JPH07154599A - Image processor - Google Patents

Abstract

PURPOSE:To reproduce an image with high fidelity by combining different intermediate tone generating systems so as to select an optimum system thereby obtaining an image with a high resolution and a high gradation stably. CONSTITUTION:Digital image data from an image input means 1 are processed by an image processing means 2, and a digital intermediate tone generating means 3 or an analog intermediate tone generating means 4 generates a binary image signal. The signal is selected by a selector 5 and an image output means 6 provides an output of an image. The means 3 is used when recycle paper is used for output paper or for a multicolor usage. The means 4 is used when high picture quality is required. When a tray sensor 9 senses a recycle paper tray or a paper quality sensor 10 senses a recycle paper sheet, the selector 5 is selected via a CPU 7 to select an output of the means 3. Furthermore, the selector 5 is selected by a user command via a user interface 8. Or the means 2 decides a picture or a character to select the selector 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for inputting digital image information, binarizing it, and outputting it.

[0002]

2. Description of the Related Art When digital image data is binarized and an image is formed by a laser beam printer, the digital image data is converted into an analog signal in order to obtain a halftone gradation, and this converted signal is cycled. There is known an image processing apparatus which expresses high resolution gradation by performing pulse width modulation in comparison with a conventional pattern signal (Japanese Patent Laid-Open No. 63-113775).
JP-A-62-39972, JP-A-62-399
73), and as a method that is simple in structure and is not affected by external factors such as temperature and paper quality, a method of binarizing digital image data by dithering and forming an image with a laser beam printer is also well known. Has been.

[0003]

However, the method of converting digital image data into an analog signal has a complicated structure, and the pulse width modulation is susceptible to external influences such as temperature, so that stable gradation is realized. However, there is a drawback in that the gradation is changed depending on the quality of the output paper. Further, in the method using dither processing or the like, a large threshold matrix must be used because a sufficient gradation cannot be obtained with the threshold matrix corresponding to one pixel, and as a result, the resolution is extremely lowered. there were.

An object of the present invention is to solve the above problems, and it is an object of the present invention to provide an image processing apparatus which has a high resolution and is capable of obtaining a stable and high gradation image regardless of paper quality and the like. .

[0005]

According to the present invention, an analog / digital converting means for converting digital image data into an analog image signal, a reference signal generating means for generating a reference signal of a predetermined cycle, the analog image signal and the analog image signal are provided. From the pulse width modulation means for comparing the reference signal with the pulse width, the pseudo halftone generation means for generating the pseudo halftone signal from the digital image data, and the pulse width modulation means and the pseudo halftone generation means. It is characterized in that it is provided with a switching selection means for switching and selecting one of the outputs and an image output means for outputting an image in response to a signal from the switching selection means. Further, according to the present invention, an analog / digital converting means for converting digital image data into an analog image signal, a reference signal generating means for generating at least two kinds of reference signals having different periods, the analog image signal and the at least 2 A plurality of pulse width modulation means for comparing pulse width modulation means for comparing with reference signals of different periods or more, pseudo halftone generation means for generating pseudo halftone signals from the digital image data, and a plurality of pulse width modulation means Of the output from the pseudo-halftone generating means, a switching selecting means for switching and selecting one of the outputs from the pseudo-halftone generating means, an image outputting means for outputting an image in response to a signal from the switching selecting means, an image information judging means and a paper quality sensor. The switching selection means is turned off according to at least the determination result of the image information determination means or the output of the paper quality sensor. Characterized in that e has to control.

[0006]

The image processing apparatus of the present invention converts digital image data into analog signals in order to obtain halftone gradation when binarizing the digital image data and forming an image with a laser beam printer or the like. The converted signal is compared with a periodic pattern signal to perform pulse width modulation to express high resolution gradation, and the digital image data is binarized by dither processing or the like to generate a laser beam. A high resolution and high gradation image is required by combining with a second means for forming an image with a beam printer or the like so that optimum image processing can be performed arbitrarily and automatically according to image information, paper quality to be output, instructions from the user, etc. The first means is used when the characters / photographs are original or the paper quality is good, and the second means is used when the characters or solid color original is bad or the paper quality is bad, and the optimum image processing is performed on all the originals. Further, even in the same document, characters, solid colors, and photograph portions are detected to separate pictograms, and the processing method is switched by this separation signal to perform optimum image processing.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of the present invention will be described below based on embodiments with reference to the drawings. FIG. 1 is a block diagram illustrating the basic configuration of the present invention. The digital image data from the image input means 1 is image-processed by the image processing means 2, and the digital halftone generating means 3 or the analog halftone generating means 4 is processed.
, A binary image signal is generated. The binary image signal is selected by the selector 5 and output from the image output means 6 as an image.
Each of these means is controlled by the CPU 7. The digital halftone generating means 3 is used when recycled paper is used as the output paper or in the case of multi-color usage, and the analog halftone generating means 4 is used when high image quality is required and the like. When recycled paper is loaded in the tray, when the tray sensor detects that the tray containing recycled paper is selected, or when the paper quality sensor detects recycled paper or similar paper. Is CPU7
The selector 5 is switched through to select the output of the digital halftone generating means 3. Further, the selector is switched through the user interface 8 according to a user's instruction. In addition, the image processing means 2 determines a picture or a character,
The selector is switched according to the determination result.

FIG. 2 is a more detailed block diagram of the image processing apparatus, and FIG. 3 is a diagram showing the construction of a copying machine to which the image processing apparatus of the present invention is applied. The image input means 1 has an image input device 1a for reading an image of a document and an analog / digital converter 1b. The image input device 1a uses the light emitted from the light source body 1a-1 shown in FIG. 3 to reflect the reflected light from the document (not shown) to the mirrors 1a-2 and 1a-.
3, 1a-4, and the light enters the lens 1a-5 and forms an image on the image sensor 1a-6.
More image signals are obtained. The image signal from the image input device 1a is converted into the analog / digital converter 1
It is converted into a digital signal by b and input to the image processing means 2.

The image processing circuit (IPS) 2a constituting the image processing means 2 is connected to an image editing circuit 2b and a halftone generation system switching circuit 11 and is controlled by a CPU (central processing unit) 7. There is. Image processing circuit 2a
Image signal R (red), G (green),
B (blue) is Y (yellow), M (magenta), C
It is converted into (cyan) and K (black) and sent to the image correction circuit 12. The image correction circuit 12 includes the image output device 6
The image signal is corrected according to the characteristics of the image correction circuit 12. The output of the image correction circuit 12 is input to the dither processing circuit 3a of the digital halftone generating means 3 and the D / A converter 4a of the analog halftone generating means 4. It

The dither processing circuit 3a is composed of the error diffusion circuit 3c and the dither processing circuit 3a shown in FIG. 5. The dithered data is fed back to the error diffusion circuit 3c and the error in binarization is distributed to the next pixel. To prevent conversion noise due to binarization error. The dither pattern is composed of a block of n pixels × 1 line (n and 1 are integers), and each pixel is compared with each threshold value a to 1 of the block to generate a pseudo halftone. The pseudo-halftone signal after the dither processing is binarized by the parallel / serial conversion circuit 3b. At this time, one pixel is divided into m (m is an integer) in the time axis direction for laser scanning to correspond to ON / OFF operation of the laser. This example will be described with reference to FIG. 6. As shown in FIG. 6b, a dither pattern is formed by blocks of 4 pixels × 3 lines to generate pseudo halftones, and parallel / serial conversion is performed to generate 1 pixel as shown in FIG. 6a. Is divided into eight.

Next, the analog halftone generation will be described. The image signal input to the D / A converter 4a becomes an analog image signal and is impedance-converted by the impedance converter constituted by the operational amplifier 4b.
It is input to the comparator 4e for 00 line and the comparator 4f for 200 line. SOS (StartOf) from the image output device 6
Scan) A horizontal synchronization signal (main scanning synchronization signal) 6b is generated by the horizontal synchronization signal generation circuit 4i in synchronization with the scanning synchronization signal 6a, and a predetermined signal is generated by the timing signal generation circuit 4g in synchronization with the signal from the oscillator 4h. The pattern signal is generated by the pattern signal generation circuit 4c by the reference signal 6c of the cycle.
Generated by. The pattern signal to be generated is a repetitive pattern signal such as a triangular wave, a sawtooth wave, a sine wave, or the like, and is generated by the pattern signal generating circuit 4c by the reference signal 6d which has passed through the 1/2 frequency dividing circuit 4j. Triangular wave, sawtooth wave, which has twice the cycle of the pattern signal,
A repetitive pattern signal such as a sine wave is generated by the pattern signal generation circuit 4d. Although not shown,
In addition to this, it goes without saying that a circuit for generating a pattern signal with a period of m times (m is an integer) may be provided. Next, this pattern signal is compared with the impedance-converted analog image signal by the comparators 4e and 4f to perform pulse width modulation to obtain a binarized signal.

An example of pulse width modulation will be described with reference to FIG. 4, in which the IPS is synchronized with the video clock shown in FIG.
The 8-bit density data (FIG. 4 (b)) is converted into analog video data by D / A conversion (FIG. 4 (c)).
This analog video data and 400-line triangular wave (Fig. 4
(D)) and a 200-line triangular wave (FIG. 4 (e)) are compared. By comparing the 400-line triangular wave with the analog video data (FIG. 4 (f)), a pulse width modulation signal for lighting the laser diode is obtained (FIG. 4 (g)). Also, 200
By comparing the line triangle wave and analog video data (see Fig. 4
(H)), a pulse width modulation signal for turning on the laser diode is obtained (FIG. 4 (i)). A specific circuit configuration of pulse width modulation will be described with reference to FIG.
It is converted into analog data by the / A converter 4a, converted into impedance, and applied to one input terminal of an operational amplifier 21 which constitutes a comparator through the filter 20. Further, the transistor 23 is periodically switched by the clock applied through the filter 22, and the triangular wave signal is repeatedly applied to the other input terminal of the operational amplifier 21 through the buffer and the coupling capacitor composed of the transistor 24. The reference signal from the D / A converter 25 is added to the triangular wave through the filter 26. By changing the reference signal level, the pulse width can be changed by changing the DC level of the triangular wave signal. There is.

The halftone image signal thus generated is switched by the selector 5 and sent to the image output device 6 to form an image. The switching by the selector 6 is performed by the output of the halftone generation method switching circuit 11 according to a signal from the image processing circuit 2a or the CPU 7. For example, the image processing circuit 2a recognizes whether the image is a character or a pattern and selects the output of the comparator 4e or 4f. That is, an analog 400 line is used for a high-resolution character portion, and an analog 200 line is used for a pattern for which a border or the like is not conspicuous, to faithfully reproduce an image. The photograph uses analog 200 lines, but in the super-highlight portion of the photograph, in the case of analog halftone, the reference signal may become unstable due to the influence of temperature, etc., and the reproduction may not be stable. In such a case, digital halftone may be selected. Further, in addition to switching the analog / digital halftone in the area, in the case of color, the switching may be performed by combining the development color and the area.
Further, the user may arbitrarily switch the digital halftone or the comparator 4e or 4f through the U / I (user interface) 8 or according to the paper quality information from the paper quality sensor 10. In other words, when using the pulse width modulation method of the halftone generation method, optimum gradation can be realized by using special paper, and when using recycled paper, colored paper, plain paper, etc. There were cases where the light could not be reproduced, but the selector was switched according to the paper quality information from the paper quality sensor 8 and a digital halftone generation method was used to obtain a stable image with better gradation than pulse width modulation. To be

Switching based on the paper quality information from the paper quality sensor 8 will be described with reference to FIGS. 8 and 9. As shown in FIG. 8, the paper 13 is irradiated with light from the light source 21, and the reflected light is input to the CCD sensor 23 through the lens 22. C
The image signal from the CD sensor 21 is processed by the processing circuit 24, the state of the paper is determined by the determination circuit 25, and sent to the switching circuit 11. The state of the paper is determined by the state of the surface color of the paper and the state of the surface of the paper. Switching of the halftone generation method depending on the state of the surface color of the paper is performed by determining whiteness as shown in FIG. 9A, and a digital halftone generation method (area A in the figure) or analog according to the degree of whiteness. Switching between the halftone generation method and the digital halftone generation method (area B in the figure), the analog halftone generation method (area C in the figure), and the switching of the halftone generation method depending on the surface condition of the paper, As shown in FIG. 9B, switching is similarly performed according to the degree of smoothness.

[0015]

As described above, according to the first aspect of the invention, it is possible to stably obtain a high-resolution and high-gradation image by combining different halftone generation methods and selecting an optimum method. Therefore, it is possible to perform faithful image reproduction. According to the second aspect of the present invention, by switching the halftone generation method depending on the paper quality, it is possible to obtain a stable high-gradation image regardless of the paper quality as in the case of using the special paper. When the character part, the image part, and the graphic part are separated, the image is an analog 200 line, the character part is an analog 400 line, and the graphic part uses a digital halftone generation method, which is optimal. It is possible to reproduce the image.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an image processing apparatus of the present invention.

FIG. 2 is a detailed block diagram of FIG.

FIG. 3 is a diagram showing a configuration of a color copying machine to which the present invention is applied.

FIG. 4 is a diagram illustrating pulse width modulation.

FIG. 5 is a diagram illustrating a pulse width modulation circuit.

FIG. 6 is a block diagram of a pseudo halftone generation circuit.

FIG. 7 is a diagram illustrating pseudo halftone generation.

FIG. 8 is a diagram illustrating a circuit for determining paper quality.

FIG. 9 is a diagram showing a relationship between a surface color, a surface state, and halftone generation.

[Explanation of symbols]

1 ... Image input means, 2 ... Image processing means, 3 ... Digital halftone generation means, 4 ... Analog halftone generation means, 5 ... Selector, 6 ... Image output means, 7 ... CPU, 8 ... User interface, 9 ... Tray Sensor, 10 ... Paper quality sensor.

Claims (2)

[Claims] 1. An analog / digital converting means for converting digital image data into an analog image signal, a reference signal generating means for generating a reference signal of a predetermined period, and a pulse comparing the analog image signal with the reference signal. A pulse width modulating means for performing width modulation, a pseudo halftone generating means for generating a pseudo halftone signal from the digital image data, and a switch for selectively selecting one of the outputs from the pulse width modulating means and the pseudo halftone generating means. An image processing apparatus comprising: selecting means and image output means for outputting an image in response to a signal from the switching selecting means. 2. An analog / digital conversion means for converting digital image data into an analog image signal, a reference signal generation means for generating at least two kinds of reference signals having different periods, the analog image signal and the at least two.
Pulse width modulation means for pulse width modulation by comparing with reference signals of different types or more, pseudo halftone generation means for generating pseudo halftone signals from the digital image data,
A switching selection means for switching and selecting one of a plurality of outputs from the pulse width modulation means and an output from the pseudo halftone generation means, an image output means for outputting an image by a signal from the switching selection means, and an image. An image processing apparatus comprising: an information judging means and a paper quality sensor, wherein the switching selection means is controlled to switch in accordance with at least the judgment result of the image information judging means or the paper quality sensor output.