Patent ID: 8830277

Claim:
A driving method of an image display device including an image display panel configured of pixels being arrayed in a two-dimensional matrix shape, each of which is made up of a first sub-pixel for displaying a first primary color, a second sub-pixel for displaying a second primary color, a third sub-pixel for displaying a third primary color, and a fourth sub-pixel for displaying a fourth color, and a signal processing unit, the method causing the signal processing unit to obtain a first sub-pixel output signal based on at least a first sub-pixel input signal and an extension coefficient α 0 to output to the first sub-pixel, to obtain a second sub-pixel output signal based on at least a second sub-pixel input signal and the extension coefficient α 0 to output to the second sub-pixel, to obtain a third sub-pixel output signal based on at least a third sub-pixel input signal and the extension coefficient α 0 to output to the third sub-pixel, and to obtain a fourth sub-pixel output signal based on the first sub-pixel input signal, the second sub-pixel input signal, and the third sub-pixel input signal to output to the fourth sub-pixel, the method comprising: obtaining the maximum value V max of luminosity at the signal processing unit with saturation S in the HSV color space enlarged by adding a fourth color, as a variable; obtaining a reference extension coefficient α 0-std at the signal processing unit based on the maximum value V max ; and determining an extension coefficient α 0 at each pixel according to the following expression (i) using the reference extension coefficient α 0-std , an input signal correction coefficient k IS based on the sub-pixel input signal values at each pixel, and an external light intensity correction coefficient k OL based on external light intensity; α 0 =α 0-std ×( k IS ×k OL +1) (i), wherein the saturation S and luminosity V(S) are represented with S =(Max−Min)/Max V ( S )=Max where Max denotes the maximum value of three sub-pixel input signal values of a first sub-pixel input signal value, a second-sub pixel input signal value, and a third sub-pixel input signal value as to a pixel, and Min denotes the minimum value of three sub-pixel input signal values of the first sub-pixel input signal value, the second-sub pixel input signal value, and the third sub-pixel input signal value as to the pixel.