TWI677861B - Local dimming system adaptable to a backlight of a display - Google Patents

Abstract

An area dimming system suitable for a display backlight includes an average estimation unit that receives an image and estimates an average value thereof; a pulse width modulation gain control unit that generates a pulse width modulation gain value based on the average value; a spatial filter, It processes the complex average value in the spatial domain to enhance the complex pulse width modulation gain value, thereby generating an enhanced pulse width modulation gain value; the scene change detection unit, based on the histogram average value generated by the average estimation unit, detects Measuring scene change; time-domain filter, which executes in the time domain to generate a pulse width modulation value based on the results of enhancing the pulse width modulation gain value and detecting the scene change; a light shape simulation unit, which is based on the pulse width modulation value To generate a photometric gain; and a pixel compensation unit that performs pixel compensation of the image according to the photometric gain, thereby generating a compensated image.

Description

Area dimming system for display backlight

The invention relates to a backlight dimming, in particular to an area dimming system suitable for a light emitting diode backlight of a liquid crystal display.

A liquid crystal display (LCD) does not emit light by itself, and a backlight is required to provide illumination to the liquid crystal display. The light source of the backlight may include a light emitting diode (LED).

To enhance the contrast, backlight dimming technology is used to dynamically control the brightness of the backlight. Global dimming is one of the techniques for backlight dimming, which controls the brightness of the entire display panel at the same time. Global dimming can enhance dynamic contrast between adjacent frames. Local dimming is another backlight dimming technology that controls the brightness of a portion of the display panel of a single frame. Area dimming can enhance static contrast.

The conventional dimming method (especially the area dimming method) has the problems of luminance unevenness and flicker. More importantly, traditional area dimming methods cannot effectively reduce power consumption. Therefore, it is urgent to propose a novel mechanism to overcome the shortcomings of traditional regional dimming methods.

In view of the foregoing, one of the objectives of the embodiments of the present invention is to propose an area dimming system suitable for a light emitting diode backlight of a liquid crystal display, which can effectively reduce power consumption. In one embodiment, the area dimming system can adjust the dimming speed and avoid flicker.

According to an embodiment of the present invention, an area dimming system suitable for a display backlight includes an average estimation unit, a pulse width modulation gain control unit, a spatial filter, a scene change detection unit, a time domain filter, a light shape simulation unit, and pixel compensation. unit. The average estimation unit receives an image and estimates an average value thereof. The pulse width modulation gain control unit generates a pulse width modulation gain value according to the average value. The spatial filter processes the complex average value in the spatial domain to enhance the complex pulse width modulation gain value, thereby generating an enhanced pulse width modulation gain value. The scene change detection unit detects a scene change according to the histogram average value generated by the average estimation unit. The time-domain filter is executed in the time domain to generate a pulse width modulation value according to the result of enhancing the pulse width modulation gain value and detecting a scene change. The light shape simulation unit generates a photometric gain according to a pulse width modulation value. The pixel compensation unit performs pixel compensation of the image according to the photometric gain, thereby generating a compensated image.

The first figure shows a block diagram of an area dimming system 100 suitable for a light emitting diode backlight of a liquid crystal display according to an embodiment of the present invention. The blocks of the area dimming system 100 may be implemented using hardware (such as a digital image processor), software, or a combination thereof.

In this embodiment, the area dimming system 100 may include an average estimation unit 11 that receives an image and estimates an average value thereof. According to one of the features of this embodiment, the average value can be estimated from a histogram of the image. The average estimation unit 11 may include a maximum brightness unit 111 for determining the maximum brightness of each pixel of the image, but without distinction of colors (such as red, green, and blue). The schematic diagram of the second figure illustrates determining the maximum brightness of each pixel of the image. As illustrated in the second figure, the maximum brightness of each pixel (for example, v0 of pixel 0, v1 of pixel 1, etc.) is determined, and a bar graph as shown on the right hand side is displayed. From this, the arithmetic mean value (HGL _mean ) can be obtained as follows: Floor is a floor function whose output is less than or equal to the largest integer input.

The average estimation unit 11 may include a histogram unit 112 that generates a histogram average value based on the histogram of the image. The schematic diagram of the third figure illustrates histogram generation from an image to generate a histogram average. As illustrated in the third figure, the image is divided into a plurality of blocks, and a histogram like the right-hand side is constructed with its gray scale. These blocks may correspond to the light-emitting diodes of the backlight. Then, from the maximum gray level to the lowest gray level, the accumulated gray level count value is accumulated. When the preset gray level is reached, the corresponding gray level is set to the average histogram HGL _high , which can be expressed as follows: If Sn ≧ critical value, HGL _high = n

The average estimation unit 11 may include a weight control unit 113 for generating an average value. In this embodiment, the average value is generated based on the arithmetic mean HGL _mean and the histogram mean HGL _high . In one example, the average HGL _out can be expressed as follows: The max function outputs the maximum of the two inputs, and w ₁ and w ₂ represent weights.

The area dimming system 100 of this embodiment may include a pulse width modulation (PWM) gain control unit 12 that generates a pulse width modulation gain value according to an average value (of the average estimation unit 11). The pulse width modulation gain value is used to control the power provided to the light-emitting diode backlight. The larger the pulse width modulation gain value, the higher the total power provided to the light emitting diode backlight. The fourth graph A illustrates the relationship between the pulse width modulation gain value and the average value. In this example, the PWM gain value is linearly related to the average. The fourth graph B illustrates another relationship curve between the PWM gain value and the average value. In this example, the pulse width modulation gain value also has a linear relationship with the average value, but it rises gently at high average values. The fourth graph C illustrates another relationship curve between the pulse width modulation gain value and the average value. In this example, the pulse width modulation gain value has a non-linear relationship with the gamma correction of the average value. In this embodiment, the pulse width modulation gain value may be generated according to a lookup table generated in advance to save calculation time.

The area dimming system 100 of this embodiment may include a spatial filter 13 that processes the average HGL in the spatial domain to enhance the pulse width modulation gain value, thereby generating an enhanced pulse width modulation gain value. . The fifth graph A illustrates the pulse width modulation gain value, and the fifth graph B illustrates the elements of the spatial filter, which correspond to the pulse width modulation gain value of the fifth A graph. In an example, the spatial filter performs the operations shown in the fifth diagram A and the fifth diagram B to generate the enhanced pulse width modulation gain value HGL 'as follows: If HGL'_tmp1 ≧ 255 then HGL'_temp1 = 255 HGL'_tmp2 = Max (HGL0, HGL1,… HGL98) If HGL'_tmp <HGL then HGL '= HGL otherwise HGL' = HGL'_tmp

The area dimming system 100 of this embodiment may include a scene change detection unit 14 that detects a scene change based on the histogram average (of the histogram unit 112).

The area dimming system 100 of this embodiment may include a temporal filter 15 which is based on the enhanced pulse width modulation gain value (of the spatial filter 13) and the scene change detection (of the scene change detection unit 14). The measurement results are executed in the time domain to adjust the dimming speed and prevent flicker, thereby generating a pulse width modulation value.

According to another feature of this embodiment, the time domain filter 15 may provide a power constraint mode so that the pulse width modulation value may be limited to a maximum value. In this embodiment, the pulse width modulation values can be limited according to the sum of the pulse width modulation values, wherein the pulse width modulation values respectively correspond to the light-emitting diodes of the backlight.

The area dimming system 100 of this embodiment may include a light shape imitation unit 16 that generates a luminance gain according to a pulse width modulation value (of the time domain filter 15). The area dimming system 100 may further include a pixel compensation unit 17 that performs pixel compensation of the image according to the photometric gain (of the light shape simulation unit 16), thereby generating a compensated image. Photometric gain can be expressed as follows: Photometric gain = (photometric) ^{(-1 / r)} where r represents a gamma value.

In one embodiment, in the peaking mode, the pulse width modulation value is weighted and then fed to the light shape simulation unit 16. Assuming the current in the normal (or original) mode is original_I, the current in the peak mode is peak_I, and the pulse width modulation value in the normal mode is original_PWM, then the pulse width modulation value in the peak mode is Peak_PWM can be expressed as follows: (Peak_I / Original_I) represents the peak weight.

The area dimming system 100 of this embodiment may include an error diffusion unit 18 for performing error diffusion on the compensated image. Error diffusion can be achieved by truncating at least one least significant bit (LSB). For example, a 14-bit compensation image is deleted into 12 bits. This can effectively reduce the contour effect to improve the image quality.

The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of patent application of the present invention; all other equivalent changes or modifications made without departing from the spirit disclosed by the invention should be included in the following Within the scope of patent application.

100‧‧‧area dimming system

11‧‧‧ average estimation unit

111‧‧‧Maximum brightness unit

112‧‧‧ Histogram Unit

113‧‧‧weight control unit

12‧‧‧Pulse width modulation gain control unit

13‧‧‧spatial filter

14‧‧‧Scene change detection unit

15‧‧‧Time Domain Filter

16‧‧‧light shape simulation unit

17‧‧‧pixel compensation unit

18‧‧‧ Error Diffusion Unit

HGL‧‧‧ Histogram Grayscale

Mean‧‧‧ average

The first figure shows a block diagram of an area dimming system suitable for a light emitting diode backlight of a liquid crystal display according to an embodiment of the present invention. The schematic diagram of the second figure illustrates determining the maximum brightness of each pixel of the image. The schematic diagram of the third figure illustrates histogram generation from an image to generate a histogram average. The fourth graphs A to C illustrate the relationship between the pulse width modulation gain value and the average value. The fifth A diagram illustrates the pulse width modulation gain value. The fifth diagram B illustrates the elements of the spatial filter, which correspond to the pulse width modulation gain values of the fifth diagram A.

Claims (17)

An area dimming system suitable for a display backlight includes: an average estimation unit that receives an image and estimates an average value of its brightness; a pulse width modulation gain control unit that generates a pulse width modulation based on the average value A variable gain value; a spatial filter that processes the plurality of averages in the spatial domain to enhance the complex pulse width modulation gain value, thereby generating an enhanced pulse width modulation gain value; a scene change detection unit, which is based on the A histogram average value generated by an average estimation unit to detect scene changes; a time-domain filter that executes in the time domain to generate pulse widths based on the enhanced pulse width modulation gain value and the results of the detected scene changes A modulation value; a light shape analog unit that generates a photometric gain according to the pulse width modulation value; and a pixel compensation unit that performs pixel compensation of the image according to the photometric gain, thereby generating a compensated image. According to the area dimming system applicable to the backlight of the display according to the first patent application scope, the average value is estimated based on the histogram of the image. The area dimming system suitable for a display backlight according to item 1 of the scope of the patent application, wherein the backlight includes a light-emitting diode backlight. According to the area dimming system applicable to the backlight of the display according to item 3 of the scope of the patent application, the average estimation unit includes a maximum brightness unit, which determines the maximum brightness of each pixel of the image to obtain an arithmetic average. According to the area dimming system for display backlight described in item 4 of the scope of the patent application, the average estimation unit includes a histogram unit that generates an average histogram based on the histogram of the image. According to the area dimming system applicable to the backlight of the display according to item 5 of the scope of the patent application, the generation of the average value of the histogram includes the following steps: dividing the image into a plurality of blocks, and constructing the histogram with its gray scale, These blocks correspond to the light-emitting diodes of the backlight; and from the maximum grayscale to the lowest grayscale, the accumulated grayscale counts are accumulated. When the preset threshold is reached, the corresponding grayscale is set to the average value of the histogram. According to the area dimming system for display backlights described in item 4 of the scope of the patent application, the average estimation unit includes a weight control unit that generates the average value based on the arithmetic average value and the histogram average value. The area dimming system applicable to the backlight of a display according to item 7 of the scope of the patent application, wherein the average value is the maximum value of the arithmetic mean value and a weighted sum, and the weighted sum is the arithmetic mean value and the histogram The weighted sum of the averages. According to the area dimming system applicable to the backlight of the display according to item 3 of the scope of the patent application, the pulse width modulation gain value is used to control the power provided to the light emitting diode backlight, and the pulse width modulation gain value is more Larger, the higher the power provided to the light-emitting diode backlight. According to the area dimming system applicable to the backlight of the display according to the first item of the scope of the patent application, the pulse width modulation gain value is generated according to a lookup table, which includes a plurality of the pulse width modulation gain value and a corresponding average value. According to the area dimming system applicable to the backlight of the display according to item 3 of the scope of the patent application, the time-domain filter provides a power limiting mode, so that the pulse width modulation value is limited to a maximum value. According to the area dimming system applicable to the backlight of the display according to item 11 of the scope of the patent application, it limits the pulse width modulation value according to the sum of the pulse width modulation values, wherein the pulse width modulation values respectively correspond to the Backlit light-emitting diode. According to the area dimming system applicable to the backlight of the display according to the first item of the patent application scope, in the peak mode, the pulse width modulation value is weighted and then fed to the light shape simulation unit. According to the area dimming system applicable to the backlight of the display according to item 13 of the scope of the patent application, the pulse width modulation value is peak_PWM in peak mode, which is expressed as follows: The current in the normal mode is original_I, the current in the peak mode is peak_I, and the pulse width modulation value in the normal mode is original_PWM. (Peak_I / original_I) represents the peak weight. According to the area dimming system applicable to the backlight of the display according to item 1 of the scope of the patent application, it further includes an error diffusion unit that performs error diffusion on the compensated image. According to the area dimming system applicable to the backlight of the display according to item 15 of the scope of the patent application, the error diffusion unit performs the error diffusion by deleting at least one least significant bit of the compensation image. The area dimming system suitable for a display backlight according to item 1 of the scope of the patent application, wherein the display includes a liquid crystal display.