A computing device that implements an image or video encoder, wherein the computing device is adapted to perform a method comprising: encoding image or video content for which values of quantization parameter vary according to a relationship between a luma component and chroma components, wherein the encoding includes: setting a picture-level chroma QP offset for encoding of a slice of a picture; and performing chroma deblock filtering of at least part of the slice, wherein derivation of a control parameter for the chroma deblock filtering of the part of the slice considers the picture-level chroma QP offset; and outputting at least part of a bitstream including the encoded content, wherein the control parameter depends on a variable qP I derived as: qP I = QP Q + QP P + 1 » 1 + cqp _ offset, wherein variables QP Q and QP P represent luma QP values for blocks on either side of an edge in the part of the slice on which deblock filtering is performed, wherein variable cqp_offset represents the picture-level chroma QP offset, wherein the picture-level chroma QP offset is separately signaled for two different chroma components of the picture, and wherein values of the control parameter are computed separately for the two different chroma components; characterized in that said setting further includes setting a slice-level chroma QP offset for encoding of said slice of a picture; and the derivation of said control parameter for the chroma deblock filtering of the part of the slice does not consider said slice-level chroma QP offset. encoding image or video content for which values of quantization parameter vary according to a relationship between a luma component and chroma components, wherein the encoding includes: setting a picture-level chroma QP offset for encoding of a slice of a picture; and performing chroma deblock filtering of at least part of the slice, wherein derivation of a control parameter for the chroma deblock filtering of the part of the slice considers the picture-level chroma QP offset; and setting a picture-level chroma QP offset for encoding of a slice of a picture; and performing chroma deblock filtering of at least part of the slice, wherein derivation of a control parameter for the chroma deblock filtering of the part of the slice considers the picture-level chroma QP offset; and outputting at least part of a bitstream including the encoded content, wherein the control parameter depends on a variable qP I derived as: qP I = QP Q + QP P + 1 » 1 + cqp _ offset, wherein variables QP Q and QP P represent luma QP values for blocks on either side of an edge in the part of the slice on which deblock filtering is performed, wherein variable cqp_offset represents the picture-level chroma QP offset, wherein the picture-level chroma QP offset is separately signaled for two different chroma components of the picture, and wherein values of the control parameter are computed separately for the two different chroma components; characterized in that said setting further includes setting a slice-level chroma QP offset for encoding of said slice of a picture; and the derivation of said control parameter for the chroma deblock filtering of the part of the slice does not consider said slice-level chroma QP offset.