DCT-Domain Inverse Motion Compensation (IMC) Extract the Prediction Block in the DCT-Domain Previous Algorithms Pre-compute Qij [Chang & Messerschmitt, 93] Factorize Qij [Merhav & Bhaskaran, 97] Approximate Qij [Assuncao & Ghanbari, 98] Use the shared information in each macro-block [Song & Yeo, 00] 8x8 w h

Windowing Effect (in 1-D) x1(n) x2(n) y(n)= x1(n) + x2(n) X1(n) Y(n)= X1(n) + X2(n) X2(n)

Local Bandwidth Constrained DCT Domain IMC Neighboring Pixels Are Highly Correlated in Images DCT coefficients L1 = [5, 0, 1, 0, 0, 0, 0, 0] L2 = [3, 2, 0, 1, 0, 0, 0, 0] L3 = [x, x, x, x, 0, 0, 0, 0] x: element needs computation

Experimental Results Reduce the Computing Time by 25-30% at 4 Mb/s, Time to convert a P frame to an I frame at bit rate of 4 Mb/s and 1 Mb/s (Unit: seconds) Reduce the Computing Time by 25-30% at 4 Mb/s, 45-55% at 1Mb/s Average PSNR Degradation is Less Than 0.3 dB Similar results for B frames Can Work on Top of Other Fast Methods S. Liu, and A. C. Bovik, “Local Bandwidth Constrained Fast Inverse Motion Compensation for DCT-Domain Video Transcoding ”, IEEE Trans. On Circuits and Systems for Video Technology, revised

[Chang & Messerschmitt, 93] DCT-Domain IMC [Liu & Bovik, 01] [Song & Yeo, 00] [Chang & Messerschmitt, 93] [Merhav & Bhaskaran, 97] [Assuncao & Ghanbari, 98] [Liu & Bovik, 01]

Look-Up-Table (LUT) Based DCT Domain IMC Model DCT Coefficients as Laplacian Distribution [Smoot & Rowe, 96] The Value of is Estimated as 0.0284 Let , Pre-compute the Results for Coefficients with 800KB Memory Required LUT Can Be Shared by Multi- ple Processes , , Probability Values of DCT AC coefficients

Table: The average time to convert one P or B frame to an I frame Experimental Results Table: The average time to convert one P or B frame to an I frame (Unit: Second)   Video sequence Chang’s method LUT based method P frame B frame Foreman 0.3137 0.4738 0.0931 0.1423 Coastguard 0.2374 0.3417 0.0912 0.1190 Mobile 0.3487 0.4136 0.1462 0.2000 Stefan 0.2057 0.3667 0.0780 0.1416 Saves More Than 50% of Computing Time Reduces Jerkiness S. Liu, and A. C. Bovik, “Look-Up-Table Based DCT Domain Inverse Motion Compensation ”, ICIP 2001