Jae-Won Cho

An Oblivious Watermarking for 3-D Polygonal Meshes Using Distribution of Vertex Norms

Although it has been known that oblivious (or blind) watermarking schemes are less robust than nonoblivious ones, they are more useful for various applications where a host signal is not available in the watermark detection procedure. From a viewpoint of oblivious watermarking for a three-dimensional (3-D) polygonal mesh model, distortionless attacks, such as similarity transforms and vertex reordering, might be more serious than distortion attacks including adding noise, smoothing, simplification, remeshing, clipping, and so on. Clearly, it is required to develop an oblivious watermarking that is robust against distortionless as well as distortion attacks. In this paper, we propose two oblivious watermarking methods for 3-D polygonal mesh models, which modify the distribution of vertex norms according to the watermark bit to be embedded. One method is to shift the mean value of the distribution and another is to change its variance. Histogram mapping functions are introduced to modify the distribution. These mapping functions are devised to reduce the visibility of watermark as much as possible. Since the statistical features of vertex norms are invariant to the distortionless attacks, the proposed methods are robust against such attacks. In addition, our methods employ an oblivious watermark detection scheme, which can extract the watermark without referring to the cover mesh model. Through simulations, we demonstrate that the proposed approaches are remarkably robust against distortionless attacks. In addition, they are fairly robust against various distortion attacks

Robust watermarking on polygonal meshes using distribution of vertex norms

Most watermarking techniques for 3-D mesh models have mainly focused on robustness against various attacks, such as adding noise, smoothing, simplification, re-meshing, clipping, and so on. These attacks perceptually damage the stego model itself. Unlike watermarking of other multimedia data, serious attacks for 3-D meshes includes similarity transform and vertex re-ordering. They can fatally destroy the watermark without any perceptual degradation of the stego model. In this paper, we propose a new watermarking technique for 3-D polygonal mesh model, which modifies the distribution of vertex norms according to watermark bit to be embedded. In particular, the proposed employs blind watermark detection technique, which extracts the watermark without referring to cover meshes. The simulation results show that the proposed is remarkably robust against similarity transform and vertex re-ordering.

3-D mesh sequence compression using wavelet-based multi-resolution analysis

In this paper, we present two compression methods for irregular three-dimensional (3-D) mesh sequences with constant connectivity. The proposed methods mainly use an exact integer spatial wavelet analysis (SWA) technique to efficiently decorrelate the spatial coherence of each mesh frame and also to adaptively transmit mesh frames with various spatial resolutions. To reduce the temporal redundancy, the first proposed method applies multi-order differential coding (MDC) to the temporal sequences obtained from SWA. MDC determines the optimal order of the differential coder by analyzing the variance of prediction errors. Comparing with the first order differential coding (FDC) scheme, the method can improve the compression performance. The second proposed method applies temporal wavelet analysis (TWA) to the temporal sequences. In particular, this method offers spatio-temporal multi-resolution coding. Through simulations, we prove that our methods enable efficient lossy-to-lossless compression for 3-D mesh sequences in a single frame work.

Wavelet analysis based blind watermarking for 3-d surface meshes

As most previous wavelet analysis based 3-D mesh watermarking methods embed the watermark information into wavelet coefficients arranged in a certain order, they have not been used as blind schemes since the connectivity information must be exactly known in the watermark extraction process. In this paper, we propose a blind watermarking method based on wavelet analysis for 3-D mesh model. Two new techniques are introduced. One is to exploit the statistical features of scale coefficients on an approximation (low resolution) level for watermark embedding. Another is to extract the hidden watermark, not from the same resolution level as used in embedding process, but directly from the spatial domain. As the proposed watermark detection does not require the wavelet analysis, any pre-processing such as registration and re-sampling, is not needed. These techniques allow to detect the watermark without referring to the original meshes. In addition, the proposed are applicable directly to irregular meshes by using irregular wavelet analysis. Through simulations, we prove that our method is fairly robust against various attacks including topological ones.

Echo Watermarking in Sub-band Domain

Echo hiding is a method for embedding information, called watermark, into an audio signal. In general, echo hiding is processed in the time domain by convolving audio signal with echo kernel, without any consideration of the frequency characteristics. In this paper, we propose an echo hiding technique, which inserts echo into sub-band signal so as to take account into the frequency characteristics. The proposed echo hiding enables to embed high-energy echo, while minimizing the host audio quality distortion. In addition, the proposed allows increasing watermark capacity, since it is possible to embed simultaneously some watermark bits into different sub-band signals. The simulation results show that the proposed is more effective than the conventional echo hiding, in terms of watermark capacity and robustness against various attacks.

A 3-D mesh sequence coding using the combination of spatial and temporal wavelet analysis

In this paper, we present a wavelet-based progressive compression method for isomorphic 3-D mesh sequence with constant connectivity. Our method reduces the spatial and temporal redundancy by using both spatial and temporal wavelet analysis. To encode geometry information, each mesh frame is decomposed into a base mesh and its spatial wavelet coefficients of each resolution level by spatial wavelet analysis filter bank. The spatially transformed sequence is decomposed into several sub-band signals by temporal wavelet analysis filter bank. The resulting signal is encoded by using an arithmetic coder. Since an isomorphic mesh sequence has the same connectivity over all frames, the connectivity information is encoded only for the first mesh frame. The proposed method enables both progressive representation and lossless compression in a single framework by multi-resolution wavelet analysis with a perfect reconstruction filter bank. Our method is compared with several conventional techniques including our previous work.

A Robust Blind Water Marking for 3D Meshes Using Distribution of Scale Coefficients in Irregular Wavelet Analysis

We propose a new method for watermarking of 3D surface mesh. After irregular wavelet analysis, the watermark is embedded in the scale coefficients. We modify the mean of the distribution of the vertex norm of the approximation mesh in order to obtain blind scheme which does not require the original mesh for detection. Experimental results show the effectiveness of the proposed algorithm both in terms of invisibility and robustness against simplification and progressive lossy compression

A robust blind audio watermarking using distribution of sub-band signals

In this paper, we propose a statistical audio watermarking scheme based on DWT (Discrete Wavelet Transform). The proposed method selectively classifies high frequency band coefficients into two subsets, referring to low frequency ones. The coefficients in the subsets are modified such that one subset has bigger (or smaller) variance than the other according to the watermark bit to be embedded. As the proposed method modifies the high frequency band coefficients that have higher energy in low frequency band, it can achieve good performances both in terms of the robustness and transparency of watermark. Besides, our watermark extraction process is not only quite simple but also blind method.

FFS: A fast peer-to-peer file sharing approach for mobile devices

With the emergence of mobile devices and the rapid growth in mobile networks, file sharing became a common activity. However, in order to share files between mobile devices, users need to use different software systems depending on situations, which makes it tedious and inconvenient. In this paper, we propose FFS, a fast file sharing approach for peer-to-peer file sharing. FFS overcomes network limitations with an approach that dynamically selects a suitable one among various NAT traversal techniques.

Quality measurement for transmitted audio data using distribution of sub-band signals

Recently, the remarkable progress of network technology has increased the requirement for transmission of high quality multimedia data. By the trend, it has been issued to investigate an efficient methodology for quality measurement of transmitted multimedia data. In this paper, we propose a new audio quality measurement technique to substitute for a typical quality measurement tool, RMSE (root mean squared error). The proposed method modifies the variance of sub-band signals to perform the estimation of audio quality at the transmitter, the receiver is able to estimate the quality distortion of transmitted audio data by calculating the distance between the variance and the reference value representing the characteristics of sub-band signals, so called eve (estimated variance error). The proposed is as no reference technique, it does not require the original data to measure the audio quality. On the Gaussian noise channel with several standard deviations, we prove that the proposed scheme has good performance, and it is a novel alternative to RMSE.