Tien-Hsu Lee

Hybrid LMS-MMSE inverse halftoning technique

The objective of this work is to reconstruct high quality gray-level images from bilevel halftone images. We develop optimal inverse halftoning methods for several commonly used halftone techniques, which include dispersed-dot ordered dither, clustered-dot ordered dither, and error diffusion. At first, the least-mean-square (LMS) adaptive filtering algorithm is applied in the training of inverse halftone filters. The resultant optimal mask shapes are significantly different for various halftone techniques, and these mask shapes are also quite different from the square shape that was frequently used in the literature. In the next step, we further reduce the computational complexity by using lookup tables designed by the minimum mean square error (MMSE) method. The optimal masks obtained from the LMS method are used as the default filter masks. Finally, we propose the hybrid LMS-MMSE inverse halftone algorithm. It normally uses the MMSE table lookup method for its fast speed. When an empty cell is referred, the LMS method is used to reconstruct the gray-level value. Consequently, the hybrid method has the advantages of both excellent reconstructed quality and fast speed. In the experiments, the error diffusion yields the best reconstruction quality among all three halftone techniques.

Precise and fast error tracking for error-resilient transmission of H.263 video

A precise error tracking scheme for robust transmission of real-time H.263 video is presented. By utilizing a feedback channel, the decoder reports the addresses of corrupted blocks induced by transmission errors back to the encoder. With these negative acknowledgments, the encoder can precisely calculate and track the propagated errors by examining the backward motion dependency for each pixel in the current encoding frame. With this precise tracking, the error-propagation effects can be terminated completely by INTRA refreshing the affected macroblocks. In addition, by utilizing the four-corner tracking approximation and the linear motion model, a fast algorithm is also developed to further reduce the computation and memory requirements. The simulations show that both schemes yield significant video quality improvements in error-prone environments. The advantages of the low memory requirement and the low computation complexity are particularly suitable for real time implementation.

Restart marker regulation technique for progressive JPEG image coding in mobile communications

In this letter, an error-robust and JPEG compliant progressive image compression scheme over wireless channels is presented. The use of restart markers in the JPEG standard provides the resynchronization function for error handling. Unfortunately, misinterpreted markers may cause serious error damage due to the error propagation. Therefore, a restart marker regulation technique is proposed here to preprocess restart markers at the decoding end. All erroneous restart markers are corrected and rearranged in the correct order. After decoding, isolated erroneous restart intervals are detected and further processed by the error concealment to reduce image degradation. The simulations demonstrate that the proposed scheme does significantly improve the image quality in error-prone environments.

Robust transmission of progressive JPEG image coding in wireless communications

We present an error-robust progressive JPEG image compression scheme over wireless channels. It utilizes a resynchronization regulation technique to isolate erroneous blocks, and then corresponding error concealment techniques are applied to reduce the error damage.

Synchronous backward error tracking algorithm for H.264 video coding

The objective of this paper is to develop a robust error-resilient algorithm, called the Synchronous Backward Error Tracking (SBET), to completely terminate the error propagation effects in the error-prone environment for H.264 video coding. The motivation is that if the state of the decoder is available to the encoder, i.e., the state of the encoder can synchronize to the state of the decoder, the effect of error propagation can be entirely terminated because all predictions are based on the same references. Therefore, we assume that a feedback channel is available and the encoder can be aware of the decoders error concealment by any external means. The pixel-based Precise Backward Error Tracking (PBET) is modified and utilized to track the error locations and reconstruct the state of the decoder in the encoder. The proposed method only involves memory access, simple addition and multiplication operations for the error-contaminated pixels to achieve encoder-decoder synchronization. By observing simulation results, the rate-distortion performance of the proposed algorithm is always better than that of the conventional algorithms. Specifically, SBET outperforms PBET up to 1.21 dB under 3% slice error rate for the QCIF format Foreman sequence. In addition, instead of forced INTRA refreshing, the phenomenon of burst bit rate can be avoided.

Adaptive Lossy Error Protection architecture in H.264 video transmission

Systematic Lossy Error Protection (SLEP) is a robust error resilient mechanism which uses Wyner-Ziv coding to protect the video bitstream. In this paper, we propose a low overhead adaptive lossy error protection (ALEP) mechanism that provides a good trade-off between the error resilience and decoded video quality. The proposed method can generate appropriate redundant slices to provide proper error correction capability for varying channel conditions. The proposed method maintains good video quality at low packet loss rate compared to original SLEP and still provides sufficient error correction capability at high packet loss rate in our simulation results. It achieves 2–3 dB PSNR improvement at 5% packet loss rate for various video sequences in our simulations.

Error-robust H.263 video coding system

This paper presents an error resilient H.263 video compression system over noisy channels. We develop a video segment regulation algorithm at the decoder to efficiently identify and correct erroneous start codes and block addresses. In addition, a parity-embedded error detection technique is also implemented to enhance the error detection capability of the decoder at the macroblock-layer. After performing above two approaches, the decoder can report the accurate addresses of detected corrupt blocks back to the encoder via a feedback channel. With these negative acknowledgments, the precise error tracking algorithm is developed at the encoder to precisely calculate and trace the propagated errors for INTRA refreshing the contaminated blocks. Simulation results show that the proposed system yields significant video quality improvements over the motion compensated concealment by PSNR gains of 4 to 6 dB at bit rate around 32 kbps in error-prone DECT environments. In particular, this system complies with the H.263 standard and has the advantages of low memory requirement and computation complexity that are suitable for practical real-time implementation.

Enhanced-MMSE inverse halftoning using table-lookup vector quantization

The objective of this work is to reconstruct high quality gray-level images from bi-level halftone images. We develop optimal inverse halftoning methods for several commonly used halftone techniques, which include dispersed-dot ordered dither, clustered-dot ordered dither, and error diffusion. At first, the least-mean-square (LMS) adaptive filtering algorithm is applied in the training of inverse halftone filters and the optimal mask shapes are computed for various halftone techniques. In the next step, we further reduce the computational complexity by using lookup tables designed by the minimum mean square error (MMSE) method. The optimal masks obtained from the LMS method are used as the default filter masks. Finally, we propose the enhanced MMSE inverse halftone algorithm. It normally uses the MMSE table lookup method for its fast speed. When an empty cell is referred, the LMS method is used to reconstruct the gray-level value. Consequently, the proposed method has the advantages of both excellent reconstructed quality and fast speed. In the experiments, the error diffusion yields the best reconstruction quality among all three halftone techniques.

Precise error tracking for terminating error propagation effects in H.263 video transmission

WE present a robust real-time video coding scheme that complies with the H.263 standard. By utilizing a feedback channel, the corrupted macroblocks (MBs) due to transmission errors are accurately evaluated and precisely tracked in the encoder. Without dependency trees wide-spanning to unnecessary areas, the error propagation effects are terminated completely by INTRA refreshing the affected MBs. Our simulations show significant video quality improvements in error prone environments.