Hamid Reza Tohidypour

Content adaptive complexity reduction scheme for quality/fidelity scalable HEVC

There has been significant interest in developing a scalable version of the High Efficiency Video Coding (HEVC) standard. As expected, the HEVC scalable video version increases the complexity of the codec compared to the non-scalable counterpart. In this paper, we propose an adaptive early-termination interlayer motion prediction mode search that significantly reduces HEVC/SVCs coding complexity by up to 85.77%, while maintaining the overall bitrate.

Adaptive search range method for spatial scalable HEVC

Presently, the scalable extension of the HEVC standard (known as SHVC) is under development. One of the main issues with SHVC is its increased complexity compared to its non-scalable counterpart (i.e., HEVC). Reducing the complexity of SHVC is important, especially for real-time applications. In this paper, we propose an adaptive search range method that reduces the coding complexity of HEVC with spatial scalability by up to 30.27%, while maintaining the overall bitrate.

Robust quantisation index modulation-based approach for image watermarking

In this study, a robust image watermarking based on the quantisation index modulation (QIM) method is proposed. Conventional QIM methods employ a fixed quantisation step-size that results in poor robustness of the algorithm. Here, the quantisation step-size in the QIM method is adaptively selected using a power-law function and with the aid of the side information, the proposed method is invariant to gain and rotation attack. To keep the watermark imperceptible and increase its robustness, the low-frequency components of high-entropy image blocks are used for data hiding. The analytical error probability and embedding distortion are derived and assessed by simulations on artificial signals. The optimum parameter in the power-law function is obtained based on minimising the error probability. Experimental results confirm the superiority of the proposed technique against common attacks in comparison with the recently proposed methods.

A Novel Gain Invariant Quantization-Based Watermarking Approach

This paper presents a novel quantization-based information hiding approach, which is invariant to gain attack. In the presented scheme, the host signal vector is first divided into two parts, then lp-norm of each vector is calculated. The watermark bits are embedded by quantizing the ratio of the lp-norm of each part. The decoding scheme is performed blindly using the Euclidean distance. Due to the use of division function, the proposed method is robust to scaling attacks. The analytical error probability and embedding distortion are derived and assessed by simulations on artificial signals. The optimum parameter in the lp-norm function is obtained based on minimizing the error probability. Experimental results confirm the superiority of the proposed technique against common attacks in comparison with the existing state-of-the-art methods.

A content adaptive complexity reduction scheme for HEVC-based 3D video coding

3D-HEVC is aiming at utilizing the advanced tools present in HEVC to efficiently code multiview video content. The computational complexity of this codec is significantly increased and is a challenge for real-time applications. In our study, we propose an adaptive early-termination inter and intra prediction mode search that reduces the 3D-HEVC coding complexity by utilizing the correlations between views, while maintaining the overall video quality.

Probabilistic Approach for Predicting the Size of Coding Units in the Quad-Tree Structure of the Quality and Spatial Scalable HEVC

The scalable extension of HEVC (known as SHVC), the recent scalable video coding standard, results in an improved compression performance at the cost of significant increase in computational coding complexity. One of the main factors that contribute to the SHVC encoder complexity is choosing the best partitioning structure for the coding tree units (CTUs). Our study focuses on developing a scheme for predicting the CTU structure in the quality and spatial scalable extension of HEVC. The proposed scheme uses the CTU partitioning structure of the already encoded CTUs in the enhancement layers (ELs) and base layer (BL) to predict the coding unit sizes of the to-be-encoded CTUs in the EL. Performance evaluations confirm that our proposed complexity reduction scheme significantly reduces the execution time of the SHVC encoder, while maintaining the overall quality of the coded streams.

Compression efficiency of HDR/LDR content

High Dynamic Range (HDR) imaging is capable of delivering a wider range of luminance and color gamut compared to Standard Dynamic Range (SDR), offering to viewers a visual quality of experience close to that of real-life. In this study, we evaluate the quality of coded original HDR streams and HDR streams reconstructed from SDR videos and metadata, both compressed by the HEVC standard. Our evaluations have shown that the single HDR approach is largely preferred over the SDR counterpart.

A low complexity mode decision approach for HEVC-based 3D video coding using a Bayesian method

The 3D extension of High Efficiency Video Coding (HEVC) standard (3D-HEVC) aims at improving coding efficiency by introducing new and unique approaches for utilizing correlations between the different views of a scene. Reported coding efficiency, however, comes at the expense of increased computational complexity. For real-time applications, reducing the computational complexity of 3D-HEVC is very important. In this paper, we propose an adaptive fast mode assigning method based on a Bayesian classifier that reduces 3D-HEVCs coding complexity by up to 51.95%, while maintaining the overall quality and bitrate.

A novel quantization-based watermarking approach invariant to gain attack

In this paper, a novel quantization-based information hiding approach which is invariant to gain attack is presented. For the data embedding, the host vector signal is first divided into two separate vectors. Then the ratio of the magnitude of the vectors is quantized according to the watermark data. The decoding scheme is performed blindly using the euclidean distance. The performance of the proposed method is analytically studied and assessed by simulations on artificial signals. The proposed method is applied to various test images as well. The experimental results confirm the superiority of the proposed technique against common attacks in comparison with the recently proposed methods.

A new representation for speech frame recognition based on redundant wavelet filter banks

Although the conventional wavelet transform possesses multi-resolution properties, it is not optimized for speech recognition systems. It suffers from lower performance compared with Mel Frequency Cepstral Coefficients (MFCCs) in which Mel scale is based on human auditory perception. In this paper, some new speech representations based on redundant wavelet filter-banks (RWFB) are proposed. RWFB parameters are much less shift-sensitive than those of critically sampled discrete wavelet transform (DWT), so they seem to feature better performance in speech recognition tasks because of having better time-frequency localization ability. However, the improvement is at the expense of higher redundancy. In this paper, some types of wavelet representations are introduced, including a combination of critically sampled DWT and some different multi-channel redundant filter-banks down-sampled by 2. In order to find appropriate filter values for multi-channel filter-banks, effects of changing the zero moments of proposed wavelet are discussed. The corresponding method performances are compared in a phoneme recognition task using time delay neural networks. It is revealed that redundant multi-channel wavelet filter-banks work better than conventional DWT in speech recognition systems. The proposed four-channel higher density discrete wavelet filter-bank results in up to approximately 8.95% recognition rate increase, compared with critically sampled two-channel wavelet filter-bank.