US 7,065,257 B2 · Image processing method and apparatus

Abstract

In an image conversion method and apparatus, luminance Y3 of each pixel of a converted image is obtained by use of an expression Y3=C1Y1+C2Y2 and from luminance Y1 of a corresponding pixel of a source image, luminance Y2 of a corresponding pixel of a low frequency image, and C1 and C2 which are functions of the luminance Y2. Since C1+C2 is constant when Y2≦T2, contrast of a low frequency component can be prevented from decreasing. In a portion in which the luminance Y2 of the low frequency image is low, the low frequency image is enhanced. In a portion in which the luminance Y2 of the low frequency image is high, the low frequency image is suppressed. In a method and apparatus for detecting noise level of an original signal in real time, a plurality of local regions are set on an input image in such a manner that the local regions are distributed uniformly over the entire area of an image. In each local region, determination as to whether or not luminance is saturated is performed. Variation in luminance is detected in each of a plurality of unsaturated local regions. Noise level is determined on the basis of the detected variation.

Claims22

Dependent claims

An image conversion method of processing a source image in which each pixel has a luminance value, in order to compress the dynamic range of the image in terms of brightness, the method comprising:

a low-frequency-image extraction step of extracting a low frequency image consisting of a low frequency component of the source image in terms of variation in luminance;
a coefficient determination step of obtaining two coefficients C1 and C2 from luminance Y2 of each pixel of the low frequency image corresponding to luminance Y1 of a corresponding pixel of the source image;
and
a linear computation step of obtaining luminance Y3 of a corresponding pixel of a converted image by use of an expression Y3=C1Y1+C2Y2 and from the two coefficients C1 and C2, the luminance Y1 of the corresponding pixel of the source image, and the luminance Y2 of the pixel of the low frequency image, wherein
each of the coefficients C1 and C2 is a continuous function of luminance Y2 of a relevant pixel of the low frequency image;
the coefficient C1 is positive or zero;
and
the coefficient C2 is a monotonic decreasing function in a broad sense, in a continuous first range where the luminance Y2 assumes a minimum value, such that the coefficient C2 assumes a positive value, becomes zero, and then assumes a negative value, and is a monotonic increasing function in a broad sense, in a continuous second range where the luminance Y2 assumes a maximum value, such that the coefficient C2 assumes a negative value or zero.

5 more elements

An image conversion apparatus for processing a source image in which each pixel has a luminance value in order to compress the dynamic range of the image in terms of brightness, the apparatus comprising:

low-frequency-image extraction means for extracting a low frequency image consisting of a low frequency component of the source image in terms of variation in luminance;
first and second coefficient determination means for obtaining two coefficients C1 and C2, respectively, from luminance Y2 of each pixel of the low frequency image output from the low-frequency-image extraction means;
linear computation means for obtaining luminance Y3 of a corresponding pixel of a converted image by use of an expression Y3=C1Yi+C2Y2 and from the two coefficients C1 and C2 obtained by the first and second coefficient determination means, the luminance Y2 of the pixel of the low frequency image output from the low-frequency-image extraction means, the luminance Y2 having been used for determination of the coefficients C1 and C2, and luminance Y1 of a corresponding pixel of the source image, wherein
each of the coefficients C1 and C2 is a continuous function of luminance Y2 of a relevant pixel of the low frequency image;
the coefficient C1 is positive or zero;
and
the coefficient C2 is a monotonic decreasing function in a broad sense, in a continuous first range where the luminance Y2 assumes a minimum value, such that the coefficient C2 assumes a positive value, becomes zero, and then assumes a negative value, and is a monotonic increasing function in a broad sense, in a continuous second range where the luminance Y2 assumes a maximum value, such that the coefficient C2 assumes a negative value or zero.

4 more elements

Dependencies are inferred from the claim text.

Image processing method and apparatus

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Image processing method and apparatus

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Abstract

Claims22