Automatic tone adjustment by contrast gain-control on edges
AssigneeEastman Kodak Company
InventorHsien-Che Lee
Life of this patent
Estimating the term…
Abstract
A method of reducing the dynamic range of an input image for effectively rendering the input image on an output display medium, the method comprises the steps of extracting detail signals and coarse signals from the input image; generating contrast gain-control signals from the input image by detecting coarse scale edges; modifying the detail signals according to the contrast gain signals; and, adding the modified detail signals to the coarse signals to obtain an output image.
Claims16
A method of reducing the dynamic range of an input image for effectively rendering the input image on an output display medium, the method comprising the steps of:
- (a) extracting detail signals and coarse signals from the input image;
- (b) generating contrast gain-control signals from the input image by detecting coarse scale edges;
- (c) modifying the detail signals according to the contrast gain signals;
- and,
- (d) adding the modified detail signals to the coarse signals to obtain an output image.
A method of reducing the dynamic range of an input image I so that it can be rendered effectively on an output display medium, comprising the steps of:
- (a) constructing a tone scale curve T from the input image I;
- (b) mapping the input image I through the tone scale curve T to produce a tone-scaled image I′=T(I);
- (c) constructing a mask image of weighting factors, W, from the input image such that W varies from 1.0 in regions where edge contrast is low to 0.0 in regions where edge contrast is high;
- and,
- (d) producing an output image, Iout=W H(I)+(1−W) H(I′)+L(I′), where H(I) is the high-pass filtered input image, H(I′) is the high-pass filtered tone-scaled image, and L(I′) is the low-pass filtered version of the tone-scaled image I′.
A method of reducing the dynamic range of an input image I so that it can be rendered effectively on an output display medium, comprising the steps of:
- (a) constructing a tone scale curve T from the input image I;
- (b) mapping the input image I through a tone scale curve T to produce a tone-scaled image I′=T(I);
- (c) producing a difference image D=I−I′ by subtracting the tone-scaled image from the input image;
- (d) producing a modified difference image, D′, by processing the difference image D through a plurality of band-pass and high-pass filters;
- and,
- (e) adding the modified difference image D′ to the tone-scaled image I′ to produce a dynamic range compressed output image.
A method of reducing the dynamic range of an input image I so that it can be rendered effectively on an output display medium, comprising the steps of:
- (a) constructing a tone scale curve T from the input image I;
- (b) mapping the input image I through the tone scale curve T to produce a tone-scaled image I′=T(I);
- (c) producing a difference image D=I−I′ by subtracting the tone-scaled image from the input image;
- (d) generating contrast gain-control signals G from the input image;
- (e) producing a modified difference image, D′, by passing the difference image D through an edge-detecting filter bank where edge signals in each spatial-scale are modulated by the said contrast gain-control signals G;
- and,
- (f) adding the modified difference image D′ to the tone-scaled image I′ to produce a dynamic range compressed output image.
A method of generating a tone-scale curve from an image for dynamic range compression, comprising the steps of:
- (a) computing a histogram from the input image;
- (b) finding a low end, a median point, and a high end of the input values from the histogram at some fixed percentiles;
- (c) mapping the low end point to a black level of the output medium with a higher than normal local slope;
- (d) mapping the median point to a medium gray level of the output medium with a normal contrast;
- and,
- (e) mapping the high end point to a white level of the output medium with an adjustable contrast, depending on the shape and the range of an upper tail of the histogram.
A method of image contrast enhancement using contrast gain-control signals for suppressing banding artifacts, comprising the steps of:
- (a) decomposing an input image into edge gradients of several spatial scales;
- (b) generating contrast gain-control signals G from the original input image;
- (c) enhancing each edge gradient signal by modifying its amplitude according to separately generated contrast gain-control signals G in step (b);
- and,
- (d) reconstructing an enhanced output image from the modified edge signals of step (c).
Dependencies are inferred from the claim text.