TW202013332A - Local dimming system adaptable to a backlight of a display - Google Patents

Abstract

A local dimming system includes a mean estimation unit that estimates a mean value of an image; a PWM gain control unit that generates a PWM gain value according to the mean value; a spatial filter that performs on a plurality of the mean values in spatial domain to enhance a plurality of the PWM gain values, thereby generating enhanced PWM gain values; a scene change detection unit that detects scene change according to a histogram mean value generated by the mean estimation unit; a temporal filter that performs in temporal domain according to the enhanced PWM gain values and a result of scene change detection, thereby generating PWM values; a light shape imitation (LSI) unit that generates luminance gain according to the PWM value; and a pixel compensation unit that performs pixel compensation on the image according to the luminance gain, thereby resulting in a compensated image.

Description

Area dimming system suitable 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.

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

To improve contrast, backlight dimming technology is used to dynamically control the brightness of the backlight. Global dimming is one of the techniques of backlight dimming, which simultaneously controls the brightness of the entire display panel. Global dimming can improve the dynamic contrast between adjacent frames. Local dimming is another backlight dimming technology that controls the brightness of a portion of the display panel in a single frame. Area dimming can improve 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, there is an urgent need to propose a novel mechanism to overcome the shortcomings of traditional area dimming methods.

In view of the above, one of the objectives of the embodiments of the present invention is to provide a regional 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 the image and estimates its average value. The pulse width modulation gain control unit generates the 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 the scene change according to the average value of the histogram generated by the average estimation unit. The time domain filter is executed in the time domain according to the enhanced pulse width modulation gain value and the result of detecting scene changes to generate the pulse width modulation value. The light shape simulation unit generates the photometric gain according to the pulse width modulation value. The pixel compensation unit performs pixel compensation of the image according to the photometric gain, thus 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 can be implemented using hardware (such as a digital image processor), software, or a combination thereof.

其中floor代表取整函數(floor function)，其輸出小於或等於輸入的最大整數。In this embodiment, the area dimming system 100 may include an average estimation unit 11 that receives images and estimates the average value. According to one of the features of this embodiment, the average value can be estimated based on the 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 regardless of color (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. By this, the arithmetic mean (arithmetic mean value) HGL _mean can be obtained as follows:

Where floor represents a rounding function (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 based on the histogram of the image. The schematic diagram of the third figure illustrates generating the histogram average based on the histogram of the image. As illustrated in the third figure, the image is divided into complex blocks, and the gray scale is used to construct a histogram on the right hand side. These blocks can correspond to the light-emitting diodes of the backlight. Then, from the maximum gray scale to the lowest gray scale, the count value of the gray scale is accumulated. When the preset threshold is reached, the corresponding gray scale is set to the histogram average HGL _high , which can be expressed as follows: If S31+S30+...+ Sn≧critical value then HGL _high =n

其中max函數輸出二個輸入當中的最大值，w₁ 、w₂ 代表權重。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 average value HGL _mean and the histogram average value HGL _high . In an example, the average value HGL _out can be expressed as follows:

The max function outputs the maximum value 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, which generates a pulse width modulation gain value according to the 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 pulse width modulation gain value has a linear relationship with the average value. The fourth graph B illustrates another relationship curve between the pulse width modulation gain value and the average value. In this example, the pulse width modulation gain value is also linear with the average value, but it rises gently at the high average value. The fourth graph C illustrates another relationship between the pulse width modulation gain value and the average value. In this example, the pulse width modulation gain value and the average value have a non-linear relationship of gamma correction. In this embodiment, the pulse width modulation gain value can be generated according to a lookup table generated in advance to save calculation time.

若HGL’_tmp1≧255 則HGL’_temp1=255 HGL’_tmp2=Max(HGL0, HGL1, … HGL98)

若HGL’_tmp＜HGL 則HGL’=HGL 否則HGL’=HGL’_tmpThe regional 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 diagram A illustrates the pulse width modulation gain value, and the fifth diagram B illustrates the elements of the spatial filter, which correspond to the pulse width modulation gain value of the fifth diagram A. In one example, the spatial filter performs the examples shown in Figures 5A and 5B 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 scene changes based on the average of the histogram (of the histogram unit 112).

The regional dimming system 100 of the present embodiment may include a temporal filter 15 (temporal filter) according to 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 result is 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 the maximum value. In this embodiment, the pulse width modulation values can be limited according to the sum of the pulse width modulation values, where 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, which generates a luminance gain according to the 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. The photometric gain can be expressed as follows: Photometric gain = (luminosity) ^(-1/r) where r represents the gamma value.

其中(高峰_I/原始_I)代表高峰權重。In one embodiment, in the peaking mode, the pulse width modulation value is weighted and then fed to the light-shaped simulation unit 16. Assuming that the current in normal (or raw) mode is raw_I and the current in peak mode is peak_I, the pulse width modulation value in normal mode is raw_PWM, then the pulse width modulation value in peak mode is Peak_PWM can be expressed as follows:

Among them (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 compensated image can be 12-bit after the bit is deleted. In this way, the contour effect can be effectively reduced to improve the image quality.

The above are only the preferred embodiments of the present invention and are not intended to limit the scope of the patent application of the present invention; all other equivalent changes or modifications made without departing from the spirit of 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: hour Domain filter 16: Light shape simulation unit 17: Pixel compensation unit 18: Error diffusion unit HGL: Histogram gray scale Mean: Average value

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 generating the histogram average based on the histogram of the image. The fourth graph to the fourth graph illustrate the relationship between the pulse width modulation gain value and the average value. The fifth figure A 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 value of the fifth diagram A.

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: Optical analog unit

17: Pixel compensation unit

18: Error diffusion unit

Claims (17)

An area dimming system suitable for display backlight includes: an average estimation unit which receives an image and estimates its average value; a pulse width modulation gain control unit which generates a pulse width modulation gain according to the average value Value; a spatial filter that 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; a scene change detection unit that estimates based on the average The average of the histogram generated by the unit to detect scene changes; a time-domain filter, which is executed in the time domain based on the enhanced pulse width modulation gain value and the result of the detected scene changes to generate pulse width modulation Value; a light-shaped 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 based on the photometric gain, thereby generating a compensated image. The area dimming system suitable for the backlight of the display according to item 1 of the patent application scope, wherein the average value is estimated based on the histogram of the image. The area dimming system suitable for the backlight of the display according to item 1 of the patent application scope, wherein the backlight includes a light-emitting diode backlight. The area dimming system suitable for display backlight according to item 3 of the patent application scope, wherein the average estimation unit includes a maximum brightness unit, which determines the maximum brightness of each pixel of the image, based on which an arithmetic average is obtained. The area dimming system suitable for display backlight according to item 4 of the patent application scope, wherein the average estimation unit includes a histogram unit, which generates a histogram average based on the histogram of the image. The area dimming system suitable for display backlight according to item 5 of the patent application scope, wherein the generation of the average value of the histogram includes the following steps: dividing the image into complex blocks, constructing the histogram with its gray scale, the These blocks correspond to the light-emitting diodes of the backlight; and from the maximum gray scale to the minimum gray scale, the count value of the gray scale is accumulated. When the preset threshold is reached, the corresponding gray scale is set as the average value of the histogram. The area dimming system suitable for display backlight according to item 4 of the patent application scope, wherein 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 suitable for display backlight according to item 7 of the patent application scope, wherein the average value is the maximum value of the arithmetic average value and a weighted sum, the weighted sum is the arithmetic average value and the histogram Weighted sum of the average. The area dimming system suitable for display backlight according to item 3 of the patent application scope, wherein the pulse width modulation gain value is used to control the power supplied to the light emitting diode backlight, wherein the pulse width modulation gain value The larger, the higher the power provided to the light emitting diode backlight. The area dimming system applicable to the backlight of the display according to item 1 of the patent application scope, wherein the pulse width modulation gain value is generated according to a look-up table, which includes a complex number of the pulse width modulation gain value and the corresponding average value. The area dimming system suitable for display backlight according to item 3 of the patent application scope, wherein the time domain filter provides a power limiting mode, so that the pulse width modulation value is limited to a maximum value. According to item 11 of the patent application scope, the area dimming system suitable for the backlight of the display 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. The area dimming system suitable for display backlight according to item 1 of the patent application scope, wherein in peak mode, the pulse width modulation value is weighted and then fed to the light-shaped analog unit. According to item 13 of the patent application scope, the area dimming system suitable for the backlight of the display, where the pulse width modulation value is peak_PWM in peak mode, is expressed as follows:

The current in normal mode is original_I, the current in peak mode is peak_I, the pulse width modulation value in normal mode is original_PWM, (peak_I/raw_I) represents the peak weight. The area dimming system suitable for the backlight of the display according to item 1 of the scope of the patent application further includes an error diffusion unit that performs error diffusion on the compensated image. The area dimming system suitable for display backlight according to item 15 of the patent application scope, wherein 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 the backlight of the display according to item 1 of the patent application scope, wherein the display includes a liquid crystal display.

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