Patent ID: 8218625

Claim:
A method for encoding high dynamic range image data having an initial dynamic range, the method comprising: obtaining tone map data corresponding to the high dynamic range image data, the tone map data having a reduced dynamic range lower than the initial dynamic range; processing the high dynamic range image data and the tone map data by a machine to yield ratio data, the ratio data comprising ratios of values in the high dynamic range image data and corresponding values in the tone map data; generating high dynamic range information based on the ratio data; generating tone map information based on the tone map data; and, storing the high dynamic range information and the tone map information in a data structure; wherein generating the high dynamic range information comprises applying to the ratio data a correction function, the correction function based on the tone map data; the correction function is of the form: RI CORRECTED = RI × ( L ⁡ ( TM ) L ⁡ ( TM R ) ) σ or a mathematical equivalent thereof, where: L(TM) is the luminance for a pixel in the tone map data and L(TM R ) is the luminance for a corresponding pixel of tone map data that has been downsampled, and σ is a numeric Parameter; σ is a measure of variance in the ratio of L(TM) to L(TM R ) where σ is computed according to: σ = var ⁡ ( RI ) var ⁡ ( L ⁡ ( TM R ) ) .