Contour simplification and motion compensated coding

In order to solve the bottleneck problem of region-based coding scheme, which is the contour coding, lossy methods are introduced in this paper for both 2D and 3D (2D plus time) contour image(s). A non-linear filter by means of majority operation is designed to act as contour simplification for both pre-processing and post-processing of contour coding. An average of 20% gain in contour coding cost is achieved by using this filter while the contour location error is controlled within one pixel width. Afterwards, an efficient contour motion estimation and compensated coding method are presented. In order to exploit the high temporal redundancy of the contour image sequence, motion estimation and compensation are applied to the correspondent label image sequence. First frame is directly coded by Chain-code method. All the following frames are coded in motion compensated mode. Meanwhile, a fast implementation of full search motion estimation algorithm is also described. This algorithm is 2R times faster than traditional method (R is the total regional number). Within each frame, labels are divided into foreground labels and background labels. Only the noticeable prediction errors for the foreground labels are coded. Morphological filters are used to clean the prediction errors of the foreground labels. An efficient prediction error coding algorithm is then introduced based on one-side Chain-code method. The reconstruction of foreground and background regions in the decoder side is also described. Experimental results have demonstrated good performance for very low bitrate video coding applications.     

Adaptive transform tree coding of images

A tree code, asymptotically optimal for stationary Gaussian sources and squared error distortion, is applied suboptimally to encode the discrete cosine transform (DCT) of image subblocks. The variance spectrum of each block DCT is estimated and specified uniquely by a set of one-dimensional autoregressive parameters. The average pel rate for each block is allowed to vary to meet the specification of the same average distortion per block. Since the variance spectrum and rate are different for every block. so is the code tree. Comparative coding simulations with a 256×256 and 512×512 image show that DCT tree coding with postcoding is clearly superior to DCT quantization and that a variable block rate assignment gains about 3 dB over a fixed block rate assignment     

Edge-based motion compensated classified DCT with quadtree for image sequence coding

The motion compensated discrete cosine transform coding (MCDCT) is an efficient image sequence coding technique. In order to further reduce the bit-rate for the quantizied DCT coefficients and keep the visual quality, we propose an adaptive edge-based quadtree motion compensated discrete cosine transform coding (EQDCT). In our proposed algorithm, the overhead moving information is encoded by a quadtree structure and the nonedge blocks will be encoded at lower bit-rate but the edge blocks will be encoded at higher bit-rate. The edge blocks will be further classified into four different classes according to the orientations and locations of the edges. Each class of edge blocks selects the different set of the DCT coefficients to be encoded. By this method, we can just preserve and encode a few DCT coefficients, but still maintain the visual quality of the images. In the proposed EQDCT image sequence coding scheme, the average bit-rate of each frame is reduced to 0.072 bit/pixel and the average PSNR value is 32.11 dB.     

Adaptive fractional motion and disparity estimation skipping in MV-HEVC

MV-HEVC can efficiently compress multiview video data captured from different viewpoints. To achieve high coding efficiency, it consists of not only inter coding but also interview coding. The inter coding includes a motion estimation (ME) process that reduces temporal redundancies between consecutive frames, and the interview coding performs a disparity estimation (DE) that reduces interview redundancies between neighboring views. As a result, MV-HEVC needs high encoding complexity to perform both ME and DE. In order to reduce the complexity, this paper proposes an adaptive fractional ME and DE skipping method in a partitioned inter prediction unit (PU) mode, based on a result of a 2 N × 2 N inter PU coding. Experimental results show that the proposed method efficiently reduces the encoding complexity with negligible coding loss, compared to conventional methods.     

Variable complexity motion compensated error concealment in video coding

Transmission of compressed video through a data network may involve loss of data owing to channel errors and/or congestion. To conceal the effect of such errors in perceived video quality, concealment schemes happen to be an important choice in terms of their pertinence to encoder-decoder models. This paper focuses on the scenario where error bursts do not extend to more than one frame of digital video. For this, there exist block-based and pixel-based concealment techniques and their applicability is often ruled by a trade-off between perceived video quality and computational complexity. The paper proposes a variable complexity concealment technique and compares the results with existing schemes qualitatively and quantitatively for a range of MPEG test sequences and macroblock loss rates.     

Scalable video compression via overcomplete motion compensated wavelet coding

Recently, there have been a flurry of works on overcomplete motion compensated wavelet coding (OMCWC). In this paper, we address the importance of phase and focus on the design of scalable video coding algorithms within the OMCWC framework. Specifically, our new contributions consist of the following three components: (1) efficient block motion estimation techniques in the wavelet domain including hierarchical and fractional-pel block matching, (2) extend overcomplete motion compensated prediction (MCP) into overcomplete motion compensated temporal filtering (MCTF) to achieve temporal scalability (3) context modeling strategies for embedded quantization and entropy coding of 3D wavelet coefficients. Experiment results are used to demonstrate that the class of overomplete MCP/MCTF coders are capable of achieving comparable performance to other competing interframe wavelet coders.     

Error resilience of multireference motion compensated prediction in video coding

Standard coded video is vulnerable to transmission errors when transmitted over unreliable channels. The authors propose using multireference motion compensated prediction (MCP) to provide resilience to transmission errors. Both the concealment error and propagation error can be reduced in multireference MCR. First, using the multiple motion vectors associated with each coded block, a concealment scheme of low complexity with small concealment error is proposed. Then the theoretical performance limit of propagation error and coding efficiency in multireference MCP is analysed. Through a numerical solution based on the theoretical performance limit, it is found that a multireference MCP scheme can achieve greater propagation error attenuation than the traditional single-reference MCP scheme. The numerical solution also demonstrates that the performance of the multireference MCP average scheme approaches the theoretical performance limit, with coding efficiency higher than the traditional single-reference MCP scheme. Finally, results of a simulation under the assumed packet loss environment typical of the Internet are given. Simulation results demonstrate that video coding with multireference MCP performs much better than the conventional H.263 coding scheme in a lossy environment.     

Adaptive directional lifting-based wavelet transform for image coding.

We present a novel 2-D wavelet transform scheme of adaptive directional lifting (ADL) in image coding. Instead of alternately applying horizontal and vertical lifting, as in present practice, ADL performs lifting-based prediction in local windows in the direction of high pixel correlation. Hence, it adapts far better to the image orientation features in local windows. The ADL transform is achieved by existing 1-D wavelets and is seamlessly integrated into the global wavelet transform. The predicting and updating signals of ADL can be derived even at the fractional pixel precision level to achieve high directional resolution, while still maintaining perfect reconstruction. To enhance the ADL performance, a rate-distortion optimized directional segmentation scheme is also proposed to form and code a hierarchical image partition adapting to local features. Experimental results show that the proposed ADL-based image coding technique outperforms JPEG 2000 in both PSNR and visual quality, with the improvement up to 2.0 dB on images with rich orientation features.     

Bottom-up motion compensated prediction in wavelet domain for spatially scalable video coding

A new in-band motion compensation algorithm for wavelet-based video coding is proposed: the bottom-up prediction algorithm (BUP). This algorithm overcomes the periodic shift-invariance of the discrete wavelet transform (DWT) and is formalised into prediction rules using filtering operations. The combination of all prediction rules of the BUP algorithm defines a new transform: the bottom-up overcomplete DWT or BUP ODWT, which is shift-invariant. The envisaged application for the BUP algorithm is spatially scalable wavelet video coding.     

Block motion compensated coding of interlaced sequences using adaptively deinterlaced fields

Video coding algorithms using block motion compensation were first developed for progressively scanned sequences and as such, are not entirely suitable for interlaced sequences In this paper we present a new approach for block-based coding of interlaced sequences. This proposed algorithm processes the interlaced sequence as a sequence of even and odd fields by using the last decoded field, adaptively deinterlaced, for the motion compensated prediction of the current field. The deinterlacing is performed at the decoder and no extra information has to be sent to guide the adaptation. The algorithm is a simple and efficient alternative to algorithms using the last two decoded fields for the motion compensated prediction of the current field. The new approach can easily incorporate the use of fast search algorithms and allows the use of true half-pixel accuracy in the estimates of the vertical component of the motion vectors. In HDTV sequences tested, this algorithm achieves superior performance due to this half-pixel accuracy.     

Adaptive cosine transform image coding with constant blockdistortion

An adaptive block discrete-cosine transform (DCT) coding scheme is implemented with the same average distortion designated for each block. This constant distortion designation not only has perceptual advantages, but also allows the rate to vary, adjusting to the changing spectral characteristics among the blocks. The successful execution of this scheme requires a different spectral estimate for each block. To keep overhead and computation within limits, a novel technique is introduced by which a two-dimensional block spectrum is characterized by a one-dimensional autoregressive model. Simulations with images of natural scenes and medical radiology provide reconstructions with nearly uniform block distortion and very high visual and measurable quality at low rates     

Adaptive block transform coding of speech based on LPC vectorquantization

The authors describe several adaptive block transform speech coding systems based on vector quantization of linear predictive coding (LPC) parameters. Specifically, the authors vector quantize the LPC parameters (LPCVQ) associated with each speech block and transmit the index of the code vector as overhead information. This code vector will determine the short-term spectrum of the block and, in turn, can be used for optimal bit allocation among the transform coefficients. In order to get a better estimate of the speech spectrum, the authors also consider the possibility of incorporating pitch information in the coder. In addition, entropy-coded zero-memory quantization of the transform coefficients is considered as an alternative to Lloyd-Max quantization. An adaptive BTC scheme based on LPCVQ and using entropy-coded quantizers is developed. Extensive simulations are used to evaluate the performance of this scheme     

Transform coding of stereo image residuals

Stereo image compression is of growing interest because of new display technologies and the needs of telepresence systems. Compared to monoscopic image compression, stereo image compression has received much less attention. A variety of algorithms have appeared in the literature that make use of the cross-view redundancy in the stereo pair. Many of these use the framework of disparity-compensated residual coding, but concentrate on the disparity compensation process rather than the post compensation coding process. This paper studies specialized coding methods for the residual image produced by disparity compensation. The algorithms make use of theoretically expected and experimentally observed characteristics of the disparity-compensated stereo residual to select transforms and quantization methods. Performance is evaluated on mean squared error (MSE) and a stereo-unique metric based on image registration. Exploiting the directional characteristics in a discrete cosine transform (DCT) framework provides its best performance below 0.75 b/pixel for 8-b gray-scale imagery and below 2 b/pixel for 24-b color imagery, In the wavelet algorithm, roughly a 50% reduction in bit rate is possible by encoding only the vertical channel, where much of the stereo information is contained. The proposed algorithms do not incur substantial computational burden beyond that needed for any disparity-compensated residual algorithm.     

Unconstrained motion compensated temporal filtering (UMCTF) for efficient and flexible interframe wavelet video coding

We introduce an efficient and flexible framework for temporal filtering in wavelet-based scalable video codecs called unconstrained motion compensated temporal filtering (UMCTF). UMCTF allows for the use of different filters and temporal decomposition structures through a set of controlling parameters that may be easily modified during the coding process, at different granularities and levels. The proposed framework enables the adaptation of the coding process to the video content, network and end-device characteristics, allows for enhanced scalability, content-adaptivity and reduced delay, while improving the coding efficiency as compared to state-of-the-art motion-compensated wavelet video coders. Additionally, a mechanism for the control of the distortion variation in video coding based on UMCTF employing only the predict step is proposed. The control mechanism is formulated by expressing the distortion in an arbitrary decoded frame, at any temporal level in the pyramid, as a function of the distortions in the reference frames at the same temporal level. All the different scenarios proposed in the paper are experimentally validated through a coding scheme that incorporates advanced features (such as rate-distortion optimized variable block-size multihypothesis prediction and overlapped block motion compensation). Experiments are carried out to determine the relative efficiency of different UMCTF instantiations, as well as to compare against the current state-of-the-art in video coding.     

Suboptimality of the Karhunen-Loeve transform for transform coding

We examine the performance of the Karhunen-Loeve transform (KLT) for transform coding applications. The KLT has long been viewed as the best available block transform for a system that orthogonally transforms a vector source, scalar quantizes the components of the transformed vector using optimal bit allocation, and then inverse transforms the vector. This paper treats fixed-rate and variable-rate transform codes of non-Gaussian sources. The fixed-rate approach uses an optimal fixed-rate scalar quantizer to describe the transform coefficients; the variable-rate approach uses a uniform scalar quantizer followed by an optimal entropy code, and each quantized component is encoded separately. Earlier work shows that for the variable-rate case there exist sources on which the KLT is not unique and the optimal quantization and coding stage matched to a "worst" KLT yields performance as much as 1.5 dB worse than the optimal quantization and coding stage matched to a "best" KLT. In this paper, we strengthen that result to show that in both the fixed-rate and the variable-rate coding frameworks there exist sources for which the performance penalty for using a "worst" KLT can be made arbitrarily large. Further, we demonstrate in both frameworks that there exist sources for which even a best KLT gives suboptimal performance. Finally, we show that even for vector sources where the KLT yields independent coefficients, the KLT can be suboptimal for fixed-rate coding.     

Adaptive motion vector post-processing for low cost rate-distortion optimisation [video coding applications]

A novel adaptive motion vector post-processing technique is proposed to obtain near true motion vectors in order to achieve a low cost rate-distortion optimisation for very low bit rate video coding applications. Compared with an H.263 baseline model, improvements in the peak signal-to-noise ratio of up to 0.21 dB are obtained.     

Vector-scalar classification for transform image coding

This paper introduces vector-scalar classification (VSC) for discrete cosine transform (DCT) coding of images. Two main characteristics of VSC differentiate it from previously proposed classification methods. First, pattern classification is effectively performed in the energy domain of the DCT subvectors using vector quantization. Second, the subvectors, instead of the DCT vectors, are mapped into a prescribed number of classes according to a pattern-to-class link established by scalar quantization. Simulation results demonstrate that the DCT coding systems based on VSC are superior to the other proposed DCT coding systems and are competitive compared to the best subband and wavelet coding systems reported in the literature.     

Adaptive spread transform QIM watermarking algorithm based on improved perceptual models

The quantization step is one of the most important factors which affect the performance of quantization watermarking used for image copyright protection. According to the characteristic of perceptual model and the specific attacks, improved perceptual model and different implementations of perceptual model are proposed. They are incorporated into the spread transform quantization index modulation (ST-QIM) framework. The experimental results show that the four algorithms we proposed in this paper can reduce the noise attacks and facilitate common digital image processing operations. Among these, adaptive ST-QIM based on further modified Watson model (ST-QIM-fMW-SS) and adaptive ST-QIM based on modified sensitivity model (ST-QIM-MS-SS) have better performance.