1. Field of the Invention
The present invention relates to a display device which lowers the chroma of a display image, thereby to attain the power saving of backlight.
2. Description of the Related Art
It is desired of a liquid-crystal display device to reduce the power of backlight for power saving. It is stated in JP-A-11-65531 that, in order to attain lowered power with the degradation of an image suppressed, image data are adjusted so as to raise the transmission factor of a liquid-crystal display screen, whereupon the luminance of the backlight is lowered to a corresponding degree. Concretely, using the maximum gray level or histogram of the image data, a gray level at which cumulative frequencies from the maximum gray level arrive at a fixed rate is detected by a data analysis unit, and this gray level is outputted as a threshold gray level. A backlight control unit reduces the backlight luminance to a display luminance at the detected threshold gray level. In interlocking with the backlight control unit, a data adjustment unit converts the image data whose gray levels are from “0” to the threshold gray level, into digital signals of full scale. Thus, it is intended to attain the lowered power without degrading an image of high luminance and high chroma.
In case of the image of high luminance/high chroma, however, the threshold gray level becomes high, and hence, the effect of reducing the luminance of the backlight is low. Especially in a case where the luminance of characters is high is a game screen or the like, the threshold gray level becomes high even when the luminance of the image itself is low, so that the backlight luminance cannot be reduced. Therefore, a power reduction effect based on the backlight adjustment interlocked with the image becomes low on the average, in a display device in a field where the image of high luminance/high chroma is outputted in many chances.
USPTO Backgrounds
USPTO Backgrounds