In general, in liquid crystal display apparatuses that perform color display, one pixel is divided into three sub-pixels: a red pixel provided with a color filter that transmits red light, a green pixel provided with a color filter that transmits green light, and a blue pixel provided with a color filter that transmits blue light. Although the color filters provided in the three sub-pixels enable the color display, about two-thirds of backlight light with which the liquid crystal panels are irradiated are absorbed by the color filters. As a result, there is a problem in that the color filter type liquid crystal display apparatuses have low light use efficiency. Accordingly, color-field sequential liquid crystal display apparatuses that perform the color display without using the color filters attract attention.
In the common liquid crystal display apparatuses that adopt the field sequential method, one frame period during which one screen is displayed is divided into three fields. Although each field is also called a sub-frame, the term “field” is consistently used in the following description. For example, one frame period is divided into a field (red field) in which a red screen is displayed on the basis of red components of an input image signal, a field (green field) in which a green screen is displayed on the basis of green components of the input image signal, and a field (blue field) in which a blue screen is displayed on the basis of blue components of the input image signal. Displaying each primary color in the above manner causes a color image to be displayed in the liquid crystal panel. Since the color display is performed in the above manner, it is not necessary to provide the color filters in the color-field sequential liquid crystal display apparatuses. Accordingly, the light use efficiency of the color-field sequential liquid crystal display apparatuses is about three times higher than that of the color filter type liquid crystal display apparatuses. Consequently, the color-field sequential liquid crystal display apparatuses are appropriate for increase in luminance and reduction in power consumption.
In this description, a combination of the value of data about the red components, the value of data about the green components, and the value of data about the blue components is referred to as “an RGB combination.” For example, “R=128, G=32, and B=255” is an example of one RGB combination. In this example, the value of data about the red components has a value of 128, the value of data about the green components has a value of 32, and the value of data about the blue components has a value of 255. The value of data is typically a gradation value.
In the liquid crystal display apparatuses, image display is performed by controlling the transmittance of each pixel with voltage (liquid crystal applied voltage). It takes several milliseconds from a time when writing of data into each pixel (application of the voltage) is started to a time when the transmittance at the pixel reaches a target transmittance. Accordingly, in the color-field sequential liquid crystal display apparatuses, a backlight of the corresponding color is switched from a turned-off state to a turned-on state after the liquid crystal responds in each field to some extent.
In the liquid crystal display apparatuses, sufficient image quality may not be achieved, for example, in display of a movie due to a low response speed of the liquid crystal. Accordingly, a driving method called overdrive driving (overshoot driving) has hitherto been adopted as a countermeasure against the low response speed of the liquid crystal. The overdrive driving is a driving method in which drive voltage that is higher than predetermined gradation voltage corresponding to the value of data about the input image signal of the current frame or drive voltage that is lower than the predetermined gradation voltage corresponding to the value of data about the input image signal of the current frame is supplied to the liquid crystal panel depending on a combination of the value of data about the input image signal of the first previous frame and the value of data about the input image signal of the current frame. In other words, in the overdrive driving, compensation is performed so as to enhance the temporal change (not the special change) of the value of data for the input image signal. Adopting such overdrive driving causes the liquid crystal to respond so that the transmittance substantially reaches a target value (target transmittance) in each field in the current color filter type liquid crystal display apparatuses.
The following Patent Literatures in Citation List are known in association with the invention in this description. PTL 1 discloses an invention related to a compensation operation of color impurity in a color sequential LCD image display apparatus. According to this invention, a signal of each color is compensated on the basis of a signal of a preceding color. For example, when the colors are displayed in the order of “blue, green, and red”, the signal of green is compensated on the basis of the signal of blue. In addition, PTL 2 discloses an invention related to color reproducibility in a time-division color liquid crystal display apparatus. According to this invention, scanning timing of a time-division three-primary-color light emitting apparatus is delayed by an amount corresponding to an optical response speed of the liquid crystal and a non-light-emitting period corresponding to the optical response time of the liquid crystal is provided. In writing of data into each pixel, gamma correction is performed, which is based on a result of comparison between data about the previous field (the first previous field of the current field) and data about the current field.
USPTO Backgrounds
USPTO Backgrounds