A pixel in a picture is pre-processed by determining at least one bound for a luma component value of the pixel in a second color space based on a transfer function of a desired linear luminance value of the pixel in a third color space. A luma component value in the second color space is then selected for the pixel within an interval comprising multiple luma component values in the second color space and 5 bounded by the at least one bound. A color of the pixel is represented by the luma component value and two chroma component values in the second color space. The pre-processing enables selection of a suitable luma component value for the pixel in a computationally efficient way by limiting the number of luma component values that are available for the particular pixel.