中口 俊哉

本稿では、MICCAI 2012本会セッションおよびワークショップそれぞれの概要を紹介し、特に興味深い報告について内容を解説する。

プロジェクター・カメラシステムによる拡張現実感技術を用いた外科手術支援システムが注目されている.このシステムは患者の体表に直接映像を投影することで,低侵襲手術の視覚的課題を克服している.しかし,投影面の材質による画質への影響はまだ検討されていない.そこで本研究では,人体体表に投影した画像の画質評価を行い,その結果について考察した.

近年,立体表示モニタの普及が進んでいるが,立体映像の視聴中における人体への影響や視覚特性など基礎的特性が未解明の状態である.そこで本研究では,輻輳と調節にも関連する基礎的特性として立体表示中のコントラスト感度関数を計測した.視差は6段階に設定し,それぞれにおけるコントラスト感度関数を得た.

これまで室内照明としては蛍光灯や白熱電球が一般的であり,また,近年はLED照明が使用されてきたが,省エネルギー性やデザイン性の観点から有機ELパネルが次世代の照明技術として注目を浴びている.そこで,本研究では有機EL照明が生体に与える影響を主観的,客観的に検証した.実験は卓上での作業を想定したタスクを設定し,長時間のタスクにより起きる生体影響を主観的評価によって検証する単一刺激評価,二種類の照明間において視覚疲労の違いを評価する二重刺激評価を行った.単一刺激評価ではタスク中の自律神経活動状態をモニタリングすることで,有機EL照明とその他の照明が生体に与える影響の違いについて検討した.

3D映像は様々な分野で普及しており,その普及に件い3D映像が生体に与える影響が様々な手法で検証されている.しかしながら両眼に映る画面輝度が生体に与える影響についてはまだ解明されていない.そこで二重刺激,単一刺激による主観評価を行い,画面輝度が生体へ及ぼす影響を検証した.二重刺激では輝度変化による影響が示され,長時間の視聴による単一刺激よりも映像を比較する二重刺激が画面輝度による生体影響を評価するのに適していることが示された.また,同条件の実験を複数回行うことで実験の再現性について検証し,実験精度の確認,検証を行った.

胃がんは日本で最も罹患率の高いがんである。また、胃がんの他臓器への浸潤の有無は手術の外科的治療方針に大きく影響を与えるため、CT画像などから術前に診断されていることが望ましい。しかし、がんの境界が不明瞭であるためその診断が難しいという問題点があった。そこで、本研究では患者の体勢を上向きと横向きで撮影した2組のCT画像を用いて胃がん膵浸潤の有無を示す指標を提案する。その指標は、胃と膵臓の相対的な動きを計算することで求められると予想される。胃と膵臓の相対的な動きを算出するために患者の体勢を変えて撮影した2組のCT画像に対して3段階のレジストレーションを行った。レジストレーションの後、胃と膵臓付近の変化量マップが求められた。診断補助のためにその変化量マップを可視化しCT画像に重ね合わせた。提案手法を11人の胃がん患者に適用し、提案した指標の定量的な評価実験を行った。実験の結果、提案した指標の有用性が示された。(著者抄録)

Uneven distribution of skin color is one of the biggest concerns about facial skin appearance. Recently several techniques to analyze skin color have been introduced by separating skin color information into chromophore components, such as melanin and hemoglobin. However, there are not many reports on quantitative analysis of unevenness of skin color by considering type of chromophore, clusters of different sizes and concentration of the each chromophore. We propose a new image analysis and simulation method based on chromophore analysis and spatial frequency analysis. This method is mainly composed of three techniques: independent component analysis (ICA) to extract hemoglobin and melanin chromophores from a single skin color image, an image pyramid technique which decomposes each chromophore into multi-resolution images, which can be used for identifying different sizes of clusters or spatial frequencies, and analysis of the histogram obtained from each multi-resolution image to extract unevenness parameters. As the application of the method, we also introduce an image processing technique to change unevenness of melanin component. As the result, the method showed high capabilities to analyze unevenness of each skin chromophore: 1) Vague unevenness on skin could be discriminated from noticeable pigmentation such as freckles or acne. 2) By analyzing the unevenness parameters obtained from each multi-resolution image for Japanese ladies, agerelated changes were observed in the parameters of middle spatial frequency. 3) An image processing system modulating the parameters was proposed to change unevenness of skin images along the axis of the obtained age-related change in real time. © 2011 SPIE.

眼底検査は眼球内を観察して診断でき、血管も直接観察できる部位として様々な疾患の早期発見のためにも重要な検査対象である.しかし,従来の眼底画像における血管抽出は低解像度のデータベースを用いて評価していることが一般的であり,血柱反射の変化のような高解像度撮影において顕著となる特徴による影響が考慮されていない.そこで本研究では,高解像度眼底画像に適した血管の自動抽出法を提案する.画像全体で血管のコントラストを強調し,画像ピラミッドを作成する.各画像においてMatched Filterと領域検出を適用し,それらの結果を元の解像度で統合することにより血管抽出を行う.手動抽出の結果を正解として3枚の画像について評価した結果,真陽性の平均値が0.860,偽陽性の平均値が0.033であった.

In this article, we present hyperspectral analysis of the tongue and correlation between its color and values of thyroid hormones. In Kampo medicine (Japanese traditional herbal medicine), the tongue acts as a mirror reflecting the internal state of the body. By assessing the patient's complexion of the tongue, we are able to assess the changes including initial change of typical hyper-/hypothyroidism. However, examination methods in Kampo is empirical and require much experience. Therefore, we performed hyperspectral tongue analysis to turn the empirical observation into the change in substantial factor. One hundred hyperspectral tongue images and blood samples were acquired from 50 outpatients. The principal component analysis was performed for tongue color spectra, and correlation to thyroid hormones was calculated with the vector rotation method. As the result, TH4 showed large correlation with the tongue color spectra. Our method would help non-invasive screening in low cost. The tongue examination seems to be reliable for acquiring the state of the body. © 2011 IEEE.

In this work, we propose a shape-based liver segmentation approach using a patient specific knowledge. In which, we exploit the relation between consequent slices in multi-slice CT images to update the shape template that initially determined by the user. Then, the updated shape template is integrated with the graph cuts algorithm to segment the liver in each CT slice. The statistical parameters of the liver and non-liver tissues are initially determined according to the initial shape template and it is consequently updated from the nearby slices. The proposed approach does not require any prior training and it uses a single phase CT images however, it is talented to deal with complex shape and intensity variations. The proposed approach is evaluated on 20 CT images with different kinds of liver abnormalities, tumors and cysts, and it achieves an average volumetric overlap error of 6.4% and average symmetric surface distance (ASD) of 0.8 compared to the manual segmentation. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

Proving the security of cancelable biometrics and other template protection techniques is a key prerequisite for the widespread deployment of biometric technologies. BioEncoding is a cancelable biometrics scheme that has been proposed recently to protect biometric templates represented as binary strings like iris codes. Unlike other template protection schemes, BioEncoding does not require user-specific keys or tokens. Moreover, it satisfies the requirements of untraceable biometrics without sacrificing the matching accuracy. However, the security of BioEncoding against smart attacks, such as correlation and optimization-based attacks, has to be proved before recommending it for practical deployment. In this paper, the security of BioEncopding, in terms of both non-invertibility and privacy protection, is analyzed. First, resistance of protected templates generated using BioEncoding against brute-force search attacks is revisited rigorously. Then, vulnerabilities of BioEncoding with respect to correlation attacks and optimization based attacks are identified and explained. Furthermore, an important modification to the BioEncoding algorithm is proposed to enhance its security against correlation attacks. The effect of integrating this modification into BioEncoding is validated and its impact on the matching accuracy is investigated empirically using CASIA-IrisV3-Interval dataset. Experimental results confirm the efficacy of the proposed modification and show that it has no negative impact on the matching accuracy. Copyright © 2011 The Institute of Electronics, Information and Communication Engineers.

We evaluate the influences on visual strain and visually-induced motion sickness in observing 3D image. Based on the SSQ analysis, it is clear that the correlation between visual strain and physical factors of 3D display is more than 90%.

In this article, we propose a hyperspectral imaging system and automatic hyperspectral image processing method to extract the uncoated area of the tongue for the clinical inspection of Kampo medicine (Japanese traditional herbal medicine). The automatic processing methods were built based on the analysis of nine taken hyperspectral image. The effectiveness of the method was confirmed by applying to other eight hyperspectral images.

A method is proposed to separately model the mechanical dot gain and the optical dot gain. First, an iterative algorithm is proposed to estimate the spatio-spectral transmittance of ink layer from the spatio-spectral reflectance of color halftone print measured with the reflection optical microscope attached with the liquid crystal tunable filter (LCTF). The spatio-spectral transmittance of ink layer is not affected by the optical dot gain and is only affected by the mechanical dot gain. Next, a model is proposed to estimate the effective dot coverage using the estimated spatio-spectral transmittance of ink layer. It corresponds to the analysis of mechanical dot gain. Next, a model is proposed to estimate Yule-Nielsen's n parameter using the effective dot coverage. It corresponds to the analysis of optical dot gain. Finally, the prediction accuracy of the proposed model is evaluated by the ΔE 94 between the measured and predicted spectral reflectance of offset printing images with cyan and magenta inks. The prediction accuracy of the proposed model was significant since the average ΔE94 and the maximum ΔE94 of all samples between the measured spectral reflectance and the predicted spectral reflectance were 0.62 and 1.37, respectively.

近年CT画像から臓器を抽出、再構築することは術前計画や診断支援など広く活用されている。中でもインタラクティブなシステムは、全自動のシステムに比べ安定した精度で抽出を行うことができると言われている。本研究では抽出が難しいとされる膵臓の抽出に着目した。そこでレベルセット法の速度関数に、インタラクティブな領域抽出と相性の良いグラフカット法によるエッジ項を追加することで精度向上を図った。観測者の入力による画像のエッジ信頼度を用いることでレベルセット法とグラフカット法を領域ごとに選択する。画像からエッジが判断できる部分ではレベルセット法による領域抽出を行い、エッジが判断できない部分ではグラフカット法による抽出処理結果を使用する。2症例について評価を行い、従来手法に比べ平均約1%、最大約14%の精度向上が見られた。また、ワーストケースについても底上げされており、より実用性が増した。(著者抄録)

We evaluate the influences on visual strain and visually-induced motion sickness in observing 3D image. Based on the SSQ analysis, it is clear that the correlation between visual strain and physical factors of 3D display is more than 90%. © 2010 SID.

In this paper, we present a novel method for protecting biometric templates that can be represented as binary sthngs and apply it to iris templates generated using Daugman's like approach, iris codes. The proposed method is capable of generating a large number of different compact revocable binary codes from the true iris codes by dividing the iris code into equal length words and using each word to address a single bit in a user-specific randomly generated bit string. This random encoding process ensures irreversibility even if the protected code and the user specific random key are known to attackers. Unlike most of the existing cancelable biometrics schemes, our scheme satisfies all the requirements of the cancelable biometrics construct without a significant loss in recognition performance.

This paper describes achromatic/chromatic spatio-velocity contrast sensitivity functions (SV-CSFs) and their application to video quality assessment (VQA). SV-CSF is a modulation transfer function of the human visual system, and consists of the relationship among visual contrast sensitivities, spatial frequencies and velocities of objects. For simulating perceived videos, SV-CSFs are applied to filter original and distorted videos. The criteria in our VQA method are obtained by calculating CIELAB color differences between filtered videos. From the experimental results for the validation, it was shown that the proposed VQA method is a more efficient VQA method than conventional methods. © 2010 IEEE.

In many medical applications, the automatic segmentation of deformable organs from medical images is indispensable and its accuracy is of a special interest. However, the automatic segmentation of these organs is a challenging task according to its complex shape. Moreover, the medical images usually have noise, clutter, or occlusion and considering the image information only often leads to meager image segmentation. In this paper, we propose a fully automated technique for the segmentation of deformable organs from medical images. In this technique, the segmentation is performed by fitting a nonlinear shape model with pre-segmented images. The kernel principle component analysis (KPCA) is utilized to capture the complex organs deformation and to construct the nonlinear shape model. The presegmentation is carried out by labeling each pixel according to its high level texture features extracted using the overcomplete wavelet packet decomposition. Furthermore, to guarantee an accurate fitting between the nonlinear model and the pre-segmented images, the particle swarm optimization (PSO) algorithm is employed to adapt the model parameters for the novel images. In this paper, we demonstrate the competence of proposed technique by implementing it to the liver segmentation from computed tomography (CT) scans of different patients. © 2010 Copyright SPIE - The International Society for Optical Engineering.

In this paper, spatio-velocity contrast sensitivities were measured by using red-green and blue-yellow grating stimuli. The results show the contrast sensitivities at the spatial frequencies over one cycle-per-degree decrease gradually as the velocities of the stimuli increase.

CT画像中の臓器や組織の形状を3次元的に提示することは診断支援、医療教育などに大変有用であるが、各臓器の表面形状を3次元的に抽出する必要がある。中でも膵臓は周囲を他の臓器に囲まれて境界が不明瞭であるため、抽出が困難とされている。本研究では利用者の知識を簡易に活用するインタラクティブ抽出手法を提案する。初めに利用者の手によりCT画像中から膵臓全体を含む領域を粗く指定する。次に、この領域の境界上の任意の点と、同領域の中心線上の最近傍点とを結び、その線分におけるCT値変化の微係数を計算、微係数の最大値をその方向におけるエッジ信頼度と定義する。このようにして作成したエッジ信頼度分布を自動抽出手法に利用することで不鮮明な輪郭部における形状の漏出エラーを抑制した新しい形状抽出を実現した。本研究ではChan-VeseモデルのLevel set抽出手法に適用し、安定かつ高精度に膵臓形状を得ることができた。(著者抄録)

The accurate size of affected parts is important for various diagnoses. We propose a method to measure the three-dimensional length of those parts using an endoscope with a tiny magnetic tracking sensor. In this method, an endoscopist manually points the stereo correspondence in two endoscopic images for triangulation. The manual pointing is more reliable compared with automatic stereo correspondence techniques. We analyzed the accuracy of this method by using the rigid object in the experimental environment without metallic objects. It is shown that the endoscope geometry of the triangulation mainly affects the error. Therefore, the endoscope geometry should be considered for practical use.

画像評価は銀塩写真，印刷，CRTテレビを中心に長い歴史を通して地道な研究が行われ，今日の高い画質を持つ多様なディジタル画像システムへと発展してきた．画質評価の研究は，主観評価と対応の良い物理評価パラメータを見いだす研究として行われてきたが，いまだに完全なる解明はなされていない．本稿では，銀塩写真，印刷，CRTに代表されるアナログ画像から最近のフラットパネルディスプレイやインクジェットプリンタに至る画質の問題を概観する．まず主観評価と客観評価の基礎から解説し，視覚特性と画質，更に高次な表現パラメータである質感について述べる．また画質と深く関連している疲労についての研究成果など，筆者の研究室で行っている研究を中心に概説する．

Modified conventional method for capturing light field using mirror ball is proposed to extend the capturing light field. Two types of mirror sphere array pattern is introduced to capture the rays from various directions and positions passed the light fields and inter-reflected rays by neighbored sphere are also considered to capture the light field. Amount and direction of those captured rays are evaluated by the ratio of the acquired light fields and it is shown that the rays can be captured precisely and effectively compared with conventional method. It is also shown that the method is significant for the appearance of computer generated synthetic object. © 2008 Society for Imaging Science and Technology.

In our previous paper, we have developed a projector-Based color matching system for print industry. In this system, a color of print can be matched lo the desired color to minimize the color difference between print and projected images. However, in this color matching, it is necessary to observe and measure the projector image under the dark room. In this paper, we proposed a new color correction method for projector image under dim illumination based on the C1ECAM02. As well known, in the dim room, the color gamut of reproduced image becomes narrow compared with the gamut in the darkroom. M. Ashdown et al. proposed a method to compress the color gamut in the CIEL*u*v* color space. However, the chromatic adaptation according to the change of white point of the illumination is not considered in this method. Therefore we introduce C1ECAM02 for color matching under the dim viewing condition. Chromatic and achromatic channels in CIECAM02 space are calculated from an input image and the chromatic channels are compressed to match the possible projection range of output under the illumination. The images obtained by conventional and proposed algorithms are evaluated by the psychophysical experiment used memory matching. As a result, it was shown that the proposed method can improve the color appearance under dim illumination. © 2008 Society for Imaging Science and Technology.

We analyzed the influence of ambient lighting to the appearance of still images displayed on the LCD. Four different images under the illumination from the background and over the head were observed and rated by SD method. We found that the appearance is well correlated to the average chromaticity of image and illumination.