1. Field of the Invention
The present invention relates to a technique of determining a driving parameter for overdrive of a liquid crystal display device.
2. Description of the Related Art
Recently, liquid crystal display devices have been used as TV receivers and the display devices of PCs. However, in a liquid crystal display device, the response speed of the liquid crystal is relatively low until actual display with respect to the change rate (e.g., frame rate) of an input video signal, and hence an afterimage can be generated when, for example, a moving image is displayed. As a driving method for improving the response speed of a liquid crystal display device, there has been proposed a so-called overdrive driving method of correcting and outputting the video signal of the current display frame in accordance with a combination of a video signal of a display frame (current display frame) as a current display target and the video signal of the immediately preceding display frame (for example, Japanese Patent No. 3305240).
In addition, Japanese Patent Laid-Open No. 2001-343956 discloses a method of enhancing the effect of improving liquid crystal response speed by driving one frame upon dividing it into fields, and performing overdrive driving for the first field.
FIG. 10 is a block diagram for explaining an overdrive driving circuit. Referring to FIG. 10, reference numeral 1000 denotes an overdrive correction processing unit; 120, a frame memory; and 110, a display output unit. The overdrive correction processing unit 1000 includes a correction amount determination unit 1001, a correction table 1002, and a correction amount adding unit 1003.
The overdrive correction processing unit 1000 receives the video signal of the current frame and the video signal of the immediately preceding frame stored in the frame memory 120. The correction amount determination unit 1001 calculates a correction amount in accordance with a combination of the signal levels of the two frames. If, for example, the video signal level of the current frame is higher than that of the immediately preceding frame, the correction amount determination unit 1001 calculates a correction amount so as to drive the liquid crystal panel at a liquid crystal driving voltage higher than a normal driving voltage. In contrast, if the video signal level of the current frame is lower than that of the immediately preceding frame, the correction amount determination unit 1001 calculates a correction amount so as to drive the liquid crystal panel at a liquid crystal driving voltage lower than the normal liquid crystal driving voltage.
The correction amount determination unit 1001 reads out a correction amount corresponding to a combination of video signal levels by referring to the correction table 1002. Note that only representative combinations of video signal levels may be stored in the correction table 1002, and other combinations may be calculated by using an interpolation function. The data to be stored in the correction table 1002 are determined based on the result obtained by measuring a liquid crystal response speed for each signal level combination.
The correction amount adding unit 1003 adds or subtracts the correction amount determined by the correction amount determination unit 1001 to or from the video signal of the current frame. The display output unit 110 converts the corrected input video signal into a liquid crystal panel driving signal.
It is known that a liquid crystal response speed changes depending on an operating environment such as a temperature. That is, depending on an operating environment, the liquid crystal response speed which is set when data to be stored in the correction table 1002 is determined differs from the liquid crystal response speed of an actually used display device. In this case, a calculated overdrive driving correction amount is not an appropriate value, and hence the liquid crystal response speed cannot be sufficiently improved. In addition, an edge portion of a moving image is unnaturally colored.
Japanese Patent Laid-Open No. 2005-70799 discloses a liquid crystal display device which stops overdrive driving based on an instruction from a user or changes the enhancement conversion degree. In addition, Japanese Patent Laid-Open No. 2006-243325 discloses a liquid crystal display device which is provided with an arithmetic circuit so as to reduce a correction table to be used when a correction amount is to be changed in accordance with the temperature of the liquid crystal display device, an instruction from the user, the characteristics of an image, and the like.
When the correction amount for overdrive driving is to be adjusted by user operation, the user may adjust the correction amount without specifically knowing what kind of image a target image is. In addition, the user may set a correction amount with a purpose different from the primary purpose of implementing overdrive driving. Setting an inappropriate correction amount in this manner will lead to problems such as coloring of an edge portion of a moving image and an increase in noise.
The present invention provides a technique of allowing a user to more easily set a correction amount in overdrive driving of a liquid crystal display device.