KR20080016016A - Apparatus and method for color gamut mapping of color image - Google Patents

Abstract

An apparatus and a method for mapping the color gamut of a color image are provided to enhance the color reproduction of a display device in real time by measuring a color display difference on-line or off-line and downloading a function to correct the difference to a 3-D LUT(LookUp Table) properly. A color gamut conversion apparatus consists of a 3-D LUT(100), a tetrahedral location calculator(200), and a tetrahedral interpolator(300). The 3-D LUT(100) stores conversion values corresponding to upper "n" bits of an input color image. The tetrahedral location calculator(200) finds the location of a tetrahedron containing a new color gamut mapping value through lower "n" bits of the input image and calculates the height of the tetrahedron. Using the 3-D conversion data outputted from the 3-D LUT(100) and the height data outputted through the tetrahedral location calculator(200), the tetrahedral interpolator(300) executes tetrahedral interpolation. In this case, the 3-D LUT(100) outputs 3-D color conversion values corresponding to 4 apexes of the tetrahedron.

Description

Apparatus and method for color gamut mapping of color image}

1A to 1D are views for explaining a method for converting color signals used in a conventional display device;

2 is a block diagram illustrating an apparatus for converting color gamut according to an embodiment of the present invention;

3 is a view showing the internal configuration of a three-dimensional tetrahedral lookup table according to the present invention,

4 is a view for explaining the operation of the tetrahedral calculation unit according to the present invention in detail,

5 is a view for explaining the operation of the tetrahedral interpolation unit in detail according to the present invention,

6 is yet another view for explaining in detail the actual configuration of the three-dimensional tetrahedral lookup table according to the present invention.

7 is yet another view for explaining in detail the actual configuration of the three-dimensional tetrahedral lookup table according to the present invention.

Explanation of symbols on the main parts of the drawings

100: three-dimensional tetrahedral lookup table 120: address decoder

140: lookup table unit 160: data switch unit

200: tetrahedral interpolation unit 300: tetrahedral position calculation unit

The present invention relates to a device that improves the color reproducibility of a display when a display device outputs an image in real time, and can correct color reproducibility caused by a difference in color reproduction mechanisms between display devices using a gamut mapping method. The present invention relates to a device and a method for correcting a color of an input image in real time according to characteristics of a display device by using a three-dimensional lookup table and a tetrahedral interpolation method.

Recently, not only CRT but also large screen PDP TV, LCD TV, etc. are being developed. Projection TV using PRT, DLP, LCD, LCoS, etc. has been developed competitively, and it has been spotlighted as a display device for high definition HDTV. As the various types of display devices are developed and utilized, color reliability becomes very important. Color reliability is a problem of displaying different colors for the same video signal input because each display device has unique display characteristics. . This problem may occur in the case of displaying different colors for the same signal input due to physical, electrical and kinematic differences in the manufacturing process even for the same type of display device as well as other kinds of displays. In particular, recently developed display devices have a large difference in color reproducibility due to lack of stability for each component due to continuous technology development. Therefore, studies are currently being made to overcome these differences, but there are difficulties in considering all the differences in the phosphors used, the characteristics of the color filters, and the differences in the brightness level generation characteristics of each color.

Currently, in the case of most display devices, various characteristics of the display device are adjusted using the circuit shown in FIG. 1A. That is, the brightness, contrast, hue and saturation of the display screen are adjusted using the circuit shown in FIG. 1A. In such a structure, it is possible to adjust the color reproduction characteristics required in a specific display device, but there is a difficulty in adjusting the difference in the color reproduction characteristics of the heterogeneous display device. That is, as mentioned above, different display devices have different color reproduction mechanisms, different types of phosphors or color filters are used, and gamma characteristics for expressing various brightness levels are different. Different colors are reproduced.

In order to solve this problem, as shown in FIG. 1B, an RGB value outputted for each RGB value input is stored and used so that an arbitrary RGB input value corresponds to an output value of each display device. To display the desired color reproducibility. However, this method is theoretically the most complete method, but there are great difficulties in actual implementation. That is, to implement such a three-dimensional lookup table requires 256x256x256x3 bytes of storage space, and when implemented as an ASIC requires about 500 million gates of hardware, it is impossible to implement in hardware.

Although the idea of FIG. 1B is used to reduce the amount of hardware required, a method of appropriately reducing the resolution of the 3D lookup table may be used. The related structures are shown in FIGS. 1C and 1D.

In this case, the size of the 3D lookup table is greatly reduced by using the structure as shown in FIG. 1C, and the rest is implemented using the 3D interpolation technique. This technique reduces the conversion resolution of converting an input RGB image into an output RGB image and does not produce a big difference in overall image quality. In addition, for the actual implementation of the 3D lookup table of FIG. 1C, as shown in FIG. 1D, several 1D lookup tables are connected and used in parallel.

When performing the actual gamut mapping experiment using the 3D lookup table, 8 lookup tables are required because the cube is used.However, when the tetrahedral interpolation method is used, the interpolation is performed using 4 lookup tables. Higher performance hardware can be expected than conventional methods, such as simple and high speed processing.

In the present invention, in order to further optimize the structure of the existing resolution-reduced 3D lookup table, tetrahedral interpolation is used to further simplify the structure of the lookup table and optimize the amount of memory and hardware implementation cost through optimization of the interpolation method. There is a purpose.

In addition, the present invention can be applied regardless of the type of display device and can be applied in real time, and can be implemented at low cost with simple hardware configuration than the existing method, and can be implemented at high speed while improving color reproduction of various display devices. It is an object of the present invention to implement an apparatus and method for converting color gamut of color images.

A color gamut conversion apparatus of the present invention for achieving the above object includes a three-dimensional lookup table that stores a conversion value corresponding to the upper n bits of an input color image, and includes a new gamut mapping value through lower m bits of the input image. A tetrahedral calculation unit for finding the position of the tetrahedron and calculating the height, and a tetrahedral interpolation unit for performing tetrahedral interpolation with the three-dimensional transformation data output from the three-dimensional lookup table and the height data output through the tetrahedral calculation unit.

Here, the 3-D lookup table (3-D difference LUT) is a device for storing the conversion value corresponding to the input R, G, B value. When implementing this three-dimensional lookup table, there are various problems in configuring a three-dimensional lookup table directly. Actually, it consists of four one-dimensional lookup tables, an address decoder section for finding a location where the converted data is stored, and a data switch section.

Each of the four one-dimensional lookup tables used for the construction of the three-dimensional lookup table part provides one vertex data of the tetrahedron, and four one-dimensional lookup tables simultaneously provide color conversion data for one input image. Allow the device to calculate the appropriate conversion value.

The address decoder unit calculates the position where the corresponding data is stored for each of the R, G, and B input values, and stores the converted data off-line and on-line. Is involved in the operation of generating the converted data.

The data switch unit is necessary to optimally configure the overall hardware structure. The data provided by the four lookup tables form the vertices of the tetrahedron, but the vertex positions of the tetrahedrons change according to the R, G, and B values of the input image. To do it.

The tetrahedral calculator consists of a tetrahedral position calculation unit that finds the position of the tetrahedron including the color gamut conversion value among the six tetrahedrons in the cube, and a tetrahedral height calculation unit that calculates the height of the tetrahedron used in the interpolation unit.

The tetrahedral position calculation unit performs an operation for finding a tetrahedron including the final interpolation point P in a cube out of the upper n bits of the input image.

The tetrahedral height calculation unit changes the height commonly used for interpolation corrosion according to the six tetrahedrons included in the cube.The tetrahedral interpolation section applies the transformed value and the height value directly to the interpolated part. It plays a role in making this happen.

Finally, the tetrahedral interpolator uses the four tetrahedral vertices input from the lookup table and the tetrahedral height data input from the tetrahedral position calculator to convert the color conversion data R ', G', and B 'corresponding to the R, G, and B input images. It performs the role of outputting.

On the other hand, the color gamut conversion method of the color image of the present invention comprises the steps of (a) storing the three-dimensional color conversion data corresponding to the upper n bits of the input color image in the three-dimensional lookup table, (b) the lower m bits of the input image Computing the position and height of the tetrahedron containing the conversion value by comparing the size of the (c) the tetrahedral interpolation using the tetrahedral data output from the three-dimensional lookup table and the height data of the tetrahedron output from the tetrahedral calculator Performing the steps.

Here, the step of storing the conversion values in the three-dimensional lookup table may include calculating the addresses of four one-dimensional lookup tables using the input R, G, and B values, and color data provided by the four one-dimensional lookup tables. The method further includes a data switching step of rearranging the order properly to facilitate tetrahedral interpolation.

Hereinafter, with reference to the drawings will be described the present invention in more detail.

FIG. 2 is a block diagram illustrating an apparatus for converting color gamut of a color image according to the present invention. Referring to FIG. 2, the apparatus for converting color gamut of a color image according to the present invention may include a three-dimensional lookup table (3-D LUT) unit 100. And a tetrahedral position calculating unit 200 and a tetrahedral interpolator unit 300.

First, the 3D lookup table unit 100 is an apparatus that stores the converted values corresponding to the input R, G, and B values.

The three-dimensional lookup table 100 is actually composed of four one-dimensional lookup tables, an address decoder section, and a data switch section.

FIG. 3 is a diagram illustrating the configuration of the address decoder 120, the four one-dimensional lookup table 140, and the data switch 160 forming the lookup table 100.

3D lookup table 100 is composed of a one-dimensional lookup table 140 of the same depth (depth) as shown in Figure 3 and each one-dimensional lookup table provides one vertex data of one tetrahedron The four one-dimensional lookup tables for the input image simultaneously provide the conversion values, so that the tetrahedral interpolator 300 can calculate the appropriate conversion values.

Referring to FIG. 3, the address decoder 120 calculates a location where data corresponding to each of the R, G, and B input values is stored, and stores the converted data offline and the converted data online. It is involved in the generating operation.

The data switch 160 part is not necessarily required, but by placing this block, the overall hardware structure can be optimally configured. The data provided by the four lookup tables 140 constitute tetrahedral vertices, but the vertex positions of the tetrahedrons change according to the R, G, and B values of the input image. To be able to perform

The four lookup table units 140 are apparatuses for storing corresponding R, G, and B values inputted to the 3D lookup table 100.

As shown in FIG. 1C, in the case of the existing three-dimensional lookup table, the lookup table is used to store color conversion results with respect to input R, G, and B input values. At this time, instead of storing the conversion values for all input signals, the input signal level is properly sampled to store only the conversion values of limited representative coordinates. For example, to store the color conversion value in the sampled portion of the 32-level unit of the color signal to construct a three-dimensional lookup table, the color conversion value may be stored using the upper 3 bits of the color signal. If Rin, Gin, and Bin are represented respectively, and the color conversion function is expressed as gm _component (.), The color conversion values stored in the lookup table can be expressed as follows.

Rout [7: 0] = gm _red (Rin [7: 5], Gin [7: 5], Bin [7: 5]) (1)

Gout [7: 0] = gm _green (Rin [7: 5], Gin [7: 5], Bin [7: 5]) (2)

Bout [7: 0] = gm _blue (Rin [7: 5], Gin [7: 5], Bin [7: 5]) (3)

As a result of performing various color conversions using this structure, in most cases, it is not necessary to store 8-bit or 10-bit full image information for each of R, G, and B signals in order to store conversion rules. Storing only the values can significantly reduce storage space and overall hardware implementation costs.

In addition, even when considering the high-speed operation of 160MHz, the color conversion operation can be calculated in 5 ~ 7 pixels by adding all the memory read operation, 3D interpolation operation, tetrahedral position calculation, etc. You can get it.

The tetrahedral calculation unit 200 performs a role of finding a tetrahedron in the cube including conversion values R ', G', and B 'values corresponding to R, G, and B inputs, as shown in FIG. 4A. The position of the tetrahedron including the transformed value can be obtained by comparing the magnitudes of the lower m-bit values r, g, and b of the input image. As shown in FIG. 4B, the cube is divided into six tetrahedrons. Is as follows.

Tetrahedron T1: b ?? g> r

Tetrahedron T2: g> r> b

Tetrahedron T3: g> b ?? r

Tetrahedron T4: r ?? b> g

Tetrahedron T5: b> r ?? g

Tetrahedron T6: r ?? g ?? b

The tetrahedral position calculating unit may obtain a tetrahedron including a gamut width conversion value by comparing the lower m bits of the input image as described above.

Finally, the tetrahedral interpolation unit 200 for obtaining P (R ', G', B ') values of FIG. 5 uses the ratio of the volume of the tetrahedron. In FIG. 5, transformation values corresponding to four vertices of the tetrahedron are defined as A, B, C, and D, respectively, and the volume of the tetrahedron consisting of three points and P except X among A, B, C, and D is VX, and ABCD. If V is defined as the volume of the entire tetrahedron, the final color gamut conversion value P is

(4)

(4)

Is calculated. In this equation, the ratio of total volume V to each volume VX is equal to the ratio of height, so the above equation can be simplified. Since the heights vary depending on the six tetrahedra, the tetrahedral interpolation equation has six cases as follows.

(5)T1:

(5)

(6)T2:

(6)

(7)T3:

(7)

(8)T4:

(8)

(9)T5:

(9)

(10)T6:

10

In this tetrahedral interpolation equation, the height according to the tetrahedron is calculated by the tetrahedral position calculation unit and inputted to the tetrahedral interpolation unit. You can calculate for each of the green and blue components.

In constructing the tetrahedral interpolation unit 300 there are some additional considerations.

As a first consideration, in order to perform the above tetrahedral interpolation for each given Rin, Gin, and Bin color input signal, first, the color conversion data of the four tetrahedral vertices surrounding the color input signals Rin, Gin, and Bin values are obtained. It should be available at the same time. For this purpose, the three-dimensional lookup table is actually composed of four one-dimensional lookup tables as shown in FIG. In FIG. 3, LUTs 0 to 3 are configured as a one-dimensional lookup table having a depth of 256 and a width of 8x3 = 24.

In addition, the address decoder 120 of FIG. 3 may use the information of the upper n bits of the current color input value to provide a color conversion value at a vertex of the cube including the color input value. That is, when n = 3, each color input value is divided into eight sections and has nine color conversion value storage positions for each color input channel for interpolation.

In this case, 9x9x9 = 729 coordinate points are divided into four one-dimensional lookup tables 140 and stored. For example, the mapping values for Rin = 0, Gin = 0, and Bin = 0 are stored at the first address of LUT0, and the mapping values for Rin = 32, Gin = 0, and Bin = 0 are the first of LUT1. It is stored at the address and each point of the cube including the origin is evenly stored at the first address of LUT0 ~ LUT3. In this way, all three-dimensional data can be stored in four one-dimensional lookup tables, and an example of selecting the lookup table is shown in detail in FIGS. 6 and 7.

In the case of Fig. 6, when the bin values are 0, 128, and 256 (specially considered for interpolation), the positions of the lookup table in which mapping values of the entire three-dimensional region are stored are shown. As can be seen in this figure, we can use the one-dimensional lookup table from LUT0 to LUT3 to store the mapping value of the corresponding coordinate of each tetrahedron for a specific bin value. In the case of FIG. 7, when the bin values are 32 and 160, the location of the lookup table in which mapping values of the entire 3D region are stored, and LUT0 to LUT3 may be used.

As shown in FIG. 4A, since eight vertices of the cube are composed of four LUTs, LUT0 and LUT3 have one vertex, and LUT1 and LUT2 have three vertex data. This is because the tetrahedron is divided by a diagonal line sharing method. At this time, the addresses of LUT1 and LUT2 vary according to the slope including the color gamut conversion value P.

By alternately using the shapes shown in FIGS. 6 and 7, the lookup table selection area of the entire cube can be configured by overlapping nine pieces. The cube is composed of LUT0 to 3 and shared by the upper n-bit value of the input image. The values of the lookup table constituting the diagonal line are different, and the positions of the remaining two lookup tables are selected by the lower m bits of the input image. For example, for inputs with Rin = 35, Gin = 35, and Bin = 35, a cube is selected that uses LUT1 and LUT0 as a diagonal diagonal. T6 tetrahedron is selected for the tetrahedron containing P point. That is, the point A brings LUT1, the point B LUT3, the point C LUT2, and the point D bring color conversion data from LUT0.

By configuring the one-dimensional lookup table 140 as described above, the three-dimensional lookup table 100 may be optimally configured in one dimension, and in this case, four one-dimensional lookup tables having the same size are configured. For example, in the case of LUT0 of FIG. 3, as shown in FIG. 6, there are 21 color gamut mapping data stored in LUT0. Such lookup table data exists in Bin [7: 5] = 0, 4, 8. Bin [7: 5] = 1, 2, 3, 5, 6, and 7 are present. Therefore, the total LUT0 consists of 183 addresses. In this case, Rin [7: 5] = 8 has an address in only one lookup table to simplify address calculation. Therefore, there are addresses that LUT0 cannot use. There are 61 addresses. Therefore, the total address size required by LUT0 is 244. All other LUTs follow the same rules as LUT0 except for Rin [7: 5] = 8, Bin [7: 5] = 8, and Gin [7: 5] = 8 (LUT0). It consists of. Thus, when configuring LUTs with hardware, the total memory uses 256 memory sizes for all LUTs.

As a second consideration, the output of each one-dimensional lookup table does not output specific position vertex data of the tetrahedron, but the data of arbitrary vertex positions are output. That is, as in the previous example, the output of LUT0 may correspond to point A or point D of the tetrahedron of FIG. 5, and may provide a value corresponding to all positions of the tetrahedron according to the input data value. In this case, the complexity of the interpolator will be increased later. Therefore, as shown in FIG. 3, the data switch unit 160 is placed at the output of the four one-dimensional lookup tables so that the position of the data is properly changed for any input data so that interpolation is always performed according to the same rule. 200) can be optimally configured.

As described above, the present invention has proposed a hardware structure capable of improving color reproducibility of various display devices. Various display apparatuses are currently being developed, but even the same display apparatus displays different kinds of colors with respect to the same color signal input for each set, and when the types of display apparatuses are changed, larger color errors are generated. This method provides a method of improving color reproducibility of a display device in real time by appropriately downloading a function for measuring a difference of color displays offline or online and correcting the difference to a three-dimensional lookup table.

In addition, the present invention provides a more efficient hardware structure using a tetrahedral interpolation method than the interpolation method of the conventional color reproducibility improving device. That is, in the conventional color reproducibility improving apparatus, a complex three-dimensional interpolation method was used to output interpolation results with improved color reproducibility for each color signal input. In the present invention, a tetrahedral interpolation capable of outputting the interpolation results by a simple operation. The method can reduce hardware costs and provide faster results while maintaining overall performance.

Due to the reduced hardware implementation cost, there is an advantage in high speed processing, and a display device of 1080P resolution or a high speed display device of UXGA level, which is recently developed, can be effectively implemented and applied.

In addition, although the preferred embodiment of the present invention has been shown and described above, the present invention is not limited to the above-described specific embodiment, the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

Claims (17)

In the color gamut conversion device for converting the gamut width that is the entire color space of the color signal of the input image, the device, A three-dimensional lookup table unit for storing a conversion value corresponding to the upper n bits of the input color image; A tetrahedral calculator for finding a position of a tetrahedron including a new gamut mapping value through lower m bits of the input image and calculating a height; And a tetrahedral interpolation unit for performing tetrahedral interpolation with the three-dimensional transformation data output from the three-dimensional lookup table and the height data output through the tetrahedral calculation unit.  The method of claim 1, wherein the three-dimensional lookup table A color gamut conversion device characterized by outputting three-dimensional color conversion values corresponding to four vertices of a tetrahedron The method of claim 2, wherein the three-dimensional lookup table An address decoder configured to calculate a location where corresponding data is stored for each of R, G, and B input values; A lookup table unit for providing vertex data of one tetrahedron and comprising four one-dimensional lookup tables for one input image; A switch unit for changing the positions of vertices of the tetrahedrons according to R, G, and B values of the input image, and converting them to a constant position; Color gamut conversion device characterized in that configured to include The method of claim 3, wherein the address decoder unit Color gamut conversion device characterized in that it calculates the position where the corresponding data is stored for each R, G, B input value and is involved in the operation of storing the converted data offline and generating the converted data online. The method of claim 3, wherein the one-dimensional lookup table unit Four-dimensional lookup table provides a conversion value for one input image so that the vertex data of the tetrahedron are simultaneously output so that an appropriate conversion value can be calculated by the tetrahedral interpolator. The method of claim 3, wherein the switch unit The data constituting the vertices of the tetrahedrons provided by the four lookup tables change the positions of the vertices of the tetrahedron according to the R, G, and B values of the input image. Color gamut conversion apparatus characterized in that to perform The method of claim 3, wherein the lookup table unit (2 ⁿ +1) ㅧ (2 ⁿ +1) ㅧ (2 ⁿ +1) This is the same structure as the 3D lookup table. Color gamut conversion device characterized in that it is stored in the form that can be provided at the same time the color conversion value at the vertex of the containing tetrahedron The method of claim 1, wherein the tetrahedral calculation unit A tetrahedral position calculator for comparing the size of the lower m bits of the input image and outputting the position of the tetrahedron including the transform value; And a tetrahedral height calculator configured to calculate a distance between one side of the tetrahedron and the converted value by using the lower m bits of the input image. The method of claim 9, wherein the tetrahedral position calculation unit The tetrahedron that contains the color gamut conversion value in the hexahedron determined by the upper value of the input image is compared with the sizes of the lower r, g, and b values of the input image. Color gamut conversion device characterized by calculating the tetrahedron The method of claim 9, wherein the tetrahedral height calculation unit A gamut conversion device comprising calculating a height from one side of a tetrahedron to a conversion value P necessary for easily performing tetrahedral interpolation at a rear end of a tetrahedron including a gamut conversion value. The method of claim 1, wherein the color interpolation unit Tetrahedral interpolation is performed by determining the position of the tetrahedron including the three-dimensional color conversion value corresponding to four vertices of the tetrahedral provided by the three-dimensional lookup table and the color conversion value using the lower m bits of the input image. A color gamut conversion device characterized by outputting a color conversion value of a point inside a tetrahedron In the color gamut conversion apparatus for converting a color gamut, which is the entire color space of a color signal of an input image, the method includes: A three-dimensional lookup table storing a transform value corresponding to the upper n bits of the input color image; A tetrahedral calculation step of finding a position of a tetrahedron including a new gamut mapping value through lower m bits of the input image and calculating a height; A tetrahedral interpolation step of performing tetrahedral interpolation with the three-dimensional transformation data output from the three-dimensional lookup table and the height data output through the tetrahedral calculation unit; The method of claim 12, wherein the three-dimensional lookup table An address decoder step of calculating a position where corresponding data is stored for each of R, G, and B input values; A lookup table step of providing vertex data of one tetrahedron and including four one-dimensional lookup tables for one input image; A switch step of changing the positions of the vertices of the tetrahedron according to the R, G, and B values of the input image and converting them to a constant position; Color gamut conversion method characterized in that configured to include The method of claim 12, wherein the tetrahedral calculation unit A tetrahedral position calculating step of comparing the magnitudes of the lower m bits of the input image and outputting the position of the tetrahedron including the transform value; And a tetrahedral height calculation step of calculating a distance between one side of the tetrahedron and the conversion value using the lower m bits of the input image. The method of claim 12, wherein the color interpolation unit Perform tetrahedral interpolation by determining the position of the tetrahedron including the three-dimensional color conversion values corresponding to the four vertices of the tetrahedral provided by the three-dimensional lookup table and the color conversion values using the lower m bits of the input image. And outputting a color conversion value of a point inside the tetrahedron. The method of claim 2, wherein the three-dimensional lookup table An address decoder configured to calculate a location where corresponding data is stored for each of R, G, and B input values; A lookup table unit for providing vertex data of one tetrahedron and comprising four one-dimensional lookup tables for one input image; Color gamut conversion device characterized in that configured to include The method of claim 12, wherein the three-dimensional lookup table An address decoder step of calculating a position where corresponding data is stored for each of R, G, and B input values; A lookup table step of providing vertex data of one tetrahedron and including four one-dimensional lookup tables for one input image; Color gamut conversion method characterized in that configured to include

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