KR102438248B1 - Dimming control circuit, liquid crystal display including the dimming control circuit, and dimming control method of the liquid crystal display - Google Patents

Abstract

In order to simplify calculation logic when calculating the total amount of light reaching a pixel to be analyzed by local dimming, the liquid crystal display device of the present invention determines a dimming value for determining a dimming value for each block based on an analysis result of input image data. Set an analysis mask of a certain size and select a pixel to be analyzed while shifting the analysis mask in units of 1 pixel on the virtual display screen having the dimming value for each block, a light amount calculation unit for calculating a total amount of light reaching the pixel to be analyzed based on a dimming value and a ratio of overlapping areas of the effective blocks; and a data modulator for compensating for a luminance change due to a dimming value.

Description

Dimming control circuit, liquid crystal display including same, and dimming control method thereof

The present invention relates to a dimming control circuit, a liquid crystal display including the same, and a dimming control method therefor.

Liquid crystal display devices are used in portable computers such as notebook PCs, office automation devices, audio/video devices, indoor and outdoor advertisement display devices, and the like. A liquid crystal display displays an image by using a thin film transistor (hereinafter, "TFT") as a switching element. The transmissive liquid crystal display, which occupies most of the liquid crystal display, displays an image by controlling the electric field applied to the liquid crystal layer to modulate the light incident from the backlight unit.

The image quality of the liquid crystal display is influenced by the contrast characteristic. There is a limit to improving the contrast characteristic only by modulating the light transmittance of the liquid crystal layer by controlling the data voltage applied to the liquid crystal layer. In order to improve contrast characteristics, a backlight dimming method of adjusting the luminance of a backlight unit according to an image has been proposed. The backlight dimming method includes a global dimming method for adjusting the luminance of the entire display surface and a local dimming method for locally adjusting the luminance of the display surface. The global dimming method may improve the dynamic contrast measured between the previous frame and the next frame. The local dimming method can improve static contrast, which is difficult to improve with the global dimming method, by locally controlling the luminance of the display surface within one frame period.

In the conventional local dimming method, as shown in FIG. 1 , input data is mapped to virtual blocks BLK divided in a matrix form on a display screen of a display panel, and a representative value of input data is derived for each block BLK. In addition, the brightness of the backlight (light sources) is locally controlled by determining a dimming value for each block BLK according to the representative value, and input data is modulated to compensate for insufficient brightness due to the dimming value adjustment.

After local dimming, the amount of light is determined by determining an analysis area of a predetermined size surrounding the block BLK including pixels as shown in FIG. 2, and reaching the analysis target pixel (current pixel) within the analysis area. It is determined by the total amount of light. In the conventional local dimming method, in order to calculate the amount of light reaching the current pixel, a light profile is measured according to a shape of a backlight unit, and sampling coefficient values are stored in advance. The conventional local dimming method simulates the amount of light reaching each pixel using the dimming value and sampling coefficient values for each block (BLK), derives the insufficient luminance by local dimming according to the simulated light amount, and inputs the amount of luminance reward data. At this time, since the amount of light reaching each pixel is determined through a pixel-by-pixel interpolation process, that is, it is determined by interpolating sampling coefficient values surrounding the corresponding pixel, the conventional local dimming method has a large logic size. requires

Accordingly, it is an object of the present invention to provide a dimming control circuit capable of simplifying calculation logic when calculating the total amount of light reaching a pixel to be analyzed by local dimming, and a liquid crystal display including the same, and a dimming control method thereof have.

In order to achieve the above object, a liquid crystal display device of the present invention includes a display panel in which a plurality of pixels are disposed, a backlight unit including a plurality of light sources for irradiating light to a rear surface of the display panel, and data of an input image. A dimming value determiner that determines a dimming value for each block based on the analysis result, sets an analysis mask of a certain size, and performs analysis while shifting the analysis mask in units of 1 pixel on a virtual display screen having the dimming value for each block a light quantity calculator that selects a target pixel and calculates a total amount of light reaching the analysis target pixel based on dimming values of effective blocks overlapping the analysis mask and a ratio of overlapping areas of the effective blocks; and a data modulator which modulates the input image data based on a gain value to compensate for a luminance change due to the dimming value for each block.

The light amount calculator calculates the total amount of light reaching the analysis target pixel by adding all products between the dimming values of the effective blocks overlapping the analysis mask and the overlap area ratios of the effective blocks.

The liquid crystal display device further comprises a gain calculation unit for dividing the amount of light before dimming by the total amount of light, and calculating the gain value that equalizes the luminance before and after dimming by performing 1/γ power exponent calculation on the divided result, The amount of light before dimming is the sum of the amount of light reaching the pixel to be analyzed when all light sources are turned on at maximum brightness, and is a predetermined constant value.

The liquid crystal display device further includes a light source driver for driving the light sources in units of blocks based on a duty ratio of a pulse width modulation signal adjusted according to the dimming value for each block.

In addition, the dimming control circuit according to the present invention includes a dimming value determiner that determines a dimming value for each block based on an analysis result of input image data, sets an analysis mask of a certain size, and sets the analysis mask for each block A pixel to be analyzed is selected while shifting in units of 1 pixel on a virtual display screen having a dimming value, and the analysis target pixel is reached based on the dimming value of the effective blocks overlapping the analysis mask and the overlapping area ratio of the effective blocks and a light amount calculator for calculating a total amount of light to be used, and a data modulator for compensating for a luminance change due to a dimming value for each block by modulating the input image data based on a gain value according to the total amount of light.

In addition, according to the present invention, there is provided a dimming control method for a liquid crystal display device having a display panel in which a plurality of pixels are disposed and a backlight unit including a plurality of light sources and irradiating light to a rear surface of the display panel. Determining a dimming value for each block based on the analysis result, setting an analysis mask of a certain size, shifting the analysis mask in units of 1 pixel on a virtual display screen having the dimming value for each block, and selecting an analysis target pixel calculating a total amount of light reaching the pixel to be analyzed based on a dimming value of effective blocks overlapping the analysis mask and a ratio of overlapping areas of the effective blocks; and a gain value according to the total amount of light and compensating for a luminance change due to the dimming value for each block by modulating the input image data.

According to the present invention, when calculating the total amount of light reaching a pixel to be analyzed by local dimming, since sampling coefficient values and interpolation calculations as in the prior art are not used, calculation logic can be simplified and manufacturing cost can be reduced accordingly.

1 and 2 are diagrams for explaining a conventional local dimming method.
3 is a view showing a liquid crystal display device according to an embodiment of the present invention.
4 is a diagram showing the configuration of a dimming control circuit of the present invention.
5 is a diagram showing an example in which a surface light source is divided into blocks for local dimming implementation;
6 is a view showing a local dimming method of the present invention for calculating a total amount of light reaching a pixel to be analyzed by local dimming;
7 is a view showing a comparison of the resultant image according to the conventional local dimming method and the resultant image according to the local dimming method of the present invention.
8 is a flowchart sequentially showing a dimming control method of a liquid crystal display according to the present invention.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. 3 to 8 .

3 shows a liquid crystal display device according to an embodiment of the present invention.

Referring to FIG. 3 , a liquid crystal display according to an embodiment of the present invention includes a display panel 10 , a timing controller 11 , a source driver 12 , a gate driver 13 , a dimming control circuit 14 , and a light source driver. (15), and a backlight unit (16).

The display panel 10 includes two glass substrates and a liquid crystal layer formed therebetween. A plurality of data lines DL and a plurality of gate lines GL cross each other on the lower glass substrate of the display panel 10 . The liquid crystal cells Clc are arranged in a matrix on the display panel 10 by the intersecting structure of the data lines DL and the gate lines GL. Each of the liquid crystal cells Clc includes a TFT, a pixel electrode 1 connected to the TFT, and a storage capacitor Cst. A black matrix, a color filter, and a common electrode 2 are formed on the upper glass substrate of the display panel 10 . The common electrode 2 is formed on the upper glass substrate in a vertical electric field driving method such as TN (Twisted Nematic) mode and VA (Vertical Alignment) mode, IPS (In Plane Switching) mode and FFS (Fringe Field Switching) mode and It is formed on the lower glass substrate together with the pixel electrode 1 in the same horizontal electric field driving method. The liquid crystal cells Clc include R liquid crystal cells for red display, G liquid crystal cells for green display, and B liquid crystal cells for blue display. The R liquid crystal cell, the G liquid crystal cell, and the B liquid crystal cell constitute one unit pixel for color realization. A polarizing plate is attached to each of the upper glass substrate and the lower glass substrate of the display panel 10 , and an alignment layer for setting a pretilt angle of the liquid crystal is formed on the inner surface in contact with the liquid crystal.

The timing controller 11 supplies digital image data RGB input from a system board on which an external video source is mounted to the dimming control circuit 14 , and modulated data R'G modulated by the dimming control circuit 14 . 'B') is supplied to the source driver 12 . The timing controller 11 includes timing control signals DDC for controlling the operation timings of the source driver 12 and the gate driver 13 based on the timing signals Vsync, Hsync, DE, and DCLK from the system board. GDC) occurs. The timing controller 11 inserts an interpolation frame between frames of an input image signal input with a frame frequency of 60 Hz and multiplies the data timing control signal DDC and the gate timing control signal GDC to 60×N (N is The operation of the source driver 12 and the gate driver 13 can be controlled with a frame frequency of Hz (a positive integer greater than or equal to 2).

The source driver 12 includes a number of data drive integrated circuits. The data drive integrated circuit stores a shift register for sampling the clock signal, a register for temporarily storing the modulated data (R'G'B') of the input image, and stores data by one line in response to the clock signal from the shift register. A latch for simultaneously outputting one line of stored data, a digital/analog converter for selecting positive/negative gamma voltages under reference to a gamma reference voltage corresponding to the digital data value from the latch, positive/negative polarity and a multiplexer for selecting the data line DL to which the analog data converted by the gamma voltage is supplied, and an output buffer connected between the multiplexer and the data line DL. The source driver 12 latches the modulated data R'G'B' according to the data timing control signal DDC from the timing controller 11, and uses the latched modulated data R'G'B'. The positive/negative gamma compensation voltage is converted into positive/negative analog data voltage, and then supplied to the data lines DL.

The gate driver 13 includes a plurality of gate drive integrated circuits. The gate drive integrated circuit includes a shift register, a level shifter for converting an output signal of the shift register to a swing width suitable for driving a TFT of a liquid crystal cell, an output buffer, and the like. The gate driver 13 sequentially outputs scan pulses (or gate pulses) according to the gate timing control signal GDC from the timing controller 11 and supplies the scan pulses (or gate pulses) to the gate lines GL. Select a line.

The dimming control circuit 14 analyzes digital data (RGB) of the input image from the timing controller 11 in units of virtual blocks divided in a matrix form on the display screen of the display panel 10 to obtain a representative value of each block. derive And, the dimming control circuit 14 determines the dimming value for each block of the backlight unit 16 according to the representative value for each block, and selects a pixel to be analyzed while shifting an analysis mask of a certain size in units of 1 pixel, The total amount of light reaching the analysis target pixel is calculated based on the dimming values of the effective blocks overlapping the analysis mask and the overlapping area ratio of the effective blocks. The dimming control circuit 14 calculates a gain value of a pixel to be analyzed based on the total amount of light, and modulates (R'G'B') the input image data based on the gain value. Compensate for insufficient luminance.

The light source driver 15 drives the light sources in block units based on a duty ratio of a pulse width modulation (hereinafter, "PWM") signal input from the dimming control circuit 14 . The duty ratio of the PWM signal is determined according to the dimming value for each block. The on and off times of the light sources are controlled by the duty ratio of the PWM signal.

The backlight unit 16 divides a surface light source irradiated to the display panel 10 including a plurality of light sources into blocks in a matrix form. The backlight unit 16 may be implemented as either a direct type or an edge type. The direct backlight unit 16 has a structure in which a plurality of optical sheets and a diffusion plate are stacked under the display panel 10 , and a plurality of light sources are disposed under the diffusion plate. The edge-type backlight unit 16 has a structure in which a plurality of optical sheets and a light guide plate are stacked under the display panel 10 , and a plurality of light sources are disposed on a side surface of the light guide plate. The light sources may be implemented as point light sources such as light emitting diodes (LEDs).

4 shows the dimming control circuit 14 in detail.

Referring to FIG. 4 , the dimming control circuit 14 includes a dimming value determiner 141 , a duty adjuster 142 , a light amount calculator 143 , a gain calculator 144 , and a data modulator 145 . to provide

The dimming value determiner 141 converts the digital data RGB of the input image into virtual blocks BLK[1,1] to BLK[n] divided in a matrix form on the display screen of the display panel 10 as shown in FIG. ,m]) unit to derive representative values for each block. The representative value for each block may be obtained by deriving the maximum grayscale value from among the RGB values of pixels in each block and dividing the total of these maximum values by the number of pixels included in the block. The representative value for each block may be selected as an Average Picture Level (APL) value of each block. The dimming value determiner 141 may determine a dimming value DIM for each block by mapping a representative value for each block to a preset dimming curve. The dimming value DIM for each block may be determined to be high in a block having a high representative value and low in a block having a low representative value.

The duty control unit 142 adjusts the duty ratio of the input PWM signal for each block based on the dimming value (DIM) for each block from the dimming value determiner 141 and then outputs the PWM signal with the adjusted duty ratio to the light source driver 15 . ) is supplied to The duty ratio of the PWM signal may be adjusted to be large in a block having a high dimming value DIM and to be small in a block having a low dimming value DIM. As the duty ratio of the PWM signal is larger, the light sources are controlled to be bright, and as the duty ratio of the PWM signal is smaller, the light sources are controlled to be dark. The duty adjuster 142 may be included in the light source driver 15 .

The light amount calculation unit 143 sets an analysis mask having a size of (P (number of blocks) × P (number of blocks)) (P is a positive integer of 3 or more) as shown in FIG. 6 , and then dims the analysis mask for each block A pixel to be analyzed is selected while shifting in units of 1 pixel on a virtual display screen having a value. The light amount calculator 143 calculates the total amount of light reaching the analysis target pixel based on the dimming values of the effective blocks overlapping the analysis mask and the overlap area ratio of the effective blocks. In other words, the light amount calculator 143 may calculate the total amount of light reaching the analysis target pixel by adding all products between the dimming value of each effective block overlapping the analysis mask and the overlap area ratio. For example, in the case of FIG. 6 , the total amount of light reaching the pixel to be analyzed is expressed by Equation 1 below.

The light amount calculator 143 does not need to store sampling coefficient values in advance as in the related art in order to calculate the total amount of light reaching the analysis target pixel. Since these sampling coefficient values vary depending on the type of backlight unit (direct type, horizontal 1 edge type, horizontal 2 edge type, vertical 1 edge type, vertical 2 edge type, 4 edge type, etc.), conventional logic for calculating the total amount of light was inevitably changed depending on the shape of the backlight unit. On the other hand, since the logic of the present invention for calculating the total amount of light does not use any sampling coefficient values, there is no limitation according to the display device model, and it can be equally applied to any type of backlight unit. That is, the logic of the present invention has very good compatibility compared to the prior art.

In addition, since the light amount calculator 143 does not perform an interpolation operation as in the prior art in order to calculate the total amount of light reaching the pixel to be analyzed, the size of the calculation logic for calculating the total light amount can be significantly reduced compared to the related art.

The gain calculation unit 144 calculates a gain value of a pixel to be analyzed for luminance compensation based on the total amount of light calculated by the light amount calculation unit 143 . The gain calculation unit 144 compares the total amount of light of each of the analysis target pixels, that is, the amount of light after dimming by local dimming, with the amount of light before dimming by non-local dimming, and obtains a gain for each analysis target pixel. Calculate the value. Here, the amount of light before dimming is the sum of the amounts of light reaching the corresponding analysis target pixel when all light sources are turned on at the maximum brightness, and is a constant value predetermined as a constant value. The gain calculation unit 144 calculates the pre-dimming light amount BL reaching the analysis target pixel during non-local dimming as in Equation 2 below under the premise that the luminance during non-local dimming and the luminance during local dimming are the same. During local dimming, it is divided by the amount of light (BL′) after dimming that reaches the pixel to be analyzed, and the 1/γ-power exponent operation is performed on the divided result to obtain a gain value (K) that makes the luminance before and after local dimming equal. .

In Equations 1 and 2, Data represents a data value of an input image input to a pixel to be analyzed, and Data' represents a modulated data value obtained by multiplying a data value of an input image by a gain value.

The gain calculation unit 144 may perform the division and exponentiation operations in units of pixels using an operation algorithm that may be implemented as a lookup table.

The data modulator 145 modulates the data RGB of the input image to be applied to the pixel based on the gain value GAIN of the pixel input from the gain calculator 144 to modulate the modulated data R'G'B. ') is created. The data modulator 145 may increase the up-modulation width of data as the gain value GAIN is high, and may decrease the up-modulation width of data as the gain value GAIN is low.

7 shows a comparison of the resultant image according to the conventional local dimming method and the resultant image according to the local dimming method of the present invention.

7A shows that the total amount of light is calculated for each sampling point unit by using the dimming value for each block and the sampling coefficient values stored in advance, and then the total amount of light and the corresponding gain are calculated for each pixel through interpolation operation. It is the image display result according to the conventional local dimming that implements dimming. 7(b) shows the realization of local dimming by calculating the total amount of light reaching the analysis target pixel based on the dimming value of the effective blocks overlapping the analysis mask and the overlapping area ratio of the effective blocks and the resulting gain value in units of pixels It is an image display result according to the local dimming of the present invention.

The dimming control circuit 14 of the present invention can reduce the logic size for local dimming by 92% or more compared to the prior art while implementing image contrast quality similar to that of the prior art. The present invention can be optimized for models where the logic size must be small. The present invention can reduce the manufacturing cost by reducing the logic size for local dimming. Since the present invention does not use the sampling coefficient values, the memory for storing the sampling coefficient values can be eliminated.

8 shows a dimming control method of a liquid crystal display according to an embodiment of the present invention.

This dimming control method maps and analyzes the data (RGB) of the input image to virtual blocks divided in a matrix form on the display screen of the display panel to calculate a representative value (APL) of the data for each block. Then, a dimming value is determined for each block based on the representative value of the data (S10 to S30).

This dimming control method drives the light sources in block units by adjusting the duty ratio of the input PWM signal for each block based on the determined dimming value (S40).

In this dimming control method, after setting an analysis mask having a predetermined size, a pixel to be analyzed is selected while the analysis mask is shifted in units of 1 pixel on a display screen having a dimming value for each block. This dimming control method calculates the total amount of light reaching the analysis target pixel based on the dimming values of the effective blocks overlapping the analysis mask and the overlapping area ratio of the effective blocks. In other words, this dimming control method can calculate the total amount of light reaching the pixel to be analyzed by adding all products between the dimming value of each effective block overlapping the analysis mask and the overlap area ratio (S50 to S60).

In this dimming control method, a gain value of a pixel to be analyzed for luminance compensation is calculated based on the total amount of light. This dimming control method calculates a gain value for each analysis target pixel by comparing the total amount of light of each pixel to be analyzed, that is, the amount of light after dimming by local dimming, with the amount of light before dimming by non-local dimming, respectively. do (S70).

This dimming control method compensates for the lack of brightness due to the dimming value for each block by modulating the data (RGB) of the input image to be applied to the pixel based on the gain value of the pixel to generate the modulated data (R'G'B'). do (S80).

As described above, in the present invention, when calculating the total amount of light reaching the pixel to be analyzed by local dimming, the calculation logic can be simplified because conventional sampling coefficient values and interpolation calculation are not used, and thus the manufacturing cost is increased. can reduce

Those skilled in the art from the above description will be able to see that various changes and modifications can be made without departing from the technical spirit of the present invention. Accordingly, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

10: display panel 11: timing controller
12: source driver 13: gate driver
14: dimming control circuit 15: light source driver
16: backlight unit 141: dimming value determining unit
142: duty control unit 143: light amount calculation unit
144: gain calculation unit 145: data modulation unit

Claims (11)

a display panel on which a plurality of pixels are disposed;
a backlight unit including a plurality of light sources and irradiating light to a rear surface of the display panel;
a dimming value determiner configured to determine a dimming value for each block based on an analysis result of the input image data;
Set an analysis mask of a certain size, select a pixel to be analyzed while shifting the analysis mask in units of 1 pixel on a virtual display screen having the dimming value for each block, and the dimming values of effective blocks overlapping the analysis mask a light amount calculation unit for calculating a total amount of light reaching the analysis target pixel based on a ratio of overlapping areas of the effective blocks; and
and a data modulator that modulates the input image data based on a gain value according to the total amount of light to compensate for a luminance change due to the dimming value for each block,
The light amount calculation unit,
A liquid crystal display for calculating the total amount of light reaching the analysis target pixel by adding all products between the dimming values of the effective blocks overlapping the analysis mask and the overlapping area ratios of the effective blocks. delete The method of claim 1,
Further comprising: a gain calculation unit that divides the amount of light before dimming by the total amount of light, and calculates the gain value that equalizes the luminance before and after dimming by performing 1/γ power exponent calculation on the divided result,
The amount of light before dimming is the sum of the amount of light reaching the pixel to be analyzed when all light sources are turned on at maximum brightness, and is a predetermined constant value. The method of claim 1,
and a light source driver for driving the light sources in units of blocks based on a duty ratio of a pulse width modulation signal adjusted according to the dimming value for each block. a dimming value determiner configured to determine a dimming value for each block based on an analysis result of the input image data;
Set an analysis mask of a certain size, select a pixel to be analyzed while shifting the analysis mask in units of 1 pixel on a virtual display screen having the dimming value for each block, and the dimming values of effective blocks overlapping the analysis mask a light amount calculation unit for calculating a total amount of light reaching the analysis target pixel based on a ratio of overlapping areas of the effective blocks; and
and a data modulator that modulates the input image data based on a gain value according to the total amount of light to compensate for a luminance change due to the dimming value for each block,
The light amount calculation unit,
A dimming control circuit for calculating a total amount of light reaching the analysis target pixel by adding all products between dimming values of the effective blocks overlapping the analysis mask and a ratio of overlapping areas of the effective blocks. delete 6. The method of claim 5,
Further comprising: a gain calculation unit that divides the amount of light before dimming by the total amount of light, and calculates the gain value that equalizes the luminance before and after dimming by performing 1/γ power exponent calculation on the divided result,
The amount of light before dimming is the sum of the amounts of light reaching the pixel to be analyzed when all light sources are turned on at maximum brightness, and is a predetermined constant value. A dimming control method for a liquid crystal display device having a display panel on which a plurality of pixels are disposed, and a backlight unit including a plurality of light sources to irradiate light to a rear surface of the display panel, the dimming control method comprising:
determining a dimming value for each block based on an analysis result of the input image data;
Set an analysis mask of a certain size, select a pixel to be analyzed while shifting the analysis mask in units of 1 pixel on a virtual display screen having the dimming value for each block, and the dimming values of effective blocks overlapping the analysis mask calculating a total amount of light reaching the analysis target pixel based on a ratio of overlapping areas of the effective blocks; and
Compensating for a luminance change due to the dimming value for each block by modulating the input image data based on a gain value according to the total amount of light,
The step of calculating the total amount of light,
A dimming control method of a liquid crystal display for calculating a total amount of light reaching the analysis target pixel by adding all products between dimming values of the effective blocks overlapping the analysis mask and a ratio of overlapping areas of the effective blocks. delete 9. The method of claim 8,
The method further comprises dividing the amount of light before dimming by the total amount of light, and calculating the gain value that equalizes the luminance before and after dimming by performing 1/γ power exponent calculation on the divided result,
The amount of light before dimming is the sum of the amount of light reaching the pixel to be analyzed when all light sources are turned on at maximum brightness, and is a predetermined constant value. 9. The method of claim 8,
and driving the light sources in block units based on a duty ratio of a pulse width modulation signal adjusted according to the dimming value for each block.

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