JPS59163954A - Method for forming color picture - Google Patents

Abstract

PURPOSE:To attain the formation of a picture excellent in quality sence even on a high density part by detecting a black density component from an input picture data and generating the high and low density balck levels in a prescribed rate even when the black density component is prescribed value or over. CONSTITUTION:A composite video signal including each color signal of R, G, B and a synchronizing signal is led to an AD converting circuit 2 via an interface 1, a gradation signal of the picture signals R, G, B is converted into a digital signal at the circuit 2, and the number of lines is stored in a line memory 3. A data in the memory 3 is processed for processings such as color conversion, gamma conversion, masking processing and background color elmination or the like at each picture element at a picture processing circuit 4, converted into cyan, magenta, yellow and black signals, and further converted into an application voltage to each head and inputted to a head driver 6. In this case, the circuit 4 detects the black density component and when the detected value is larger than a prescribed value, the high and low density levels of a black colored member are generated at a prescribed rate, allowing to form a picture having good quality sense even with a high density component.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a color image forming method for forming a color image having halftones using coloring materials. In particular, it concerns how to reproduce high-density areas.

<Description of the Prior Art> Generally, the amount of coloring materials such as ink and toner used increases in high-density areas of an image, so the original gradation information is lost due to ink flow and smearing, resulting in deterioration of image quality. Put it away.

In particular, in the case of a color image, even if the undercolor is removed, a large amount of ink still adheres to the high-density areas, so the image quality is not degraded.

When a half-tone image of a Japanese person's face is created, most of the hair is expressed as a high-density area, so the texture of the hair is lost, resulting in a problem of deterioration of the overall quality of the image.

<Objective of the Invention> In view of the above points, the present invention aims to provide a color image forming method capable of forming an image having good texture even in high density areas.

<Description of Embodiments> FIG. 1 shows a block diagram of signal processing when the present invention is applied to an inkjet color printer.

A video signal of an image, for example, a composite video signal containing R, G, and B color signals and a synchronization signal, is input to the video signal interface 1. Here, the signal is synchronized and sampled and held by a sample and hold circuit. This signal is led to the next stage AD conversion circuit 2, and the gradation signals of the image signals R, G, and B are converted into digital signals. This digital signal is stored in the next line memory 6 for an appropriate number of lines. Here, fins are generally taken in the vertical direction, but it is clear that the fins can also be taken in the horizontal direction. Next, the data in this line memory is processed by an image processing circuit for each pixel, such as color conversion, γ conversion, masking processing, undercolor removal, etc.
The signals are converted into magenta, yellow, and black signals, and further converted into voltage values applied to each head, which are input to the head driver 6. Each inkjet head 9 ejects an amount of ink corresponding to the magnitude of the applied voltage to express hue and density.

Ten thousand seven'! The system controller 5, which controls the sequence of printers, generates a head drive signal, a carriage motor drive signal, and a paper feed signal at a timing corresponding to the input image signal, and drives the head driver 6, carriage motor driver 7, and paper feed motor, respectively. The inkjet head 9. is supplied to the driver 8, and the inkjet head 9. Carriage motor and its mechanism iQ, paper feed motor and its mechanism 11
is controlled, and the reproduced image of the input video signal is printed on the recording medium.

FIG. 2 is a detailed block diagram of the image processing circuit 4 of FIG. 1.

The R, C, and B signals are converted into cyan by the CMY converter 21.

It is converted into magenta and yellow density signals G + M r Y. Next, after being converted into γ5 by the γ converting unit 22, the black density BK is determined by the smudge generating unit 26.

The black density BK is, for example, BK=amin(CIM+Y)
It can be determined as +β. For example, α and β are α=1. β20, and min (C, M, Y) indicates the lowest concentration among the C, M, and Y concentrations. Then, if BK is larger than a certain threshold value, black is also used, and if BK is smaller, black is not used and only six colors are used.

When using CM black, subtract the black component from each value of Kai Machikari,
One each of cyan, magenta, and yellow. After this,
The masking section 25 performs color correction, and the voltage conversion section 26 uses analog electric current JE values Vc and VM to drive each head.
, Vy, K-converted to y8 and transferred to the head driver 6.

Next, the operation of the noise superimposing section 24 will be explained. Here, the black density BK determined by the smudge generating section 26 and the predetermined threshold L1 are
Compare L1 (If BK, add dither noise to BK and output the new BK value as 1-.Ll>B
If it is K, the value of BK is output as is.

The BK, C, M, and Y thus obtained are input to the masking section 25, subjected to color correction, and output to the head drive circuit.

FIG. 6 is a block diagram showing a method of noise superimposition.

The input to B' is compared with a threshold L1 by a comparator 61. BK)Ll, the switch 66 is turned to the left, and the adder 62 superimposes dither noise on BK. BK≦L1
At 0 o'clock, 0 is added to the right side of the switch 33 line, so the input BK is output as is.

The dither noise generating section 64 generates corresponding dither pattern components with reference to the main scanning direction X and the sub-scanning direction Y.

For example, using 2X2'7) IJ socks as shown in Figure 4.
・When using, select cells in the matrix (modz
The power of the 0 dither in which the component corresponding to moa2Y) is output as dither noise, that is, the difference Dp between the maximum value and the minimum value in the dither matrix components, is determined in consideration of the threshold value L1. Dpi reflection density threshold level L1 of 1150~
1/2 is desirable.

FIG. 5 is a diagram showing the appearance characteristics of the black component according to this embodiment. When the input level of the black component is low, the output density changes linearly. In other words, the diameter of the black ink dots also changes linearly to express light gradation. However, when the input level of the black component exceeds the predetermined level L1, high and low output density areas appear alternately. That is, the diameter of the black ink dots becomes larger or smaller. Therefore, the output image will not be solid black.

In this case, the minimum reflection density expressed by black ink 'c Ls = 0.5, L 1 = 1.0, Dp
=0.20. Note that it is desirable that the value of Ll be 50% or more of the maximum density that can be reproduced with black ink.

This embodiment can be realized by software using a microcomputer, and the results of C, M, Y, and BK for each set of R and JB can be realized in advance by dividing RlG and B into steps of, for example, 5 bits. It can also be implemented in hardware by storing it in the form of a table in ROM. In addition to using a dither pattern as noise as in this embodiment, a random number generator may also be used.

Further, in this embodiment, an inkjet printer is used as the glintter, but any glintter that can change the output density may be used as an electrophotographic printer.

Any number of glitters can be used, such as a thermal transfer printer.

Explanation of the effect> In this way, by adding dither noise etc. to the BK above a certain threshold value of 51, areas with a lot of coloring material such as ink and places with a little coloring material in the high density area are randomly or at a predetermined ratio. By creating a gradation image, it is possible to make it appear to the human eye that gradation is expressed even in high-density areas, making it possible to give the image an impression of extremely high quality. .

Although this method is not a faithful reproduction in the strict sense, it does provide an image quality that gives a good impression to the human eye.

In particular, in the expression of black hair, the moderate amount of noise in the black part gives the impression that the information about the hair is being reproduced, and ii!
II quality can be improved.

[Brief explanation of drawings]

Fig. 1 is a control block diagram of an inkjet printer to which "nonexplosion" can be applied, Fig. 2 is a detailed circuit diagram of the signal processing circuit 4 of Fig. 1, and Fig. 6 is a detailed circuit diagram of the noise superimposition section of Fig. 2. FIG. 4 is a diagram showing an example of a dither pattern, and FIG. 5 is an input/output characteristic diagram of a black component according to this embodiment. In the figure, 1 is a video signal interface, 2 is an A
D converter, 4 is an image processing circuit, 9 is an inkjet head, 23 is a smudge generating section 2.27! I is a noise superimposition unit, 61
64 represents a comparator, and 64 represents a dither noise generator. 28

Claims (1)

[Claims] In a color image forming method that forms a color image using four types of coloring materials: cyan, magenta, yellow, and black, a black density component is detected from input image data, and when the black density component is larger than a predetermined value, A predetermined ratio of areas with high and low density levels expressed by black coloring material,
Or a color image forming method in which the color image is generated randomly.