A method for decoding a coded image or picture in a coded video sequence in a decoder, the image or picture representing a projection on a planar surface of a non-planar surface, the decoder employing a de-quantization step and an inverse transform step, the method comprising: obtaining at least one interim delta quantizer parameter, QP, value of at least one first block of a plurality of first blocks, comprising establishing a delta QP map of the plurality of first blocks; decoding a QP value pertaining to a second block; combining a delta QP value and the QP value to generate a final QP value; and inverse quantizing at least one value related to the second block using the final QP value, the at least one value related to the second block being a transform coefficient of the second block; wherein if respective spatial positions of samples in the second block are included in a single first block of the plurality of first blocks of the delta QP map, setting the delta QP value to an interim delta QP value of the single first block; the method being characterised in that: if the respective spatial positions of the samples in the second block are included in multiple first blocks of the plurality of first blocks of the delta QP map, the method further comprises determining, using interim delta QP values of the multiple first blocks, an interim delta QP value that results in a numerically smallest final QP value when combined with the QP value pertaining to the second block; and setting the interim delta QP value, that results in the numerically smallest final QP value, as the delta QP value. obtaining at least one interim delta quantizer parameter, QP, value of at least one first block of a plurality of first blocks, comprising establishing a delta QP map of the plurality of first blocks; decoding a QP value pertaining to a second block; combining a delta QP value and the QP value to generate a final QP value; and inverse quantizing at least one value related to the second block using the final QP value, the at least one value related to the second block being a transform coefficient of the second block; wherein if respective spatial positions of samples in the second block are included in a single first block of the plurality of first blocks of the delta QP map, setting the delta QP value to an interim delta QP value of the single first block; the method being characterised in that: if the respective spatial positions of the samples in the second block are included in multiple first blocks of the plurality of first blocks of the delta QP map, the method further comprises determining, using interim delta QP values of the multiple first blocks, an interim delta QP value that results in a numerically smallest final QP value when combined with the QP value pertaining to the second block; and setting the interim delta QP value, that results in the numerically smallest final QP value, as the delta QP value. if the respective spatial positions of the samples in the second block are included in multiple first blocks of the plurality of first blocks of the delta QP map, the method further comprises determining, using interim delta QP values of the multiple first blocks, an interim delta QP value that results in a numerically smallest final QP value when combined with the QP value pertaining to the second block; and setting the interim delta QP value, that results in the numerically smallest final QP value, as the delta QP value.