JPH066588A - Color printer - Google Patents

Abstract

PURPOSE:To obtain the color printer whose saturation is not decreased due to overlapping between color ink and black ink and in which no color fluctuation takes place even when a screen angle is changed. CONSTITUTION:A black ink quantity decision means 2 decides a K signal based on Y, M, C signals inputted from a color data quantity input means 1. A color data quantity decision means 4 receives the Y, M, C signals and the K signal to decide Y', M', C' data by an under color elimination processing. A back ink quantity correction means 5 receives the Y', M', C' signals and the K signal to correct a black ink quantity according to equation of K'=K/(alpha.p+1), where p is a screen overlap probability and a is a blur ratio. A screen generating means 6 generates a screen for each color and a print means 7 implements 4-color print.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus mainly using full color data as an input source, and in particular, three colors of cyan, magenta and yellow and black ink are printed in halftone dots to form an image. The present invention relates to a data correction method and device.

[0002]

2. Description of the Related Art Full-color printing uses yellow, cyan,
It is performed by mixing the three primary colors of magenta and the four colors of black. Originally, it is possible to reproduce all colors with only cyan, magenta, and yellow inks, but black ink is used to improve the black density, which is insufficient with a mixture of three color inks, and to save color inks. It is done with the added four colors. The operation of separating the gray component from this color component and replacing it with black ink is the undercolor removal (UCR = Under Color
Removal). Japanese Unexamined Patent Publication No. 61-13259 is disclosed as an apparatus using this processing. FIG. 8 shows a conceptual diagram of the processing of this conventional example. JP 61-132
According to No. 59, the density signals of three colors are represented by Y for yellow, M for magenta, and C for cyan, and K = MIN (Y, M, C) (MIN (a, b, c) is a, b , A function for selecting the minimum value of c) K ″ = gamma conversion for UCR (K) Y ′ = Y−K ″ M ′ = M−K ″, C ′ = C−K ″ K ′ = gamma conversion (K) It is stated that ideal color reproduction can be performed by printing with Y ', M', C ', and K'determined as described above.

[0003]

However, the following problems occur when printing is performed in the ink jet printer with the ink amount thus determined.

An ink jet printer ejects ink droplets onto an image receiving paper to form an image, and other ink droplets are printed on other ink droplets in advance than when an ink droplet is directly printed on the image receiving paper. At that time, even if printing is performed with the same amount of ink, bleeding easily occurs. As a method of indicating the difference in the bleeding method, it is possible to use the ratio of the printing dot areas. Let S1 be the dot area of the ink droplet directly printed on the image receiving paper, and let S2> S1 ... S2 if the dot area of the ink droplet when another ink droplet is printed on top of the other ink droplet is range S2. And the ratio of S1 is α + 1. (Α is a bleeding ratio) S2 = (1 + α) S1 α = S2 / S1-1 ... As the coverage area of the ink of one dot is increased from S1 to S2, the density is felt by the eyes. When the black ink is printed after printing the color ink for the reason as described above, the density of the image formed by the black ink overlaps with the color ink, and the density increases, resulting in a decrease in the saturation. There was a problem that it would end up. With respect to the decrease in the saturation due to such a cause, the gamma conversion process and the UCR process for uniformly converting the black density have different effects depending on the input image and cannot be a fundamental solution. Further, since the overlapping of the color ink dots and the black ink dots changes depending on the states of the halftone screen formed by the color inks and the halftone screen formed by the black inks, the color also changes when the screen angle is changed.

The present invention solves such problems.
It is an object of the present invention to provide a color printer in which saturation does not decrease due to overlapping of color ink and black ink, and color variation does not occur even if the screen angle is changed.

[0006]

A color printer according to the present invention comprises printing means for recording an image with three colors of yellow, magenta and cyan and black ink, color data input means for Y, M and C, and A black amount determining means for determining the amount of K data from the Y, M, C signals, and a screen for inputting information on the state of the halftone dots formed by Y, M, C, K (at least the angle and number of halftone dots). Information input means, color data amount determination means for inputting the Y, M, C signals and the K signal, performing undercolor removal processing, and determining output color data, and inputting the K signal and the screen information. Then, using the overlapping probability p between the screens formed by K and the ink other than K and the bleeding ratio α, a black ink amount correction unit that reduces the black ink amount according to the following equation K ′ = K / (α · p + 1), The black amount correction means and the color data amount determination means For each color each pixel output, comprising a screen forming means for forming a different screen for each color, characterized by printing the data from the screen forming unit.

[0007]

FIG. 1 is a functional block diagram of an embodiment of the present invention, in which reference numeral 1 is color data input means, 2 is black amount determination means,
3 is a screen information input means, 4 is a color data amount determining means, 5 is a black amount correcting means, 6 is a screen forming means, and 7 is a printing means. The printing unit is composed of an inkjet printing mechanism. The recording density is 300 dpi in both the main scanning direction and the sub scanning direction, the number of dots is 2400 in the main scanning direction and 3300 in the sub scanning direction, and the recording screen size is about 200.
mm × 275 mm.

FIG. 2 shows a system schematic diagram of an embodiment of the present invention. Reference numeral 101 is a data input unit, 1011 is an 8-bit data bus, 1012 is a screen data bus, 101
3 is a control signal line, 1014 is a CPU bus, 102 is a central control unit (CPU), 103 is an address control unit, 10
Reference numeral 4 is an image memory unit for four screens, 105 is a black amount determination unit, 1
Reference numeral 06 is a YMC data creation unit, 107 is a halftone dot data conversion unit, 108 is a serial head having a drive circuit, 109
Is a printing mechanism.

Next, how the printer of the present invention forms a screen will be briefly described with reference to FIG. Figure 3
Is a basic dither matrix size, b is a matrix shift amount, and N is a repeating matrix size. In a printer, by properly arranging basic halftone dots made up of a × a pixels, it is possible to form halftone dots having a screen angle. When the displacement vector is u = (a, b), the obtained screen angle θ
Is calculated from θ = tan ⁻¹ (a / b). A square threshold matrix size N corresponding to one cycle of a halftone dot using the values a and b of the displacement vector u is N = LCM (a, b) × (b / a + a / b). However, LCM (a, b) represents the least common multiple of a and b.

If | u | = √ (a ² + b ² ), then
The screen line number (line / inch) is L = minimum recording density / | u | (line / inch). In other words, the screen cannot be configured with any number of lines and angles, and it takes a discrete state depending on the minimum recording density (300 dpi in this embodiment) of the printing mechanism. This is shown in FIG. (The value of b can take a negative value, but it is omitted because the difference from the positive value is only the screen angle becomes negative.) Therefore, the information input as screen information is the screen frequency and screen angle. It is up to the user to specify which screen is specified, but by comparing the input screen information with FIG.
CP the dither pattern that can form the closest screen
The selection is made by the U 102, and the halftone dot data conversion unit 107 is notified. Regarding the screen angle, it is generally said that the moire is smallest when the angle difference between the colors is 30 °. The screen frequency is 100 for printing.
About 150 to 150 lines are used. The same applies to any screen, but in the present embodiment, for the sake of explanation, the dither patterns shown in FIGS. 5A, 5B, 5C, and 5D are used. . These dither patterns correspond as follows.

(A) a = 2, b = 0, N = 2, θ = 0 °, L = 150 (lpi) (b) a = 2, b = 1, N = 5, θ = 26.6 °, L = 134 (lpi) (c) a = 2, b = -1, N = 5, θ = -26.6 °, L = 134 (lpi) (d) a = 2, b = 2, N = 4, θ = 45 °, L = 106 (lpi) FIGS. 6 (a), (b), (c), and (d) show the patterns of (a), (b), (c), and (d) of FIG. The state of output halftone dots is shown in a region of 10 × 10 pixels. Let's look at how the screens formed in this way and the screens overlap. In order to check the overlap of the screens, it suffices to look in a matrix having the least common multiple (NLCM) of the screen repetition periods N as one side. 7 (a), (b),
FIG. 5C shows the overlap between the patterns (a) and (b) shown in FIG. 5 at the minimum density. In this case, NLCM = 10 and pmin = 5/100 = 1/20 when the overlap at the minimum density is the minimum overlap probability pmin. Since the dot overlap increases as the input data increases, the overlap probability p can be calculated by the product of the value obtained by normalizing the smaller input data value by the NLCM value and the minimum overlap probability. This can be expressed by the following formula. Assuming that A and B are input data and the values are from 0 to 255, p = pmin × MIN (A, B) / 255 × NLCM ² (where MIN (A, B) is the smaller of A and B) Function to be selected) How to correct black data in the printer of the present invention will be described. The area ratio ak of black ink is corrected by ak '. Assuming that the bleeding ratio is α, the area ratio of the black ink in the portion overlapping with the color inks is (α + 1) ak ′.
The area ratio of the non-overlapping portion is ak '. If the overlapping probability with the color ink is p, then ak = p (α + 1) ak ′ + (1-p) ak ′ = (α · p + 1) ak ′, and ak ′ = ak / (α · p + 1). . It can be seen that the black density can be corrected by multiplying the value of black data by 1 / (α · p + 1) and reducing the amount of black data. Since ak and ak 'are area ratios, they are rewritten to correspond to the input data.

K ′ = K / (α · p + 1) ... Next, the processing procedure will be described. When the image data consisting of 1 byte per pixel and 1 color is input from the data input unit 101,
Each color of YMC is stored in the memory planes Y, M, C of the image memory unit 104 for each color. After storing the entire screen, the CPU 102 stores the color information Y _{ij at} the same position,
M _ij , C _ij (i and j are positive integers indicating horizontal and vertical positions)
Is read from each plane of the image memory unit 104YMC and is input to the black amount determination unit 105. The black amount determination unit 105 finds the minimum value of the Y _ij , M _ij , and C _ij data, and calculates the black data K.
Determine _ij .

K _ij = MIN (Y _ij , M _ij , C _ij ) ... The determined black data K is stored in K _ij of the K plane of the image memory unit 104. After determining the black ink amount for all pixels, C
The PU 102 receives from the image memory unit 104 Y _ij , M _ij ,
C _ij and K _ij are sequentially called and input to the YMC data creation unit 106 to perform the undercolor removal processing.

Y _ij ′ = Y _ij −K _ij M _ij ′ = M _ij −K _ij C _ij ′ = C _ij −K _{ij The} Y _ij , M _ij , and C _ij data subjected to the _undercolor removal processing are again image memos. The data is written at the same position on each plane of the print portion 104YMC.

After the processing in the YMC data creating section 106 is completed, the CPU 102 sequentially calls Y _ij , M _ij , C _ij , and K _ij from the image memory section 104 to perform black amount correction processing. The CPU 102 determines the overlapping state of the screen formed by the ink having the largest data value among Y _ij , M _ij , and C _ij and the screen formed by the black ink based on the screen information of each color from the screen data bus 1012. The minimum common multiple NLCM of the minimum overlap probability pmin and the screen repetition period N, which are tabulated in advance, are loaded. The overlap probability p is calculated based on an equation. For example, suppose that the ink having the largest data value among Y _ij , M _ij , and C _ij is Y _ij.
If the screen constituted by the ink is the pattern (b) shown in FIG. 5 and the screen constituted by the K ink is the pattern (a) shown in FIG. 5, then p = (1/20) × MIN (Y _ij , K _ij ) / 255 × 102 After that, K _ij ′ is obtained based on the equation.

K _ij ′ = K _ij / (α · p + 1) Further, the bleeding ratio α can be corrected more reliably by having a mechanism for switching the image receiving paper used for printing and ink. After that, the CPU 102 writes K _ij 'into the same position of the K plane of the image memory unit 104YMC again.

After the processing in the black amount correction unit 106 is completed, the data in the image memory 104 is called for each color by the number of dots of the serial head 107 in the sub-operation direction.
It is sent to the halftone dot data conversion unit 106. The halftone data converter 106 stores a threshold matrix of the repetition cycle N corresponding to the designated screen, and the input data is binarized by comparing it with the threshold. The binarized data is sent to the drive circuit of the serial head 107, and the printing mechanism 1
It is printed at 08. As described above, one serial dot line is printed for each color, and the same printing is repeated on the entire screen.

The method referred to in the present embodiment is only the full black method, but the expansion to the skeleton black method should be K = K-threshold if K = MIN (Y, M, C) K> threshold in the equation. For example, it can be easily done by setting K = 0, and there is no essential difference.

[0019]

As described above, according to the present invention, the saturation does not decrease due to the overlapping of the color ink and the black ink,
It is possible to provide a color printer that does not change color even if the screen angle is changed.

[Brief description of drawings]

FIG. 1 is a functional block diagram illustrating processing according to the present invention.

FIG. 2 is a block diagram showing an outline of a system of an embodiment according to the present invention.

FIG. 3 is a diagram for explaining screen formation according to the present invention.

FIG. 4 is a list view of screens formed in the present invention.

5A to 5D are diagrams showing an example of a pattern of output halftone dots in a halftone dot data conversion unit according to the present invention.

6A to 6D are diagrams for explaining output halftone dots in the present invention.

7A to 7C are views for explaining the overlap of the patterns of FIGS. 5A and 5B according to the present invention.

FIG. 8 is a diagram illustrating a conventional example.

[Explanation of symbols]

 1 Color data input means 2 Black amount determination means 3 Screen information input means 4 Color data amount determination means 5 Black amount correction means 6 Screen forming means 7 Printing means 8 Black amount gamma conversion processing 9 UCR gamma conversion processing 101 Data input section 1011 8-bit data bus 1012 screen data bus 1013 control signal line 102 central control unit 103 address control unit 104 image memory unit (Y, M, C, K planes) 105 black amount determination unit 106 YMC data creation unit 107 halftone dot data conversion Part 108 Serial head 109 Printing mechanism

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04N 1/46 9068-5C

Claims (2)

[Claims] 1. A printing means for recording an image with three colors of yellow, magenta, cyan and black ink, a color data input means for yellow, magenta, cyan (hereinafter Y, M, C), and the color data input. Black amount determination means for determining the amount of black (hereinafter K) data from the Y, M, C signals output from the means, and the state of the halftone dots formed by Y, M, C, K (at least the angle of the halftone dots Screen information input means for inputting information on the number of lines (hereinafter referred to as screen information), and inputting the Y, M, C signals and the K signal, performing undercolor removal processing, and determining output color data. Color data amount determining means, the K signal and the screen information are input, and the overlapping probability p between the screens formed by the inks other than K and K
And a coefficient (hereinafter, a bleeding ratio) α indicating the difference between the bleeding on the black ink receiving paper and the bleeding on the color inks, the black amount is calculated according to the following equation K ′ = K / (α · p + 1). And a screen forming unit for forming a different screen for each color for each pixel of each color output from the black amount correction unit and the color data amount determination unit. A color printer characterized by printing with data from a means. 2. The color printer according to claim 1, further comprising a mechanism for switching the bleeding ratio α depending on the image receiving paper and ink used for printing.