Patent ID: 11170478

Abstract:
To allow a better determination of an image of a different luminance dynamic range (in particular as characterised by a different maximum luminance a.k.a. peak brightness) than an input image, the present application teaches several variants of a luminance processor (501) arranged to calculate an output luminance of a pixel of an output image (Im_LDR; Im3000 nit) having a second luminance dynamic range characterized by a second peak brightness (PB_LDR; PB_MDR) from an input luminance of a spatially collocated pixel of an input image (MAST_HDR) having a first luminance dynamic range characterized by a first peak brightness (PB_HDR), characterized in that the luminance processor comprises: a gain calculation unit (514) arranged to calculate a multiplication factor (gL) being a function of the input luminance and a luminance mapping function (FLM); a maximum calculation unit (601) arranged to calculate a strength value (V) which is the maximal one of the three red, green and blue color components of the color of the pixel of the input image, wherein those components are either linear red, green and blue color components or a power of those linear red, green and blue color components; an overflow calculator (602) arranged to calculate an overflow measure (T) indicating how close to the upper gamut boundary the output luminance is; a gain factor modification unit (603) arranged to determine an alternative gain factor (F1(gL)) in case the overflow measure is larger than a threshold (G), and arranged to keep the original gain factor otherwise, and arranged to output one of those as a final gain factor (gF); and a multiplier (530) to multiply the input color (R′G′B′_nrm) by the final gain factor (gF) to obtain an output color (R′G′B′_HDR) having the output luminance.