The present invention relates to a color space correction circuit in a display apparatus that comprises a display device (a display) such as an organic electroluminescence (“EL”) device.
Although an organic EL device is a hopeful display device, the organic EL device can stand improvement so as to make an organic EL display marketable.
At present, main problems with the organic EL device include, for example, (1) service life, (2) luminance, (3) display uniformity, (4) color reproducibility, (5) gradation expression, and (6) contrast reduction due to an influence of external light. It is considered to be important to improve the color reproducibility if the organic EL device is to be applied to a television set.
Performances of the organic EL display largely depend on materials. A color reproduction region is, in particular, determined by respective chromaticity coordinates of luminous materials of R, G and B. Actually, however, low color purities of the luminous materials prevent ensuring sufficient color reproducibility in the color reproduction region according to an NTSC standard.
As drastic measures to improve the color purities, it is necessary to take device-related measures such as an improvement in organic materials and an improvement in a light extraction efficiency structure. However, it takes lots of time to achieve the device-related improvements. In addition, if the color purities of the present luminous materials are improved, the life is shortened, that is, the improvement in the color purities is a trade-off for the life. Thus, it takes lots of time to achieve the improvements. To promote making the organic EL display marketable, it is also necessary to take measures from viewpoints of a system.
It is an object of the present invention to provide a color space correction circuit in a display apparatus that can improve color reproducibility.
A color space correction circuit according to the present invention comprises: means for holding optimal R, G and B correction values at chromaticity coordinate points corresponding to a white, primary colors and complementary colors, respectively, in a color reproduction region of a display on a chromaticity diagram; means for connecting the respective chromaticity coordinate points corresponding to the primary colors and the complementary colors to the chromaticity coordinate point corresponding to the white in the color reproduction region of the display on the chromaticity diagram, thereby dividing the color reproduction region of the display into a plurality of areas and judging to which area the chromaticity coordinate points corresponding to input signals belong; and means for correcting R, G and B values for the input signals based on optimal R, G and B correction values corresponding to the chromaticity coordinate points that correspond to three vertexes of the area to which the chromaticity coordinate points corresponding to the input signals are judged to belong, and based on the R, G and B values for the input signals.
The optimal R, G and B correction values at the chromaticity coordinate points corresponding to the white, the primary colors, and the complementary colors, respectively, in the color reproduction region of the display on the chromaticity diagram are calculated from the chromaticity coordinate points corresponding to the white, the primary colors and the complementary colors in a target predetermined color reproduction region on the chromaticity diagram, the chromaticity coordinate points corresponding to the white, the primary colors and the complementary colors in the color reproduction region of the display on the chromaticity diagram, and the target chromaticity coordinate point corresponding to the white on the chromaticity diagram. As the target predetermined color reproduction region on the chromaticity diagram, the color reproduction region according to the NTSC standard is used, for example. The optimal R, G and B correction values at the chromaticity coordinate points corresponding to the white, the primary colors and the complementary colors, respectively, in the color reproduction region of the display on the chromaticity diagram may be set by a subjective evaluation.
A corrected luminance of an R when only the R is used differs from the corrected luminance of the R at white 100%, a corrected luminance of a G when only the G is used differs from the corrected luminance of the G at white 100%, or a corrected luminance of a B when only the B is used differs from the corrected luminance of the B at white 100%.
A corrected video signal level of an R when only the R is used differs from the corrected video signal level of the R at white 100%, a corrected video signal level of a G when only the G is used differs from the corrected video signal level of the G at white 100%, or a corrected video signal level of a B when only the B is used differs from the corrected video signal level of the B at white 100%.
A corrected luminance of a cyan, that is the complementary color for an R, when only the cyan is used differs from a sum of a corrected luminance of a G at white 100% and a corrected luminance of a B at white 100%, a corrected luminance of a magenta, that is the complementary color for the G, when only the magenta is used differs from a sum of a corrected luminance of the R at white 100% and the corrected luminance of the B at white 100%, or a corrected luminance of yellow, that is the complementary color for the B, when only the yellow is used differs from a sum of the corrected luminance of the R at white 100% and the corrected luminance of the G at white 100%.
A corrected video signal level of a cyan, that is the complementary color for an R, when only the cyan is used differs from a sum of a corrected video signal level of a G at white 100% and a corrected video signal level of a B at white 100%, a corrected video signal level of a magenta, that is the complementary color for the G, when only the magenta is used differs from a sum of a corrected video signal level of the R at white 100% and the corrected video signal level of the B at white 100%, or a corrected video signal level of yellow, that is the complementary color for the B, when only the yellow is used differs from a sum of the corrected video signal level of the R at white 100% and the corrected video signal level of the G at white 100%.
An optimal chromaticity coordinate point corresponding to a cyan that is the complementary color for an R in the color reproduction region of the display on the chromaticity diagram is set at a position shifted from a point of an intersection between a line that passes the chromaticity coordinate point corresponding to the R and the chromaticity coordinate point corresponding to the white in the color reproduction region of the display and a line that passes the chromaticity coordinate point corresponding to a G and the chromaticity coordinate point corresponding to a B in the color reproduction region of the display; toward the chromaticity coordinate point corresponding to the G or the chromaticity coordinate point corresponding to the B.
An optimal chromaticity coordinate point corresponding to a magenta that is the complementary color for the G in the color reproduction region of the display on the chromaticity diagram is set at a position shifted from a point of an intersection between a line that passes the chromaticity coordinate point corresponding to the G and the chromaticity coordinate point corresponding to the white in the color reproduction region of the display and a line that passes the chromaticity coordinate point corresponding to the R and the chromaticity coordinate point corresponding to the B in the color reproduction region of the display, toward the chromaticity coordinate point corresponding to the R or the chromaticity coordinate point corresponding to the B.
An optimal chromaticity coordinate point corresponding to a yellow that is the complementary color for the B in the color reproduction region of the display on the chromaticity diagram is set at a position shifted from a point of an intersection between a line that passes the chromaticity coordinate point corresponding to the B and the chromaticity coordinate point corresponding to the white in the color reproduction region of the display and a line that passes the chromaticity coordinate point corresponding to the R and the chromaticity coordinate point corresponding to the G in the color reproduction region of the display, toward the chromaticity coordinate point corresponding to the R or the chromaticity coordinate point corresponding to the G.
An optimal chromaticity coordinate point corresponding to a cyan that is the complementary color for an R in the color reproduction region of the display on the chromaticity diagram is set at a point of an intersection between a line that passes the chromaticity coordinate point corresponding to a G and the chromaticity coordinate point corresponding to a B in the color reproduction region of the display and a line that passes the chromaticity coordinate point corresponding to the R and the chromaticity coordinate point corresponding to the white in a target predetermined color reproduction region on the chromaticity diagram.
An optimal chromaticity coordinate point corresponding to a magenta that is the complementary color for the G in the color reproduction region of the display on the chromaticity diagram is set at a point of an intersection between a line that passes the chromaticity coordinate point corresponding to the R and the chromaticity coordinate point corresponding to the B in the color reproduction region of the display and a line that passes the chromaticity coordinate point corresponding to the R and the chromaticity coordinate point corresponding to the white in the target predetermined color reproduction region on the chromaticity diagram.
An optimal chromaticity coordinate point corresponding to a yellow that is the complementary color for the B in the color reproduction region of the display on the chromaticity diagram is set at a point of an intersection between a line that passes the chromaticity coordinate point corresponding to the R and the chromaticity coordinate point corresponding to the G in the color reproduction region of the display and a line that passes the chromaticity coordinate point corresponding to the B and the chromaticity coordinate point corresponding to the white in the target predetermined color reproduction region on the chromaticity diagram.
An embodiment in which the present invention is applied to a display apparatus that comprises an organic EL device will be described hereinafter with reference to the drawings.
1. Description of Color Reproducibility Problems
The following problems occur if color purities of R, G and B are low:
(1) low color reproducibility for primary colors,
(2) poor balance of luminances of the primary colors, and
(3) shift of color phases of complementary colors.
The respective problems will be described while referring to chromaticity coordinate characteristics according to the NTSC standard and those on the organic EL display.
(1) Color Reproducibility for Primary Colors
Referring to
Chromaticity coordinates of W (White), R (Red), G (Green) and B (Blue) according to the NTSC standard are as follows.
W (0.310, 0.316), R (0.67, 0.33), G (0.21, 0.71), B (0.14, 0.08)
Chromaticity coordinates of *W (White), *R (Red), *G (Green) and *B (Blue) on the organic EL display are as follows.
*W (0.310, 0.316), *R (0.65, 0.34), *G (0.30, 0.63), *B (0.17, 0.17)
The chromaticity coordinates of the *G and *B on the organic EL display are, in particular, located at positions closer to white rather than those of the G and B according to the NTSC standard, respectively. Therefore, the organic EL display cannot produce depths of the primary colors.
(2) Balance of Luminances of Primary Colors
According to the NTSC standard, an RGB luminance ratio at white 100% is 3:6:1. Consequently, on a display having good color purities, the RGB luminance ratio is close to 3:6:1 at white 100%.
On the other hand, on a display having low color purities, the RGB luminance ratio for realizing white 100% is largely deviated from that according to the NTSC standard. As shown in
(3) Shift of Color Phases of Complementary Colors
A complementary color for the R is C (Cyan), that for the G is M (Magenta), and that for the B is Y (Yellow).
As shown in
As for the problem (1), it is difficult to solve it by circuit technique. As for the problems (2) and (3), they can be solved by the circuit technique. In this embodiment, by realizing an optimal luminance ratio in each color space, the problems (2) and (3) are solved and the color reproducibility is improved.
2. Description of Method of Improving Color Reproducibility
In this embodiment, the RGB luminance ratio is optimized at each of the chromaticity coordinate points *W, *R, *G, *B, *C, *M and *Y corresponding to W, R, G, B, C, M and Y, respectively, in the color reproduction region of the organic EL display, and the optimized RGB luminance ratio is expanded to all the color spaces. The improvement in the color reproducibility is thereby realized. Specifically, a correction processing is performed in the following steps of procedures:
(1) calculate an RGB luminance ratio at WB (White Balance) (RGB luminance ratio at white 100%);
(2) calculate an optimal luminance of each of the primary colors (R, G B) in the color reproduction region of the display on the chromaticity diagram at each color 100%;
(3) calculate an optimal luminance of each of the complementary colors (C, M, Y) in the color reproduction region of the display on the chromaticity diagram at each color 100%;
(4) calculate optimal R, G and B correction values at the chromaticity coordinate points corresponding to the white, the primary colors and the complementary colors, respectively, in the color reproduction region of the display based on calculation results of (1) and (2); and
(5) Correct input video signals using the respective R, G and B correction values calculated at the step (4).
In
2-1. Description of Method of Calculating RGB Luminance Ratio at WB (White Balance)
LWr, LWg and LWb in the luminances with correction which are not subjected to normalization on the organic EL display shown in
First, the chromaticity coordinates of R, G and B in the color reproduction region of the organic EL display are assumed as R (xr, yr), G (xg, yg) and B (xb, yb), respectively, and a target chromaticity coordinate of the target white is assumed as W (xw, yw). The RGB luminance ratio is a ratio of R, G and B expressed by the following equations (1).
If K1 is assumed as K1=R+G+B and L is a target luminance of the white, the luminances LWr, LWg and LWb of the respective R, G and B for W are expressed by the following equations (2)
LWr=(L/K1)×R
LWg=(L/K1)×G (2)
LWb=(L/K1)×B
In this example, the LWr, LWg and LWb are 30, 40 and 30, respectively (LWr=30, LWg=40 and LWb=30) as shown in
2-2. Description of Method of Calculating Optimal Luminances of Respective Primary Colors (R, G, B) at Each Color 100% in Color Reproduction Region of Display on Chromaticity Diagram
The optimal luminances at the chromaticity coordinate points *R, *G and *B corresponding to the respective primary colors (R, G, B) in the color reproduction region of the organic EL display are calculated. First, the LRr, LGg and LBb in the luminances with correction which are not subjected to normalization on the organic EL display shown in
The method of calculating the LRr, LGg and LBb in the luminances with correction which are not subjected to normalization on the organic EL display will first be described.
The NTSC standard luminances at the chromaticity coordinate points *R, *G and *B corresponding to the respective primary colors (R, G, B) in the color reproduction region of the organic EL display are assumed as optimal luminances at the chromaticity coordinate points *R, *G and *B corresponding to the respective primary colors (R, G, B) in the color reproduction region of the organic EL display.
A case of calculating the NTSC standard luminance (0, LGg, 0) at the chromaticity coordinate point *G corresponding to the G in the color reproduction region of the organic EL display will be described herein.
Referring to
A position at which a line that passes the W and the *G intersects a line that connects the G to the Y is assumed as G′. As shown in
The value x is calculated by the following equation (3).
As shown in
The values y and z are calculated by the following equations (4) and (5), respectively.
Accordingly, the original luminance LGg on the NTSC standard chromaticity coordinate at the *G is (30y/100)+60+(10z/100).
Likewise, the optimal luminance (LRr, 0, 0) at the chromaticity coordinate point *R corresponding to the R in the color reproduction region on the organic EL display, and the optimal luminance (0, 0, LBb) at the chromaticity coordinate point *B corresponding to the B in the color reproduction region on the organic EL display are calculated. In this example, LRr, LGg and LBb are 40, 72 and 16, respectively (LRr=40, LGg=72 and LBb=16) as shown in
Next, the calculated LRr, LGg and LBb are subjected to normalization. The luminances LRr, LGg and LBb are subjected to normalization so as to satisfy LRr′+LGg′+LBb′=LWr+LWg+LWb if normalized luminances are LRr′, LGg′ and LBb′.
The normalized luminances LRr′, LGg′ and LBb′ are calculated by the following equations (6).
LRr′={LRr/(LRr+LGg+LBb)}×100
LGg′={LGg/(LRr+LGg+LBb)}×100 (6)
LBb′={LBb/(LRr+LGg+LBb)}×100
In this example, LRr′, LGg′ and LBb′ are 31, 56 and 13 (LRr′=31, LGg′=56 and LBb′=13), respectively, as shown in
2-3. Description of Method of Calculating Optimal Luminances of Respective Complementary Colors (C, M, Y) in Color Reproduction Region of Display on Chromaticity Diagram at Each Color 100%
Optimal luminances at the chromaticity coordinate points *C, *M and *Y corresponding to the respective complementary colors (C, M, Y) on the organic EL display are calculated. First, LCG, LCb, LMr, LMb, LYr and LYg in the luminances with correction which are not subjected to normalization on the organic EL display shown in
The method of calculating the LCG, LCb, LMr, LMb, LYr and LYg in the luminances with correction which are not subjected to normalization on the organic EL display will first be described.
A case of calculating the optimal luminance (LYr, LYg, 0) at the chromaticity coordinate point *Y corresponding to the Y in the color reproduction region of the organic EL display will be described herein with reference to
In
It is assumed that a point at which a line that connects the B to the W intersects a segment that connects the *G to the *Y is Y′. This point Y′ is the closest color to the Y according to the NTSC standard in the color reproduction region of the organic EL display. The luminance of the point Y′ relative to the color reproduction region of the organic EL display is calculated as the optimal luminance of the *Y.
As shown in
The value x is calculated by the following equation (7).
The input signal (%) corresponding to the *Y is (100, 100, 0), and the R, G and B luminances corresponding to the Y are (30, 40, 0) on the organic EL display. As shown in
Likewise, the optimal luminances (0, LCg, LCb) at the chromaticity coordinate point *C corresponding to the C in the color reproduction region of the organic EL display, and the optimal luminances (LMr, 0, LMb) at the chromaticity coordinate point *M corresponding to the M in the color reproduction region of the organic EL display are calculated. In this example, LCG, LCb, LMr, LMb, LYr and LYg are 40, 20, 25, 30, 25 and 40, respectively (LCG=40, LCb=20, LMr=25, LMb=30, LYr=25 and LYg=40) as shown in
The calculated LCG, LCb, LMr, LMb, LYr and LYg are subjected to normalization. The luminances LCG, LCb, LMr, LMb, LYr and LYg are subjected to normalization so that a sum of the luminances of the respective complementary colors is a sum of luminances of two single colors that can synthesize the complementary colors.
If normalized luminances of the luminances LCG, LCb, LMr, LMb, LYr and LYg are LCG′, LCb′, LMr′, LMb′, LYr′ and LYg′, respectively, the LCG′, LCb′, LMr′, LMb′, LYr′ and LYg′ are calculated by the following equations (8).
In this example, the LGG′, LCb′, LMr′, LMb′, LYr′ and LYg′ are 46, 23, 20, 24, 33 and 53, respectively, (LGG′=46, LCb′=23, LMr′=20, LMb′=24, LYr′=33 and LYg′=53) as shown in
2-4. Description of Method of Calculating Optimal R, G and B Correction Values at Chromaticity Coordinate Points Corresponding to White, Primary Colors and Complementary Colors, respectively, in Color Reproduction Region of Display
As shown in Table 1, optimal R, G and B correction values (correction signals) for the input video signals corresponding to the W, R, G, B, C, M and Y are calculated. That is, Rw, Gw, Bw, Rs, Gs, Bs, Gc, Bc, Rm, Bm, Ry and Gy in the correction signals shown in
First, Rw, Rs, Rm and Ry are calculated from LWr, LRr, LMr and LYr, respectively. The LWr, LRr, LMr and LYr are generically denoted by LQr. It is assumed that a maximum value of the LWr, LRr, LMr and LYr is Lmax, and that a correction value for the Lmax is 100%. As shown in
Likewise, Gw, Gs, Gc and Gy are calculated from LWg, LGg, LCg and LYg, respectively. In addition, Bw, Bs, Bc and Bm are calculated from LWb, LBb, LCb and LMb, respectively.
2-5. Description of Method of Correcting Input Video Signal Using Correction Values
As shown in
S1: R>G>B (area *W−*Y−*R)
S2: G>R>B (area *W−*Y−*G)
S3: G>B>R (area *W−*C−*G)
S4: B>G>R (area *W−*C−*B)
S5: B>R>G (area *W−*M−*B)
S6: R>B>G (area *W−*M−*R)
S7: R=G>B (line *W−*Y)
S8: G=B>R (line *W−*C)
S9: B=R>G (line *W−*M)
S10: R>G=B (line *W−*R)
S11: G>B=R (line *W−*G)
S12: B>R=G (line *W−*B)
S13: R=G=B (*W)
Herein, a case in which the magnitude relationship among the input video signals is R>G>B will be described. If the magnitude relationship among the input video signals is R>G>B, the chromaticity coordinate points corresponding to the respective input video signals belong to the S1. The area S1 is a triangle area having the *W, *Y and *R as vertexes. Therefore, the input video signals are corrected based on correction values for the *W, *Y and *R, respectively.
Table 2 shows correction values (output signals) for the input video signals corresponding to the W, Y and R.
The method of calculating the correction values (Rout, Gout, Bout) for the input video signals (Rin, Gin, Bin) will be described.
The correction values Rout, Gout and Bout are expressed as functions of the input video signals Rin, Gin and Bin, respectively, as expressed by the following equations (9)
Rout=(a1×Rin+b1×Gin+c1×Bin)/100
Gout=(a2×Rin+b2×Gin+c2×Bin)/100 (9)
Bout=(a3×Rin+b3×Gin+c3×Bin)/100
Herein, a1, a2, a3, b1, b2, b3, c1, c2 and c3 are correction coefficients.
By assigning the values shown in Table 2 to the above equations (9), the correction coefficients a1 to c3 can be calculated.
To calculate the correction coefficients a1, b1 and c1, for example, the values in Table 2 are assigned to the equation that expresses Rout in the equations (9). If so, the following simultaneous equations (10) are obtained.
Rw={100×a1+100×b1+100×c1}/100
Ry={100×a1+100×b1}/100 (10)
Rs={100×a1}/100
By solving the above simultaneous equations (10), a1=Rs, b1=Ry−Rs, and c1=Rw−Ry are obtained.
The correction coefficients a1 to c3 in the equations (9) are expressed as follows.
a1=Rs, b1=Ry−Rs, c1=Rw−Ry
a2=0, b2=Gy, c2=Gw−Gy
a3=0, b3=0, c3=Bw
Accordingly, the correction formulas for the area S1 are expressed by the following equations (11).
Rout={Rs×Rin+(Ry−Rs)×Gin+(Rw−Ry)×Bin}/100
Gout={Gy×Gin+(Gw−Gy)×Bin}/100 (11)
Bout={Bw×Bin}/100
In this way, the correction formulas for the respective areas S1 to S13 are obtained.
2. Description of Color Space Correction Circuit
The input video signals Rin, Gin and Bin are transmitted to a magnitude judgment section 10, and also transmitted to an Rout calculation section 21, a Gout calculation section 22 and a Bout calculation section 23.
The correction values Rw, Ry, Rm and Rs are applied to the Rout calculation section 21. The correction values Gw, Gc, Gy and Gs are applied to the Gout calculation section 22. The correction values Bw, Bm, Bc and Bs are applied to the Bout calculation section 23.
The magnitude judgment section 10 judges which of the 13 conditions shown in Table 3 each input video signal corresponds to, and outputs a selection signal (SELECT) corresponding to the corresponding condition. This selection signal represents which of the areas S1 to S13 the chromaticity coordinate of each input video signal corresponds to. The selection signal output from the magnitude judgment section 10 is applied to the respective calculation sections 21, 22 and 23.
The respective calculation sections 21, 22 and 23 correct the input video signal Rin, Gin and Bin by the correction formulas (correction formulas before being divided by 100 shown in
The signals Rout, Gout and Bout corrected by the respective calculation sections 21, 22 and 23 are transmitted to a DAC (Digital-to-Analog Converter) 30, and converted into analog signals by the DAC 30.
The Rout calculation section 21 includes a multiplier 41 that multiplies the Rin by a correction coefficient, a multiplier 42 that multiplies the Gin by a correction coefficient, a multiplier 43 that multiplies the Bin by a correction coefficient, an adder 44 that adds a multiplication result of the multiplier 42 to that of the multiplier 41, an adder 45 that adds a multiplication result of the multiplier 43 to that of the multiplier 44, and a bit shift circuit 46 that shifts an addition result of the adder 45 to the right by eight bits so as to divide an addition result of the adder 45 by 100.
Further, the Rout calculation section 21 includes a circuit that generates the correction coefficient according to the selection signal for the Rin, a circuit that generates the correction coefficient according to the selection signal for the Gin, and a circuit that generates the correction coefficient according to the selection signal for the Bin. The circuit that generates the correction coefficient according to the selection signal for the Rin is composed by a selection circuit 51. The circuit that generates the correction coefficient according to the selection signal for the Gin is composed by three subtractors 52, 53 and 54, and a selection circuit 55. The circuit that generates the correction coefficient according to the selection signal for the Bin is composed by two subtractors 56 and 57 and a selection circuit 58.
If the input video signals correspond to the condition of, for example, R<G<B, the magnitude judgment section 10 outputs the selection signal “1” that represents the area S1. The selection circuit 51 selects and outputs Rs, the selection circuit 55 selects and outputs Ry−Rs, and the selection circuit 58 selects and outputs Rw−Ry. Accordingly, the multiplier 41 performs an operation of Rs*Rin. The multiplier 42 performs an operation of (Ry−Rs)*Gin. The multiplier 43 performs an operation of (Rw−Ry)*Bin.
The adder 44 performs an operation of Rs*Rin+(Ry−Rs)*Gin, and the adder 45 performs an operation of Rs*Rin+(Ry−Rs)*Gin+(Rw−Ry)*Bin. The bit shift circuit 46 shifts the addition result of the adder 45 to the right by eight bits.
The ADC 30 will next be described.
A black-side reference voltage that is an output voltage when the input signal is black, and a white-side reference voltage that is an output voltage when the input signal is white are applied to the ADC 30 for each of the R, G and B signals. Based on
Generally, input/output characteristics of the ADC are adjusted so that the input signal corresponding to the white is a maximum value among the input signals as shown in
Number | Date | Country | Kind |
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2003-031541 | Feb 2003 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP04/01301 | 2/6/2004 | WO | 8/5/2005 |