JPS62233981A - Picture processor - Google Patents

Abstract

PURPOSE:To remove the interruption or the notches of a character or a fine line with a reproductivity of half tone maintained and to obtain a reproducing picture of high definition by performing the binarization according to the relative relation of picture elements adjacent to a remakable picture element. CONSTITUTION:A digital picture signal of the multigradation from a picture data input part 19 is latched to latches 20, 21 synchronously with a picture element clock, the levels of the picture elements A, B are compared in a comparator 24, an output is inputted to a pattern signal generating part 25 and used as a pattern signal change over signal. The pattern signal generating part 25 generates a saw-tooth wave of rightward rise or rightward fall according to the scale relation of the adjacent picture elements A, B of the remakable picture element X. The pattern signal is compared with the picture signal converted to an analog voltage value by a D/A converter 22 and a resistance 23 by a comparator 26 and the pulse duration modulated picture signal is outputted to a picture output part 33.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image processing device that processes an image signal including halftone tones.

[Prior Art] When converting a digital image signal into a binary image and forming an image using a laser beam printer, the digital image signal is converted into an analog signal in order to obtain halftone gradation, and the converted signal is converted into an analog signal. , a method has been proposed in which a pulse width modulated binary signal is generated by comparing it with a periodic pattern signal such as a triangular wave.

FIG. 2 shows a specific example of this method. The digital image signal is latched by latch 1 with the image clock and synchronized. This image signal is transmitted to the D/A converter 2
is converted into an analog image signal. The output of the D/A converter 2 is converted into a voltage level by a resistor 3 and then input to one input terminal of a comparator 4. On the other hand, a periodic signal such as a sawtooth wave or a triangular wave is generated from the pattern signal generation circuit 5, inputted to the other input terminal of the comparator 4, and compared with the above-mentioned analog image signal. The output is a pulse width modulated video signal. This pulse width modulated image signal is input to a modulation circuit that modulates, for example, a laser beam, and a halftone image is formed on a recording medium (not shown) by turning the laser beam ON10FF according to the pulse width. Note that the image clock and the triangular wave are synchronized with the BD scratch signal.

This method is certainly effective for halftone images, but for images such as characters and thin lines as shown in Figure 3, the edges may be jagged or the lines may be interrupted. There are some problems. FIG. 4 is a diagram for explaining this.

Vxx' in Fig. 4 indicates the image signal read from the section x-x' in Fig. 3, and by comparing this image signal with the sawtooth type shown by the dotted line superimposed on this image signal, Pulse width modulation is performed to obtain a reconstructed image such as Pl. It is desirable that two black lines be reproduced in the reproduced image P1, but the lines are broken into small pieces, degrading the quality of the reproduced characters.

[Problems to be Solved by the Invention] The present invention has been made to eliminate such conventional problems, and it is possible to improve the reproducibility of halftones from the relative level relationship of pixels adjacent to the pixel of interest. To provide an image processing device capable of obtaining a high-quality reproduced image by eliminating discontinuities and jaggedness of characters and thin lines while maintaining the quality.

Furthermore, the present invention provides an image processing device in which the reproducibility of halftones is further improved based on the relative relationship between a pixel of interest and adjacent pixels.

[Means for Solving the Problem] As a means for solving this problem, the image processing apparatus of the present invention includes a determining means for determining the relative relationship between at least two pixels adjacent to a pixel of interest, and the determining means. comprises a voltage output means for outputting a voltage with a waveform corresponding to the determination result, and a binarization means for outputting a binary signal having a time width corresponding to the magnitude of the voltage outputted by the voltage output means and the image signal. .

Further, another image processing device includes a first determining means for determining a relative relationship between at least two pixels adjacent to a pixel of interest;
a second determining means for determining a relative relationship between a pixel of interest and an adjacent pixel; and a voltage outputting means for outputting a voltage having a waveform corresponding to the determination result of the first determining means and the second determining means. , and binarization means for outputting a binary signal having a time width corresponding to the magnitude of the voltage outputted by the voltage outputting means and the image signal.

[Operation] In this configuration, the image processing device of the present invention performs binarization according to the relative relationship between pixels adjacent to the pixel of interest.

Furthermore, binarization is performed by paying attention to the relative relationships between pixels adjacent to the pixel of interest and the relative relationships between the pixel of interest and adjacent pixels.

[Example] FIGS. 5(a) and 5(b) show the relationship between the pixel of interest X and its adjacent pixels A and B, and the pattern signals corresponding thereto. In this example, a sawtooth wave is used as a pattern signal, and a sawtooth wave upward to the right and a sawtooth wave downward to the right are generated with the pixel of interest X as the center, as shown in FIGS. 5(a) and (b). The switching is performed depending on the size relationship between the left and right adjacent pixels A and B. The basic idea of this embodiment is to detect the pixel levels on the left and right sides of the pixel of interest, and to make the blacker (higher level) pixel side black, in order to reduce the discontinuity of thin lines as described above. Match pattern signals. That is, when sawtooth waves as shown in FIGS. 5(a) and 5(b) are used as pattern signals, FIG.
In the case of the descending sawtooth wave shown in a), a pulse width modulated signal starting from the right side of the pixel is obtained, as shown in Fig. 5(b).
In the case of a sawtooth wave rising to the right, a pulse width modulated signal is obtained starting from the left side of the pixel. From now on, if the starting point of the pulse width modulation waveform of the pixel of interest is set to the side with a higher level, a continuous signal can be obtained for two pixels without interruption of the thin line, and the above-mentioned problem can be solved.

Figures 5(a) and 5(b) are based on this idea, and when the relationship between two adjacent pixels A and B is A<B as in Figure 5(a), the As shown in Figure 5 (b), A>
In the case of H, a sawtooth wave rising to the right is given as a pattern signal for the pixel of interest.

FIG. 1 is a block diagram of the image processing apparatus of this embodiment. Multilevel digital image signals from the image data input section 19 are latched by latches 20 and 21 in synchronization with the pixel clock. Here, the input of the latch 20 is as shown in FIG. 5(a).
Assuming pixel B explained in (b), its output is pixel X1
Further, the output of the latch 21 corresponds to the pixel A. Therefore, the levels of pixels A and B are compared by a comparator 24. This output is High when A>B, and iLow when A≦B.

The output of this comparator 24 is the pattern signal generator 25
The signal is input to the signal and used as a pattern signal switching signal. That is, when the pattern signal switching signal is High, a sawtooth wave going upward to the right is generated, and when it is Low, a sawtooth signal going downward to the right is generated. This pattern signal and an image signal converted into an analog voltage value by a D/A converter 22 and a resistor 23 are compared by a comparator 26 to obtain a pulse width modulated image signal. An image is output to the image output section 33 based on this image signal.

FIG. 6 is an explanatory diagram of the effects of this embodiment. The image signal is
This is a reading of the portion Xx' in FIG. 3 in the same way as in the explanation of the conventional example. It can be seen from FIG. 6 that this embodiment is effective as a countermeasure against the line discontinuity seen in the conventional example shown in FIG.

Although this embodiment can improve the reproducibility of thin lines such as characters, in low-contrast areas, the pattern signal may switch irregularly and the image may become grainy, resulting in less than desirable image reproduction. Therefore, in addition to the magnitude relationship between adjacent pixels, the level difference between the pixel of interest is also detected, and if the level difference is less than a certain value, it is determined that it is a low contrast portion and the pattern signal is not switched.

FIG. 7 shows an image processing device according to another embodiment for this purpose, in which the pixel of interest X and adjacent pixels A and B are added to the image processing device shown in FIG.
This adds a function to detect level differences. The level difference between the pixel of interest X and pixel A is determined by a subtracter 28, and the level difference between the pixel of interest X and pixel B is determined by a subtracter 27.

Although this difference signal may be input directly to the pattern signal generating section 25, in this case, the threshold values Pa and Pb set by the threshold value setting circuit 32 and 31 are compared with the respective difference signals a and b using the comparators 30 and 29. and inputs the comparison signal to the pattern signal generation section 25. If Paha, and Pa>b
In this case, it is determined that it is a low contrast portion, and a pattern signal for low contrast is generated without performing the pattern signal switching as described above.

FIG. 8 is a block diagram of an example in which the pattern generation in FIG. 1 is realized by a computer. CPU80, ROM81
and RAM82.

The operation of the processing program stored in the ROM 81 will be explained according to the flowchart shown in FIG.

First, in step S91, the levels of A, B, and X are stored in the RAM 82.
Load into. In step S92, A>B is checked, and if A>B, in step 397, the upper right pattern is selected and generated, and one pixel is processed. If A≦B, the calculation lX-A I is performed in step S93, and step S
94, check lX-Al<Pa, and lX-A
If l≧Pa, in step 398, a downward-sloping pattern is generated and one pixel is processed. In step S94, lX-
If Al < Pa, calculate lX-B1 in step S95, check l I do. l X-B l
If <Pb, step 397 selects 1 in the upper right pattern.
Performs pixel processing. Hereinafter, the above processing is performed for all pixels.

Note that the pattern may be generated by storing the pattern in the FLAM 82 and converting the read data into analog data using a D/A converter.

As explained above, by detecting the level relationship between the pixel of interest and its neighboring pixels, and switching the pattern signal based on the results, it is possible to maintain the reproducibility of halftones and improve the reproducibility of thin lines such as characters. You can improve. Furthermore, by detecting low contrast areas and not applying the above-described processing to such areas, it is possible to further improve image quality.

[Effects of the Invention] The present invention eliminates discontinuities and jaggedness in characters and fine lines while ensuring the reproducibility of intermediate tones based on the relative level relationship of pixels adjacent to the pixel of interest, resulting in high-quality reproduced images. It is possible to provide an image processing device that can obtain the following.

Furthermore, an image processing device has been provided in which the reproducibility of halftones is further improved based on the relative relationship between a pixel of interest and adjacent pixels.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the image processing device of this embodiment, Fig. 2 is a block diagram of the image processing unit of the conventional example, Fig. 3 is an original drawing, Fig. 4 is an explanatory diagram of processing in the conventional example, and Fig. 5. (a) and (b) are diagrams showing the relationship between adjacent pixels and the pattern signal at that time in this embodiment, FIG. 6 is an explanatory diagram of processing in this embodiment, and FIG. 7 is image processing in another embodiment. FIG. 8 is a block diagram of the apparatus, FIG. 8 is a block diagram of this embodiment realized by a computer, and FIG. 9 is a flowchart of the processing program. In the figure, 19... image data input section, 20.21...
Latch, 22...D/A converter, 23...Resistor, 24.26, 29.30...Comparator, 27°28...Subtractor, 25...Pattern generator, 31°32. ...Threshold value, 33...Image output section, 80...
-cpU181...ROM, 82...RAM. Patent applicant: Canon Co., Ltd. Figure 2 Figure 4 Figure 5 (a) (E))
A>B 8th F! A Figure 9

Claims (7)

[Claims] (1) In an image processing device that processes an image signal including a halftone image, there is provided a determining means for determining the relative relationship between at least two pixels adjacent to a pixel of interest, and a voltage waveform corresponding to the determination result of the determining means. and a binarization means that outputs a binary signal having a time width corresponding to the magnitude of the voltage outputted by the voltage outputting means and the image signal,
An image processing device characterized by performing binarization according to a relative relationship between pixels adjacent to a pixel of interest. (2) The image processing apparatus according to claim 1, wherein the determining means determines the magnitude of two pixel levels adjacent to the pixel of interest. (3) The image processing device according to claim 1, wherein the voltage outputted by the voltage output means has a cycle that is an integral multiple of the pixel signal. (4) In an image processing device that processes an image signal including halftone tone, a first determining means for determining a relative relationship between at least two pixels adjacent to a pixel of interest, and a relative relationship between the pixel of interest and an adjacent pixel. a second determining means for determining the relationship;
Voltage output means for outputting a voltage with a waveform corresponding to the discrimination results of the first discrimination means and the second discrimination means, and a time width corresponding to the magnitude of the voltage outputted by the voltage output means and the image signal. and a binarization means for outputting a binary signal, and performs binarization by paying attention to the relative relationships between pixels adjacent to the pixel of interest and also the relative relationships between the pixel of interest and adjacent pixels. Image processing device. (5) The image processing apparatus according to claim 4, wherein the first determining means determines the magnitude of two pixel levels adjacent to the pixel of interest. (6) The second discriminating means determines the level of the pixel of interest and the adjacent pixel level.
5. The image processing apparatus according to claim 4, wherein the image processing apparatus determines a level difference between two pixel levels. (7) The image processing device according to claim 4, wherein the voltage outputted by the voltage output means has a cycle that is an integral multiple of the pixel signal.