Patent Document ID: 20030052979
Application ID: 10232692
Patent Status: 0

Claim One:
1. 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 C 1 and C 2 from luminance Y 2 of each pixel of the low frequency image corresponding to luminance Y 1 of a corresponding pixel of the source image; and a linear computation step of obtaining luminance Y 3 of a corresponding pixel of a converted image by use of an expression Y 3 &equals;C 1 Y 1 &plus;C 2 Y 2 and from the two coefficients C 1 and C 2, the luminance Y 1 of the corresponding pixel of the source image, and the luminance Y 2 of the pixel of the low frequency image, wherein each of the coefficients C 1 and C 2 is a continuous function of luminance Y 2 of a relevant pixel of the low frequency image; the coefficient C 1 is positive or zero; and the coefficient C 2 is a monotonic decreasing function in a broad sense, in a continuous first range where the luminance Y 2 assumes a minimum value, such that the coefficient C 2 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 Y 2 assumes a maximum value, such that the coefficient C 2 assumes a negative value or zero.