JP3203933B2 - Color material amount conversion method in image formation on different printing materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming apparatus such as a color printer or a color printer, or a color which gives a similar color even when the color values of the printing medium are different between the multicolor image forming apparatuses. The present invention relates to a method for converting a material amount.

[0002]

2. Description of the Related Art In recent years, various types of color printers have been used, and between printing and color printers, or
There is a demand for a match in color reproduction between various color printers or when the color values of the printing medium are different. In general, in the two multicolor image forming apparatuses A and B, the color material amount at A is converted into the color value by the conversion means α for converting the color material amount at A into the color value, and the color value at B is converted into the color value. By converting the color value into the color material amount in B by the conversion means β for converting into the color material amount, the same color value can be obtained by converting the color material amount in A into a color material amount in both color reproducible ranges. It can be converted into the given color material amount in B.

In this manner, a reference color value space is determined (L ^* a ^* b ^* , RGB, etc.), and the conversion means between the color material amount and the color value of the multicolor image forming apparatus is determined by a look-up table method, By realizing by means of a network, an approximation formula, or the like, it is possible to convert the amount of a color material that gives a similar color value between colors in both color reproducible ranges between arbitrary multicolor image forming apparatuses. Conventional techniques using a neural network include Japanese Patent Application Laid-Open Nos. Hei 2-241271 and Hei 4
Japanese Patent Application Laid-Open No. 83471/1993 and a reference to the look-up table method include Kodera, "Color reproduction in digital print", Journal of the Institute of Image Electronics Engineers of Japan 14.5.1985.
Etc.

[0004]

However, when the color values of the printing materials used are different, for example, between the multi-color image forming apparatuses A and B having different printing materials, A
The color value of the image when the color material amounts are zero in all, that is, the color value of the printing medium a itself in A, that is, the white color in A is a color value that cannot be reproduced in B or a color value that can be reproduced. Even if there is, the color material amount at B which gives the same color value does not become zero. Naturally, an image in which the color material amount in B is not zero is different from the color of the printing medium b itself in B, and human vision considers the color of the printing medium b itself as white. Therefore, there is a problem that an image reproducing white in A does not look white.

[0005] The present invention is applicable to both the case where the white color in A is a color value that cannot be reproduced in B, and the case where the color material amount in B which gives the same color value even if it can be reproduced is not zero. It is an object of the present invention to provide a color material amount conversion method in which the white color at A corresponds to the white color at B, and the images formed by A and B give similar colors.

[0006]

In order to achieve the above object, the present invention is directed to a method for forming a multicolor image on different printing materials a and b with the same or different multicolor image forming apparatuses. Converting means α for converting the amount of color material for forming an image on the printing medium a into the color value of the image formed thereby
And converting means β for converting the color value into a color material amount for forming an image on the printing medium b,
In the color material amount conversion method for converting the color material amount for the print medium a into the color material amount for the print medium b giving the same color, the conversion unit α includes a color material for the print medium a. From the amount, the contribution of the spectral reflectance of the printing medium a itself to the spectral reflectance of the image formed on the printing medium a with the color material amount is calculated according to the contribution ratio of the printing medium b itself. The conversion into a color value corresponding to the spectral reflectance obtained by replacing with the reflectance is performed.

Further, according to a second aspect of the present invention, there are provided n types of color materials used for forming an image on a printing medium a, and the amount of each color material is a
When 1 to an%, the contribution of the spectral reflectance of the printing medium a itself, which is to be the spectral reflectance of the image on the printing medium a,
_{(1-a 1/100)} × (1-a 2/100) ×. . .
It is an _{× (1-a n / 100} ). A third aspect of the present invention provides a color material for forming an image on a printing medium a when forming a multicolor image on different printing mediums a and b by the same or different multicolor image forming apparatuses. By using a conversion means α for converting the amount into a color value and a conversion means β for converting the color value into a color material amount for forming an image on the printing medium b. In the color material amount conversion method for converting the amount of the color material to the amount of the color material for the printing medium b giving the same color, the converting means β includes a color material used when forming an image on the printing medium b. Are m types and the amount of each color material is b ₁ ~
When the _{b m%, (1-b} 1/100) × (1-b 2
/ 100) ×. . . X (1−b _m / 100) as the contribution ratio, and the contribution of the spectral reflectance of the printing medium b itself to the spectral reflectance of the image formed with the amount of the coloring material for the printing medium b is the above contribution The color value corresponding to the spectral reflectance obtained by replacing the spectral reflectance of the printing medium a itself according to the ratio is converted into the color material amount for the corresponding printing medium b.

The color material amounts are RGB, CMY, CMYK
The color values are Munsell color system (OSA19
43), L ^* a ^* b ^* , L ^* u ^* v ^* (CIE197
6, JISZ8729), XYZ (CIE1964, J
ISZ8701), X10Y10Z10 (CIE1964, J
ISZ8701), HVC, YIQ, YUV, Yxy, etc., are generally used, but the means of the present invention is not limited to any of the above.

When RGB is used as the color material amount, R, G, and B are each set to a percentage value, and a ₁ = 100−
R, a ₂ = 100-G, a ₃ = 100-B, or b _{1
= 100-R, b 2 =} 100-G, or if b ₃ = 100-B.

[0010]

The operation of the present invention will be described below with reference to the drawings. In the conversion of the color material amount between the multi-color image forming apparatuses A and B having different printing materials, the operation of the conventional method is as shown in FIGS. From 101,
The conversion α to the color value 103 of the image formed with the color material amount is performed, and the conversion means β104 converts the color value 103 into the image B having the color value necessary for forming the image having the color value B. The conversion β to the color material amount 105 is performed, and the conversion means α and the conversion means β
Are connected via the color value 103, the conversion of the color material amount 101 at A → the color value 103 → the color material amount 105 at B can be performed. The formed image and the image formed in B by the color material amount 105 in B have the same color value 103.

On the other hand, according to the first and second aspects of the present invention, when the conversion means α102 converts the color material amount in A into a color value, the image formed in A with the color material amount Is not converted into the color value itself, but the contribution of the spectral reflectance of the printing medium a itself used in A to the spectral reflectance of the image formed with the color material amount by A is calculated according to the contribution ratio. The conversion into a color value corresponding to the spectral reflectance obtained by replacing the spectral reflectance of the printing medium b itself used in B with the spectral reflectance is performed. This conversion is hereinafter referred to as conversion α ′ (see FIG. 4). In the multicolor image forming apparatus A, the contribution rate of the spectral reflectance is W
Spectral reflectances R ₁ (λ) of images formed with the same color material amount on two types of printing materials a ₁ and a ₂ having different spectral reflectances of ₁ (λ) and W ₂ (λ). , R ₂ (λ), and K (λ) = (R ₁ (λ) −R ₂ (λ)) / (W ₁ (λ)
−W ₂ (λ)), the contribution K (λ) as a function of the wavelength of light is
The required combination of the color material amounts may be obtained, or when the multicolor image forming apparatus A forms an image by the area gradation method, the contribution ratio is determined by the fact that the printing medium is covered with the color material. Since the area ratio is almost equal to the area ratio of the unexposed portion, this area ratio may be used as the contribution ratio. In the case of the halftone dot method among the area gradation methods, the area ratio is determined by n types of color materials used in A and each color. when wood weight of _{a 1 ~a n%, (1} -a 1/100) ×
_{(1-a 2/100)} ×. . . _{× (1-a n / 100} )
This may be used as the contribution ratio.

Using this contribution ratio, as shown in FIG.
From the spectral reflectance 301 of the image of A, the printing medium a used in A
The spectral reflectance 304 obtained by subtracting the spectral reflectance 303 obtained by multiplying the spectral reflectance 302 of the print itself by the above-described contribution is multiplied by the spectral reflectance 305 of the print medium b itself used in B by the above-described contribution. The obtained spectral reflectances 306 are added to obtain a spectral reflectance 307. In the conversion α, the color material amount
In contrast to the conversion to the color value corresponding to 1, the conversion α ′ converts the color material amount to a color value corresponding to the spectral reflectance 307. As a result, in the conversion α, as shown in FIG. 2, the color value 208 corresponding to all the color material amounts in A at zero was different from the color value 209 of the printing medium b itself in B. In α ′, since the contribution of the spectral reflectance is 100%, all the spectral reflectance is replaced with the spectral reflectance of the printing medium b.
As shown in FIG. 4, the color value 408 corresponding to all the color material amounts in A at zero is the color value 409 of the printing medium b itself used in B.
Will be the same as Here, 409 is the same color value as 209.

Further, A which gives a color value having a small contribution ratio of the spectral reflectance (a color value relatively distant from the color value 408).
Since the replacement amount of the spectral reflectance is small, the color material amount at is converted to the color material amount at B which is close to the case of the conversion α, and the color material amount at A which gives a color value with a contribution ratio of 0 is obtained. In this case, the color material amount is converted into the color material amount in B which gives exactly the same color value. According to the third and fourth aspects of the present invention, when the conversion means β104 converts a color value into a color material amount at B,
B required to form an image giving that color value in B
Is not converted into the color material amount itself, but the contribution of the spectral reflectance of the printing medium b itself used in B to the spectral reflectance of the image formed with the certain color material amount by B is used as the contribution ratio. Accordingly, a conversion to a certain color material amount is performed such that the color value corresponding to the spectral reflectance obtained by replacing the spectral reflectance of the printing medium a itself used in A becomes the input color value. This conversion is hereinafter referred to as conversion β ′ (see FIG. 6).

The contribution ratio of the above-mentioned spectral reflectance can be obtained by various methods in the same manner as described above. Assuming that m kinds of color materials are used in B and the amount of each color material is b _{1 to} b _m %, (1−1) b ₁
/ 100) × (1-b 2/100) ×. . . × (1-b
_m / 100). Using this contribution, as shown in FIG. 5, a spectral reflectance 503 obtained by multiplying the spectral reflectance 502 of the print medium b itself used in B by the above-mentioned contribution from the spectral reflectance 501 of the image of A, as shown in FIG. The spectral reflectance 506 obtained by multiplying the spectral reflectance 504 obtained by the subtraction by the spectral reflectance 505 of the printing medium a itself used in A and the above-described contribution ratio.
Are added to obtain a spectral reflectance 507.

In the conversion β, the color value corresponding to the spectral reflectance 401 is converted into the color material amount, whereas in the conversion β ′, the color value corresponding to the spectral reflectance 407 is converted into the color material amount. As a result, in the conversion β, as shown in FIG. 2, the color value 209 corresponding to all the color material amounts in B is zero and different from the color value 208 of the printing medium a in A itself. In β ′, since the contribution of the spectral reflectance is 100%, all the spectral reflectances of the printing medium a are replaced with the spectral reflectances of the printing medium a. Therefore, as shown in FIG. Value609
Is the same as the color value 608 of the printing medium a itself used in A. Here, 608 is the same color value as 208.

Further, the color material amount at A which gives a color value having a small contribution ratio of the spectral reflectance is smaller than the color material amount at B which is close to the case of the conversion β because the replacement amount of the spectral reflectance is small. In the case of the color material amount at A which gives a color value with a contribution ratio of 0, it is converted into the color material amount at B which gives exactly the same color value. As described above, according to any of the claimed inventions, with respect to the color material amount in A that gives a color value that is less affected by the difference in the color value of the printing medium itself, the color material B that gives the same color value as much as possible is used. And the color material amount in A that gives a color value that is greatly affected by the difference in the color values of the print medium, the color material amount in A that gives a color value close to the color value of the print material used in B Is converted to the color material amount at the time, and the switching is performed so as to be continuous and visually natural, so that the white at A corresponds to the white at B, and
An object of the present invention is to provide a color material amount conversion method in which images formed by A and B give similar colors.

In the above description, the multi-color image forming apparatuses A and B
However, the description has been given of the case of two different multicolor image forming apparatuses, but the same can be applied to a case where a single or the same multicolor image forming apparatus handles different printing materials. Further, it is also possible to cause the conversion result of the conversion method of the present invention to perform the same operation as a result by one conversion means γ (see FIG. 7). For example, according to the color material amount conversion method of the present invention, the conversion result of cmy% value at A → L ^* a ^* b ^* value → cmy% value at B is converted into the table contents of one lookup table method. Alternatively, by making one neural network learn, the conversion from the cmy% value at A to the cmy% value at B may be performed by one conversion means.

[0018]

An embodiment of the present invention will be described below. As the multicolor image forming apparatus A, a printing press for calibration is used, and as the multicolor image forming apparatus B, a sublimation printer S6600-30 of Mitsubishi Electric is used. First, 2 of each color material of cyan, magenta and yellow
A chart image having 216 sets of combinations of 0% is prepared, and a spectral colorimeter X-Rite 938 manufactured by X-Rite is used to measure the spectral reflectance of the chart output from the printing press for calibration and the printing medium itself. The measurement of the spectral reflectance of the chart output from the sublimation type printer and the printing medium itself is performed.

FIG. 8 shows the measurement results of the spectral reflectance of the printing medium itself used in the proofing printer and the sublimation printer. From this spectral reflectance, a 2 degree field of view, D
When an L ^* a ^* b ^* value (hereinafter, referred to as a Lab value) at 50 illuminations is determined, a printing medium of A (printing press for calibration). . . 92.9 0.17 2.04 Substrate to be printed on B (sublimation printer). . . 95.3 1.23 -7.00 As suggested by the Lab value, the printing medium of the proofreading press appears relatively yellow compared with the printing medium of the sublimation printer, and conversely, the printing medium of the sublimation printer is It looks relatively pale when compared with the printing medium of.

The conversion means α and β are realized using neural networks. The spectral reflectance R (λ) of the chart of the color material amounts c, m, and y% output in A
According to the present invention, R ′ (λ) = R (λ) + K (λ) × (−Wa (λ) + Wb (λ)) K (λ) = (1−c / 100) × (1 −m / 100) × (1-y / 100) Wa (λ): Spectral reflectance of the printing medium of the printing press for calibration Wb (λ): Converted to the spectral reflectance of the printing medium of the sublimation printer, Lab obtained from Cmy value and this R '(λ)
Correspondence (conversion α ′) with the value is realized by the conversion means α, and correspondence (conversion β) between the Lab value obtained from the spectral reflectance of the chart output in B and the cmy value of B is realized by the conversion means β. The result of the color material amount conversion is learned by a neural network which is another conversion means γ from the conversion means α and the conversion means β, and the color material amount conversion from A to B is performed. The results are shown below.

[0021] The reason why the cmy% of B is not all 0 is due to a calculation error. As can be seen by comparing the Lab value with the Lab value (95.3, 1.23, -7.00) of the printing medium of B,
Almost indistinguishable from the color of the printing substrate. For comparison, the results for the conventional method are As shown in the above, cmy% in B is a large value, and A
In the image of B, the part that looks white in the image of B does not look white.

[0022]

In addition, visually good color matching can be obtained in the conversion of a natural image, and the effectiveness of the present invention has been confirmed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a color material amount conversion method, and is a basic configuration diagram of the present invention.

FIG. 2 is a conceptual diagram of conventional color material amount conversion.

FIG. 3 is an explanatory diagram of the correction of the spectral reflectance in the first and second embodiments of the present invention.

FIG. 4 is a conceptual diagram of color material amount conversion according to claims 1 and 2 of the present invention.

FIG. 5 is an explanatory diagram of the spectral reflectance correction in the third and fourth embodiments of the present invention.

FIG. 6 is a conceptual diagram of color material amount conversion according to claims 3 and 4 of the present invention.

FIG. 7 is a configuration diagram in a case where the result obtained by the color material amount conversion method of the present invention is realized by one conversion unit.

FIG. 8 is a graph of the spectral reflectance of the printing medium used in the examples. The vertical axis indicates the spectral reflectance (%), and the horizontal axis indicates the wavelength (nm).

[Explanation of symbols]

202... A region of the color value space in which the color material amount space in A is converted by the conversion α 203... A region of the color value space in which the color material amount space is converted to B by the conversion β 205. ..A certain color material amount at A 206... 205 corresponding to the color value 207... 206 corresponding to 206, a color material amount at B 208... When all the color material amounts at A are zero .. 209... The color values of the color material at B when all the color material amounts are zero 301... The spectral reflectance of an image formed with a certain color material amount by A. The spectral reflectance of the printing object b itself used in the spectral reflectances 304... B obtained by subtracting 303 from the spectral reflectances 304... Spectral reflectance 306 ... 305 Spectral reflectance resulting from multiplying the contribution rate by 307 ... 304 Spectral reflectance 402 as a result of adding 306 to ... A region 403 in a color value space in which the color material amount space in A is converted 403... A region 405 in a color value space in which the color material amount space in B is converted into a color material amount space in B 405. The color values 407... Corresponding to the color amounts 406... 405 and the color material amounts 408 at B 408... A color value 501 when the color material amount at B is all zero; a spectral reflectance of an image formed with a certain color material amount by B; 503 ... 502 Spectral reflectance as a result of multiplying the contribution by 504 ... 504 Spectral reflectance as a result of subtracting 503 from 501 505 ... Spectral reflectance of the printing medium a itself used in A 506 ... Spectral reflectance of the result of multiplying 505 by the contribution rate 507... Spectral reflectance of the result of adding 506 to 504. 602. An area 603 of a color value space in which a space is converted 603... An area 605 of a color value space which is converted into a color material amount space in B by the conversion β '605... The color value corresponding to 605, the color material amount of B corresponding to 607... 606, and the color value corresponding to the color material amount of B at 608. Color value when all material amounts are zero

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/60 G06T 1/00 510 H04N 1/46

Claims (3)

(57) [Claims] When a multicolor image is formed on different printing materials a and b by the same or different multicolor image forming apparatus, the amount of a color material for forming an image on the printing material a is determined. By using a converting means α for converting the color values of the image formed by the above and a converting means β for converting the color values to a color material amount for forming an image on the printing medium b, In the color material amount conversion method for converting the color material amount for the body a into the color material amount for the print body b giving the same color, the converting means α converts the color material amount for the print body a The contribution of the spectral reflectance of the printing medium a itself to the spectral reflectance of an image formed on the printing medium a with the amount of the color material is calculated based on the spectral reflectance of the printing medium b itself according to the contribution rate. Characterized in that a color material amount is converted into a color value corresponding to the spectral reflectance obtained by replacing Type of actuation method. Wherein when the color material amount colorant in n type to be used for forming an image on the printed body a is a ₁ ~a _n%, the occupying the spectral reflectance of the image on the printing material a the contribution ratio of the spectral reflectance of the printing material a _{itself, (1-a 1/100} ) × (1
-A _2/100) ×. . . Obtained by _{× (1-a n / 100} ), the color material amount conversion method of claim 1. 3. When a multicolor image is formed on different printing materials a and b by the same or different multicolor image forming apparatuses, the color material amount for forming an image on the printing material a is determined by a color value. By using a converting means α for converting the color values into a color material amount for forming an image on the printing medium b, and a color material amount for the printing medium a. Is converted into a color material amount for the printing medium b that gives the same color, the converting means β converts the image on the printing medium b
The color materials used for forming are m types and the amount of each color material is b _{1 to} b
When the _{m%, (1-b 1} /100) × (1-b 2 /
100) ×. . . × (1-b _m / 100) is the contribution rate
Then, the contribution of the spectral reflectance of the printing medium b itself to the spectral reflectance of the image formed with the amount of the coloring material for the printing medium b is determined by the spectral reflection of the printing medium a itself according to the contribution rate. A color material amount conversion method for converting a color value corresponding to a spectral reflectance obtained by replacing with a ratio into a color material amount for a corresponding printing medium b.