JPH03214864A - Color picture processor - Google Patents

Abstract

PURPOSE:To prevent color irregularity and the change of color quality for each printing by modulating the pulse width of an input color picture signal based on a pulse pattern. CONSTITUTION:A multilevel digital color picture signal is converted to an analog signal, and a pulse pattern generator 2 prepares a reference signal 11 by a clock frequency-divided from a high-speed clock. A PWM signal 12 is obtained by comparing 3 the signals 10 and 11, and is stored in a shift register 5. One kind out of the 8 kinds of delay patterns in the register 5 is selected by a selector 6. At this time, a delay pattern information is written in for each color at a pattern generator 7 by a CPU 9. And when the final output of the whole line of each color is ended, it changes to the next color, it is operated by a different pattern corresponding to the color in the generator 7, and the four colors of Y, M, C, B, are superimposed at the final printing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color image processing device, for example, to a device that performs pulse width modulation on a color input image flaw to form a color 8-power image. be.

[Prior art] Conventionally, in this type of device,
As described in No. 66, etc., a method is used to remove color moiré by performing pulse width modulation by comparing a reference signal and an image signal of different phases for each color.

Problems to be Solved by the Invention However, when an image is formed by scanning a laser beam onto a photosensitive drum using the rotation of a polygon mirror, as in a color laser printer, in reality, there are problems such as uneven rotation of the polygon mirror. , misregistration of each color occurs. For this reason, even if the phase is shifted for each color, there may be areas where the colors overlap on a single screen, resulting in color unevenness, or the color tone may change each time it is printed. The disadvantage was that problems such as

Also, JP-A-62-183670, JP-A-62-18
No. 3676. Japanese Patent No. 183,680/1983 discloses a method of removing moiré by varying the amount of delay of the reference signal for each line. However, when trying to obtain an output image with the same pattern for each color in a color image, uneven rotation of the motor that occurs in color laser printers and misalignment of the register 1 for each color will result in color unevenness and printing. The problem was that each time the color was changed, the color changed.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and an object thereof is to provide a color image processing device that can prevent color unevenness and color changes from print to print.

[Means for Solving the Problems] In order to solve the above-mentioned problems and achieve the objectives, a color image processing device according to the present invention includes an input means for inputting a color image signal, and a reference. generating means for generating a pulse pattern, modulating means for pulse width modulating the input color image signal based on the generated pulse pattern, and delaying the pulse width modulated color image signal and generating a plurality of pulse patterns. forming means for forming a delay pattern; and determining means for determining one pattern from the plurality of types of spread patterns formed based on the number of lines and color of the manually inputted color image signal;
The apparatus is characterized by comprising an output means for outputting the determined delay pattern as a final output.

[Operation] According to this configuration, the input means inputs a color image signal, the generation means generates a reference pulse pattern, and the modulation means converts the input color image signal into pulses based on the generated pulse pattern. The forming means delays the pulse width modulated color image signal to form a plurality of delay patterns, and the determining means delays the pulse width modulated color image signal to form a plurality of delay patterns based on the number of lines and colors of the input color image signal. One pattern is determined from the seed delay patterns, and the output means outputs the determined delay pattern as the final a-force. [Embodiments] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that this embodiment, which will be explained below,
Let us take as an example a color image processing device adapted to a laser beam printer.

First, an example of pulse modulation in this embodiment will be explained.

FIGS. 2A to 2D are diagrams showing output patterns of pulse width modulation (PWM) for each color according to an embodiment of the present invention.

The unit of this PWM is two pixels (2P), and in the case of M (magenta) (Figure 2A), % pixels (P/2) per line, and in the case of Y (yellow) (Figure 2A). 2
B), 1/4 pixel (P/4) per line, C(
In the case of (cyan) (Figure 2C), 7/4 pixels (7P/4) for each line, and in the case of Bk (black) (2nd
(D figure), the phase is delayed by 4/4 pixels (4P/4) for each line.

By doing this, Y. M. When the four colors of C and Bk are overlapped, the dots overlap in a random manner depending on the position.

Next, the configuration of this embodiment will be explained.

FIG. 1 is a block diagram showing the configuration of an embodiment of a color image processing apparatus of the present invention. In the figure, l indicates a D/A converter that converts a digital color image signal from a digital signal to an analog signal, and 2 indicates a pulse pattern generator that generates a pulse pattern for pulse modulating the analog color image signal. , 3 indicates a converter which performs pulse width modulation by comparing the analog color image signal output from the D/A converter 1 and the pulse pattern output from the pulse pattern generator 2.

4 indicates an amplifier that amplifies the PWM signal output from the converter 3, 5 indicates a shift register that delays the amplified PWM signal, and 6 indicates a pattern generator 7, which will be described later.
A selector for selecting a delay pattern formed in the shift register 5 based on a pattern output from the shift register 5 is shown. Here, in this embodiment, as shown in FIG.
Since the unit of WM is two pixels, and the delay of 1/4 pixel is the unit of delay amount, eight types of PWM patterns are formed by the delay of the shift register 5. Therefore, the selector 6 is a circuit that selects one type of delay pattern from eight types of delay patterns formed in the shift register 5 and outputs it as the final output to a printer mechanism (not shown). That is,
As shown in FIG. 2, the selector 6 delays each line by 172 pixels for M (magenta), delays 1/4 pixel for each line for Y (yellow), and delays C(
cyan), delay 374 pixels for each line, and
If it is k (black), it works by delaying each line by 474 pixels. 8 indicates a counter for counting horizontal synchronization signals. The counter 8 is a circuit that repeatedly counts up to eight horizontal synchronizing signals so that when eight horizontal synchronizing signals are counted, counting starts again from the first one. Reference numeral 7 denotes a pattern generator, which is a RAM, stores patterns for each color, and outputs a pattern according to the count from the counter 8 to the selector 6. The final output from the selector 6 is controlled.

Reference numeral 9 denotes a CPU, which outputs patterns for each color to the pattern generator 7 and controls the final output output from the selector 6.

Next, the operation of the color image processing apparatus described above will be explained.

FIG. 3 is a timing chart illustrating timing for explaining an example of the final output of this embodiment, and FIG. 4 is a diagram illustrating a method of forming a PWM signal of this embodiment.

First, a multivalued digital color image signal (one of Y, M, C.Bk) is sent from an image reading device (not shown).
is converted into an analog signal 10 by a D/A converter l. On the other hand, in order to generate a reference signal (triangular wave), the pulse pattern generator 2 generates a reference signal (triangular wave) 11 using a clock frequency-divided from a high-speed clock. or,
By comparing the analog color image signal 10 and the reference signal 11 by the comparator 3, a PWM (pulse width modulation) signal 12 is formed.

Here, when the comparator 3 inputs the reference signal 11 from the pulse pattern generator 2 and the analog color image signal 10 from the D/A converter 1 and compares both signals, that is, as shown in FIG. As shown in FIG.
is output to the shift register 5 via the amplifier 4.

When the PWM signal 12 is input to the shift register 5, it is delayed by the shift register 5. shift register 5
The selector 6 selects one of the eight delay patterns. Here, the eight types of delay patterns are:
This is a pattern based on a PWM signal delayed from 074 to 7/4 pixels.

Further, delay pattern information for causing the selector 6 to select each line is written in advance by the CPU 9 to the pattern generator 7 for each color. Counter 8 is
The count value is advanced while counting the horizontal synchronizing signal, while the selector 6 selects a delay pattern from the shift register 5 in accordance with the pattern written in the pattern generator 7. FIG. 3 shows the timing when outputting the Y (yellow) pattern (final output) shown in FIG. 2. For Y (yellow), each line is delayed by 174 pixels, so as shown in Figure 3, the first line has a delay of 0, the second line has a delay of 1/4, and the third line has a delay of 1/4. The final output is made with a delay of 2/4°, etc.Similarly, although not shown, the M
(magenta), the first line has a delay of ゛O“ 2
Delay “2/4” on the 3rd line Delay “4” on the 3rd line
/4°, etc., and in the case of C (cyan), the first line has a delay of “O”, the second line has a delay of “7/4”, and the third line has a delay of “6/4”.
In addition, in the case of Bk (black), the lth line has a delay of 0, the 2nd line has a delay of 4/4°, and the 3rd line has a delay of 0/4.
”, etc., to produce the final output.

In this way, when the final output of all lines for each color is completed, the next color is moved on, and the above operation is performed using another pattern according to the color stored in the pattern generator 7, and the final output is completed. In printing, four colors, Y, M, C, and Bk, are superimposed.

As explained above, according to this embodiment, the rotation unevenness of the polygon mirror motor that occurs in color laser printers, the misregistration of the registers for each color, and the speed unevenness of the paper conveyance system can be resolved for each color. By changing the pattern,
It is possible to suppress the occurrence of color unevenness and changes in color tone that occur each time a print is made, and the image quality can always be stabilized.

Now, in the above-described embodiment, four patterns are generated using the pattern generator 7, but a random number generation circuit may be used to set the same random delay pattern for all four colors.

Furthermore, in the embodiment described above, as shown in FIG.
Each output pattern of Y, M, C, Bk is Y: 1/4 pixel, M: 2/4 pixel, C: 7/4 pixel, E
k: 4/4 pixel delay, but the present invention is not limited to this, and various modifications can be made without departing from the spirit of the present invention. In this case, for example,
The combination of Y, M, C, Bk and delay is Y: 2/4 pixel, M: 1/4 pixel, C: 4/4 pixel. Bk
: It may be a delay of 7/4 pixels. Furthermore, any combination of four of the eight delay values from 074 to 7/4 pixels may be used. Further, in the above embodiment, two pixels are treated as one unit, but it goes without saying that the present invention is not limited to this, and one unit may be other than two pixels.

FIGS. 5A to 5D are diagrams showing output patterns of PWM signals for each color, which are modified examples of this embodiment. Figure 5A~
As shown in FIG. 5D, when one unit is one pixel, there are four combinations of delays of 074 to 374 pixels (O/4 to 3/4P). Also, the delay method is every 8 lines in Figures 2A to 2D;
In Figures A to 5D, the period is every 4 lines. This is because the amount of delay is in units of 1/4 pixel. however,
Since the delay can be modified in various ways depending on how the clock is divided, the unit of delay can be set to 1/2" pixel by dividing the clock by 2n (n is a constant).

Further, in the above-mentioned embodiment, the pattern generator 7 based on RAM was used, but the present invention is not limited to this. It is also possible to write a pattern of (Y, M, C, Bk) and change the address for each color using the counter 8.

Furthermore, although the above-described embodiments have been explained using a laser beam printer as an example, the present invention is not limited to this; it is also applicable to facsimile machines etc. that have an output mechanism that employs a laser beam method. Needless to say, it is.

[Effects of the Invention] As described above, according to the present invention, it is possible to suppress the occurrence of color unevenness and changes in color tone that occur each time printing is performed, and it is also possible to always stabilize image quality.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a color image processing device according to the present invention, and FIGS.
A diagram showing the output pattern of WM, FIG. 3 is a timing chart showing the timing for explaining an example of the final output of this embodiment, FIG. 4 is a diagram explaining the method of forming the PWM signal of this embodiment, and FIG. 5A. 5D is a diagram showing an output pattern of PWM signals for each color, which is a modification of this embodiment. In the figure, 1... D/A converter, 2... Pulse pattern generator, 3... Converter, 4... Amplifier,
5...Shift register, 6...Selector, 7...
Pattern generator, 8...counter, 9...CPU.

Claims (2)

[Claims] (1) In a color image processing device, an input means for inputting a color image signal, a generation means for generating a reference pulse pattern, and a pulse width of the input color image signal based on the generated pulse pattern. a modulating means for modulating; a forming means for delaying the pulse width modulated color image signal to form a plurality of types of delay patterns; and a forming means for delaying the pulse width modulated color image signal to form a plurality of types of delay patterns; 1. A color image processing apparatus, comprising: determining means for determining one pattern from a plurality of types of delay patterns; and output means for outputting the determined delay pattern as a final output. (2) The determining means includes a storage means for storing delay pattern information for selecting a delay pattern corresponding to each color and each line, and a storage means for storing delay pattern information for selecting a delay pattern corresponding to each color and each line, and a plurality of types of 2. The color image processing apparatus according to claim 1, further comprising selecting means for selecting one pattern from among the delay patterns.