In this paper, we propose a partial decoding method with limited memory usage for high-speed thumbnail extraction. The proposed method performs a partial inverse transform and a partial intra prediction in order to reconstruct pixels for intra prediction and thumbnails. Thereafter, the reconstructed pixels at the bottom and right line of the block are stored in the line buffer and the thumbnail buffer without being stored in the decoded picture buffer with full resolution. H.264/AVC, HEVC and VP9 video codecs have different coding structures, prediction and transforms; however, the proposed algorithm can be applied to the corresponding codecs in the same manner. In order to evaluate the performance of the proposed method, we implemented the proposed algorithm for H.264/AVC, HEVC and VP9. We found that the thumbnail extraction time of the proposed method decreased by 66% in H.264/AVC, 52% in HEVC and 48% in VP9 as compared to the full decoding method.

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