Method and device for driving an image display apparatus and controlling a display backlight based on content

1. A method for driving an image display device comprising at least one backlight lamp and a display screen, the method comprising the acts of:

receiving an image data signal;

based on the image data signal, calculating a content-related backlight control signal for the backlight lamp for setting intensity of the backlight lamp;

generating an average signal that represents a time-average of power consumed by the backlight lamp;

comparing the average signal with a reference signal;

based on the calculated content-related backlight control signal, taking into account result of the said comparing act, generating an actual backlight control signal for the backlight lamp,

wherein the act of generating the actual backlight control signal comprises the acts of:

setting a maximum value for the actual backlight control signal;

defining a first transition value and a second transition value higher than or equal to the first transition value;

generating the actual backlight control signal equal to ξ times the calculated content-related backlight control signal if the calculated content-related backlight control signal is less than the first transition value, wherein ξ is a predetermined factor;

generating the actual backlight control signal equal to the maximum value if the calculated content-related backlight control signal is higher than the second transition value;

generating the actual backlight control signal to have a value lower than ξ times the calculated content-related backlight control signal and lower than the maximum value if the calculated content-related backlight control signal is between the first transition value and the second transition value, and

increasing the maximum value when the average signal is lower than the reference signal.

2. The method according to claim 1 , wherein, if the image data signal represents dark scenes, the backlight is dimmed, whereas if the image data signal represents bright scenes, the backlight is boosted;

wherein the amount of boost is limited such that the time-average of the power consumed by the backlight lamp does not exceed a predetermined level.

3. The method according to claim 1 , wherein ξ is equal to 1.

4. The method according to claim 1 , wherein, between the first transition value and the second transition value, a function that describes a relationship between the generated actual backlight control signal and the calculated content-related backlight control signal has a second derivative that is always negative.

5. The method according to claim 1 , wherein the function that describes the relationship between the generated actual backlight control signal and the calculated content-related backlight control signal is a continuous function.

6. The method according to claim 1 , wherein the function that describes the relationship between the generated actual backlight control signal and the calculated content-related backlight control signal can be continuously differentiated.

7. The method according to claim 1 , wherein, if the average signal is higher than the reference signal, the maximum value is reduced.

8. The method according to claim 1 , wherein the maximum value is proportional to a difference between the reference signal and the average signal.

9. The method according to claim 1 , wherein, at a certain time, the average signal represents power actually consumed by the backlight lamp averaged over a time period with a predetermined duration immediately before said time.

10. The method according to claim 1 , further comprising the acts of:

based on the image data signal, generating a screen control signal for the display screen;

if the screen control signals of an image are within a range lower than a maximally possible value, increasing the screen control signals while decreasing the calculated content-related backlight control signal.

11. A display apparatus, comprising an image display device including at least one backlight lamp and a display screen, the apparatus comprising a controller having:

a light output coupled to the backlight lamp for providing a content-related backlight control signal,

a pixel control output coupled to the display screen for providing pixel control signals;

an image input for receiving an image data signal,

a reference input for receiving a reference signal,

a power average input for receiving an average signal; and

a calculator configured to calculate the average signal representing a time-average of power consumption by the backlight lamp, the calculator being coupled to the power average input of the controller;

wherein the controller is configured to perform the acts of:

receiving the image data signal;

based on the image data signal, calculating the content-related backlight control signal for the backlight lamp for setting intensity of the backlight lamp;

generating the average signal;

comparing the average signal with the reference signal to form a comparison result;

based on the calculated content-related backlight control signal and the comparison result, generating an actual backlight control signal for the backlight lamp,

wherein the act of generating the actual backlight control signal comprises the acts of:

setting a maximum value for the actual backlight control signal;

defining a first transition value and a second transition value higher than or equal to the first transition value;

generating the actual backlight control signal equal to ξ times the calculated content-related backlight control signal if the calculated content-related backlight control signal is less than the first transition value, wherein ξ is a predetermined factor;

generating the actual backlight control signal equal to the maximum value if the calculated content-related backlight control signal is higher than the second transition value;

generating the actual backlight control signal to have a value lower than ξ times the calculated content-related backlight control signal and lower than the maximum value if the calculated content-related backlight control signal is between the first transition value and the second transition value, and

increasing the maximum value when the average signal is lower than the reference signal.

12. The display according to claim 11 , wherein said calculator is incorporated in a feedback loop having an input coupled to the light output of the controller.