JP3294871B2 - Halftone dot area extraction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dot area extracting apparatus for extracting a color dot area from a color document image in which a picture and a character are mixed.

[0002]

2. Description of the Related Art In order to improve the image quality of an output image in a color copier or a color facsimile, or to improve a compression ratio in a color filing apparatus or a color image transmission apparatus, various image area separation methods have been proposed. It has been put to practical use.

In such an image area separating method, an original in which characters and pictures are mixed is mainly input to a computer by image input means such as a scanner, and is separated into a pattern part and a character part based on the input digital data. This is a method for performing a process suitable for the region.

In general, a picture area of a printed matter is a halftone image. Therefore, there is an image area separation technique in which the accuracy of separation between a picture and a character is improved by extracting the halftone dot. FIG.
FIG. 1 is a diagram for explaining a conventional halftone dot extraction method. The halftone dot extraction is performed as follows. That is, the peak detector detects the peak peak pixel and the valley peak pixel of the halftone dot for each pixel using the density information of the image signal P (P is, for example, one color of the RGB input signal). The halftone dot candidate area detection unit sets the small area S as a halftone dot candidate area if the number of peak pixels included in the small area S having a predetermined size is equal to or greater than a predetermined threshold. Further, in the halftone dot area determination unit, the small area of interest S
Then, it is determined whether or not the small area of interest S is a halftone dot or a non-halftone dot from the determination result of the halftone dot candidate area of the surrounding small area S ′, and the result is output.

When a halftone dot is extracted on a color image, the above-described processing is performed in parallel on each of the three RGB (or YMC) signals, and the logical sum of the finally obtained result is obtained. Extract halftone dots.

[0006]

In the above-mentioned conventional method, the halftone extraction processing is performed in parallel with respect to three RGB signals, so that three sets of halftone extraction circuits are required, and the hardware scale is large. There was a problem of becoming.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a halftone dot area extracting apparatus for extracting color halftone dots with high accuracy with a small amount of hardware.

[0008]

According to a first aspect of the present invention, there is provided a dot region extracting apparatus for extracting a dot region from a color image signal, comprising: Detecting means for detecting peak and valley peak pixels from the G signal; detecting means for detecting peak and valley peak pixels from the B signal; and detecting means for detecting each of the detecting means. A logical sum means for calculating a logical sum of the detection outputs; and a number of peak pixels output from the logical sum means and included in a region of a predetermined size.
Means for extracting a halftone dot area based on the number .

According to a second aspect of the present invention, there is provided a halftone dot region extracting apparatus for extracting a halftone dot region from a color image signal.
Detecting means for detecting a peak peak pixel from a signal; detecting means for detecting a peak peak pixel and a valley peak pixel from a G signal; detecting means for detecting a peak peak pixel and a valley peak pixel from a B signal; a logical OR means for ORing the detection output is output from said logical sum means, predetermined
Means for extracting a halftone dot area based on the number of peak pixels included in the area having the size of .

According to a third aspect of the present invention, there is provided a halftone dot region extracting apparatus for extracting a halftone dot region from a color image signal.
Detecting means for detecting a peak pixel from a signal; detecting means for detecting a peak pixel and a valley peak pixel from a G signal; OR means for calculating a logical sum of detection outputs of the respective detecting means; output from, Ryo of predetermined size
Means for extracting a halftone dot area based on the number of peak pixels included in the area .

According to a fourth aspect of the present invention, there is provided a halftone dot region extracting apparatus for extracting a halftone dot region from a color image signal.
Detecting means for detecting a peak pixel from a signal; detecting means for detecting a peak pixel and a valley peak pixel from a G signal; detecting means for detecting a peak pixel from a B signal; and a detection output of each of the detecting means. A logical sum means for calculating a logical sum;
The output from the OR means is included in an area of a predetermined size.
Means for extracting a halftone dot area based on the number of peak pixels to be included.

[0012] In the present invention of claim 5, wherein a halftone dot area extracting device for extracting a halftone area from a color image signal, a positive
Detecting means for detecting a peak peak pixel from a signal having a maximum density value among the normalized R signal, G signal, and B signal; and detecting the peak pixel by the detecting means and including the peak pixel in an area of a predetermined size.
Means for extracting a halftone dot area based on the number of mountain peak pixels . Claim 6
Now, let's extract the dot area from the color image signal.
An extraction device for detecting the density values of R signal, G signal and B signal.
Detecting means for detecting a peak pixel from a signal obtained by performing a linear operation.
Is detected by the detection means and included in an area of a predetermined size.
Extract the halftone dot region based on the number of peak peak pixels
Means.

[0013]

The peak detector detects the peak pixel and the valley peak pixel of the halftone dot for each pixel using the RGB signal.
In the halftone dot candidate area detection unit, if the number of peak pixels included in a small area of a predetermined size is equal to or more than a predetermined threshold, the small area is detected as a halftone candidate area, and the halftone area determination unit is
A halftone dot area is extracted from the logical sum of the detection results of the halftone dot candidate areas detected using the R, G, and B image signals. As a result, the dot area determination unit is shared, and the circuit is simplified as compared with the conventional dot extraction circuit.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be specifically described below with reference to the drawings. As described above, the conventional halftone dot extraction system includes three sets of halftone dot extraction circuits, performs halftone dot extraction for each of the RGB signals, and determines the final halftone area by the logical sum of the extraction results. However, in the present invention, by partially sharing the three sets of halftone dot extraction circuits,
The amount of hardware has been reduced. Hereinafter, a halftone dot extraction method according to the present embodiment in which the amount of hardware is reduced will be described in detail.

<Embodiment 1> In this embodiment, the logical sum of the detection result of the halftone dot candidate area detected using the R, G, B image signals is obtained, and based on the result, the halftone area of the halftone dot area is calculated. The judgment is performed. FIG. 1 is a block diagram of the color halftone extraction method according to the first embodiment. FIG.
In the above, the peak detecting unit 1, the halftone dot candidate area detecting unit 2, and the halftone area determining unit 4 are the same as those of the above-described conventional one.

The halftone dot candidate area detecting section 2 extracts a halftone dot candidate area corresponding to each color signal, and if any of the color signals is a halftone dot candidate area, the OR circuit 3 indicates the halftone dot candidate area. A signal is output, and the area is regarded as a halftone dot candidate area, and the halftone area determination unit 4 determines a halftone area. As a result, the dot area determination unit 4 is shared, and the amount of hardware is reduced.

<Embodiment 2> In this embodiment, the logical sum of the detected peak pixels is obtained using the R, G, and B image signals, and a halftone dot candidate area is detected based on the result. Further, a dot area is determined. FIG.
Shows a block configuration of the second embodiment. According to the second embodiment, the halftone dot candidate area detection unit 2 and the halftone area determination unit 4 can be shared.

In the above embodiment, the peak pixel is detected for the same pixel by the R, G, and B image signals. For example, when using a color scanner,
The types of halftone dots that can be extracted by the R, G, and B image signals are as follows. That is, R signal-black halftone, cyan halftone G signal-black halftone, magenta halftone, cyan halftone (however,
B signal-Becomes a part of black halftone dot, yellow halftone dot and magenta halftone dot, so it is part of cyan halftone dot and magenta halftone dot except black halftone dot and low halftone dot ratio. Is based on multiple image signals.
The peak pixel can be detected.

Therefore, in another embodiment of the present invention, only the halftone dots that cannot be extracted by the representative signal (for example, G signal) are extracted by another image signal, so that the hardware amount of the peak pixel detecting unit is reduced. Can be optimized to

<Embodiment 3> For example, when a G signal is selected as a representative signal, halftone dots that cannot be extracted by the signal are a cyan halftone dot and a yellow halftone dot with a low halftone dot ratio. Since a region having a low halftone dot ratio is extracted by a peak pixel and a region having a high halftone dot ratio is extracted by a valley peak pixel, the detection unit for detecting a peak pixel from the R signal of the present embodiment uses FIG. As shown in (1), in order to detect a cyan halftone dot having a low halftone dot ratio, only a mountain peak pixel detection unit 11 is provided.

A yellow dot which cannot be extracted by the G signal is extracted by detecting a peak pixel and a valley peak pixel of the B signal. The peak pixels detected using the R, G, and B image signals are OR-connected by the OR circuit 3 in the same manner as in the second embodiment, and the halftone dot candidate area detection unit 2 based on the result. Then, the halftone dot candidate area is detected, and then the halftone area determination unit 4 determines the halftone area.

As described above, according to the third embodiment, the circuit for detecting the valley peak pixel of the R signal can be omitted as compared with the configuration of the second embodiment. Although the valley peak pixel detection circuit for the R signal is omitted in the above-described embodiment, the present embodiment is not limited to this, and the hardware of the peak pixel detection unit may be changed according to the characteristics of the input device. The configuration can be optimized.

<Embodiment 4> As described above, in the conventional halftone dot extraction method, it is assumed that all halftone areas are extracted, and all three signals of R, G, and B are processed in the same manner. However, there is a case where only a part of a halftone dot region needs to be extracted depending on how to use the halftone dot extraction. The fourth embodiment is an embodiment in a case where it is not necessary to extract all the halftone dots. For example, when halftone dots are extracted for the purpose of removing halftone moire, yellow moire is not necessarily detected as halftone dots since moire is hardly noticeable. Therefore, in the fourth embodiment, FIG.
As shown in (1), the peak detection circuit for detecting the yellow dot by the B signal is deleted from the configuration of the third embodiment.

Fifth Embodiment A fifth embodiment is another embodiment in which it is not necessary to extract all the halftone dots as in the fourth embodiment. The adaptive coding method proposed by the present applicant earlier (Japanese Patent Application No. Hei 3-3271).
In the dot extraction in No. 36), it is necessary to extract the halftone dots of MCK in order to remove the moire, and to extract the highlight halftone dots in order to improve the separation accuracy of the picture area. That is, in order to extract the MCK halftone dot + the highlight Y halftone dot, in the fifth embodiment, as shown in FIG.
Is detected by the peak pixel of the R and B signals, and the remaining halftone dot region is detected by the G signal.

When the image area is separated into the picture area and the character area in the adaptive coding method, or when the background stains in copying or the like are removed, particularly, the background and the highlight picture area are separated with high precision. It is necessary, and one of the effective separation methods is a method of extracting highlight halftone dots.

Still another embodiment of the present invention relates to a method for extracting such a highlight halftone dot. As described above, the halftone dot extraction is to extract a halftone dot region by locally detecting a peak peak and a valley peak from density information, but a halftone dot using R, G, B single color signals. In the extraction of (1), since the spectral sensitivity is extremely different depending on the ink color, the peak component of the color halftone dot with low spectral sensitivity is lost, and as a result, it becomes difficult to extract the halftone dot.

Therefore, in this embodiment, as described later,
By generating a composite color that retains the RGB peak components, a color halftone dot is detected using one signal. The following describes an example of highlight halftone extraction when generating a composite color using the maximum value of RGB density values, and highlight halftone extraction when generating a composite color by linear synthesis of RGB density values. An example will be described.

<Embodiment 6> In this embodiment, the maximum value of the RGB density values (that is, the RGB
In this embodiment, when one of the signals has a peak component, the density value of the signal becomes the maximum of the three signals), and the highlight halftone dot is detected based on the composite color. .

FIG. 6 is a block diagram showing the configuration. First, the input values of the RGB signals from the scanner are normalized. That is, this is a process for equalizing the gray balance of the scanner input values in RGB. For example, when an image close to pure white such as blank paper is read by a scanner, generally, the input data does not have the same RGB values. For example, R = 20, G = 5, B = 1 at 256 gradations
It takes a value such as 0.

If the maximum value of the RGB density values is used as the value of the composite color in a state where the gray balance is distorted, a color signal having a peak component cannot be selected accurately. Therefore, normalization is performed for each color component. . Next, the density values of the normalized RGB signals are compared, and the maximum density value is used as the value of the composite color. In this embodiment, since only the highlight halftone dot is detected, a mountain peak is detected from the generated composite color. Then, similarly to the above-described embodiment, the halftone dot candidate area is detected,
A halftone dot area is determined, and a halftone dot is extracted.

<Embodiment 7> This embodiment is an embodiment in which a synthesized color is generated by linearly synthesizing RGB density values, and a highlight halftone dot is detected based on the synthesized color. FIG. 7 is a block diagram of a seventh embodiment. First, the value of the composite color is calculated by linear operation of the density values of the RGB signals. The following equation is used as the linear operation.

P = Rr * (R + Rd) + Gr * (G + Gd) + Br * (B + Bd) where P is a composite color value, R, G, and B are scanner input values, and Rr, Rd, Gr, Gd, Br and Bd are arbitrary constants.

As the respective constants, for example, the following are selected. That is, as the value of P, Y, M,
It is desirable that each halftone dot of C can be detected equally, and each coefficient is determined so that the values of P for only Y, only M, and only C are almost equal, and the following values are obtained.

Rr = 0.384, Gr = 0.229, Br = 0.507 Rd = 4 Gd = 3 Bd = 0 Since the above values depend on the input characteristics of the scanner,
Of course, if the input conditions are different, the value must be changed.

If there is a peak component in any of RGB, the composite color P linearly calculated can also hold the peak component. Thereafter, halftone dots are extracted based on the composite colors in the same manner as in the above-described embodiment.

In each of the above embodiments, RGB
Although the halftone dot is extracted from the signal, the image signal may be YMC. The concept of reducing the amount of hardware according to the present embodiment is also applicable to other halftone dot extraction methods.

[0037]

As described above, according to the present invention, after extracting the halftone dot candidate areas corresponding to each color signal,
If any of the color signals is a dot candidate area, the area is regarded as a dot candidate area and the determination of the halftone area is performed. Therefore, it can be constituted by a set of halftone area determination circuits. In addition, the amount of hardware for extracting a dot area can be reduced.

According to the present invention, after a peak pixel corresponding to each color signal is extracted, if a peak pixel is detected in any of the color signals, the pixel is regarded as a peak pixel and the halftone dot candidate area is determined. Since the detection and the determination of the halftone dot area are performed, it can be constituted by one set of halftone dot candidate area detection circuits and one set of halftone dot area determination circuits, and the amount of hardware for extracting halftone dot areas is reduced. can do. Also, since the type of peak pixel to be extracted can be changed for each color signal, the hardware configuration of the peak detection circuit can be optimized according to the type of halftone dot to be extracted,
The amount of hardware for extracting a halftone dot region can be reduced.

According to the present invention, halftone dots are detected after converting a plurality of color signals input from the scanner into one color signal. Therefore, halftone dots of all ink colors of YMCK are converted into one color signal. Can be extracted with high accuracy.

According to the present invention, since the maximum value of a plurality of color signals input from the scanner is set as the value of one color signal, color dots having a low dot ratio are extracted with high accuracy by a simple circuit. be able to.

According to the present invention, since a single color signal value is generated by performing a linear operation on a plurality of color signals input from a scanner, a color halftone dot having a low halftone ratio is extracted with high accuracy. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a block diagram of a second embodiment of the present invention.

FIG. 3 is a block diagram of a third embodiment of the present invention.

FIG. 4 is a block diagram of a fourth embodiment of the present invention.

FIG. 5 is a block diagram of a fifth embodiment of the present invention.

FIG. 6 is a block diagram of highlight dot extraction according to the present invention.

FIG. 7 is a block diagram of highlight dot extraction according to another embodiment.

FIG. 8 is a block diagram of a conventional halftone dot extraction method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Peak detection part 2 Halftone dot candidate area detection part 3 OR circuit 4 Halftone area determination part

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-84879 (JP, A) JP-A-2-112077 (JP, A) JP-A-2-29296 (JP, A) JP-A-5-29 83544 (JP, A) JP-A-3-219774 (JP, A) JP-A-5-63970 (JP, A) JP-A 5-227425 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (6)

(57) [Claims] 1. A halftone dot region extracting apparatus for extracting a halftone dot region from a color image signal, comprising: detecting means for detecting a peak peak pixel and a valley peak pixel from an R signal; and a peak peak pixel and a valley peak from a G signal. Detection means for detecting pixels;
Detecting means for detecting peaks peak pixel and valleys peak pixel from the B signal, a logical OR means for ORing the detected outputs of the respective detection means, output from said logical sum means, the predetermined large
Means for extracting a halftone dot region based on the number of peak pixels included in the size region. 2. A halftone dot region extracting apparatus for extracting a halftone dot region from a color image signal, comprising: detecting means for detecting a peak peak pixel from an R signal; and detecting peak and valley peak pixels from a G signal. Detecting means, detecting means for detecting peak peak pixels and valley peak pixels from the B signal, logical sum means for calculating the logical sum of the detection outputs of the respective detecting means, and a predetermined size outputted from the logical sum means. Included in the area
Means for extracting a halftone dot region based on the number of peak pixels . 3. A halftone dot region extracting apparatus for extracting a halftone dot region from a color image signal, comprising: detecting means for detecting a peak peak pixel from an R signal; and detecting peak and valley peak pixels from a G signal. Detecting means, a logical sum means for calculating a logical sum of detection outputs of the respective detecting means, and a peak pixel output from the logical sum means and included in a region of a predetermined size
Means for extracting a halftone dot region based on the number of dot regions. 4. A halftone dot region extracting apparatus for extracting a halftone dot region from a color image signal, comprising: detecting means for detecting a peak peak pixel from an R signal; and detecting peak and valley peak pixels from a G signal. Detecting means, detecting means for detecting a peak peak pixel from the B signal, logical OR means for calculating the logical sum of the detection outputs of the respective detecting means, and output from the logical OR means and included in an area of a predetermined size Means for extracting a dot area based on the number of peak pixels to be extracted. 5. A halftone dot region extracting apparatus for extracting a halftone dot region from a color image signal, wherein a peak value of a peak value pixel is determined from a signal having a maximum density value among normalized R, G, and B signals. Detecting means for detecting, the detection means ,
Means for extracting a halftone dot region based on the number of mountain peak pixels included in a region of a predetermined size . 6. A halftone dot region is extracted from a color image signal.
A halftone dot region extracting apparatus, comprising: an R signal, a G signal, and a B signal.
Detect peak pixel from signal obtained by linearly calculating density value
Detecting means, and a predetermined size
Halftone area based on the number of mountain peak pixels included in the area
Means for extracting halftone dots.
Output device.