Method and apparatus for estimating color temperature, photographing apparatus, and method and apparatus for determining exposure

A color temperature estimating method, comprising the steps of:

• obtaining a theoretical reference sensor output value represented by summation or integration of the product of a spectral energy distribution of an object having a known color temperature, a spectral sensitivity distribution of a photometric system, and a spectral reflectance distribution defined by an expression;
• acquiring an actual sensor output value by measuring at least a portion of light reflected from a body which is exposed to light emitted from a light source whose color temperature is to be estimated;
• calculating a spectral reflectance distribution for each of a plurality of color temperatures such that a difference between said theoretical reference sensor output value and said actual sensor output value becomes a minimum, to obtain plural spectral reflectance distributions;
• calculating the sum of abnormal components of said obtained spectral reflectance distributions whose maximum values exceed 1.0 as an evaluation value, for each of said plurality of color temperatures, so as to obtain a plurality of evaluation values;
• and
• estimating a color temperature corresponding to a minimum value of said plurality of evaluation values as the color temperature of said light source whose color temperature is to be estimated.

A photographing apparatus having a color temperature estimating apparatus which comprises:

• a memory for previously storing a theoretical reference sensor output value represented by summation or integration of the product of a spectral energy distribution of an object having a known color temperature, a spectral sensitivity distribution of a photometric system, and a spectral reflectance distribution defined by an expression;
• actual sensor output value acquiring means for acquiring an actual sensor output value by measuring at least a portion of light reflected from a body which is exposed to light emitted from a light source whose color temperature is to be estimated;
• spectral reflectance distribution computation means for calculating a spectral reflectance distribution for each of a plurality of color temperatures which makes a difference between said theoretical reference sensor output value and said actual sensor output value a minimum, to obtain plural spectral reflectance distributions;
• evaluation value computation means for calculating the sum of abnormal components of said obtained spectral reflectance distributions whose maximum values exceed 1.0 as an evaluation value, for each of said plurality of color temperatures, so as to obtain a plurality of evaluation values;
• and
• estimating means for estimating a color temperature corresponding to a minimum value of said plurality of evaluation values as the color temperature of said light source whose color temperature is to be estimated.

An exposure amount determining method, comprising the steps of:

• obtaining a theoretical reference sensor output value represented by summation or integration of the product of a spectral energy distribution of an object having a known color temperature, a spectral sensitivity distribution of a photometric system, and a spectral reflectance distribution defined by an expression;
• acquiring an actual sensor output value by measuring at least a portion of light reflected from a body which is exposed to light emitted from a light source whose color temperature is to be estimated;
• calculating a spectral reflectance distribution for each of a plurality of color temperatures such that the difference between said theoretical reference sensor output value and said actual sensor output value becomes a minimum, to obtain plural spectral reflectance distributions;
• calculating the sum of abnormal components of said obtained spectral reflectance distributions whose maximum values exceed 1.0 as an evaluation value, for each of said plurality of color temperatures, so as to obtain a plurality of evaluation values;
• estimating a color temperature corresponding to a minimum value of said plurality of evaluation values as the color temperature of said light source subject to color temperature estimation;
• and
• determining an amount of exposure used for printing an image of a photographic film on a photosensitive material, on the basis of an estimated color temperature and the photometric data such that the gray of the image becomes identical to the gray obtained at the estimated color temperature.

An exposure amount determining apparatus, comprising:

• a memory for previously storing a theoretical reference sensor output value represented by summation or integration of the product of a spectral energy distribution of an object having a known color temperature, a spectral sensitivity distribution of a photometric system, and a spectral reflectance distribution defined by an expression;
• actual sensor output value acquiring means for acquiring an actual sensor output value by measuring at least a portion of light reflected from a body which is exposed to light emitted from a light source whose color temperature is to be estimated;
• spectral reflectance distribution computation means for calculating a spectral reflectance distribution for each of a plurality of color temperatures which makes a difference between said theoretical reference sensor output value and said actual sensor output value a minimum, to obtain plural spectral reflectance distributions;
• evaluation value computation means for calculating the sum of abnormal components of said obtained spectral reflectance distributions whose maximum values exceed 1.0 as an evaluation value, for each of said plurality of color temperatures, so as to obtain a plurality of evaluation values;
• estimating means for estimating a color temperature corresponding to a minimum value of said evaluation values as the color temperature of said light source whose color temperature is to be estimated;
• and
• exposure amount determining means for determining an amount of exposure used for printing an image of a photographic film on a photosensitive material, on the basis of an estimated color temperature and the photometric data such that the gray of the image becomes identical to the gray obtained at the estimated color temperature.