JPS60109968A - Color recording system - Google Patents

Abstract

PURPOSE:To obtain a color correcting system suitable for digital color recording by correcting the optical energy range of an input system and an output system and deciding the recording area rate of plural colors to three color signals from an input device. CONSTITUTION:A color separation output signal 802 of red R, green G and blue B components is outputted and inputted to a processing section 803 from a television camera 801 of an input device. The R, G, B signals are proportional signal to the incident energy where the white level is taken as 1 and the black level is taken as 0. The processing section 803 calculates the 6 kinds of ink area rates per unit area to the R, G, B inputs according to a prescribed print area calculating formula based on the reflectance data of the color component stored in a memory 807 and outputs the area rate satisfying a condition formula among the rates as a density signal 804 of cyan (c), magneta (m) and yellow (y). The signal 804 is inputted to a nonlinearity converting circuit 805 having a conversion table correcting the nonlinear characteristic and inputted to a print section 806 as signals c', m', y' whose nonlinearity is corrected.

Description

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

[Prior art]

Conventionally, in the fields of color printing and photography, color correction methods using (1) masking equations and (2) Neugeba's equation are known as techniques for more faithfully reproducing colors. On the other hand, color recording devices have been changing over time from expressing halftones using a conventional analog recording method to expressing halftones using a digital recording method.

Typical examples of analog halftone expression methods include color photography and color electrophotography, and these color reproductions are performed using three subtractive primary colors, yellow, Y, and Y, on a recording material P as shown in Figure 1.
Each of the cyan C and magenta M inks forms a complete layer structure.

On the other hand, representative examples of digital halftone expression methods include multicolor overlay printing, inkjet recording, and binary recording using electrophotography. In these color reproductions, the inks of a plurality of colors on the recording material P do not form a complete layer structure as shown in FIG.

By the way, the above-mentioned masking equation is defined as an equation based on 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 Fig. 1, but the additive side cannot be applied to a color superposition system with a partial layer structure as shown in Fig. 2. It is difficult to perform complete color correction using the masking equation. On the other hand, in the Neugeba equation, the overlapping area of printing ink is random, and the area ratio of the overlapping part is proportional to the product of the size of each ink area. 0, which is an equation formed on the assumption that
Therefore, it can be applied to cases where the printing ink is randomly overlapped due to screening or processing, as seen in the color overlap in printing, but in cases such as the one shown in Figure 2, the color correction can be completely performed using the Neugeba equation. It's difficult to do. Moreover, there is no general solution to the Neugeba equation, and only approximate solutions can be obtained.

As you can see from the above explanation, color correction based on digital recording is conventional! There was a drawback that the Sking equation or the Neugeba equation could not handle liquid-containing conditions.

〔the purpose〕

The present invention has been made in view of the above points, and it is an object of the present invention to provide a color correction method suitable for digital color recording. The purpose of this invention is to provide a color recording system capable of reproducing color images. ) Practical implementation method will be explained in two steps. (A) Theoretical background Considering the case of full color display by digital six-color superposition K, cyan is the six primary color of the subtractive color method.

If magenta and yellow are represented by C, M, and Y, there are six combinations as shown in FIG. 6. Digital halftone expression is determined by how much ink is filled in a unit area, that is, the ink area ratio per unit area. Therefore, if the unit area of the white recording material is 1, then
The area ratio occupied by the dots of each ink of magenta M and shea yC is y and tm.

If C, white W, black, red R, green G, blue B, yellow Y,
The area ratio for each color of magenta M and cyan C is the fourth
It will look like the figure.

A detailed study of the ink combination (A) in Figure 3 shows that each ink (Y, M, (3) is applied to the recording paper as shown in Figure 5).
Let Ry, R, , Re be the respective reflectances of red H for incident light when printed on top, and the overlapping portion of two or six colors of Y, M, and C inks is Y + M.

The reflectance of M+G, Y-1, Y+M+C and the recording paper P itself is R31m + RnLc! +R1C+R
ymC+R” is 0 in reality R, oh!F Rm
y is 0. This is because when the order of overlapping yellow and magenta inks is reversed, the light reflectance of each color as a result of overlapping is different. Here, it is assumed that the suffix is attached starting from the ink closest to the recording paper.

In the case of (a) in Figure 6, the red component light energy R reflected from the printed matter is RT = (1-ff) RW + (ff--) By + (71
1-C) Rym+CRymc.

Similarly, the light energy components GT+BT of the green and blue components for FIG.

GT = (1-ff)Gw+(31-”)Gy+(-
-') Gym+GGyyxcBT = (1-ff)B
w+(ff-)By+(--')Bym+CBync-
In this way, the light energy components for each color light are calculated for each of FIG. 3.

Figure 5 is a model of the printing condition shown in Figure 6, with red and green.

It is the reflected energy from printed matter when each unit of blue color light is given.

On the other hand, the range of light energy that the input-side detector receives from the original varies greatly depending on factors such as whether the original is a transmissive type or a reflective type, the recording material used in the original, etc., and its value is 0, which indicates the relative energy. The light energy range and the light energy range from the output printed matter do not fall within the same range, and some correction is required between the two.

FIG. 10 illustrates these relationships. (A) When the ti input original 501 is a transparent original, it shows the optical energy ER + EG + EB of each color to the detector, and the range is ideally (C ), 0≦ER≦1, 0≦EG
≦1.0≦EB≦1. On the other hand, the range of light energy on the print side 502 is, for example, in the case of red light, assuming that the white background reflectance of the printed matter 502 is RW and the black background reflectance is R, the range of the red light energy ER' from the printed matter 502 is R, ≦ E.R.
'≦Rw. Similarly for other colored lights, KG≦EG
'≦GW・B≦EB'≦BW 0 In general, the white background reflectance Rw<1 and the black background reflectance RK>0.

In this way, the optical energy ranges on the input side and output side are not equal. This is the eleventh method for correcting this. Here, ER' is RT in FIG. 6, and R in FIG.
Substituting ER/ in the above formula for T, (RW RK) (ER1
)=(Ry-Rw)y+(Rym-Ry)m+(Rx
Rym) c. Similarly, other colored lights are organized as shown in FIG. 7.

Note that the reflectance of two colors or six colors stacked can be considered as the product of the reflectance of each color, for example, Rym=
Ry, Rrrt=1. R,,=R,,R,.

Compared to using conventional color correction equations, the advantages of using the color correction equation based on FIG. Then, by substituting this into ER*EG+EB in the equation shown in FIG. 7, the area ratios y, m, and c of the ink to be directly printed are determined.

(2) Compared to conventional methods based on color correction equations, there is no need for complementary color conversion, the concept can be unified using energy proportional elements throughout the processing section, and there is no need to introduce the concept of density as in the past. Good too.

(6) In the case of conventional masking equations, there was a problem that the additive side did not hold due to color superposition, but with this method, it is only necessary to measure the reflectance of the result of color superposition and substitute it into the color correction equation. On the additive side, the problem of the proportionality law not being satisfied disappears.

(4) Appropriate ink area ratio y that corrects the original light energy and the original energy of the printed material, that is, the range of light energy on the input side and the output side.

m and c can be obtained.

(B) Practical Implementation Method The concrete implementation method shown in FIG. 7 will be explained using FIGS. 8 and 9.

801 in FIG. 8 is an input device, for example, a six-tube television camera. 802 is a color separation output signal from the television camera 801, which includes red R, green G, and blue.

Each component pressure of Roux B is decomposed and enters the processing section 803.

These R, G, B signals are 1 for white W and 0 for black K.
807, which is a signal proportional to the incident light energy.
is a memory that stores the reflectance of each color component (for example, the above-mentioned R, , R, , Rc, etc.). For example, the operator inputs each reflectance in the formula shown in Figure 7 from the outside using a keyboard, and the data is input. It's a place to remember. Based on the reflectance data stored in the memory 807 and based on FIG. 3'8+”Sl
+'6) is calculated. And these six ways (y, m,
The one satisfying the conditional expression (C) is searched from among (a) to (c), and the one satisfying the conditional expression is output as a density signal of each color.

A flowchart showing the procedure in the processing unit 803 is shown in FIG. In step 901, the television camera 801
Obtain output data R, G, and B signals. Step 902 performs R and G according to the formula shown in FIG.

6 types of yi with B input data as ERr, EG, EB, respectively.

y++4. cl(i=1~6) and convert the result to C'/11-11'1)~(ys, 7F16 I'l
l) Remember this. Step 903 selects (3' 1 +-1
Set 1 to 1 to select rCI). Step 90
In step 4, (yi, mi, cl) are read with a value of 1.

The condition determination flow in steps 905 to 910 is the result of calculating the six conditional expressions (a) to (f) shown in FIG.
It determines whether yi, mi, ("i) are satisfied, and the combination of recording areas of y, m, and c to be printed is determined based on the input R, G, and B values. If (yi, mi, cl) read in step 904 does not satisfy any of the conditional expressions, 1 is added to 1 in step 912 to obtain the 5th order ('/ ' r -' + ' i
). A result that satisfies this conditional expression is output as a density signal for each color in step 911. In FIG. 8, the outputs y, m of the processing unit 803
, c output 804 is obtained. 806 is a color printing unit which realizes a full color image by superimposing dots of six colors (yellow, magenta, cyan). For example, a color inkjet printer. The reflectance characteristic of the print result versus the input data value of the printing unit 806 is 0 where a nonlinear region exists.
This is because even though the number of printed dots is linear with respect to the input data to the printing unit 806, the reflectance from the printed dots generally has nonlinear characteristics due to the overlapping portions between the printed dots. Therefore, 805 is a nonlinear conversion circuit having a conversion table for correcting this nonlinear characteristic.
Of C1), the value ° that satisfies the conditional expression is input to the printing unit 806 through the nonlinear conversion circuit 805 and printed on a recording material such as paper.

As is clear from the above explanation, the input TV output signals R,
The ink filling ratio (recording area ratio) of the three colors to be printed is determined directly from G and B without passing through the complementary color conversion circuit. Furthermore, once this ink filling ratio is determined, it is possible to uniquely determine the dot matrix in the digital halftone expression method.

Although the optical energy ranges on the input side and the output side are corrected linearly, non-linear correction may be performed depending on the characteristics.

Alternatively, it may be a memory table that is addressed by a color signal input to the processing unit 803 and outputs a recording signal.

It goes without saying that this method can also be applied to laser beam printers and thermal printers.In addition, the data R, G, and B to be recorded can be obtained by reading a thick document using a solid-state image sensor in addition to data from a television camera. The data may be data from a device, an image file device such as a magnetic or optical disk, or data transmitted via a line.

The present invention can be applied to either a method in which the size of a recording dot corresponding to a pixel itself is changed to represent shading, or a method in which a pixel is composed of a plurality of unit dots and the shading is represented by the number of dots.

〔effect〕

As explained above, according to the present invention, it is possible to achieve accurate oak recording with corrected optical energy characteristics on the input side and the output side.

In addition, in the digital recording method that expresses halftones by the density of the number of dots recorded in a unit area, and in the digital color recording method that expresses many colors by overlapping multiple color inks, three colors from the input device are used. Signal (R, 'G, B
), each density signal of the three colors to be easily printed (ylm
, C) By changing, the following 0 points have a great effect. 0 (1) The additive side due to color overlap and the inconvenience of the law of proportion not being satisfied are eliminated, and faithful color reproduction is possible for a wide variety of input documents. .

(2) Conventionally, in order to perform color corrections due to the additive side and the law of proportion not being satisfied, it is optimal to have a specialized operator operate a large number of adjustment knobs, etc. in order to determine the color conversion parameters that match each input document. The output conditions were determined, but by using the method of the present invention, the optimal color correction can be automatically performed for any input document simply by inputting in advance the actual measured data of the reflectance of each color and each color ink layer. It can be done in a specific manner.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing the layer structure of ink on the recording material, Figure 6 is a diagram showing combinations of C, M, and Y, and Figure 4 is a diagram showing the area ratio of each color in the combination shown in Figure 6. Figure 5 is a diagram showing reflectance, Figure 6 is a diagram showing reflected color light energy for ink combinations, Figure 7 is a diagram showing the formula shown in Figure 6 in combination with input energy, Figure 8 shows the method of the present invention, where Y is yellow, M is magenta, C is cyan,
R is reflectance, P is recording material, 801 is TV camera, 8
03 is a processing unit, 807 is a memory 0 (a) (0)
O\) (=)ke,)(hen 4th eye 5th layer

Claims (1)

[Claims] In a color recording method that reproduces colors by overlapping recording of multiple colors of ink, when determining the recording area ratio of multiple colors for three different signals from the input device, it is necessary to consider the light energy range of the input system and output system. A color recording method characterized by correction.