1. One or more computer-readable memory or storage devices storing instructions that, when executed by a computing device, perform a method of rendering a high dynamic range digital image as a lower dynamic range digital image, the method comprising: tone mapping each of plural sample values in a high dynamic range digital image to a respective lower dynamic range value; calculating a local contrast value for each of the tone-mapped sample values; deriving a residual signal for each of the tone-mapped sample values, the deriving based at least in part on the respective local contrast value; and calculating sample values for a lower dynamic range digital image based at least in part on the tone-mapped sample values and the respective residual signals.