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A DSP Solution to Error Concealment in Digital Video

A DSP Solution to Error Concealment in Digital Video. Eduardo Asbun and Edward J. Delp. Video and Image Processing Laboratory ( VIPER) Purdue Multimedia Testbed School of Electrical and Computer Engineering Purdue University West Lafayette, IN 47907-1285 +1 765 494 1740

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A DSP Solution to Error Concealment in Digital Video

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  1. A DSP Solution to Error Concealment in Digital Video Eduardo Asbun and Edward J. Delp Video and Image Processing Laboratory (VIPER) Purdue Multimedia Testbed School of Electrical and Computer Engineering Purdue University West Lafayette, IN 47907-1285 +1 765 494 1740 +1 765 494 0880 (fax) email: ace@ecn.purdue.edu http://www.ece.purdue.edu/~ace

  2. Outline • Introduction • Error Concealment • Fast Near-Optimal Approach • Current Work • Conclusions

  3. VIPER Research Projects • Scalable Video and Image Compression • color still image compression (CEZW) • high and low bit rate video compression (SAMCoW) • ATM, Internet, and wireless video • Error Concealment • Content Addressable Video Databases (ViBE) • Scene Change Detection and Identification • Multimedia Security: Digital Watermarking • Embedded Real-Time Image and Video Processing

  4. VIPER Research Projects • Multiresolution Edge Detection • Analysis of Mammograms • Binocular Shape Reconstruction

  5. Error Concealment in Digital Video • Scenario: • Compressed digital video streams are transmitted over ATM or wireless networks • Cell or packet loss due to channel errors or congestion causes data to be dropped in the channel • When MPEG video is transmitted, macroblocks and motion vectors are missing from the stream • Visual quality is lower • Potential loss of synchronization

  6. Error Concealment in Digital Video • Problem: • Given an encoded video bit stream, how can the stream be packed into ATM cells and transmitted over a lossy channel in such a way to minimize the effect of cell losses? • How can the bit stream be processed to conceal cell loss? • Detect where the lost data is located • Process the bit stream to conceal the lost data

  7. Applications of Error Concealment • All set-top decoder boxes will require some form of error concealment running in real-time • This requires simple and robust approaches that can be implemented on DSP-based embedded systems

  8. Forms of Error Concealment • Active Error Concealment: • Error control coding • Retransmission • Unequal error protection • Passive Error Concealment: • Postprocessing of video stream to reconstruct missing data • Necessary in many applications where active error concealment fails or cannot be used

  9. Passive Error Concealment:Statistical Spatial Approach • Missing information is reconstructed based on data from undamaged portions of the current frame • Each frame is modeled as a Markov Random Field • A maximum a posteriori (MAP) estimate of the missing macroblocks is obtained using this model • Optimal solution obtained iteratively • Drawback: time consuming

  10. Passive Error Concealment:Fast Near-Optimal Approach • The median of the neighbors of a missing pixel is an approximate MAP estimate • Attractive for real-time implementation due to its simplicity • Consists of two stages: • Initialization • Filtering

  11. Initialization Stage

  12. Filtering Stage

  13. Objective • Implement fast near-optimal approach in real-time • This technique will be used on MPEG video over ATM and in Internet video • The Texas Instruments TMS320C6201 will be used

  14. Current Work: Error Concealment System • As a proof of concept, focus on implementing the fast near-optimal error concealment technique using a C6x-based Spectrum Signal Detroit board • Transmission of MPEG video over ATM involves the implementation of real-time MPEG encoder and decoder • Simulate this stage by randomly dropping 8x8 blocks of pixels from uncompressed frames

  15. Block Diagram of Error Concealment System

  16. System Description • The C6201-based Detroit board is used as a computational engine • Video is digitized using a Matrox Corona board • Digitized frames are transferred to the Detroit board where they are processed • After processing is completed, frames are transferred back to the Corona board for display

  17. System Block Diagram

  18. Implementation Details • Video format used is ITU-601 (CCIR-601), YUV 4:1:1, 720x480 pixels • Frames are transferred from the digitizer into the on-board memory of the Detroit board via the PCI bus • Kernel of the error concealment system is 3x3 median filter • Hand-optimized assembly routine implemented • 126 cycles for 3x3 short integers

  19. Results

  20. Conclusion • Implemented fast near-optimal error concealment technique on the TMS320C6x • Current Work: • Motion Compensation (MPEG-4) • Future Work: • Real-time wavelet compression algorithm (SAMCoW)

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