Atsushi KOIKE

Multiview images captured by multicamera systems are generally not uniform in colour domain. In this paper, we propose a novel colour correction method of multicamera systems that can (i) be applied to not only dense multicamera system, but also sparse multicamera configuration and (ii) obtain an average colour pattern among all cameras. Our proposed colour correction method starts from any camera on the array sequentially, following a certain path, for pairs of cameras, until it reaches the starting point and triggers several iterations. The iteration stops when the correction applied to the images becomes small enough. We propose to calculate the colour correction transformation based on energy minimisation using a dynamic programming of a nonlinearly weighted Gaussian-based kernel density function of geometrically corresponding feature points, obtained by the modified scale invariant feature transformation (SIFT) method, from several time instances and their Gaussian-filtered images. This approach guarantees the convergence of the iteration procedure without any visible colour distortion. The colour correction is done for each colour channel independently. The process is entirely automatic, after estimation of the parameters through the algorithm. Experimental results show that the proposed iteration-based algorithm can colour-correct the dense/sparse multicamera system. The correction is always converged with average colour intensity among viewpoint, and out-performs the conventional method. (C) 2010 Elsevier Inc. All rights reserved.

The authors study a method for objective measurement of perceived picture quality for high definition video based on the full reference framework. The proposed method applies seven spatio-temporal image features to estimate perceived quality of pictures degraded by compression coding. Computer simulation shows that the proposed method can estimate perceived picture quality at a correlation coefficient of above 0.91. © 2009 SPIE-IS&amp T.

In this paper, the authors propose a novel method to measure the perceived picture quality of H.264 coded video; based on hybrid no reference framework. The latter term means that the proposed model uses only receiver-side information for objective video quality assessment, but analyzes both the compressed bitstream and baseband signals of the decoded picture to improve the estimation accuracy of the subjective quality. The proposed method extracts quantizer-scale information from the bit-stream along with two spatiotemporal image features from the baseband signal, which are integrated to express the overall quality using the weighted Minkowski metric. A computer simulation shows the proposed method can estimate the subjective quality at a correlation coefficient of 0.909 whereas the PSNR metric, which is referred to as a benchmark, correlates the subjective quality at a correlation coefficient of 0.773.

The authors study an objective method to estimate perceptual picture quality of the coded pictures based on No Reference framework. The proposed method extracts two image features that reflect the significance of blocking and flickering artifacts and estimates the subjective quality by weighted sum of the image features. Computer simulations show that the proposed method can estimate subjective quality at a correlation coefficient of 0.754.

This paper presents a novel method to represent a real 3D world using IBR (Image-based Rendering) technology. The major achievement is realization of "walk-through" experience, in which audiences can see the scene of sport games as if they were the player, while the conventional IBR method cannot provide such an experience. The key idea is a newly introduced framework "locally divided ray space" to capture the ray inside the scene. Consequently, the proposed algorithm can generate a virtual image inside the scene using multiple real images captured from outside. In this paper, the outline of the proposed method as well as the possible demonstration at the conference venue is described.

In this research, we address the problem of 3-D model generation from disparity maps. Given an inaccurate 3-D model, dense multiview images are generated. Disparity maps between each pair are estimated using stereo matching algorithm. The disparity maps are projected into space as depth candidates. The kernel classifier is applied to the depth candidates for each layer of candidates from ground, and the candidates with higher probability values are selected for further fine-tuning process. In fine-tuning step, the best location of the border of the objects in each layer from ground is determined using dynamic programming. Finally the 3-D model is generated. Using the generated 3-D model, we regenerate the dense multiview images and disparity maps. We perform the same process for several iterations until the changes in the generated 3-D model are small. Experimental result shows we can eventually enhance the quality of the 3-D model within a few iterations in comparison with the starting 3-D model.

In this paper, we propose geometry based image-based rendering method for sparse multicamera system using multiple local ray-space representation and 3-D model generation. In this system, the quality of walk-through view experience is impaired by inaccurate camera parameters and 3-D model. In order to eliminate these affects, we enhance the reconstructed local ray-spaces using stereo matching approach. Hence, free viewpoint rendering quality is improved significantly for walk-through image synthesis. Experimental results for several multiview sequences verify the effectiveness of our approach.

The authors study a method of estimating perceived picture quality for multimedia applications based on the full reference framework. Since multimedia applications usually have less capability in display and communication channels than television broadcasting, an objective quality model should be developed considering a low-resolution, low-frame-rate video format and low-bit-rate video coding that applies a high compression ratio. The proposed method therefore applies the blockiness of the picture, time variance of MSE and temporal PSNR degradation as indices of objective picture quality. Computer simulation shows that the proposed method can estimate perceived picture quality at a correlation coefficient of above 0.94.

We proposed divided ray space based method generating free viewpoint video using circular arrayed multi-viewpoint video. However, there were vertical gaps in free viewpoint videos, since vertical disparity cannot be acquired. So, by using new format of ray space described by horizontal disparity values that we have proposed in order to compress ray space data, vertical disparity can be realized exactly since vertical disparity can be calculated with the horizontal disparity.

Digital terrestrial broadcasting in Japan specifies a service profile not only for fixed receivers in the home, but also for personal mobile terminals such as acellular phones and PDAs. Services for personal mobile terminals are expected to become more attractive with sufficient functionality and flexibility by utilizing the network connectivity of mobile terminals. In order to verify the possibilities of digital television broadcasting (DTV) services for personal mobile terminals and clarify technical problems at the commercial level, we developed a prototype mobile terminal capable of receiving digital terrestrial broadcasting in addition to the Internet. This paper describes the assumed DTV service for personal mobile terminals and the technical architecture of the developed mobile terminal with regard to the hardware and the software. Several experiments using the developed mobile terminal were conducted and the performance was evaluated.

This paper proposes an efficient coding scheme for remote medical communication systems, or "telemedicine systems". These systems require a technique which is able to transfer a large volume of data such as X-ray images effectively. We developed a hierarchical image coding and transmission system in order to achieve an efficient transmission of medical images over the Internet. The coding system employs a lossless hierarchical coding scheme with wavelet transform to be applied for each segment within a whole image. Furthermore, it uses Golomb-Rice(GR) codes both for high efficiency coding and high speed decoding. The client-server system based on the proposed scheme is implemented with Java language. The system implementation proves that the proposed system is very suitable for telemedicine through a ISDN or LAN environment in terms of high speed medical image transmission and decoding with normal personal computers.