An image encoding/decoding method and apparatus are provided. An image decoding method performed by an image decoding apparatus may comprise determining prediction mode characteristic information based on a color format of a current block, determining a prediction mode type of a lower-layer block split from the current block based on the prediction mode characteristic information, obtaining the lower-layer block by splitting the current block based on the prediction mode type of the lower-layer block, and decoding the lower-layer block based on the prediction mode type of the lower-layer block. The prediction mode type of the lower-layer block comprises a first prediction mode type specifying that both an intra prediction mode and an inter prediction mode are available, a second prediction mode type specifying that only the intra prediction mode is available and a third prediction mode type specifying that only the inter prediction mode is available. Based on a first condition for the current block being satisfied, the prediction mode characteristic information has a first value, and the first condition comprises a case where a color format of the current block is a monochrome format or a 4:4:4 format. Based on the first condition for the current block being not satisfied, the prediction mode characteristic information has a second value or a third value based on at least one of a color format, split mode or size of the current block.

An image encoding/decoding method and apparatus are provided. An image decoding method performed by an image decoding apparatus may comprise determining prediction mode characteristic information based on a color format of a current block, determining a prediction mode type of a lower-layer block split from the current block based on the prediction mode characteristic information, obtaining the lower-layer block by splitting the current block based on the prediction mode type of the lower-layer block, and decoding the lower-layer block based on the prediction mode type of the lower-layer block. The prediction mode type of the lower-layer block comprises a first prediction mode type specifying that both an intra prediction mode and an inter prediction mode are available, a second prediction mode type specifying that only the intra prediction mode is available and a third prediction mode type specifying that only the inter prediction mode is available. Based on a first condition for the current block being satisfied, the prediction mode characteristic information has a first value, and the first condition comprises a case where a color format of the current block is a monochrome format or a 4:4:4 format. Based on the first condition for the current block being not satisfied, the prediction mode characteristic information has a second value or a third value based on at least one of a color format, split mode or size of the current block.

A method for intra prediction of a video block, comprising: padding of luminance reference samples rows for a chroma component of a current block vertically aligned with a largest coding unit (LCU) boundary; applying a filter F to reconstructed luma samples of a luma component of the current block and to luma samples in selected position neighboring to the current block, to obtain filtered reconstructed luma samples, wherein a shape of the F is same for blocks in the LCU; obtaining linear model coefficients, based on the filtered reconstructed luma samples; and performing cross-component prediction based on the obtained linear model coefficients and the filtered reconstructed luma samples of the current block, to obtain a prediction value of the chroma component of the current block.

A method for intra prediction of a video block, comprising: padding of luminance reference samples rows for a chroma component of a current block vertically aligned with a largest coding unit (LCU) boundary; applying a filter F to reconstructed luma samples of a luma component of the current block and to luma samples in selected position neighboring to the current block, to obtain filtered reconstructed luma samples, wherein a shape of the F is same for blocks in the LCU; obtaining linear model coefficients, based on the filtered reconstructed luma samples; and performing cross-component prediction based on the obtained linear model coefficients and the filtered reconstructed luma samples of the current block, to obtain a prediction value of the chroma component of the current block.

According to embodiment(s) of the present document, computational overhead and complexity can be reduced by using a 0th-order exponential Golomb coding scheme (ue(v)) for procedures of parsing syntax elements/information about absolute values of luma/chroma ALF filter coefficients. In addition, coding using ue(v) can be efficiently performed by fixing the range of values of the information about the absolute values of the luma/chroma ALF filter coefficients.

According to embodiment(s) of the present document, computational overhead and complexity can be reduced by using a 0th-order exponential Golomb coding scheme (ue(v)) for procedures of parsing syntax elements/information about absolute values of luma/chroma ALF filter coefficients. In addition, coding using ue(v) can be efficiently performed by fixing the range of values of the information about the absolute values of the luma/chroma ALF filter coefficients.

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.

A down-sample video coding system is provided. A decoding system receives to be decoded data from a bitstream for one or more pictures of a video. Each picture includes pixels having different color components. The decoding system receives up-down-sampling parameters that are applicable to a current video unit in the received data. The up-down-sampling parameters include different subsets for different color components. The decoding system decodes the data to reconstruct the current video unit. The decoding system up-samples the reconstructed current video unit according to the up-down-sampling parameters. The different color components of the current video unit are up-sampled according to different subsets of the up-down-sampling parameters.

A down-sample video coding system is provided. A decoding system receives to be decoded data from a bitstream for one or more pictures of a video. Each picture includes pixels having different color components. The decoding system receives up-down-sampling parameters that are applicable to a current video unit in the received data. The up-down-sampling parameters include different subsets for different color components. The decoding system decodes the data to reconstruct the current video unit. The decoding system up-samples the reconstructed current video unit according to the up-down-sampling parameters. The different color components of the current video unit are up-sampled according to different subsets of the up-down-sampling parameters.