JPS60109967A - Color recording system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a color recording system that reproduces colors using inks of a plurality of colors including black.

[Prior art]

Conventionally, in the fields of color printing and photography, a color correction method using (1) a masking equation and (2) a Neugeba equation has been known as a technique for reproducing colors with high fidelity.

On the other hand, color recording devices have been changing over time from halftone expression using a conventional analog recording method to halftone expression using a digital recording method.

Typical examples of analog halftone expression methods include color photography,
There are color electrophotography methods, etc. These colors are reproduced using the subtractive color method on the recording material P as shown in Figure 1.
1 cyan C each ink is complete.

It forms a golden layered composition.

On the other hand, representative examples of digital halftone expression methods include a multicolor overlay printing method, an inkjet recording method, and a binary recording method using electrophotography. In these color reproductions, multiple colored inks do not form a complete layer structure as shown in Figure 2.

By the way, the above-mentioned masking equation is defined as an equation established on the basis of the additive side and based on the density of the printed matter. Therefore, this equation can be applied to a color superposition system with a complete layer structure as shown in Figure i1, but the additive side cannot be applied to a color superposition system with a partial layer structure as shown in Figure 2. Is it difficult to perform complete color correction using equations? The Neugeba equation is an equation formed on the premise that the overlapping areas of printing inks are random and the area ratio of the multiple overlapping parts is proportional to the product of the sizes of the areas of each ink. Therefore, it can be fully applied when the overlapping of printing inks is random due to screen corner processing, etc., as seen in the overlapping of colors in printing, but in cases such as the one shown in Figure 2, even the Neugeba equation can be applied completely. Color correction is difficult.

As is clear from the above explanation, the color correction equation based on digital recording has a drawback that it cannot be completely processed by the conventional masking equation or the Neugeba equation.

In addition, for the purpose of achieving good halftone expression, black, which is reproduced by overlapping all of Y, M, and C, is reproduced separately using black ink, as shown in Figure 2 (■). A so-called inking process may be performed. This processing requires processing such as minimum value detection to detect black data and so-called undercolor removal to remove black components from other color data. This requires complicated arithmetic circuits, etc., and this has problems such as slowing down the processing speed.

Further, a color copying machine has been proposed which separates a color original into colors, reads them photoelectrically, and reproduces a color image based on the reading signals. As described above, in a copying machine, the optical energy of reflected light or transmitted light from a document varies greatly depending on the material of the document and the reading method.1 Also, each color signal obtained by photoelectrically reading is relative. It is. The light energy of the image whose color is reproduced according to the read signal obtained in this way may differ from the light energy of the original document, and as a result, faithful image reproduction may not be possible.

〔the purpose〕

The present invention has been made in view of the above points, and an object of the present invention is to provide a color recording method that is suitable for digital color recording.

〔Example〕

The present invention will be further explained below with reference to the drawings.The present invention will be explained in two parts: (6) theoretical background and (B) practical implementation method.

(a) Theoretical Background Let us consider a case where a large number of colors are digitally expressed using a recording area of two colors and black, as shown in Figure 2).

The printing ink is prepared by adding black to the three primary colors of the subtractive color method, namely yellow (1), magenta, cyan (Q, and black 4).When printing on recording paper P, black and other inks are prepared. In principle, any color can be reproduced by selecting and printing a maximum of two colors out of the three colors.Above 3.
There are six combinations for color reproduction by selecting two of the three colors in the recording order of colors Y, M, and C from the bottom.

This is shown in FIG.

The area ratio of each ink for Y, M, C, per unit area J)
If y, m, c, k, then (a) in Figure 3 ~
The area ratios for each composite color in case (f) are shown in Figure 4 (a) ~
It becomes like (to). However, the unit area was set to 1.

Next, the light energy of each color reflected from the printed matter reproduced by each ink combination is calculated.

The respective reflectances when printed with each single color ink on recording paper P are red light reflectance R8% green light reflectance GS% blue light reflection rate Bs
shall be. Here, 5ii)'ymyc+ is a suffix that distinguishes the cases in which y is yellow, m is magenta, C is cyan, and k is black ink. Similarly, the respective reflectances when two different colored inks are overlapped are red light reflectance Rd, green light reflectance Gd, and blue light reflectance Bd.
shall be.

Here, d is a combination of two of the three colors y, m, and c, and for example, Rym indicates the red light reflectance when magenta ink is layered on yellow ink.

Generally, even if two inks of the same color are stacked, the reflectance will differ depending on the order in which they are stacked. Therefore, when determining the suffix to indicate the order of the recording ink layers on the recording paper P, L, Ry
m is the red light reflectance when there is yellow p on the recording paper P and magenta on the yellow. That is, Rym'
x, Rmy. Further, the suffix W is attached to the reflectance from the white background portion.

FIG. 5 shows the state of red light reflection in four areas of white, black, yellow, and red when ink is recorded as shown in FIG. 3(a).

From the area ratio of each color shown in Figure 3 (a), the total red light reflection energy RT in Figure 4 is R7 = (1-(k+y))Rw 10 kRk + mRym
+(y−m)Ry.

Similarly, the reflected energy for green light G1 and blue light B, GT
When IBT is calculated and Equation 1 is transformed, it becomes as shown in column (a) of Table 1.

This value is used to model the printing condition as shown in Figure 5.
It is the relative value of the original energy reflected from the printed material when green and blue color light is given. On the other hand, the range of light energy that a photodetector on the input side of a television camera or the like receives from the original varies greatly depending on various conditions such as whether the original is a transmissive or reflective original and the material of the original. Furthermore, the light energy range on the input side and the light energy range from the output printed matter are generally not in the same range, and some kind of correction is required between the two.

FIG. 6 illustrates these relationships, and shows the case where the input document 501 is a transparent document. In this case, the range of light energy ER for red light to the detector is ideally (as shown in Q, 0≦ER≦1), and also for light of other colors O≦EC≦1° 0≦EB≦1.On the other hand, (I19 indicates the light energy of the printed matter 502, and the range of light energy reflected from the printed matter 502 on the printing side is
For example, in the case of red light, if the reflectance of the white background of the printed matter is Rw and the reflectance of the black background is Rw, then the range of the red light energy Ed is (
As shown in 1, swimming ≦FfB ≦Rw. In fact, the reflectance Rw from a white background is smaller than l, and the reflectance from a black background is greater than 0. Similarly for other colored lights, Gk≦
E'G≦Be.

Bk≦EK≦Bw. In this way, the light energy E from the original and the light energy E from the printed matter! The ranges of and are not equal ψ. In order to correct the optical energy range between the input side and the output side, linear correction is performed as shown in FIG.

Hard pigeon 1 Therefore, ER= -...Eyo, -. The value E& corrected in this way is defined as RT in Table 1. Therefore, in RT, Ek of the above formula
Substituting (Rw-Rk) (E, H-1) = (Rk
-Rw) k+(Ry-Rw) y+(Rym-Ry)
m.

Similarly, other colored lights are arranged, and the relational expressions for all the combinations shown in FIG. 3 are as shown in Table 2.

As a result, the light energy related to the images on the input side and the output side is corrected.

The advantages of using the color correction equation based on Table 2 compared to the case of using the conventional color correction equation are as follows: Then, in the formula in Table 2, 1 (=ER1G=EG.

B11 is the area ratio y of ink to be directly printed.

At the same time as nl, c, and k are determined, two colors to be selected from three printing ink colors other than black are automatically determined.

(2) Compared to the case based on conventional color correction equations, there is no need for complementary color change, and undercolor removal is automatically performed, so there is no need to newly remove black ink components (3) Conventional In the case of the masking equation of On the other hand, the problem of the law of proportionality not being satisfied disappears.

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

(5) Light energy characteristics on the input side of the document reading device, etc.
It is possible to correct the deviation in the range from the light energy characteristics on the output side and perform faithful image reproduction.0 (c) Practical implementation method A specific implementation method for achieving color correction according to Table 2 is described in Section 8.
As shown in Fig. 9. Reference numeral 601 in FIG. 8 is a human-powered device having a photodetector, such as a three-tube television camera. 602 is a color separation output signal from the television camera 601; R (red);
It is decomposed into G (I#) and B (blue) components and processed by the processing section 60.
Enter 3. The KGB signal is a proportional signal that relatively represents the incident light energy, with white being 1 and black being O. Reference numeral 60B denotes a memory for storing the reflectance of each color component, and is used to store each reflectance entered externally by an operator using a keyboard, for example, so as to set it in the formula in Table 2.

603 indicates each printing ink for each of the six color combinations (A) to (F) for jrt, e, and B based on Table 2, based on the reflectance of each color stored in the memory 608. Area ratio y,
m, c, and k are output as 604.

The R, G, and B signals from the television camera 602 are substituted as they are into each of "Rt EQ v Ell" in Table 2.

Therefore (k+ *'JIerllq)Ck2rY2+C
t)Cks*msvYs)Ckatm4. c4) (k5
．． m5. The six calculation results of c, ) (k, , c6.y8) are calculated. Of these 6 calculation results, there is always one that satisfies the conditional expression, so it is necessary to check it. is selected.

FIG. 9 is a flowchart showing the processing procedure in the processing unit 603. In step 701, three color signals B, G, and R are inputted from the input device 601. Step 702 is the processing section 6
The ink area ratio (ki
, yi, mi, ci) as input signal B.

G and 几 are respectively calculated as EBv EG v ER according to Table 2 and stored. In step 03, (k+ y 'h ymt e
Set i to 1 to output Ct). Step 7
In step 04, the six calculation results stored in step 702 are sequentially read out according to the value of i, and the steps 707 to 1 are sequentially read out.
At o, it is determined whether the conditional expressions (a) to (e) are satisfied.

For example, if it is determined in step 705 that the calculation result (k+e)+ym+) satisfies conditional expression (a), the process moves to step 711 and prints black, yellow, and magenta at an area ratio of yl and ml, respectively. and do not print cyan C.

If conditional expression (0) is not satisfied in step 705, it is determined in step 706 whether conditional expression (b) is satisfied. In this way, the selection of the color to be printed and the area ratio of the ink to be printed are determined in one step 717.
output to an external printing device, etc.

607 is a printing unit that records an image according to input data, such as an inkjet printer.

In the printing unit 607, the reflectance of the print result with respect to the input data is not necessarily linear.

This is because although the input data versus the number of printed dots is linear, the input data versus the printed dot area is no longer linear due to the overlapping area between the dots. In order to correct this nonlinearity, a five correction circuit 605 having a nonlinear correction table is provided.

Therefore, the printing area ratios c, m, y, k to be printed outputted from Table 1 or Table 2 are non-linearly corrected and outputted as c', rr/, y', k' as the output 606. is input.

As is clear from the above explanation, the combination of ink colors to be printed and the area ratio to be printed with the selected color ink are determined directly from the input TV camera output signals 1 (, G, B) without passing through the complementary color conversion circuit. be done.

At the same time, the black area ratio for inking and the related undercolor removal processing are executed without providing a dedicated circuit.

The black ink to be printed must be printed uniformly with as little overlap as possible with other color inks. As an example, two dither patterns are provided as shown in Figure 10, and the dither l pattern is 0 for black ink and 5 for other color inks when digitally expressing 1!1 tone according to the area ratio. )
This can be achieved by distinguishing between the two.

This explanation uses an inkjet printer as an example, but
Needless to say, the present invention can also be applied to other laser beam printers, boolean printers, etc.

Further, in the above-mentioned correction of the optical energy between the original document and the printed matter, linear correction is used in this embodiment, but non-linear correction may be performed depending on the characteristics. In this case as well, by substituting the non-linear formula into Table 1 to obtain the arithmetic expression, the area ratio of the ink can be similarly obtained according to this expression.

Furthermore, the R, G, and B data to be recorded may also be data read from an image file, data transmitted over a line, or the like. - Furthermore, the present invention can be applied to both a system in which the size of the recording dot itself is changed and a system in which a pixel is constituted by a plurality of sets of certain unit dots.

Alternatively, a table may be used that is addressed by an input color signal and outputs a recording signal.

[Effect] As explained above, according to the present invention, the color human signal R,
Directly from G and B, the characteristics of the input side and output side of the image are corrected, and the combination of ink colors to be printed is selected, and the area ratio to be printed of the selected color ink and black ink is determined. It becomes possible to achieve color reproduction〇

[Brief explanation of the drawing]

1 and 2 are diagrams showing the overlapping state of ink in color reproduction, FIG. 3 is a block diagram of black and other two colors of printing, and FIG. 1 shows the processing procedure of the processing unit 603. The flowchart shown in FIG. 1 is a diagram showing a dither pattern suitable for the present invention. Y----yellow, M-m-magenta, C--cyan, K-111 black (black), P-recording material, 601
------- Television camera, 603--1 processing section, 607--printing section, 608-11~memory, Applicant: Canon Co., Ltd. (<) (b) 0\) に) e) to) fE(q EcTEB

Claims (1)

[Claims] In a color recording device that reproduces colors using inks of multiple colors including black, a one-man system and an output system are used to determine the recording combination of black and multiple color inks and their recording area ratios based on the three-color color signals from the input device. A color recording method characterized by correcting the optical energy range with the system.