JP3099435B2 - Image area determination device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for processing a multivalued image, and more particularly to an image area judging apparatus for judging a character area and a photograph area.

[0002]

2. Description of the Related Art In a general image, a character image emphasizes the density difference between a character and its background image in order to clearly express the outline of the character, and a photographic image expresses a photograph with good gradation. For this reason, a method of correctly expressing the density of an image and performing faithful gradation expression has been widely used.

However, in an image in which characters and photographs are mixed, the two requirements are contradictory operations. Therefore, if the character region is emphasized, the gradation of the photograph region is different from the original image, and if the photograph region is emphasized. There is a problem that the outline of the character area is lost.

In order to solve this problem, it is necessary to correctly identify a character area and a photographic area of an image, and to emphasize a density difference or perform faithful gradation expression according to each area. As a conventional method of the identification, there is a method proposed by one of the present inventors (see Japanese Patent Application No. 3-33206). This utilizes the properties of character images and photographic images, and by constantly monitoring both the image density and the amount of change, it is possible to identify portions where the image density is at an intermediate level to some extent and where the amount of change in density is large. This is a method for determining a character area.

[0005]

In a normal character / photo mixed image, the character region and the photograph region are located at a certain position, and the character region and the photograph region are alternately repeated at a small interval. There is no. This is effective information for separating the text / photo mixed image. Since the above information is not used in the conventional method described above, for example,
There is a drawback that a part having a certain amount of change in the photograph area may be erroneously determined as a character area. Further, it has been proposed to correct the determination based on the determination result of the peripheral area after all the determinations are completed, but there is a disadvantage that the processing speed is reduced and the apparatus scale is increased.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image area judging apparatus which can eliminate the above-mentioned drawbacks by utilizing the above-mentioned effective information and can accurately and easily identify a character area and a photograph area. .

[0007]

According to the present invention, there is provided an image area determining apparatus comprising means for determining whether an input multivalued image is a character area or a photograph area and outputting an area determination signal. A density detection circuit for outputting a density signal indicating whether or not the density value of the multi-valued image falls between two preset density thresholds, and the area corresponding to a peripheral area of the pixel of interest A density change threshold value determining circuit for setting and outputting a first density change threshold value based on the determination signal; and a change amount of the density value of the multi-valued image being equal to or less than the first density change threshold value. A density change detection circuit that outputs a density change signal indicating whether or not the density change signal is present, and receives the density signal and the density change signal, and indicates that the density signal is between the two density thresholds. From the first concentration change threshold The multi-value image a photograph area to indicate that a small, characterized by comprising a region determination circuit for outputting the area identification signal it is determined that otherwise is a character region.

Further, the present invention, the concentration change threshold value determination circuit includes a determination storage memory for storing the type of the region determination signal determination result stored in the determination storage memory
Weighted sum circuit, the weighted sum with a preset second and concentration change operation was carried out of the first concentration change threshold was seeking a weighted sum of the inputs the determination result shiso in the peripheral region of the pixel of interest are And an arithmetic circuit for outputting a threshold value.

[0009]

According to the present invention, in order to accurately and easily distinguish between a character region and a photograph region of an image, the character and photograph judgment results of the already determined region are used.

[0010] In a general character and photograph mixed image,
The character region and the photograph region exist to some extent in a position-dependent manner, and are not scattered. Therefore, if there are many pixels determined to be a character area in a peripheral area of a pixel to be determined (a pixel of interest), it is highly possible that the pixel of interest is a character area. When there are many pixels in the region, the possibility that the pixel of interest is a photograph region increases.

In the present invention, the density change threshold value determination circuit determines the density change threshold value using the character / photo determination result in the peripheral area. In the case where there are many photographic areas in the peripheral area, it is easy to determine that the area is a photographic area.

The density change threshold value determination circuit stores the area determination signal, that is, the character / photo determination result of the already determined area in the memory, and obtains the weighted sum of the peripheral area of the pixel of interest. The weighted sum is added or multiplied by a preset second density change threshold, and a first density change threshold is output.

[0013]

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

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a density change threshold value determining circuit, and FIG. FIG. 13 is a block diagram showing another example.

The present embodiment is directed to an image area determining apparatus having means for determining whether an input image signal 5 of a multi-valued image is a character area or a photograph area and outputting an area determination signal 9. A density detection circuit 1 for outputting a density signal 8 indicating whether or not the density value of the multi-valued image falls between two preset density thresholds 6 and 7; A density change threshold value determining circuit 4 for determining and outputting a first density change threshold value 11 based on an area determination signal 9 for at least one pixel; A density change detection circuit 2 for outputting a density change signal 10 indicating whether or not the density is below; a density signal 8 and a density change signal 10;
The density signal 8 is between the two density thresholds 6 and 7 and the density change signal 10 is
An area determination signal 9 indicating that the multi-valued image is a photographic area when it is smaller than the above, and a text area otherwise.
Is output.

The density change threshold value determination circuit 4 receives a region determination signal 9 and stores the determination result, and a weighted sum circuit 14 for obtaining a weighted sum of the determination results of the peripheral region of the target pixel. An addition circuit 15 or a multiplication circuit 16 as an arithmetic circuit that performs addition or multiplication of the weighted sum and a preset second density change threshold value 12 and outputs a first density change threshold value 11 Contains.

Next, the operation of this embodiment will be described.

The multi-valued image input from the scanner is input as an image signal 5. Here, the image signal 5 is a multi-level signal. For example, if the signal is an 8-bit signal, the level ranges from level 0 to level 255. It is assumed that the level 0 corresponds to perfect white, the level 255 corresponds to perfect black, and the level between them corresponds to a color having a density corresponding to the value.

The image signal 5 is first input to the density detection circuit 1. A density threshold 6 and a density threshold 7 which are set in advance are input to the density detection circuit 1, and the density level of the image signal 5 is between these two density thresholds or not. Find out what. If the density level of the input image signal 5 is between the two density thresholds, a level "1" indicating "ON" is output as the density signal 8, and the density signal 8 is output between the two thresholds. If not, a level “0” indicating “off” is output.

On the other hand, the image signal 5 is inputted to the density change detection circuit 2 simultaneously with the density detection circuit 1. The density change detection circuit 2 constantly monitors the value of the image signal 5. If the amount of change in the density level of the image signal 5 is smaller than the value of the density change threshold 11 (described later), the density change signal 10 is used. ,
A level “1” indicating “ON” is output.
A level “0” indicating “OFF” is output.

Only when the density signal 8 and the density change signal 10 are simultaneously "ON", the area determination circuit 3 determines that the image signal 5 at that time is a photographic area and outputs the area determination signal 9. Then, a level “1” indicating a photographic area is output, and if either or both of the density signal 8 and the density change signal 10 are “OFF”, a level “0” indicating a character area is output.

The above operation will be further described with reference to FIG. 4 showing the relationship between the density level of the image signal 5 and the density change. FIG. 4 is a graph in which the vertical axis indicates the density level of the image signal 5 and the horizontal axis indicates the amount of change in the density level. In this example, the density threshold 6
Is the density level 200, the density threshold value 7 is the density level 100, and the density change threshold value 11 is the density change level 80. The density thresholds 6 and 7 described with reference to FIG. 1 are drawn as horizontal lines a and b, and the density change threshold 11 is drawn as a vertical line c.
Therefore, the density signal 8 in the description of FIG. 1 determines whether the density level of the input image signal 5 is between the horizontal line a and the line b, that is, the density level is between 200 and 100. The density change detection circuit 2 determines whether the amount of change in the density level of the image signal 5 is on the left side of the vertical line c, that is, whether the change in the density level is smaller than 80.

The area determination signal 9 is "ON" only when both the density signal 8 and the density change signal 10 are "ON". Therefore, when the image signal 5 is a hatched portion in the center of FIG. Is determined as a photographic region, and a portion where the density is not abrupt and the variation is not abrupt is determined as a character region.

Here, the density threshold value 6 and the density threshold value 7
Is empirically determined in advance. The density change threshold value 11 is obtained by correcting the density change threshold value 12 from the density change threshold value determination circuit 4 using the determination result of the peripheral area.

In the density change threshold value determining circuit 4 shown in FIG. 2, the determination storage memory 13 stores the image determination result of the pixel whose image area has been determined, that is, "1" or "0" as the area determination result in FIG. Is stored as shown in FIG. A weighting factor A shown in FIG.
A weighted sum of the determination results of the peripheral region of the pixel of interest is calculated using ij, and the sum is summed with a density change threshold value 12 set in advance by an addition circuit 15 to obtain a density change threshold value 11. Supplied as

Here, the calculation of the weighted sum circuit 14 is as follows: its output is S1, the judgment result is Mij, the weighting coefficient is Aij, and the coefficient is α
Is performed based on the following equation (1).

S 1 = α ｛ΣG (Mij) · Aij / ΣAij｝ G (Mij) = 1 (Mij = 1: for a photograph) = − 1 (Mij = 0: for a character) (1) When there are many pixels determined to be characters in the area, the density change threshold may be decreased, and when there are many pixels determined to be photographs in the peripheral area, the density change threshold may be increased. When the density determination result is "0", the density change threshold value is controlled by converting the value to -1 and obtaining a weighted sum. That is, when there are many characters in the peripheral area, the output of the weighted sum circuit 14 is negative, and conversely, when there are many photographs in the peripheral area, the output becomes positive. The density change threshold value 11 increases or decreases.

The density change threshold value determination circuit 4 in FIG. 3 is another example of the density change threshold value determination circuit. The difference from FIG. 2 is that the adder 15 is replaced by a multiplier 16. Are the same as in FIG.

Here, the weighted sum circuit 14 calculates the output as S2, the judgment result as Mij, the weighting coefficient as Aij, and the coefficient as β
Is performed based on the following equation (2).

S 2 = β ｛ΣMij · Aij / ΣAij｝ Mij = 1 (in the case of a photograph) = 0 (in the case of a character) (2) That is, as described above, there are many pixels determined to be characters in the peripheral area. When the number of pixels determined to be photographs in the peripheral area is large, the density change threshold may be increased. Therefore, in the case of FIG. 3, the output of the weighted sum circuit 14 is close to 0 when there are many characters, and close to 1 when there are many photographs. The density change threshold 11 is controlled by multiplying the density change threshold 12 by the product.

In this embodiment, the peripheral area is 12 pixels as shown in FIG. 5, but various cases such as a larger area and a smaller area are conceivable. Further, the weighting coefficient can be set to an appropriate value according to the size and shape of the surrounding area.

Alternatively, the calculation result for the pattern of the determination result of the peripheral area may be obtained in advance, and this may be stored in the ROM, and the density change threshold value 11 may be obtained by inputting the pattern of the determination result.

In the above-described embodiment, the density change detection circuit 2 monitors the change in the density level of the image signal 5 which is continuously input, but various realization methods can be considered. For example, the difference in density level between adjacent pixels may be used as the amount of change in density, or a group of several pixels around the pixel of interest may be defined as one area, and the density level of the highest density pixel in that area The difference between the density of the target pixel and the density level of the pixel with the minimum density may be used as the amount of change in the density of the target pixel.

Further, it is a matter of course that the image signal 5 may be once passed through a high-pass filter such as a differentiating circuit, and the value thereof may be used as a change in density. FIG. 7 shows an example of coefficient values of a high-pass filter composed of 3 × 3 pixels.

In this embodiment, two density thresholds, ie, the density threshold 6 and the density threshold 7, are set. However, if the density threshold 6 is a value of level 255, If the change is smaller than the density change threshold 11 and the density is higher than the density threshold 7, the area is determined to be a photographic area. When the density threshold value 7 is the value of the level “0”, if the density change is smaller than the density change threshold value 11 and the density is smaller than the density threshold value 6, the photographic area is determined. Is determined.

[0036]

As described above, according to the present invention, the character area and the photographic area can be accurately and simply determined from the density information of the document and the determination result of the peripheral area with a simple configuration. .

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing an example of a density change threshold value determining circuit.

FIG. 3 is a block diagram showing another example of the density change threshold value determination circuit.

FIG. 4 is a diagram showing an example of the relationship between the density of an image signal 5 and a density change.

FIG. 5 is a diagram showing an example of a determination storage memory 13;

FIG. 6 is a diagram illustrating an example of a weight coefficient of the weighted sum circuit 14.

FIG. 7 shows a filter that passes an image signal 5 in FIG.
The figure which shows an example of the coefficient value at the time of being comprised by a pixel.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Density detection circuit 2 Density change detection circuit 3 Area judgment circuit 4 Density change threshold value determination circuit 5 Image signal 6, 7 Density threshold 8 Density signal 9 Area judgment signal 10 Density change signal 11, 12 Density change threshold 13 judgment storage memory 14 weighted sum circuit 15 addition circuit 16 multiplication circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60 G06T 7/00-7/60

Claims (2)

(57) [Claims] 1. An image area determination device comprising means for determining whether an input multi-valued image is a character area or a photograph area and outputting an area determination signal, wherein the density value of the multi-valued image is determined in advance. a concentration detecting circuit for outputting a density signal which indicates whether not enter or enter between the set two concentration threshold based on the area identification signal for the peripheral area of the pixel of interest
Shown Te and density change threshold value determination circuit which sets and outputs a first concentration change threshold, whether the amount of change in density value of the multilevel image not there below the first concentration change threshold A density change detection circuit that outputs a density change signal, and receives the density signal and the density change signal, and indicates that the density signal is between the two density thresholds, and the density change signal is the first density change signal. An area determination circuit that outputs the area determination signal that indicates that the multi-valued image is a photographic area if the density change is smaller than a threshold, and a text area otherwise. Area determination device. Wherein said concentration change threshold value determination circuit includes a determination storage memory for storing the type of the region determination signal determination result, the determination result of the peripheral region of the pixel of interest stored in the determination storage memory comprising a weighted sum circuit for obtaining a weighted sum of the input perilla, and an operation circuit for outputting the first concentration change threshold performs an operation of a second concentration change threshold set in advance and the weighted sum The image area determination device according to claim 1.