Optimizing high dynamic range images for particular displays

Abstract

Color transformation apparatus () for calculating resultant colors (RGB) of pixels of an output image for a display with a display peak brightness (PB_D) starting from input colors (R,G,B) of pixels of an input image (Im_in) having a maximum luma code corresponding to a first image peak brightness (PB_H) which is different from the display peak brightness, said color transformation apparatus comprising: a color transformation determination unit () arranged to determine a color transformation (g) from color processing specification data (MET) comprising at least one tone mapping function (CC) for at least a range of pixel luminances received via a metadata input (), which color transformation specifies the calculation of at least some pixel colors of an image having corresponding to its maximum luma code a second image peak brightness (PB_L), which is different from the display peak brightness (PB_D) and the first image peak brightness (PB_H), and whereby the division of the first image peak brightness by the second image peak brightness is either larger than 2 or smaller than ½ ; a scaling factor determination unit () arranged to determine a resultant common multiplicative factor (gt), said scaling factor determination unit comprising:—a capability metric determination unit arranged to determine a metric for locating positions of display peak brightnesses between the first image peak brightness (PB_H), and the second image peak brightness (PB_L) and outside that range; and—a resultant multiplier determination unit arranged to determine from the display peak brightness (PB_D), the metric, and the color transformation the resultant common multiplicative factor (gt), and wherein the color transformation apparatus () further comprises a scaling multiplier () arranged to multiply a linear RGB color representation of the input colors with the resultant common multiplicative factor (gt).