JPS62198266A - Color picture information processor - Google Patents

Abstract

PURPOSE:To form an excellent picture without any moire by adopting different phases of a pattern signal to apply pulse width modulation to each color component signal of a color picture signal from respective color components. CONSTITUTION:Phase shift circuits 26, 26' making the phase of a frequency of a triangle wave serving as pattern signal at each color component different are provided. When a digital multi-value color is inputted, the triangle wave having different phases from respective color components applies pulse width modulation at respective color components. On the other hand, digital color data is converted into an analog video signal by a D/A converter 3 and the result is inputted to one input of a comparator 8. The comparator 8 compares the analog video signal and the triangle wave having different phases from each color to output a binary-coded picture signal.

Description

[Detailed Description of the Invention] [Field of Application in Ti Industry] The present invention relates to a color image information processing device, and particularly to a color image information processing device that forms an output image by pulse width modulating each color component that constitutes an input image signal. Regarding equipment.

[Prior Art] The applicant of the present application has proposed a color image information processing device that performs pulse width modulation for each color component signal by comparing each color component constituting a color image signal with a pattern wave such as a triangular wave.

First, the input digital color image signal is once converted into an analog signal, and this analog signal is compared with a periodic pattern signal such as a triangular wave to perform pulse width modulation and generate a binary signal.

At this time, the period of the pattern signal is switched between a single-density image, such as a character image, where resolution is important, and a half-tone image, where reproducibility is important, such as a photographic image.

FIG. 4 shows a block diagram of a processing circuit that pulse width modulates a video signal, which was previously proposed by the applicant of the present invention. There is.

Here, for example, an 8-bit video signal 200 is input in synchronization with a video clock (VCLK) 201 and latched into a latch 202. 203 is a D/A converter,
The 8-bit video signal is converted into an analog video signal 204 and input to one of the input terminals of a comparator 205.

Further, the original clock (ORCLK) 206 is input to a frequency dividing circuit 207, and the frequency is switched by a switch 208 and output.

Note that VCLK201 is a clock obtained by dividing 0RCLK206 by two. Now, after the clock switched by the switch 208 passes through the buffer 209 and the integrating circuit 210, the amplifier 21 is biased by the bias circuit 211.
2 to the other input terminal of the comparator 205, and pulse width modulation is performed by the comparator 205.

[Problems to be Solved by the Invention] A device that performs color image processing using pulse width modulation has the disadvantage that when the phases of the triangular waves are aligned for each color component, "moiré" occurs, making it impossible to obtain a good output image. It turns out that there is.

The present invention has been made to improve the color image processing device proposed by the applicant as described above, and provides a color image information processing device that eliminates moiré and forms good output images. There is a particular thing.

[Means for solving the problem] As a means for solving this problem, for example, in the block diagram of the color image information processing device shown in FIG. 1, the phase of the frequency of the triangular wave, which is the pattern signal for each color component, A phase shift circuit 26°26' is provided.

[Operation] In the configuration shown in FIG. 1, when digital multivalued color data is input, pulse width modulation is performed for each color component using a triangular wave having a different phase for each color component. On the other hand, the digital color data is converted into an analog video signal by the D/A converter 3 and input to one terminal of the comparator 8. The comparator 8 outputs a binarized image signal by comparing the analog digital signal with a triangular wave having a different phase for each color.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of a color image information processing apparatus according to this embodiment.

The operation will be explained below.

Data converted into digital multi-value data (video R54, video G55, video B56) of each color component is input to this block diagram.

Furthermore, since the conversion circuits for multi-value data of each color component (red, green, blue) are the same, the processing of the multi-value image signal (video R54) of the red component will be described here.

In the figure, 1 is an 8-bit latch, and 2 is a buffer memory that stores several bytes of image data. 3 is a D/A converter that converts 1 byte of data from latch 1 into analog signal 2.
Convert to 3. 4 uses several bytes of image data in the buffer memory 2 and the latest video R signal to identify, for example, whether it is a character image or a halftone image, and determines the type of image.
This is an image area determination circuit that outputs a determination result 9 to the PU 12.

5 is a frequency dividing circuit which inputs the clock 0CLK27 and outputs the clock 28 of the latch 1 and the D/A converter, and two types of clocks having different frequencies. 6 is a changeover switch for selecting the output clock of the frequency dividing circuit. Here, the wavelength becomes shorter when it is on the A" side, and becomes longer when it is on the "B" side. 7 is a triangular wave generator. 8 is a comparator, and the triangular wave 20 and the analog R signal 23 and outputs the logical value.

Reference numeral 12 includes a ROM containing a control program or data for controlling the entire apparatus by a CPU, and a RAM as a work area, and a flowchart shown in FIG. 3, which will be described later, is stored in the ROM. Further, each image area determination circuit 4 outputs determination results 9 to 11 to the CPU 12, and based on these, the CPU 12 outputs control signals 13 to 15 for each changeover switch 6, and You will need to switch to one of the following.

Further, 2F is a clock 0CLK that is synchronized with the video clock of each video signal 54 to 56, and is commonly input to each frequency dividing circuit 5. The clock 0CLK is generated, for example, in synchronization with the output of a beam detector that detects a predetermined scanning position of the laser beam, and is synchronized every - times of horizontal scanning. The signal frequency-divided by the frequency dividing circuit 5 is input to a triangular wave generator to generate a triangular wave. The triangular wave is phase-shifted in the G and B signals by phase shift circuits 26 and 26'. Further, the phase shift may be implemented by a delay circuit. As a result, the triangular waves 20 to 22 have different phases.

The triangular wave generated here and the signal pulse width modulated by the comparator 8 are shown in FIG.

In FIG. 2, "R" is D in the video R54 signal.
/VIDE converted to analog signal by A converter 3
O level 23 and triangular wave 2 generated from triangular wave generator 7
It is a timing chart showing 0.

In addition, "G" and "B" are each analog signal 24.25
This is a timing chart of triangular waves 21.22, and the output pulses from comparator 8 are V-R16, V-G17. V-B
181C was shown.

As is clear from this timing chart, since the frequencies of the respective clocks to the frequency dividing circuit 5 are different, it can be seen that even if the input image level does not change, the output pulses are not formed at the same timing.

In this way, by making the phase of the triangular wave different for each color component, the input image signal (video R54, G55.B
56) Even if there is no change, "moiré" may occur in the output image because the signals for forming the output image (V-R16, V-G17, V-B18) are not repeatedly output in the same pattern. There will be no.

Also, in FIG. 2, when the image area determination circuit 4 detects a change in the image area, the frequency of each triangular wave changes by changing the changeover switch 6, Also, the triangular wave 20 for each color component
, 21, and 22 have different phases, similar effects can be obtained.

The switching process by the changeover switch 5 as described above will be explained according to the flowchart shown in FIG.

First, in step S1, the determination results for each color component from the image area determination circuit 4 are read. Next, in step S2, it is determined whether the changeover switches 6 are currently connected to the "A" side.
Or, it is determined whether it is connected to the 'B' side. If it is determined that it is connected to the 'A' side, the process goes to step S3, and if it is connected to the 'B' side, it is determined that it is connected to the 'A' side. If the determination is negative, the process advances to step S5.

Now, in step S3, if it is determined that one of the determination results for each color component inputted in step S1 is a halftone image, the respective changeover switches 6 are connected to the "B" side, and the process ends. Furthermore, if it is determined in step S3 that the image is a single-density image, there is no need to switch the changeover switch 6 from the A'' side, and the process ends immediately.

Also, in step S2, the current changeover switch 6 is set to "B".
If it is determined that it is connected to the side, the process moves to step S5, but in step S5, similarly to step S3, it is determined whether the determination result read from the image area determination circuit 4 for each color component is a single density image or not. Determine whether it is a halftone image. At this time, if even one of the judgment results for each color component is determined to be an IL-density image, the changeover switch 6 is connected to the "A" side, and if it is a halftone image, the changeover switch 6 is connected to the "B" side. Since there is no need to switch from

[Effects of the Invention] As described above, according to the present invention, by making the phase of the pattern signal for pulse width modulating each color component signal of a color image signal different for each color component, a good output without moiré can be achieved. It becomes possible to form an image.

[Brief explanation of drawings]

FIG. 1 is a block diagram of this embodiment, FIG. 2 is a timing chart of this embodiment, FIG. 3 is an operation flowchart of this embodiment, and FIG. 734 is a block diagram proposed by the applicant of the present application. In the figure, 1...Latch, 2...Buffer memory, 3...
...D/A converter, 4...image area determination circuit, 5...
- Frequency divider circuit, 6... Selector switch, 7... Triangular wave generator, 8... Comparator, 9-11... Judgment result signal, 13-15... Control signal, 16-17. ...Binary image signal, 20-22...Screen clock, 23-
25... Analog video signal, 26.26'... Phase shift circuit, 27... 0CLK, 50... Color image signal, 51... Digital conversion section, 52... Binary conversion section, 53... Image output section, 54... Video R1
55...Video G, 56...Video B. Patent applicant Canon Co., Ltd. 2 drawings

Claims (4)

[Claims] (1) A signal that is pulse width modulated for each color component signal is processed to form an output image from each color component signal constituting a color image signal and a pattern signal having a different phase for each color component signal. color image information processing device. (2) a determining means for determining the type of image for each of the color component signals; 2. The color image information processing apparatus according to claim 1, further comprising frequency switching means for changing the frequency of the pattern signal. (3) The color image information processing apparatus according to claim 2, wherein the types of images are a single density image and a halftone image. (4) The color image information processing apparatus according to claim 2, wherein the frequency switching means lowers the frequency when determining that the type of image is a halftone image.