A method of encoding a high dynamic range image. First converting the high dynamic range image to an image of lower luminance dynamic range by applying scaling the high dynamic range image to a predetermined scale of the luma axis. Next, applying a sensitivity tone mapping which changes the brightness of pixel colors falling within at least a subrange comprising the darker colors in the high dynamic range image. Then applying a gamma function. Finally, applying an arbitrary monotonically increasing function mapping the lumas resulting from the sensitivity tone mapping and gamma adjustments to output lumas of a lower dynamic range image.Producing in an image signal a codification of the pixel colors of the lower luminance dynamic range image and outputting in the image signal values encoding the functional behavior of the above color conversions as metadata, or values for the inverse functions.