Image data is encoded for distribution in a lower bit-depth format. The image data has a range that is less than a maximum range and is mapped to the lower bit depth format using a mapping such that a ratio of a range of the lower bit depth representation to a maximum range of the lower bit depth representation is greater than a ratio of the range of the image data to a maximum range of the image data. Metadata characterizing the mapping is associated with lower bit depth representation. The metadata may be used downstream to reverse the mapping so that tonal detail is better reproduced.