KR101705895B1 - Color reproduction method and display device using the same - Google Patents

Abstract

The present invention relates to a color reproduction method comprising the steps of converting source RGB data having a gamut of a standard size into first XYZ color space data, converting the first XYZ color space data into a color space Converting the color space data reflecting the brightness of the surrounding environment into second XYZ color space data, inverting the second XYZ color space data into RGB data to obtain the modulation values, And modulating the source RGB data with a modulation value output from a lookup table selected from among the first through third lookup tables according to the brightness of the surrounding environment .

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color reproduction method,

The present invention relates to a color reproduction method for adaptively adjusting colors according to the external environment of a display apparatus.

The display device has been improved in color reproduction performance while developing in the direction of high resolution and high definition. The display device has different gamut depending on the field of use. In order to correct the inconsistency of the gamut, the color gamut that can be represented by the display device, that is, the gamut, varies depending on the characteristics of the display device. Recent light color display devices have a broader color range than the standard color gamut.

Various gamut mapping methods have been proposed as a method for converting the gamut of a standard standard into the gamut of a color gamut display device. The known gamut mapping method is disclosed in Korean Patent Laid-Open Publication No. 10-2008-0030339 (Apr. 04, 04), Korean Laid-Open Patent Publication No. 10-2008-0016362 (2008. 02. 21) 2008-0015673 (Feb. 20, 2008). Conventional gamut mapping methods proposed in Korean Patent Laid-Open Publication No. 10-2008-0030339 briefly describe a color gamut mapping method in which color spaces such as RGB or CMYK are classified into brightness (L), chroma , C) and color (Hue, H) data, scaling and adjusting the color brightness of the source device to match the brightness range of the source device with the brightness range of the reproducing device, Modifying the color brightness of the source device by adjusting the gamut of the source device based on the gamut of the reproducing device, mapping the color of the modified source device to the gamut of the reproducing device, mapping the gamut gamut to CMYK or RGB Into a color space.

Conventional gamut mapping methods have the following problems.

(1) Conventional gamut mapping methods can only reproduce colors in a specific condition, for example, in a dark room, so that it is impossible to reproduce an accurate color when the external environment changes.

(2) Since each of the conventional gamut mapping methods is optimized for a specific source device and a specific reproducing device, the best gamut mapping result can not be obtained when the general gamut mapping method is applied. Therefore, conventional gamut mapping methods are difficult to implement an image-dependent global algorithm.

(3) The conventional gamut mapping method is incompatible. Since the gamut mapping is performed using the data between the gamut boundary of the source device and the reproducing device, even if the same gamut mapping algorithm is applied, the degree of gamut mapping of the reproducing device changes when the source device is changed as shown in FIG.

The present invention provides a color reproduction method and an apparatus using the same that reproduce accurate colors according to standard specifications in a display device under any use environment.

The color reproduction method of the present invention includes: converting source RGB data having a gamut of a standard size into first XYZ color space data; Converting the first XYZ color space data into color space data reflecting the brightness of a surrounding environment of the display device; Converting the color space data reflecting the brightness of the surrounding environment into the second XYZ color space data; Converting the second XYZ color space data into RGB data to obtain modulation values; And modulating the source RGB data with a modulation value output from a lookup table selected from among the first through third lookup tables according to the brightness of the surrounding environment by using the optical sensor and the brightness of the surrounding environment of the display device, .
Wherein the modulation values include first modulation values set in the first lookup table to modulate the source RGB data when the white luminance of the surrounding environment is 20% brighter than the white luminance of the image displayed on the display device, The second modulation values set in the second lookup table to modulate the source RGB data when the white luminance of the image displayed on the display device is 20% smaller than the white luminance of the image displayed on the display device, And third modulation values set in the third lookup table to modulate the source RGB data.

The color space data reflecting the brightness of the surrounding environment includes color space data defined by CIECAM02 (CIE Color Appearance Model 2002).

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A display device of the present invention includes a display panel; An optical sensor for sensing a brightness of a surrounding environment of the display panel; And a gamut conversion unit for modulating the source RGB data with the modulation values output from the lookup table selected from among the first through third lookup tables according to the brightness of the surrounding environment sensed by the optical sensor.

The present invention adaptively adjusts the gamut of an input image according to a change in illuminance of an actual use environment of a display device using a human perceptual color space model reflecting a surrounding environment. As a result, the present invention can reproduce accurate colors according to standard specifications in a display device under any use environment. Furthermore, the present invention can reproduce colors in accordance with standard specifications in a photo-color display device, and can accurately reproduce colors on a display device independently of the gamut of the source device or the input image.

1 is a diagram showing an example of a conventional conventional gamut mapping method.
2 is a flowchart illustrating a color reproduction method according to an embodiment of the present invention.
Fig. 3 is a view showing observation conditions determined according to the brightness of the surrounding environment of the display device. Fig.
4 is a diagram showing a linear correction method of RGB data.
FIG. 5 is a view showing lookup tables in which modulation values calculated by the color reproduction method of FIG. 2 are set.
6 is a block diagram showing a display device according to an embodiment of the present invention.
FIGS. 7 and 8 are diagrams showing experimental results of the present invention. FIG.

The present invention detects a surrounding environment (or an external environment) of a display device in real time and adaptively adjusts a gamut of an input image according to a change in illuminance of an actual use environment of a display device using a cognitive color space model reflecting the surrounding environment do. Here, CIECAM02 (CIE Color Appearance Model 2002) is an example of the cognitive color space model reflecting the surrounding environment. The external environment defined in CIECAM02 is divided into average brightness, dim brightness, and dark brightness. The average brightness is a brightness when the ambient brightness of the display device is higher than the white brightness of the scene or image displayed on the display device. Specifically, the brightness of the surrounding environment white is 20% Is the brightness of the case where it is brighter. The blurred brightness refers to the brightness when the ambient brightness of the display device is lower than the white luminance of the scene or image displayed on the display device. Specifically, the luminance of the surrounding white color is 20% of the white luminance of the scene or image displayed on the display device. Is the brightness in the darker case. The dark brightness is the brightness when there is substantially no brightness of the surrounding environment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Like reference numerals throughout the specification denote substantially identical components. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

2 to 4 show a color reproduction method according to an embodiment of the present invention.

2 to 4, the color reproduction method of the present invention includes a normalization calculation process as shown in Equation 1 and a de-gamma correction calculation process as shown in Equation 2, And converting the source RGB color space of the standard standard into the XYZ color space (S1).

Here, R _8-bit , G _8-bit , and B _8-bit are nonlinear 8-bit RGB input signals (0 to 255)

R ' _sRGB , G' _sRGB , and B ' _sRGB respectively denote normalized nonlinear RGB input signals (0 to 1).

Where R _sRGB , G _sRGB , and B _sRGB are the degamma linear source RGB input signals (0-1).

Here, XYZ is a 1931 CIEXYZ tristimulus value converted by a 3x3 matrix.

Then, the color reproduction method of the present invention converts the XYZ color space into the JCh color space defined in CIECAM02, and detects the color gamut of the image displayed on the display device even when the brightness (average (avg.) / Dim / dark) (J), saturation (C), and hue (H) in the JCh color space according to the brightness of the surrounding environment of the display device so that the color gamut of the display device can always be recognized as a standard gamut The brightness of the environment can be detected by the light sensor connected to the display. A method for converting XYZ to JCh color space is a computation process for determining the observation condition as shown in FIG. 3 by taking XYZ data, XwYwZw (XYZ value of white point) data and the luminance L _A of the surrounding environment as inputs, 4 to 8 to calculate an ambient luminance coefficient k, a luminance level adaptation coefficient F _L , an inductive coefficient N _bb and N _cc , an exponential nonlinearity z, and a relative luminance Yb of the surrounding environment. The parameters c, Nc, F of the viewing condition of FIG. 3 are determined by the luminance L _A of the ambient environment sensed by the optical sensor. c is a variable value of Equation (16), Nc is a variable value of Equation (17), and F is a variable value of Equation (10).

A method of converting XYZ to JCh color space is an operation process of converting XYZ data and XwYwZw values into RGB (LMS space) through a CIECAM02 3 × 3 matrix using Equation (9), using Equation (10) Calculating an adaptive degree D, calculating a compliant tristimulus response R _C , G _C, and B _C using Equation (11), calculating a Hunt-Pointer_Estevez color space using Equation (12) A calculation process of calculating the compressed data (R ^' _a , G ^' _a , B ^' _a ) by applying nonlinear compression after adaptation using Equation 13, an arithmetic process of calculating a and b using Equation (14) A calculation process of calculating the color h using Equation 15, a process of calculating the brightness J using Equation 16, and an arithmetic process of calculating the saturation C using Equation 17 .

The color reproduction method of the present invention inversely transforms the JCh color space into the XYZ color space. (S3) A method of inversely transforming the JCh color space into the XYZ color space uses Equation (18) A calculation process for calculating t from the brightness (J), an calculation process for calculating et from the hue (h) of the JCh color space using Equation 19, A from Aw and brightness (J) using Equation calculation process, using equation 21 t, et, color (h), and the a calculation process for calculating a, b, using equation 22 a, a, from b R ^{_'a, G'} _a, which And B ^' _a , an arithmetic process for calculating R', G 'and B' values using Equation 23, an arithmetic process for calculating Rc, Gc and Bc values using Equation 23, And calculating the RGB value and the XYZ color space of the LMS color space using equations (25) and (26).

The coefficient values and parameters included in equations (4) to (26) are defined in the JCh color space conversion algorithm according to the CIECAM02 specification, and thus their definitions are omitted.

Next, the color reproduction method of the present invention converts a XYZ value calculated by the equation (26) shown in FIG. 4 into RGB color space values (R _out , G _out , B _out ) and then applies a linear scalar. of the modulation values of _{(R 'out, g' out} , B 'out) and inverse transform _{in. (S4) X r, max} , X g, max, X b, max is a display device (or the reproduction device) in FIG. 4 Means the maximum gradation value.

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The color reproduction method of the present invention implements modulation values of data calculated through steps S1 to S4 as a lookup table. (S5) A lookup table receives input image data (RGB) from a source device as an input address, (R ' _out , G' _out , B ' _out ) stored in the memory. The modulation values of the lookup table are divided into average brightness (Average), dim brightness (dim), and dark brightness (dark) as shown in FIG. Thus, the lookup table includes three lookup tables that are selected according to the ambient brightness of the display device.

6 is a block diagram showing a display device according to an embodiment of the present invention.

6, the display device of the present invention includes a display panel 100, a data driving circuit 12, a scan driving circuit 13, a timing controller 11, an optical sensor 15, a gamut conversion unit 10, , And a system board (14).

The display panel 100 may include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an inorganic electroluminescent device and an organic light emitting diode A display panel of a flat panel display device such as an electroluminescence device (EL) including a light emitting diode, a diode, and an OLED. The display panel 100 includes data lines D1 to Dm to which data voltages are supplied, scan lines G1 to Gn to which scan pulses are supplied, data lines D1 to Dm and scan lines G1 to Gn ≪ / RTI > formed at the intersections of the pixel regions.

The data driving circuit 12 receives the digital video data R ' _out G ' _out B ' _out ) and latches and converts the data into data of a parallel data system. The data driving circuit 12 converts the data into a gamma compensation voltage to generate a data voltage and supplies the data voltage to the data lines D1 to Dm of the display panel 100. [

The scan driver circuit 13 sequentially supplies a scan pulse (or a gate pulse) synchronized with the data voltage to the scan lines G1 to Gn of the display panel 100 under the control of the timing controller 11. [

Timing coat roller 11 is modulated by the color gamut conversion unit 10, the digital video data (R _'out G ' _out B ' _out ) to the data driving circuit 12. The timing controller 11 inputs timing signals such as a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE and a dot clock CLK from the system board 14 And generates timing control signals for controlling the operation timings of the data driving circuit 12 and the scan driving circuit 13.

The optical sensor 15 converts the ambient brightness of the display device into an electrical signal and transmits it to the system board 14.

The system board 14 is connected to a broadcast receiving circuit and an external video source interface circuit to receive video data from the source device. The system board 14 includes a system on chip (SoC) including an optical sensor receiving circuit, a user interface, a graphic processing circuit and a scaler, and transmits digital video data RGB to the gamut converting unit 10 And transmits the timing signals Vsync, Hsync, DE, and CLK to the timing controller 11. In addition, the system board 14 transmits the ambient brightness data ADB received through the optical sensor receiving circuit to the gamut converter 10.

The gamut converting unit 10 stores the lookup tables shown in FIG. 5, receives the surrounding brightness data ADB, selects a lookup table corresponding to the surrounding brightness, inputs source data RGB to the selected lookup table, The data of the modulation value selected in (R ' _out G ' _out B ' _out . The gamut changing unit 10 may be embedded in the timing controller 11. [

FIGS. 7 and 8 are diagrams showing experimental results of the present invention. FIG.

Referring to Figs. 7 and 8, in this experiment, the display device was selected as the liquid crystal display device. The experiment modulated the original image data with the modulation values of the selected lookup table according to the ambient brightness while changing the ambient brightness of the liquid crystal display device. According to the experimental results, the inventors of the present invention have confirmed that the color gamut perceived by the observer has become the standard gamut even if the ambient brightness of the liquid crystal display device is changed.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Therefore, 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: gamut converter 11: timing controller
12: data driving circuit 13: scan driving circuit
14: System board 15: Light sensor
100: display panel

Claims (11)

Converting source RGB data having a gamut of a standard size into first XYZ color space data;
Converting the first XYZ color space data into color space data reflecting the brightness of a surrounding environment of the display device;
Converting the color space data reflecting the brightness of the surrounding environment into the second XYZ color space data;
Converting the second XYZ color space data into RGB data to obtain modulation values;
Detecting a brightness of a surrounding environment of the display device using an optical sensor and modulating the source RGB data with a modulation value output from a lookup table selected from among first through third lookup tables according to the brightness of the surrounding environment Including,
The modulation values include,
The first modulation values set in the first lookup table to modulate the source RGB data when the white luminance of the surrounding environment is 20% brighter than the white luminance of the image displayed on the display device,
The second modulation values set in the second lookup table to modulate the source RGB data when the white luminance of the surrounding environment is 20% smaller than the white luminance of the image displayed on the display device, and
And third modulation values set in the third lookup table to modulate the source RGB data when there is no luminance of the surrounding environment. The method according to claim 1,
Wherein the color space data reflecting the brightness of the surrounding environment includes color space data defined by CIECAM02 (CIE Color Appearance Model 2002). delete delete delete Display panel;
An optical sensor for sensing a brightness of a surrounding environment of the display panel; And
And a gamut conversion unit for modulating the source RGB data with the modulation values output from the lookup table selected from among the first through third lookup tables according to the brightness of the surrounding environment sensed by the optical sensor,
The modulation values include,
The first modulation values set in the first lookup table to modulate the source RGB data when the white luminance of the surrounding environment is 20% brighter than the white luminance of the image displayed on the display device,
The second modulation values set in the second lookup table to modulate the source RGB data when the white luminance of the surrounding environment is 20% smaller than the white luminance of the image displayed on the display device, and
And third modulation values set in the third lookup table to modulate the source RGB data when there is no luminance of the surrounding environment. The method according to claim 6,
Wherein the color space data reflecting the brightness of the surrounding environment includes color space data defined by CIECAM02 (CIE Color Appearance Model 2002). delete delete delete The method according to claim 6,
The display device includes:
A display device, a liquid crystal display device, a field emission display (FED), a plasma display panel (PDP), and an electroluminescent device (EL).

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