JP2005192019A - Color conversion circuit, image display device and image processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform appropriate color conversion without increasing circuit scale and cost in a display device such as an STN type liquid crystal display, of which the gradation characteristics are not linear on a chromaticity coordinate. <P>SOLUTION: A color conversion circuit is applied, for example, to an image display device and an image processor and applies the color conversion to input image data. Generally, the color conversion of image data is performed so as to conform to color property of the display device which displays the image data. The color conversion processing is performed by a matrix operation using a matrix coefficient, wherein the matrix coefficient used for the operation is determined based on luminance component of the input image data. Thus, the matrix operation for the color conversion changes not based on a fixed coefficient but based on the luminance component of the input image data. Though there is a display device of which the gradation characteristics are not linear on the chromaticity coordinate and the color property fluctuates by a luminance level, etc., depending on characteristics of the display device, the color conversion conforming to such a display device is performed since the matrix coefficient is changed based on the luminance component of the input image data by the above-mentioned color conversion circuit. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to color conversion processing of image data, and more particularly to color conversion processing by matrix calculation.

  In an image display device that displays image data, processing for adjusting display characteristics of image data according to characteristics of a display device such as a CRT or LCD is performed. As typical image processing, color conversion processing is performed on input image data, and then gradation characteristic correction (also referred to as gamma correction) according to the characteristics of the display device is performed to display an image on the display device.

  An example of an image display device that performs color conversion processing by 3 × 3 matrix calculation and performs gradation characteristic correction (gamma correction) using a three-dimensional lookup table (LUT) is described in Patent Document 1.

  However, if a three-dimensional lookup table is used, the amount of data to be stored becomes enormous, which increases the circuit scale and inevitably increases costs.

  On the other hand, there is an image display apparatus that performs image processing by color conversion processing using a 3 × 3 matrix operation and gradation characteristic correction using a one-dimensional lookup table. In this case, since the look-up table is one-dimensional and the matrix calculation coefficient is also fixed, color conversion suitable for the characteristics of the display device cannot be sufficiently performed when the display device is a liquid crystal display device. Sometimes.

  In the case of a liquid crystal display device, the gradation characteristics may not be a straight line on the chromaticity coordinates. In particular, in STN liquid crystal and the like, since display is performed in the birefringence mode, there is a tendency that the gradation characteristics are not linearly changed on the chromaticity coordinates because each RGB color is colored depending on the gradation value.

  FIG. 11 shows an example of color characteristics of a certain liquid crystal display device. In FIG. 11, the color in the chromaticity coordinates is a color range that can be visually recognized by humans, and the sRGB color space, which is a standard color reproduction standard, is located inside the color range. Now, it is assumed that the color characteristic at a certain luminance level of a certain liquid crystal display device is a characteristic C1. If the gradation characteristic of the liquid crystal display device is linear on the chromaticity coordinates, the color characteristics at other luminance levels also coincide with the characteristic C1. Therefore, if color conversion is performed by the color conversion processing circuit in the image display device so that the characteristic C1 is within the sRGB color space (see arrow 72), the sRGB color is displayed on the liquid crystal display device regardless of the luminance level. Display is possible in the standard color space.

  However, when the gradation characteristics are not linear on the chromaticity coordinates, the color characteristics at other luminance levels do not coincide with C1, and may exhibit different characteristics such as the characteristic C2, for example. In this case, even if the same color conversion processing (shown by the arrow 72) as in the case of the characteristic C1 is performed, the characteristic C2 at the luminance level cannot be contained in the standard color space of sRGB.

  In general, color conversion processing using a 3 × 3 matrix operation is an arithmetic processing for converting the axis of each color in the color space, so that the gradation characteristics are not linear on the chromaticity coordinates as described above. That is, if the gradation characteristic is distorted and the color characteristic C differs depending on the luminance level as in the above example, it cannot be corrected sufficiently.

Japanese Patent Laid-Open No. 9-271036

  The present invention has been made in view of the above points. For example, an STN type liquid crystal display device such as an STN type liquid crystal display device has a gradation characteristic that is not linear on the chromaticity coordinates without increasing the circuit scale and cost. Another object of the present invention is to provide a color conversion circuit, an image display device, and an image processing method capable of performing appropriate color conversion.

  In one aspect of the present invention, the color conversion circuit includes: a matrix calculation unit that performs color conversion of input image data by matrix calculation using matrix coefficients; and the matrix coefficient based on a luminance component of the input image data. And a matrix coefficient setting unit to be determined.

  The color conversion circuit is applied to, for example, an image display device or an image processing device, and performs color conversion on input image data. In general, color conversion of image data is performed so as to match the color characteristics of a display device that displays the image data. The color conversion process is performed by matrix calculation using matrix coefficients. Here, the matrix coefficient used for the calculation is determined based on the luminance component of the input image data. Therefore, the matrix calculation for color conversion changes based on the luminance component of the input image data, not a fixed coefficient. Depending on the characteristics of the display device, the gradation characteristics may not be linear on the chromaticity coordinates, and the color characteristics may vary depending on the luminance level. According to the above color conversion circuit, the luminance component of the input image data Since the matrix coefficient is changed based on this, color conversion suitable for such a display device can be performed.

  In one aspect of the color conversion circuit, the input image data is RGB color image data, and the matrix coefficient setting unit includes a luminance calculation unit that generates luminance data from the RGB color image data; A coefficient calculation unit that sets the matrix coefficient based on luminance data. In this aspect, luminance data is generated from RGB input image data, and matrix coefficients are determined based on the luminance data. Therefore, color conversion based on the luminance component of the input image data is possible.

  In another aspect of the color conversion circuit, the coefficient calculation unit may multiply the matrix coefficient by multiplying a predetermined coefficient by the adjustment coefficient, an adjustment coefficient determination part that determines an adjustment coefficient based on the luminance data. An adjustment calculation unit to be determined. In this aspect, an adjustment coefficient is prepared for each luminance data, and the matrix coefficient can be adjusted by a simple process by multiplying this by a predetermined coefficient.

  In one preferred embodiment, the adjustment coefficient determination unit includes a register that holds the adjustment coefficient corresponding to the luminance data for each of the RGB colors. By holding the adjustment coefficient in the register, it is possible to quickly obtain the adjustment coefficient corresponding to the luminance data.

  In another preferred embodiment, the adjustment coefficient determination unit includes a look-up table that stores a common adjustment coefficient having a fixed value, and a register that holds an adjustment coefficient for each color of RGB. An adjustment coefficient can be obtained by multiplying the adjustment coefficient stored in the lookup table by the adjustment coefficient for each color held in the register.

  In another aspect of the color conversion circuit, the input image data is RGB color image data, and the matrix coefficient setting unit determines the color of the color based on the luminance component of the color image data of the RGB colors. A matrix coefficient to be multiplied with the input image data is set.

  In this aspect, matrix coefficients are determined for RGB input image data based on the luminance component for each color. Therefore, color conversion based on the luminance component of the input image data is possible.

  In another aspect of the color conversion circuit, the coefficient calculation unit includes an adjustment coefficient determination unit that determines an adjustment coefficient based on a luminance component of each color image data of each of the RGB colors, and the adjustment coefficient is set to a predetermined coefficient. An adjustment calculation unit that multiplies and determines the matrix coefficient. In this aspect, the matrix coefficient can be adjusted by a simple process by preparing an adjustment coefficient for each color image data and multiplying this by a predetermined coefficient.

  In one preferred embodiment, the adjustment coefficient determination unit includes a register that holds the adjustment coefficient corresponding to the luminance component of the color image data of each color for each of the RGB colors. By holding the adjustment coefficient in the register, it is possible to quickly obtain the adjustment coefficient corresponding to the luminance data.

  In another preferred embodiment, the adjustment coefficient determination unit includes a look-up table that stores a common adjustment coefficient having a fixed value, and a register that holds an adjustment coefficient for each color of RGB. An adjustment coefficient can be obtained by multiplying the adjustment coefficient stored in the lookup table by the adjustment coefficient for each color held in the register.

  In another aspect of the present invention, an image display device includes the above-described color conversion circuit, a gradation correction unit that performs gradation correction on the image data color-converted by the color conversion circuit, and the gradation-corrected image data. And a display unit for displaying. By applying the color conversion circuit to the image display device, color conversion suitable for the characteristics of the display device can be performed, and display quality can be improved.

  In another aspect of the present invention, an image processing method includes: a matrix coefficient setting step for setting a matrix coefficient based on a luminance component of input image data; and a matrix operation using the set matrix coefficient. And a matrix operation step for performing color conversion.

  According to the image processing method described above, the color conversion process is performed by matrix calculation using matrix coefficients. Here, the matrix coefficient used for the calculation is determined based on the luminance component of the input image data. Therefore, the matrix calculation for color conversion changes based on the luminance component of the input image data, not a fixed coefficient. Depending on the characteristics of the display device, the gradation characteristics may not be linear on the chromaticity coordinates, and the color characteristics may vary depending on the luminance level. According to the image processing method described above, the luminance component of the input image data Since the matrix coefficient is changed based on this, color conversion suitable for such a display device can be performed.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[Image display device]
FIG. 1 is a block diagram showing a schematic configuration of an image display apparatus to which a color conversion circuit of the present invention is applied. As illustrated, the image display apparatus 100 includes an image processing circuit 101 and an image display unit 102. Examples of the image display device 100 include a mobile phone, a portable terminal, a PDA, and a digital camera.

  The image processing circuit 101 performs color conversion processing, gradation characteristic correction processing including gamma correction, and the like on the image data D1 input from the outside, and supplies the corrected image data D10 to the image display unit 102. Note that the image processing circuit 101 also receives a clock signal CLK synchronized with the image data D1. The image display unit 102 includes a display device such as a CRT or LCD (Liquid Crystal Display), for example, and displays the corrected image data D10.

[Image processing circuit]
FIG. 2A is a block diagram showing an internal configuration of the image processing circuit 101 shown in FIG. As illustrated, the image processing circuit 101 includes a color conversion calculation unit 10, a gradation correction unit 20, and a color reduction processing unit 30.

  The color conversion calculation unit 10 is a part to which the color conversion circuit of the present invention is applied, performs color conversion processing to desired color characteristics on the image data D10 input from the outside, and the image data D2 after color conversion Is supplied to the gradation correction unit 20. The input image data D10 is RGB digital data of 8 bits for each color, and the color conversion calculation unit 10 performs color conversion processing by 3 × 3 matrix calculation shown in FIG. The image data D2 after color conversion is also RGB data of 8 bits for each color. In addition to the image data D1, a register control signal Sc is input to the color conversion calculation unit 10.

  The gradation correction unit 20 performs gamma correction as gradation characteristic correction on the color-converted image data D2, and supplies the corrected image data D3 to the color reduction processing unit 30. The corrected image data D3 is also RGB 8-bit data for each color. Note that the register control signal Sc is input to the gradation correction unit 20.

  The color reduction processing unit 30 performs color reduction processing on the image data D3 after gamma correction. As described above, the image data D3 after gamma correction is 8-bit data for each RGB color, and the color reduction processing unit 30 converts the upper 6 bits into, for example, 6-bit data for each RGB color, and the lower 2-bit data. Based on the above, dither processing is applied to supply 6-bit RGB image data D10 (corresponding to 8 bits for each color by dither processing) to the image display apparatus 102.

  Depending on the display capability of the image display unit 102, the color reduction processing unit 30 can also supply 8-bit image data of each color to the image display unit 102 without performing the color reduction process. For example, when the image display unit 102 has an 8-bit display capability for each color, the color reduction processing unit 30 may supply 8-bit image data D10 for each color to the image display unit 102 without performing the color reduction processing. On the other hand, if the image display unit 102 has only 6-bit display capability for each color, the color reduction processing unit 30 can create 6-bit image data for each color by the color reduction processing and supply the image data to the image display unit 102. In addition to the image data D3 after the gamma correction, the color reduction processing unit 30 is supplied with a register control signal Sc, and a horizontal synchronization signal Hsync and a vertical synchronization signal Vsync synchronized with the image data D1.

  Note that in an actual image display apparatus, γ-corrected data is often input as the input image data D1. In this case, the input image data is input to the color conversion calculation unit 10 by performing inverse γ conversion. Then, the color conversion calculation unit 10 performs color conversion on the linear image data and inputs it to the gradation correction unit 20. The gradation correction unit 20 performs γ correction in consideration of the characteristics of the display device used for the image display unit 102.

[Color conversion operation section]
Next, the color conversion calculation unit 10 will be described in detail.

(First embodiment)
FIG. 3 shows the configuration of the color conversion arithmetic unit 10a according to the first embodiment. The color conversion calculation unit 10a includes multipliers 11 to 13, an adder 14, a register value control unit 15, multipliers 41 to 43, a luminance calculation unit 44, and an adjustment coefficient calculation unit 45a. The 3 × 3 matrix operation shown in (b) is performed. Coefficients a1 to c1, a2 to c2, and a3 to c3 to be multiplied by the multipliers 11 to 13 are generated by the register value control unit 15, the luminance calculation unit 44, the adjustment coefficient calculation unit 45a, and the multipliers 41 to 43. And supplied to each multiplier 11-13.

  Specifically, the multiplier 11 multiplies R (red) data Rin in the image data D1 by coefficients a1 to c1 and outputs the result to the adder 14. Multiplier 12 multiplies G (green) data Gin in image data D1 by coefficients a2 to c2, and outputs the result to adder 14. The multiplier 13 multiplies the B (blue) data Bin of the image data D1 by coefficients a3 to c3 and outputs the result to the adder 14. The adder 14 adds the outputs of the multipliers 11 to 13 to generate Rout, Gout, and Bout, and outputs these as image data D2.

  The color characteristics of the output image data D2 (that is, Rout, Gout, and Bout) change according to the coefficients a1 to c1, a2 to c2, and a3 to c3 set by the register value control unit 15. If the coefficients a1, b2 and c3 are set to “1” and other count values are set to “0”, the input image data D1 and the output image data D2 have the same color characteristics. For example, when the output image data D2 is desired to have a color characteristic in which red is stronger, the coefficients a1 to c1 multiplied by Rin may be set larger.

  The present invention is characterized in that the coefficients a1 to c3 are set based on the luminance component of the input image data. Specifically, the coefficient to be set in the multipliers 11 to 13 is determined by the register value control unit 15, the luminance calculation unit 44, the adjustment coefficient calculation unit 45 a, and the multipliers 41 to 43. Hereinafter, this process will be described.

  As shown in FIG. 3, the luminance calculation unit 44 receives RGB three-color input image data (color image data) Rin, Gin, and Bin, and calculates luminance data Y according to the following equation.

Y = 0.299Rin + 0.587Gin + 0.114Bin (Formula 1)
This equation is an example of an equation for calculating the luminance data Y, and the coefficients for the input image data of each color are not limited to the above example.

  The luminance calculation unit 44 inputs, for example, the upper 8 bits of the luminance data Y calculated in this way to the adjustment coefficient calculation unit 45a. The adjustment coefficient calculation unit 45a is configured by a register. That is, the adjustment coefficient calculator 45a holds the adjustment coefficient α1 for adjusting the coefficients a1, b1, and c1 to be multiplied by the multiplier 11 with respect to the input image data Rin. In this example, since the luminance data Y supplied from the luminance calculation unit 44 is 8 bits (0 to 255), the adjustment coefficient calculation unit 45a has 8 bits (256 types) corresponding to the 8-bit luminance data Y. The adjustment coefficient α1 is held. Then, the adjustment coefficient α 1 corresponding to the luminance data Y input from the luminance calculation unit 44 is input to the multiplier 41.

  Similarly, the adjustment coefficient calculator 45a holds an adjustment coefficient α2 for adjusting the coefficients a2, b2, and c2 to be multiplied by the multiplier 11 with respect to the input image data Gin. Furthermore, an adjustment coefficient α3 for adjusting the coefficients a3, b3 and c3 to be multiplied by the input image data Bin by the multiplier 11 is held. Therefore, the adjustment coefficient calculator 45a reads the adjustment coefficients α1 to α3 corresponding to the value of the luminance data Y input from the luminance calculator 44 from the internal register, and supplies the adjustment coefficients α1 to α3 to the multipliers 41 to 43, respectively.

  On the other hand, the register value control unit 15 holds fixed-value basic coefficients A1 to A3, B1 to B3, and C1 to C3. These basic coefficients are set by the register control signal Sc. The multiplier 41 calculates the adjusted coefficients a1, b1, and c1 by multiplying the basic coefficients A1, B1, and C1 supplied from the register value control unit 15 by the adjustment coefficient α1 supplied from the adjustment coefficient calculation unit 45a. And supplied to the multiplier 11. That is, the multiplier 41 performs the following multiplication.

a1 = α1 × A1,
b1 = α1 × B1 (Formula 2)
c1 = α1 × C1
Similarly, the multiplier 42 multiplies the basic coefficients A2, B2, and C2 supplied from the register value control unit 15 by the adjustment coefficient α2 supplied from the adjustment coefficient calculation unit 45a to adjust the adjusted coefficients a2, b2, and c2 is calculated and supplied to the multiplier 12. That is, the multiplier 42 performs the following multiplication.

a2 = α2 × A2,
b2 = α2 × B2 (Formula 3)
c2 = α2 × C2
Furthermore, the multiplier 43 multiplies the basic coefficients A3, B3, and C3 supplied from the register value control unit 15 by the adjustment coefficient α2 supplied from the adjustment coefficient calculation unit 45a to adjust the adjusted coefficients a3, b3, and c3. Is calculated and supplied to the multiplier 13. That is, the multiplier 43 performs the following multiplication.

a3 = α3 × A3,
b3 = α3 × B3 (Formula 4)
c3 = α3 × C3
The multipliers 11 to 13 multiply the adjusted coefficients a1 to a3, b1 to b3 and c1 to c3 supplied in this way to the input image data Rin, Gin and Bin, and the adder 14 adds the results. Output image data D2 (Rout, Gout, and Bout). That is, the multipliers 11 to 13 and the adder 14 perform the matrix operation shown in FIG.

  Thus, according to the color conversion calculation unit 10 of the present invention, the adjustment coefficient calculation unit 45a multiplies each input image data according to the luminance data Y generated based on the input image data Rin, Gin, and Bin. Adjust the coefficients of the power matrix operation. Therefore, by appropriately determining the adjustment coefficients α1 to α3, even when using a display device whose gradation characteristics are not linear, the matrix calculation coefficient is changed according to the luminance component of the input image data, and the chromaticity coordinates are changed. By moving the position of each color in, appropriate color conversion can be performed.

(Second embodiment)
Next, a second embodiment of the color conversion calculation unit will be described. In the first embodiment, as described above, the luminance data Y is calculated from the input image data, and the adjustment coefficients α1 to α3 are determined on the basis of this to adjust the matrix coefficients. On the other hand, in the second embodiment, adjustment coefficients β1 to β3 are determined based on the luminance component of the input image data of each color, and the matrix coefficient is adjusted for each color.

  FIG. 4 shows the configuration of the color conversion arithmetic unit 10b according to the second embodiment. Compared to the color conversion unit 10a according to the first example, the point that a switcher 46 is provided instead of the luminance calculation unit 44 and the internal configuration of the adjustment coefficient calculation unit 45b are different from the first example.

  The switcher 46 selects one of the input image data Rin, Gin, and Bin and supplies it to the adjustment coefficient calculator 45b in order. The adjustment coefficient calculation unit 45b is a register that holds adjustment coefficients β1 to β3 corresponding to 8-bit input image data of each color, that is, R image data, G image data, and B image data. Accordingly, the adjustment coefficient calculation unit 41 outputs the adjustment coefficient β1 for adjusting the coefficient to be multiplied with the input image data Rin based on the input image data Rin. Similarly, the adjustment coefficient calculator 41 outputs an adjustment coefficient β2 for adjusting a coefficient to be multiplied with the input image data Gin based on the input image data Gin, and based on the input image data Bin, An adjustment coefficient β3 for adjusting a coefficient to be multiplied with the input image data Gin is output.

  The subsequent processing is basically the same as in the first embodiment. That is, the multiplier 41 calculates the adjusted coefficients a1, b1, and c1 by multiplying the basic coefficients A1, B1, and C1 output from the register value control unit 15 by the adjustment coefficient β1, and supplies them to the multiplier 11. To do. The multiplier 42 multiplies the basic coefficients A2, B2, and C2 output from the register value control unit 15 by the adjustment coefficient β2, calculates adjusted coefficients a2, b2, and c2, and supplies them to the multiplier 12. The multiplier 43 calculates the adjusted coefficients a3, b3, and c3 by multiplying the basic coefficients A3, B3, and C3 output from the register value control unit 15 by the adjustment coefficient β3, and supplies the calculated coefficients to the multiplier 13. Then, the multipliers 11 to 13 and the adder 14 perform the matrix operation shown in FIG. 2B to generate data D2.

  In this embodiment, the luminance data Y is not calculated, but the adjustment coefficient is determined based on the image data of each color. Since the input image data Rin, Gin, and Bin for each color includes a luminance component for each color, and the adjustment coefficient calculator 45b sets the adjustment coefficient according to the level of each input image data, the first embodiment Similarly to the above, the matrix coefficient can be adjusted in consideration of the luminance component of the input image data.

(Third embodiment)
Next, a third embodiment of the color conversion calculation unit will be described. In the third embodiment, the processing performed in the color conversion calculation section is the same as that in the first embodiment, but the configuration of the adjustment coefficient calculation section is different. That is, the adjustment coefficient calculation unit 45a according to the first embodiment is configured by a register, but the adjustment coefficient calculation unit 45c according to the third embodiment uses a look-up table (LUT).

  FIG. 5 shows the configuration of the color conversion arithmetic unit 10c according to the third embodiment. The components other than the adjustment coefficient calculator 45c are the same as those of the color conversion calculator 10a (see FIG. 3) according to the first embodiment. That is, the luminance data Y is obtained from the input image data Rin, Gin, and Bin, the adjustment coefficients α1 to α3 are determined according to this, and the basic coefficients A1 to A3, B1 to B3, and C1 to C3 are multiplied and adjusted. The subsequent coefficients a1 to a3, b1 to b3, and c1 to c3 are determined. Then, the multipliers 11 to 13 and the adder 14 perform matrix calculation shown in FIG. 2B, and output image data D2 (Rout, Gout, and Bout) after color conversion.

  FIG. 6A schematically shows the internal configuration of the adjustment coefficient calculator 45c of the third embodiment. The adjustment coefficient calculator 45 c includes registers 51 to 53, multipliers 54 to 56, and an LUT 57. The stored contents of the LUT 57 are shown in FIG. The LUT 57 stores a basic adjustment coefficient αlut corresponding to the value of the luminance data Y. On the other hand, the registers 51 to 53 hold adjustment coefficients Xr, Xg, and Xb for each color. In this example, since the luminance data Y is 8-bit data as described above, each of the registers 51 to 53 holds 256 adjustment coefficients Xr, Xg, and Xb corresponding to the luminance data Y of 0 to 255, respectively. doing.

  The adjustment coefficients α1 to α3 finally output from the adjustment coefficient calculator 45c are generated by multiplying the basic adjustment coefficient αlut stored in the LUT 57 by the adjustment coefficient Xr, Xg or Xb for each color. Is done. For example, referring to FIG. 6B, when the basic adjustment coefficient αlut stored in the LUT 57 is multiplied by the adjustment coefficient Xr for each color held in the register 51, the result shown in FIG. An adjustment coefficient α1 is obtained. Similarly, when the basic adjustment coefficient αlut stored in the LUT 57 is multiplied by the adjustment coefficient Xg for each color held in the register 52, an adjustment coefficient α2 shown in FIG. 6B is obtained. Note that the characteristics of the adjustment coefficients α1 and α2 are merely examples.

  Next, the operation of the circuit will be described with reference to FIG. First, the luminance data Y is input to the registers 51 to 53 and the LUT 57. The LUT 57 outputs the adjustment coefficient αlut corresponding to the input luminance data Y to the multipliers 54 to 56. On the other hand, each of the registers 51 to 53 supplies adjustment coefficients Xr, Xg, and Xb corresponding to the input luminance data Y to the multipliers 54 to 56, respectively. The multipliers 54 to 56 multiply the adjustment coefficient αlut and the adjustment coefficients Xr, Xg, and Xb for each color to calculate and output the adjustment coefficients α1 to α3.

  As described above, in this embodiment, when the adjustment coefficient calculation unit is configured using the LUT, the adjustment coefficients α1 to α3 can be calculated based on the coefficient αlut in one LUT. There is no need to provide it, and the circuit scale can be reduced. Note that the third embodiment performs the same processing as the first embodiment, and it goes without saying that the coefficients of the color conversion matrix can be appropriately changed based on the luminance data as in the first embodiment. .

(Fourth embodiment)
Next, a fourth embodiment of the color conversion calculation unit will be described. In the fourth embodiment, the processing performed in the color conversion calculation section is the same as that in the second embodiment, but the configuration of the adjustment coefficient calculation section is different. That is, the adjustment coefficient calculation unit 45b according to the second embodiment is configured by a register, but the adjustment coefficient calculation unit 45d according to the fourth embodiment uses a look-up table (LUT).

  FIG. 7 shows the configuration of the color conversion arithmetic unit 10d according to the fourth embodiment. The components other than the adjustment coefficient calculation unit 45d are the same as those of the color conversion calculation unit 10b (see FIG. 4) according to the second embodiment. That is, the adjustment coefficients β1 to β3 are determined according to the input image data Rin, Gin, and Bin, respectively, and the basic coefficients A1 to A3, B1 to B3, and C1 to C3 are multiplied to adjust the adjusted coefficients a1 to a3. , B1 to b3, and c1 to c3 are determined. Then, the multipliers 11 to 13 and the adder 14 perform matrix calculation shown in FIG. 2B, and output image data D2 (Rout, Gout, and Bout) after color conversion.

  FIG. 8A schematically shows the internal configuration of the adjustment coefficient calculation unit 45c of the fourth embodiment. The adjustment coefficient calculation unit 45d includes registers 61 to 63, multipliers 54 to 56, and an LUT 57. For example, as shown in FIG. 8B, the LUT 57 stores an adjustment coefficient for Gin in the input image data. That is, in this case, the adjustment coefficient βlut = β2.

  On the other hand, the registers 61 to 63 hold adjustment coefficients Xr, Xg, and Xb for each color. In this example, since the luminance data Y is 8-bit data as described above, each of the registers 51 to 53 holds 256 adjustment coefficients Xr, Xg, and Xb corresponding to the luminance data of 0 to 255, respectively. ing. However, since βlut = β2 in this example, the adjustment coefficient Xg is “1” for all inputs.

  The adjustment coefficients β1 to β3 finally output from the adjustment coefficient calculation unit 45d are generated by multiplying the basic adjustment coefficient βlut stored in the LUT 57 by the adjustment coefficient Xr, Xg, or Xb for each color. Is done. For example, referring to FIG. 8B, when the basic adjustment coefficient βlut stored in the LUT 57 is multiplied by the adjustment coefficient Xr for each color held in the register 61, the result shown in FIG. An adjustment factor β1 is obtained. Similarly, when the basic adjustment coefficient βlut stored in the LUT 57 is multiplied by the adjustment coefficient Xb for each color held in the register 63, an adjustment coefficient β3 shown in FIG. 8B is obtained. Note that the characteristics of the adjustment coefficients β1 and β3 are merely examples.

  Next, the operation of the circuit will be described with reference to FIG. First, the input image data Rin, Gin, and Bin of each color are input to the registers 61 to 63, and the input image data Gin is input to the LUT 57. The LUT 57 outputs the adjustment coefficient βlut corresponding to the input image data Gin to the multipliers 54 to 56. On the other hand, each of the registers 61 to 63 supplies adjustment coefficients Xr, Xg, and Xb corresponding to the input image data to the multipliers 54 to 56, respectively. The multipliers 54 to 56 multiply the adjustment coefficient βlut and the adjustment coefficients Xr, Xg, and Xb for each color to calculate and output the adjustment coefficients β1 to β3.

  As described above, in this embodiment, when the adjustment coefficient calculation unit is configured using the LUT, the adjustment coefficients β1 to β3 can be calculated based on the coefficient βlut in one LUT. There is no need to provide it, and the circuit scale can be reduced. In the above example, the coefficients stored in the LUT 57 correspond to the input image data Gin, but instead, the coefficients may correspond to the input image data Rin or Bin, or may not correspond to any of them. . That is, in any case, the adjustment coefficients β1 to β3 may be obtained by multiplying the coefficients stored in the LUT 57 by the adjustment coefficients Xr, Xg, and Xb for each color.

  The fourth embodiment performs the same processing as the second embodiment, and appropriately changes the coefficient of the color conversion matrix based on the luminance component of the input image data of each color as in the second embodiment. Of course you can.

[Tone correction part]
Next, the gradation correction unit will be described. FIG. 9 shows a schematic configuration of the gradation correction unit 20 according to the first embodiment. As illustrated, the gradation correction unit 20 includes LUTs 21 and 22, a linear interpolation calculation circuit 23, and a register value control unit 24. The LUTs 21 and 22 respectively store gamma characteristics for 64 gradations (corresponding to 6 bits) as input gradation values and 256 gradations as output gradation values. Since the image data D2 output from the color conversion operation unit 10 is 8 bits for each color of RGB (corresponding to 256 gradations), the gradation correction characteristic data stored in the LUTs 21 and 22 is based on the number of gradations of the input image data. Has been reduced. Thereby, the capacity of the RAM and the like constituting the LUTs 21 and 22 can be reduced. FIG. 9A shows a portion corresponding to only R data among the three colors of RGB, but G data and B data have the same configuration.

  The LUTs 21 and 22 store gradation correction characteristic data (gamma characteristics). The gradation correction characteristic can be shown by a graph showing the relationship between the input gradation value and the output gradation value. In the LUT, the address corresponding to the input gradation value has the data corresponding to the output gradation value. Is remembered. Therefore, if the gradation value of a certain pixel in the input image data is set as the input gradation value, the data stored in the LUT address corresponding to the input gradation value is output as the output gradation value. In this example, the input gradation value is 64 gradations, and the output gradation value is 256 gradations.

  In the LUTs 21 and 22 shown in FIG. 9A, the same gradation correction characteristic data is stored. The reason for providing two LUTs is that, in the linear interpolation calculation by the linear interpolation calculation circuit 23, output tone values at two end points having characteristics to be subjected to linear interpolation are required.

  In FIG. 9A, the LUT 21 receives the upper 6 bits Rout (7..2) of R data of a certain pixel in the image data D2. In the following description, the parentheses in the notation Rout () indicate the target bit. For example, Rout (7..0) is indicated for all 8 bits, and Rout (1..0) is indicated for the lower 2 bits. The LUT 21 outputs the output gradation value when the R data is the input gradation value to the linear interpolation arithmetic circuit 23 as Xn.

  On the other hand, the LUT 22 receives the gradation value Rout-1 (7..0) that is one lower than the Rout (7..0) input to the LUT 21 as the input gradation value, and the corresponding output gradation value Xn. −1 is output to the linear interpolation operation circuit 23. In addition, the lower 2 bits Rout (1..0) of the same pixel are supplied to the linear interpolation calculation circuit 23.

  FIG. 9B schematically shows the linear interpolation calculation performed by the linear interpolation calculation circuit 23. As described above, the input image data is 8 bits for each color of RGB, whereas the input gradation value of the gradation correction characteristic data stored in the LUTs 21 and 22 is 6 bits (64 gradations). There is only. Therefore, it is necessary to interpolate the output gradation value corresponding to the input gradation value for 2 bits which is insufficient by the linear interpolation calculation circuit 23. As shown in FIG. 9B, the linear interpolation calculation circuit 23 outputs the output gradation value Xn corresponding to the input gradation value Rout (7..2) of a certain pixel and the input gradation one lower than it. Between the output gradation value Xn-1 corresponding to the value Rout-1 (7..0), the three output gradation values are linearized based on the value of the lower 2 bits Rout (1..0) of the pixel. Performs interpolation. Thus, the linear interpolation calculation circuit 23 can create gradation correction characteristic data for 256 gradations (8 bits) using the LUTs 21 and 22 for 64 gradations (6 bits).

[Color reduction processing section]
Next, the color reduction processing unit will be described in detail. As shown in FIG. 10, the color reduction processing unit 30 converts 8-bit image data D3 of R, G, and B output from the gradation correction unit 20, that is, R (lut_out), G (lut_out), and B (lut_out) into bit slices and The image data is reduced to 6-bit image data for each color by dither processing and output as image data D10. FIG. 10 shows a configuration example of the color reduction processing unit 30. FIG. 10 shows only the portion corresponding to the R data among the three RGB colors, but the G data and the B data have the same configuration.

  In FIG. 10, the color reduction processing unit 30 includes 2-bit counters 31 and 32, a dither matrix circuit 33, an adder 34, a switcher 35, and a register value control unit 36. In the dither matrix circuit 33, a known 4 × 4 dither matrix is used.

  The counter 31 outputs a 2-bit X address Xad to the dither matrix circuit 33 by counting the clock signal CLK synchronized with the image data D3. The counter 31 is reset by the horizontal synchronization signal Hsync. The counter 32 counts the horizontal synchronization signal Hsync, thereby outputting a 2-bit Y address Yad to the dither matrix circuit 33. The counter 32 is reset by the vertical synchronization signal Ysync.

  The dither matrix circuit 33 supplies a value defined in the dither matrix to the adder 34 as R (D_out) based on the input X address Xad and Y address Yad. The adder 34 adds the R data R (lut_out) output from the gradation correction unit 20 and the upper 2 bits of the value R (D_out) output from the dither matrix circuit 33, and the upper 6 bits of the result. Is output to the input terminal b of the switcher 35 as R (ADD_out). In this way, the 8-bit image data D3 for each color of RGB supplied from the gradation correction unit 20 is reduced to 6-bit image data for each color. Since dither processing is applied, 6-bit image data for each color has color characteristics equivalent to 8 bits for each color.

  The output of the switcher 35 is switched according to the register value output from the register value control unit 36 based on the register control signal Sc. When the input terminal a of the switcher 35 is selected, 8-bit image data for each color of RGB that is not subjected to color reduction processing is output as image data D10. When the input terminal b of the switcher 35 is selected, 6-bit image data of each RGB color obtained by the color reduction process is output as the image data D10.

  As described above, the example of the image display device to which the color conversion circuit of the present invention is applied has been described mainly using the display device using liquid crystal as an example, but the present invention is not limited to this, and a plasma display (PDP), It can also be applied to organic EL display devices, field emission displays (FED), etc. In particular, the organic EL is effective because the display characteristics are influenced by the material characteristics, so that non-linear characteristics are easily generated, and the intermediate luminance characteristics need to be adjusted.

1 is a block diagram of an image display device to which a color conversion circuit of the present invention is applied. FIG. 2 is a block diagram showing an internal configuration of the image processing circuit shown in FIG. 1. It is a block diagram of a first embodiment of a color conversion operation unit. It is a block diagram of 2nd Example of a color conversion calculating part. It is a block diagram of 3rd Example of a color conversion calculating part. FIG. 6 is a block diagram of an adjustment coefficient calculation unit shown in FIG. 5. It is a block diagram of 4th Example of a color conversion calculating part. It is a block diagram of the adjustment coefficient calculating part shown in FIG. It is a block diagram of the gradation correction | amendment part shown in FIG. FIG. 2 is a block diagram of a color reduction processing unit shown in FIG. 1. It is a figure which shows the example of the color reproduction space of a certain display device.

Explanation of symbols

10 color conversion operation unit, 11-13 multiplier, 14 adder, 20, 20a, 20b gradation correction unit, 21, 22, 25-28 LUT, 23 linear interpolation operation circuit, 29 data switcher, 30 color reduction processing unit, 31, 32 counter, 33 dither matrix circuit, 34 adder, 35 switcher, 41 to 43 multiplier, 44 luminance calculation unit, 45 adjustment coefficient calculation unit, 46 switcher, 100 image display device

Claims (11)

A matrix calculation unit that performs color conversion of input image data by matrix calculation using matrix coefficients;
A color conversion circuit comprising: a matrix coefficient setting unit that sets the matrix coefficient based on a luminance component of the input image data. The input image data is RGB color image data,
The matrix coefficient setting unit generates a luminance data from the RGB three-color image data,
The color conversion circuit according to claim 1, further comprising: a coefficient calculation unit that sets the matrix coefficient based on the luminance data. The coefficient calculation unit includes an adjustment coefficient determination unit that determines an adjustment coefficient based on the luminance data;
The color conversion circuit according to claim 2, further comprising: an adjustment calculation unit that determines the matrix coefficient by multiplying a predetermined coefficient by the adjustment coefficient.   The color conversion circuit according to claim 3, wherein the adjustment coefficient determination unit includes a register that holds the adjustment coefficient corresponding to the luminance data for each of the RGB colors.   The color conversion according to claim 3, wherein the adjustment coefficient determination unit includes a lookup table that stores a common adjustment coefficient having a fixed value, and a register that holds an adjustment coefficient for each color of RGB. circuit. The input image data is RGB color image data,
2. The color conversion circuit according to claim 1, wherein the matrix coefficient setting unit sets a matrix coefficient to be multiplied with the input image data of the color based on a luminance component of the image data of the RGB colors. The coefficient calculation unit, an adjustment coefficient determination unit that determines an adjustment coefficient based on a luminance component of image data of each of the RGB colors;
The color conversion circuit according to claim 6, further comprising an adjustment calculation unit that determines the matrix coefficient by multiplying a predetermined coefficient by the adjustment coefficient.   The color conversion circuit according to claim 7, wherein the adjustment coefficient determination unit includes a register that holds the adjustment coefficient corresponding to a luminance component of color image data of the color for each of the RGB colors.   The color conversion according to claim 8, wherein the adjustment coefficient determination unit includes a lookup table that stores a common adjustment coefficient having a fixed value, and a register that holds an adjustment coefficient for each color of RGB. circuit. A color conversion circuit according to any one of claims 1 to 9,
A gradation correction unit that performs gradation correction on the image data color-converted by the color conversion circuit;
An image display device comprising: a display unit configured to display the gradation-corrected image data. A matrix coefficient setting step for setting the matrix coefficient based on the luminance component of the input image data;
And a matrix calculation step of performing color conversion of input image data by matrix calculation using the set matrix coefficient.

Images