Perceptually-aware bilateral filtering for quality improvement in low bit rate video coding

Proceedings of: Picture Coding Symposium (PCS 2012). Krakow, Poland, May 7-9, 2012Perceptual coding has become of great interest in modern video coding due to the need for higher compression rates. Many previous works have been carried out to incorporate perceptual information to hybrid video encoders, either modifying the quantization parameter according to a certain perceptual resource allocation map or preprocessing video sequences for removing information that is not perceptually relevant. The first strategy is limited by the presence of blocking artifacts and the second one lacks of adaptation to video content. In this paper, a novel and simple approach is proposed, which performs a smart filtering prior to the encoding process preserving both the structural and motion information. The experiments prove that the use of proposed method implemented on an H.264 encoder significantly improves its perceptual quality for low bit rates.Publicad

The AV1 Constrained Directional Enhancement Filter (CDEF)

This paper presents the constrained directional enhancement filter designed for the AV1 royalty-free video codec. The in-loop filter is based on a non-linear low-pass filter and is designed for vectorization efficiency. It takes into account the direction of edges and patterns being filtered. The filter works by identifying the direction of each block and then adaptively filtering with a high degree of control over the filter strength along the direction and across it. The proposed enhancement filter is shown to improve the quality of the Alliance for Open Media (AOM) AV1 and Thor video codecs in particular in low complexity configurations.Comment: 5 page

Investigation of the effectiveness of video quality metrics in video pre-processing.

This paper presents an investigation of the effectiveness of current video quality measurement metrics in measuring variations in perceptual video quality of pre-processed video. The results show that full-reference video quality metrics are not effective in detecting variations in perceptual video quality. However, no reference metrics show better performance when compared to full reference metrics, particularly, Naturalness Image Quality Evaluator (NIQE) is notably better at detecting perceptual quality variations

HDR Image Watermarking

In this Chapter we survey available solutions for HDR image watermarking. First, we briefly discuss watermarking in general terms, with particular emphasis on its requirements that primarily include security, robustness, imperceptibility, capacity and the availability of the original image during recovery. However, with respect to traditional image watermarking, HDR images possess a unique set of features such as an extended range of luminance values to work with and tone-mapping operators against whom it is essential to be robust. These clearly affect the HDR watermarking algorithms proposed in the literature, which we extensively review next, including a thorough analysis of the reported experimental results. As a working example, we also describe the HDR watermarking system that we recently proposed and that focuses on combining imperceptibility, security and robustness to TM operators at the expense of capacity. We conclude the chapter with a critical analysis of the current state and future directions of the watermarking applications in the HDR domain

Contributions to reconfigurable video coding and low bit rate video coding

In this PhD Thesis, two different issues on video coding are stated and their corresponding proposed solutions discussed. In the first place, some problems of the use of video coding standards are identi ed and the potential of new reconfigurable platforms is put to the test. Specifically, the proposal from MPEG for a Reconfigurable Video Coding (RVC) standard is compared with a more ambitious proposal for Fully Configurable Video Coding (FCVC). In both cases, the objective is to nd a way for the definition of new video codecs without the concurrence of a classical standardization process, in order to reduce the time-to-market of new ideas while maintaining the proper interoperability between codecs. The main difference between these approaches is the ability of FCVC to reconfigure each program line in the encoder and decoder definition, while RVC only enables to conform the codec description from a database of standardized functional units. The proof of concept carried out in the FCVC prototype enabled to propose the incorporation of some of the FCVC capabilities in future versions of the RVC standard. The second part of the Thesis deals with the design and implementation of a filtering algorithm in a hybrid video encoder in order to simplify the high frequencies present in the prediction residue, which are the most expensive for the encoder in terms of output bit rate. By means of this filtering, the quantization scale employed by the video encoder in low bit rate is kept in reasonable values and the risk of appearance of encoding artifacts is reduced. The proposed algorithm includes a block for filter control that determines the proper amount of filtering from the encoder operating point and the characteristics of the sequence to be processed. This filter control is tuned according to perceptual considerations related with overall subjective quality assessment. Finally, the complete algorithm was tested by means of a standard subjective video quality assessment test, and the results showed a noticeable improvement in the quality score with respect to the non-filtered version, confirming that the proposed method reduces the presence of harmful low bit rate artifacts

Inverse tone mapping

The introduction of High Dynamic Range Imaging in computer graphics has produced a novelty in Imaging that can be compared to the introduction of colour photography or even more. Light can now be captured, stored, processed, and finally visualised without losing information. Moreover, new applications that can exploit physical values of the light have been introduced such as re-lighting of synthetic/real objects, or enhanced visualisation of scenes. However, these new processing and visualisation techniques cannot be applied to movies and pictures that have been produced by photography and cinematography in more than one hundred years. This thesis introduces a general framework for expanding legacy content into High Dynamic Range content. The expansion is achieved avoiding artefacts, producing images suitable for visualisation and re-lighting of synthetic/real objects. Moreover, it is presented a methodology based on psychophysical experiments and computational metrics to measure performances of expansion algorithms. Finally, a compression scheme, inspired by the framework, for High Dynamic Range Textures, is proposed and evaluated