Display device and driving method thereof

1. A display device comprising:

a set period setting unit which sets, as a set time, a time for which a set period elapses from a time at which a first area included in an input image is detected as a still area; and

a gain generator which gradually decreases an initial level of a gain value down to a saturation level having a lowest value of the gain value from the set time,

wherein the set period setting unit differently sets the saturation level of the gain value and a final level of the gain value, corresponding to grayscale values of the first area and a load value of the input image,

wherein the load value is an average value of grayscale values of an entirety of an area of the input image, and

wherein the final level is the gain value corresponding to a time at which it is detected that the first area is not the still area.

2. The display device of claim 1 , wherein the gain generator increases the gain value up to the final level, after a predetermined period elapses from a time at which the gain value reaches the saturation level, and

wherein the predetermined period is from the set time to the time at which it is detected that the first area is not the still area.

3. The display device of claim 2 , wherein the set period setting unit:

calculates histogram values of pixels constituting the first area by the grayscale values of the first area; and

calculates the histogram value of a pixel having a largest grayscale value among the pixels.

4. The display device of claim 3 , wherein the set period setting unit:

sets the set period to become shorter as the histogram value becomes larger; and

sets the set period to become longer as the histogram value becomes smaller.

5. The display device of claim 4 , wherein the gain generator:

sets the final level of the gain value to become smaller as the histogram value becomes larger; and

sets the final level of the gain value to become larger as the histogram value becomes smaller.

6. The display device of claim 5 , wherein the gain generator:

sets the saturation level of the gain value to become larger as the histogram value becomes larger; and

sets the saturation level of the gain value to become smaller as the histogram value becomes smaller.

7. The display device of claim 6 , wherein the set period setting unit:

sets the set period to become longer as the load value of the input image becomes larger; and

sets the set period to become shorter as the load value of the input image becomes smaller.

8. The display device of claim 7 , wherein the gain generator:

sets the final level of the gain value to become larger as the load value becomes larger; and

sets the final level of the gain value to become smaller as the load value becomes smaller.

9. The display device of claim 8 , wherein the gain generator:

sets the saturation level of the gain value to become smaller as the load value becomes larger; and

sets the saturation level of the gain value to become larger as the load value becomes smaller.

10. The display device of claim 9 , further comprising:

a still area detector which detects the first area of the input image as the still area, and provide the grayscale values of the first area; and

a load calculator which calculates, as the load value, an average value of the grayscale values of the entirety of the area of the input image.

11. A method for driving a display device including a set period setting unit and a gain generator, the method comprising:

setting, by the set period setting unit, as a set time, a time for which a set period elapses from a time at which a first area included in an input image is detected as a still area; and

gradually decreasing, by the gain generator, an initial level of a gain value down to a saturation level having a lowest value of the gain value from the set time,

wherein the set period setting unit differently set the saturation level of the gain value and a final level of the gain value, corresponding to grayscale values of the first area and a load value of the input image,

wherein the load value is an average value of grayscale values of an entirety of an area of the input image, and

wherein the final level is the gain value corresponding to a time at which it is detected that the first area is not the still area.

12. The method of claim 11 , wherein the gradually decreasing the initial level of the gain value down to the saturation level of the gain value includes increasing, by the gain generator, the gain value up to the final level, after a predetermined period elapses from a time at which the gain value reaches the saturation level, and

wherein the predetermined period is from the set time to the time at which it is detected that the first area is not the still area.

13. The method of claim 12 , wherein the setting, as the set time, the time for which the set period elapses from the time at which the first area included in the input image is detected as the still area includes:

calculating, by the set period setting unit, histogram values of pixels constituting the first area by the grayscale values of the first area; and

calculating, by the set period setting unit, the histogram value of a pixel having a largest grayscale value among the pixels.

14. The method of claim 13 , wherein the setting, as the set time, the time for which the set period elapses from the time at which the first area included in the input image is detected as the still area includes:

setting, by the set period setting unit, the set period to become shorter as the histogram value becomes larger; and

setting, by the set period setting unit, the set period to become longer as the histogram value becomes smaller.

15. The method of claim 14 , wherein the gradually decreasing the initial level of the gain value down to the saturation level of the gain value includes:

setting, by the gain generator, the final level of the gain value to become smaller as the histogram value becomes larger; and

setting, by the gain generator, the final level of the gain value to become larger as the histogram value becomes smaller.

16. The method of claim 15 , wherein the gradually decreasing the initial level of the gain value down to the saturation level of the gain value includes:

setting, by the gain generator, the saturation level of the gain value to become larger as the histogram value becomes larger; and

setting, by the gain generator, the saturation level of the gain value to become smaller as the histogram value becomes smaller.

17. The method of claim 16 , wherein the setting, as the set time, the time for which the set period elapses from the time at which the first area included in the input image is detected as the still area includes:

setting, by the set period setting unit, the set period to become longer as the load value of the input image becomes larger; and

setting, by the set period setting unit, the set period to become shorter as the load value of the input image becomes smaller.

18. The method of claim 17 , wherein the gradually decreasing the initial level of the gain value down to the saturation level of the gain value includes:

setting, by the gain generator, the final level of the gain value to become larger as the load value becomes larger; and

setting, by the gain generator, the final level of the gain value to become smaller as the load value becomes smaller.

19. The method of claim 18 , wherein the gradually decreasing the initial level of the gain value down to the saturation level of the gain value includes:

setting, by the gain generator, a middle level of the gain value to become smaller as the load value becomes larger; and

setting, by the gain generator, the middle level of the gain value to become larger as the load value becomes smaller.

20. The method of claim 19 , wherein the display device further includes a still area detector and a load calculator, and

wherein the method further comprises:

detecting, by the still area detector, the first area of the input image as the still area, and providing the grayscale values of the first area; and

calculating, the load calculator, as the load value, an average value of the grayscale values of the entirety of the area of the input image.