US Patent 9699482 HDR image encoding and decoding methods and devices

An image encoder includes an input for a high dynamic range input image (M_HDR); an image grading unit arranged to allow a human color grader to specify a color mapping from a representation (HDR_REP) of the high dynamic range input image defined according to a predefined accuracy, to a low dynamic range image (Im_LDR) by a human-determined color mapping algorithm. The image encoder is configured to output data specifying the color mapping (Fi(MP_DH)). Further, the image encoder includes an automatic grading unit configured to derive a second low dynamic range image (GT_IDR) by applying an automatic color mapping algorithm to one of the high dynamic range input image (M_HDR) and the low dynamic range image (Im_LDR).