JP3529505B2 - Display method of color image using monochromatic light - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image display method using monochromatic light, and more particularly to a method for displaying a color image composed of a plurality of pixels.

[0002]

2. Description of the Related Art Generally, a color image is displayed as a set of a plurality of pixels, and one pixel is represented by three primary colors. The three primary colors used at this time differ depending on the display medium. That is, when a so-called display such as a CRT or a liquid crystal display device is used as a display medium, the RG
When the B three primary color system is used and a print medium such as a paper surface is used as the display medium, the CMY three primary color system (and K added thereto) is generally used.
Such a color image display method using the three primary color system is used in an extremely wide field because it can present an image close to a natural color to the human eye.

Recently, a method of displaying a color image by using a set of pixels composed of a diffraction grating has been proposed. For example, in Japanese Patent Application Laid-Open No. 3-206401, Japanese Patent Application No. 6-177504, etc., a color image is obtained by using a RGB three-primary color system and arranging pixels composed of a diffraction grating on a plane. A method of displaying with a diffraction grating is disclosed.

[0004]

When a color image is displayed using the three primary color system, it is necessary to display one pixel in three colors. However, when the three colors cannot be physically overlapped on a plane, it is necessary to divide one pixel into three subpixels and present each color in each subpixel. For example, in a color display device or the like, one pixel is composed of three sub-pixels, and R, G, and B colors are displayed on each sub-pixel. Further, in a color image represented by a diffraction grating, one pixel is also composed of three subpixels, and each subpixel is formed with a diffraction grating for generating R, G, B diffracted light. become. In this way, when one pixel is divided into three sub-pixels and a predetermined color is displayed as a composite color presented by each sub-pixel, the brightness is reduced to 1/3 as compared with the case where the predetermined color is presented by one pixel as a whole. Will be reduced. Further, since the limit of resolution is governed not by the size of one pixel but by the size of one sub-pixel, the resolution is also reduced to 1/3.

Another problem with the method of displaying a color image using this three-primary color system is that color shift easily occurs. For example, it is known that a so-called conversion shift phenomenon occurs in a CRT display device, and that a so-called inter-color misregistration phenomenon occurs in printing.

It is therefore an object of the present invention to provide a color image display method capable of improving display brightness and resolution and suppressing the occurrence of color misregistration.

[0007]

[Means for Solving the Problems]

(1) A first aspect of the present invention is a plurality of pixels.
To display a color image consisting of individual pixels,
First subpixel represented by at least two subpixels
Represents the first monochromatic light λα with the first luminance or density u.
The second monochromatic light λβ is supplied to the second sub-pixel at the second luminance.
Alternatively, it is displayed with the density v and used for each individual pixel.
Color light and its brightness or density are set independently.
In the color image display method to be defined, a three-primary color system that can express monochromatic light in the visible wavelength range with a positive pixel value is defined, and a color image that represents each pixel in this three-primary color system is prepared. And a vector λ indicating an arbitrary monochromatic light λα in the color solid of the three primary color system.
Of the various composite colors represented by the vector composition formula “u · λα + v · λβ” that uses α and a vector λβ indicating an arbitrary monochromatic light λβ, the same position as the pixel color of each pixel forming the color image Alternatively, the step of associating the composite color occupying the neighboring position with the pixel concerned and the respective factors “u, λα, v, λ of the vector composition formula showing the corresponding composite color for each pixel forming the color image
.beta. ", the first monochromatic light .lambda..alpha. displayed on the first sub-pixel and its brightness or density u, and the second monochromatic light .lambda..beta. displayed on the second sub-pixel and its brightness or density v. And the steps of determining and.

(2) A second aspect of the present invention relates to the above-mentioned first aspect .
In the display method according to the aspect,
In addition to defining a finite number of monochromatic lights in the visible wavelength range as monochromatic lights corresponding to the vectors λα and λβ in λα + v · λβ ”, there are finite values of the coefficients u and v in the vector composition formula“ u · λα + v · λβ ”. Define a discrete value, define a finite number of composite colors based on these finite number of monochromatic lights and discrete values, and define a pixel color of the pixels forming the color image among the defined finite number of composite colors. A composite color occupying the same position or a nearby position is selected, and the selected composite color is associated with the pixel.

(3) A third aspect of the present invention is based on the above-mentioned second aspect .
In the display method according to the aspect (1), based on the vector composition formula “u · λα + v · λβ” indicating the selected composite color,
The first sub-pixel in which a diffraction grating having a pitch corresponding to the wavelength of the monochromatic light λα is arranged in the display area corresponding to the coefficient u, and the monochromatic light λ
A second sub-pixel in which a diffraction grating having a pitch corresponding to the wavelength of β is arranged in the display area corresponding to the coefficient v is prepared, and the corresponding pixel is expressed by these sub-pixels. .

(4) A fourth aspect of the present invention is based on the above-mentioned second aspect .
In the display method according to the aspect (1), based on the vector composition formula “u · λα + v · λβ” indicating the selected composite color,
The first sub-pixel that appears as a spot when a beam having the wavelength of the monochromatic light λα is irradiated on a predetermined display surface with an intensity corresponding to the coefficient u, and a beam having the wavelength of the monochromatic light λβ is set as the coefficient v. A second sub-pixel that appears as a spot when a predetermined display surface is illuminated with a corresponding intensity is formed, and the corresponding pixel is expressed by these sub-pixels.

(5) A fifth aspect of the present invention is based on the above-mentioned second aspect.
~ In the display method according to the fourth aspect, a finite number of composite colors
The pixel color of the pixels that make up the color image
Compositing with the smallest spatial distance to the position in the color solid
Select a color and associate the selected composite color with the pixel.
It is a scam.

(6) A sixth aspect of the present invention is based on the above-mentioned second aspect.
~ In the display method according to the fourth aspect, a finite number of composite colors
The pixel color of the pixels that make up the color image
The spatial distance with respect to the position in the color solid
Select one of the composite colors in the
It is made to correspond to a pixel.

(7) A seventh aspect of the present invention is based on the above-mentioned second aspect.
~ In the display method according to the fourth aspect, any three primary color table
Select for each finite number of pixel colors expressed in the color system.
Prepare a table that associates the composite color to be selected,
Use this table to find out which pixel
The color is selected.

[0015]

[0016]

DETAILED DESCRIPTION OF THE INVENTION

<<<< Primary Color System >>>> Here, an embodiment will be described while explaining the present invention based on its basic principle. FIG. 1 shows an RG generally used for displaying a color image on a display device such as a CRT.
It is a figure which shows the color solid of B color system. This color solid is R,
It is a cube defined in a three-dimensional coordinate system having three coordinate axes of G and B, and one point P in this color solid represents one color represented by the combination of the three primary colors of R, G, and B. It will be. For example, one point P shown in the figure has a coordinate value (rp, gp, bp) in this color solid, and a primary color R having a brightness value (or a density value, the same below) rp and a brightness value. g
A color represented as a mixed color of a primary color G having p and a primary color B having a luminance value bp is shown.

The points in the color solid shown in FIG. 1 all have coordinate values in the range of 0 to 1. However, not all the colors can be expressed only by the points in the color solid, and the color solid can be expressed. There are also colors that are represented by outside points. For example,
In FIG. 1, one point Q outside the color solid has a coordinate value (rq, gq, -bq) outside this color solid, and in particular, the B coordinate value has a negative value. As such, although one color Q theoretically corresponds to one point Q including a negative coordinate value, such a color is actually used as the three primary colors RG.
It is impossible to reproduce in B. This can be easily understood by considering the following example. Now, it is assumed that three light beams of RGB are prepared and are irradiated on a predetermined display surface. At this time, the intensity of the light beam R is rp,
Let gp be the intensity of the light beam G and bp be the intensity of the light beam B.
Then, by combining the three spots formed on the display surface by these three light beams, the color corresponding to one point P in the color solid of FIG. 1 can be reproduced. Similarly, in order to reproduce a color corresponding to one point Q outside the color solid of FIG. 1, the intensity of the light beam B needs to be −bq, but in reality, the intensity of the light beam is negative. Since it cannot be physically set to a value, the color corresponding to one point Q is R after all.
It cannot be reproduced depending on the combination of three primary colors of GB.

In addition to the above, CMY is also used as the three primary color system.
Although several color systems such as color systems are known, the colors that can be reproduced in practical use will be slightly different depending on which color system is used. As for the RGB color system, the International Commission on Illumination (CIE) established its standard in 1931. In the RGB color system established by this CIE, R
= 700 nm, G = 546.1 nm, B = 435.8n
m and the standard wavelengths of the three primary colors RGB are defined, which is an international standard. However, this RGB color system cannot represent all monochromatic light spectra in the visible wavelength range. Spectral closed curve S shown in FIG.
Is a closed curve obtained by connecting points corresponding to the color of monochromatic light (light having a single wavelength) from 380 nm to 660 nm. It is protruding. Therefore, in the RGB color system, there is monochromatic light in the visible wavelength range that cannot be expressed. Similarly, in the CMY color system, there is monochromatic light in the visible wavelength range that cannot be expressed.

Therefore, an XYZ color system that replaces the RGB color system and the CMY color system is known. FIG. 2 is a diagram showing a color solid of the XYZ color system. This color solid is a cube defined in a three-dimensional coordinate system having three coordinate axes of X, Y, and Z, and one point P in this color solid is X,
One color represented by the combination of the three primary colors of Y and Z will be shown. For example, one point P shown in the drawing has coordinate values (xp, yp, zp) in this color solid, and a primary color X having a luminance value xp and a primary color Y having a luminance value yp
A color represented as a mixed color of a primary color Z having a luminance value zp is shown. Similarly, one point Q has a coordinate value (xq, yq, zq) in this color solid. And brightness value x
A color represented as a mixed color of a primary color X having q, a primary color Y having a luminance value yq, and a primary color Z having a luminance value zq is shown. Here, although the points P and Q in the RGB color system shown in FIG. 1 and the points P and Q in the XYZ color system shown in FIG. 2 respectively represent the same color,
The coordinate values in each color system will be different. In the illustrated example, the point Q is outside the color solid in the RGB color system, but is inside the color solid in the XYZ color system.

It should be noted that, in this XYZ color system, 380 nm to 660 corresponding to the visible wavelength range.
A spectral closed curve S obtained by connecting points corresponding to the color of monochromatic light (light having a single wavelength) up to nm is
The point is that the X-axis, the Y-axis, and the Z-axis are all located in a quadrant that takes positive values. In other words, since the triaxial coordinate values of the points on the spectral closed curve S are all positive values,
The color of monochromatic light in the visible wavelength range can always be actually reproduced by the XYZ color system. For reference, X for monochromatic light from 425 nm to 660 nm
The specific values of the luminance value (x, y, z) in the YZ color system are shown in the table below.

[0021]

[Table 1] The three primary colors X, Y and Z are respectively the three primary colors R, G and B.
However, the XYZ color system itself should be a color system based on a reference color of a virtual additive color mixing system, and all three primary colors X, Y, and Z are not visible monochromatic light. Of course, this XYZ color system also includes colors that cannot be recognized by human eyes.

Conversion from the RGB color system to the XYZ color system is as follows.

[0023]

[Equation 1] Can be uniquely performed by the formula. That is,
In order to convert the color represented by the point P (r, g, b) in the RGB color system shown in FIG. 1 (the color of the RGB color system) into the color of the XYZ color system, (r , G, b) may be substituted to calculate the value of (x, y, z). The obtained (x, y, z) becomes the coordinate value of the point P (x, y, z) in the XYZ color system shown in FIG. Therefore, the image data represented by the RGB color system is converted into XYZ
In order to convert the image data expressed in the color system, the pixel value (r, g, b) of each pixel may be converted into the pixel value (x, y, z) based on the above formula. .

<<<< Color Synthesis on Two-Dimensional Chromaticity Diagram >>
> By the way, the color expression using the three-dimensional coordinate system as shown in FIG. 2 is an expression in a three-dimensional space, which is inconvenient for discussion on paper. Therefore, a method of performing standardization so that the sum of three coordinate values becomes 1 and expressing this XYZ color system on a two-dimensional plane is generally used.
The XY chromaticity diagram shown in FIG. 3 represents the XYZ color system shown in FIG. 2 on a two-dimensional plane by using such a method. For example, the point P (xp, yp, z in FIG.
p), x = xp / (xp + yp + zp) y = yp / (xp + yp + zp) x and y are obtained by standardization as shown in FIG.
On the Y chromaticity diagram, corresponding points are plotted at the positions corresponding to the two-dimensional coordinate values (x, y). The spectral closed curve S shown in FIG. 2 is also a two-dimensional closed curve on the XY chromaticity diagram of FIG. In the XY chromaticity diagram of FIG. 3, wavelengths of 420 nm to 660 n are formed on the substantially U-shaped spectrum closed curve S.
The position of the monochromatic light within the section of m is plotted and shown every 20 nm. Here, the end point on the short wavelength side (point of 420 nm)
And the end point on the long wavelength side (point of 660 nm) are connected by a straight line, and a closed region is formed by the spectrum closed curve S. The color corresponding to an arbitrary point within the closed region inside the spectrum closed curve S is a monochromatic Instead of light, it becomes a composite color obtained by combining a plurality of monochromatic lights. It is known that a color corresponding to an arbitrary point in this closed region can be expressed by combining three monochromatic lights corresponding to predetermined three points on the spectral closed curve S.

On the other hand, it is known that when two monochromatic lights corresponding to two predetermined points on the spectral closed curve S are combined, a color on a line segment L connecting the two points can be expressed. This principle is shown in the XY chromaticity diagram of FIG. In the example of FIG. 4, one point λα (monochromatic light having a wavelength of 500 nm) and one point λβ (monochromatic light having a wavelength of 580 nm) on the spectrum closed curve S are selected, and a line segment L is drawn between both points. ing. in this case,
A color corresponding to an arbitrary point on the line segment L is a monochromatic light having a wavelength of 500 nm corresponding to the point λα and a wavelength 580 corresponding to the point λβ.
It can be expressed by synthesizing with the monochromatic light of nm. Which color on the line segment L will be the synthesized color,
It is determined based on the composition ratio. That is, the wavelength is 500n
As the synthesis ratio of the monochromatic light of m is increased, the color closer to the point λα is expressed, and as the synthesis ratio of the monochromatic light of wavelength 580 nm is increased, the color closer to the point λβ is expressed.

By the way, there are innumerable line segments L connecting arbitrary two points on the spectral closed curve S, and geometrically, a line segment L passing through an arbitrary point in the closed region surrounded by the spectral closed curve S. Are innumerable. Therefore, the color of any point in this closed region (all colors that can be recognized by human beings are included here) is always represented by the synthesis of monochromatic light corresponding to two points on the spectral closed curve S. The combination of the two monochromatic lights is endless.
Therefore, in principle, even if only two types of monochromatic light are used, it is possible to express all the colors in this closed region, and the degree of freedom is considerably high. Focusing on this high degree of freedom, it can be seen that even if one of the two types of monochromatic light is fixed, all the colors in the closed region can be expressed. FIG. 5 is an XY chromaticity diagram showing a color expression method when one monochromatic light is fixed as described above. In this example, the wavelength λα of the first monochromatic light is fixed at 420 nm. Thus, the first
Even if the wavelength λα of the monochromatic light is fixed, if the wavelength λβ of the second monochromatic light is free, all the colors in this closed region can be represented. This is because the wavelength λβ of the second monochromatic light can be set freely, and even if one end point λα of the line segment is fixed, the other end point λβ can move freely on the spectrum closed curve S.

This means that the color corresponding to an arbitrary point within the closed region surrounded by the spectral closed curve S can be expressed by synthesizing a monochromatic light of 420 nm and another monochromatic light. . That such a principle is correct can be seen from the spectral sensitivity characteristic of the cone in the human eye shown in FIG. Generally, there are three types of cones that are stimulated by the three primary colors of RGB in the human eyeball, and the spectral sensitivity characteristics S _R , S _G , and S _B of these cones are as shown in the graph of FIG. Is known to become. Here, it can be seen that the sensitivity characteristics S _R and S _G overlap with each other, and that the two cones can be simultaneously stimulated by the same monochromatic light. The peak position of the sensitivity characteristic S _B is located near 420 nm as shown by the broken line in the figure. Therefore,
The cone having the sensitivity characteristic S _B is stimulated by the monochromatic light λα having a fixed wavelength of 420 nm, and the cone having the sensitivity characteristic S _R and the sensitivity characteristic S _G are caused by the monochromatic light λβ having the variable wavelength.
By stimulating the cones with, it is possible to stimulate all three cones with two monochromatic lights, and to express almost all colors that humans can recognize. Become. The basic idea of the present invention is to perform color expression by combining two monochromatic lights based on such a principle.

<<< Color Composition by Three-Dimensional Vector >>>>
As described above, the method of performing color expression by combining two monochromatic lights can be described as vector combining in the three-dimensional coordinate system. For example, in the XYZ color system shown in FIG. 7, an arbitrary color within the color solid is represented by a vector from the origin O. That is, the point P on the spectrum closed curve S
The color of monochromatic light corresponding to (xα, yα, zα) is the origin O
Is represented by a vector λα from this point to another point P (xβ, yβ, z) on the spectral closed curve S.
The color of monochromatic light corresponding to β) is represented by a vector λβ that goes from the origin O to this point (the vector symbols are omitted in the present specification due to restrictions of electronic application, and the symbols “λα, λβ” are used. Will be used as a symbol indicating a specific monochromatic light or its wavelength, and also as a vector indicating a point corresponding to this monochromatic light on a color solid). Here, a vector synthesis expression “C = u · λα + v · using the vectors λα and λβ and predetermined coefficients u and v.
Considering “λβ”, the vector C represented by this vector composition formula represents a composite color P (xαβ, yαβ, zαβ) expressed by combining two monochromatic lights λα, λβ. In the above vector composition formula, the coefficients u,
When one of v is zero and the other is 1, the composite color indicated by the vector C indicates the monochromatic light itself. Therefore, in this specification, the word "composite color" means "color of monochromatic light".
Will be used in a broad sense that also includes.

As described above, unlike the RGB color system, the XYZ color system is a three-primary color system that can express all monochromatic light in the visible wavelength range with positive coordinate values. Both λα and λβ can be expressed by a combination of (x, y, z) having positive coordinate values. Also,
The colors in the closed region (all colors that can be recognized by humans) in the XY chromaticity diagram of FIG. 4 or 5 can also be expressed by a combination of (x, y, z) having positive coordinate values, and these colors can be represented. When represented by the above vector composition formula “C = u · λα + v · λβ”, the coefficients u and v are always positive values. By the way, R
If a similar vector synthesis is attempted in the GB color system, (r,
When trying to vector-synthesize a specific color represented by a combination of g and b), the coefficients u and v sometimes take a negative value, which causes a problem in practical use. Because
This is because the coefficients u and v indicate the brightness values of the monochromatic lights λα and λβ, respectively, and therefore, if they take a negative value, such monochromatic lights cannot be realistically generated. It is for this reason that the color of each pixel is represented in the XYZ color system in the present invention.

After all, in the XYZ color system (x, y,
The color represented by the pixel value z) can be represented by a composite color of two monochromatic lights λα and λβ. Specifically, the following method may be used to obtain the combination of two monochromatic lights. First, in a color solid of the XYZ color system as shown in FIG. 7, a vector λα indicating an arbitrary monochromatic light λα
Consider various composite colors corresponding to the vector C represented by the vector composition formula “C = u · λα + v · λβ” using the vector λβ indicating the arbitrary monochromatic light λβ. These composite colors will be represented as a point at the tip position of the arrow of the vector C in the color solid. Further, a pixel having a pixel value of (x, y, z) in the XYZ color system is
In the color solid, it is represented as a point at the position indicated by the point P (x, y, z). Therefore, the position of the tip of the arrow is point P.
A vector C that occupies the same position as (x, y, z) is obtained, and a vector composition formula “C =
u.lamda..alpha. + v.lamda..beta. ", the combination of two specific monochromatic lights .lamda..alpha. and .lamda..beta.

<<< Infinite Number of Monochromatic Lights and Coefficients Having Discrete Values >>>> As shown in the XY chromaticity diagram of FIG. 4, an arbitrary point within the closed region surrounded by the spectral closed curve S is defined as There are innumerable theoretically the passing line segment L. This is the line segment L
Theoretically, as the monochromatic lights λα and λβ which are the end points of, the arbitrary points (that is,
This is because any wavelength within a continuous wavelength range of 420 nm to 650 nm can be obtained. However, in practice, it is difficult to display a color image using such infinite kinds of monochromatic light. In particular, as will be described later, in the case of expressing monochromatic light using a diffraction grating, it is extremely difficult to prepare an infinite variety of diffraction gratings, and in practice, it is limited to a limited number of diffraction gratings. There is a need to. Therefore, in an example described later, 10 types of monochromatic light are defined in steps of 25 nm from monochromatic light having a wavelength of 425 nm to monochromatic light having a wavelength of 650 nm. Figure 8
Represents the 10 types of monochromatic light defined in this way as X
It is plotted in the Y chromaticity diagram.

If the monochromatic light to be used is limited to such 10 types, the end points constituting the line segment L are
Since it is necessary to select from the types of monochromatic light, there are only combinations that select two out of 10 types, that is, there are only 45 combinations in total. The 45 line segments shown in FIG. 8 show this combination. Then, when only these 10 types of monochromatic light are used, only the colors corresponding to the points on the 45 line segments can be expressed.

Further, so far, two monochromatic lights λα, λ
The coefficients u and v when combining β have been described on the assumption that they can take continuous values. However, in the case of expressing monochromatic light using a diffraction grating, as described later,
There is no choice but to make these coefficients u and v take discrete values. In the example described later, the coefficients u and v are 0, 1/31, 2
/ 31, 3/31, 4/31, ..., 30/31, 31 /
It takes any of 32 discrete values of 31 (0
≤u, v≤1).

As described above, assuming that a finite number of monochromatic lights and coefficients having discrete values are used, a color having an arbitrary pixel value of (x, y, z) in the XYZ color system is completely obtained. The same color cannot be accurately represented by two monochromatic lights. For example, as shown in FIG. 9, XYZ
Even if there is a pixel color represented as a point at the position indicated by the point P (x, y, z) in the color solid of the color system, the position of the tip of the arrow indicates the point P (x, y, z). ), The vector C that occupies the same position as that of) does not always exist. In such a case, the vector C in which the tip position of the arrow occupies a position near the point P (x, y, z) is used instead. In the example of FIG. 9, the position of the tip of the arrow of the vector C is the point P (xαβ, yαβ, z
αβ), which does not completely match the point P (x, y, z), but the distance d between them is within the allowable error range, and the point P (xαβ, yαβ, zαβ) is the point P (xαβ, yαβ, zαβ). (X, y, z)
It can be said to be a point near. Therefore, a vector composition formula “C = u · λα + v · λ” for the vector C is obtained.
.beta. ", the two monochromatic lights .lambda..alpha. and .lambda..beta.
The pixel color corresponding to (x, y, z) will be approximately expressed.

In the case of the above example, two monochromatic lights λα and λβ
Is any one of 10 types of monochromatic light defined in advance, and the values to be taken by the two coefficients u and v are 32
It can be one of the discrete values in the street. Therefore, if the same monochromatic light is allowed to be selected from the 10 types of monochromatic lights as the two monochromatic lights, the vector synthesis formula “C = u · λ
The vector C represented by “α + v · λβ” is (32 × 1
0 + 32 × 10) = 320 ² types exist.
That is, in FIG. 9, P (xαβ, yαβ, zα
Since point corresponding to beta) will be present ways 320 ^2, from the viewpoint of the 320 ^two types, a predetermined point P (x,
It suffices to select only one point that coincides with (y, z) or a nearby point. In other words, from the composite color of 320 ^two types synthesized by vector synthesis, the predetermined point P (x,
Only one composite color to be associated with the pixel color represented by y, z) needs to be selected.

The first method for making such selection is to calculate the spatial distance d in the color solid with respect to the predetermined point P (x, y, z) for each of the 320 ² points indicating the composite color. However, this is a method of selecting a composite color having the smallest spatial distance d. Second for making similar choices
The method (2) is a method in which the allowable error range E is defined in advance, and when a composite color whose spatial distance d satisfies d <E is found, the composite color is immediately selected. In this second method, the first composite color satisfying the condition of d <E is selected.

If the first method is adopted, theoretically the closest composite color is selected, whereas if the second method is adopted, the closest composite color is not necessarily selected. However, in practice, the first method cannot always be said to be superior. In the first method, it is necessary to perform calculation for obtaining the spatial distance d for all the composite color of 320 ^two types, whereas computation load becomes enormous, in the second method, the allowable error range E If a certain value is set as, the composite color may be selected relatively quickly, and if a composite color that satisfies the conditions is obtained, it is not necessary to perform calculation for the remaining composite colors. The calculation load is reduced.

Another advantage of the second method over the first method is that a more preferable composite color can be selected in practical use. For example, when only one composite color in the vicinity of a predetermined pixel color is selected, the spatial distance between the first candidate composite color and the pixel color is d1, and the second candidate composite color and the pixel color are separated from each other. It is assumed that the spatial distance is d2. Then, if d1 <d2 in this case, theoretically, the first candidate composite color is the color closest to the pixel color, and according to the first method described above, the first candidate composite color is Will be selected. However, in the first candidate composite color, u = 1/31, v = 2/32, and the coefficient values are all close to zero, whereas in the second candidate composite color, u = 3.
When the coefficient values are 0/31 and v = 28/32, which are all close to 1, it is preferable in practice to select the second candidate composite color. This is because the coefficient values u and v are values indicating the brightness or density when displaying monochromatic light, and therefore it is preferable to use as large values as possible in order to display a clear image. In the second method, if the spatial distance is calculated and the condition is determined in order from the composite color having the largest coefficient value u and v, the second candidate composite color in the above example is d <E. If the condition is satisfied, the second candidate composite color is selected.

<<< Outline of Color Image Display Method According to Present Invention >>>> Next, an outline of a color image display method according to the present invention will be described with reference to FIG. Here, an outline of a process of performing color image display according to the present invention based on an original image represented by the RGB color system will be described. In the original image represented by the RGB color system, pixel values (r, g,
b) is defined. To display such a pixel Q1 on a CRT display or the like, as shown in the upper left of FIG. 10, three sub-pixels Q11, Q12, Q1 are included in the pixel Q1.
3, the primary color R is displayed in the sub-pixel Q11 with the brightness r, the primary color G is displayed in the sub-pixel Q12 with the brightness g, and the primary color B is displayed in the sub-pixel Q13 with the brightness b. However, in such a display method, since one pixel is divided into three sub-pixels, there are problems that overall luminance and resolution are lowered, and color deviation between the three primary colors occurs. That's right.

Therefore, the pixel values (r, g,
b) is converted into pixel values (x, y, z) of the XYZ color system, and a point P is placed in the color solid of the XYZ color system as shown in FIG.
Find (x, y, z). Such (r, g, b) →
The conversion of (x, y, z) can be uniquely performed based on the above-mentioned formula. Next, by the method described above, a composite color occupying the same position as this point P (x, y, z) or a position near it is obtained, and this composite color is associated with the original pixel Q1. Then, each factor “u, λ” of the vector composition formula “u · λα + v · λβ” for the associated composite color
α, v, λβ ”, the first monochromatic light λα displayed on the first subpixel and its luminance u, and the second monochromatic light λβ displayed on the second subpixel and its luminance v. To decide. And finally, as shown in the upper right of FIG.
Two sub-pixels Q21 and Q22 are defined in 2 and the first monochromatic light λα is displayed in the first sub-pixel Q21 with the luminance u, and the second monochromatic light λβ is displayed in the second sub-pixel Q22. Display with brightness v.

The pixel Q1 shown in FIG. 10 is a display of a specific pixel by the conventional general RGB color system, and the pixel Q2 is a display of the same pixel by the method of the present invention. In short, in the color image display method according to the present invention, two subpixels are defined in one pixel, and the first monochromatic light λα is displayed at the first luminance u in the first subpixel. , The second monochromatic light λβ is displayed at the second luminance v on the second sub-pixel. Moreover, the important point is that in the image display by the RGB color system,
While three primary colors of primary color R, primary color G, and primary color B are always displayed in each sub-pixel, in the image display according to the present invention, for each pixel, the monochromatic light displayed in the sub-pixel is displayed. It is different. In other words, the monochromatic light used and its brightness are set independently for each pixel.

More specifically, in the conventional image display method based on the general RGB color system (the same applies to the CMY color system), the color displayed in the sub-pixel is always the primary color in any pixel. It is fixed to three primary colors of R, primary color G, and primary color B, and the brightness values (the density values in the case of the CMY color system) of these three primary colors are different between individual pixels.
On the other hand, in the image display method according to the present invention, a specific combination of monochromatic lights is not fixed, and an independent combination of monochromatic lights occurs for each pixel. Of course, the brightness value (value u, v) for each monochromatic light is also independent for each pixel. For example, pixel 1: λα = 420 nm, u = 18/32, λβ = 580 nm, v
= 22/32 pixel 2: λα = 550 nm, u = 10/32, λβ = 650 nm, v
= 12/32 pixel 3: λα = 480 nm, u = 14/32, λβ = 560 nm, v
= 15/32 pixel 4: λα = 500 nm, u = 23/32, λβ = 620 nm, v
= 32/32, four elements λα, u, λβ, v are set independently for each pixel.

The pixel Q1 shown in FIG. 10 is divided into three sub-pixels, while the pixel Q2 is divided into two sub-pixels. Therefore, according to the present invention, the problem that the luminance and the resolution are reduced due to the use of the sub-pixels, or the problem that the color misregistration occurs is solved by 3/2 times as compared with the conventional method.

In the example shown in FIG. 10, the pixel Q2 has 2 pixels.
Although it is divided into one sub-pixel Q21 and Q22, it is also possible to divide into a larger number of sub-pixels. For example, 4
It is divided into two sub-pixels Q21a, Q21b, Q22a and Q22b, the first monochromatic light λα is displayed in the sub-pixels Q21a and Q21b with a luminance u, and the second monochromatic light is displayed in the sub-pixels Q22a and Q22b. It is also possible to adopt a method of displaying λβ with brightness v. In short, according to the present invention, the vector composition formula “C = u · λα + v · λ” is set in one pixel.
Any form of sub-pixel may be used as long as the composite color formed by the two monochromatic lights λα and λβ represented by “β” is displayed.

[0045]

The present invention will be described below based on illustrated embodiments.

§1. Conventional color image using a diffraction grating
Image display method A seal using a diffraction grating is generally used as a counterfeit prevention seal for credit cards, video tapes, etc., and a method of displaying a color image on an image display medium using such a diffraction grating is proposed. Has been done. For example, Japanese Patent Application No. 6-177504 discloses a method in which each pixel is composed of a diffraction grating, a color is expressed by a grating line pitch of this diffraction grating, and brightness is expressed by a display area of the diffraction grating. Has been done.

FIG. 11 is a side view showing a state in which such a diffraction grating G is being observed. When observing from a direction inclined by an angle φ with respect to the irradiation direction of the white light while irradiating the white light from above the diffraction grating G vertically, a diffraction phenomenon based on the Bragg equation of p · sin φ = n · λ is obtained. Occur. here,
p is the grating line pitch of the diffraction grating, φ is the diffraction angle, λ is the wavelength of the diffracted light obtained in the direction of this diffraction angle φ, and n is the order of the diffracted light. Therefore, if the observation direction is fixed (φ is constant) and only the first-order diffracted light (n = 1) is considered, the wavelength λ of the diffracted light observed in this fixed observation direction is It will be uniquely determined based on the pitch p of the grating.

Here, let us consider more specific numerical values. For example, consider the case of observing from an observation direction such that φ = 30 ° in FIG. 11. Then, sin
Since φ = 1/2, when n = 1 for the first-order diffracted light, the above equation becomes p · (1/2) = λ. That is, in this observation direction, the first-order diffracted light having a wavelength of (1/2) of the diffraction grating pitch p is observed. Therefore, for example, the wavelength of each primary color in the RGB color system is approximated to the primary color R = 600 nm,
Assuming that the primary color G is set to 500 nm and the primary color B is set to 400 nm, the first-order diffracted light having the wavelength of the primary color R is obtained from the diffraction grating having the pitch p = 1.2 μm under the above observation conditions, and the pitch p = 1.0 μm. From the diffraction grating of 1
Next-order diffracted light is obtained, and the first-order diffracted light of the wavelength of the primary color B is obtained from the diffraction grating with the pitch p = 0.8 μm.
Thus, the three types of diffraction gratings can display the three primary colors of the RGB color system. That is, if one pixel is composed of three sub-pixels and the above-mentioned three types of diffraction gratings are formed in these three sub-pixels, respectively, the entire pixel can provide an arbitrary color of the RGB color system. Can be displayed.

On the other hand, the brightness of each sub-pixel can be adjusted by the display area. For example, as shown in FIG. 12, five types of diffraction grating patterns P11 to P15 having different diffraction grating formation regions V are prepared. In each case, the outer frame corresponds to the entire area of the sub-pixel, but the diffraction grating is not necessarily formed in this entire area, and only in the diffraction grating forming area V having a predetermined area. Are formed. In the diffraction grating pattern P11, since the area of the diffraction grating formation region V is set to 0, this pattern P
Even if 11 is assigned to the sub-pixel, the brightness of the diffracted light becomes 0. On the other hand, in the diffraction grating pattern P15, the area of the diffraction grating forming region V is set to be equal to the area of the outer frame. Therefore, if this pattern P15 is assigned to the sub-pixel, the brightness of the diffracted light becomes maximum. . In FIG. 12, the area ratio of the diffraction grating formation region V to the outer frame is shown below each diffraction grating pattern. Although only five types of diffraction grating patterns P11 to P15 are shown here, the area ratio is
0/31, 1/31, 2/31, 3/31, ..., 30 /
If a total of 32 types of diffraction grating patterns of 31, 31/31 are prepared, it is possible to express brightness in 32 steps (5 bit gradation expression) for one primary color.

As described above, the color can be set by the pitch of the grating lines of the diffraction grating, and the brightness can be set by the display area (area of the diffraction grating forming region V). For example, as shown in FIG. , 32 levels of luminance expression for one primary color are prepared, and 32 kinds of diffraction grating patterns respectively associated with pixel values 0 to 31 are prepared (only five typical levels are shown in the figure). If this is prepared for each primary color, it is possible to display a color image having a gradation expression of 5 bits for each primary color.

In order to actually display a color image using these diffraction grating patterns, for example, allocation as shown in FIG. 14 (a) may be performed. In this example, each square shows one sub-pixel, and one pixel is composed of three sub-pixels arranged in the horizontal direction. That is, each of Q1, Q2, and Q3 in the figure constitutes one pixel. R1 and G written in the three sub-pixels in the pixel Q1
The symbol 1, B1 indicates any one of the diffraction grating patterns shown in FIG. Where R
1 is one pattern in the row of R in FIG. 13, G1 is one pattern in the row of G in FIG. 13, and B1 is one pattern in the row of B in FIG. The same applies to the sub-pixels forming the pixels Q2 and Q3. However, the arrangement order of the three primary colors for the three sub-pixels is made different in the pixels Q1, Q2, Q3, but this is a consideration for obtaining more uniform color characteristics. Figure 14 (b)
Is another example in which the arrangement order of the three primary colors is changed. Figure 15
FIG. 14 is a diagram showing a state in which a diffraction grating pattern is actually allocated on a medium based on the allocation shown in FIG.

The conventional color image display method using the diffraction grating has been briefly described above, but it has already been pointed out that this method has some problems. That is, in this method, one pixel is divided into three sub-pixels,
In addition, as shown in FIG. 15, since the area where the diffraction grating is not formed occupies a considerable area, there is a problem that the overall brightness is lowered. Also, the limit of resolution depends on the size of each sub-pixel, so
If the pixel is composed of three sub-pixels, only one third of the originally obtained resolution can be realized. Furthermore, if there is a positional error in the arrangement of the individual sub-pixels, color shift will occur.

§2. Color of the invention using a diffraction grating
Outline of Image Display Method Therefore, an embodiment in which the present invention is applied to a color image display method using this diffraction grating will be described below. In this embodiment, instead of the diffraction grating pattern shown in FIG.
The diffraction grating pattern shown in is prepared. For convenience of illustration,
Although only 3 × 5 = 15 patterns are shown here, 10 × 32 = 320 patterns are actually prepared. That is, regarding color, the wavelength is 425 nm.
From (diffraction grating pitch p = 0.85 μm), the wavelength is 650 nm in steps of 25 nm (diffraction grating pitch p = 1.3 μm).
m), a total of 10 types of monochromatic light are prepared, and the brightness (indicated by the brightness value u or v) is 0/3.
1,1 / 31, 2/31, 3/31, ..., 30/31,
A total of 32 gradations of 31/31 are prepared.

FIG. 17 shows a list of the diffraction grating patterns shown in FIG. From the total of 320 patterns shown in this list, select two predetermined patterns and arrange the two selected patterns as shown in the table below. Pixel Q1 will be represented (in other words, the individual patterns are respectively subpixels Q11, Q1).
2 will be configured). In the example shown in FIG. 17, monochromatic light of wavelength λ3 (475 nm) is displayed in sub-pixel Q11 with luminance (2/31), and monochromatic light of wavelength λ7 (575 nm) is sub-pixel Q12 with luminance (30/31). It is displayed inside. As described above, the color of the pixel Q1 displayed as the composite color of the two sub-pixels Q11 and Q12 is XY shown in FIG.
As described above, the color is a color represented by a predetermined composite vector C in the color solid of the Z color system, and this vector C is represented by the vector composite expression “C = u · λα + v · λβ”.

The combination of selecting two patterns from the 320 patterns shown in the list of FIG. 17 is 3 if the same pattern is allowed to be selected redundantly.
It will exist ways 20 ^2. Then, each of these combinations represents a composite color corresponding to one point in the color solid shown in FIG. As described above, in the method according to the present invention, in the color solid of the XYZ color system,
When the pixel color indicated by the point P (x, y, z) is given, one composite color in the vicinity of the point P is selected, and the pixel display is performed by the selected composite color. Specifically, in FIG. 18, the spatial distance d between the point P (x, y, z) and the tip of the arrow of the vector C indicating the predetermined composite color.
Is calculated and the composite color having the smallest spatial distance d is selected, or one composite color having the spatial distance d within a predetermined allowable error range E is selected. To calculate the spatial distance d, specifically,

[0056]

[Equation 2] The following geometric calculation formula may be used. Where x, y,
z is each coordinate value of the point P (x, y, z), xα, yα, z
α is the tip point P (xα, y of the arrow of the monochromatic light vector λα
α, zα) and xβ, yβ, zβ are coordinate values of the tip point P (xβ, yβ, zβ) of the arrow of the monochromatic light vector λβ.

§3. Color of the invention using a diffraction grating
Procedure of Image Display Method Next, a specific procedure of the color image display method of the present invention using a diffraction grating will be described based on the flowchart of FIG. Here, the procedure for displaying one pixel represented by the RGB color system by the method according to the present invention will be described. In the RGB color system, one pixel has three primary colors RG.
It is represented by the pixel value (r, g, b) for each B. Therefore, first, in step S1, this pixel value (r, g, b) is input. Here, 0 ≦ r, g, b
A pixel value standardized so that ≦ 1 is input.
Subsequently, in step S2, the pixel value (r, g, b) of the RGB color system is converted into the pixel value (x,
y, z). As described above, this conversion can be uniquely performed based on the conversion formula. The reason why the following processing is performed by the XYZ color system instead of the RGB color system is that the monochromatic light in the visible wavelength range can be expressed by all positive pixel values in the XYZ color system, as described above. Therefore, the coefficients u and v of the vector composition formula “C = u · λα + v · λβ” for obtaining the composite vector C indicating the required composite color are always positive (when the coefficients u and v become negative, Diffraction gratings will have to be formed in areas with negative areas, making them physically unrealizable).

Next, in steps S3 to S7, initial values of various parameters are set. First, step S
In 3, the initial value of the allowable error range E is set to 0.1 / 31. In the embodiment described here, not a method of obtaining a composite color having the shortest spatial distance d but a method of obtaining a composite color satisfying the condition that the spatial distance d is less than a predetermined allowable error range E is adopted. In step S3, the initial value of this allowable error range E is set. In the following step S4, the initial value of the first monochromatic light λα is set to 650 nm, and in step S5, the initial value of the second monochromatic light λβ is set to 425 nm. Further, in step S6, the initial value of the luminance value u for the first monochromatic light λα is set to 1.0, and in step S7, the second monochromatic light λα.
The initial value of the brightness value v for β is set to 1.0.
After all, in such an initial setting, in the list shown in FIG. 17, the bottom row (3) of the rightmost column (column of λ10) is set.
1/31 = 1.0 column) pattern and the leftmost column (λ1 column) bottom row (31/31 = 1.0 column)
The combination with the pattern is the first candidate composite color.

In the following step S8, the spatial distance d on the color solid between this composite color and the color represented by the original pixel value (x, y, z) is calculated, and this space is calculated in step S9. The allowable error range E in which the distance d is set in step S3
It is determined whether it is less than. Note that instead of calculating the spatial distance d in the three-dimensional space and determining whether d <E, one-dimensional separation Δx in the X-axis direction,
The one-dimensional distance Δy in the Y-axis direction and the one-dimensional distance Δz in the Z-axis direction are calculated separately, and the error e related to the one-dimensional distance set instead of the three-dimensional allowable error range E is used to calculate Δx. If the conditions of <e, Δy <e, and Δz <e are satisfied, it may be determined to be within the error range.

In the determination at step S8,
If the difference is greater than or equal to the error, the process proceeds from step S10 to step S11, the brightness value v is reduced by (1/31), and the process from step S8 is repeated. In this way, the brightness value v for the second monochromatic light λβ changes from the initial value 1.0 (31/31) to 30/31, 29/31,
Is updated, and the spatial distance d for the new composite color and the allowable error range E are compared each time. Thus, even if the brightness value v = 0, if the composite color within the error is not found, the process proceeds from step S10 to step S12 to step S13, and the brightness value u is (1/3
It is decreased by 1) and the processing from step S7 is repeated. Thus, the luminance value u for the first monochromatic light λα
From the initial value 1.0 (= 31/31) to 30/31,
29/31, ... And the procedure of steps S7 to S13 is repeatedly executed.

Thus, if the composite color within the error is not found even if the luminance value u = 0, the process proceeds from step S12 to step S14 to step S15, where the wavelength of the second monochromatic light λβ is 25 nm. Increase (λβ =
450 nm), and the processing from step S6 is repeated. Thus, the second monochromatic light λβ has an initial value of 425.
nm is updated to 450 nm, 475 nm, ... And the procedure of steps S6 to S15 is repeatedly executed. Then, even if λβ = λα = 650 nm, if the composite color within the error is not found, the process proceeds from step S14 to step S16 to step S17, where the wavelength of the first monochromatic light λα is reduced by 25 nm. (Λα = 625n
m)), and the processing from step S5 is repeated.
In this way, the first monochromatic light λα is updated from the initial value of 650 nm to 625 nm, 600 nm, ... And the steps S5 to S17 are repeatedly executed.

In this way, even if the processing for all the composite colors is completed, if no composite color within the error is found, the process proceeds from step S16 to step S18, and the allowable error range E is set to (0.1 / 31). Only, the condition is gently set again, and the process from step S4 is repeated again. According to such a procedure, a composite color that always satisfies the condition of step S9 is found at the end, and at that time, from step S9 to step S1.
Proceed to step 9 to determine the composite color. That is, the value of “u, λα, v, λβ” at that time is fixed, and the pixel represented by the pixel value (x, y, z) of the XYZ color system is the vector composition formula “C = U · λα + v · λβ ”.

The composite color selected in this procedure is not necessarily the one having the smallest spatial distance d, but is the first one of the composite colors that satisfies the condition that the spatial distance d is less than the allowable error range E. However, in practice, the method of this procedure is more advantageous than the method of finding the composite color having the smallest spatial distance d. The first reason is
In step S3, if it an initial value of the allowable error range E set somewhat loosely, the initial setting remains in composite color is found highly likely, and performing the calculation in step S8 for all composite color of 320 ^two ways This is because there is a high possibility that a composite color to be selected is found before and the calculation load is reduced. The second reason is that a more practically preferable composite color may be selected than the composite color having the smallest spatial distance d. In the initial settings of steps S6 and S7, the initial values of the brightness values u and v are 1.0, and the method of gradually decreasing to 0 is adopted. Therefore, the probability that a combination with a larger luminance value is selected is increased. From a practical point of view, it is preferable to select a composite color having a larger luminance value, even if the spatial distance d is slightly larger, because a clearer display can be performed.

The number of combinations of pixel values (r, g, b) input in step S1 is actually a finite number. For example, if r, g, and representing the respectively 0-31 32 gradations of b, all combinations of pixel values (r, g, b) is a 32 ^triplicate. Therefore, this 32
^The procedure shown in FIG. 19 is executed for all ^three combinations, and “u, λα, v, λβ” is calculated for each.
By performing the processing for obtaining the value of, it is possible to create a “(r, g, b) → (u, λα, v, λβ) conversion table” as shown in FIG. Once such a conversion table is created, the conversion table is used to immediately generate the composite color (u, λα, v, λβ) to be selected for any pixel value (r, g, b). It is convenient because you can get it.

§4. Concrete table on diffraction grating recording medium
Illustrated Mode FIG. 21 (a) is a diagram showing a state in which a display for two pixels is performed by the method according to the present invention. Each of the pixels Q1 and Q2 is composed of two sub-pixels. The first sub-pixel Q11 forming the pixel Q1 displays the monochromatic light λα1 with the luminance value u1, and the second sub-pixel Q12 displays the monochromatic light λβ1 with the luminance value v1. Similarly, the first sub-pixel Q21 forming the pixel Q2 has a monochromatic light λα2.
Is displayed with the brightness value u2, and the monochromatic light λβ2 is displayed with the brightness value v2 in the second sub-pixel Q22. In the pixels Q1 and Q2, the arrangement of the first subpixel and the second subpixel is left / right reversed because the monochromatic light λα displayed in the first subpixel is performed when the procedure shown in FIG. 19 is executed. Is the second
Since the color is always on the long wavelength side (red side) as compared with the monochromatic light λβ displayed on the sub-pixel of,
This is to replace β to ensure overall color uniformity. FIG. 21 (b) is a diagram showing a state in which a diffraction grating pattern is actually assigned in the pixels Q1 and Q2.

FIG. 22 is a diagram showing another example of a specific display mode by the method according to the present invention. This example shows one mode of displaying a color image composed of a pixel matrix of M rows and N columns. Here, it is assumed that pixel values (r, g, b) in the RGB color system are given to the individual pixels arranged in M rows and N columns. In this embodiment, as shown on the right side of FIG. 22, a unit subpixel array consisting of two rows and two columns is defined, and this unit subpixel array is assigned to each pixel. After all, one pixel is represented by four sub-pixels. In order to display one pixel given a pixel value (r, g, b) by the method according to the present invention, first, this pixel value (r, g, b) is displayed.
The composite color (u, λα, v, λβ) corresponding to is calculated. For this, the procedure shown in FIG. 19 may be executed, or the table shown in FIG. 20 may be used.

Next, the obtained composite color (u, λα, v, λ
β) is displayed as shown in FIG. That is,
In the upper left and lower right sub-pixels of the figure, the first monochromatic light λα forming the composite color is displayed with the luminance value u, and in the lower left and upper right sub-pixels of the figure, the second monochromatic light forming the composite color is displayed. The monochromatic light λβ is displayed with the brightness value v. Of course, in the method according to the present invention, it is only necessary to display one pixel by at least two sub-pixels. Although it may be used, the pixel shape and the subpixel shape can be made the same by using the unit subpixel array of 2 rows and 2 columns as described above. In the example shown in FIG. 23, the first monochromatic light λα is arranged at the upper left and the lower right, and
The monochromatic light λβ is arranged at the lower left and the upper right, and the so-called “crossing” arrangement is adopted. As described above, when the procedure shown in FIG.
This is because the color is always on the long wavelength side (red side) as compared with the second monochromatic light λβ, and therefore λα and λβ are switched to ensure overall color uniformity.

By the way, with the diffraction grating recording medium, it is possible to record a plurality of images by superimposing them on the same surface.
Here, an example in which the present invention is applied to such a superimposed recording medium will be described. Now, consider a case where images 1 and 2 as shown in FIG. 24 are prepared. Both images are
It is composed of pixels arranged in 7 rows and 7 columns, and each pixel has a pixel value (r, g,
b) is given. Now, focusing on the pixel in the 4th row and the 5th column shown by the thick frame in FIG. 24, the pixel value (r1, g1, b1) is given to the pixel of interest of the image 1, and the pixel of interest of the image 2 is assigned to the pixel of interest. When the pixel values (r2, g2, b2) are given, the four lines 5 are displayed on the diffraction grating recording medium.
Consider how to display the pixels in the column.

First, one composite color is selected based on the pixel values expressed in the RGB color system. Here, the composite color (u1, λα1, v1, λβ1) is selected with respect to the pixel value (r1, g1, b1) of the target pixel of the image 1, and the pixel value (r2, g2, g2 of the target pixel of the image 2 is selected. b2)
On the other hand, it is assumed that the composite color (u2, λα2, v2, λβ2) is selected. In this case, as in the example shown in FIG. 22, a unit sub-pixel array of 2 rows and 2 columns is defined for one pixel, and two composite colors are displayed as shown in FIG. 25 (a). is there. That is, in the upper left sub-pixel of the figure, the image 1
The first monochromatic light λα1 constituting the composite color of the
, The second monochromatic light λβ1 constituting the composite color on the image 1 side is displayed at the brightness value v1 in the lower right sub-pixel of the figure, and the second monochromatic light λβ1 of the image 2 side is displayed in the upper right sub-pixel of the figure. First to make up a composite color
Of the monochromatic light λα2 of the second monochromatic light λβ constituting the composite color on the image 1 side is displayed in the lower left sub-pixel of the figure.
2 is displayed with the brightness value v2. Moreover, regarding the upper left and lower right sub-pixels for displaying the composite color on the image 1 side, the grid line arrangement angle is set to 0 °, and the upper right and lower left sub-pixels for displaying the composite color on the image 2 side are set. Is
The grid line arrangement angle is 45 °.

FIG. 25 (b) is a diagram showing the difference between the diffraction grating patterns of the diffraction grating having the arrangement angle of 0 ° and the diffraction grating having the arrangement angle of 45 °. As described above, the diffraction gratings in which the arrangement angles of the grating lines are different are different from each other in the geometrical conditions under which the diffracted light can be observed. Therefore, the arrangement angle is 0 on the same medium.
When a diffraction grating having a rotation angle of 45 ° and a diffraction grating having an arrangement angle of 45 ° are mixed, for example, the medium is subjected to a certain geometrical condition (for example, the angle of the medium with respect to the line of sight is at a predetermined angle).
When observed with, only the diffracted light from the diffraction grating with the arrangement angle of 0 ° is observed, and when the same medium is observed under different geometric conditions, only the diffracted light from the diffraction grating with the arrangement angle of 45 ° is observed. It

Now, considering the state of observing this medium under the geometric conditions such that only the diffracted light from the diffraction grating with the arrangement angle of 0 ° is observed, the unit sub unit shown in FIG. In the pixel array, only the upper left subpixel and the lower right subpixel will be observed. Since all of these sub-pixels are sub-pixels showing a composite color on the image 1 side, the pixel color on the image 1 side is presented. On the other hand, considering the state of observing this medium under the geometric condition that only the diffracted light from the diffraction grating with the arrangement angle of 45 ° is observed, FIG.
In the unit subpixel array shown in (a), only the upper right subpixel and the lower left subpixel are observed. Since all of these sub-pixels are sub-pixels showing a composite color on the image 2 side, the pixel color on the image 2 side is presented. After all, although the same medium is used, the image 1 is displayed when observed under a certain condition, and the image 2 is displayed when observed under another condition.

Generally, when a plurality of n color images are superimposed and displayed, one group is formed by collecting n groups of two subpixels, and the grating line arrangement angle of the diffraction grating is set for each group. , And a different color image may be assigned to each set.

§5. Apparatus for Producing Diffraction Grating Recording Medium Here, an example of an apparatus for producing the diffraction grating recording medium described above will be briefly described based on the block diagram shown in FIG. The color image generation unit 1 is composed of a computer equipped with graphics application software and the like, and has a function of creating a color image as a set of many pixels in which pixel values of three primary colors by the RGB color system are defined. There is. On the other hand, the color image input unit 2
It is composed of a scanner device or the like and has a function of inputting a color image from a color original or a color film drawn on a paper surface. Whichever device is used, as a result, 32 levels of RGB pixel data can be prepared.

The RGB image data thus prepared is
It is given to the conversion processing unit 3. The conversion processing unit 3 converts the pixel value (r, g, b) of each pixel into a predetermined composite color (u,
λα, v, λβ) is performed. This conversion process is actually a simple process of pulling the conversion table 4. The conversion table 4 is a table as shown in FIG. 20, and is created in advance by the conversion table generation unit 5. The conversion table generation unit 5 has a function of creating the conversion table 4 by executing the procedure shown in FIG.

The conversion processing unit 3 brings each pixel into a state in which a specific composite color (u, λα, v, λβ) is associated. The pattern synthesizing unit 6 performs a process of assigning a predetermined pixel pattern to each of these pixels. Various diffraction grating pixel patterns as shown in FIG. 16 are prepared in the pixel pattern file 7. Actually, a total of 320 pixel patterns are prepared in the pixel pattern file 7 as shown in the list of FIG. When a specific composite color (u, λα, v, λβ) is determined, (u, λα)
One pixel pattern is selected by the combination of
Another pixel pattern is selected by the combination of (v, λβ). After all, two pixel patterns are selected for one pixel. The pattern composition unit performs a process of allocating the two pixel patterns thus selected as sub-pixels.

Since each pixel pattern is a diffraction grating pattern, the data output by the pattern synthesizing unit 6 is diffraction grating pattern data. This diffraction grating pattern data is given to the electron beam drawing device 9 via the data format conversion device 8. The data format conversion device 8 is a device that converts the data format of the diffraction grating pattern data created by the pattern synthesis unit 6 into a data format that can be handled by the electron beam drawing device 9. The electron beam drawing device 9 is a general drawing device used for making a semiconductor mask or the like, and draws a diffraction grating pattern on a predetermined medium using an electron beam to make a diffraction grating original plate 10. A large number of diffraction grating recording media 12 can be created by using this diffraction grating original plate 10 by a printing method using a press device 11.

In the example shown in the table of FIG. 17, the step of wavelength λ is set every 25 nm, but it is preferable to set this step in consideration of the drawing resolution by the electron beam drawing apparatus 9. For the first-order diffracted light with the diffraction angle φ = 30 °, the difference of 25 nm in wavelength corresponds to the difference of 50 nm in the pitch of the diffraction grating, so the electron beam drawing apparatus 9 can draw the pitch difference of 50 nm sufficiently. Need only have a resolution. The electron beam writing apparatus generally used at present has a resolution of this level. When an electron beam drawing apparatus with higher resolution is used, if the step of wavelength λ is set finer and a larger number of composite colors are prepared, higher quality color expression is possible.

§6. Display using tunable laser
Application to Ray In the above-described embodiments, the example in which the present invention is applied to the case of displaying a color image on the diffraction grating recording medium has been described. However, the present invention is widely applicable to the field of displaying a color image in general. It is a thing. Here, an example of application to a display using a wavelength tunable laser will be described.

FIG. 27 is a basic structural diagram of a display device using a general laser which has been conventionally used. The components of this display device are lasers 21, 22,
23, optical modulators 24, 25, 26, reflecting mirror 27 and dichroic mirrors 28, 29, reflecting mirror 30, galvanometer 31, relay lenses 32, 33, rotary polygon mirror 3
4, a reflecting mirror 35, and a screen 36. Laser 21,
22 and 23 respectively generate laser beams of wavelengths of three primary colors RGB, and these three laser beams pass through optical modulators 24, 25 and 26, respectively, and are combined by a reflecting mirror 27 and dichroic mirrors 28 and 29. It The thus-synthesized polychromatic laser beam passes through the reflecting mirror 30, the galvanometer 31, the relay lenses 32 and 33, the rotating polygon mirror 34, and the reflecting mirror 35, and is irradiated onto the screen 36. Since the galvanometer 31 rotates in the direction of the arrow in the figure, the spot on the screen 36 is vertically scanned, and the rotary polygon mirror 34 also rotates in the direction of the arrow in the figure.
The spot on the screen 36 is horizontally scanned. Thus, the two-dimensional color image is displayed on the screen 36.

In such a display device, since one pixel is still expressed by the three primary colors of RGB, problems such as deterioration of resolution and color shift will occur. By applying the present invention to this device, a display device as shown in FIG. 28 can be constructed. This device is obtained by substituting the components around the light source unit in the conventional device shown in FIG. And,

The wavelength modulator 42 has a function of controlling the oscillation wavelength of the wavelength tunable laser based on the given wavelength modulation signal. The wavelength modulation operation is ideal if a modulation operation that continuously changes the wavelength over a predetermined visible wavelength range can be performed, but a modulation operation that selects some discrete wavelengths is sufficient. For example, ten types of wavelength values λ1 to λ10 (425 shown in the table of FIG. 17)
(nm to 650 nm), a color image can be displayed almost in the same manner as in the embodiment of the diffraction grating recording medium described above. In any case, the wavelength tunable laser 41 and the wavelength modulator 42 constitute a monochromatic light source having a function of generating monochromatic light in the form of a beam.

The intensity modulator 43 is a device having a function of continuously or discretely modulating the intensity of the laser beam generated by the wavelength tunable laser 41. The laser beam is
The intensity indicated by the intensity modulation signal is output from the intensity modulator 43. The laser beam passes through the optical system after the reflecting mirror 30 and is finally irradiated onto the screen 36 as a spot. The configuration of these optical systems is the same as that of the conventional display device described above. Is. However, in the conventional device, the beam applied to the screen 36 was polychromatic light, whereas in this device, a monochromatic light beam is applied to the screen 36, and the spot formed on the screen 36 is It becomes a spot of monochromatic light. Since the beam passing through the optical system becomes monochromatic light as described above, an inexpensive diffraction grating can be used in place of the expensive rotary polygon mirror 34 in this device.

The control device 44 gives a wavelength modulation signal (a signal designating a wavelength) to the wavelength modulator 42 and an intensity modulation signal (a signal designating the intensity) to the intensity modulator 43.
Has the function of giving.

Now, assuming that at the first moment, a signal showing a predetermined wavelength λα is given as a wavelength modulation signal, and at the same time, a signal showing a predetermined intensity u is given as an intensity modulation signal, at that time, On the screen 36, the wavelength λ
The monochromatic light of α is irradiated with the intensity u to form the first spot. Then, at the second moment, as a wavelength modulation signal,
If a signal showing a predetermined wavelength λβ is given and at the same time a signal showing a predetermined intensity v is given as an intensity modulation signal,
At that time, the screen 36 is irradiated with the monochromatic light of the wavelength λβ with the intensity v to form the second spot. In this way, two spots are formed by time division,
The first spot is the first sub-pixel, and the second spot is the second
Assuming that the sub-pixel is, the pixel composed of two sub-pixels will be displayed on the screen 36, as in the above-described embodiments. Therefore, by performing a control such that predetermined wavelength modulation signals and intensity modulation signals for realizing a composite color to be displayed in the pixel are appropriately provided at the same timing when scanning each pixel position, the desired color is displayed on the screen 36. It becomes possible to display a color image of.

§7. Application to Color Printer Finally, an embodiment in which the present invention is applied to a color printer will be described. FIG. 29 is a basic configuration diagram of the color printer according to the present invention. This color printer has an ink holding portion 51, an ink adhering portion 52, and a control device 53. The ink holding section 51 holds a plurality of inks. These inks respectively correspond to a plurality of monochromatic lights defined with a discrete wavelength distribution within a predetermined visible wavelength range. In the illustrated example, wavelengths of 425 nm and 45
10 kinds of inks corresponding to 10 kinds of discrete monochromatic lights of 0 nm, 475 nm, ..., 625 nm, 650 nm are prepared.

However, unlike the laser light and the diffracted light from the diffraction grating, the present invention cannot be realized by using the reflected light from the commonly used ink. In order to apply the present invention to a color printer, an ink having a fluorescent property or a phosphorescent property is used. Therefore, the plurality of inks prepared in the ink holding unit 51 may be inks having a spectral characteristic corresponding to a specific wavelength. For example, as the "ink corresponding to the wavelength of 500 nm", it is ideally preferable to use "the ink that can obtain the fluorescence of the line spectrum of the wavelength of 500 nm", but in practice, "the peak position of the fluorescence spectrum is about 500 nm".
It is sufficient to use the ink that comes to the position. In short, in the present specification, the phrase "ink corresponding to monochromatic light" means "ink in which the peak position of the spectrum obtained when observing the ink is almost at the monochromatic light position".

The ink attaching portion 52 is the ink holding portion 5.
It has a function of attaching a designated ink of the plurality of inks held in the unit 1 to a designated position on a predetermined display surface 54 (usually the paper surface) with a designated density or area. The control device 53 specifies the ink, the position, and the density or the area of the ink adhering portion 52.

Now, suppose that the control device 53 gives a first control signal for adhering the predetermined ink λα1 to the position of the sub-pixel Q31 on the display surface 54 in the area u1, as shown in the figure. A layer of ink λα1 is formed in the display area having a predetermined area within the sub-pixel Q31. Subsequently, if the control device 53 gives a second control signal for adhering the predetermined ink λβ1 to the position of the sub-pixel Q32 on the display surface 54 with the area v1, as shown in the drawing, the sub-pixel A layer of ink λβ1 is formed in the display area having a predetermined area in Q32. Here, this sub-pixel Q
If the pixel Q3 is configured by 31 and Q32, the pixel Q3 has a vector synthesis expression “u1 · λα1 + v”.
The composite color represented by 1 · λβ1 ”is displayed. However, as described above, since λα1 and λβ1 do not become perfect monochromatic light wavelengths, color expression based on the basic principle of the present invention cannot be accurately performed, but this does not cause a serious problem in practical use.

In the pixel Q3 described above, the emission brightness is controlled by the area to which the ink is applied, but an example in which the brightness is controlled by the density to which the ink is applied is pixel Q3.
Shown as 4. In order to display this pixel Q4, the control device 53 gives the first control signal for causing the predetermined ink λα2 to adhere to the position of the sub-pixel Q41 on the display surface 54 with the density u2, and at the same time, the predetermined control is performed. Ink λβ2
Is applied to the position of the sub-pixel Q42 on the display surface 54 with a density v2. The ink is deposited within the entire area of the sub-pixels Q41 and Q42, but has different densities.

[0090]

As described above, according to the present invention, since a color image is displayed by expressing one pixel by two kinds of monochromatic light, the display brightness and the The resolution can be improved, and the occurrence of color misregistration can be suppressed.

[Brief description of drawings]

FIG. 1 is a diagram showing a color solid of an RGB color system which is generally used when a color image is displayed on a display device such as a CRT.

FIG. 2 is a diagram showing a color solid of an XYZ color system capable of expressing monochromatic light in the visible wavelength range with positive pixel values.

FIG. 3 is an XY chromaticity diagram expressing the XYZ color system shown in FIG. 2 on a two-dimensional plane.

FIG. 4 shows a principle that when two monochromatic lights corresponding to two predetermined points on a spectrum closed curve S are combined in the XY chromaticity diagram shown in FIG. 3, a color on a line segment L connecting the two points can be expressed. FIG.

FIG. 5 is an XY chromaticity diagram showing a color expression method when one monochromatic light is fixed.

FIG. 6 is a diagram showing a spectral sensitivity characteristic of a cone in a human eye.

FIG. 7 is a diagram for explaining the principle of performing color expression by combining two monochromatic lights as vector combining in the XYZ color system.

FIG. 8 is an XY chromaticity diagram showing a color expression method by a combination of a limited number of discretely distributed monochromatic lights.

FIG. 9 is a predetermined pixel color P expressed in an XYZ color system.
It is a figure which shows the spatial distance on a color solid of (x, y, z) and a vector synthetic color.

FIG. 10 is a diagram illustrating an outline of a color image display method according to the present invention.

FIG. 11 is a side view showing a state in which a general diffraction grating G is observed.

FIG. 12 is a diagram showing an example of a plurality of diffraction grating patterns having different areas of a diffraction grating forming region V.

FIG. 13 is a diagram showing an example of a plurality of diffraction grating patterns in which the area of the diffraction grating forming region and the grating line pitch are different.

14 is a diagram showing an allocation mode when a color image is actually displayed using the diffraction grating pattern shown in FIG.

FIG. 15 is a diagram showing a state in which a diffraction grating pattern is actually allocated on a medium based on the allocation mode shown in FIG. 14 (a).

FIG. 16 is a diagram showing an example of a diffraction grating pattern prepared when the present invention is applied to a color image display method using a diffraction grating.

FIG. 17 is a diagram showing a list of diffraction grating patterns shown in FIG.

FIG. 18 is a predetermined pixel color P expressed in an XYZ color system.
It is a figure which shows the spatial distance on the color solid of (x, y, z) and a vector synthetic color, and its calculation method.

FIG. 19 is a process for selecting a composite color (u, λα, v, λβ) in the vicinity of the pixel value (r, g, b) expressed in the RGB color system in the method according to the present invention. 6 is a flowchart showing an example of the procedure of FIG.

20 is a diagram showing a (r, g, b) → (u, λα, v, λβ) conversion table obtained by performing the process shown in FIG.

FIG. 21 is a diagram showing a state where two pixels are displayed by the method according to the present invention.

FIG. 22 is a diagram showing an example of another display mode according to the present invention.

FIG. 23 is a diagram showing a state in which one pixel is displayed in the display mode shown in FIG. 22.

FIG. 24 is a diagram illustrating a method of recording a plurality of images by superimposing them on the same surface in the present invention.

25 is a diagram showing a state in which one pixel is displayed by the method shown in FIG.

FIG. 26 is a block diagram showing an example of an apparatus for producing a diffraction grating recording medium by the method according to the present invention.

FIG. 27 is a basic configuration diagram of a conventional display device using a general laser.

28 is a basic configuration diagram of an embodiment in which the present invention is applied to the display device shown in FIG. 27.

FIG. 29 is a basic configuration diagram of an embodiment in which the present invention is applied to a color printer.

[Explanation of symbols]

1 ... Color image generation unit 2 ... Color image input unit 3 ... Conversion processing unit ((r, g, b) → (u, λα, v, λ
β)) 4 ... Conversion table 5 ... Conversion table generation unit 6 ... Pattern synthesis unit 7 ... Pixel pattern file 8 ... Data format conversion device 9 ... Electron beam drawing device 10 ... Diffraction grating original plate 11 ... Press device 12 ... Diffraction grating recording medium 21, 22, 23 ... Laser 24, 25, 26 ... Optical modulator 27 ... Reflecting mirror 28, 29 ... Dichroic mirror 30 ... Reflecting mirror 31 ... Galvanometer 32, 33 ... Relay lens 34 ... Rotating polygonal mirror 35 ... Reflecting mirror 36 ... Screen 41 ... Wavelength variable laser 42 ... Wavelength modulator 43 ... Intensity modulator 44 ... Control device 51 ... Ink holding part 52 ... Ink adhering part 53 ... Control device 54 ... Display surface (paper surface) C ... Vector d indicating composite color ... Spatial distance G in color solid ... Diffraction grating P ... Points P11 to P15 in color solid ... Diffraction grating pattern p ... Lattice line pitch Q ... Point Q in color solid 1, Q2, Q3, Q4 ... Pixels Q11, Q12, Q13, Q21, Q22, Q31, Q
32, Q41, Q42 ... Sub-pixel S ... Spectral closed curve V ... Diffraction grating formation region u, v, u1, v1, u2, v2 ... Coefficients, luminance values, density values, intensity values λα, λα1, λα2 ... First monochromatic light, wavelength of first monochromatic light, vectors λβ, λβ1, λβ2 indicating first monochromatic light ... Second monochromatic light, wavelength of second monochromatic light, vector indicating second monochromatic light

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-282717 (JP, A) JP-A-6-337622 (JP, A) JP-A-4-100088 (JP, A) JP-A-3- 206401 (JP, A) JP 5-204326 (JP, A) JP 7-146635 (JP, A) JP 8-21909 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 9/64 G02F 1/01 G09G 3/20 G09G 5/06

Claims (7)

(57) [Claims] 1. Displaying a color image composed of a plurality of pixels
In order to ensure that each pixel is
The first monochromatic light λα is first supplied to the first sub-pixel.
Brightness or density u of the second sub-pixel
The monochromatic light λβ of is displayed with the second brightness or density v,
For each pixel, the monochromatic light used and its brightness or
How to display a color image that sets the density independently
In, the step of defining a three-primary color system capable of expressing monochromatic light in the visible wavelength range by a positive pixel value and preparing a color image expressing individual pixels in this three-primary color system; Arbitrary monochromatic light λ within the color solid of the color system
A vector synthesis expression “u · λα + v · λ” using a vector λα indicating α and a vector λβ indicating arbitrary monochromatic light λβ
a step of associating a composite color occupying the same position or a neighboring position as the pixel color of each pixel forming the color image with the pixel among the various composite colors indicated by β ”; and configuring the color image. For each individual pixel, the first monochromatic light λα displayed in the first subpixel and Its brightness or density u
And a step of determining the second monochromatic light λβ displayed in the second sub-pixel and its brightness or density v, and a method of displaying a color image using monochromatic light. 2. The display method according to claim 1 , wherein a finite number of monochromatic lights in the visible wavelength range are defined as monochromatic lights corresponding to the vectors λα and λβ in the vector synthesis expression “u · λα + v · λβ”. Vector composition formula "u
.. .lamda..alpha. + V.lamda..beta. "Defines a finite number of discrete values as the values to be taken by the coefficients u and v, and defines a finite number of composite colors based on these finite number of monochromatic lights and discrete values. Among the colors, a monochromatic light is used, which is characterized in that a composite color occupying the same position as or a position near the pixel color of the pixel forming the color image is selected and the selected composite color is associated with the pixel. How to display the original color image. 3. The display method according to claim 2 , wherein the vector combination formula “u · λα + v” indicating the selected combination color is used.
Firstly, a diffraction grating having a pitch corresponding to the wavelength of the monochromatic light λα is arranged in the display region according to the coefficient u based on λβ ”.
And a second sub-pixel in which a diffraction grating having a pitch corresponding to the wavelength of the monochromatic light λβ is arranged in the display area corresponding to the coefficient v, and the expression of the corresponding pixel is represented by these sub-pixels. A method for displaying a color image using monochromatic light, which is characterized by being performed. 4. The display method according to claim 2 , wherein the vector combination formula “u · λα + v” indicating the selected combination color is used.
.Lambda..beta. ", The wavelength of the monochromatic light .lambda..beta. And the first sub-pixel appearing as a spot when a beam having the wavelength of the monochromatic light .lambda..alpha. A second sub-pixel that appears as a spot when a given beam is irradiated on a predetermined display surface with an intensity corresponding to the coefficient v, and the corresponding pixel is represented by these sub-pixels. A method for displaying a color image using monochromatic light. 5. A display method according to any one of claims 2 to 4.
In the method, from the finite number of composite colors,
The spatial distance to the position in the color solid occupied by the pixel color
Select the smallest combined color and select the selected combined color
Using monochromatic light, which is characterized in that
How to display color images. 6. A display method according to any one of claims 2 to 4.
In the method, from the finite number of composite colors,
The spatial distance to the position in the color solid occupied by the pixel color
Select and select one composite color that is within the specified error range
The feature is that the composite color is associated with the pixel
And a method for displaying a color image using monochromatic light. 7. A display method according to any one of claims 2 to 4.
In the law, for a finite number of pixel colors expressed in any three primary color system
The table that associates the composite colors to be selected.
Prepare and prepare a pair for each pixel using this table.
The feature is that the composite color to be applied is selected.
A method for displaying a color image using monochromatic light.