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    CVPR 2021 | 用于文本识别的序列到序列对比学习

    今天给大家介绍的是以色列科技大学Aviad Aberdam等人发表在CVPR2021上的一篇文章 ”Sequence-to-Sequence Contrastive Learning for Text Recognition”。作者在这篇文章中提出了一种用于视觉表示的序列到序列的对比学习框架 (SeqCLR)用于文本识别。考虑到序列到序列的结构,每个图像特征映射被分成不同的实例来计算对比损失。这个操作能够在单词级别从每张图像中提取几对正对和多个负的例子进行对比。为了让文本识别产生有效的视觉表示,作者进一步提出了新的增强启发式方法、不同的编码器架构和自定义投影头。在手写文本和场景文本数据集上的实验表明,当文本解码器训练学习表示时,作者的方法优于非序列对比方法。此外,半监督的SeqCLR相比监督训练显著提高了性能,作者的方法在标准手写文本重新编码上取得了最先进的结果。

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    A Fast QTMT Partition Decision Strategy for VVC Intra Prediction

    Different from the traditional quaternary tree (QT) structure utilized in the previous generation video coding standard H.265/HEVC, a brand new partition structure named quadtree with nested multitype tree (QTMT) is applied in the latest codec H.266/VVC. The introduction of QTMT brings in superior encoding performance at the cost of great time-consuming. Therefore, a fast intra partition algorithm based on variance and Sobel operator is proposed in this paper. The proposed method settles the novel asymmetrical partition issue in VVC by well balancing the reduction of computational complexity and the loss of encoding quality. To be more concrete, we first terminate further splitting of a coding unit (CU) when the texture of it is judged as smooth. Then, we use Sobel operator to extract gradient features to decide whether to split this CU by QT, thus terminating further MT partitions. Finally, a completely novel method to choose only one partition from five QTMT partitions is applied. Obviously, homogeneous area tends to use a larger CU as a whole to do prediction while CUs with complicated texture are prone to be divided into small sub-CUs and these sub-CUs usually have different textures from each other. We calculate the variance of variance of each sub-CU to decide which partition will distinguish the sub-textures best. Our method is embedded into the latest VVC official reference software VTM-7.0. Comparing to anchor VTM-7.0, our method saves the encoding time by 49.27% on average at the cost of only 1.63% BDBR increase. As a traditional scheme based on variance and gradient to decrease the computational complexity in VVC intra coding, our method outperforms other relative existing state-of-the-art methods, including traditional machine learning and convolution neural network methods.

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