Image display apparatus and image display method

An image display apparatus, comprising:

• an image displaying unit that includes:
• a light source unit that emits light whose luminance is adjustable;
• and
• a light modulation device configured to display an image by modulating a transmittance or a reflectance of light from the light source unit based on a signal representing the image,
• a histogram generating unit configured to generate, from the image, a histogram representing frequencies of pixels contained in level ranges associated with representative gray-scale levels;
• a light source luminance calculator configured to calculate a light source luminance that is to be set in the light source unit based on the histogram, as an object light source luminance;
• a function storing unit configured to store a level conversion function for performing level conversion of gray-scale level;
• a first evaluation value calculator configured to
• calculate first differences between a first brightness preset for each of the representative gray-scale levels and a second brightness obtained when an output gray-scale level resulting from conversion of each of the representative gray-scale levels with the level conversion function is displayed on the image displaying unit at the object light source luminance,
• calculate products of the first differences and the frequencies of the representative gray-scale levels, and
• calculate a total sum of such products as a first evaluation value;
• a second evaluation value calculator configured to
• calculate second differences between a first gradient which is a gradient of the first brightness preset for each of the representative gray-scale levels and a second gradient which is a gradient of the second brightness as when an output gray-scale level resulting from conversion of each of the representative gray-scale levels with the level conversion function is displayed on the image displaying unit at the object light source luminance,
• calculate products of the second differences and the frequencies of the representative gray-scales, and
• calculate a total sum of such products as a second evaluation value;
• a third evaluation value calculator configured to calculate a third evaluation value by giving first and second weights to the first and the second evaluation values and then summing those first and second evaluation values;
• a function acquiring unit configured to acquire a plurality of the third evaluation values by repeating performing of processing by the first to third evaluation value calculators with modification to the level conversion function and acquire an output level conversion function which is a level conversion function that has a smallest third evaluation value or the third evaluation value equal to or smaller than a threshold value;
• and
• a control unit configured to supply a signal representing a converted video resulting from conversion of the image with the output level conversion function to the light modulation device and to control the light source unit to illuminate at the object light source luminance.