Film-like tone reproduction operator

There are many ways to convert high dynamic range (HDR) images to low dynamic range (LDR) versions suitable for display. This tone renderer simulates the properties of a generic transparency (positive) film, such as Kodak's Ektachrome or Fuji's Velvia.

Unlike tone mapping operators (such as TONEMAP) that attempt to map all of the tones to be in the visible range, this one makes many values very bright or very dark. The purpose of this function is to show an alternative tone mapping rubric.