TW202012981A - Local dimming system and method adaptable to a backlight of a display - Google Patents

Abstract

A local dimming system includes a light shape imitation (LSI) unit that receives a pulse-width modulation (PWM) value generated according to content of an image, the LSI unit generating 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. The LSI unit performs LSI computation by multiplying profile data with corresponding PWM values, and adding products of multiplication, thus resulting in a light shape.

Description

Area dimming system and method suitable for display backlight

The invention relates to a backlight dimming, in particular to an area dimming system and method 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 propose a regional dimming system and method 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 a light-shaped analog unit and a pixel compensation unit. The optical shape simulation unit receives the pulse width modulation value, which is generated according to the image content, and the optical 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 light shape simulation calculation performed by the light shape simulation unit includes multiplying the profile data and the corresponding pulse width modulation value, and then adding the products to form the light shape.

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 sixth figure shows a flow chart of the light shape simulation unit 16 (first figure) of the embodiment of the present invention performing light shape simulation. First, provide the pulse width modulation value (produced by the time-domain filter 15) and profile information. In this specification, the profile data refers to the illumination light of a backlight light-emitting diode.

In step 61, light shape simulation calculation is performed on the pulse width modulation value and the profile data. Among them, the profile data is multiplied by the corresponding pulse width modulation value, and then the products are added to form the light shape. The seventh figure illustrates the light shape simulation calculation (step 61). As illustrated in the seventh figure, the profile data 1 is the illumination light of the first light-emitting diode in the first column, the profile data 2 is the illumination light of the second light-emitting diode in the first column, and so on. It is worth noting that the illuminating light will expand or diffuse to the adjacent blocks.

For the implementation of the hardware, the light shape simulation calculation (step 61) can be performed to down sample. In addition, the light shape can be limited to the preset area instead of the entire backlight. The eighth figure illustrates that the light shape simulation calculation performs the sampling rate reduction and limits the light shape to the preset area. In one embodiment, the limitation of the light shape can be achieved using a filter.

Returning to the sixth figure, in step 62, the light shape calculated in step 61 is interpolated, for example, bicubic interpolation, thereby forming an interpolated light shape. Finally, in step 63, the interpolated light shape is subjected to gamma mapping, thereby forming a simulated light shape.

The ninth figure shows a block diagram of the light-shaped simulation unit 16 (first figure) according to an embodiment of the present invention. Block 91 is used to perform light shape simulation calculations (step 61), and block 92 is used to perform interpolation (step 62) (such as bicubic interpolation) and gamma mapping (step 63).

Regarding the aforementioned light shape limitation, the corresponding profile may change due to the limitation. FIG. 10A illustrates a schematic diagram of the new contour formed by the original contour and the light shape limitation. In order to restore the original contour, the contour grouping mechanism illustrated in the tenth B figure may be used. In this embodiment, contour grouping can be performed by linear equations.

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 61: Light shape simulation calculation 62: Interpolation 63: Gamma mapping 91: Light shape simulation calculation 92: Interpolation and gamma mapping 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 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. The sixth figure shows a flowchart of the light shape simulation performed by the light shape simulation unit of the first embodiment of the present invention (the first picture). The seventh figure illustrates the light shape simulation calculation. The eighth figure illustrates that the light shape simulation calculation performs the sampling rate reduction and limits the light shape to the preset area. The ninth figure shows a block diagram of a light-shaped simulation unit (first figure) according to an embodiment of the present invention. FIG. 10A illustrates a schematic diagram of the new contour formed by the original contour and the light shape limitation. FIG. 10B illustrates a schematic diagram of a contour grouping mechanism to restore the original contour.

61: Light shape simulation calculation

62: Interpolation

63: Gamma mapping

Claims (20)

An area dimming system suitable for display backlight includes: a light-shaped analog unit that receives a pulse width modulation value, the pulse-width modulated value is generated based on an image content, and the light-shaped analog unit is based on the pulse width Modulation value to generate photometric gain; and a pixel compensation unit that performs pixel compensation of the image based on the photometric gain, thereby generating a compensated image; Correspondingly, the pulse width modulation values are multiplied, and then the products are added to form a light shape. The area dimming system suitable for display backlight according to item 1 of the patent application scope, wherein the light shape simulation unit further performs the following steps: interpolating the light shape to form an interpolated light shape. The area dimming system suitable for the backlight of the display according to item 2 of the scope of the patent application, wherein the interpolation includes bicubic interpolation. The area dimming system suitable for display backlight according to item 2 of the patent application scope, wherein the light shape simulation unit further performs the following steps: performing gamma mapping on the interpolated light shape to form an analog light shape. 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 applicable to the backlight of the display according to item 5 of the patent application scope, wherein the profile data refers to the illumination light of a light emitting diode of the backlight. The area dimming system applicable to the backlight of the display according to item 1 of the scope of the patent application, in which the sampling rate of the light shape simulation calculation is reduced. The area dimming system applicable to the backlight of the display according to item 1 of the scope of the patent application, wherein the light shape is limited to a predetermined area, not the entire backlight. According to item 8 of the patent application scope, the area dimming system suitable for the backlight of the display, wherein the limitation of the light shape is achieved by using a filter. 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. An area dimming method suitable for display backlight includes: receiving a pulse width modulation value, which is generated according to an image content; performing a light shape simulation calculation according to the pulse width modulation value to generate a photometric gain; and according to the The photometric gain performs pixel compensation of the image, thereby generating a compensated image; wherein the light shape simulation calculation includes multiplying the profile data and the corresponding pulse width modulation value, and then adding the products to form a light shape. The area dimming method suitable for the backlight of the display according to item 11 of the patent application scope further includes: interpolating the light shape to form an interpolated light shape. The area dimming method applicable to the backlight of the display according to item 12 of the patent application scope, wherein the interpolation includes bicubic interpolation. The area dimming method suitable for the backlight of the display according to item 12 of the patent application scope further includes: performing gamma mapping on the interpolated light shape to form an analog light shape. The area dimming method suitable for display backlight according to item 11 of the patent application scope, wherein the backlight includes a light-emitting diode backlight. According to the item 15 of the patent application scope, the area dimming method applicable to the backlight of the display, wherein the profile data refers to the illumination light of a light emitting diode of the backlight. The area dimming method applicable to the backlight of the display according to item 11 of the patent application scope, in which the sampling rate of the light shape simulation calculation is reduced. According to the item 11 of the patent application scope, the area dimming method applicable to the backlight of the display, wherein the light shape is limited to a predetermined area, not the entire backlight. According to the item 18 of the patent application scope, the area dimming method suitable for the backlight of the display, wherein the limitation of the light shape is achieved by using a filter. The area dimming method suitable for the backlight of the display according to item 11 of the patent application scope, wherein the display includes a liquid crystal display.

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