method and device for tonu00fcbersetzung digital images using a special wahrnemungsrichtlinien based adaptativen sigmoidalfunktion

摘要

An adaptive image tone mapping curve (170) based on perceptual preference guidelines is generated as a sigmoidal function, in which the sigmoidal function parameters (150) (slope and shift) are determined by original image statistics (149). Tone curves (170) generated for different images each have a smooth sigmoidal shape, so that the tone mapping process does not change the image histogram shape drastically. The sigmoidal function has the form: DFt(x) = 100 DIVIDED 1 + exp(- alpha (x/100 - beta )), /DF where alpha is the slope parameter (150a) and beta is the shift parameter (150b). The input value x in the sigmoidal function varies in the range Ä0, 100Ü, because the tone curve (170) is generated on an L* scale, which has values from 0 to 100. The sigmoidal tone curve (170) calculation can be implemented efficiently using simple arithmetic operations by pre-calculating and storing various factors used in the calculation of alpha and beta and by pre-generating a pair of fixed tone curves (158) with two extreme slopes and interpolating between the curves (158). IMAGE