JPS5881381A - Color image plotter device - Google Patents

Abstract

PURPOSE:To prevent the generation of moire by irregularly varying the plotting timing and time of individual picture elements with time, and shifting respective color picture elements in plotting position relatively at random. CONSTITUTION:A color picture to be plotted is stored in a picture memory 108 in the form of pictures, obtained by sampling every picture element, by colors, i.g. cyan, magenta, and yellow, and under the control of a control part 109, they are read out of the picture memory 108 successively synchronizing with a scan on a drum 100 and inputted to an arithmetic part 107. The arithmetic part 107 supplies density level signals shown by pieces of picture element information read out of the picture memory 108 to a driver 106 in the order of cyan, magenta, and yellow, and also supplies a plotting timing signal to the driver 106 at specified intervals. With this plotting timing signal, a recording light beam corresponding to each color is shifted in relative position.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color image plotter device that plots a color image using dots of a plurality of colors, and particularly relates to an improvement to prevent moiré from occurring on the plotted color image.

To create a color image, you typically use cyan, magenta,
Dot images of each color of yellow are plotted on the same sheet of paper, overlapping one another. It is known that in a color image plotted in this manner, moiré occurs when the pitches of the dots in the dot images for each color are equal, and the image quality is significantly degraded.

In order to prevent the occurrence of such moiré, a color image plotter using a contact mesh screen employs a method in which the mesh screen is rotated little by little when plotting dot images for each color.

However, the rotation of such a mesh screen generally requires tedious manual work, and there is also the problem that moiré cannot be prevented if the rotation angle is inappropriate.

Furthermore, this method is not applicable to devices that do not use contact mesh screens, such as electronic color image plotter devices.

Therefore, it is an object of the present invention to
To provide a color image plotter device which prevents the occurrence of moiré without depending on the rotation of a mesh screen.

According to the present invention, in a color image printer device that plots the pixels of a color image to be plotted as dots of corresponding colors for each color and creates the above-mentioned color image as a set of dots of a plurality of colors, it is possible to plot individual pixels. Means are provided for varying the timing irregularly over time. By the action of this means, the plot positions of the pixels of each color are changed relatively randomly, thereby preventing the occurrence of moiré.

In a preferred embodiment of the present invention, in addition to the above-mentioned means, means for correcting the density of the pixel according to the amount of variation in plotting and timing of the pixel by the means is provided to prevent moiré. Further improvement in image quality is achieved by compensating for variations in pixel position.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of an electronic color image plotter device embodying the present invention.

In the apparatus of this example, a drum 100 covered with a photoconductor is charged in advance and rotated by a motor 101.
The surface of 0 is scanned with a recording light beam, and dot images of different colors are plotted in the form of electrostatic latent images.

Then, this latent image is printed on paper using a known PPC process. Usually, dot images of cyan, magenta, and yellow colors are sequentially recorded on the drum 100, and the images are overlapped and printed on the same sheet of paper to obtain the desired color image. The main scanning of the recording light beam is performed by the rotating prism 103.
The scanning is performed in the axial direction of the drum 100 by the f-θ lens system 102, and the sub-scanning is performed in the drum circumferential direction by the rotation of the drum 100 itself.

Note that the mechanism for converting the latent image of the dot image on the drum 100 into a hard copy using the PPC process may be a known mechanism and is therefore omitted from the drawing.

The recording light beam is emitted from a light source 104;
is driven by the driver 106 as follows.

The color images to be plotted are stored in the image memory 114 as images sampled pixel by pixel for cyan, magenta, and yellow. Under the control of the control unit 109,
In synchronization with the scanning on the drum 100, pixel information indicating the density level of each cyan pixel is sequentially read out from the image memory 108 and input to the calculation section 107. This calculation section 1
The driver 106 drives the light source 104 in accordance with the output of 06, thereby recording a latent image of a cyan dot image on the drum 100, and printing it as a cyan dot image on the paper by a mechanism (not shown).

Next, the pixel information of the magenta image is stored in the image memory 108.
The latent image is read out and recorded on the drum 100 in the same way as a latent image at °C. The latent image of this magenta dot image is
This is superimposed on the yellow dot image and printed on the same sheet of paper as a magenta dot image. Finally, a yellow dot image is printed on the same sheet of paper through a similar process.

In this way, the desired color image is obtained.

Up to this point, the calculation unit 107. Although no explanation has been given regarding °C, this arithmetic unit 107 is the characteristic part of the apparatus according to the present invention. That is, it is a part that controls the plotting position of pixels and corrects pixel density.

The operation of this calculation section 107 will be explained with reference to FIG.

FIG. 3 shows an example of plotting dots, with circles indicating cyan dots and triangles indicating magenta dots.

Further, the size of the circle mark and the triangular mark indicate the size of the dot, which visually corresponds to the density of the pixel.

When plotting a cyan dot image, the calculation unit 107 outputs a density signal of a level corresponding to the density level indicated by the pixel information input from the image memory 108 to the driver 1.
06, and a plot timing signal with a constant cycle is supplied to the driver 106.

Therefore, for a cyan dot image, dots (pixels) are plotted at equal intervals with a basic pitch PC that matches the period of the plot timing signal.

The plotting position of this dot is called the normal position of the pixel. Furthermore, since the driver 106 drives the light source 104 so as to emit a recording light beam with an intensity corresponding to the level of the input density signal, the size of the dot corresponds to the density level itself of the corresponding pixel on the image memory 108. are doing.

On the other hand, when printing a magenta dot image, the calculation unit 1
07, the period of the plot timing signal is randomly varied over time, and the plot position of the dot is moved from the normal position as shown in FIG. The dot pitch Pm at this time is expressed by the following equation.

Pm-Po±δPm・,, Equation (1) Here, 22m is an amount that changes randomly over time,
The condition of 22m<Pc/2 is satisfied.

Now, the pixel information stored in the pixel memory 108 indicates the density level when the pixel is plotted at a normal position. If a pixel is plotted at a position shifted from the normal position as described above while maintaining this density level, the visual pixel density will change, which may lead to a change or deterioration of the image quality. Therefore, when plotting a magenta dot image,
A calculation unit 107 corrects the pixel density according to the deviation of the plot position from the normal position.

This correction is performed, for example, using the following equation. However, the basic pitch Pc=1.

”m= (f(XLSo+f(1-X)81)/(
f(X)+f(i-x))...Equation (2) Here, X is the amount of deviation of the plot position of the dot of interest from the normal position (see Figure 3), and 5O1S1 is These are the density levels of two pixels corresponding to normal positions before and after the plotting position of the dot of interest (density levels represented by pixel information read out from the image memory 108). Sm is the pixel density level after correction, that is, the driver 1 corresponding to the noted dot.
This is the level of the density signal given to 06.

Furthermore, various functions can be considered as f (x), but in this embodiment, the following function is used.

f(x)=upper side ■11 units...Equation (3) The above plot timing control and pixel density correction are as follows:
The same procedure is used when plotting a yellow dot image.

FIG. 2 shows an example of the arithmetic unit 107 as described above and will be described.

A clock pulse synchronized with the scanning of the drum 100 (FIG. 1) is supplied to the timing generation circuit 200 from the control section 109 (FIG. 1). The timing generation circuit 200 has a built-in counter of modulo 10, and counts up based on the input clock pulse.

201 is a random number generator, which operates only while the inhibition signal from the control unit 109 is 0''.The random number generated by the random number generator 201 is converted by the counter 202 into random numbers with equal probabilities of +1 and -1, and the timing is determined. The built-in counter of the timing generation circuit 200 counts up by 1 when +1 is input from the counter 202, and counts down by 1 when -1 is input.The carry output of the built-in counter is It is sent to driver 106 as a plot timing signal.

When plotting a cyan dot image, the inhibition signal from the control unit 109 is set to '1', and the random number generator 2
01 stops. Therefore, the plot timing signal (b) with a period (referred to as the basic period) that is 10 times the clock pulse (a) shown in FIG.
It is generated by Each pulse of this plot timing signal) corresponds to the normal position of the dot, and its fundamental period corresponds to the fundamental pinch Pc of the dot.

When plotting magenta and yellow dot images, the inhibition signal is reset to "O" and the random number generator 201 operates. Therefore, the timing generation circuit 200 outputs a signal obtained by randomizing the above plot timing signal (b). FIG. 4(C) is an example of a plot timing signal generated when plotting a magenta dot image, and FIG. 4(d) is an example of a plot timing signal generated when plotting a yellow dot image.

The timing generation circuit 200 also outputs the amount of deviation from the basic period of the generated plot timing signal (an amount corresponding to the above-mentioned X). This shift amount (X) is input to the arithmetic unit 203 together with the pixel information read out from the image memory 108. Using these inputs, the °C1 calculator 203 executes the above-mentioned equations (2) and (31) and sends the concentration signal to the driver 106.
It is configured using OM (Read Only Memory).

In FIG. 1, 105 is a sensor for detecting the recording start position of the drum 100.

The embodiment described above has a configuration in which dot images of three colors are sequentially plotted using a common mechanism. The entire mechanism shown in FIG. 1 or only the drum 100 and printing mechanism may be provided in three systems, and dot images of corresponding colors may be plotted in each system in synchronization with the movement of the paper.

As described above, the present invention changes the plot position of each color pixel relatively irregularly, so it is possible to prevent the occurrence of moiré, and the density is corrected according to the change in the plot position. Color images with extremely good image quality can be created.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of the calculation section in FIG. 1, FIG. 3 is a diagram showing an example of plotting dots, and FIG. FIG. 3 is a diagram illustrating clock pulses and plot timing signals generated when plotting each color. 100...Drum, 101...Motor, 102...
...f-theta lens system, 103...rotating prism, 10
4... Light source, 106... Driver, 107... Arithmetic unit, 108... Image memory, 109... Control unit,
200... Timing generation circuit, 201... Random number generator, 202... Counter, 203... Arithmetic unit. Agent Patent Attorney Makoto Suzuki

Claims (1)

[Claims] 1. A color image blocker device that plots pixels of a color image to be plotted as dots of corresponding colors for each color, and creates the above color image as a set of dots of a plurality of colors. By providing a means to vary the plot timing of pixels irregularly over time,
A color image plotter device characterized by relatively irregularly changing plot positions of pixels of each color. 2. The color image plotter apparatus according to claim 1, further comprising means for correcting the density of the pixel in accordance with the amount of variation in the plotting timing of the pixel by the means.