Patent Grant
8334834
1. Field of the Invention
The present invention generally relates to backlight control, and more particularly to a backlight control system and method using an overdrive lookup table.
2. Description of the Prior Art
Backlight is used to illuminate a flat panel display, such as a liquid crystal display (LCD), from the back or side of the flat panel display. The light source may be a cold cathode fluorescent lamp (CCFL), a light-emitting diode (LED) or another light source.
A constant backlight is the backlight that outputs even and constant light no matter how the image data or the ambient light has been changed. The constant backlight approach has poor dynamic contrast. In order to increase the contrast, a dynamic backlight (DBL) is thus disclosed to dynamically or adaptively adjust (overall or respective portions of) the backlight brightness in accordance with image data distribution.
Nevertheless, a normal cold cathode fluorescent lamp (CCFL) has a low response time. In other words, the CCFL requires a period of time to reach target brightness, and therefore the change of brightness of the backlight usually lags behind changes in the backlight driving signal, such as a pulse-width-modulation (PWM) duty signal. The low response-time problem may only be solved by replacing the normal but low-price CCFL with a fast-response but expensive CCFL. However, such solution is not practical to mass production considering the cost and the acceptance of general users.
For the reason that conventional backlight, particularly the dynamic backlight, could not effectively respond conforming to the requirement, a need has arisen to propose a novel dynamic backlight control scheme having faster response time without sacrificing the cost.
In view of the foregoing, it is an object of the present invention to provide a backlight control system and method that increases response time without substantially increasing the cost.
According to one embodiment, an overdrive device modifies a backlight duty signal according to a current-frame backlight duty signal and a previous-frame backlight duty signal. In the embodiment, the overdrive device is implemented by a lookup table that outputs the modified backlight duty signal. The backlight driven by the modified backlight duty signal then emits light to a display panel, thereby increasing response time of the backlight.
In the illustrated embodiment, a lookup table, such as exemplified in, but not limited to, the following Table 1 is provided (step 20). The lookup table may comprise, for example, an overdrive table that outputs an overdrive backlight duty signal (BL duty) based on a current backlight duty signal and a previous backlight duty signal, which is provided by and stored in a buffer 12. The backlight duty signal (BL duty) may be a pulse-width-modulation (PWM) signal with a pulse width proportional to the required backlight illumination.
In Table 1, the vertical axis represents the previous-frame backlight duty signal, and the horizontal axis represents the current-frame backlight duty signal. The values shown in Table 1 are provided by way of example, but not limitation, for an eight-bit system. Each value shown in Table 1 corresponds a duty cycle equal to “value/255”. For example, the value “59” in the table corresponds to a duty cycle, such as a backlight PWM duty cycle, of 23% (=59/255).
The current-frame backlight duty is compared with the previous-frame backlight duty (step 21), and the corresponding output of the overdrive table is the overdrive backlight duty.
In a case where the previous-frame backlight duty is greater than the current-frame backlight duty (i.e., DN-1>DN), a magnitude D′N smaller than the expected DN is thus retrieved as the output overdrive backlight duty (step 22B). When the previous-frame backlight duty is equal or approximately equal to the current-frame backlight duty (i.e., DN-1=DN), a magnitude D′N the same as the expected DN is thus retrieved as the output overdrive backlight duty (step 22C).
The generated overdrive backlight duty signal is then fed to a backlight or backlight module 14 to dynamically control the on and off of the light emitting elements, such as a cold cathode fluorescent lamp (CCFL), low-speed light-emitting diode (LED) or other light source in the backlight 14. The backlight 14 accordingly provides the emitted light to a display panel 16 (step 23).
According to the described embodiment of the present invention, the dynamic backlight 14 has a response time that is faster than a conventional backlight without overdriving. The present invention thus provides means for mass producing a backlight, particularly, a dynamic backlight, that possesses a faster response time without a commensurate increase in cost.
Although specific embodiments have been illustrated and described, it will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the present invention, which is intended to be limited solely by the appended claims.
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| Number | Date | Country | |
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