A method of converting a high dynamic range image (HDR 2020) comprising a pixel having a first color (C_in) having a first color saturation, into a standard dynamic range image (SDR_709) having a peak luminance of 100 nit, in which that pixel has a second color (C_out) having a second color saturation which is lower than the first color saturation, the converting comprising: - performing a color space conversion comprising applying a color matrix which maps a first RGB representation of the first color defined according to first red, green and blue primaries to a second RGB representation (RGB_sec) of that pixel color according to second red, green and blue primaries wherein the second red, green and blue primaries encompass a smaller color triangle than the first red, green and blue primaries, yielding an intermediate image (HDR_IM); - applying a reversible gamut mapping to the second RGB representation (RGB_sec), yielding a mapped color (C_map); and - applying a luminance mapping to the luminance of the mapped color, to obtain the standard dynamic range image (SDR 709) with the pixel having an output color (C_out) which has a luminance (L_Out) different than the luminance of the mapped color, and outputting the standard dynamic range image (SDR 709), characterized in that the reversible gamut mapping comprises applying a respective mapping function (F1, F2, F3) to each of the three R, G, and B color components of the second RGB representation to respectively obtain output R, G, and B color components (Ro, Go, Bo) which define the mapped color, which respective three mapping functions comprise two linear segments (501, 502), of which one of the segments corresponds to an identity transform which segment begins at a respective threshold value (TP_red, TP_green, TP_blue) of respectively the input red, green or blue color component of the second RGB representation, and the second linear segment goes from the respective threshold value (TP red, TP_green, TP_blue) to a respective minimal value (minP_red, minP_green, minP_blue) which is the most negative value occurring in the intermediate image (HDR IM) for the respective component of the second RGB representation, and wherein the respective threshold value is calculated by multiplying the values of the two components of the second RGB representation other than the color component for which the respective threshold value is calculated by respective constants (kRG, kRB) in case such values of the two components are larger than zero, and summing those two multiplied contributions: TP_red=kRG ∗ max(0,G_in)+kRB ∗ max(0, B_in); TP_green=kGR ∗ max(0,R_in)+kGB ∗ max(0, B_in); TP_blue=kBR ∗ max(0,Rin)+kBG ∗ max(0, G_in). - performing a color space conversion comprising applying a color matrix which maps a first RGB representation of the first color defined according to first red, green and blue primaries to a second RGB representation (RGB_sec) of that pixel color according to second red, green and blue primaries wherein the second red, green and blue primaries encompass a smaller color triangle than the first red, green and blue primaries, yielding an intermediate image (HDR_IM); - applying a reversible gamut mapping to the second RGB representation (RGB_sec), yielding a mapped color (C_map); and - applying a luminance mapping to the luminance of the mapped color, to obtain the standard dynamic range image (SDR 709) with the pixel having an output color (C_out) which has a luminance (L_Out) different than the luminance of the mapped color, and outputting the standard dynamic range image (SDR 709),