On the perceptual similarity of realistic looking tone mapped High Dynamic Range images

International audienceHigh Dynamic Range (HDR) images are usually displayed on conventional Low Dynamic Range (LDR) displays because of the limited availability of HDR displays. For the conversion of the large dynamic luminance range into the eight bit quantized values, parameterized Tone Mapping Operators (TMO) are applied. Human observers are able to optimize the parameters in order to get the highest Quality of Experience by judging the displayed LDR images on a realism scale. In the study presented in this paper, two TMOs with three parameters each were evaluated by observers in a subjective experiment. Although the chosen parameter settings vary largely, the chosen images appear to have the same QoE for the observers. In order to assess this similarity objectively, three commonly used image quality measurement algorithms were applied. Their agreement with the preference of the observers was analyzed and it was found that the Visual Difference Predictor (VDP) outperforms the Structural Similarity Index and the Root Mean Square Error. A threshold value for VDP is derived that indicates when two LDR images appear to have the same Quality of Experience

Comparing temporal behavior of fast objective video quality measures on a large-scale database

In many application scenarios, video quality assessment is required to be fast and reasonably accurate. The characterisation of objective algorithms by subjective assessment is well established but limited due to the small number of test samples. Verification using large-scale objectively annotated databases provides a complementary solution. In this contribution, three simple but fast measures are compared regarding their agreement on a large-scale database. In contrast to subjective experiments, not only sequence-wise but also framewise agreement can be analyzed. Insight is gained into the behavior of the measures with respect to 5952 different coding configurations of High Efficiency Video Coding (HEVC). Consistency within a video sequence is analyzed as well as across video sequences. The results show that the occurrence of discrepancies depends mostly on the configured coding structure and the source content. The detailed observations stimulate questions on the combined usage of several video quality measures for encoder optimization

Freely Available Large-scale Video Quality Assessment Database in Full-HD Resolution with H.264 Coding

International audienceVideo databases often focus on a particular use case with a limited set of sequences. In this paper, a different type of database creation is proposed: an exhaustive number of test conditions will be continuously created and made freely available for objective and subjective evaluation. At the moment, the database comprises more than ten thousand JM/x264-encoded video sequences. An extensive study of the possible encoding parameter space led to a first subset selection of 1296 configura- tions. At the moment, only ten source sequences have been used, but extension to more than one hundred sequences is planned. Some Full-Reference (FR) and No-Reference (NR) metrics were selected and calculated. The resulting data will be freely available to the research community and possible exploitation areas are suggested

Open collaboration on hybrid video quality models - VQEG joint effort group hybrid

International audienceSeveral factors limit the advances on automatizing video quality measurement. Modelling the human visual system requires multi- and interdisciplinary efforts. A joint effort may bridge the large gap between the knowledge required in conducting a psychophysical experiment on isolated visual stimuli to engineering a universal model for video quality estimation under real-time constraints. The verification and validation requires input reaching from professional content production to innovative machine learning algorithms. Our paper aims at highlighting the complex interactions and the multitude of open questions as well as industrial requirements that led to the creation of the Joint Effort Group in the Video Quality Experts Group. The paper will zoom in on the first activity, the creation of a hybrid video quality model

Boosting Paired Comparison methodology in measuring visual discomfort of 3DTV: performances of three di erent designs

International audienceThe pair comparison method is often recommended in subjective experiments because of the reliability of the obtained results. However, a drawback of this method is that the number of comparisons increases exponentially with the number of stimuli, which limits its usability for a large number of stimuli. Several design methods that aim to reduce the number of comparisons were proposed in the literature. However, their performances in the context of 3DTV should be evaluated carefully due to the fact that the results obtained from a paired comparison experiment in 3DTV may be in uenced by two important factors. One is the observation error from observer's attentiveness, in particular inverting the vote. The second factor concerns the dependence on the context in which the evaluation takes place. In this study, three design methods, namely Full Paired Comparison method (FPC), Square Design method (SD) and the Adaptive Square Design method (ASD) were evaluated by subjective visual discomfort experiment in 3DTV. The results from the FPC method were considered as the ground truth. Comparing with the ground truth, the ASD method provided the most accurate results with a given number of trials. It also showed the highest robustness against observation errors and interdependence of comparisons. Due to the e ciency of the ASD method, paired comparison experiments become feasible with a reasonably large number of stimuli for measuring 3DTV visual discomfort

Training the DNN of a Single Observer by Conducting Individualized Subjective Experiments

Predicting the quality perception of an individual subject instead of the mean opinion score is a new and very promising research direction. Deep Neural Networks (DNNs) are suitable for such prediction but the training process is particularly data demanding due to the noisy nature of individual opinion scores. We propose a human-in-the-loop training process using multiple cycles of a human voting, DNN training, and inference procedure. Thus, opinion scores on individualized sets of images were progressively collected from each observer to refine the performance of their DNN. The results of computational experiments demonstrate the effectiveness of our approach. For future research and benchmarking, five DNNs trained to mimic five observers are released together with a dataset containing the 1500 opinion scores progressively gathered from each of these observers during our training cycles

Spatio-temporal error concealment technique for high order multiple description coding schemes including subjective assessment

International audienceError resilience (ER) is an important tool in video coding to maximize the quality of Experience (QoE). The prediction process in video coding became complex which yields an unsatisfying video quality when NALunit packets are lost in error-prone channels. There are different ER techniques and multiple description coding (MDC) is one of the promising technique for this problem. MDC is categorized into different types and, in this paper, we focus on temporal MDC techniques. In this paper, a new temporal MDC scheme is proposed. In the encoding process, the encoded descriptions contain primary frames and secondary frames (redundant representations). The secondary frames represent the MVs that are predicted from previous primary frames such that the residual signal is set to zero and is not part of the rate distortion optimization. In the decoding process of the lost frames, a weighted average error concealment (EC) strategy is proposed to conceal these frames. The proposed scheme is subjectively evaluated along with other schemes and the results show that the proposed scheme is significantly different from most of other temporal MDC schemes

Standardized toolchain and model development for video quality assessment: the mission of the joint effort group in VQEG

International audienceSince 1997, the Video Quality Experts Group (VQEG) has been active in the field of subjective and objective video quality assessment. The group has validated competitive quality metrics throughout several projects. Each of these projects requires mandatory actions such as creating a testplan and obtaining databases consisting of degraded video sequences with corresponding subjective quality ratings. Recently, VQEG started a new open initiative, the Joint Effort Group (JEG), for encouraging joint collaboration on all mandatory actions needed to validate video quality metrics. Within the JEG, effort is made to advance the field of both subjective and objective video quality measurement by providing proper software tools and subjective databases to the community. One of the subprojects of the JEG is the joint development of a hybrid H.264/AVC objective quality metric. In this paper, we introduce the JEG and provide an overview of the different ongoing activities within this newly started group

Subjective Quality Evaluation of H.264 High-Definition Video Coding versus Spatial Up-Scaling and Interlacing

International audienceThe upcoming High-De nition format for video display provides high-quality content, especially when displayed on adapted devices. When combined with video coding techniques such as MPEG-4 AVC/H.264, the transmission of High-De nition video content on broadcast networks becomes possible. Nonetheless, transmitting and decoding such video content is a real challenge. Therefore, intermediate formats based on lower frame resolutions or interlaced coding are still provided to address targets with limited resources. Using these formats, the nal video quality depends on the postprocessing tools employed at the receiver to upsample and de-interlace these streams. In this paper, we compare the full-HD format to three possible scenarios to generate a full-HD stream from intermediate formats. We present the results of subjective tests that compare the visual quality of each scenario when using the same bitrate. The results show that using the same bitrate, the videos generated from lower-resolution formats reach similar quality compared to the full-HD videos

Video Quality Assessment: From 2D to 3D - Challenges and Future Trends

International audienceThree-dimensional (3D) video is gaining a strong momentum both in the cinema and broadcasting industries as it is seen as a technology that will extensively enhance the user's visual experience. One of the major concerns for the wide adoption of such technology is the ability to provide sufficient visual quality, especially if 3D video is to be transmitted over a limited bandwidth for home viewing (i.e. 3DTV). Means to measure perceptual video quality in an accurate and practical way is therefore of highest importance for content providers, service providers, and display manufacturers. This paper discusses recent advances in video quality assessment and the challenges foreseen for 3D video. Both subjective and objective aspects are examined. An outline of ongoing efforts in standards-related bodies is also provided