AN ENCODER, A DECODER AND CORRESPONDING METHODS FOR PERFORMING CHROMA DEBLOCKING FOR BLOCKS WHICH USE JOINT CHROMA CODING

A method for deblocking a chroma block edge between a first chroma block of a first image block and a second chroma block of a second image block. The method includes a decision process which includes: determining a first chroma quantization parameter for the first chroma block based on a first luma quantization parameter of a first luma block of the first image block and a chroma QP mapping table for the first chroma block; determining a second chroma quantization parameter for the second chroma block based on a second luma quantization parameter of a second luma block of the second image block and a chroma QP mapping table for the second chroma block; determining an averaged and rounded chroma quantization parameter based on the first chroma quantization parameter and the second chroma quantization parameter; and determining a threshold parameter based on the averaged and rounded chroma quantization parameter.