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Evaluating the CU-tree algorithm in an HEVC encoder
KTH, School of Computer Science and Communication (CSC).
2015 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
En utvärdering av algoritmen CU-tree i en HEVC-kodare (Swedish)
Abstract [en]

CU-tree (Coding Unit tree) is an algorithm for adaptive QP (quantization parameter). It runs in the lookahead and decreases the QP of blocks that are heavily referenced by future blocks, taking into account the quality of the prediction and the complexity of the future blocks, approximated by the inter and intra residual. In this study, CU-tree is implemented in c65, an experimental HEVC encoder used internally by Ericsson. The effects of CU-tree are evaluated on the video clips in the HEVC Common test conditions and the performance is compared across c65, x265 and x264. The results are similar across all encoders, with average PSNR (peak signal-to-noise ratio) improvements of 3-10% depending on the fixed QP offsets that are replaced. The runtime is not impaired and improvements to visual quality are expected to be even greater. The algorithm works better at slow speed modes, low bitrates and with source material that is well suited for inter prediction.

Abstract [sv]

CU-tree är en algoritm för adaptiv QP. Den körs under framåtblicken (lookahead) och minskar QP för block som refereras av många framtida block, med hänsyn tagen till prediktionens kvalitet och de framtida blockens komplexitet, approximerat av inter- och intra-skillnaden. I denna studie implementeras CU-tree i c65, en experimentell videokodare som används internt på Ericsson. Effekterna av algoritmen utvärderas på videoklippen i HEVC Common test conditions och prestandan jämförs mellan c65, x265 och x264. Resultaten är liknande i alla videokodare, med genomsnittliga PSNR-förbättringar på 3-10% beroende på vilka fasta QP-offsets som algoritmen ersätter. Körtiden påverkas inte nämnvärt och den subjektiva kvaliteten förbättras troligen ännu mer. Algoritmen fungerar bättre med långsamma hastighetsinställningar, låg bitrate samt videoinnehåll som lämpar sig väl för inter-prediktion.

Place, publisher, year, edition, pages
2015. , 37 p.
Keyword [en]
CU-tree, HEVC, AQP, video, codec, MB-tree
National Category
Computer Science
Identifiers
URN: urn:nbn:se:kth:diva-176054OAI: oai:DiVA.org:kth-176054DiVA: diva2:865774
External cooperation
Ericsson
Educational program
Master of Science in Engineering - Computer Science and Technology; Master of Science - Computer Science
Presentation
2015-09-29, Fantum, Lindstedtsvägen 24, Stockholm, 10:15 (English)
Supervisors
Examiners
Available from: 2015-10-29 Created: 2015-10-29 Last updated: 2015-11-16Bibliographically approved

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