In a method to improve the coding efficiency of high-dynamic range images coded in a perceptually quantized IPT color space (IPT-PQ), the values of the chroma components (P/T) of an input signal in IPT-PQ color space are divided by a factor of two before being encoded with standard-based encoders, such as AVC or HEVC; thus better matching the covariance characteristics of YCbCr signals. In addition, the order of the P and T chroma components may be swapped and the sign of the T chroma component may be inverted. Color transformation matrices for efficient forward and backward reshaping in the IPT-PQ color space are provided.