimum parameters for segmentation. Another problem is that although the optimum value of parameters varies spatially, conventional segmentation methods can give only one value of parameters for whole organ. In this paper, we propose a new segmentation method named hybrid segmentation of CT image based on level set segmentation. A local control parameter which can be controlled by the interactive interface used PHANToM omni is introduced for segmentation of pancreas from three dimensional CT image. It is shown that the proposed method can increase accuracy in less time than hand-written segmentation.

近年,液晶ディスプレイをはじめとした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,特に動画質を評価するための手法が盛んに研究されている.MPRTは液晶ディスプレイの動画像表示性能を評価するための指標であるが,通常水平方向のみの評価しか行われていない.この報告では,ロボットアームを用いた多方向MPRT測定システムを用いて液晶ディスプレイの動画表示性能の非等方性を明らかにし,動画表示性能の多方向計測の必要性を論じる.

視診はビデオのように時間と共に常に変化する視覚情報を用い、かつ色に大きな影響を与える照明条件が様々に異なる環境下で行われている。したがって電子カルテ、遠隔医療あるいはe-learningにおいては、常に同じ色を静止画で再現するより、ディスプレイを見ている場所の照明下で呈する色を動画像で再現する方が、はるかに有用と考えられる。また肉眼では知覚できないスペクトル情報を何らかの診断が可能となるように視覚化する場合、静止画像として提供するよりも、動画像で提供した方が疾患に特異的な所見を見つけやすいと考えられる。我々は従来よりRGB撮像系で撮影した皮膚の画像から各ピクセルの分光反射率を推定し、任意の照明下の実物の色を再現したり、あるいはメラニン、ヘモグロビンおよび酸素飽和度の分布を視覚化する方法を研究してきた。そこで今回我々は、先ほどの考え方に基づき、従来静止画像の処理に留まっていた機能を改良し、リアルタイムで動画像を表示するシステムを試作した。様々な医療分野の専門家にこのシステムの評価を依頼したところ、静止画像の提示では得られなかった、多様な用途において画期的な有用性が期待できるとの意見を引き出すことに成功した。(著者抄録)

近年、医用画像群から自動的なセグメンテーションにより臓器の3次元形状を取得し、術前計画や定量診断に利用する研究が広く行われている。しかしながら、これまで提案されている手法は、対象とする臓器に依存する多くの変動パラメータを要するため手動による形状の修正を行う必要があり短時間に臓器のセグメンテーションを行うことが困難であった。そこで本研究では短時間で低負担に臓器セグメンテーション結果を修正する手法を提案する。本手法では、3次元セグメンテーション手法としてLevel Set法を用い、手動により修正箇所を範囲選択しその内部のみで局所的にパラメータの再調節と自動抽出のやり直しを行った。本アルゴリズムを膵臓のセグメンテーションに応用することにより、処理時間が短縮され即座に膵臓再抽出の様子を確認することが可能となり、また最適パラメータを局所的に制御することで抽出精度も向上した。(著者抄録)

超音波検査において,プローブの位置を自動的に把握することは,広範囲にわたる検査部位におけるデータ収集の漏れを防ぎ,検査の再現性を高めるために非常に有効となる.そこで本研究では,簡易かつ高精度にプローブ位置を認識できるシステムの実現を目指し,プローブに複数の光学センサを組み込み,検査部位上に固定したカラーパターンを読み込むことで位置および移動方向を認識することを試みた.

Medical training systems based on virtual-reality techniques for laparoscopic surgery have been widely applied as new medical training systems. In a previous paper, we proposed the deformation model based on the beam of structural mechanics and applied this model to the simulation of the liver deformation. In this model, its calculation cost is much less than that of the 3D FEM, since the beam deformation is calculated as one-dimensional elements. However its deformation accuracy was not evaluated at that time. In this paper, our deformation model is compared with the 3D FEM by assuming that the 3D FEM organ model can simulates real deformation.

We have proposed an improved color control method for a projector-based color simulator. We use low dimensional response, which is measured with an RGB colorimetric camera to estimate spectral reflectance. In our previous work, a color simulator with a projection image was controlled color change on the basis of the ink supply. By overlapping the controlled projection image based on the spectral reflectance, this simulator helps operator to adjust the color of print more accurately. However, measuring the spectral reflectance from every point on print is expensive. To decrease the cost of spectral measurement, we propose a way of estimating method for spectral reflectance. Only three bands responses were used to estimate the spectral reflectance for the projector-based color simulator. The projection image calculated by approximate spectral reflectance reproduces the color change of the print instead of ink supply. Our color simulator with a projection image matched color accurately for 32 samples, the average color difference ΔE*94=1.05 and the maximum color difference ΔE*94=2.58.

In this paper, we compared image qualities of movies displayed on an LCD (liquid crystal display) and a PDP (plasma display panel) by conducting a subjective experiment and measuring physical properties measurements of the displays. We prepared sixteen movies with different dynamic range, saturation, contrast and colorfulness, and 42 observers rated the quality of the movies. We also measured the displays' physical properties such as the luminance, chromaticity. We analyzed the relationship between the observers' ratings and the measured physical properties and found that the distribution of the luminance histogram is an important factor that affects the observers' reactions to the movies.

We have developed an efficient BTF compression and reproducing technique based on a dichromatic reflection model. For the reproduction of the gloss appearance of rough surface, Bidirectional Texture Function (BTF) rendering is thought to be used in this system. However, efficient compression and reproduction methods are required for real-time rendering. In this paper, we propose an efficient approach of BTF rendering by separating the reflected light to the specular, the cast shadow and the invariant diffuse elements. The efficient compression for the BTF rendering is performed by applying the Local Principal Component Analysis (LPCA) to the specular and the cast shadow images, since their appearance depends on the direction of the viewing or illumination. This method performs accurate reproduction by fewer principal components in comparison with the conventional method. The final projection image in an arbitrary direction of the viewing and illumination is synthesized from the specular reflection image, the cast shadow image and the invariant diffuse reflection image. Finally, the proposed method is implemented on the appearance-based display, and demonstrated highspeed BTF rendering which is two times faster than the conventional method. © 2007, The Institute of Image Electronics Engineers of Japan. All rights reserved.

Laparoscopic surgery without ventrotomy has been widely used in recent years for quick recovery and out of pain of patients. However, surgeons are required to accumulate various experiences for this surgery since the difficulty in perceiving the positions of tissues by the limited field of view (FOV) of laparoscopes and the operational difficulties of forceps. In this paper, we propose a new laparoscopic surgery supporting system using projected images. The image of the FOV of a laparoscope is projected directly onto the abdominal surface of a patient. The shape distortion of the projected images produced by the unevenness of the abdominal surface is corrected by grating projection. The distortion due to the viewing angle of the surgeon is also corrected by using an electromagnetic tracking sensor. It is shown that the proposed system is significant to laparoscopic surgery, particularly for forceps insertion, by experiments using a model of the abdomen made with a dry box.

In surgical incision, it is known that the surgeons control surgical knives by feeling of its reaction force, therefore it is necessary to render realistic haptic for development of the surgical incision training system. In our previous paper, we reported that the surgical incision training system used three translational degree-of-freedom (3-DOF) haptic rendering without consideration of rotational forces, distribution of hardness and viscosity of tissue. In this paper, we propose 6-DOF haptic rendering model for development of incision training system with three translational and rotational forces considered hardness and velocity. In this model, it is possible to render the cut, friction and clamping force acting on a surgical knife and those forces can be displayed on the 6-DOF haptic interface device in real time. It is shown the effectiveness of 6-DOF rendering model in comparison with 3-DOF by subjective rating experiment.

An appearance-based display system has been developed to reproduce the accurate gloss appearance of real object. For the reproduction of the gloss appearance of rough surface, BTF (Bi-directional Texture Function) rendering is thought to be used in this system. However, efficient compression and reproduction methods are required for real-time rendering. In this paper, we propose an efficient approach of BTF compression based on dichromatic reflection model. This proposed method separates the reflected light to the specular, the cast shadow and the invariant diffuse elements. The efficient compression for the BTF rendering is performed by applying the LPCA (Local Principal Component Analysis) to the specular and the cast shadow images, since their appearance depends on the direction of the viewing or illumination. This method performs accurate reproduction by fewer principal components in comparison with the conventional method. The final projection image in an arbitrary direction of the viewing and illumination is synthesized from the specular reflection image, the cast shadow image and the invariant diffuse reflection image. Finally, the proposed method is implemented on the appearance-based display, and demonstrated high-speed BTF rendering which is two times faster than the conventional method. Copyright 2006 Society for Imaging Science and Technology.

Gonio spectral imaging method is significant to record the shape, reflectance spectra, gloss and texture of 3-D object for digital archives. This method, however, takes much time to record the object. In this paper, a new method based on the genetic algorithm is introduced to reduce the taking time by optimizing the configuration of camera and illumination. We confirmed the effectiveness of the method by the computer simulation. We also confirmed the significance of the algorithm by using the developed gonio spectral imaging system based on the result of computer simulation.

In this study we propose a new image enhancement technique named Dynamic Band Imaging (DBI) which changes its parameters in time. DBI is the technology based on multi-spectral estimation to enhance the endoscopie color images in order to distinguish the slight color difference more clearly. From some results of fundamental analysis by subjective evaluations, DBI represents the effectiveness for image enhancement in comparison with the typical still image evaluation. Furthermore we developed the user interface to determine many parameters easily and then some practical appropriate parameters for endoscopie diagnosis are obtained. DBI is found as the effective method to enhance medical Images. Copyright 2006 Society for Imaging Science and Technology.

The resolution of a texture image in computer graphics is determined by the camera system used to take the image. Zooming in on the object beyond the optical resolution results in a loss of edges and details. We developed a "super resolution" method that uses a database of textures and texton substitution to create plausible high-frequency detail in enlarged texture images. Conventional example-based super-resolution techniques involve a high computational cost and users must provide the optimal parameters for the input image. Using texton in the wavelet space and a pixel-based (not a patch-based) substitution reduces the computational cost.

中高年の日常生活に重大な支障をきたす変形性関節症は今後さらに増加するものと考えている.しかし,この疾患は一般に早期の段階において骨の形態的変化を伴わないためMRI等による画像診断は困難である.そこで,早期変形性関節症の診断では関節軟骨組織の外科的採取による組織学的検査が行われている.しかしながらこのような大きな侵襲を伴う検査は患者にとって望ましくない.近年の研究において,骨の形態的変化を伴わない早期の段階における造影剤の軟骨への移行速度が健康な場合に比べ遅くなることが確認されている.そこで本研究では,一定時間ごとに撮影された複数枚のMRI画像における画素値の時系列変化を定量化し,その分布を出力する.その結果,造影剤の関節軟骨部への浸透速度分布を可視化することができ,早期の変形性関節症における画像診断の可能性を示した.

内視鏡は体内の実画像情報を取得できる検査機器として,現在医療現場で多く用いられている.しかし内視鏡は視野が狭いため,全体検査時の見落としや,内視鏡の位置把握を誤り臓器を損傷してしまう事例が毎年報告されている.そこで,内視鏡検査支援システム構築に向けた臓器の3次元画像再構成を行う.本研究では,磁気位置センサと内視鏡撮影,CTを用いて,内視鏡画像と仮想内視鏡によって取得した形状データとの合成による臓器内部の3次元実画像作成法を提案する.磁気位置センサは内視鏡の鉗子口に取り付けるために内視鏡操作に影響しない.本手法を用いることで仮想内視鏡に比べてより色彩情報に長けた3次元臓器を再構成する事が可能となった.これにより,内視鏡の体内空間における病変把握が容易となる効果が期待できる.

現在の腹腔鏡下手術において,術者は経験と勘に基づいて腹腔鏡や鉗子の挿入箇所の位置決めを行っている.特に,腹腔鏡下の胃癌第2群リンパ節郭清手術では手術対象である牌動脈に膵臓が隣接し,手術の妨げとなる為,適切な挿入箇所の決定が大変重要となる.そこで,我々は挿入箇所を術前に決定するシステムの開発を行った.このシステムの実行には術前に撮影されたCT画像から膵臓と脾動脈の3次元形状の取得が必要である.脾動脈は血管造影により容易に抽出可能だが,一方膵臓は隣接臓器とのCT値の差がないため,従来強力な抽出法と言われているLevel Set法を単独で用いても,膵臓の抽出は困難であった.そこで,本研究では複数のLevel Setを用い,CT画像からの膵臓の抽出手法を提案する.