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  • 1.
    Karlsson, Linda
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Olsson, Roger
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Sjöström, Mårten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Temporal filter with bilinear interpolation for ROI video coding2006Report (Other academic)
    Abstract [en]

    In videoconferencing and video over the mobile phone, themain visual information is found within limited regions ofthe video. This enables improved perceived quality byregion-of-interest coding. In this paper we introduce atemporal preprocessing filter that reuses values of theprevious frame, by which changes in the background areonly allowed for every second frame. This reduces the bitrateby 10-25% or gives an increase in average PSNR of0.29-0.98 dB. Further processing of the video sequence isnecessary for an improved re-allocation of the resources.Motion of the ROI causes absence of necessary backgrounddata at the ROI border. We conceal this by using a bilinearinterpolation between the current and previous frame at thetransition from background to ROI. This results in animprovement in average PSNR of 0.44 – 1.05 dB in thetransition area with a minor decrease in average PSNRwithin the ROI.

  • 2.
    Karlsson, Linda S.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Spatio-Temporal Pre-Processing Methods for Region-of-Interest Video Coding2007Licentiate thesis, monograph (Other academic)
    Abstract [en]

    In video transmission at low bit rates the challenge is to compress the video with a minimal reduction of the percieved quality. The compression can be adapted to knowledge of which regions in the video sequence are of most interest to the viewer. Region of interest (ROI) video coding uses this information to control the allocation of bits to the background and the ROI. The aim is to increase the quality in the ROI at the expense of the quality in the background. In order for this to occur the typical content of an ROI for a particular application is firstly determined and the actual detection is performed based on this information. The allocation of bits can then be controlled based on the result of the detection.

    In this licenciate thesis existing methods to control bit allocation in ROI video coding are investigated. In particular pre-processing methods that are applied independently of the codec or standard. This makes it possible to apply the method directly to the video sequence without modifications to the codec. Three filters are proposed in this thesis based on previous approaches. The spatial filter that only modifies the background within a single frame and the temporal filter that uses information from the previous frame. These two filters are also combined into a spatio-temporal filter. The abilities of these filters to reduce the number of bits necessary to encode the background and to successfully re-allocate these to the ROI are investigated. In addition the computational compexities of the algorithms are analysed.

    The theoretical analysis is verified by quantitative tests. These include measuring the quality using both the PSNR of the ROI and the border of the background, as well as subjective tests with human test subjects and an analysis of motion vector statistics.

    The qualitative analysis shows that the spatio-temporal filter has a better coding efficiency than the other filters and it successfully re-allocates the bits from the foreground to the background. The spatio-temporal filter gives an improvement in average PSNR in the ROI of more than 1.32 dB or a reduction in bitrate of 31 % compared to the encoding of the original sequence. This result is similar to or slightly better than the spatial filter. However, the spatio-temporal filter has a better performance, since its computational complexity is lower than that of the spatial filter.

  • 3.
    Karlsson, Linda
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Sjöström, Mårten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    A preprocessing approach to ROI Video Coding using Variable Gaussian Filters and Variance in Intensity2005In: Proceedings Elmar - International Symposium Electronics in Marine, Zagreb, Croatia: IEEE conference proceedings, 2005, p. 65-68, article id 1505643Conference paper (Refereed)
    Abstract [en]

    In applications involving video over mobile phones or Internet, the limited quality depending on the transmission rate can be further improved by region-of-interest (ROI) coding. In this paper we present a preprocessing method using variable Gaussian filters controlled by a quality map indicating the distance to the ROI border that seeks to smooth the border effects between ROI and non-ROI. According to subjective tests the reduction of border effects increases the percieved quality, compared to using only one low pass filter. It also introduces a small improvement of the PSNR of the intensity component within the ROI after compression. With the compressed original sequence as a reference, the average PSNR was increased by 1.25 dB and 2.3 dB for 100 kbit/s and 150 kbit/s, respectively. Furthermore, in order to reduce computational complexity, a modified quality map is introduced using variance in intensity to exclude pixels, which are not visibly affected by the Gaussian filters. No change in quality is noticed when using less than 76% of the pixels.

  • 4.
    Karlsson, Linda
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Sjöström, Mårten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Improved ROI Video Coding using Variable Gaussian Pre-Filters and Variance in Intensity2005In: IEEE International Conference on Image Processing 2005, ICIP 2005: Vol. 2, 2005, p. 1817-1820, article id 1530054Conference paper (Refereed)
    Abstract [en]

    In applications involving video over mobile phones or Internet, the limited quality depending on the transmission rate can be further improved by region-of-interest (ROI) coding. In this paper we present a preprocessing method using variable Gaussian filters controlled by a quality map indicating the distance to the ROI border. The border effects are reduced introducing a small improvement of the PSNR of the intensity component within the ROI after compression, compared to using only one low pass filter. With the compressed original sequence as a reference, the average PSNR was increased by 1.25 dB and 2.3 dB for 100 kbit/s and 150 kbit/s, respectively. A modified quality map is introduced using variance to exclude pixels, which are not visibly affected by the Gaussian filters, reducing computational complexity. Using less than 76% of the pixels gives no noticeable change in quality.

  • 5.
    Karlsson, Linda
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Sjöström, Mårten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Multiview plus depth scalable coding in the depth domain2009In: 3DTV-CON 2009 - 3rd 3DTV-Conference: The True Vision - Capture, Transmission and Display of 3D Video, Proceedings, IEEE conference proceedings, 2009, p. 5069631-Conference paper (Refereed)
    Abstract [en]

    Three dimensional (3D) TV is a growing area that provides an extra dimension at the cost of spatial resolution. The multi-view plus depth representation provides a lower bit rate when it is encoded than multi-view and higher resolution than a 2D-plus-depth sequence. Scalable video coding provides adaption to the conditions at the receiver. In this paper we propose a scheme that combines scalability in both the view and depth domain. The center view data is preserved, whereas the data of the side views are extracted in layers depending on distance to the camera. This allows a decrease in bit rate of 16-39 % for the colour part of a 3-view MV depending number of pixels in the first enhancement layer if one layer is extracted. Each additional layer increases the visual quality and PSNR compared only using center view data.

  • 6.
    Karlsson, Linda
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Sjöström, Mårten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Region-of-interest 3D video coding based on depth images2008In: 2008 3DTV Conference - True Vision - Capture, Transmission and Display of 3D Video, IEEE conference proceedings, 2008, p. 121-124Conference paper (Refereed)
    Abstract [en]

    Three dimensional (3D) TV is becoming a mature technology due to the progress within areas such as display and network technology among others. However, 3D video demands a higher bandwidth in order to transmit the information needed to render or directly display several different views at the receiver. The 2D plus depth representation requires less bit rate than most 3D video representations, although the necessary views have to be rendered at the receiver. In this paper we propose to combine the 2D plus depth representation with region-of-interest (ROI) video coding to ensure a higher quality at parts of the sequence that are of interest to the viewer. These include objects close to the viewer as well as faces. This allows either the bit rate to be reduced by 12-28 % or the quality within the ROI to be increased by 0.57 - 1.5 dB, when a fixed bit rate is applied.

  • 7.
    Karlsson, Linda
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Sjöström, Mårten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Olsson, Roger
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Spatio-Temporal Filter for ROI Video Coding2006In: Proceedings of the 14th European Signal Processing Conference (EUSIPCO 2006) Florence, Italy 4-8.Sept. 2006, 2006Conference paper (Other academic)
    Abstract [en]

    Reallocating resources within a video sequence to the regions-of-interest increases the perceived quality at limited bandwidths. In this paper we combine a spatial filter with a temporal filter, which are both codec and standard independent. This spatio-temporal filter removes resources from both the motion vectors and the prediction error with a computational complexity lower than the spatial filter by itself. This decreases the bit rate by 30-50% compared to coding the original sequence using H.264. The released bits can be used by the codec to increase the PSNR of the ROI by 1.58 - 4.61 dB, which is larger than for the spatial and temporal filters by themselves.

  • 8.
    Karlsson, Linda Sofia
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Coding for Improved Perceived Quality of 2D and 3D Video over Heterogeneous Networks2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The rapid development of video applications for TV, the internet and mobile phones is being taken one step further in 2010 with the introduction of stereo 3D TV. The 3D experience can be further improved using multiple views in the visualization. The transmission of 2D and 3D video at a sufficiently perceived quality is a challenge considering the diversity in content, the resources of the network and the end-users.Two problems are addressed in this thesis. Firstly, how to improve the perceived quality for an application with a limited bit rate. Secondly, how to ensure the best perceived quality for all end-users in a heterogeneous network.

    A solution to the first problem is region-of-interest (ROI) video coding, which adapts the coding to provide a better quality in regions of interest to the viewer. A spatio-temporal filter is proposed to provide codec and standard independent ROI video coding. The filter reduces the number of bits necessary to encode the background and successfully re-allocate these bits to the ROI. The temporal part of the filter reduces the complexity compared to only using a spatial filter. Adaption to the requirements of the transmission channel is possible by controlling the standard deviation of the filter. The filter has also been successfully applied to 3D video in the form of 2D-plus-depth, where the depth data was used in the detection of the ROI.

    The second problem can be solved by providing a video sequence that has the best overall quality. Hence, the best quality for each part of the network and for each 2D and 3D visualization system over time. Scalable video coding enables the extraction of the parts of the data to adapt to the requirements of the network and the end-user. A scheme is proposed in this thesis that provides scalability in the depth and view domain of multi-view plus depth video. The data are divided into enhancement layers depending on the content’s distance to the camera. Schemes to divide the data into layers within a view and between adjacent views have been analyzed. The quality evaluation indicates that the position of the layers in depth as well as the number of layers should be determined by analyzing the depth distribution. The front-most layers in adjacent views should be given priority over the others unless the application requires a high quality of the center views.

  • 9.
    Karlsson, Linda Sofia
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Sjöström, Mårten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    A Spatio-Temporal Filter for Region-of-Interest Video CodingManuscript (preprint) (Other academic)
    Abstract [en]

    Region of interest (ROI) video coding increases the quality in regions interesting to the viewer at the expense of quality in the background. This enables a high perceived quality at low bit rates. A successfully detected ROI can be used to control the bit-allocation in the encoding. In this paper we present a filter that is independent of codec and standard. It is applied in both the spatial and the temporal domains. The filter’s ability to reduce the number of bits necessary to encode the background is analyzed theoretically and where these bits are re-allocated. The computational complexity of the algorithms is also determined. The quality is evaluated using PSNR of the ROI and subjective tests. Test showed that the spatio-temporal filter has a better coding efficiency than using only spatial or only temporal filtering. The filter successfully re-allocates the bits from the background to the foreground.

  • 10.
    Karlsson, Linda Sofia
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Sjöström, Mårten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Layer assignment based on depth data distribution for multiview-plus-depth scalable video coding2011In: IEEE transactions on circuits and systems for video technology (Print), ISSN 1051-8215, E-ISSN 1558-2205, Vol. 21, no 6, p. 742-754Article in journal (Refereed)
    Abstract [en]

    Three dimensional (3D) video is experiencing a rapid growth in a number of areas including 3D cinema, 3DTV and mobile phones. Several problems must to be addressed to display captured 3D video at another location. One problem is how torepresent the data. The multiview plus depth representation of a scene requires a lower bit rate than transmitting all views required by an application and provides more information than a 2D-plus-depth sequence. Another problem is how to handle transmission in a heterogeneous network. Scalable video coding enables adaption of a 3D video sequence to the conditions at the receiver. In this paper we present a scheme that combines scalability based on the position in depth of the data and the distance to the center view. The general scheme preserves the center view data, whereas the data of the remaining views are extracted in enhancement layers depending on distance to the viewer and the center camera. The data is assigned into enhancement layers within a view based on depth data distribution. Strategies concerning the layer assignment between adjacent views are proposed. In general each extracted enhancement layer increases the visual quality and PSNR compared to only using center view data. The bit-rate per layer can be further decreased if depth data is distributed over the enhancement layers. The choice of strategy to assign layers between adjacent views depends on whether quality of the fore-most objects in the scene or the quality of the views close to the center is important.

  • 11.
    Sjöström, Mårten
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Härdling, Peter
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Karlsson, Linda S.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Olsson, Roger
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Improved Depth-Image-Based Rendering Algorithm2011In: 3DTV Conference: The True Vision - Capture, Transmission and Display of 3D Video, 3DTV-CON 2011 - Proceedings, IEEE conference proceedings, 2011, p. Art. no. 5877183-Conference paper (Refereed)
    Abstract [en]

    The present work analyses a layered depth-image-based-rendering algorithm based on possible errors occurring with perspective 3D warping. The outcome is improvements to the algorithm that treats depth reliably for scenes containing several levels of foreground objects. The filling of holes of different kinds is addressed so that results have better visual quality. The analysis compares the results of the algorithm with a reference algorithm for the potential error types, and visual examples exhibit the consequences of the improvements. Different objective metrics give ambiguous results, which may be explained by the reduction of structure caused by the reference algorithm.

  • 12.
    Sjöström, Mårten
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Karlsson, Linda
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Performance of scalable coding in depth domain2010In: Proceedings of the SPIE, Vol 7524 : Conference on Stereoscopic Displays and Applications XXI, San Jose, CA, JAN 18-20, 2010. (Proceedings of SPIE-IS&T Electronic Imaging) / [ed] Andrew J. Woods, Nicolas S. Holliman, Neil A. Dodgson, SPIE - International Society for Optical Engineering, 2010, p. 75240A-Conference paper (Refereed)
    Abstract [en]

    Common autostereoscopic 3D displays are based on multi-view projection. The diversity of resolutions and number of views of such displays implies a necessary flexibility of 3D content formats in order to make broadcasting efficient. Furthermore, distribution of content over a heterogeneous network should adapt to an available network capacity. Present scalable video coding provides the ability to adapt to network conditions; it allows for quality, temporal and spatial scaling of 2D video. Scalability for 3D data extends this list to the depth and the view domains. We have introduced scalability with respect to depth information. It allows for an increased number of quality steps; the cost is a slight increase of required capacity for the whole sequence. Our proposed scheme is based on the multi-view-plus-depth format where the center view data are preserved, and side views are extracted in layers depending on depth values. We investigate the performance of various layer assignment strategies: number of layers, and distribution of layers in depth, either based on equal number of pixels or histogram characteristics. We further consider the consequences to variable distortion due to encoder parameters. The results are evaluated considering their bit rate verses distortion as well as visual quality appearance.

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