Diogo C. Garcia

Super Resolution for Multiview Images Using Depth Information

Mixed resolution formats have been employed in video encoding complexity reduction as well as data compression of stereoscopic video. High resolution frames within such formats may also be used as a means of enhancing lower resolution images. In this paper we present a super-resolution method for use in a mixed resolution, multiview video plus depth setup. High resolution views are initially projected onto the view point of low resolution images with the aid of available depth maps. The method introduces the use of transform-domain techniques for up-sampling the low resolution images and for appending high frequency content from projected views. The DCT is used for the necessary frequency decompositions. Results show gains over previous work for several test sequences and affirm the aptitude of transform-domain approaches for super-resolution within mixed resolution formats.

Super-resolution for multiview images using depth information

In stereoscopic and multiview video, binocular suppression theory states that the visual subjective quality of 3-D experience is not much affected by asymmetrical blurring of the individual views. Based on these studies, mixed-resolution frameworks applied for multiview systems offer great data-size reduction without incurring in significant quality degradation in 3-D video applications. However, it is interesting to recover high-frequency content of the blurred views, to reduce visual strain due to long-term exposure and to make the system suitable for free-viewpoint television. In this paper, we present a novel super-resolution technique, in which low-resolution views are enhanced with the aid of high-frequency content from neighboring full-resolution views, and the corresponding depth information for all views. Occlusions are handled by checking the consistency between views. Tests for synthetic and real image data in stereo and multiview cases are presented, and results show that significant objective quality gains can be achieved without any extra side information.

Face-Spoofing 2D-Detection Based on Moiré-Pattern Analysis

Biometric systems based on face recognition have been shown unreliable under the presence of face-spoofing images. Hence, automatic solutions for spoofing detection became necessary. In this paper, face-spoofing detection is proposed by searching for Moiré patterns due to the overlap of the digital grids. The conditions under which these patterns arise are first described, and their detection is proposed which is based on peak detection in the frequency domain. Experimental results for the algorithm are presented for an image database of facial shots under several conditions.

Least-Squares Directional Intra Prediction in H.264/AVC

A new intra-prediction mode for the H.264/AVC standard is proposed. Each pixel within a block is predicted by a weighted sum of its neighbours, according to an Nth order Markov linear model. The weights are obtained through a least-squares estimate from reconstructed data in the neighbouring blocks, so that no overhead is necessary to convey the weights to the decoder. Results show significant improvements in H.264/AVC compression for images that are rich in directional structures, and moderate improvements for the other images and sequences tested.

Analysis of the complex voltage unbalance factor behavior resulting from the variation of voltage magnitudes and angles

This paper presents the main aspects observed in analyzing Complex Voltage Unbalance Factor (CVUF) behavior resulting from the variation of voltage magnitudes and angles. The goal is to identify possible incoherencies regarding the use of the CVUF, and also to investigate whether this factor is more sensitive to variations in magnitude or angles under various voltage unbalance conditions. This study also evaluates the efficiency of the use of the CVUF angle and its association with positive component magnitudes. The results indicate that the CVUF should not be used as a single and sufficient parameter for the quantification of voltage unbalances, which highlights the need to develop a new indicator which may establish a more clear and simple association between this disturbance and its effects on electrical equipment.

Study of voltage unbalance conditions based on the behavior of the complex voltage unbalance factor (CVUF)

In this paper, an analysis of the complex voltage unbalance factor (CVUF) in three-phase lines is offered, in order to orientate future experiments in the study of the effects of voltage unbalance. The geometrical loci for constant magnitudes of the CVUF are presented, considering that the angles of the voltages are constant, and considering that the magnitudes of the voltages are constant. Furthermore, a correlation coefficient study is made between the CVUF and the negative- and positive-sequence voltage components (V2 and V1, respectively). The intention here is to determine the influence of the voltage components sequences on the magnitude and angle of the CVUF. Based on the studies described above, a series of unbalanced voltage conditions is suggested, serving as orientation for future laboratory experiments, which could lead to a better understanding of the relation between the voltage unbalance condition and its effects.

Example-based Enhancement of Degraded Video

We present an example-based approach to general enhancement of degraded video frames. The method relies on building a dictionary with non-degraded parts of the video and to use such a dictionary to enhance the degraded parts. The image degradation has to originate from a “repeatable” process, so that the dictionary image patches (blocks) are equally degraded, thus originating a dictionary with degraded blocks and their residues (differences in between degraded and original blocks). Once a match is found between a degraded block in the video and a degraded block in the dictionary, the associated residue of the latter is soft-added to the block of the former. The method is a generalization of the method for example-based super-resolution. Results are presented to demonstrate the applicability of the method to many scenarios.

Depth-map super-resolution for asymmetric stereo images

We propose a mixed-resolution coding architecture for stereo color-plus-depth images, where encoding is performed at a low resolution, except for one of the color images. Super-resolution methods are proposed for the depth maps and for the low-resolution color image at the decoder side. Experiments are carried out for several real and synthetic images and reveal a reduction in complexity at the encoder associated with average PSNR gains of the super-resolved low-resolution color image with respect to regular interpolation.

Video compression complexity reduction with adaptive down-sampling

Encoding video sequences is a computation-demanding task in high-performance codecs. Optimizing this stage may result in a substantial encoding speed-up. In this paper, we propose a faster approach to encode sequences with the H.264/AVC codec, using mixed-resolution. By having some of the frames down-sampled, the overall computation is reduced, without greatly affecting the rate-distortion performance, which remains evaluated using the sequences original resolution. In addition to this approach, a method which regards only the most frequent prediction modes of a frame is incorporated, so that the combined complexity reduction can be significant with negligible performance losses.

Transform domain semi-super resolution

This paper presents a transform-based approach to semi-super resolution. The idea of semi-super resolution is to enhance low-resolution frames from a video sequence encoded with different resolutions among frames. The proposed framework uses a DCT-based down-sampling method at the encoder process. At the decoder, DCT-based up-sampling plus high-frequency information from adjacent frames in full resolution are used to enhance interpolated low-resolution frames. The results show an increase of the overall quality without using any extra information from the encoder. The proposed technique can also outperfom previous semi-super resolution methods operating in pixel domain.