Integral imaging is a technology based on plenoptic photography that captures and samples the light-field of a scene through a micro-lens array. It provides views of the scene from several angles and therefore is foreseen as a key technology for future immersive video applications. However, integral images have a large resolution and a structure based on micro-images which is challenging to encode. A compression scheme for integral images based on view extraction has previously been proposed, with average BD-rate gains of 15.7% (up to 31.3%) reported over HEVC when using one single extracted view. As the eﬃciency of the scheme depends on a tradeoﬀ between the bitrate required to encode the view and the quality of the image reconstructed from the view, it is proposed to increase the number of extracted views. Several configurations are tested with diﬀerent positions and diﬀerent number of extracted views. Compression eﬃciency is increased with average BD-rate gains of 22.2% (up to 31.1%) reported over the HEVC anchor, with a realistic runtime increase.
The most recent video coding standard H.264 achieves excellent compression performances at many different
bit-rates. However, it has been noted that, at very high compression ratios, a large part of the available coding
resources is only used to code motion vectors. This can lead to a suboptimal coding performance. This paper
introduces a new coding mode for a H.264-based video coder, using quantized motion vector (QMV) to improve
the management of the resource allocation between motion information and transform coeffcients. Several
problems have to be faced with in order to get an efficient implementation of QMV techniques, yet encouraging
results are reported in preliminary tests, allowing to improve the performances of H.264 at low bit-rates over
The H.264/AVC1 standard of the Video Coding Experts Group (VCEG) and the Moving Pictures Experts Group
(MPEG), also known as MPEG-4 AVC, achieves significant compression gain compared to its predecessors. Not
only Inter yet also Intra coding has been greatly improved. Today VCEG encourages coding efficiency improvements
through the KTA (Key Technical Area) software,<sup>2</sup> a collection of tools that improves the H.264/AVC
standard, to prepare the next generation video codec. The work proposed in this paper has been designed in
An Intra coding scheme is proposed. A macroblock is split in 1D partitions to reduce the distance between
the pixel to encode and its predictors. Three scan orders for the partitions are available: a raster scan, a bidirectional
scan and a hierarchical scan. Predictors adapted to the shape and characteristics of the 1D partitions
are defined and finally a 1D-DCT is applied to the residual signal. Experimental results report an average bitrate
savings of 8.6% compared to the H.264/AVC standard (up to 19% on a particular sequence).
H.264/MPEG4-AVC is the latest video codec provided by the Joint Video Team, gathering ITU-T and ISO/IEC experts.
Technically there are no drastic changes compared to its predecessors H.263 and MPEG-4 part 2. It however
significantly reduces the bitrate and seems to be progressively adopted by the market. The gain mainly results from the
addition of efficient motion compensation tools, variable block sizes, multiple reference frames, 1/4-pel motion accuracy
and powerful Skip and Direct modes. A close study of the bits repartition in the bitstream reveals that motion
information can represent up to 40% of the total bitstream. As a consequence reduction of motion cost is a priority for
This paper proposes a competition-based scheme for the prediction of the motion. It impacts the selection of the motion
vectors, based on a modified rate-distortion criterion, for the Inter modes and for the Skip mode. Combined spatial and
temporal predictors take benefit of temporal redundancies, where the spatial median usually fails. An average 7% bitrate
saving compared to a standard H.264/MPEG4-AVC codec is reported. In addition, on the fly adaptation of the set of
predictors is proposed and preliminary results are provided.
In this paper, we present a novel H.264 video decoder where memory transfers and energy consumption are significantly reduced. A power-friendly solution is indeed required in mobile applications, where autonomy is a key feature. Whereas low-power design is usually regarded as a pure architectural and implementation problem, our solution is based on an algorithmic approach. We first observe that in modern hardware architectures, computational complexity plays a second role in terms of energy dissipation, which is dominated by memory transfers. We thus identify the motion compensation module as the most consuming part of the standard H.264 decoder, due to its numerous memory accesses to the reference frame(s). Through an algorithmic modification that uses concurrent embedded compression techniques and relies on the data structure of the memory, we reduce memory transfers, and hence power dissipation, while maintaining the visual quality. Experimental results prove that the new method is close to the reference H.264 baseline decoder both in terms of objective and subjective measurements. In the meantime, memory transfers have been reduced by 55% in average, implying power savings which lengthen the battery life of the mobile device, increase the reliability of the chip and lower production costs.
In this paper, a method for designing low-power video schemes is presented. Algorithms that imply a very low dissipation are required for new applications where the energy source is limited, e.g. mobile phones including a camera and video features. Whereas it can be observed that video standards are mainly designed around coding efficiency, we propose to take into account power consumption characteristics directly when designing the algorithm. More precisely, we give some guidelines for the design of low-power video codecs in the scope of modern hardware architectures and we introduce the notion of power scalability. We present an original encoder based on so-called 'Collocated Motion Estimation' designed using the proposed methodology. Experimental results show that we remain close to the coding efficiency of the reference H.264 baseline encoder while the power consumption is largely reduced in our solution. Moreoever this encoder is scalable in memory transfer and computational complexity.
This paper presents FaDA (Fast Deblocking Algorithm), a low complexity post-processing algorithm that improves the visual quality of MPEG-4 low bit rate videos displayed on mobile devices. Most of the algorithms proposed up to now to enhance the visual quality after the decoder are far too complex for this kind of devices, and unfortunately deblocking algorithms efficiency is tightly related to their complexity. FaDA achieves complexity reduction while maintaining quality thanks to two principles: 1- The artifact correction is driven by Human Visual System properties, 2- A particular attention has been paid on the design of the most consuming parts of the algorithm, following implementation guidelines. We present a complete complexity evaluation that considers not only computational charge, but also number and locality of memory accesses, data dependency, and internal data size requirements. Critical steps of the algorithm were implemented in C and optimized on a TriMedia DSP. The complexity evaluation reveals a reduction by a factor ranging between 2 and 3.5, compared to the reference MPEG-4 informative deblocking, depending on architecture and implementation. Extensive subjective tests performed on both mobile LCD screen and high resolution monitor show that FaDA average visual quality is equivalent to the reference algorithm.
In this paper, we propose an object-based variational approach for the decoding of MJPEG and MPEG1-2 video sequences. This new method improves the visual quality of the reconstructed sequence by reducing the impact of cell losses, due to the transmission of the sequences over lossy packet networks. Generally, two kinds of approaches are suggested to tackle this problem: a preventative 'network' approach tends to provide a more robust bit-stream in order to help the recovery of the lost data, for instance by adding redundancy to the bitstream, and a concealment 'image' approach, that tends to reduce visual impact resulting from the packet loss. The proposed method combines 'network' information provided by the transmission protocol, with an adapted 'image' decoding algorithm. Several experimental results demonstrate the efficiency of the decoding method: lost areas are largely recovered, compared to a standard decoding, both on the background and on the objects.
In this paper, we propose an object-based variational approach for the decoding of DV, M-JPEG, and MPEG1-2 video sequences. This new method improves the visual quality by considering simultaneously two kind of artifacts: artifacts due to compression, such as blocking effects and quantization noise, and other defects due to acquisition, transmission, or storage, such as dropouts and banding. Generally, methods improving the visual quality in video sequences consider these two kind of artifacts separately, and consist most of the time in post-processing techniques, applied to a single kind of artifact. The proposed method adopts a global approach for the decoding. It deals with the minimization of half-quadratic criteria, which allow the simultaneous estimation and restoration of backgrounds, on one side, and the moving objects detection on the other side. Each background and each object are processed separately, according to their spatial and temporal properties, to remove effectively blocking effects, quantization noise, and dropouts. Several experimental results are presented in this paper. They demonstrate the efficiency of the decoding method: blocking effects are largely removed and missing data are significantly reduced, compared to the standard decoding, resulting in a greater visual quality of the sequence.