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 multi-type 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. INDEX TERMS Asymmetric block size, fast partition decision, intra prediction, quadtree with multi-type tree, versatile video coding YIBO FAN received the B.E. degree in electronics and engineering from

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Due to the merits of decreased photon attenuation, autofluorescence, and scattering, the near‐infrared (NIR, 700–1700 nm) region is an important window in the field of biomedicine, such as in vivo fluorescence imaging, in which both the optical detection depth and the resolution/contrast have been significantly improved. In particular, for second NIR (NIR‐II, 1000–1700 nm) dyes, biological tissues have almost no background interference. Typical fluorophores have excellent spectral performance and rich functional modification sites and can be optimized into NIR dyes for bioimaging. However, as the absorption/emission wavelength of fluorophores redshift to NIR, it is challenging to keep fluorophores with satisfying brightness. Therefore, for the purpose of increasing the absorption/emission wavelength of dye while promoting its brightness, it is necessary to study the structure–property relationship of the dyes. This review introduces the influences of fluorophores’ structure on their photophysical properties, summarizes the strategies for maintaining high fluorescence brightness along with redshifted absorption/emission wavelengths, and the latest advances of highly fluorescent brightness dyes. Finally, the opportunities and challenges in this emerging field are also provided. The authors aim to provide insightful design guidelines and clear overview of highly bright NIR fluorescent dyes, which might trigger new ideas and applications.

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