Local dimming system and method adaptable to a backlight of a display

A local dimming system adaptable to a backlight of a display includes a light shape imitation (LSI) unit that receives a pulse-width modulation (PWM) value and provides a profile data for each block of the backlight; a profile analysis unit that generates an analytic mean value according to the profile data; and a diffusion compensation unit that compares the analytic mean value with a target mean value and compensates the PWM value for light diffusion according to a result of the comparison, thereby generating a compensated PWM value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to backlight dimming, and more particularly to a local dimming system and method adaptable to a light-emitting diode backlight of a liquid crystal display.

2. Description of Related Art

As liquid crystal displays (LCDs) do not produce light themselves, a backlight is required to provide illumination to the LCDs. The light source of the backlight may be composed of light-emitting diodes (LEDs).

In order to improve the contrast, a backlight dimming technique is adopted to dynamically control luminance of the backlight. Global dimming is one type of backlight dimming, in which luminance of entire display panel is controlled at the same time. The global dimming can substantially improve dynamic contrast between two consecutive frames. Local dimming is another type of backlight dimming, in which luminance of partial display panel within one frame is controlled. The local dimming can substantially improve static contrast.

Conventional dimming methods, particularly local dimming methods, suffer luminance unevenness and flickers. More importantly, conventional local dimming methods cannot effectively reduce power consumption. A need has arisen to propose a novel scheme to overcome disadvantages of conventional local dimming methods.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the embodiment of the present invention to provide a local dimming system and method adaptable to a light-emitting diode (LED) backlight of a liquid crystal display (LCD) capable of effectively compensating for light diffusion and substantially increasing a dynamic range.

According to one embodiment, a local dimming system adaptable to a backlight of a display includes a light shape imitation (LSI) unit, a profile analysis unit and a diffusion compensation unit. The LSI unit receives a pulse-width modulation (PWM) value and provides a profile data for each block of the backlight. The profile analysis unit generates an analytic mean value according to the profile data. The diffusion compensation unit compares the analytic mean value with a target mean value and compensates the PWM value for light diffusion according to a result of the comparison, thereby generating a compensated PWM value.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a block diagram illustrating a local dimming system100adaptable to a light-emitting diode (LED) backlight of a liquid crystal display (LCD) disclosed in a co-pending U.S. application Ser. No. 16/107,938, filed on Aug. 21, 2018 and entitled LOCAL DIMMING SYSTEM AND METHOD ADAPTABLE TO A BACKLIGHT OF A DISPLAY, assigned to the same assignee, the disclosure of which is incorporated herein by reference.

The local dimming system100may include a mean estimation unit11configured to receive an image and estimate a mean value thereof. The mean value may be estimated according to a histogram of the image. Specifically, the mean estimation unit11may include a maximum brightness unit111configured to determine maximum brightness of each pixel of the image regardless of colors (e.g., red, green and blue).

The mean estimation unit11may include a histogram unit112configured to generate a histogram mean value according to the histogram of the image. The mean estimation unit11may include a weighting control unit113configured to generate the mean value.

The local dimming system100may include a pulse-width modulation (PWM) gain control unit12configured to generate PWM gain value according to the mean value (from the mean estimation unit11). The PWM gain value is used to control power supplied to the LED backlight. The larger the PWM gain value is, the higher the total power supplied to the LED backlight.

The local dimming system100may include a spatial filter13configured to be performed on the mean values in spatial domain to enhance the PWM gain values, thereby generating enhanced PWM gain values. The local dimming system100may include a scene change detection unit14configured to detect scene change according to the histogram mean value (from the histogram unit112).

The local dimming system100may include a temporal filter15configured to be performed in temporal domain according to the enhanced PWM gain value (from the spatial filer13) and a result of scene change detection (from the scene change detection unit14) for the purpose of adjusting dimming speed and preventing flicker (i.e., flickerless), thereby generating PWM values.

The local dimming system100may include a light shape imitation (LSI) unit16configured to generate luminance gain according to the PWM value (from the temporal filter15), and include a pixel compensation unit17configured to perform pixel compensation on the image according to the luminance gain (from the LSI unit16), thereby resulting in a compensated image.

The local dimming system100may include an error diffusion unit18configured to perform error diffusion on the compensated image. The error diffusion may be performed by truncating at least one least significant bit (LSB), for example, truncating 14 bits to 12 bits, of the compensated image. Accordingly, contour effect may be substantially reduced to improve picture quality.

FIG. 2shows a block diagram illustrating a local dimming system200adaptable to a light-emitting diode (LED) backlight21of a liquid crystal display (LCD) according to one embodiment of the present invention. The blocks of the local dimming system200may be implemented by hardware (e.g., a digital image processor), software (e.g., computer programs) or their combinations.FIG. 3shows a flow diagram illustrating a local dimming method300adaptable to a light-emitting diode (LED) backlight21of a liquid crystal display (LCD) according to one embodiment of the present invention.

As the light emitted by the LED is generally not collimated, a profile data representing illumination irradiated by one block (corresponding to one or more LEDs) of the backlight21, may ordinarily diffuse or spread into neighbor blocks. As a result, a dynamic range of the image may be substantially reduced. For example, a bright spot is dim, while a dark spot is not dark sufficiently.FIG. 4Aschematically shows a cross-sectional view of the backlight21ofFIG. 2and associated light diffusion curves of the LEDs of the backlight21.FIG. 4Bshows a top view of a backlight illustrating a non-diffused light profile generated by a block of ideal LEDs, andFIG. 4Cshows a top view of the backlight21ofFIG. 2illustrating a diffused light profile generated by a block of real LEDs. The local dimming system200ofFIG. 2is capable of compensating for light diffusion caused by the real LEDs, thereby substantially increasing the dynamic range.

In the embodiment, the local dimming system200may include a light shape imitation (LSI) unit16that provides a profile data for each block of the backlight21(step31). As described above in conjunction withFIG. 1, the LSI unit16is coupled to receive a pulse-width modulation (PWM) value (for example, from the temporal filter15).

The local dimming system200may include a profile analysis unit22coupled to receive the profile data (from the LSI unit16) and configured to generate an analytic mean value according to the profile data (step32). The analytic mean value may be generated by a method being the same as or similar to the mean value generated by the mean estimation unit11or the enhanced PWM gain value generated by the spatial filter13in conjunction withFIG. 1as disclosed specifically in the co-pending U.S. application as mentioned above.

The local dimming system200of the embodiment may include a diffusion compensation unit23configured to compare the analytic mean value with a target mean value (which may be derived from the image inputted to the local dimming system200) (step33), and to compensate the PWM value for light diffusion according to a result of the comparison (between the analytic mean value and the target mean value), thereby generating a compensated PWM value (step34). Specifically, in the embodiment, a ratio of the target mean value to the analytic mean value (for a block of the backlight21) is first determined, and the PWM value is then multiplied by the determined ratio (as PWM compensation gain) to generate the compensated PWM value. Finally, the compensated PWM value (from the diffusion compensation unit23) is sent to a PWM compensation gain unit20, which may controllably turn on the corresponding LED of the backlight21(step35).

FIG. 5shows exemplary determined ratios associated with blocks of the backlight21. In this example, some PWM values are greatly increased by large ratios respectively in the blocks with slanted lines, while some PWM values are greatly reduced by small ratios respectively in the dotted blocks. Accordingly, the input image may be effectively compensated with enhanced dynamic range.