Determination of QP values

A QP offset value is calculated for a chroma component of a pixel in a picture of a video sequence based on a reference QP value and a factor that depends on a difference between a capture color space for the pixel and an encoded color space for the pixel. A QP value is then calculated for the chroma component based on the reference QP value reduced by the QP offset value. The calculation of QP values for chroma components based on the factor that depends on the difference between capture and encoded color spaces improves the chroma quality in an efficient way in particular for HDR and WCG video.