JP2000244736A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize gradation and to excellent hold image information by integrating pulses to images for which the gradation is considered as important. SOLUTION: This device for inputting the image data of the images of characters, photos or the coexistence, multi-value-outputting them by pulse width modulation and forming digital images is provided with an operation part 107 for selecting/instructing a gradation mode for improving the gradation and an image quality mode equivalent to a resolution mode for improving a resolution. This device is also provided with a pulse width conversion output part 102 for converting the image data of a pixel under consideration to a pulse width and outputting the position of outputting pulses by at least two kinds of right justification and left justification for the respective pixels, and it is provided with a switching signal generator 104 for alternately switching the output position of the pulse of the pixels continuous in a main scanning direction to the right justification and the left justification in the case that the gradation mode is selected/instructed by the operation part 10 and switching the output position of the pulse of he respective pixels to be one kind in the case that the resolution mode is selected/instructed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser printer, a digital copying machine, and a laser facsimile, and more particularly, to an image forming apparatus for outputting a multi-value image by a pulse width modulation method.

[0002]

2. Description of the Related Art Conventionally, in a laser printer using an electrophotographic process, the lighting time of an elliptical beam (because the size of a dot is different in a main scanning direction and a sub-scanning direction, an ellipse) is changed within one pixel. Multi-level writing of one pixel is realized by pulse width modulation (PWM). FIG. 9 (a)
Shows a state in which the elliptical beam performs main scanning. Also,
FIG. 9B shows the exposure energy distribution when the elliptical beam shown in FIG. 9A is turned on at １ ／, ／, ／ and 1 of one pixel clock. In FIG. 9B,
In the negative-positive development method, a portion where the exposure energy is higher than the visualization level thr is visualized to form a dot.

FIGS. 10 (a) to 10 (e) show that the exposure times are
The state of dot formation at / 4, 2/4, 3/4 and 1 is shown. Since the actual beam spot shows a light energy distribution approximated by a Gaussian distribution in the main scanning direction and the sub-scanning direction, it does not become an ideal rectangle. Therefore, the distribution in the sub-scanning direction is omitted.

In FIG. 11, (a) is a pixel clock,
(B) is a pixel signal, (c) is an output level, (d) is an exposure energy distribution, (e) is an output image at thr1,
(F) shows the output image at thr1. When the level of the pixel signal is H, the beam is turned on.

In pixel numbers 1 and 2, output levels 1, 1
Dots are formed in the order of / 4, and dots are formed in the order of the output levels 1/4 and 1 at pixel numbers 4 and 5.
(D) shows the exposure energy distribution at that time,
Normally, the portion above the visualization level thr1 is blackened,
The output image shown in (e) is obtained. In this case, dots having the same area ratio are formed.

However, when the beam power fluctuates or various conditions of the developing process fluctuate, the effect on the blackened area appears differently in the combination of the pixels 1 and 2 and the pixels 4 and 5.
The threshold value thr2 in FIG. 11D is based on the assumption that the visualization level is increased due to the above-mentioned fluctuations in the process conditions and the like.
In this case, dots are formed as shown in FIG. In this example, the blackening area decreases due to the increase in the visualization level, but the blackening area fluctuates near the boundary where the exposure is turned on / off. Here, the exposure is turned on / off for pixels 1 and 2.
There are two offs, four times for areas 4 and 5, and areas 4 and 5
It can be seen that the variation in the blackened area is larger in the case of.

Here, the increase in the visualization level is considered. When the visualization level decreases, the blackening area increases. However, the variation in the blackening area is larger in the pixels 4 and 5. . That is, when forming an image, it is understood that the smaller the isolation of minute dots, the smaller the influence on the fluctuation of the process conditions and the like, and that a stable image output can be obtained.

On the other hand, in the "image forming apparatus" disclosed in Japanese Patent No. 2713578, for example, the area ratio of one dot and the duty of the laser beam (the ratio of the lighting time).
The duty ratio is smaller than 100% for one dot area ratio of 100%.
There is off. In the photo mode, there is a method of expressing density by concentrating a blackened area of two adjacent pixels so that stable gradation characteristics can be obtained.

[0009]

However, the prior art as described above has the following problems. FIGS. 12A to 12H show how to express the density of only the left alignment according to the conventional method. In this case, since the pulses are not continuous, the output is not stabilized for the above-described reason. In particular, a tone jump occurs between (d) and (e), and the gradation characteristics deteriorate.

In the density expression in which two pixels are defined as one unit according to the method shown in FIG. 12, the following problem occurs when the method is applied to an image containing a thin line such as a character.
This problem will be described with reference to FIGS.
FIG. 7A shows how to read a parallel vertical line document. Here, lines having substantially the same thickness are located near the center of each of two pixels continuous in the main scanning direction. At this time, the thickness of the line is equal to or less than half of one pixel. In this case, as shown in FIG. 7B, the reproduced image of the left pixel is blackened from the left end to a portion corresponding to twice the original image, but the right pixel is not blackened at all. In this case, the average density of the two pixels is appropriate. However, if the original image is not the two lines but only the left line, the appropriate amount of blackening is equivalent to the line width, but the amount of blackening is twice that of the original image. It will be reproduced as a thick line. Conversely, if the original image is only the right line, the right pixel is not blackened at all, and the line disappears in the reproduced image. For this reason, there has been a problem that the image becomes darker or thinner or disappears depending on the image position of the document.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and integrates a pulse into an image where importance is placed on gradation, thereby stabilizing gradation and maintaining image information well. The first purpose is to do so.

It is a second object of the present invention to eliminate the bias of the image by matching the positional relationship between the image which emphasizes the gradation and the image which emphasizes the resolution.

[0013]

In order to achieve the above object, in an image forming apparatus according to the first aspect, image data of characters / photos to be imaged or an image in which these are mixed are inputted. In an image forming apparatus that outputs multi-values to the input image data by pulse width modulation to form a digital image, at least a gradation mode for improving gradation and a resolution mode for improving resolution are provided. An image quality mode selecting means for selecting and indicating a corresponding image quality mode, converting the input image data of the target pixel into a pulse width, and outputting a pulse output position for each pixel in at least two types, right-justified and left-justified. When the gradation mode is selected / instructed by the pulse width conversion output unit and the image quality mode selection unit, the output positions of the pulses of the continuous pixels in the main scanning direction are shifted right and left. Alternately switching a Pasuru switching means for switching the output position of the pulse of each pixel so that one type if the resolution mode is selected and instructed,
It is provided with.

Further, in the image forming apparatus according to the present invention, image data of a character / photo to be imaged or an image in which these are mixed is input, and the input image data is multi-valued by pulse width modulation. In an image forming apparatus that outputs and forms a digital image, at least an image area separating unit that separates an area between a gradation image and a resolution image and outputs an image area determination signal, A pulse width conversion output unit that converts image data into a pulse width and outputs a pulse output position for each pixel in at least two types, right-justified and left-justified, and an image area determination signal output by the image area separation unit. In the case of the gradation image, the output position of the pulse of the continuous pixel in the main scanning direction is alternately switched between right alignment and left alignment, and in the case of the resolution image, the output position of the pulse of each pixel is set to 1 And Pasuru switching means for switching so that the classes are those comprising a.

Further, in the image forming apparatus according to the third aspect, image data of a character / photo to be imaged or an image in which these are mixed are input, and the input image data is multi-valued by pulse width modulation. In an image forming apparatus that outputs and forms a digital image, at least an image area separating unit that separates an area between a gradation image and a resolution image and outputs an image area determination signal, A pulse width conversion output unit that converts image data into a pulse width and outputs a pulse output position for each pixel in at least three types: right alignment, left alignment, and center alignment; and an image area output by the image area separation unit. Based on the discrimination signal, in the case of a gradation image, the output position of the pulse of the continuous pixel in the main scanning direction is alternately switched between right alignment and left alignment, and in the case of the resolution image, the pulse output of each pixel is output. And Pasuru switching means for switching the position to centered, those provided with.

Further, in the image forming apparatus according to the present invention, the image area separating means includes an edge detecting means for detecting an edge of a character or a line drawing, and a dot detecting means for detecting a halftone dot of a printed document. Means.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the image forming apparatus of the present invention will be described in detail with reference to the accompanying drawings.

Embodiment 1 (System Configuration) FIG. 1 is a block diagram showing an example of a system configuration including an image processing apparatus according to Embodiment 1 of the present invention. For example, an image forming apparatus such as a digital copying machine This is a block diagram of the main part of the system. In the figure, reference numeral 101 denotes a scanner that optically scans a document to be read and outputs digital image data, and 102 denotes a scanner 1
01, a pulse width conversion output unit that converts the image data of the target pixel of the image input into a pulse width as described later;
A pulse switch 103 selects and outputs a right-aligned pulse or a left-aligned pulse, a switching signal generator 104 generates a signal for switching between a right-aligned pulse and a left-aligned pulse for each pixel, and 105 receives a laser diode (LD). An LD driver that modulates and outputs with a pulse, an image forming unit that finally forms an image on recording paper by a predetermined image forming process (in this example, an electrophotographic method is used), and an image quality mode 107 that is selected by an operator An operation unit for inputting a command.

The pulse width conversion output unit 102 includes a right-aligned pulse generator 108 for outputting a right-aligned pulse and a left-aligned pulse generator 108 for outputting at least two types of right-aligned pulses and left-aligned pulses for each pixel. And a left-aligned pulse generator 109 for outputting a pulse.

(Image Processing Operation) Next, an example of pulse width output using a right-aligned pulse and a left-aligned pulse, which is a feature of the present invention, will be described. FIG. 5 is an example of pulse width output according to the embodiment of the present invention.
(B) shows a left-aligned pulse, and (c) shows a center-aligned pulse (described later). In the apparatus shown in FIG. 1, the pulses output from the right-aligned pulse generator 108 and the left-aligned pulse generator 109 of the pulse width conversion output section 102 are switched by a switching signal generator based on an image quality mode selection signal from the operation section 107. 5A, a right-aligned pulse is used for the left pixel and a left-aligned pulse is used for the right pixel, as shown in FIG.

That is, when the image quality mode selection signal is a mode in which the gradation is emphasized, control is performed so that a right-aligned pulse and a left-aligned pulse are alternately changed every other pixel for pixels that are continuous in the main scanning direction. And a blackening process is performed. Also,
When the image quality mode selection signal selects a mode that emphasizes the resolution, control is performed so that the pulse output position of each pixel is one type.

FIG. 6 shows a process of performing the blackening process by alternately changing and controlling the right-aligned pulse and the left-aligned pulse. As shown in the drawing, while the continuous pulse is maintained, all the pixels are blackened while gradually affecting the density fluctuation.

At this time, the left pixel 601a and the right pixel 601
The pixel b is blackened by an amount corresponding to the density of the image data input thereto. This state is shown in FIG. Since the blackened portions are combined around the boundary between both pixels of the left pixel 601a and the right pixel 601b, stable gradation characteristics are obtained, and each pixel is blackened by an amount corresponding to the original image. . For example, in the case of only the right line from the original image, the left pixel is a white dot, but the left pixel is reproduced as a dot blackened by an amount corresponding to the original image. Therefore, problems such as missing or abnormally emphasized image information are resolved.

Although the case of one-dot quinary is described here as an example, the present invention is not limited to this. For example, 16 values per dot, 64
It may be a case where the number of multi-values is large, such as a value, a 256 value, or the like, and can be applied to a case of a ternary or quaternary value.

Here, when the multi-valued number is relatively small such as 5 values or 16 values, the gradation can be increased by using the dither method. A 2 × 1 matrix with two pixels as one unit is combined and prioritized as shown in FIG.
FIG. 8B shows a configuration of the second matrix. As a result, the reproducible gradation can be increased. Hereinafter, it is possible to similarly extend to a 2 × N matrix.

In the above-described pulse width control example, the gradation is stabilized by performing the processing in units of two pixels.
On the other hand, the resolving power is 1/1 when compared with the processing of one pixel unit.
2 will be degraded. That is, there are two types of images: originals that emphasize gradation, such as photographs and paintings, and originals that emphasize resolution, such as characters and line drawings. The processing in units of two pixels is disadvantageous for a document whose resolution is important.
Therefore, an operator selects an optimum image quality mode through the operation unit 102 according to the original, performs two pixel processing for the image quality mode emphasizing gradation, and performs one pixel processing for the image quality mode emphasizing resolution. By performing the unit processing, a good reproduced image can be obtained.

[Second Embodiment] (System Configuration) FIG. 2 is a block diagram showing an example of a system configuration including an image processing apparatus according to a second embodiment of the present invention. This configuration is different from the above-described configuration in which the operation unit 107 of FIG. 1 supplies the image quality mode selection signal to the switching signal generator 104, in which an image area separating unit 201 is provided. It is configured to supply an image area discrimination signal. Therefore, the other components and their functions are the same as those in FIG. 1, and thus the same reference numerals as in FIG.

That is, the image area separation unit 201 outputs an image area determination signal for determining an image quality mode most suitable for the original. In this case, it is also possible to configure so as to determine which processing is appropriate after scanning all the originals. Here, the image area is determined for each pixel in real time, and two pixels are determined. It is configured to switch between unit processing and one pixel unit processing. Therefore, even when a photographic image and a character image are mixed in one document, the image can be reproduced well.

An image area separation unit 201 performs an image area determination process on image data read by the scanner 101 and controls the switching signal generator 104. FIG. 4 is a block diagram illustrating an internal configuration of the image area separation unit 201. As shown in the figure, the image area separation unit 201 has two types of determination functions: an edge detection unit 401 that detects edges of characters and line drawings, and a halftone detection unit 402 that detects halftone dots of a printed document. Have.

Here, the reason why the dot detection unit 402 is provided is as follows.
This is to avoid erroneously determining a halftone dot image having a coarse line frequency as a character image. The image area determination signal is obtained by integrating the determination results of both the edge detection unit 401 and the halftone dot detection unit 402. That is, an area in which the edge of the input image data is detected and no halftone dot is detected is determined as a “character portion” that emphasizes the resolution, and the H level is output. It is determined to be a "photo section" and an L level is output.

Now, referring to FIG.
When the image area discrimination signal is at the L level and is "photograph part", the right-aligned pulse and the left-aligned pulse are alternately selected so that the processing is performed in units of two pixels. On the other hand, when the image area discrimination signal is "character portion" at the H level, a left-justified pulse is always selected so as to perform one pixel unit processing. In the case of the "character portion", it is needless to say that a right-aligned pulse may be selected.

(Image Processing Operation) The pulse width control in the apparatus shown in FIG.
However, in the first embodiment, the pulse width control is performed based on the image quality mode (emphasis on gradation / resolution) designated by the operation unit 102. On the other hand, in the second embodiment, The difference is that the determination is performed based on the image area determination signal by the image area separation unit 201.

That is, when the image area separation unit 201 determines that the image area is an image area where importance is placed on gradation, the output position of the pulse of the continuous pixel in the main scanning direction is alternately changed to right alignment and left alignment. . On the other hand, when it is determined that the image area emphasizes the resolution, the output position of the pulse of each pixel is controlled to be one type.

[Embodiment 3] FIG. 7 (d) shows a reproduced image by one-pixel unit processing using a left-justified pulse. As shown in FIG. 7C, in the two-pixel unit processing according to the present invention, the center of the blackened region is the center (boundary) of the two pixels forming a pair. On the other hand, as shown in FIG.
When a left-justified pulse is used as the pixel unit processing, the center of the blackened region is biased to the left of the pixel. For this reason,
The image of the "character portion" is reproduced at a position slightly shifted to the left with respect to the image determined as the "photo portion". Therefore, in the third embodiment, the left-aligned pulse and the right-aligned pulse are
A centering pulse as shown in FIG. 5C is used. Hereinafter, the configuration and the like will be described.

(System Configuration) FIG. 3 is a block diagram showing an example of a system configuration including an image processing apparatus according to Embodiment 3 of the present invention. This configuration has an image area separation unit 201 as in FIG. 2 described above, and further includes a pulse width conversion unit including a right-aligned pulse generator 108, a left-aligned pulse generator 109, and a center-aligned pulse generator 302 with respect to FIG. Output unit 301
And a pulse switch 303 that switches between three types of pulse signals from the pulse width conversion output unit 301.
Therefore, the other components and their functions are the same as those in FIG. 1, and thus the same reference numerals as in FIG.

(Image Processing Operation) Switching Signal Generator 104
When the image area discrimination signal input from the image area separation unit 201 is a "photograph part", a right-aligned pulse and a left-aligned pulse are alternately selected so as to perform two-pixel unit processing. On the other hand, when the image area discrimination signal is a "character portion", a centering pulse is always selected as shown in FIG.

In the above embodiment, a monochrome image has been described as an example, but the present invention can also be applied to a color image.

[0038]

As described above, according to the image forming apparatus of the present invention (claim 1), the gradation mode can be selected / selected.
When instructed, the output position of the pulse of the continuous pixel in the main scanning direction is alternately switched between right alignment and left alignment. When the resolution mode is selected and instructed, one type of output position of the pulse of each pixel is provided. , The gradation characteristics are stabilized for an image in which the gradation is important, and the image information can be stored well.

Further, according to the image forming apparatus of the present invention (claims 2 and 4), based on the image area discrimination signal output by the image area separating means, in the case of a gradation image, the main scanning direction Since the output position of the pulse of the continuous pixel is switched alternately between right alignment and left alignment, and in the case of the above-mentioned resolution image, the output position of the pulse of each pixel is switched so as to be of one type. It is possible to stabilize the gradation characteristics for an image in which the importance is placed on the image and to store the image information well.

Further, according to the image forming apparatus of the present invention (claims 3 and 4), in the case of a gradation image, the main scanning direction is determined based on the image area discrimination signal output by the image area separating means. In the case of the resolution image, the output position of the pulse of each pixel is alternately switched between right alignment and left alignment, and the output position of the pulse of each pixel is switched to the center alignment. The positional relationship between the image and the image that emphasizes the resolution is matched, and the bias of the image can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a system configuration example including an image processing device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a system configuration example including an image processing device according to a second embodiment of the present invention;

FIG. 3 is a block diagram illustrating a system configuration example including an image processing device according to a third embodiment of the present invention;

FIG. 4 is a block diagram illustrating an internal configuration of an image area separation unit in FIGS. 2 and 3;

FIG. 5 is an explanatory diagram showing right-aligned, left-aligned, and center-aligned pulse signals according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a dot pattern of a two-pixel unit process according to the embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a state of dot blackening.

FIG. 8 is a diagram illustrating two-pixel unit processing according to the embodiment of the present invention;
It is explanatory drawing which shows the example applied to * 2, (a) has shown the priority.

FIG. 9 is an explanatory diagram showing a conventional beam spot and exposure energy distribution.

FIG. 10 is an explanatory diagram showing a dot pattern for each exposure time in the related art.

FIG. 11 is an explanatory diagram showing an example of expressing a density in a binary pixel multi-value method as used in a photograph mode.

FIG. 12 is a diagram for explaining a main pattern in the related art.

[Explanation of symbols]

 Reference Signs List 101 scanner 102 pulse width conversion output unit 103 pulse switching unit 104 switching signal generator 105 LD driver 106 imaging unit 107 operation unit 201 image area separation unit 401 edge detection unit 402 halftone dot detection unit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C262 AA24 AA26 AA27 AB07 AC11 BB14 BB20 BB44 DA03 EA02 EA08 EA16 2H027 DB01 EB01 FA30 5C077 LL19 MP02 MP05 MP06 MP07 NN17 PP27 PP28 PP47 PQ04 PQ05 PQ08 TT03

Claims (4)

[Claims] 1. An image forming apparatus for inputting image data of a character / photo to be imaged or an image in which these are mixed, and outputting multi-valued to the input image data by pulse width modulation to form a digital image. At least an image quality mode selecting means for selecting and indicating an image quality mode corresponding to a tone mode for improving the tone and a resolution mode for improving the resolution; and a pulse width for inputting the image data of the target pixel. To
Pulse width conversion output means for outputting at least two types of positions for outputting a pulse for each pixel, right-justified and left-justified; and main scanning when the gradation mode is selected and designated by the image quality mode selecting means. A pulse switch that alternately switches the output position of the pulse of the pixel continuous in the direction between right alignment and left alignment, and switches the output position of the pulse of each pixel to one type when the resolution mode is selected and instructed. And an image forming apparatus. 2. An image forming apparatus for inputting image data of a character / photo to be imaged or an image in which these are mixed and outputting multi-values to the input image data by pulse width modulation to form a digital image. At least, an image area separating unit that separates an area between a gradation image and a resolution image and outputs an image area determination signal, and converts the input image data of the target pixel into a pulse width,
A pulse width conversion output unit that outputs at least two types of right-aligned and left-aligned positions for outputting a pulse for each pixel; and a case of a gradation image based on an image area determination signal output by the image area separation unit. A pulse switching means for alternately switching the output position of the pulse of a pixel continuous in the main scanning direction between right alignment and left alignment, and switching the output position of the pulse of each pixel to one type in the case of the resolution image. An image forming apparatus comprising: 3. An image forming apparatus for inputting image data of a character / photo to be imaged or an image in which these are mixed, and outputting multi-values to the input image data by pulse width modulation to form a digital image. At least, an image area separating unit that separates an area between a gradation image and a resolution image and outputs an image area determination signal, and converts the input image data of the target pixel into a pulse width,
A pulse width conversion output unit that outputs at least three types of positions for outputting a pulse for each pixel, that is, right alignment, left alignment, and center alignment; and a gradation characteristic based on an image area determination signal output by the image area separation unit. In the case of an image, a pulse switching unit that alternately switches the output position of a pulse of a continuous pixel in the main scanning direction between right alignment and left alignment, and in the case of the resolution image, switches the output position of a pulse of each pixel to center alignment. An image forming apparatus comprising: 4. The apparatus according to claim 2, wherein said image area separating means includes an edge detecting means for detecting an edge of a character or a line drawing and a halftone detecting means for detecting a halftone dot of a printed document. Or the image forming apparatus according to 3.