JPH0716236B2 - Color recording method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color recording method in which color reproduction is carried out by superimposing dots of one color or two colors of three color inks of yellow, magenta and cyan and dots of black ink.

2. Description of the Related Art Conventionally, in the fields of color printing and photography, color correction methods using (1) masking equation and (2) Neugeber equation are known as techniques for more faithful color reproduction. On the other hand, the color recording apparatus has changed from the halftone expression by the conventional analog recording method to the halftone expression by the digital recording method with the times.

Color photographs are a typical example of analog halftone expression.
Color electrophotography is available. As shown in FIG. 1, in these color reproductions, the inks of the three subtractive primary colors yellow Y, magenta M, and cyan C on the recording material P form a complete layer structure.

On the other hand, typical examples of the digital halftone expression method include a multicolor overlay printing method, an ink jet recording method, and a binary recording method by an electrophotographic method. These color reproductions are shown in Fig. 2 (A).
Ink of a plurality of colors does not form a complete layer structure as in the above.

By the way, the above-mentioned masking equation is defined as an equation established based on the density of the printed matter based on the additive rule. Therefore, this equation can be applied to the color superimposing method of complete layer structure as shown in Fig. 1, but the additive rule can be applied to the color superimposing method of partial layer structure as shown in Fig. 2. First of all, it is difficult to make a perfect color correction using the masking equation. The Neugeber equation is an equation formed on the assumption that the overlapping area of the printing ink is random and the area ratio of the overlapping portion is proportional to the product of the sizes of the ink areas. Therefore, as can be seen in color superposition in printing, it can be sufficiently applied when the superposition of printing inks is random due to screen angle processing, etc., but in the case of Fig. 2, the Neugeber equation is also used completely. It is difficult to correct the color.

As can be seen from the above description, the color correction equation based on digital recording has a drawback that it cannot be completely processed by the conventional masking equation or Neugeber equation.

For the purpose of achieving good halftone expression, black reproduced by superimposing all Y, M, and C is separately reproduced by black ink as shown in FIG. 2B. A so-called black marking process may be performed. For this processing, minimum value detection for black data detection and so-called undercolor removal for removing black components from other color data are required. For this purpose, a memory for data storage and There is a problem that a complicated arithmetic circuit or the like is required and the processing speed is reduced due to this.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and from three color component signals that do not include black, yellow, magenta,
The object is to determine the recording area ratios of the four color inks of yellow, magenta, cyan, and black by a simple procedure without obtaining the minimum value of the three color signals of cyan.

EXAMPLES Hereinafter, the present invention will be further described with reference to the drawings.

In explaining the present invention, (A) theoretical background, (B)
The practical implementation method will be explained in two stages.

(A) Theoretical background Consider the case where two colors and a large number of colors are digitally expressed by the recording areas of black as shown in FIG. 2 (B).

As the printing inks, three subtractive primary colors and four black colors, that is, yellow (Y), magenta (M), cyan (C), and black (K) inks are prepared. When printing on the recording paper P, In principle, any color can be reproduced by selecting and printing a maximum of two colors from black and the other three colors.
There are six combinations for selecting two colors from the above three colors. This is shown in FIG.

Assuming that the area ratio of each ink of Y, M, C, K is y, m, c, k per unit area, the area ratio of each composite color in the cases of (a) to (f) in FIG. It becomes like the figure. However, the unit area was 1.

Next, the light energy of each color reflected from the printed matter color-reproduced by each ink combination is calculated. A specific description will be given by taking the case of FIG. 4 (a) as an example.

Respective reflectances when printed with each single color ink on the recording paper P are red light reflectance Rs, green light reflectance Gs, and blue light reflectance Bs.
Here, s is indicated by y, m, c, k, y is yellow, m is magenta, c is cyan, and k is a suffix for distinguishing the case where black ink is used. Similarly, the respective reflectances when two different color inks are overlaid are the red light reflectances.
Rd, green light reflectance Gd, and blue light reflectance Bd. Where d is y,
It is a combination of two of the three colors m and c. Therefore, Rym indicates the red light reflectance when the yellow ink and the magenta ink are overlapped. Generally, even when two inks of the same color are stacked, the reflectance differs depending on the stacking order. Therefore, the suffices are determined so as to indicate the order of the recording ink layers on the recording paper P, and Rym is the red light reflectance when the recording paper P has yellow and magenta on the yellow. That is,
Rym ≠ Rmy. Further, the suffix W is attached to the reflectance from the white background portion.

FIG. 5 shows a red light reflection state with respect to four areas of white background, black, yellow and green when ink is recorded as shown in FIG.

From the area ratio of each color shown in FIG. 4 (a), the total red light reflection energy R _{T in} FIG. 5 becomes R _T = {1- (k + y)} Rw + kRk + mRym + (ym) Ry. Then, R _T −Rw = (Rk−Rw) k + (Ry−Rw) y + (Rym−Ry) m.

Similarly, for green light G and blue light B, the reflected energy G _T , B _T
When is calculated, it becomes as shown in column (a) of Table 1. The conditional expression is 1 ≧ y ≧ m ≧ 0 depending on the combination of FIG. Further, for black ink K, 1 ≧ k ≧ 0. On the other hand, black K
And the sum of the area ratios of yellow Y is 1 or less, so 1 ≧ k + y
≧ 0.

Here, among the respective reflectances, one having a reflectance considerably close to 1 by actual measurement or the like is set to 1, and one having a reflectance substantially close to 0 is set to 0. That is, assuming that Rm = Ry = Gy = Rw = Gw = Bw = 1 Rc = Gm = By = Rk = Gk = Bk = 0, the respective formulas in Table 1 are simplified and shown in Table 2.
Further, the reflectance of the portion where the two color inks overlap can be considered as a product of the reflectances of the two colors, for example, Rmy = Rm · Ry.

The advantages of using the color correction equation based on Table 1 or 2 are listed below compared to the case of using the conventional color correction equation. (1) The three color signal components from the input device are represented by R, G, wherein the R = R _T of the first table or the second table when the _{B, G = G T, B} = B T and to the area ratio y of ink to be printed directly, m, c, when k is determined At the same time, two colors to be selected from three colors of printing ink except black are automatically determined.

(2) Complementary color conversion is not required as compared with the case where the conventional color correction equation is used as a basis, and the undercolor removal is automatically performed so that it is not necessary to newly remove the black ink component.

(3) In the case of the conventional masking equation, the additive rule failure due to color superposition has been a problem, but according to this method, by measuring the reflectance of the result of color superposition and substituting it in the color correction equation, The problem of non-fulfillment of the additive rule and the proportional rule disappears.

(4) The area ratio of black ink to be printed is automatically determined by the input signal RGB at the same time as that of other colors.

(B) Practical Implementation Method A specific implementation method for achieving the color correction according to Tables 1 and 2 is shown in FIGS. 6 and 7. An input device 601 in FIG. 6 is, for example, a three-tube television camera. Reference numeral 602 denotes a color separation output signal from the television camera 601, which is R (red), G (green), and B.
It is decomposed into (blue) components and enters the processing unit 603. The RGB signal is an incident light energy proportional signal in which white is 1 and black is 0. Reference numeral 608 denotes a memory for storing the reflectance of each color component, for example, for storing each reflectance input by the operator from the outside with a keyboard so as to be set in the formula of Table 1. That is, if the above-mentioned approximate data is stored in the memory 608, the correction according to the simplified correction formula in Table 2 is performed. Reference numeral 603 is each printing ink for each of the six color combinations (a) to (f) for R, G, B inputs based on each color reflectance stored in the memory 608 based on Table 1 or Table 2. The area ratios y, m, c, k are obtained and output as 604. First
To the table or Table 2 from the TV camera 602 for R _T , G _T , B _T
Substitute the R, G, B signals as they are. Therefore, (k ₁ , y ₁ , m ₁ )
_{(K 2, y 2, c} 2) (k 3, m 3, y 3) (k 4, m 4, c 4) (k 5, m 5, c 5)
_Six calculation results of (k ₆ , c ₆ , y ₆ ) are calculated. Of these six calculation results, there is inevitably one that satisfies the conditional expression, and by checking it, one of the combinations of colors in (a) to (f) in FIG. 3 is selected. It

FIG. 7 is a flow chart showing the processing procedure in the processing unit 603. In step 701, the three color signal B, G,
Enter R. Step 702 calculates and stores the six types of ink area ratios (ki, yi, mi, ci) of each color to be printed by the processing unit 603 according to Table 1 or Table 2. In step 703, i is set to 1 in order to output (k ₁ , y ₁ , m ₁ c ₁ ) out of the stored six area ratios. In step 704, the six calculation results stored in step 702 are sequentially read according to the value of i, and it is determined in the next steps 707 to 710 whether the conditional expressions (a) to (e) are satisfied.

For example, if it is determined in step 705 that the calculation result (k ₁ , y ₁ , m ₁ ) satisfies the conditional expression (a), the process moves to step 711 and black is changed.
The area ratio of k ₁ , yellow is y ₁ , and magenta is m ₁ , and cyan c is not printed.

If the conditional expression (a) is not satisfied in step 705, it is determined whether or not the conditional expression (b) is satisfied in step 706. In this way, the selection of the color to be printed and the area ratio of the ink to be printed are determined, and output in step 717 to an external printing device or the like.

A print unit 607 records an image according to input data,
For example, an ink jet printer. In the printing unit 607, the reflectance of the print result with respect to the input data is not always linear. This is because the input data versus the number of printing dots is linear, but the input data versus the printing dot area is not linear due to the overlapping area between the dots. A correction circuit 605 having a non-linear correction table is provided to correct this non-linearity.

Accordingly, the printing area ratios c, m, y, k to be printed, which are output from Table 1 or 2, are non-linearly corrected and become the output 606, which is c ', m', y ', k'. Is entered.

As can be seen from the above description, the combination of ink colors to be printed and the area ratio to be printed of the selected color inks are determined without directly passing through the complementary color conversion circuit from the input TV camera output signals R, G, B. It At the same time, the black area ratio for blackening and the underlying color removal processing related thereto are executed without providing a dedicated circuit.

It is a necessary condition that the black ink k to be printed is printed so as not to overlap with other color inks as much as possible. This is an example, and two dither patterns are provided as shown in FIG.
This can be achieved by distinguishing the dither pattern for digital gradation expression according to the area ratio from that for black ink (K) and that for other color inks (A).

In this description, the ink jet printer is taken as an example,
It goes without saying that it can be applied to other laser beam printers, thermal printers and the like.

Further, the R, G, B data to be recorded may be data read from the image file, data transmitted via a line, or the like.

Further, the present invention can be applied to both a method of changing the size of a recording dot corresponding to a pixel and a method of forming a pixel by a set of a plurality of unit dots.

Effect As described above, according to the present invention, the color input signals R, G,
A combination of ink colors to be printed can be selected directly from B, and the area ratio of the selected color ink and black ink to be printed is simultaneously determined.

Further, the undercolor removal corresponding to the black ink has already been executed, and it is not necessary to newly remove the undercolor.

In addition, the inconvenience of the addition rule and proportionality rule failure due to color overlapping is eliminated, and faithful color reproduction is possible for a wide variety of input originals. By adjusting a large number of adjustment knobs to determine the color conversion parameters by a specialized operator, the operation of determining the optimum output condition is not necessary, and by inputting the reflectance of each color and each color ink stack in advance, Optimal color correction can be automatically performed for all input documents.

Effect As described above, according to the present invention, in the color recording method in which the color is reproduced by the dot of the black ink and the dot of one color or two colors of the three color inks of yellow, magenta, and cyan, The reflectances of the three color inks and two of the three color inks are overlapped without obtaining the minimum values of the three color signals of yellow, magenta, and cyan from the color component signals of the three colors not including black. By determining the area ratios of the two inks of the above three color inks and the black ink based on the reflectance of the combination and the reflectance of the black ink, the color component signals of the three colors not including black are converted into yellow. , A simple procedure without finding the minimum value of the three color signals of magenta, cyan,
The recording area ratios of the four color inks of yellow, magenta, cyan and black can be determined.

[Brief description of drawings]

FIGS. 1 and 2 are diagrams showing ink overlapping states in color reproduction, FIG. 3 is a diagram showing types of combinations of black K and other two colors, and FIG. 4 is each color area ratio of the combination shown in FIG. Showing the figure,
FIG. 5 is a diagram showing reflectance, FIG. 6 is a block diagram showing a circuit configuration example for achieving the present invention, and FIG. 7 is a processing unit 603.
Fig. 8 is a flow chart showing the processing procedure of Fig. 8, and Fig. 8 is a diagram showing a dither pattern suitable for the present invention. Y …… Yellow M …… Magenta C …… Cyan K …… Black (black) P …… Recording material 601 …… TV camera 603 …… Processing unit 607 …… Printing unit 608 …… Memory

Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number for FI H04N 1/46 (56) Reference JP-A-55-10067 (JP, A) JP-A-56-123540 (JP , A) Japanese Patent Publication 4-41550 (JP, B2)

Claims (1)

[Claims] 1. A color recording method for reproducing a color by superimposing dots of one color or two colors of three color inks of yellow, magenta, and cyan and dots of a black ink, and three colors not including black. Without calculating the minimum values of the three color signals of yellow, magenta, and cyan from the component signals, the respective reflectances of the inks of the three colors, the reflectances of the two inks of the three color inks, and the reflectances of the black inks are superposed. A color recording method, characterized in that the area ratio of two inks of the three color inks and the black ink is determined based on the reflectance.