US 7,023,580 B2 · System and method for digital image tone mapping using an adaptive sigmoidal function based on perceptual preference guidelines

Abstract

An adaptive image tone mapping curve based on perceptual preference guidelines is generated as a sigmoidal function, in which the sigmoidal function parameters (slope and shift) are determined by original image statistics. Tone curves 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: t ⁢ ( x ) = 100 1 + exp ⁢ ( - α ⁢ ( x / 100 - β ) ) , where α is the slope parameter and β is the shift parameter. The input value x in the sigmoidal function varies in the range [0, 100], because the tone curve is generated on an L* scale, which has values from 0 to 100. The sigmoidal tone curve calculation can be implemented efficiently using simple arithmetic operations by pre-calculating and storing various factors used in the calculation of α and β and by pre-generating a pair of fixed tone curves with two extreme slopes and interpolating between the curves.

Claims20

Dependent claims

A digital image system capable of receiving digital image data representing at least part of a digital image and mapping said digital image data onto the range of an output device, said digital image system comprising:

an image statistics processor capable of calculating at least one current image statistic based on said digital image data;
calculation logic connected to receive said at least one current image statistic from said image statistics processor and further being capable of calculating at least one tone curve parameter based on said at least one current image statistic and at least one perceptual preference, said perceptual preference specified with respect to said output device in order to obtain from said output device a visually perceptible behavior that corresponds to said perceptual preference;
and
a tone curve generator connected to receive said at least one tone curve parameter from said calculation logic and further being capable of generating a tone curve using said at least one tone curve parameter and a sigmoidal function, said tone curve being used to map said digital image data onto the range of said output device.

1 more element

A method for mapping digital image data representing at least part of a digital image onto the range of an output device, said method comprising:

receiving said digital image data at a digital image system;
calculating at least one current image statistic based on said digital image data;
calculating at least one tone curve parameter based on said at least one current image statistic and at least one perceptual preference, said perceptual preference specified with respect to said output device in order to obtain from said output device a visually perceptible behavior that corresponds to said perceptual preference;
and
generating a tone curve using said at least one tone curve parameter and a sigmoidal function, and using said tone curve to map said digital image data onto the range of said output device.

2 more elements

Dependencies are inferred from the claim text.

System and method for digital image tone mapping using an adaptive sigmoidal function based on perceptual preference guidelines

Life of this patent

System and method for digital image tone mapping using an adaptive sigmoidal function based on perceptual preference guidelines

Life of this patent

Abstract

Claims20