JPH09261460A - Image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the degradation of picture quality by avoiding erroneous discrimination by separating image areas more than twice at least, making a parameter for discriminating an original based on the first image area separation discrimination different from a parameter for locally discriminating the areas at the time of main scan, and utilizing only the high-certainty information when discriminating an original. SOLUTION: A parameter storage part 9 stores the 1st parameter for the time of prescan and the 2nd parameter for the time of main scan. At the time of prescan, only an edge separator circuit 10 is operated and an edge is detected while using the 1st parameter with which it is difficult to detect the edge. A decision circuit 11 decides an original image and counts the edges. When that value is more than a prescribed threshold value, it is decided that the original contains characters, and the result is stored 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method in which, when image area separation is performed a plurality of times, the first image area separation determination criterion and the subsequent image area separation determination criteria are changed. .

[0002]

2. Description of the Related Art At present, in an image processing apparatus such as a color copying machine, when processing and reproducing an original in which a character area and a picture area are mixed, the area of the image is recognized by a so-called image area separation technique. However, the processing is switched between the character portion and the pattern portion in one document. As a conventional color copying machine using such an image area separating technique, for example, there is one described in Japanese Patent Publication No. 7-22330.

The above-mentioned conventional apparatus performs image area separation during so-called pre-scanning without image forming processing to perform area determination (character area / halftone area), and processing is performed in main scanning in accordance with the determined result. The parameter is switched. Further, in the area identification signal processing circuit described in Japanese Patent Laid-Open No. 5-145751, the image area separation result at the time of prescan is stored in the storage device, and the processing is performed by using the result stored in the storage device at the main scan. Switch.

[0004]

As described above, in the above-mentioned conventional apparatus, the image area separation processing is premised on the so-called local processing, and the processing always involves an erroneous determination. Specifically, in many cases, characters are determined based on edge information. Therefore, when trying to determine character edges with high accuracy, patterns such as photographic paper edges and halftone dot images are also detected. The number of locations that are erroneously determined as character edges increases. In particular, when it is attempted to detect even the internal crushing of a character as a character edge, the tendency becomes even stronger. In other words, if the judgment is made during pre-scan at the level of detecting even the internal crushing of characters as character edges, it is judged that the halftone dot pattern having a structure similar to the character is a character original, especially locally. Causes a problem in the processing of. This becomes a problem especially in the case of an original containing only a picture that does not include a character area.

The present applicant has previously proposed an image processing method in which halftone dot separation, which is one of image area separations during prescan, is activated, and image area separation during main scan is controlled based on the information ( (See Japanese Patent Laid-Open No. 4-180350). In this method, it is determined whether or not a halftone image is included in the prescan, and if it is determined that the halftone image is not included, the halftone determination in the main scan is turned off. As a result, it is possible to reduce the deterioration of the image quality due to the local erroneous halftone dot determination. On the contrary, when it is determined that the halftone image is included in the pre-scan, the halftone separation is activated even in the main scan.

By the way, if the parameters are set so as to positively separate the halftone dot area, the image of the photographic printing paper, especially the so-called silk development, is also judged as the halftone dot. In particular, if the highlight or dark part of the halftone image is judged as a halftone dot area, the tendency is strong. I will judge. As a result, for example, Japanese Patent Laid-Open No. 6-
As performed by the image processing apparatus described in Japanese Patent Publication No. 197218, based on the above prescan information,
When performing the process of switching the color correction coefficient of the print original / print paper original, a problem arises in that the color correction processing for the print original is performed on the silk photographic paper original.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to perform image area separation at least twice or more and to judge a document based on the first image area separation judgment. Image processing that avoids erroneous determination and prevents deterioration of image quality by changing the parameters of the above and the parameters for locally determining the area during the main scan, and using only highly accurate information when determining the document. To provide a method.

[0008]

In order to achieve the above object, according to the invention of claim 1, an original is read out as a digital signal and image area separation is performed on the original a plurality of times.
In the image processing method for switching the processing within the original based on the separation result, the first image area separation determination criterion and the second or subsequent image area separation determination criterion for predetermined area detection are changed. I am trying.

According to a second aspect of the present invention, there is provided an image processing method, wherein an original is read out as a digital signal, image area separation is performed on the original a plurality of times, and processing within the original is switched based on the separation result. In order to make it difficult to detect a predetermined area, the criterion for the first image area separation is set higher than the criterion for the second and subsequent image area separations.

According to a third aspect of the present invention, when the image area separation is first performed, an image forming process of a predetermined color is performed.

According to a fourth aspect of the invention, the predetermined area is a character edge area.

According to a fifth aspect of the present invention, the predetermined area is a print dot area.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be specifically described below with reference to the drawings. <Embodiment 1> FIG. 1 shows the structure of Embodiment 1 of the present invention.
In the figure, 1 is an image input device such as a scanner, and 2 is a Log that converts a linear reflectance signal into a linear density signal.
A conversion circuit, a filter circuit including a smoothing filter and an edge emphasis filter, a color correction circuit for converting a cmy signal into YMC of a complementary color, a UCR circuit for performing processing for subtracting a K signal from each color material signal, Reference numeral 6 denotes a dither circuit for expressing halftones using dither for characters and pictures, and reference numeral 7 denotes an image output device such as a printer.

Reference numeral 8 is a color separation circuit for separating color areas from the original, 9 is a parameter storage section for storing parameters for prescanning and main scanning, and 10 is an edge for separating character edges using the parameters. Separation circuit, 11 is a judgment circuit for judging an area based on the separation result of the separation circuit, 12
Is a counting circuit for counting the character edge pixels, 13 is a determination circuit for determining whether or not a character is included in the document based on the count value, and 14 is a determination result storage circuit for storing the determination result of the determination circuit 13. is there.

First, the outline of FIG. 1 will be described. The image input device 1 (resolution is 400 dpi) such as a scanner outputs rgb data (8 bits each) which is almost linear with respect to the reflectance. Next, Lo is pre-processed for performing color correction at a later stage.
The logarithmic conversion is performed in the g conversion circuit 2, and the density linear c
Generate my data.

The filter circuit 3 is composed of a circuit in which a smoothing filter and an edge emphasizing filter as shown in FIG. 2 are connected in series, and when a signal from a judging circuit 11 described later is a black character or a color character. In the above, the smoothing filter is made to be through and only the edge enhancement processing is performed.

The color correction circuit 4 converts the cmy signal into a complementary color YMC signal in consideration of the characteristics of the image input device 1 and the image output device 7. As a color correction method, linear approximation, so-called masking method, tetrahedral interpolation method, triangular prism interpolation method, and the like have been proposed, and color correction is performed using these methods. At this time, the K signal is simultaneously calculated from min (C, M, Y).

The UCR circuit 5 switches the processing as follows based on the area determination signal from the determination circuit 11. That is, for the black character area, K is made to be through and C = M
= Y = 0. For the color character area, K is through, C is through, M is through, and Y is through. For other than the above, that is, K '= 0.6 × K C' (M ', Y') = C (M, Y) ) -K '.

Then, the dither circuit 6 prepares two kinds of dither tables (dither matrices) having different sizes (not shown), and when the signal from the judging circuit 11 is a black character or a color character, the size is determined. Of the dither table (eg, 1 × 1), and in other cases, the dither table of larger size (eg, 2 × 2) is used to send the data to the image output device 7.

The image area separating section, which is a main characteristic part of the present invention, will be described in detail below. The image area separation unit of the first embodiment includes an edge separation circuit 10 and a color separation circuit 8, and a second embodiment described later includes a halftone dot separation circuit 15. Among them, the edge separation circuit 10 and the halftone dot separation circuit 15 are described, for example, in the paper “Image area separation method of mixed image of character / picture (halftone dot, photograph)”.
(Journal of the Institute of Electronics, Information and Communication Engineers, Vol. J75-DI1
No. 1 pp39-47 January 1992), "4.2 Edge Area Detection" method is used.

The edge separation circuit 10 is a circuit for detecting an edge area of a character in a document. In this embodiment, for example, the method described in the above-mentioned paper is used as the character edge detection method. According to this method, edge enhancement is applied to input image data of 64 gradations, then ternarization is performed using two types of fixed thresholds, and the continuity of black pixels and white pixels after ternarization is detected by pattern matching. If at least one black continuous pixel and one white continuous pixel are present in the block of 5 pixels, the block of interest is determined to be an edge region, and if not, it is determined to be a non-edge region.

Here, the ternarization parameters for edge region detection are switched between prescan and main scan. At the time of pre-scanning, parameters for which it is difficult to detect edges are set. As a result, the criterion for determining the image area separation becomes high, and the inside of a character or the like is not detected as an edge, but the area erroneously detected as a character in a halftone dot image is reduced.

As an example of the parameters to be prepared, the following parameters are set, for example. For pre-scan; white pixel <32/255, black pixel ≧ 192/255 For main scan; white pixel <64/255, black pixel ≧ 128/255 Color separation circuit 8 detects chromatic portion from original It is a circuit to do. As this color separation method, for example, JP-A-3-260
The chromatic / achromatic color region separation method described in Japanese Patent No. 878 is used. In this method, the difference between the R, G, and B digital signals is obtained, and when the maximum difference is equal to or larger than a predetermined threshold value, it is determined that the color is chromatic.

The operation of the first embodiment will be described below. (During prescan) In the configuration of the embodiment shown in FIG. 1, the processing unit that operates during prescan is surrounded by a dotted line. The pre-scan here means not only the case where the color scanner actually scans the original, but also the case of the first use when the input image is stored in the memory and is used a plurality of times.

As shown by the dotted line in FIG. 1, the edge separation circuit 10 performs edge separation using the parameters for prescan read from the parameter storage unit 9. The determination circuit 11 ignores the color separation result during the prescan. Then, the determination circuit 11 makes a determination with respect to all images, and causes the counting circuit 12 to count the character edge pixels (the character edge block when processed in block units). When the count value is equal to or larger than a predetermined threshold value, the determination circuit 13 determines that the input original contains characters, and holds the determination result in the determination result storage circuit 14 until the main scan.

(During main scan) The one-drum type color copying machine performs a total of four scans for each CMYK plate,
The four-drum type performs one scan to reproduce a color image. However, as described above, when all images are stored in the memory and used multiple times, the scanner does not operate.

By the above-mentioned prescan, it is determined whether or not the original contains characters. If a character is included, normal image area separation is performed. That is, the edge separation circuit 10 that performs edge separation on the input image data using the parameters for main scan, and the color separation circuit 8
Operate in parallel, and the respective judgment results are input to the judgment circuit 11.

In the judging circuit 11, when the pixel of interest is an edge and is an achromatic color, it is judged as a black character, and when it is an edge and a chromatic color, it is judged as a color character, and the others are judged as a pattern. To do. As described above, the processing is switched for each pixel according to the result.

On the other hand, if no character is included in the pre-scan determination, for example, as an example of the control, the image area separation process is turned off and the entire surface is subjected to the pattern process. Alternatively, it is also an effective method to reset the parameters that are easy to determine the pattern as the respective parameters of the image area separation before starting the main scan. This reduces the possibility of erroneous separation in the pattern area. However, although it tends to cause erroneous separation with respect to characters, it does not substantially cause a problem because the characters do not exist, or the existence of the characters is considerably small.

As described above, in the first embodiment, at the time of pre-scanning, the photographic printing paper edge or halftone dot image that does not include characters is erroneously recognized as a document with characters, and unnecessary image area separation is performed in the main scan, and There will be no local misjudgment. Then, as described above, when it is determined that the character is not included in the prescan, the image area separation is turned off in the main scan, and the pattern processing may be performed on the entire document.

<Second Embodiment> FIG. 3 shows the structure of a second embodiment of the present invention. Image reproduction system (that is,
Since the steps from the image input device to the image output device) are the same as those in the first embodiment, the description thereof will be omitted.

The process switching of the second embodiment is performed for the filter process and the color correction process. That is, if there is a halftone dot in the document as a result of the determination during the pre-scan, the color correction processing is performed by selecting the color correction coefficient for the print document during the main scan. If there is no halftone dot, the color correction processing is performed by selecting the color correction coefficient for the photographic paper original. This color correction coefficient switching is
The same color correction coefficient is used for one document, not locally.

On the other hand, the switching of the filter processing is locally performed within the document. That is, the strength of the smoothing filter is changed in the halftone / non-halftone area. This is because halftone dot originals may deteriorate the image quality called moiré and require strong smoothing. However, if strong smoothing processing is performed on areas other than that, the image will only blur, so Perform local adaptive processing. When it is determined that there is no halftone dot during the pre-scan, weak smoothing or through processing is performed on the entire surface during the main scan.

The image area separating section, which is a main characteristic part of the present invention, will be described in detail below. The image area separation unit according to the second embodiment includes a halftone dot separation circuit 15.

The halftone dot separation circuit 15 is a circuit for detecting a halftone dot (print) area in the original. This detection method also uses the “4.1 halftone dot area detection” method described in the above-mentioned paper. This method focuses on the fact that the density change between the color halftone dot area and the black and white halftone dot area is significantly different from the density change in the character area, and performs peak pixel detection, halftone dot area detection, and halftone dot area correction. This is to separate the dot areas.

The peak pixel is detected by, for example, in a block of 3 × 3 pixels, the density level L of the central pixel is higher or lower than that of all the surrounding pixels, and
The density levels a and b of the diagonal pixels existing diagonally across L and the central pixel are | 2 × L−a−b |> TH for all four pairs.
When it is (fixed threshold), the central pixel is set as the peak pixel. The detection of the halftone dot area is performed, for example, in four blocks each including 4 × 4 pixels, if there are two or more blocks including the peak pixel, the target block is set as the halftone dot candidate area, and the other blocks are non-halftone dots. Determined as a candidate area. After determining the halftone dot / non-halftone dot candidate region, if four or more of the nine blocks centering on the target block are halftone dot candidate regions, the target block is set as the halftone dot region, and otherwise the target block is selected. It is a non-dot area.

Here, the peak pixel detection parameter TH in halftone dot area detection is switched between prescan and main scan. At the time of prescan, parameters that make it difficult to detect halftone dots are set. As a result, the highlight or dark portion of the halftone image is no longer detected as a halftone dot, but it is less likely to be erroneously determined as a halftone dot for a photographic printing paper original, particularly a silk development original.

The relationship between the prescan parameters and the main scan parameters to be prepared is as follows.

TH (during pre-scan)> TH (during main scan) The operation of the second embodiment will be described below. (During prescan) The processing unit that operates during prescan is surrounded by a dotted line. As indicated by the dotted line in FIG. 3, the halftone dot separation circuit 15 operates using the prescan time parameters read from the parameter storage unit 9. The determination circuit 16 makes a determination on all the images and counts the halftone dot pixels (halftone dot block when processing in block units) 17.
Count with. When the count value is equal to or larger than a predetermined threshold value, the determination circuit 18 determines that the input original includes halftone dots,
The determination result is stored in the determination result storage circuit 1 until the main scan.
Hold at 9.

(At the time of main scanning) It was determined by the above-mentioned prescan whether or not there is a halftone dot area in the document. When there is a halftone dot area, the color correction circuit 4 performs color correction processing using the color correction coefficient for the print original, and when there is no halftone dot area, it uses the color correction coefficient for the photographic paper original. Perform color correction processing. Details of the setting method of each color correction coefficient are described in JP-A-6-197218.

Further, when there is a halftone dot area in the document, the halftone dot separation circuit 15 operates during the main scan. During this operation, the main scan parameters read from the parameter storage unit 9 are used. Then, the smoothing process as shown in FIG. 2 is performed on the halftone dot region, and the process other than the halftone dot region is not smoothed but only the edge enhancement process is performed. However, the coefficient of the smoothing filter differs depending on the characteristics of the scanner and the image you want to obtain, but basically, for the halftone dot area, strong smoothing that does not cause moire is performed, and for the other areas, It does not deviate from the gist of the present invention unless a very strong smoothing is performed.

On the other hand, when there is no halftone dot area in the original,
At the time of the main scan, the halftone dot separation may be turned off, and the entire surface may be made to be through without smoothing.

In the second embodiment, the original is determined by the pre-scan and the local application processing accompanied by the image area separation is performed by the main scan, but the present embodiment is not limited to this. Various changes are possible. For example, a color copying machine, particularly a one-drum type machine, reproduces an image in a frame-sequential manner for each KCMY plate in order, so at the time of the first K plate, the original judgment using image area separation is performed using a parameter having a high judgment standard. (And in fact, local processing switching is also performed for image area separation, or uniform processing is performed only for the K plate), and in other plates after that, image area separation is performed using a parameter with a low criterion level. It may be performed. As a result, the prescan is not performed, so that the image reproduction process can be performed at high speed.

[0044]

As described above, according to the first and second aspects of the present invention, the document type is specified by using the image area separation in the prescan, and the processing is performed in the main scan based on the result. Change in a big way (that is, for the entire manuscript),
At the same time, in the image processing method in which the image area separation is performed even during the main scan and the gradation processing is locally switched, the criterion for the determination performed during the pre-scan is set higher than that during the main scan, so the accuracy is high. It can be determined based on only the location. As a result, there is no possibility of erroneous processing for global processing switching that causes large image quality deterioration due to erroneous determination.

According to the third aspect of the invention, the image can be reproduced at high speed because the pre-scan is not performed in the one-drum type color copying machine.

According to the fourth aspect of the invention, at the time of pre-scanning, it is determined whether or not the original includes characters, based on the area information that is clearly the character edge. For an original document only made of photographic paper or printing, for example, the character detection image area separation can be turned off at the time of main scanning, and therefore, there is no local erroneous separation, so that the image quality can be greatly improved.

According to the fifth aspect of the present invention, during the prescan, whether or not the original includes halftone dots based on the halftone dot area information of the intermediate level (halftone dot 50%) which is obviously halftone dots. Therefore, it is possible to avoid erroneously determining photographic printing paper, especially silk photographic printing paper, as printing (halftone dot). For example, when switching the color correction coefficient with the above-mentioned halftone dot area information, The image quality can be improved.

[Brief description of drawings]

FIG. 1 shows a configuration of a first exemplary embodiment of the present invention.

FIG. 2 shows a specific example of a filter circuit.

FIG. 3 shows a configuration of a second exemplary embodiment of the present invention.

[Explanation of symbols]

 1 Image Input Device 2 Log Conversion Circuit 3 Filter Circuit 4 Color Correction Circuit 5 UCR Circuit 6 Dither Circuit 7 Image Output Device 8 Color Separation Circuit 9 Parameter Storage 10 Edge Separation Circuit 11, 13 Judgment Circuit 12 Counting Circuit 14 Judgment Result Storage Circuit

Claims (5)

[Claims] 1. An image processing method in which an original is read out as a digital signal, image areas are separated from the original a plurality of times, and processing within the original is switched based on the separation result. An image processing method, characterized in that the first image area separation criterion and the second or later image area separation criterion are changed. 2. An image processing method in which an original is read out as a digital signal, image areas are separated from the original a plurality of times, and processing within the original is switched based on the separation result. An image processing method characterized in that the determination criterion for the first image area separation is set higher than the determination criteria for the second and subsequent image area separations so as to be difficult. 3. The image processing method according to claim 1, wherein an image forming process of a predetermined color is performed when the image area separation is first performed. 4. The image processing method according to claim 1, wherein the predetermined area is a character edge area. 5. The image processing method according to claim 1, wherein the predetermined area is a print dot area.