An image-signal processing unit comprising a first and second luminance calculation block, a correction-value calculation block, and a subtraction block, is provided. The first luminance calculation block calculates a first luminance corresponding to the sum of a plurality of primary color light components. Each of them is multiplied by a coefficient from a first coefficient combination. The second luminance calculation block calculates a second luminance corresponding to the sum of a plurality of the primary color light components. Each of them is multiplied by a coefficient from a second coefficient combination. The correction-value calculation block calculates a luminance correction value according to the second luminance if the first luminance is greater than a threshold value. The subtraction block calculates a corrected luminance by subtracting the luminance correction value from the first luminance.
