JP6023148B2 - Display device - Google Patents

Description

  The present invention relates to a display device in which one pixel is composed of RGBW (red, green, blue, and white) sub-pixels, and input RGB data is converted into R′G′B′W data for display.

  FIG. 1 shows an example of a dot arrangement of a matrix type organic EL (OLED) panel in which one pixel is constituted by three subpixels (dots) of normal red, green, and blue (R, G, B). FIG. 3 shows an example of a dot arrangement of a matrix type organic EL panel that uses white (W) in addition to R, G, and B. In FIG. 2, RGBWs are arranged in the horizontal direction, and in FIG. 3, RGBWs are arranged in 2 × 2 pixels.

  The RGBW type is intended to reduce power consumption and improve luminance as a panel by using W dots having higher luminous efficiency than R, G, and B. As a method for realizing an RGBW type panel, a method using an organic EL element that emits each color for each dot, and a method for realizing dots other than W by overlaying red, green, and blue optical filters on a white organic EL element There is.

  FIG. 4 is a CIE1931 chromaticity diagram showing an example of chromaticity of white (W) used as a white pixel in addition to the three primary colors of normal red, green, and blue (R, G, B). . The chromaticity of W does not necessarily need to match the reference white color of the display.

  FIG. 5 shows a method of converting an RGB input signal that can display the reference white color of the display into an RGBW image signal when R = 1, G = 1, and B = 1.

  First, when the emission color of the W dot does not match the reference white color of the display, the following calculation is performed on the input RGB signal to normalize the emission color of the W dot (S11).

  Here, R, G, and B are input signals, Rn, Gn, and Bn are normalized red, green, and blue signals, and a, b, and c are R = 1 / a, G = 1 / b, and B, respectively. When = 1 / c, the coefficient is selected so that the luminance and chromaticity are equal to W = 1.

Examples of the most basic S, F2, and F3 arithmetic expressions are as follows.
S = min (Rn, Gn, Bn) (2)
F2 (S) =-S Formula 3
F3 (S) = S (4)

  In this case, for (Rn, Gn, Bn) obtained in S11, in S12, S (the minimum value among the normalized RGB components) is calculated by Equation 2 (S12), and the obtained S is converted to Rn. , Gn, Bn to obtain Rn ′, Gn ′, Bn ′ (S13, S14). Further, S is output as it is as a white value (Wh) (S15).

  In this case, it can be seen that the closer the color of the pixel to be displayed is to an achromatic color, the higher the ratio of lighting W dots. Therefore, the greater the proportion of achromatic colors in the displayed image, the lower the power consumption of the panel compared to using only RGB.

  Similarly to the normalization of the W dots to the emission color, if the emission color of the W dots does not match the reference white of the display, normalization to the last reference white is performed (S16). The normalization to the last reference white performs the following calculation.

  Normally, there are few images composed only of pure colors, and W dots are used in most cases, so that the overall power consumption is lower on average than when only RGB pixels are used.

Further, when M is a constant of 0 ≦ M ≦ 1, and the following equations are used for F2 and F3, the usage rate of W dots varies depending on the value of M.
F2 (S) = − MS Formula 6
F3 (S) = MS (7)

  From the viewpoint of power consumption, it is best to use M = 1, that is, a usage rate of 100%. However, in terms of visual resolution, it is better to select a value of M so that all RGBW lights up as much as possible (see Patent Document 1).

  FIG. 6 shows a schematic diagram of the conversion method in this case, assuming that normalization is not performed. For the input signal, the minimum value S in RGB is obtained (S21), and the obtained S is multiplied by a constant M to determine white (Wh) (S22). This Wh is output and subtracted from each RGB component (S23) to obtain converted R ', G', and B '.

JP 2006-003475 A

  Here, in such a display device having RGBW sub-pixels and the W usage rate set to less than 100%, an RGB signal having a bit width larger than the input bit width of the D / A converter of the RGBW source driver. Is input without reducing the gradation of the input signal as much as possible.

The present invention relates to a conversion device that converts input RGB data into R′G′B′W data in a display device that constitutes one pixel by RGBW (red, green, blue, white) subpixels, and the conversion A display unit that performs display based on the R′G′B′W data converted by the unit, and t bits, which are the bit widths of the colors of the input RGB data, are included in the R′G′B′W data. (I) W usage rate is m / n (m and n are relatively prime integers, m <n), and (ii) 1 unit Changes in W data are equivalent to changes in R ', G' and B 'in (m / n) units, respectively, and (iii) t input bits are expressed as u integer bits and (tu) fractional bits. , (Iv) W is a value obtained by rounding the minimum value among the three colors of input RGB data into integer bits of u. _{When 0} is defined, and (v) a value obtained by rounding down the decimal point of n / 2 is defined as [n / 2], W data is a value W _{0 obtained} by rounding the minimum value of input RGB data to the integer bit number of u. , − [N / 2] to + [n / 2] are selected from a plurality of added values , whereby u output bits are represented as u integer bits, and t input bits are u When expressed as an integer bit and a fractional bit of (tu), (m / n) units of R′G′B ′ data to be converted in accordance with the change of the one unit of W data are obtained. (M / n) W is added to the R′G′B ′ data converted corresponding to the W data to obtain converted RGB components, and the input RGB data and converted data corresponding to each W data The sum of the absolute values of the errors with the RGB components is calculated by weighted addition. From the above, the value of R′G′B ′ and the value of W that minimize the error are determined.

Further, the present invention provides a conversion unit that converts input RGB data into R′G′B′W data in a display device in which one pixel is composed of RGBW (red, green, blue, white) subpixels; A display unit that performs display based on the R′G′B′W data converted by the conversion unit, and t bits that are the bit widths of the colors of the input RGB data are R′G′B′W (I) The usage rate of W is set to m / n (m and n are relatively positive integers, m <n), and (ii) 1 The change in unit W data is equal to the change in R ', G' and B 'in (m / n) units respectively, and (iii) t input bits are integer bits of u and fractional bits of (tu) (Iv) rounded the minimum value among the three colors of the input RGB data to integer bits of u Was a W _0, (v) if n / 2 value obtained by truncating the decimal is defined as [n / 2], W data value W with rounded minimum value of the input RGB data to the number of integer bits of u _A plurality of values obtained by adding an integer in the range of − [n / 2] to + [n / 2] to ₀ are selected, whereby the u output bit is represented as an integer bit of u, and the t input bit is When expressed as an integer bit of u and a fractional bit of (tu), R'G'B 'data in (m / n) units to be converted according to the change in the W data in 1 unit is obtained. Then, (m / n) W is added to the R′G′B ′ data converted corresponding to each W data to obtain the converted RGB component, and the input RGB data is L as the first point. ^* u ^* v ^* or ^L * ^a * ^{b *} of expressed are converted in a color system, each W data RGB components after conversion corresponding is the table is converted in the same color system as the color system as a second point, the distance between the second point and the first point is that a minimum It is characterized by.

  According to the present invention, it is possible to display an input signal having a larger number of gradations than the maximum number of gradations of the display panel so as not to impair the gradation as much as possible.

It is a figure which shows the example of a subpixel structure of the organic electroluminescent panel using RGB dot. It is a figure which shows the example of a subpixel structure of the organic electroluminescent panel using RGBW dot. It is a figure which shows the example of a subpixel structure of the organic electroluminescent panel using RGBW dot. It is a figure showing the position of chromaticity of RGBW primary color on a CIE1931 chromaticity diagram. It is a figure which shows the example of the process which converts an RGB input signal into an RGBW image signal. It is a figure which shows the other example of the process which converts an RGB input signal into an RGBW image signal. It is a figure which shows the example of the state of input RGB and R'G'B'W after conversion. It is a figure which shows the other example of the state of input RGB and R'G'B'W after conversion. It is a figure which shows the other example of the state of input RGB and R'G'B'W after conversion. It is a figure which shows the other example of the state of input RGB and R'G'B'W after conversion. It is a figure which shows the structural example for performing determination which determines W. It is a figure which shows the structural example for performing determination which determines W. It is a figure which shows the structure of a display apparatus.

  Hereinafter, embodiments of the present invention will be described.

"Description of conversion contents"
Assume that t ≧ u, input RGB is t bits for each color, and R′G′B′W is u bits for each color. Further, the upper u bits of the input RGB are considered to be an integer part, the lower (t−u) bits are assumed to be a decimal part, and R′G′B′W after conversion is considered to be an integer. If the amount of light is proportional to the input data, the theoretical amount of light emitted for each color is
L _r1 = k _r R Formula 8
L _g1 = k _g G (Formula 9)
L _b1 = k _b B Formula 10
It can be expressed. Here, k _r , k _g , and k _b are proportional constants.

Further, the light emission after conversion is such that when the W usage rate M is m / n (m, n is a positive integer, m ≦ n),
L _r2 = k _r R ′ + k _r (m / n) W Expression 11
L _g2 = k _g G ′ + k _g (m / n) W Expression 12
L _b2 = k _b B ′ + k _b (m / n) W Expression 13
It becomes.

  If the bit widths of R ′, G ′, B ′ and W are the same and the maximum number of gradations is the same, the coefficient of W is m / n times the coefficient of R ′, G ′, B ′. Therefore, it can be seen that the amount of light emission corresponding to one gradation of W is m / n times that of R ′, G ′, and B ′.

Here, if W ′ is an integer and p is an integer of 0 ≦ p <n, (m / n) W is
(M / n) W = W ′ + p / n
Expressions 11 to 13 are expressed by L _r2 = k _r (R ′ + W ′ + p / n), respectively, Expression 14
L _g2 = k _g (G ′ + W ′ + p / n) Expression 15
L _b2 = k _b (B ′ + W ′ + p / n) Expression 16
Can be rewritten.

By the way, since the number of bits of R′G′B′W is equal to or less than the number of bits of input RGB, an error may occur during conversion, and the errors ΔLr, ΔLg, ΔLb of the light emission amounts of the respective colors are
ΔL _r = L _r1 −L _r2 = k _r (R− (R ′ + W ′ + p / n)) Equation 17
ΔL _g = L _g1 −L _g2 = k _g (G− (G ′ + W ′ + p / n)) Equation 18
_{ΔL b = L b1 -L b2 =} k b (B- (B '+ W' + p / n)) ··· formula 19
It becomes.

Here, since the values of R ′, G ′, and B ′ are selected so that the integer part of ΔL _r / k _r , ΔL _g / k _g , ΔL _b / k _b is 0, ΔL _r / k _r , ΔL _{g / k g, ΔL b /} k b is the value less than 1. Further, p varies depending on the value of W, and there are n patterns of 0, 1 / n, 2 / n,... (N−1). Therefore, there are n types of errors ΔL _r , ΔL _g , and ΔL _b, respectively. Therefore, if W that takes the minimum value is selected, the error can be minimized. n different values of p / n exist in any range from W to W + n−1, when the value of W is increased by a (a positive integer less than n) and when decreased by (n−a) Takes the same value.

Assuming that the maximum integer not exceeding x with respect to the real number x is represented by [x], the value of W is usually
W ₀ = [min (R, G, B)] Equation 20
Ask for.

For W ₀ , there is always a value of W that minimizes the error in the range of W ₀ − [n / 2] or more and W ₀ + [n / 2] or less. If it is desired to approach n, W that minimizes the error within this range should be selected. However, (m / n) W is
0 ≦ (m / n) W ≦ min (R, G, B)
It is necessary to satisfy.

  Hereinafter, the configuration of the embodiment will be described based on the drawings.

“Embodiment 1”
FIG. 7 shows an example in which the R′G′B′W value for each color of 4 bits is obtained by a conventional method from the RGB input signal of 6 bits for each color and the usage rate M of W = 3/4.

If the input RGB is an integer part 4 bits, a fraction part 2 bits and each color R = 9.75, G = 11.75, B = 7.75,
(M / n) W ₀ = (m / n) [min (9.75, 11.75, 7.75)] = (3/4) × [7.75] = (3/4) × 7 = 5.25
It becomes.

Here, when R ′, G ′, and B ′ are obtained using the obtained (m / n) W ₀ ,
R ′ = [R− (m / n) W ₀ +0.5] = [9.75−5.25 + 0.5] = [5.0] = 5
G ′ = [G− (m / n) W ₀ +0.5] = [11.75−5.25 + 0.5] = [7.0] = 7
B ′ = [B− (m / n) W ₀ +0.5] = [7.75−5.25 + 0.5] = [3.0] = 3
It becomes. Here, 0.5 is added at the end in order to round off the fraction.

When the RGB components r, g, and b at this time are obtained,
r = R ′ + (m / n) W ₀ = 5 + 5.25 = 10.25
g = G ′ + (m / n) W ₀ = 7 + 5.25 = 12.25
b = B ′ + (m / n) W ₀ = 3 + 5.25 = 8.25
Thus, each color has a value shifted by 0.5 from the input RGB.

Each time 1 is added to or subtracted from the value of W _0, the value of each color increases or decreases by m / n = 3/4 = 0.75, so adding 2 to W ₀ or subtracting 2 results in an error. I understand that it will disappear. In this case, R ′, G ′, and B ′ are recalculated with the new W value.
When W = 9,
R ′ = [R− (m / n) W + 0.5] = [9.75−6.75 + 0.5] = [3.50] = 3
G ′ = [G− (m / n) W + 0.5] = [11.75−6.75 + 0.5] = [5.50] = 5
B ′ = [B− (m / n) W + 0.5] = [7.75−6.75 + 0.5] = [1.50] = 1
When W = 5,
R ′ = [R− (m / n) W + 0.5] = [9.75−3.75 + 0.5] = [6.50] = 6
G ′ = [G− (m / n) W + 0.5] = [11.75−3.75 + 0.5] = [8.50] = 8
B ′ = [B− (m / n) W + 0.5] = [7.75−3.75 + 0.5] = [4.50] = 4
It becomes.

In both cases, the error between the input RGB and the converted RGB component is R− (R ′ + (m / n) W) = 0.
G− (G ′ + (m / n) W) = 0
B− (B ′ + (m / n) W) = 0
It becomes.

  FIG. 8 shows a case where W = 9.

By the way, the fraction of input RGB can be expressed as q (1/2) ⁽ tu) where q is an integer of 0 <q <2 ^{( tu)} . Therefore, when n is equal to 2 ^(tu) , there exists a value of p that satisfies p / n = q (1/2) ^(tu) , that is, p = q, and W is selected appropriately. The error can be reduced to zero.

  In this embodiment, (tu) = 2 satisfies the above condition, and the fractions are the same for all three colors, so that the error can be reduced to zero for all colors. In other words, it is possible to find a value of W that can express the gradation of the input as it is. As a special example, whenever a monochrome image having the same RGB value is input, a display corresponding to the gradation of the input RGB can be performed.

“Embodiment 2”
As in the first embodiment, the R′G′B′W value of 4 bits for each color is obtained from the RGB input signal of 6 bits for each color, and the usage rate M of W is considered as M = 3/5.

FIG. 9 shows an example obtained by a conventional method. If the input RGB is R = 9.75, G = 11.75, and B = 7.75,
(M / n) W ₀ = (m / n) [min (9.75, 11.75, 7.75)] = (3/5) × [7.75] = (3/5) × 7 = 4.20.

Here, when R ′, G ′, and B ′ are obtained using the obtained (m / n) W ₀ ,
R ′ = [R− (m / n) W ₀ +0.5] = [9.75−4.20 + 0.5] = [6.05] = 6
G ′ = [G− (m / n) W ₀ +0.5] = [11.75−4.20 + 0.5] = [8.05] = 8
B ′ = [B− (m / n) W ₀ +0.5] = [7.75−4.20 + 0.5] = [4.05] = 4
It becomes.

When the RGB components r, g, and b at this time are obtained,
r = R ′ + (m / n) W ₀ = 6 + 4.20 = 10.20
g = G ′ + (m / n) W ₀ = 8 + 4.20 = 12.20
b = B ′ + (m / n) W ₀ = 4 + 4.20 = 8.20
It becomes.

Here, when a difference between input RGB and converted RGB component values is obtained,
R−r = 9.75-10.20 = −0.45
G-g = 11.75-12.20 = -0.45
B−b = 7.75−8.20 = −0.45
It becomes.

  P / n obtained by changing the value of W is 0, 0.2, 0.4, 0.6, or 0.8, and the closest to 0.75 is 0.8. is there.

When 1 is added to the value of W ₀ ,
(M / n) W = (m / n) × 8 = 0.6 × 8 = 4.8, and the error is minimized in the vicinity of W = 7. W = 8 obtained by adding 1 to W ₀ It can be seen that it is.

When R ′, G ′, and B ′ are recalculated with the value of W,
R ′ = [R− (m / n) W + 0.5] = [9.75−4.80 + 0.5] = [5.45] = 5
G ′ = [G− (m / n) W + 0.5] = [11.75−4.80 + 0.5] = [7.45] = 7
B ′ = [B− (m / n) W + 0.5] = [7.75−4.80 + 0.5] = [3.45] = 3
It becomes.

RGB components r, g, b are
r = R ′ + (m / n) W = 5 + 4.80 = 9.80
g = G ′ + (m / n) W = 7 + 4.80 = 11.80
b = B ′ + (m / n) W = 3 + 4.80 = 7.80
The error from the input RGB is
R−r = 9.75−9.80 = −0.05
G-g = 11.75-11.80 = -0.05
B−b = 7.75−7.80 = −0.05
It becomes.

  FIG. 10 shows the relationship between input RGB and converted RGB components when W = 8.

  In the above embodiment, the usage rate of the finally determined W value deviates considerably from the target value m / n. This is because the bit width of R′G′B′W is as small as 4 bits. by. Also, when n is increased, the influence on the W usage rate is increased.

  In the above embodiment, since all the fractions of the input RGB are the same, the optimum value of W is the same for any color. If the fraction of each color value is different, change the fraction value selection method as shown in (1) and (2) below, depending on what is important as the fidelity of the image. Is preferred.

  (1) In this example, R ′ is set so that the absolute value of the sum of the differences between the input RGB data and the RGB components in the converted R′G′B′W data is minimized. The value of G′B ′ and the value of W are determined.

As an example, consider an input in which the difference in bit width between the input RGB and the R′G′B′W input is 2 bits, and R = 9.75, G = 11.25, and B = 7.00. When W usage rate M = 3/5,
(M / n) W ₀ = (m / n) [min (9.75, 11.25, 7.00)] = (3/5) × [7.00] = (3/5) × 7 = 4.20.

Using (m / n) W ₀ obtained here, R ′, G ′, and B ′ are obtained.
R ′ = [R− (m / n) W ₀ +0.5] = [9.75−4.20 + 0.5] = [6.05] = 6
G ′ = [G− (m / n) W ₀ +0.5] = [11.25-4.20 + 0.5] = [7.55] = 7
B ′ = [B− (m / n) W ₀ +0.5] = [7.00−4.20 + 0.5] = [3.3] = 3
It becomes.

When the RGB components r, g, and b at this time are obtained,
r = R ′ + (m / n) W ₀ = 6 + 4.20 = 10.20
g = G ′ + (m / n) W ₀ = 7 + 4.20 = 11.20
b = B ′ + (m / n) W ₀ = 3 + 4.20 = 7.20
It becomes.

Here, when a difference between input RGB and converted RGB component values is obtained,
R−r = 9.75-10.20 = −0.45
G-g = 11.25-11.20 = 0.05
B−b = 7.00−7.20 = −0.20
It becomes.

The absolute value of the sum of the differences between each input RGB and the converted RGB component is
| (R−r) + (G−g) + (B−b) |
= | (9.75-10.20) + (11.25-11.20) + (7.00-7.20) | = 0.6
It becomes.

Similarly, when W is (W ₀ -2), (W ₀ -1), (W ₀ +1), and (W ₀ +2), the absolute value of the sum of the differences is obtained.
| (9.75-10.00) + (11.25-11.00) + (7.00-7.00) | = 0.00
| (9.75-9.60) + (11.25-11.60) + (7.00-6.60) | = 0.20
| (9.75-9.80) + (11.25-10.80) + (7.00-6.80) | = 0.60
| (9.75-9.40) + (11.25-11.40) + (7.00-7.40) | = 0.20
Thus, the value of W taking the minimum value of 0.00 is (W ₀ −2) = 5.

It is also possible to multiply each difference by a weight. For example, the luminance component greatly contributes to the visual gradation characteristics, but the size of the luminance component differs for each color. Therefore, it is also preferable to multiply the weight corresponding to the luminance component of each color. If the weight of each color of RGB is 0.3, 0.6, 0.1, respectively,
| 0.3 (9.75-10.20) +0.6 (11.25-11.20) +0.1 (7.00-7.20) | = 0.125
| 0.3 (9.75-10.00) +0.6 (11.25-11.00) +0.1 (7.00-7.00) | = 0.075
| 0.3 (9.75-9.60) +0.6 (11.25-11.60) +0.1 (7.00-6.60) | = 0.125
| 0.3 (9.75-9.80) +0.6 (11.25-10.80) +0.1 (7.00-6.80) | = 0.275
| 0.3 (9.75-9.40) +0.6 (11.25-11.40) +0.1 (7.00-7.40) | = 0.025
In this case, the value of W that takes the minimum value of 0.025 is (W ₀ +2) = 9.

  FIG. 12 is a block diagram of the determination part.

A plurality of types of W are determined based on the minimum value of input RGB. At this time, an integer in a range of − [n / 2] to + [n / 2] is added to a value W _{0 obtained} by rounding the minimum value min (R, G, B) of input RGB to a predetermined number of bits. , W are determined (S31). Here, [n / 2] is a value obtained by rounding down the decimal point of n / 2. Also, here, the decimal value of the minimum value in the three colors of the input RGB data is rounded down, and the value rounded to the number of bits supplied to the panel is W ₀ = [min (R, G, B)]. However, when rounding to the number of bits supplied to the panel, it may be rounded off or rounded up.

  Next, (m / n) W is added to the obtained R ′, G ′, and B ′ to obtain r, g, and b as RGB components at this time (S 32). Next, based on the obtained r, g, and b corresponding to each W, the sum of absolute values of errors from the original RGB is calculated (S34). In this example, the total error is calculated by weighted addition. Then, the value of W is determined by selecting the smallest one of the absolute values of the obtained errors (S35).

(2) In the example of FIG. 11, W is determined such that the sum of errors in each RGB component is minimized. In this example, a color system such as L ^* u ^* v ^* or L ^* a ^* b ^* is selected so that the color difference is minimized.

Both are the color systems recommended by the CIE in 1976, and a fixed distance in the color system is determined so that there is a substantially perceptual difference in the uniform rate in any region. Accordingly, L ^* u ^* v ^* or L ^* a ^* b ^* before and after conversion are obtained, and fractional values that minimize the color difference defined by the following equations are selected.

ΔEuv = ((ΔL ^* ) ² + (Δu ^* ) ² + (Δv ^* ) ² ) ^1/2 Equation 21

Here, ΔL ^* , Δu ^* , and Δv ^* are differences between L ^* , u ^* , and v ^* before and after conversion, respectively.

ΔEab = ((ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² ) ^1/2 Equation 22

Here, ΔL ^* , Δa ^* , and Δb ^* are differences between L ^* , a ^* , and b ^* before and after conversion, respectively.

For simplicity, only the luminance difference ΔL ^* may be calculated and the value of W that minimizes it may be selected.

FIG. 12 is a block diagram of the determination portion, which is described by adopting a color system such as L ^* a ^* b ^* . In S41 and S42, r, g, and b are calculated as in the case of FIG. Then, the obtained r, g, b are converted into L ^* , a ^* , b ^* (S43). Next, L ^* , a ^* , b ^* obtained from r, g, b after R′G′B′W conversion obtained in S43, and input RGB as they are in L44, L ^* , a ^* , The b ^* converted L ^* , a ^* , b ^* are compared to calculate the sum of errors (S45). Also in this case, a weighting calculation may be performed. Of these, the one with the lowest error is selected and the value of W is determined (S46).

  Thus, according to the present embodiment, it is possible to perform optimal conversion when converting RGB data into R′G′B′W data.

  FIG. 13 shows the configuration of the display device of this embodiment. The RGB data to be displayed is input to the RGB → R′G′B′W conversion unit. As described above, the RGB → R′G′B′W conversion unit 10 determines the RGB data before the conversion and the R′G′B′W after the conversion based on the minimum value of the RGB data and the usage rate of W. W is determined so that the difference between r, g, and b which are RGB components in the data is small, and R′G′B′W data is calculated. Then, the obtained R'G'B'W data is sent to the display panel 12, and display is performed by controlling the light emission of each pixel based on the data.

  10 RGB → R′G′B′W conversion unit, 12 display panel.

Claims (3)

In a display device in which one pixel is composed of RGBW (red, green, blue, white) subpixels,
A conversion unit that converts input RGB data into R′G′B′W data;
A display unit that performs display based on the R′G′B′W data converted by the conversion unit,
T bits which are the bit widths of the respective colors of the input RGB data are larger than u bits which are the bit widths of the respective components of the R′G′B′W data,
(I) Let the usage rate of W be m / n (m and n are relatively positive integers, m <n),
(Ii) A change in 1 unit of W data is equal to a change in R ′, G ′ and B ′ of (m / n) units, respectively.
(Iii) t input bits are represented as integer bits of u and fractional bits of (tu),
(Iv) The value obtained by rounding the minimum value among the three colors of the input RGB data into integer bits of u is W ₀ ,
(V) When a value obtained by rounding down the decimal point of n / 2 is defined as [n / 2],
W data, the minimum value of the input RGB data to a value W ₀ that rounding to integer number of bits of u, - more selected from [n / 2] ~ + [ n / 2] value obtained by adding an integer ranging from And
Thereby,
If u output bits are represented as integer bits of u and t input bits are represented as integer bits of u and fractional bits of (tu),
(M / n) units of R′G′B ′ data to be converted in response to the change of the one unit of W data are obtained,
(M / n) W is added to R′G′B ′ data converted corresponding to each W data, and converted RGB components are obtained,
The total of absolute values of errors between input RGB data and converted RGB components corresponding to each W data is calculated by weighted addition,
A display device characterized in that a value of R′G′B ′ and a value of W that minimize an error are determined from absolute values of the obtained error . In a display device in which one pixel is composed of RGBW (red, green, blue, white) subpixels,
A conversion unit that converts input RGB data into R′G′B′W data;
A display unit that performs display based on the R′G′B′W data converted by the conversion unit,
T bits which are the bit widths of the respective colors of the input RGB data are larger than u bits which are the bit widths of the respective components of the R′G′B′W data,
(I) Let the usage rate of W be m / n (m and n are relatively positive integers, m <n),
(Ii) A change in 1 unit of W data is equal to a change in R ′, G ′ and B ′ of (m / n) units, respectively.
(Iii) t input bits are represented as integer bits of u and fractional bits of (tu),
(Iv) The value obtained by rounding the minimum value among the three colors of the input RGB data into integer bits of u is W ₀ ,
(V) When a value obtained by rounding down the decimal point of n / 2 is defined as [n / 2],
W data, the minimum value of the input RGB data to a value W ₀ that rounding to integer number of bits of u, - more selected from [n / 2] ~ + [ n / 2] value obtained by adding an integer ranging from And
Thereby,
If u output bits are represented as integer bits of u and t input bits are represented as integer bits of u and fractional bits of (tu),
(M / n) units of R′G′B ′ data to be converted in response to the change of the one unit of W data are obtained,
(M / n) W is added to R′G′B ′ data converted corresponding to each W data, and converted RGB components are obtained,
Input RGB data is converted and represented as a first point in a color system of L ^* u ^* v ^* or L ^* a ^* b ^* ,
The converted RGB component corresponding to each W data is expressed as a second point after being converted in the same color system as the color system ,
The display device characterized in that a distance between the first point and the second point is minimized. The display device according to claim 1 or 2,
A display device using n such that n = 2 ^(tu) .

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