JPH03219774A - Picture processor - Google Patents

Abstract

PURPOSE:To obtain an optical processing signal by selecting respectively an output signal of a photographic area processing section when an input picture is a photographic area, an output signal of a dot area processing section when an input picture is a dot area, and an output signal of a wire frame area processing section when an input picture is a wire frame area. CONSTITUTION:An area separation circuit 5 separates each picture element of an input picture into a wire frame area, a dot or a photograph and outputs the result of separation of each picture element to a picture signal selection circuit 6. The circuit 6 based on the result of area separation sent from the circuit 5 selects and outputs an output signal of a binarizing processing circuit 2 in the case of a wire frame, an output signal of a mean error minimum processing circuit 3 in the case of a dot area and an output signal of a dither processing circuit 4 in the case of a photographic area respectively. Thus, a picture signal applied with the optimum processing in response to each area of photograph, dot and wire frame in the input picture is outputted from the circuit 6. The picture signal outputted from the circuit 6 is used to reproduce the picture, then the gradation is emphasized as to the photograph, moire is eliminated and the gradation is emphasized as to the dot picture.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image processing device for optimally processing and reproducing an image containing a mixture of photographs, halftone dots, and line drawings for each region.

[Conventional technology]

In general, an image called a document image usually includes a mixture of continuous tone photographs, black and white dots, and line drawings such as characters and lines. When playing back such images using a digital copying machine or facsimile, in order to improve the quality of the reproduced image, ■ For line drawings, reproduce them clearly so that the lines are not cut off ■ For photographs: , Reproducing with emphasis on smoothness (gradation) ■ Regarding halftone dots, it is desirable to remove moiré and reproduce with emphasis on gradation.

One method for achieving the above objective is, for example, to perform the following image processing. That is, (1) Binarization processing is applied to the line drawing area after edge enhancement.

■ A spiral dithering process, which is one of systematic dithering methods, is applied to the photographic area.

■ For the halftone dot area, after the smoothing process, perform the same spiral dither process as in ■.

[Problem to be solved by the invention]

By the way, in order to implement the above method, it is necessary to separate all the pixels of the input image into a photo area, a halftone area, and a line drawing area. However, with regard to character separation, most conventional methods target characters on a white background with nothing in the background, and it is difficult to accurately separate characters existing on halftone dots. Therefore, the adaptive processing described above is not applied to characters existing on the halftone dots, resulting in a problem that the reproduced image becomes unclear.

On the other hand, one method of performing image processing without segmenting the input image as described above is to distribute the error between the image information of the pixel of interest and the image information of the pixel of interest after dither processing to surrounding pixels. There is a method using the so-called minimum average error method, which performs dither processing, or an error diffusion method similar to this method.

This method is characterized in that a reproduced image of a certain level can be obtained without segmenting the input image, and the characters on the halftone dots are easier to see than the region separation method, but on the other hand, the white There has been a problem in that the sharpness (resolution) of characters on the ground, especially small characters on a white background, is insufficient.

In addition, when using the conventional area separation method described above, the halftone dots are subjected to spiral dither processing after smoothing processing, but halftone dot images with a low number of lines (for example, 65 lines or 85 lines)
In the case of lines), the distance between the halftone dots is wide, so the fixed smoothing filter of about 3 x 3 pixels or 5 x 5 pixels, which is used conventionally, cannot sufficiently smooth the image, and it may not be possible to completely remove moiré. There were also problems that occurred.

The present invention has been made based on the above circumstances, and its purpose is to make line drawings such as characters and lines clear regardless of whether they are on a white background or halftone dots, and to emphasize gradation in photographs. Regarding halftone dots, it is an object of the present invention to provide an image processing device that can adaptively reproduce images by removing moiré and emphasizing gradation. Still another object of the present invention is to provide an image processing device that can adaptively change processing between halftone dots with a high number of lines and halftone dots with a low number of lines, and remove moiré regardless of the number of lines of the halftone dots.

[Means to solve the problem]

In order to achieve the above object, a first image processing device of the present invention includes means for converting an input image into a digital multi-value image signal, and photographic area processing for performing systematic dither processing on the converted digital multi-value image signal. , a halftone area processing section that performs dither processing on the converted digital multi-value image signal using the minimum average error method or error diffusion method, and a line that performs binarization processing on the converted digital multi-value image signal! an area processing unit;
Based on pixel information within a predetermined local area of the converted digital multilevel image signal, each pixel in the input image is converted into a photo area,
an area separation unit that separates into either a halftone area or a line drawing area; and a processing signal of one of the photographic area processing unit, halftone area processing unit, or line drawing area processing unit is selected according to the separation result of the area separation unit. and an image signal selection section that outputs the image signal.

Further, a second image processing device of the present invention further simplifies the configuration of the first image processing device by separating the input image into two areas, a line drawing area and a pattern area other than line drawings,
means for converting an input image into a digital multivalued image signal;
a picture area processing section that performs dither processing using the minimum average error method or error diffusion method on the converted digital multi-value image signal; a line drawing area processing section that performs binarization processing on the converted digital multi-value image signal; an area separation unit that separates each pixel in the input image into a line drawing area and other picture areas based on pixel information in a predetermined local area of the digital multilevel image signal; and an image signal selection section that selects and outputs a processed signal from either the picture area processing section or the line drawing area processing section.

Furthermore, the third image processing device of the present invention is configured to change the processing content between halftone dots with a high number of lines and halftone dots with a low number of lines, and converts an input image into a digital multivalued image signal. an image converting means, a line drawing/low line number halftone area processing unit that performs binarization processing on the converted digital multi-value image signal, and a photo/high-resolution image processing unit that performs systematic dither processing on the converted digital multi-value image signal. A line number halftone area processing unit separates each pixel in the input image into either a photo area, a halftone area, or a line drawing area based on pixel information of a predetermined local area of the converted digital multilevel image signal. an area separation unit, a dot number determination unit that determines the number of dots in a halftone area in an input image from the converted digital multivalued image signal, and a determination result of the dot number determination unit and the area separation unit. a comprehensive determination section that determines the processing signal to be selected based on the region separation result; and a comprehensive determination section that determines the processing signal to be selected based on the region separation result; and an image signal selection section that selects and outputs one of the processed signals.

The halftone line number determining unit detects pixels corresponding to peaks and valley peaks of halftone dots based on pixel information of a predetermined local area of the digital multilevel image signal,
The number of pixels corresponding to a mountain peak and the number of pixels corresponding to a valley peak in a predetermined small area may be counted, and the number of halftone dots may be determined based on the larger of the two counts.

[For production]

In the case of the first image processing device, each pixel of the input image is separated into one of a photo area, a halftone area, and a line drawing area by the area separation unit. According to this separation result, the image signal selection section selects the output signal of the photo area processing section when the input image is a photo area, the output signal of the halftone area processing section when the input image is a halftone area, and the output signal of the halftone area processing section when the input image is a halftone area. In this case, the output signals of the line drawing area processing sections are selected and outputted.

Therefore, even if photographs, halftone dots, and line drawings are mixed in an image, it is possible to adaptively select and output the optimal processing signal according to each area of the photograph, halftone dots, and line drawings, and to output text and line drawings. It is possible to reproduce images with sharpness for line drawings such as images, emphasis on gradation for photographs, and removal of moiré and emphasis on gradation for halftone dots. Moreover, even if the characters on the halftone dots are separated as halftone dots, the output signal of the halftone area processing section that has been dithered using the minimum average error method or the error diffusion method is selected, so the characters on the halftone dots can also be separated. The image is sharpened to a certain level, and the characters on the halftone dots do not become blurred as in the past, and the image can be reproduced clearly regardless of whether it is on a white background or on the halftone dots.

In the case of the second image processing device, each pixel of the input image is separated by the region separation unit into two regions: a line drawing region and a picture region consisting of other halftone dots and photographs.

According to this separation result, the image signal selection section selects and outputs the processed signal of the line drawing area processing section when the input image is a line drawing area, and the processing signal of the picture area processing section when the input image is a picture area. . As a result, for the picture area, that is, the halftone dots (including characters on the halftone dots) and the photograph, the image signal processed by the picture area processing section by the minimum average error method or the error diffusion method, and for the line drawing area, the image signal is processed by the line drawing An image signal sharpened by a dedicated line drawing area processing section is selected and output. Therefore, compared to the first image processing device, it is possible to achieve optimal image reproduction according to the image area while simplifying the circuit configuration.

In the case of the third image processing device, each pixel of the input image is separated into one of a photo area, a halftone dot area, and a line drawing area in the area separation unit, and the number of halftone dots in the input image is determined by the number of halftone dots. It is determined in the determination section. Then, the general judgment unit determines the processing signal to be selected based on the area separation result and the halftone dot number judgment result, and for line drawings and halftone dots with low line number, the line drawing/low line number halftone dot area processing unit determines the processing signal to be selected. The processed image signal is selectively outputted, and for photographs and high-line-number halftone dots, the image signal processed by the photograph/high-line-number halftone area processing section is selectively output. Therefore, processing can be adaptively changed between halftone dots with a high number of lines and halftone dots with a low number of lines, and moiré can be removed regardless of the number of lines of the halftone dots.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

A first embodiment of the invention is shown in FIG. This first embodiment corresponds to the first image processing apparatus described above. In order to simplify the explanation, an example will be described in which the reproduced image is a monochrome value image. If the reproduced image is in color, the image processing described below may be performed in parallel on each of the color signals YMC after color separation and color correction of the original image, and finally, the respective results may be combined.

In FIG. 1, the input image signal is a means for converting an original image into a digital multivalued image signal, for example, 400 dpi.

This is a digital multivalued image signal obtained by reading an original image using a scanner with approximately 64 gradations.

The sharpening processing circuit 1 is a circuit that enhances the edges of an input digital multivalued image signal. The binarization processing circuit 2 is a circuit that binarizes the image signal whose edges have been enhanced by the sharpening processing circuit 1 using a predetermined darkness value. The sharpening processing circuit 1 and the binarization processing circuit 2 constitute a line drawing area processing section. In addition, as the sharpening processing circuit 1, for example, the following (1
) is used as an MTF correction filter.

That is, as shown in FIG.
y, and the output image signal is gx+y, the dark values TX and V for binarization are determined by the following equation (2).

The minimum average error processing circuit 3 is a circuit that performs dither processing using the minimum average error method on the input digital multivalued image signal. This average error minimum processing circuit 3 constitutes a halftone area processing section.

The minimum average error method is to determine the darkness value for each pixel position for binarization so that the density error between the original image and the binarized dot image is minimized on average, and then calculate the density value according to this darkness value. This is a method of binarizing a digital multivalued image signal.

(2) Here, αa, 1 is a weighting coefficient, and ek, L is a density error between the input image signal and the output image signal. The weighting coefficients .alpha., . . . are given, for example, as a matrix as shown in equation (3) below, and pixels close to the currently focused pixel 'XIF are given the greatest weighting.

However, * is the pixel of interest fX+V. The dither processing circuit 4 is a circuit that performs systematic dither processing such as spiral dither suitable for photography.

This dither processing circuit 4 constitutes a photographic area processing section.

As will be described later, the area separation circuit 5 separates each pixel in the input image into one of a photo area, a halftone area, and a line drawing area based on pixel information within a predetermined local area of the digital multilevel image signal. It is a circuit.

The image signal selection circuit 6 is a circuit that selects and outputs the output signal of either the binarization processing circuit 2, the average error minimum processing circuit 3, or the dither processing circuit 4 according to the separation result of the region separation circuit 5.

To explain the operation of the first embodiment, a digital multivalued image signal is input to a region separation circuit 5, a sharpening processing circuit 1, an average error minimum processing circuit 3, and a dither processing circuit 4, respectively.

The digital multi-level image signal input to the sharpening processing circuit 1 is subjected to edge and edge enhancement in the sharpening processing circuit 1, and then binarized in the binarization processing circuit 2 to remove characters, lines, etc. in the input image. It is output as an image signal with the line drawing portion sharpened.

The digital multilevel image signal input to the average error minimum processing circuit 3 is binarized by the above-mentioned average error minimum method, and moiré is generated for halftone dots in the input image and characters (including lines) on the halftone dots. It is output as an image signal that has been removed and subjected to gradation processing.

Further, the digital multi-valued image signal input to the dither processing circuit 4 is binarized by a spiral dither suitable for photographs, and is output as an image signal in which the photographic portion of the input image is converted into a gray scale.

On the other hand, the area separation circuit 5 separates each pixel of the input image into either a line drawing area, a halftone area, or a photograph, as will be described later, and outputs the separation result of each pixel to the image signal selection circuit 6.

Based on the region separation results sent from the region separation circuit 5, the image signal selection circuit 6 selects the output signal of the binarization processing circuit 2 in the case of a line drawing region, and selects the minimum average error in the case of a halftone region. The output signal of the processing circuit 3 or, in the case of a photographic area, the output signal of the dither processing circuit 4 is selected and output.

Therefore, the image signal selection circuit 6 outputs an image signal that has been optimally processed according to each area of the photograph, halftone dot, and line drawing in the input image. If an image is reproduced using the image signal output from the image signal selection circuit 6, not only characters on a white background but also characters existing on halftone dots will be made clearer, and the gradation of photographs will be improved. With regard to halftone dots, moiré is removed and an image is reproduced with emphasis on gradation.

A specific example of the configuration of the area separation circuit 5 in FIG. 1 is shown in FIG. In the figure, 501 is a photo area separation circuit that separates each pixel in the input image into a photo area and a non-photo area, and 502 is a halftone area separation circuit that separates each pixel in the input image into a halftone area and a non-halftone area. It is a circuit.

In order to separate each pixel in the input image into three areas: photo, halftone dot, and line drawing, the two circuits 501 and 502 first separate each pixel in the input image into the photo area and the halftone area. Then, an AND logic is applied between the image area determined to be a non-photo area by the photo area separation circuit 501 and the image area determined to be a non-halftone area by the halftone area separation circuit 502, and the non-photo area is An image area that is large and determined to be a non-halftone area may be set as a line drawing area.

As the photographic area separation circuit 501 in FIG. 3, for example, the circuit disclosed in Japanese Patent Application Laid-Open No. 61-225974 can be used. Further, as the halftone dot area separation circuit 5.2, for example, a circuit as shown in FIG. 4 can be adopted.

The halftone area separation circuit 502 shown in FIG. 4 will be explained below.

The pole detection unit 503 is a circuit that detects peak or valley pixels (hereinafter referred to as "peak pixels") that form halftone dots. For example, if we take the case of detecting mountain peak pixels,
Using a mask with a size of 3 x 3 pixels as shown in FIG. Lc is detected as a mountain peak pixel. Note that in order to detect the valley peak pixel, the direction of the second inequality sign (4) may be reversed.

However, TI (1 is the dark value halftone dot candidate region detecting section 504 detects pixels that become the halftone dot candidate region based on the peak pixels of the peaks and valleys detected by the above-mentioned extreme point detecting section 503. Figure 6 (al
As shown in , when processing in units of blocks, the peak pixel counts of peaks and valleys in the block of interest are counted, and when the total is greater than a predetermined darkness value, the number of pixels in the block of interest is counted. All pixels (hatched pixels) are detected as a halftone dot candidate area. Further, as shown in FIG. 6(b), when processing is performed pixel by pixel, when the total number of peak pixels of peaks and valleys in the block of interest is larger than a predetermined darkness value, the block of interest A pixel of interest (hatched pixel) within the block is detected as a halftone dot candidate area.

The halftone dot area determination unit 505 includes the halftone dot candidate area detection unit 50.
Based on the detection result of step 4, it is finally determined whether each pixel is a halftone dot area or not. That is, as shown in FIG. 7(a), when processing is performed in units of broncs, the number of halftone dot candidate blocks in the block of interest and a predetermined plurality of blocks around it is counted, and this number is determined in advance. When the number is larger than a predetermined number, all pixels (hatched pixels) in the block of interest are determined to be a halftone dot area.

On the other hand, as shown in FIG. 7(b), when processing is performed pixel by pixel, the number of halftone dot candidate pixels in surrounding pixels within a predetermined range including the pixel of interest is counted, and this number When the number is larger than a predetermined number, the pixel of interest (hatched pixel) is determined to be a halftone dot area.

By performing each of the above-described processes on all pixels of the input image, all pixels can be separated into halftone areas and non-halftone areas. Therefore, if the area separation circuit shown in FIG. 3 is constructed using the halftone area separation circuit shown in FIG. 4, each pixel in the input image can be separated into three areas: photo, halftone, and line drawing. can.

A second embodiment of the invention is shown in FIG. This second embodiment corresponds to the second image processing device described above, in which the halftone dots and the photograph are combined into one picture area, and the input image is divided into two areas: this picture area and the line drawing area. By performing this processing, the circuit configuration of the first embodiment is further simplified.

In FIG. 8, the average error minimum processing circuit 3 used in FIG. 1 is used as a picture area processing section for processing a picture area consisting of halftone dots and photographs. As previously mentioned,
When using the minimum average error method or the error diffusion method, it is possible to obtain reproduced images at a constant level for photographs, halftone dots, characters on halftone dots, etc., excluding characters on a white background (including lines).

Therefore, the halftone dots and the photograph in the input image are combined into one picture area, and this picture area is used by the average error minimum processing circuit 3.
Even if the processing is performed all at once, the same processing effect as in the first embodiment can be obtained.

In the case of the example shown in FIG. 8, the area separation circuit 5' needs to separate all pixels of the input image into two areas, a line drawing area and a picture area, but to realize this, a circuit as shown in FIG. Just adopt it. The area separation circuit of FIG. 9 has the same circuit configuration as the area separation circuit 5 of FIG.
The photographic area judgment output of 01 and the halftone area judgment output of the halftone area separation circuit 502 are ORed, and this logical result (=
The photographic area (10 halftone dot area) is determined as a picture area.

According to the separation result of the area separation circuit 5, the image signal selection circuit 6 selects the output signal of the binarization processing circuit 2 when the separation result is a line drawing area, and selects the minimum average error when the judgment result is a picture area. The output signals of the processing circuit 3 are selected and outputted. Therefore, it is possible to obtain optimal reproduced images according to the two areas of line drawing and picture.

In the embodiments shown in FIGS. 1 and 8, the minimum average error method is used in the halftone area processing section and the pattern area processing section, but an error diffusion method may be used instead. It is something.

A third embodiment of the invention is shown in FIG. This third embodiment corresponds to the third image processing device described above,
Line drawings such as characters and halftone dots with a low number of lines (e.g. 85 lines or less)
are combined into one line drawing/low line number halftone dot area, and a photograph and high line number halftone dots (for example, 100 lines or more) are combined into one as a photograph/high line number halftone dot area, and input. By separating the image into these two areas and processing them, moiré can be removed regardless of the number of halftone dots.

In FIG. 10, a region separation circuit 5 is a circuit that separates all pixels in an input image into three regions: line drawing, photograph, and halftone dot. As the region separation circuit 5, the region separation circuit 5 used in FIG. 1 can be used.

The line drawing/low line number halftone area processing section is a circuit for performing image processing suitable for line drawing areas such as characters and low line number halftone dot areas, and! ! #It is composed of a sharp processing section 1 and a binarization processing section 2. As the sharpening processing section 1 and the binarization processing section 2,
The sharpening processing circuit 1 and the binarization processing circuit 2 used in FIG. 1 can be used.

The photo/high line count halftone area processing unit is a circuit for performing image processing suitable for photo areas and high line count halftone area, and includes a smoothing processing circuit 7 and systematic dithering such as spiral dither. It is composed of a processing circuit 8. As the smoothing processing circuit 7, for example, when processing halftone dots by dividing them into 100 lines or more and 85 lines or less, a smoothing filter such as the following equation (6) is used.

The smoothing filter in the smoothing processing circuit 7 can be used depending on the number of halftone dots to be separated. For example, when separating halftone dots at 65 lines, the following ( 7) A smoothing filter as shown in equation 7 may be used. Alternatively, a plurality of smoothing filters such as formulas (61 and (71) may be prepared and selected adaptively depending on the processing.

As will be described later, the halftone dot number determination circuit 9 is a circuit that determines whether the number of halftone dots included in the input image is, for example, 100 or more or 85 or less.

The comprehensive determination section 10 is a circuit that determines the processing signal to be selected according to the determination conditions (1) to (4) below, based on the determination result of the halftone line number determination section 9 and the area separation result of the area separation section 5. That is, ■ When a line drawing area signal is output from the area separation circuit 5 ■ A halftone dot area signal is output from the N area separation circuit 5, and the halftone line number determination circuit 9 determines that the halftone area is a halftone dot with a low line count. (
85 lines or less), it instructs the image signal selection circuit 6 to select the processing signal of the line drawing/low line number halftone area processing section, and When the signal is output ■ A halftone dot region signal is output from the region separation circuit 5, and the halftone dot number determination circuit 9 determines that the halftone dot region has a high number of dots (
100 lines or more), it instructs the image signal selection circuit 6 to select the processing signal of the photo/high line number halftone area processing section.

To explain the operation of the third embodiment, a digital multivalued image signal is input to each of the area separation circuit 5, the halftone line number determination circuit 9, the sharpening processing circuit 1, and the smoothing processing circuit 7.

The digital multivalued image signal input to the sharpening processing circuit 1 is edge-enhanced by the sharpening processing circuit 1, and then binarized by the binarization processing circuit 2 to remove the line drawing area and the low line count of 85 lines or less. It is output as an image signal that has been subjected to image processing suitable for the halftone area.

Further, the digital multi-level image signal inputted to the smoothing processing circuit 7 is smoothed by a smoothing filter as shown in (6) 2 above in the smoothing processing circuit 7, and then processed by a dither processing circuit 8 using a spiral dither etc. The signal is then systematically dithered and output as an image signal that has been subjected to image processing suitable for photographic areas and halftone dot areas with a high number of lines of 100 lines or more.

On the other hand, the region separation circuit 5 separates each pixel in the input image into a line drawing region, a halftone dot region, or a photographic region, and sends the separation result to the comprehensive determination section 10.

Further, as will be described later, the halftone line number determination circuit 9 determines whether the number of lines in the halftone dot portion in the input image is 100 or more or 85 or less, and uses the determination result for comprehensive judgment. Send to Department 10.

The comprehensive determination section 10 determines the image area according to the determination conditions (1) to (4), and sends the determination signal to the image signal selection circuit 6. The image signal selection circuit 6 selects the image signal output from the binarization processing circuit 2 in the case of a line drawing area and a halftone dot area with a low line count of 85 lines or less based on the judgment signal of the comprehensive judgment unit 10. In the case of a photographic area and a halftone area with a high number of lines of 100 lines or more, the image signal output from the dither processing circuit 8 is selected and output. Therefore, in the case of this third embodiment, the line drawing/low line number halftone dot image that is likely to cause moiré due to the small fixed size smoothing filter is processed by the line drawing/low line number halftone dot area processing unit. Since the image is processed in the image processing step, there is no risk of moiré occurring in halftone dot areas with a low number of lines, unlike in the conventional method.

A specific example of the configuration of the halftone dot number determination circuit 9 in FIG. 10 is shown in FIG.

The halftone line number determination circuit 9 in FIG. 11 is, in principle, the same circuit as the halftone area separation circuit 502 in FIG. When the following T8) and (91 formulas hold true at the same time, the center pixel is detected as a peak pixel.In order to detect a valley peak pixel, the direction of the inequality sign in formula (8) is used to detect the valley peak pixel. You can reverse it.

However, at T112, the dark value extreme point pixel density calculation unit 902 calculates the peak pixel density within a predetermined small block, for example, a small block of 16×16 pixel size, based on the detection results of peak and valley peak pixels in the extreme point detection unit 901. The number P1 and the number P of valley peak pixels
2 to find the number of peak pixels and the number of valley peak pixels, respectively.

The halftone dot number determination unit 903 includes the pole pixel density calculation unit 90
The larger value of the two count values P, , P, obtained in step 2 is compared with a predetermined threshold value T113 prepared in advance, and P<
When TH3, the small block (or the representative surface element of the small block) is determined to be a halftone dot with a low number of lines (in the above example, a halftone dot with 85 lines or less), and when P≧T113, the corresponding The 8-small block (or the representative surface element of the small block) is determined to be a halftone dot with a high number of lines (in the above example, a halftone dot with 100 lines or more).

Note that the size of the small block for calculating the peak pixel number in the pole pixel density calculation unit 902 and the halftone line number determination unit 9
If you change the value of darkness value TH3 for judgment in 03,
Halftone dots can be separated and determined at any line number position.

The halftone dot number determination circuit illustrated in FIG. 11 determines the number of halftone dots for each small block consisting of a predetermined local area. It is also possible to configure the system to globally determine the number of dots from a set of small blocks. For example, the above 16
Judgment result of small block of x16 pixel size is 16x16
The number of halftone dots can be determined by collecting blocks and taking a majority vote among the 16×16 blocks.

〔Effect of the invention〕

As is clear from the above description, when the image processing apparatus according to claim (1) is used, when reproducing an image containing a mixture of photographs, halftone dots, and line drawings, text on a white background is (including lines), as well as letters on halftone dots, we emphasize gradation for photographic images, and remove moiré and gradation for halftone images. It is possible to adaptively reproduce images with emphasis on

Furthermore, when using the image processing apparatus according to claim (2),
It is possible to adaptively realize optimal processing according to the image area while further simplifying the circuit configuration.

Furthermore, when the image processing apparatus according to claims (3) and (4) is used, when reproducing an image containing a mixture of photographs, halftone dots, and NIA images, the input image is converted into double-headed lines and halftone dots with a low number of lines. This method separates the area into photographic areas and high-line dot areas, and performs image processing appropriate for each area. It is possible to prevent the occurrence of moire even in halftone images with a low number of lines, and it is possible to realize higher quality image reproduction.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the first embodiment of the present invention, FIG. 2 is an explanatory diagram of dither processing using the minimum average error method, and FIG. 3 is a specific example of the area separation circuit for the first embodiment. Block diagram: Fig. 4 is a block diagram showing a specific example of the halftone dot area separation circuit; Fig. 5 is an explanatory diagram of peak pixel detection; Fig. 6 is an explanatory diagram of halftone candidate area detection; Fig. 7 is a halftone dot FIG. 8 is a block diagram of a second embodiment of the present invention, and FIG. 9 is a block diagram showing a specific example of a region separation circuit for the second embodiment. FIG. 10 is a block diagram of the third embodiment of the present invention;
The figure is a block diagram showing a specific example of the halftone dot number determination circuit for the second embodiment. 1... Sharpening processing circuit 2... Binarization processing circuit 3... Average error minimum processing circuit 4... Dither processing circuit 5.5'... Area separation circuit 6... Image signal selection circuit 7... Smoothing processing circuit 8... Dithering processing circuit 9... Halftone line number judgment circuit 10... Comprehensive judgment section "-1711 (!1701 Huu-go-Over-mesh Flo-So 2
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Claims (4)

[Claims] (1) In a device that reproduces an image containing a mixture of photographs, halftone dots, and line drawings, means for converting an input image into a digital multi-value image signal, and a photo area for performing systematic dither processing on the converted digital multi-value image signal. a processing section, a halftone area processing section that performs dither processing on the converted digital multi-value image signal using the minimum average error method or an error diffusion method, and a line drawing area that performs binarization processing on the converted digital multi-value image signal. a processing unit; converting each pixel in the input image into a photographic area, based on pixel information within a predetermined local area of the converted digital multilevel image signal;
an area separation unit that separates into either a halftone area or a line drawing area; and the photographic area processing unit according to the separation result of the area separation unit;
An image processing device comprising: an image signal selection unit that selects and outputs a processed signal from either a halftone area processing unit or a line drawing area processing unit. (2) In a device that reproduces an image containing a mixture of photographs, halftone dots, and line drawings, means for converting an input image into a digital multi-value image signal, and applying a minimum average error method or an error diffusion method to the converted digital multi-value image signal. a picture area processing unit that performs dither processing on the converted digital multi-value image signal; a line drawing area processing unit that performs binarization processing on the converted digital multi-value image signal; an area separation unit that separates each pixel in the input image into a line drawing area and other picture areas based on the separation result of the area separation unit; and a processing signal of either the picture area processing unit or the line drawing area processing unit according to the separation result of the area separation unit. An image processing device comprising: an image signal selection unit that selects and outputs an image signal. (3) A device that reproduces an image containing a mixture of photographs, halftone dots, and line drawings, which includes an image conversion means for converting an input image into a digital multivalued image signal, and a binarization process for the converted digital multivalued image signal. a line drawing/low line number halftone dot area processing section for performing systematic dither processing on the converted digital multilevel image signal; an area separation unit that separates each pixel in the input image into a photo area, a halftone dot area, or a line drawing area based on pixel information of a local area; a dot number determining unit that determines the number of dots in the dot area; a comprehensive determining unit that determines a processed signal to be selected based on the determination result of the dot number determining unit and the area separation result of the area separation unit; and an image signal selection section that selects and outputs either the processing signal of the line drawing/low line number halftone dot area processing section or the photograph/high line number halftone dot area processing section according to the judgment result of the comprehensive judgment section. An image processing device characterized by: (4) In the image processing device according to claim (3), the halftone dot number determination section determines pixels corresponding to the peaks and valleys of the halftone dots based on pixel information of a predetermined local area of the digital multilevel image signal. , and count the number of pixels corresponding to the mountain peak and the number of pixels corresponding to the valley peak in a predetermined small area, respectively.
An image processing apparatus characterized in that the number of halftone dots is determined based on the larger of the two counted values.