Patent ID: 8111235
Filing Date: 2012-02-07
Classification: G09G

Abstract:
1. An image display apparatus comprising: an image display unit having a light source configured to be able to adjust the light source luminance in n steps from dark luminance to bright luminance and a light modulating unit configured to display an image by modulating the transmittance or the reflectance of light from the light source on the basis of an input image signal; a histogram generating unit configured to generate a histogram which correlates representative gray-scale levels which are representatives of respective gray-scale level ranges divided at every predetermined number of gray-scale levels in one frame of an input image to frequencies of pixels included in the respective gray-scale level ranges; a function generating unit configured to generate predetermined m types of gray-scale level conversion functions for converting predetermined j preset gray-scale levels into output gray-scale levels which can be displayed by the light modulating unit; a first brightness calculating unit configured to calculate predetermined values of first brightness of the respective j preset gray-scale levels; a second brightness calculating unit configured to calculate second values of brightness to be displayed on the image display unit at the respective output gray-scale levels obtained by converting the respective preset gray-scale levels in each combination of the j preset gray-scale levels, the n steps of light source luminance and the m types of gray-scale level conversion functions; a first difference calculating unit configured to calculate first differences between the first values of brightness and the second values of brightness in each combination of the j preset gray-scale levels, the n steps of light source luminance and the m types of gray-scale level conversion functions; a first multiplying unit configured to calculate first products multiplying the first differences by the frequencies for the respective representative gray-scale levels corresponding to the preset gray-scale levels used for calculating the first differences; a first summation calculating unit configured to calculate first evaluation values, which are sums of the first products for the all j preset gray-scale levels; a first brightness gradient calculating unit configured to calculate predetermined values of first brightness gradient of the respective j preset gray-scale levels; a second brightness gradient calculating unit configured to calculate second values of brightness gradient to be displayed on the image display unit at the respective output gray-scale levels obtained by converting the respective preset gray-scale levels in each combination of the j preset gray-scale levels, the n steps of light source luminance and the m types of gray-scale level conversion functions; a second difference calculating unit configured to calculate second differences between the first values of brightness gradient and the second values of brightness gradient in each combination of the j preset gray-scale levels, the n steps of light source luminance and the m types of gray-scale level conversion functions; a second multiplying unit configured to calculate second products multiplying the second differences by the frequencies for the respective representative gray-scale levels corresponding to the preset gray-scale levels used for calculating the second differences; a second summation calculating unit configured to calculate second evaluation values, which are sums of the second products for the all j preset gray-scale levels; a weighted linear sum calculating unit configured to calculate weighted linear sums of the first evaluation values and the second evaluation values in each combination of the n steps of light source luminance and the m types of gray-scale level conversion functions; a determination unit configured to determine the weighted linear sum which is equal to or smaller than a predetermined threshold value or the minimum value from among the respective weighted linear sums; a control parameter selecting unit configured to select an optimum light source luminance and an optimum gray-scale level conversion function corresponding to the determined weighted linear sum; and a control unit configured to provide a converted image converted from the input image by the optimum gray-scale level conversion function to the light modulating unit and set the light source to emit light at the optimum light source luminance for one frame of the input image.