JP2675984B2 - Image processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for modulating and outputting image information. 2. Description of the Related Art In a conventional image processing apparatus for processing a color image signal, three colors of yellow (Y), magenta (M), cyan (C) or four colors of black (BK) are added. By using a color material, the image signal is subjected to pulse width modulation to change the area of pseudo halftone dots, and gradation expression is performed to obtain a full-color print. However, when the two-dimensional array period of pseudo halftone dots on the paper slightly shifts between the colors due to various scanning irregularities of the printer, unevenness of the paper feed, expansion and contraction of the paper, and the like, high-frequency moire with coarse pitch occurs. There was a drawback that the color unevenness was conspicuous and the image quality was significantly deteriorated. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional examples, and it is possible to obtain a high-quality color reproduced image with high resolution and good gradation without color unevenness. It is an object of the present invention to provide an image processing device that can be used. In order to achieve the above object, the image processing apparatus of the present invention has the following configuration.
That is, input means for inputting the first color component signal and the second color component signal which form a color image signal and are represented by a plurality of bits for each pixel, and the color image signal input by the input means. A first pattern signal having a period corresponding to a plurality of pixels as a cycle and the first color component signal are compared,
Pulse width modulation signal generation means for generating a pulse width modulation signal by comparing the second color component signal with a second pattern signal having a phase and a cycle different from those of the first pattern signal. And With the above structure, a color image signal is formed,
A color image signal including a first color component signal and a second color component signal represented by a plurality of bits for each pixel is input, and a period corresponding to a plurality of pixels of the input color image signal is one cycle. The first pattern signal and the first color component signal are compared with each other, and the second color component signal is further compared with the second pattern signal whose phase and cycle are different from those of the first pattern signal to obtain a pulse width. Operates to generate a modulated signal. Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. [Description of Configuration of Image Processing Device (FIG. 1) (FIG. 2)]
FIG. 1 is a block diagram of an image processing apparatus according to an embodiment. Reference numeral 1 denotes a digital data output device, which performs color conversion and A / D conversion of image data from a CCD color sensor (not shown) or a video camera, Each pixel data is converted into digital data having density information of a predetermined bit, divided into each color component, and output. This digital data may be stored in a memory, or may be input from an external device through communication or the like. When the color printing section sequentially performs the printing operation for each color, as shown in the figure, one of the color component signals Y, M, C, and BK is selected by the selector 2, and digital-analog conversion is performed. It is input to the device (D / A converter) 3 and converted into an analog quantity. The converted analog pixel signal 15 is sequentially input to one terminal of the comparison circuit 4. On the other hand, the pattern signal generator 5 outputs the triangular wave pattern signal 1 at a cycle of once for every predetermined pixel of the digital data output from the digital data output device 1.
6 is output and input to the other terminal of the comparison circuit 4. Reference numeral 7 is an oscillator for generating a reference clock signal 19. Reference numeral 8 denotes a timing signal generating circuit, which counts down a clock signal 19 from the oscillator 7 in synchronization with a horizontal synchronizing signal 17 from the horizontal synchronizing signal generating circuit 6 to, for example, 1/4 cycle, and then outputs the pixel clock 9 and The screen clock 10 or the like is output. The pixel clock 9 is used as the transfer clock of the digital data and the latch timing of the D / A converter 3. The horizontal synchronizing signal 17 may be generated internally or may be given from the outside. In the present embodiment, since this device is applied to a laser printer, the horizontal synchronizing signal is a well-known beam detect (BD) signal generated for each line. The comparison circuit 4 compares the analog-converted pixel signal 15 and the signal level of the pattern signal 16,
The pulse width modulated binary image data 18 is output. Then, this pulse width modulated binary image data 1
8 is input to, for example, a modulation circuit for modulating the laser beam, and the output signal of the modulation circuit turns the laser on / off according to the pulse width of the image data to form a halftone image on the recording medium. . This is performed for each of the Y, M, C, and BK signals, and the signals are superimposed to obtain a full-color print. FIG. 2 is a diagram for explaining the signal timing of each part of the apparatus shown in FIG. Here, the pixel clock 9 is a signal obtained by counting down the reference clock signal 19 into a quarter cycle by the timing signal generation circuit 8,
It is output in synchronization with the horizontal synchronization signal 17. The pixel clock 9 is used by the D / A converter 3 and the digital data output device 1
And is used as a pixel data transfer clock. The screen clock 10 is a timing generation circuit 8
The pixel clock 9 obtained by the above is further counted down by the timing generation circuit 8 and is obtained here by counting down the pixel clock 9 to a quarter cycle. That is, the screen clock 10 is a synchronization signal for generating the pattern signal 16 (for example, a triangular wave), and the pattern signal generator 5 is passed through the selector 13.
Is normally input by the signal line 20 (without delay). As is apparent from FIG. 2, the analog pixel signal 15 and the pattern signal 16 are compared by the comparator 4, and when the analog pixel signal 15 is larger, it is set to 1 and when it is smaller, it is set to 0 and the binary image is obtained. Data 18 is created and output. As described above, the image processing apparatus according to the present embodiment performs substantially continuous pulse width modulation by converting a digital image signal into an analog image signal once and comparing it with a triangular wave having a predetermined period, thereby improving gradation. A high quality image output is obtained. [Description of Timing Generation Circuit (FIG. 3)
(FIG. 4)] FIG. 3 shows the configuration of the timing generating circuit 8. A method of outputting Y, M, C, and BK color signals on screens having different numbers of lines will be described with reference to FIG. The timing generating circuit 8 is a 1/2 frequency dividing circuit 3
0, 1/3 frequency divider 31, 1/4 frequency divider 32, 1/5
It has a frequency dividing circuit 33 and a selector 34, and the selector 34 keeps the pixel clock 9 as it is or each frequency dividing circuit 30 to 3
The color select signal 12 selects one clock signal from among the clock signals having the periods of 2 pixel clocks, 3 pixel clocks, 4 pixel clocks, and 5 pixel clocks generated by 3 as the screen clock. For example, in the case of the Y signal, a clock signal 38 having a period of 5 pixel clocks, in the case of the M signal, a clock signal 37 of the 4 pixel clocks, and in the case of the C signal, a clock signal 36 of the 3 pixel clocks. , 2 for BK signal
Select the clock signal 35 with a period corresponding to the pixel clock,
Each is used as the screen clock 10. The screen clocks 10 having different numbers of lines (cycles) selected for each color signal in this manner are input to the pattern signal generator 5, and the pattern signal generator 5 outputs the Y signal as shown in FIG. For the triangular wave 38, M of 5 pixel period
A triangular wave 37 having a 4-pixel cycle is output for a signal, a triangular wave 36 having a 3-pixel cycle for a C signal, and a triangular wave 35 having a 2-pixel cycle for a BK signal. This is input to one terminal of the comparison circuit 4 and compared with the analog pixel signal 15 of each color to form a pulse width modulation signal having a different number of lines for each color as shown in FIG. [Explanation of pixel array of two-dimensional halftone dots (Fig. 5) (6th
[Fig.]] Here, the angle of the screen, that is, the direction of the two-dimensional array of pseudo halftone dots, becomes 90 degrees (vertical screen) unless the delay time is switched by the selector 13 for each sub-scanning line, for example, one line. If each pixel is delayed by one pixel clock, it becomes -45 degrees. As described above, it is possible to output each color signal with a different number of lines and a different screen angle. Next, a method of changing the two-dimensional array period of pseudo halftone dots for each of Y, M, C, and BK color signals, that is, a method of forming a pseudo halftone dot array having a different screen angle for each color will be described. For example, consider a case where a screen angle of -45 degrees is formed when the screen clock 10 has a cycle of 4 pixel clocks. First, the counter 11
The horizontal synchronizing signal 17 is counted with. In this case, the counter 11 is a quaternary counter and the first line, the second line, and the third line.
The number of lines of the fourth and fourth lines is counted, and the selector 13 selects the output terminal for outputting the screen clock 10 based on the output of the counter 11. A delay line 14 is connected to the output terminal of the selector 13, and the delay time is determined depending on which delay line 14 the screen clock passes through. The screen clock 21 having the same cycle and different delay time for each line.
Is output. Now, for example, in order to form a screen angle of -45 degrees, from the screen clock of the first line,
Set the screen clock for lines 2, 3 and 4 to 1
Pixel clock, 2 pixel clock, and 3 pixel clock are delayed. In this way, when the screen clocks 21 having different delay times of four lines are input to the pattern signal generator 5 in the 4-line cycle, the pattern signal 16 whose delay time changes in the 4-line cycle as shown in FIG. The signal is output from the signal generator 5 and input to one terminal of the comparison circuit 4. At that time, for example, when an analog pixel signal 15 having a uniform level as shown in FIG. 5 is input to the other terminal of the comparison circuit 4, it is compared with the pattern signal 16 for each line and the binary image is obtained. Data 18 is the first line 5
0, 2nd line 51, 3rd line 52, 4th line 53
And a screen angle of -45 degrees is formed. The pattern of the screen clock 21 at this time is two-dimensionally expressed as shown in FIG. 6 (a). That is, FIG. 6 (a) shows a pattern of a screen angle of -45 degrees when the screen clock 21 has a cycle of once every 4 pixel clocks, and shows that the shaded portion is first blackened. There is. However, in this embodiment, the analog pixel signal 15
Is a continuous pulse width modulation, and is not digitally blackened pixel by pixel. 6 (b), (c), and (d), the screen clock 21 is 4
Screen angle is +45 degrees in each pixel clock cycle,
A pattern of ± 26.6 degrees and 90 degrees is shown. [An example of another screen clock pattern
(Fig. 7) to (Fig. 9)] Figs. 7 (a) to (c) show the case where the screen clock is a two-pixel clock. Fig. 7 (a) shows a screen angle of -45 degrees. 7 (b) shows a pattern having a screen angle of +45 degrees, and FIG. 7 (c) shows a pattern having a screen angle of 90 degrees. 8 (a) to 8 (c) show the case where the screen clock is a three-pixel clock. FIG. 8 (a) shows a screen angle of −45 degrees, and FIG. 8 (b) shows +45 degrees. FIG. 8 (c) shows 9
The pattern of 0 degrees is shown. In FIGS. 9 (a) and 9 (b), the screen angle is-.
Patterns other than 45 degrees, +45 degrees, and 90 degrees are shown. In FIG. 9 (a), the screen angle is −26.6 degrees,
The figure (b) has shown the pattern of +26.6 degrees. If the screen clock 10 is the pixel clock 9 itself, only a screen angle of 90 degrees (vertical screen) can be obtained. Then, the color select signal 12 enables the selector 34 and the selector 13 to select a screen having a different number of screen lines and a different screen angle for each color signal. For example, for the Y signal, the 5 pixel clock of FIG. 9 (a), the screen of −26.6 degrees, and for the M signal, the 4 pixel clock of FIG. 6 (b), +
The screen of 45 degrees, the 3-pixel clock of FIG. 8 (a) for the C signal, the screen of −45 degrees, the 2-pixel clock of FIG. 7 (c) for the BK signal, the screen of 90 degrees. You can choose. Generally, the larger the screen ruling, that is, the finer the resolution, the smaller the screen ruling.
That is, the rougher the image, the better the gradation. In this case, the resolution is emphasized for BK, the resolution and the gradation are balanced for C and M, and the resolution for Y may be visually inconspicuous even if the resolution is slightly reduced. Even if only the screen ruling is changed for each color, the overlap of the four colors on the paper is one-dimensionally averaged. However, when the screen angle is also changed for each color, the overlap of the four color materials is two-dimensional. And the color unevenness is further reduced. Regarding the number of screen lines, the number of lines can be further finely changed by using a signal obtained by directly dividing the reference clock signal, and if a plurality of clock generators having different frequencies are provided, the number of lines can be changed. The number setting can be adjusted more finely. As described above, according to this embodiment, by outputting the Y, M, C, and BK color signals on the screens having different numbers of lines, the balance of resolution and gradation can be changed for each color, and full color As a print, a high-resolution print with high resolution and good gradation can be obtained. Further, by further changing the screen angle for each color signal, when four colors are superimposed on paper, the overlap of the color materials is further averaged. Therefore, there is an effect that color unevenness due to various scanning unevenness of the printer, paper feeding speed unevenness, paper expansion and contraction, etc. is reduced. Although high-frequency moire with a fine pitch occurs, it is visually inconspicuous because it is averaged macroscopically. Further, according to this embodiment, the screen clock synchronized with the horizontal synchronizing signal is formed by using the reference clock 19 having a frequency higher than the frequency of the synchronizing signal for generating the pattern signal (triangular wave). It is possible to generate a desired pattern signal for each scanning line at an accurate timing. Therefore, the grayscale information is pulse-width modulated almost steplessly using the pattern signal generated at an accurate timing, so that a reproduced image of high quality can be obtained. Although the waveform of the pattern signal used in this embodiment is a triangular wave, a sawtooth wave, a sine wave, a trapezoidal wave or the like may be used. As described above, according to the present invention, the phase of the pattern signal for generating the pulse width modulation signal is made different between the first color component signal and the second color component signal. Thus, moire is prevented, and the cycle of the pattern signal is made different between the first color component signal and the second color component signal, so that the first color component signal and the second color component signal are random. Therefore, there is an effect that moiré can be prevented more effectively. In addition, the resolution of the input digital color component signal is also saved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of an image processing apparatus according to an embodiment of the present invention. FIG. 2 is a timing chart of signals of various parts of the image processing apparatus according to the embodiment. FIG. 3 is a configuration diagram of a timing generation circuit according to the present exemplary embodiment. FIG. 4 is a waveform diagram of a pattern signal in the present embodiment. FIG. 5 is a waveform diagram showing the relationship between the pattern signal and the binarized image data in this embodiment. FIG. 6 is a diagram showing an example of a screen clock pattern. FIG. 7 is a diagram showing a pattern example when the screen clock is a two-pixel clock. FIG. 8 is a diagram showing an example of a pattern when the screen clock is 3 pixels. FIG. 9 is a diagram showing another screen clock pattern example. [Explanation of Codes] 1 Digital data output device 2, 13, 34 Selector 3 D / A converter 4 Comparator 5 Pattern signal generator 6 Horizontal sync signal generation circuit 7 Oscillator 8 Timing signal generation circuit 9 Pixel clock 10, 21 Screen Clock 11 Counter 12 Color select signal 14 Delay line 15 Analog pixel signal 16 Pattern signal 17 Horizontal sync signal 18 Binary image data 19 Reference clock signal

Claims (1)

(57) [Claims] It composes a color image signal and is represented by multiple bits per pixel.
Multiple images of I have been the first color component signal and input means for inputting a second color component signals, the color image signals input by said input means
A first pattern signal having a period corresponding to the prime
A pulse for generating a pulse width modulation signal by comparing with the first color component signal and comparing the second color component signal with a second pattern signal having a phase and a cycle different from those of the first pattern signal. An image processing apparatus comprising: a width modulation signal generating means.