1. 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

2. 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)

3. 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

4. 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

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

6. Look-Up-Table (LUT) Based DCT Domain IMC
Model DCT Coefficients as Laplacian Distribution [Smoot & Rowe, 96]
The Value of is Estimated as
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

7. 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