Sub Menu

Quality Improvement?

Computation Time

Conclusions

The Team:
Scott Chin
Anup Misra

Supervisor:
Dr. Wu Sheng Lu

ELEC499A
August 2003

Results

Quality Improvement?

The following plot shows a comparison of the power-to-signal-noise ratio when using DWT and DCT. Six GOPs of a video sequence were encoded at 90% compression ratio. The following plot was calculated for the luminance component only.

As seen from the graph, the PSNR of the DWT encoded sequence is constantly at least 3dB higher than the DCT frames. Also note that each maximum peak corresponds to an I frame in the GOP structure. Therefore it has the highest PSNR. However, as errors propogate through the GOP, the PSNR of the DCT frames degrades much faster than the DWT frames. The PSNR difference from the I frame and the last B frame in the GOP is only approximately 1dB for the DWT encoded sequence; But for the DCT encoded sequence, this differenece is almost 3dB.

Back to Top


Computation Time

The following table summarizes the encoding and decoding times for four video sequences. Note that these computation times are calculated for each GOP, averaged over four GOPs. The calculation times are in minutes.

Encoding - DWT
Encoding - DCT
Decoding - DWT
Decoding - DCT
tempete
10.68
1.04
10.14
0.62
mobile
10.36
0.99
9.66
0.59
edberg
10.72
1.21
10.44
0.55
football
11.32
1.14
10.02
0.65


From this table we see that the encoding time for DWT is consistently longer but only by 30-75 seconds. The decoding time for DWT is also longer but only by approximately 30 seconds.

As a final note, these calculations were executed in Matlab and a 1GHz desktop PC.

Back to Top


Conclusions

As seen from the results, the Wavegen codec shows that a DWT based codec can be superior to a DCT based codec . We saw improvement in picture quality with comparable computation time. We were pleased with the results and we believe that wavelet based compression will play an integral role in the future of video coding standards.

Back to Top