Luminance-Preserving Color Conversion

With the advent of new television standards introducing ultrahigh definition and high dynamic range, backward compatibility with older devices becomes an issue. We propose a method for converting footage produced in BT.2100 colorimetry to a BT.709 compliant representation. The process preserves each pixel's luminance and is fully reversible. Technically, our approach determines the exact polygonal shape of the effective BT.2100 and BT.709 gamuts at a given luminance and maps colors from one to the other by desaturating them.