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After coding of screen content, it can be observed that repeated index map patterns exists in different CU blocks of the picture. While the present coding technique of palette indices exploits the local redundancy of pixels in the same block, there is a potential need for reducing the redundancy of non-local contents in the screen picture. This problem can be approached by introducing a new predictively coding mode, along with INDEX and COPY_ABOVE modes, to address the non-local repeated patterns. The solution to this problem is stated as follows.
When a CU is being coded in a palette mode, an additional predictive coding mode COPY_PATTERN is introduced. If a sample is chosen to code in COPY_PATTERN mode, it will copy the value in the prediction block directly. Like INDEX and COPY_ABOVE mode, a run value is specified corresponding to the number of samples to be copied in COPY_PATTERN mode. The motion information of the reference block is signalled in the same way as the inter mode with size 2Nx2N and reference block can be generated by motion compensation. The motion information is obtained during inter mode decision and no additional motion estimation burden is required [72]. The illustration of the new coding mode is shown in Figure 4.5.
Figure 4.5. Illustration of COPY_PATTERN mode.
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The results of using the new predictive coding mode COPY_PATTERN is shown in the next chapter and analysis is conducted with respect to the existing coding modes.
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Chapter 5
RESULTS AND ANALYSIS 5.1 Test Conditions 5.2 Measuring Quality PSNR 5.3 BD PSNR 5.4 BD Bitrate 5.5 Rate Distortion Plot 5.6 Summary
Chapter 6
CONCLUSIONS AND FUTURE WORK 6.1 Conclusions
In this thesis a detailed study of Screen Content coding technique “Palette Mode” is conducted. A new coding technique for coding palette index map, COPY_PATTERN, is implemented on HM reference software HM16.4 for Screen Content Coding SCM 4.0. The present coding modes for palette index map deals with local correlation of the pixels and reduces local pixel redundancy, which acts as the first stage of coding the index map. The implemented method exploits the non-local pixel correlation and is the second stage of coding the palette index map. The combination of coding techniques to exploit local and non-local sample correlation contributes to the multi-stage predictively coding scheme of palette index map.
6.2 Future Work
Along with the traditional transverse scan of the index map, next is to see rotated index map scan. In rotated index scan, the horizontal and vertical scans are rotated to start the scan from the end of the block. A CU-level flag is used to indicate whether to apply the rotation [76]. Modification on the palette run coding can be studied in order to indicate whether or not the current pixel is the first pixel in the line. If so, a flag is signalled into the bitstream, indicating whether it ends at the last pixel in certain line. If so, the number of whole lines (L) the current run spans is coded into the bitstream using coefficient coding function with order 0. Instead of directly signalling L, a mapping process is used to map maximal feasible value to zero and shift L up by 1 if it is less than the maxima. Otherwise, it falls back to normal palette run length coding with an independent set of context models [76].
Appendix A Test Sequences [77]
A1. CAD Waveform (Resolution: 1920x1080)
A2. CG Twist Tunnel - Animation (Resolution: 1280x720)
A3. PCB Layout (Resolution: 1920x1080)
A4. Video Conferencing and Desktop Sharing (Resolution: 1280x720)
A5. Web Browsing (Resolution: 1280x720)
Appendix B
Acronyms
ACT - Adaptive Color Transform
AVC – Advanced Video Coding
AMVP- Advanced Motion Vector Prediction
BCIM - Base Colors and Index Map
CU- Coding unit
CTU- Coding tree unit
CABAC - Context adaptive binary arithmetic coding
CAVLC - Context Adaptive Variable Length Coding
DBF- Deblocking Filter
DFT – Discrete Fourier Transform
DCT – Discrete Cosine Transform
DST – Discrete Sine Transform
DPB - Decoded Picture Buffer
DC – Direct Current
IBC - Intra block copy (
FDIS- Final Draft International Standard
HD- High definition
HEB- High Efficiency Binarization
HEVC-High Efficiency Video Coding
HTB- High Throughput Binarization
ITU-T - International Telecommunication Union (Telecommunication Standardization Sector)
IEC - International Electrotechnical Commission
ISO – International Standards Organization
JBIG- Joint Bi-level Image Experts Group
JPEG - Joint photographic experts group
JCT-VC- Joint collaborative team on video coding
LCU- Larger Coding Unit
MPEG-Moving picture experts group
MRC- Mixed Raster Content
PPS – Picture Parameter Set
PU – Prediction Unit
RSQ - Residual Scalar Quantization
SAO - Sample Adaptive Offset
SCC - Screen Content Coding
SPS – Sequence Parameter Set
TU-Transform units
UHD - Ultra-high-definition
VCEG – Video Coding Experts Group
VCL-Variable Code Length
WPP - Wavefront Parallel Processing
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Biographical Information
Nagashree Mundgemane was born in Karnataka, India in 1990. She received her Bachelor’s degree in Electronics and Communication at Visvesvaraya Technological University, Karnataka in 2013. She joined The University of Texas at Arlington to pursue her Master’s degree in Fall 2013. She has worked in Multimedia Processing Lab under Dr. Rao from Fall 2014 to Fall 2015. After graduation, she has plans to pursue her career in the fields of Signal Processing and Communications to make the best use of the knowledge acquired.
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