DCT Domain Image & Video Processing

Shizhong Liu and Alan C. Bovik

Fast Algorithms for DCT-domain Inverse Motion Compensation

Discrete cosine transform (DCT) based digital video coding standards such as MPEG and H.26x are becoming more widely adopted for multimedia applications. Since the standards differ in their format and syntax, video transcoding, where a compressed video bit-stream is converted from one format to another format, is of interest for purposes such as channel bandwidth adaptation and video composition. DCT-domain video transcoding is generally more efficient than spatial domain transcoding. However, since the data is organized block by block in the DCT-domain, inverse motion compensation becomes the bottleneck for DCT-domain methods. In this project, we propose a novel local bandwidth constrained fast inverse motion compensation algorithm operating in the DCT-domain. Relative to Chang's algorithm [Chang' 93], the proposed algorithm achieves computational improvement of 25% to 55% without visual degradation. A by-product of the proposed algorithm is a reduction of blocking artifacts in very low bit-rate compressed video sequences. The proposed algorithm can be combined with other fast methods presented in the literature for more computational savings. We also present a look-up-table (LUT) based implementation method by modeling the statistical distribution of the DCT coefficients in natural images and video sequences. By this method, we obtain a further another 31-48% improvement in computation. The memory requirement of the LUT is about 800KB which is reasonable. Moreover, the LUT can be shared by multiple DCT-domain video processing applications running on the same computer or video server.

[Slides] [Poster]

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, accepted for publication, Jan. 2002.
S. Liu and A. C. Bovik, "Look-up-table based DCT domain inverse motion compensation," Proc. IEEE International Conference on Image Processing, October 7-10, 2001, Thessaloniki, Greece.
S. Liu and A. C. Bovik, "Local bandwidth constrained fast inverse motion compensation for DCT domain video transcoding," Proc. IEEE International Conference on Acoustics,Speech, and Signal Processing, May 7-11, 2001, Salt Lake City, UT.

Foveation Embedded Video Transcoding

Video transcoding is a key technology to support video communications over heterogeneous networks. Although quite a bit of research effort has been made in video transcoding due to its wide applications, most video transcoding techniques proposed in the literature are optimized based on the simple Mean Squared Error (MSE) metric which doesn't cooperate with the Human Vision System (HVS) very well. In this paper, foveation, a property of the HVS, is exploited in video transcoding. The proposed foveation embedded DCT domain video transcoding can reduce the bit rate without compromising visual quality or achieve better subjective quality for a given bit rate by shaping the compression distortion according to the foveated contrast sensitivity function of the HVS.

[Slides]

S. Liu and A. C. Bovik, "Foveated Video Transcoding," Proc. IEEE Int. Conf. on Image Processing, Rochester, NY, Sept. 22-25, 2002, Submitted.

H. R. Sheikh, S. Liu, Z. Wang and A. C. Bovik, "Foveated Multipoint Videoconferencing at Low Bit Rates," Proc. IEEE Int. Conf. on Acoustics, Speech, and Signal Proc., May 13-17, 2002, Orlando, FL, accepted for publication.

Fast and Memory Efficient DCT-domain Video Transcoder for Wireless Video

Wireless video is one of the important applications supported by upcoming 3G mobile communication systems. In this project, we proposed a fast and memory efficient DCT-domain video transcoder to convert a high quality MPEG1/2 video bit stream into a low bit rate MPEG4 stream with low spatial resolution for wireless video access. Compared to existing approaches, the proposed video transcoder can save more than 50% of required memory. Furthermore, the computational complexity of the proposed method is less than 30% of that required by the existing methods. However, the video quality achieved by the proposed method and by existing methods is hardly distinguishable for target bit rates of 384 kb/s and 256 kb/s, as shown in our experimental results.

[Slides]

S. Liu and A. C. Bovik, "A Fast and Memory Efficient Video Transcoder for Low Bit Rate Wireless Communications," Proc. IEEE Int. Conf. on Acoustics, Speech, and Signal Proc., May 13-17, 2002, Orlando, FL, accepted for publication.

DCT-domain Blind Measurement and Reduction of Blocking Artifacts

Blocking artifact is one of the most annoying artifacts in block DCT-based image/video compression standards (e.g., JPEG, MPEG and H.263) when images are coded at low bit-rates. To efficiently assess the severity of the blocking artifact in a compressed image bit-stream, a method for DCT-domain blind measurement of blocking artifacts is first proposed in this project. By constituting a new shifted block across any two adjacent blocks, the blocking artifact is modeled as a 2-D step function in the new shifted block. A fast DCT-domain algorithm has been derived to constitute the new block and extract all parameters needed by the blind measurement of blocking artifacts, which exploits several properties of the human vision system (HVS). According to the local visibility measure of blocking artifacts, a novel DCT-domain method is then developed to adaptively reduce the blocking effect, if necessary. Experimental results show that the proposed measure of blocking artifacts is effective and stable across a wide variety of images, and our blocking artifact reducing method exhibits satisfactory performance as compared to other post-processing techniques. The proposed technique has low computational cost hence can be used for real-time image/video quality monitoring and control, especially in those applications where image/video is processed directly in the DCT-domain.

[Slides]

S. Liu and A. C. Bovik, "Efficient DCT-domain Blind Measurement and Reduction of Blocking Artifacts", IEEE Trans. on Circuits and Systems for Video Technology, accepted for publication, Apr. 2001.

S. Liu and A. C. Bovik, "DCT domain blind measurement of blocking artifacts in DCT-coded images," Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing, May 7-11, 2001, Salt Lake City, UT.