Encoding a high dynamic range image (M_HDR), comprising: 1. converting the high dynamic range image to an image of lower luminance dynamic range (LDR_o) by applying the acts of: a) scaling the high dynamic range image to a predetermined scale of the luma axis such as [0,1], b) a sensitivity tone mapping which changes the brightnesses of pixel colors falling within at least a subrange comprising the darker colors in the high dynamic range image, c) a gamma function, and d) applying an arbitrary monotonically increasing function mapping the lumas resulting from performing the acts b and c to output lumas of the lower dynamic range image (LDR_o); and 2. outputting in an image signal (S_im) a codification of the pixel colors of the lower luminance dynamic range image (LDR_o), and 3. outputting in the image signal (S_im) values encoding the functional behavior of the above color conversions as metadata, or values for the inverse functions, which metadata allows to reconstruct a high dynamic range image (Rec_HDR) from the lower luminance dynamic range image (LDR_o).