Patent ID: 8207932

Claim:
A method for determining a tonescale adjustment curve parameter, said method comprising: a) generating an image luminance histogram for an image to be displayed, said luminance histogram comprising bin values; b) weighting said histogram bin values from said image luminance histogram with distortion weight values, wherein said distortion weight values correspond to a particular source light illumination level, thereby creating weighted histogram values; c) combining said weighted histogram values to obtain distortion values for each of said source light illumination levels, said distortion values each estimating a sum of respective magnitude errors between each of a plurality of pixels' displayed values when illuminated at a respectively associated said source light illumination level and said pixels' displayed values if illuminated by a reference illumination level; d) selecting a source light illumination level for said image wherein said selecting is based on said distortion values; e) filtering said selected source light illumination level to determine a filtered source light illumination level; f) generating a tonescale adjustment curve based on said filtered source light illumination level and a strength factor; where g) said magnitude errors are calculated using the following equation: d -> ⁡ ( x , bl ) = {  x - x min ⁡ ( bl )  2 x ≤ x min ⁡ ( bl ) 0 x min ⁡ ( bl ) < x < x max ⁡ ( bl )  x - x max ⁡ ( bl )  2 x max ⁡ ( bl ) ≤ x where x min and x max are the clipping limits, x is an image code value and bl is the source light illumination level.