JP2001169099A - Picture reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a picture reproducing device improving the quality of a character by executing an optimum processing at every area in an original. SOLUTION: A digital picture data from a picture input device 1 is edge- emphasized in an edge emphasis filtering circuit 2 and a smoothing filtering circuit 3 executes smoothing. An 1×1 multivalue dither processing circuit 4 executes an edge area multivalue dither processing (1) and a 2×1 multivalue dither processing circuit 5 executes a non-edge area multivalue dither processing (2). A selection circuit 6 receives the control signal of image area separation and selects the signal of a different halftone processing in edge area/non-edge area. An image area separation circuit 7 judges whether a noticed pixel is the edge area or the non-edge area. A boundary pixel detection part 8 detects a boundary pixel by using an image area separation result. A printer 9 receives a signal from the selection circuit 6 or the signal of the boundary pixel or not and reproduces the picture where the occurrence of a white stripe in a switch part is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image reproducing apparatus, and more particularly to an image reproducing apparatus applied to a color digital copying machine, a color facsimile, and the like.

[0002]

2. Description of the Related Art Conventionally, an image reproducing apparatus generally inputs a document using a device such as a scanner and reproduces an image using a device such as a printer using image data subjected to predetermined image processing. Further, as another application destination, an apparatus having a function of processing and outputting color image data obtained via a network is also included.

In a conventional digital copying machine, for example, based on a technique called image area separation, gradation processing such as filtering processing for a character edge portion and a non-character edge portion, gamma conversion processing, and dither screen processing are performed. An image reproducing apparatus for improving the character image quality by adaptively switching and executing the image processing is provided (see the paper "Image Area Separation Method for Character / Pattern (Dot, Photo) Mixed Image)".
(Transactions of the Institute of Electronics, Information and Communication Engineers, Vol.J-75-D-II No.1 pp39-47
(See January 1992), a color image reproducing apparatus disclosed in JP-A-03-089677, and the like.

[0004] Although the character image quality is dramatically improved by the above-described method (mechanism), there is a problem that a white streak appears inside the character due to a printer or screen processing inside the character. Processing is taken. The printer used here is capable of writing multi-valued data and has a resolution of about 400 dpi to 600 dpi such that each pixel has a fixed left phase (or fixed right phase) and a color material such as toner is sequentially embedded. Assume a photographic printer.

FIG. 8 shows an example in which writing is performed by left phase control, and shows how toner increases from the left side by pulse width modulation or the like. Then, the printer having such a writing mechanism switches the screen between the character edge area and the non-character edge area. In this case, in the above-described conventional apparatus, the character edge region is a region expanded from the actual character edge (solid line in FIG. 9) to the character background (dashed line a in FIG. 9). This is a region that has been expanded up to the point (broken line B in FIG. 9).

FIG. 10 shows an example of a conventional 2 × 1 dither table. For example, in a character edge region, a multivalued dither of 1 × 1 pixel is used, and in a non-character edge region, 2 (main) ×
Multilevel dither of one (sub) pixel is used. The dither here refers to a dither table in which one pixel as shown in FIG. 10 is filled, and then the other pixel starts to be filled.

Japanese Patent Application Laid-Open No. 3-89677 is a prior art example 1 similar to the present invention in the technical field. The content of the first conventional example is to improve the character image quality by detecting a character edge portion using an image area separation technique, and adaptively switching gradation processing such as filter processing, gamma processing, and screen processing in the same part. It is an example of a device. The technical point of this conventional example is to ensure the determination accuracy even at the time of zooming.

[0008]

However, in the above-mentioned prior art, when the above-described multi-valued dither is used, white streaks (white spots) may still occur inside characters. FIG.
FIG. 10 is a diagram for explaining a conventional “white spot inside a character”.

FIG. 11 is a schematic diagram of a case where a character having a width of 4 pixels extending in the sub-scanning direction is formed into a character edge area of one pixel for simplification of description and reproduced at half the density. In this case, there is a problem that white spots are more conspicuous in a printer that reproduces images with less toner dust and high resolution.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image reproducing apparatus which improves character image quality by performing optimal processing for each area in a document.

More specifically, a first object of the present invention is to switch the screen processing to a character edge portion and other regions by using image area separation and reproduce the same, and to generate white streaks in the switching portion. It is an object of the present invention to provide an image reproducing apparatus for suppressing the above.

A second object of the present invention is to provide a method for suppressing the occurrence of defects in other parts of an image depending on the separation performance of image area separation when the writing phase for pixels in the same area is made particularly random as specific suppression means. I do. Accordingly, an object of the present invention is to provide an image reproducing apparatus that performs processing for suppressing white streak generation only within a character (high density portion).

[0013]

According to a first aspect of the present invention, there is provided an image separating apparatus for determining a character edge area / non-character edge area with respect to digital image data; At least 2 for image data
Image data processing means for performing predetermined kinds of processing, and selecting means for selecting any one of at least two types of image data processed by the image data processing means based on the determination result of the image area separating means. It is characterized by comprising.

According to a second aspect of the present invention, in the first aspect of the present invention, the image reproducing apparatus has a boundary pixel detecting means for detecting a boundary pixel by using a determination result of the image area separating means. Is characterized in that the writing phase at the boundary is controlled to be different from that of the other parts.

According to a third aspect of the present invention, in the second aspect, the detection of the boundary pixel is based on a determination as to whether the target pixel is an edge area or a non-edge area.

According to a fourth aspect of the present invention, in the third aspect, it is characterized in that it is determined whether the edge area is a character edge or a non-character edge.

The invention according to claim 5 is the invention according to claim 3 or 4.
In the described invention, the edge area is a character edge area /
It is characterized in that it is determined whether the area is a non-character edge area and further whether it is inside a character.

According to a sixth aspect of the present invention, in the invention of any of the second to fifth aspects, the image reproducing apparatus performs white / black determination for determining white / black inside the character with respect to the digital image data. Means for controlling the phase only in the high density portion inside the character.

According to a seventh aspect of the present invention, in the invention according to any one of the second to sixth aspects, when the process is switched based on the information on the area, the writing phase at the boundary of the area inside the character is changed to another part. It is characterized in that it is controlled so as to be different from.

According to an eighth aspect of the present invention, in any one of the second to seventh aspects, the writing phase at the boundary is randomly controlled.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an image reproducing apparatus according to the present invention will be described in detail with reference to the accompanying drawings. Referring to FIGS. 1 to 7, there is shown an embodiment of an image reproducing apparatus according to the present invention.

FIG. 1 is a block diagram showing an image reproducing apparatus according to a first embodiment of the present invention. FIG. 2 shows a processing example of the edge enhancement filter. FIG. 3 shows a processing example of the smoothing filter. FIG. 4 shows a processing example of a mask for detecting a pixel corresponding to a boundary. FIGS. 5 and 6 show the effects of the image reproducing apparatus according to the embodiment of the present invention. FIG. 7 is a block diagram showing an image reproducing apparatus according to a second embodiment of the present invention. FIG. 8 is a diagram illustrating left phase control.

<First Embodiment> Hereinafter, a first embodiment of the present invention will be described in detail. FIG. 1 is a processing block diagram of the image reproducing apparatus according to the first embodiment of the present invention.
In FIG. 1, an image reproducing apparatus according to a first embodiment of the present invention includes an image input apparatus (hereinafter, referred to as a scanner) 1 such as a scanner, and an edge emphasis filtering circuit that performs edge emphasis by a filter process called convolution. 2, a smoothing filtering circuit 3 for similarly performing smoothing, and a 1 × 1 multi-value for performing a multi-value dither process (1) for an edge region using a table or the like (however, since it is a 1 × 1 dither, it is actually a primary conversion). The dither processing circuit 4 performs multi-value dither processing (2) for non-edge areas using a table or the like 2
A × 1 multi-level dither processing circuit 5 and a selection circuit 6 which receives a control signal for image area separation and selects a signal of halftone processing 1 in an edge area, and selects a signal of halftone processing 2 in a non-edge area
An image area separation circuit 7 for determining whether the pixel of interest is an edge area or a non-edge area, a boundary pixel detection unit 8 for detecting a boundary pixel using the image area separation result, and a selection circuit 6 And a printer 9 which is an image output device that reproduces an image by receiving a signal indicating whether the pixel is a boundary pixel or not.

Next, the outline of the first embodiment of the present invention shown in FIG. 1 will be described. An original (not shown) is read by the scanner 1 and density data (400 dpi in this case) is read.
8 bits) is output. The output signal is input to the edge enhancement filtering circuit 2, the smoothing filtering circuit 3, and the image area separation circuit 7. The edge emphasis filtering circuit 2 is a process for a character edge region, and is a process performed to correct "drow" of a character edge.
Specific filter coefficients are shown in FIG.

On the other hand, the smoothing filtering circuit 3 is a process for a non-character edge region, and is particularly a process for suppressing the occurrence of moire in a halftone dot pattern and for preserving the gradation of the pattern. FIG. 3 shows various filter coefficients. FIG. 4 is a processing example of a mask for detecting a pixel corresponding to a boundary, in which pixel “0” is a character edge and pixels “1” to “1”.
Indicates that at least one of “8” is a non-character edge.

Further, the multi-valued dither processing circuit (1 × 1 multi-valued dither) 4 has a shape slightly higher than a linear gamma curve (particularly shown in the figure) in order to preserve the resolution of character edges. Preparing the conversion table in (1) will provide a preferable image.

On the other hand, the multi-value dither processing circuit (2 × 1 multi-value dither) 5 for the non-character edge area is a dither process as shown in FIGS. 5 and 6, for example. This process emphasizes the preservation of gradation.

The selection circuit 6 receives an area signal from an image area separation circuit 7 to be described later, and outputs an output signal from the 1 × 1 multi-valued dither processing circuit 4 if it is a character edge area, or an output signal from the non-character edge area if it is a non-character edge area. An output signal from the 2 × 1 multi-level dither processing circuit 5 is selected.

The image area separating circuit 7 is a processing block for detecting a character edge area in a picture. For the purpose of explanation, here is the paper, "Image Area Separation Method for Mixed Images of Text / Pattern (Dot, Photo)" (Transactions of the Institute of Electronics, Information and Communication Engineers, Vol.J-75-D- II N
o.1 pp39-47 / see January 1992).

In the method described above, the inside of a character that is somewhat thick becomes a non-character edge region, and a cross section of a certain character is divided into regions such as a character edge, a non-character edge, and a character edge. The boundary pixel detection unit 8 activates the target pixel as a boundary pixel when the target pixel is a character edge pixel and at least one non-edge pixel exists around the target pixel. This mask is shown in FIG.

The printer 9 reproduces an image using an image reproduction signal from the selection circuit 6 and a signal for controlling a writing phase. First, the printer used here is capable of 1-dot multi-level writing (256 gradations), and when writing in a pulse width modulation manner, the right phase that fills from the right, and conversely the left phase It is assumed that write control of a left phase that can be filled from the beginning can be performed.

Here, two methods will be described as specific examples of the conventional method for suppressing white spots in characters. When writing is performed by random phase control at the first boundary pixel, a result as shown in FIG. 5 is obtained with respect to the result of not performing phase control, and the white spots inside the character are less noticeable. Is obtained.

Further, when writing is performed at the second boundary pixel by alternately controlling the left and right phases depending on the position of the sub-scan, the result of not performing the phase control is shown in FIG.
Is obtained, and an effect is obtained that, as described above, white spots inside the character become less noticeable.

<Second Embodiment> FIG. 7 shows a second embodiment of the present invention.
It is a processing block diagram of the image reproducing device which is the embodiment of FIG. In FIG. 7, the image reproducing apparatus according to the second embodiment of the present invention is different from the first embodiment in that a black / white determining unit 10 is added.

In the above-described first embodiment, the control is performed on the boundary pixels between the character edge region and the non-character edge region. On the other hand, in the second embodiment of the present invention, the control is performed. Performing this processing only in a high density area inside a character is effective in that no problem occurs in other parts. In particular, in the case of performing the random control of the phase, the random processing does not always cause a defect (abnormal) image in a normal picture, depending on the separation performance. Therefore, as shown in FIG. 7, a black / white determination unit 10 is provided, and the phase control is performed only on the inside of the character, that is, only on the high density portion. In this way, even if the phase control (especially random) is performed in areas other than the character edge area due to the erroneous determination of the area separation, the area is relatively insensitive to the picture area of the high density part. A trade-off problem caused by performing the control is suppressed.

It should be noted that the black / white determination unit 10 can easily make a determination by preparing an appropriate threshold and comparing it. A condition for determining a boundary pixel is that a black pixel is A
What is necessary is just to add by an ND command.

In the first embodiment of the present invention, only the phase of the character edge pixels at the boundary is controlled, but the non-character edge pixels at the boundary, that is, the picture pixels are controlled.
Similar effects can be expected.

In order to detect a non-character edge pixel at the boundary, in a 3 × 3 mask, if the center pixel is a non-edge pixel and there is at least one character edge pixel in the periphery,
It is only necessary to activate the center pixel.

Further, in the present invention, the method of writing the phase has been described by switching between the right phase and the left phase. However, if the printer can also perform medium phase control such as increasing from the center to the periphery, the boundary may be written. The same effect can be expected when the writing method is used for the character edge pixels and the non-character edge pixels of the part, and the writing method is performed in the other part, for example, from the left phase.

In the outline of the above embodiment, the image is reproduced by switching the screen between the character edge portion and the other region using the image area separation technique. For example, 1 × 1 dither processing is used in the former area, and 2 × 1 dither processing is used in the latter area.

Further, it is assumed that the present apparatus performs writing in a pulse width modulation manner, for example, it is possible to control writing from the right / writing from the left. Then, for a pixel belonging to the separation boundary, for example, in FIG. 9, (a) random write phase and (b) write phase control based on position information are performed.

In an apparatus for generating an output image from image data, an image area separation technique for separating a character edge area / non-character edge area is used. By providing a mechanism for suppressing missing characters, the aim is to further improve the character image quality. Furthermore, the above-mentioned mechanism can be implemented with good cost performance.

[0043]

As is apparent from the above description, the image reproducing apparatus of the present invention determines a character edge area / non-character edge area for digital image data, and determines at least two types of digital image data. Is performed, and one of at least two types of image data after the processing is selected based on the determination result. Therefore, when the screen processing is switched and reproduced for the character edge portion and the other region using the image area separation, the writing control (for example, pulse width modulation) of the pixel corresponding to the separation boundary portion is performed. By doing so, generation of white streaks (white spots) in the switching unit can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an image reproducing apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating filter coefficients illustrating an example of processing of an edge enhancement filter.

FIG. 3 is a diagram illustrating filter coefficients illustrating a processing example of a smoothing filter.

FIG. 4 shows a processing example of a mask for detecting a pixel corresponding to a boundary.

FIG. 5 shows an effect example 1 by dither processing.

FIG. 6 shows an effect example 2 by dither processing.

FIG. 7 is a block diagram showing an image reproducing apparatus according to a second embodiment of the present invention.

FIG. 8 is a diagram illustrating “left phase control”.

FIG. 9 is a diagram illustrating an example of a conventional character edge processing.

FIG. 10 shows an example of a conventional 2 × 1 dither table.

FIG. 11 is a diagram illustrating a white spot in a conventional character.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image input device 2 edge enhancement filtering circuit 3 smoothing filtering circuit 4 1 × 1 multi-value dither processing circuit 5 2 × 1 multi-value dither processing circuit 6 selection circuit 7 image area separation circuit 8 boundary pixel detection unit 9 printer 10 black / White judgment section

Claims (8)

[Claims] An image area separating unit configured to determine a character edge area / non-character edge area with respect to digital image data; and an image data processing unit configured to perform at least two types of predetermined processing on the digital image data. And selecting means for selecting any of at least two types of image data processed by the image data processing means based on the determination result of the image area separating means. Playback device. 2. The image reproducing apparatus according to claim 1, further comprising: a boundary pixel detecting unit configured to detect a boundary pixel by using a determination result of the image area separating unit. 2. The image reproducing apparatus according to claim 1, wherein the control is performed as follows. 3. The image reproducing apparatus according to claim 2, wherein the detection of the boundary pixel is based on whether the target pixel is an edge area or a non-edge area. 4. The apparatus according to claim 3, wherein the edge area is determined to be a character edge / non-character edge. 5. A determination as to whether the edge area is a character edge area / non-character edge area,
The image reproducing apparatus according to claim 3, further comprising determining whether the character is inside a character. 6. The image reproducing apparatus according to claim 1, further comprising a white / black determining unit for determining white / black inside the character with respect to the digital image data, and controlling the phase only in a high density portion inside the character. The image reproduction device according to claim 2, wherein the image reproduction is performed. 7. The switching of the processing based on the information of the area, wherein a writing phase at a boundary of the area inside the character is controlled to be different from other phases.
7. The image reproducing apparatus according to any one of claims 1 to 6, 8. The image reproducing apparatus according to claim 2, wherein a writing phase at the boundary is controlled at random.