Disclosed herein are a video-decoding method and apparatus and a video encoding method and apparatus, and more particularly a method and an apparatus which perform region-differential image encoding/decoding using a recovered image. In accordance with an encoding method according to an embodiment, a recovered low-quality image is generated by performing encoding on an original image and a recovered high-quality image is generated using the recovered low-quality image. An image is segmented into multiple regions, and encoded reconstruction information for generating a reconstructed high-quality image is generated by performing encoding on the image.

A method and a device for inversely transforming transform coefficients of a current block are disclosed. A method for predicting a current block according to a first mode, includes the steps of: on the basis of a partition mode syntax element, partitioning the current block into non-rectangular blocks; determining an intra-predicted intra block and an inter-predicted inter block among the non-rectangular blocks; and deriving prediction samples of a first area including the inter block on the basis of motion information, and deriving prediction samples of a second area including the intra block on the basis of an intra prediction mode.

A method and a device for inversely transforming transform coefficients of a current block are disclosed. A method for predicting a current block according to a first mode, includes the steps of: on the basis of a partition mode syntax element, partitioning the current block into non-rectangular blocks; determining an intra-predicted intra block and an inter-predicted inter block among the non-rectangular blocks; and deriving prediction samples of a first area including the inter block on the basis of motion information, and deriving prediction samples of a second area including the intra block on the basis of an intra prediction mode.

An in-loop filtering procedure for improving the picture quality of a reconstructed image (video) can be performed. The in-loop filtering procedure can be also performed on a picture divided into sub pictures. According to embodiments of the present document, sub picture-related information and in-loop filtering-related information can be efficiently signaled.

An in-loop filtering procedure for improving the picture quality of a reconstructed image (video) can be performed. The in-loop filtering procedure can be also performed on a picture divided into sub pictures. According to embodiments of the present document, sub picture-related information and in-loop filtering-related information can be efficiently signaled.

The inter prediction method comprises: determining a prediction mode parameter of a current block; determining a GPM parameter of the current block in response to that the prediction mode parameter indicates that a GPM is used to determine inter prediction of the current block; determining a first prediction value of a first partition of the current block and a second prediction value of a second partition of the current block; determining a weight index of a sample in the current block based on the GPM parameter of the current block; determining a first weight value and a second weight value of the sample in the current block based on the weight index of the sample in the current block; performing weighted combination of the first prediction value and the second prediction value to obtain the inter prediction of the current block.

The inter prediction method comprises: determining a prediction mode parameter of a current block; determining a GPM parameter of the current block in response to that the prediction mode parameter indicates that a GPM is used to determine inter prediction of the current block; determining a first prediction value of a first partition of the current block and a second prediction value of a second partition of the current block; determining a weight index of a sample in the current block based on the GPM parameter of the current block; determining a first weight value and a second weight value of the sample in the current block based on the weight index of the sample in the current block; performing weighted combination of the first prediction value and the second prediction value to obtain the inter prediction of the current block.

Methods and devices are provided for reducing the decoding latency introduced by LMCS. In one method, during decoding of a coding unit (CU), a plurality of reconstructed luma samples is selected from a first pre-determined region neighboring to a second pre-determined region where the CU is located, an average of the plurality of reconstructed luma samples is calculated, and the average of the plurality of reconstructed luma samples is used directly, without any clipping, in deriving a chroma residual scaling factor for decoding the CU.

Methods and devices are provided for reducing the decoding latency introduced by LMCS. In one method, during decoding of a coding unit (CU), a plurality of reconstructed luma samples is selected from a first pre-determined region neighboring to a second pre-determined region where the CU is located, an average of the plurality of reconstructed luma samples is calculated, and the average of the plurality of reconstructed luma samples is used directly, without any clipping, in deriving a chroma residual scaling factor for decoding the CU.

Methods, devices and systems for video coding and encoding, which include conforming to constraints on collocated pictures, are described. One example method of video processing includes performing a conversion between a video including a current picture and a bitstream of the video, wherein the bitstream conforms to a format rule, and wherein the format rule specifies that the bitstream includes a flag for disabling a use of a temporal motion vector prediction tool for the current picture based on whether a reference picture in a decoded picture buffer has a spatial resolution and a scaling window offset that are identical to that of the current picture.