In the example of FIG. 1, the chroma QG 121 has four corresponding luma QP values (QPLuma), because the chroma QG 121 overlaps with four different luma QGs 171-174. These four luma QP values of the chroma QG 121 results in four possible chroma QP values after applying the chroma QP offsets (QPoffset_pps, QPoffset_slice, QPoffset_quant_group) from the PPS offset 132 and QG1 offset 141. A coding unit in the chroma QG 121 therefore can have one of these four possible chroma QP values, depending on the underlying luma QG that the coding unit falls into. Likewise, the chroma QG 123 overlaps with two different luma QGs 181-182, and a coding unit in the chroma QG 123 can have one of two possible chroma QP values depending on the underlying luma QG that the coding unit falls into.
On the other hand, the chroma QG 122 has only one corresponding luma QP value, because the chroma QG 122 falls completely within a luma QG 175 (or encompasses the exact same set of coding units as the luma QG 175). Consequently the coding units in the chroma QG 122 all have the same chroma QP value after applying the chroma QP offsets.
