Flexible and effective High Dynamic Range image coding

This paper presents an algorithm based on a two-layer coding scheme, where the original information is represented by means of a Low Dynamic Range (LDR) image, obtained by applying a tone mapping operator to the original HDR (High Dynamic Range), plus an enhancement layer, which allows to recover the full dynamic range. More specifically, the original HDR is represented with a format similar to the well known RGBE, which uses a shared exponent to compactly represent floating point numbers. With respect to the original RGBE, here the mantissa is composed by an approximation of the LDR image while the shared exponent represents the enhancement layer. This particular choice allows to split the original HDR into a color image, the mantissa, and a grayscale image, the exponent, which are very smooth signals that can be efficiently compressed by conventional image coding methods. With respect to already proposed similar schemas, two desirable features are then provided: a high coding efficiency, combined with the possibility to retrieve a displayable version of the original content.