1. A video encoding method comprising: applying a color conversion model to a first picture to generate a second picture, wherein the color conversion model is represented using a 3D look-up table (LUT) comprising one or more octants, and an octant comprises parameters for defining a color gamut conversion for the octant and wherein the parameters associated with the 3D LUT are coded with a precision; and generating a video bitstream comprising a color mapping parameter precision indicator indicative of the precision and the parameters associated with the 3D LUT.