JP2003198868A - Image processing apparatus, image reader, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the degradation of image quality due to misjudgment having been caused in conventional image area discrimination because of the misjudgment caused in an edge part. <P>SOLUTION: The image processing apparatus includes an area extension section for extending a discrimination area so as to avoid disturbance in an edge part of a character image due to the misjudgment. <P>COPYRIGHT: (C)2003,JPO

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 image data, an image reading apparatus and an image forming apparatus having the image processing apparatus, and more particularly to an image area discrimination technique for character images.

[0002]

2. Description of the Related Art When a color image is formed on a recording material or a color image is displayed on a display, it differs depending on whether the image to be recorded or displayed is a character or a non-character image. Image processing is generally performed. That is, processing is performed on a character image so that an image having a hard gradation characteristic is formed in order to make the outline of the image clear, and halftone is well expressed for other than the character image. Therefore, processing is performed so that an image having a soft gradation characteristic is formed.

Since there are not a few images in which a character image and a photographic image coexist in one page, it is common to perform image processing for a character image and image processing for other than a character image, depending on the part of the image. For this reason, image determination is performed for each image area to determine whether or not it is a character image, and in many cases image determination is performed in pixel units.

Further, it is discriminated whether the image is chromatic color or achromatic color. The chromatic color image is formed by using color ink or color toner, and the achromatic image is formed by using black ink or black toner. An image is being formed. The chromatic / achromatic color discrimination is also performed for each image area, that is, for each pixel.

In distinguishing between a character image and a non-character image, brightness, brightness, etc. are compared between adjacent pixels or between adjacent areas composed of a plurality of pixels, and if the difference in brightness is a predetermined value or more, it is determined to be a character image. However, when it is smaller than a predetermined value, it is generally performed as a non-character image. In the chromatic / achromatic color discrimination, it is determined that the chromatic color is a chromatic color if the saturation of a pixel or a region composed of a plurality of pixels is equal to or more than a predetermined value, and it is determined to be an achromatic color if the saturation is less than the predetermined value. .

[0006]

In the conventional image discrimination,
As shown in FIG. 3B, there may be a case where an achromatic color character area mm is mixed in the chromatic color character area ym and an image of a distorted edge portion is formed. This is because the saturation of the color character edge portion is close to the saturation of the black character edge portion, and it is difficult to distinguish the two. FIG. 3B is an example, and FIG.
Contrary to (b), the chromatic color portion may coexist in the edge portion of the black character.

The present invention solves such a problem in the conventional image discrimination and enables the reproduction of an image without the disturbance of the edge portion, and an image reading apparatus having such an image processing device. An object is to provide an image forming apparatus.

[0008]

The above-mentioned objects of the present invention are achieved by the following inventions.

1. A character area detection unit that discriminates a character area from a non-character area, a chromatic area detection unit that discriminates a chromatic color area from an achromatic color area, an area expansion unit that expands a chromatic color area or an achromatic color area, and a black character area detection unit. An image processing apparatus having.

2. The chromatic area detection unit includes a saturation calculation unit that calculates saturation from image data, a threshold generation unit that generates a threshold value, and a determination unit that determines chromatic color / achromatic color using the threshold value. The image processing apparatus according to 1 above.

3. 3. The image processing apparatus according to 1 or 2 above, wherein the area expansion unit sets pixels around the target pixel to be chromatic when the target pixel is chromatic.

4. 3. The image processing apparatus according to 1 or 2 above, wherein the area expansion unit sets the pixels around the target pixel to an achromatic color when the target pixel is an achromatic color.

5. The black character area detection unit determines that the character is a black character when it is determined that the character is a character and achromatic color, and otherwise determines the color area. The image processing device according to item 1.

6. Any one of the above-mentioned 1 to 5 is characterized in that it has an image processing means for performing an image processing different from the image processing on the area other than the character area, for the area determined to be a character by the character area detecting unit. The image processing device according to item.

7. The saturation calculator is configured to display B image data, G
Saturation is calculated using an arithmetic expression that includes image data and R image data, and at least one of the weighting factors of the B image data, the G image data, and the R image data in the arithmetic expression is The image processing device according to any one of the items 2 to 6, wherein the image processing device has different values.

8. The threshold value generation unit inputs a variable threshold value to the determination unit.
The image processing device according to item.

9. An image reading apparatus comprising the image processing apparatus according to any one of 1 to 8 above.

10. An image forming apparatus comprising the image processing apparatus according to any one of 1 to 8 above.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to describing the embodiments of the present invention, a conventional image processing apparatus will be described with reference to FIG. The arrow indicates the flow of the image data D. Image data D is B (blue),
It has G (green) and R (red) luminance data, and the luminance data of each color is composed of, for example, 8-bit data.

The character area detection unit 1 compares the parameters representing the brightness of the image between adjacent pixels, for example, the brightness and the brightness, and the difference in the parameter values between the pixels is equal to or larger than a predetermined threshold value. If it is smaller than the threshold value, it is determined to be a non-character image. Chromatic area detection unit 2
Has a saturation calculator 4 and a determiner 5. The saturation calculator 4 calculates the saturation of the pixel.

The calculation of chroma (Chroma) is performed, for example, by
This is done using equation (1).

[0022]

[Equation 1]

In equation (1), Red, Green,
Blue is a luminance value of each color, and is composed of, for example, 8-bit data. a, b, and c are weighting factors for each channel, and a = b = c = 1.

For calculation of saturation, CIEL * a * b
* Can also be used. In addition, the output of each channel is not an absolute value, for example, (Red-White)
^It may be a squared value such as ² .

The determination unit 5 outputs the output of the saturation calculation unit 4 to a threshold value K.
And outputs a chromatic color signal when K ≦ Chroma and outputs an achromatic color signal when K> Chroma. When the output of the character area detection unit 1 indicates a character area and the output of the chromatic area detection unit 2 indicates an achromatic color, the black character area detection unit 3 determines that the character area is a black character area and outputs a signal indicating the black character area. And outputs a signal indicating the color area in other cases.

In such a conventional image processing apparatus, the output of the chromatic area detection unit 2 at the edge portion of the color character may be close to the output of the chromatic area detection unit 2 at the edge portion of the black character. Differently from the original image, the image data for forming the image shown in FIG. 3B is output as described above.

The disturbance of the edge portion of the character image as shown in FIG. 3 (b) changes variously depending on the value of the threshold value K. When the threshold value K is increased, the edge portion of black characters is likely to be mixed with the color image portion, so that the edge portion is easily disturbed.

Next, the image processing apparatus according to the embodiment of the present invention will be described with reference to FIG. In FIG. 2, the character area detection unit 1, the black character area detection unit 3, and the determination unit 5 are the same as those in FIG.

The saturation calculator 4 is the saturation calculator 4 in FIG.
Similarly, the saturation Chroma is calculated using the equation (1). However, the weighting factors a, b, and c are not equal in value.
For example, different weighting factors such as a = b = 1 and c = 6 are used. As a result, in the formula (1), calculation is performed using R luminance, G luminance, and B luminance having different weightings.

The formula (1) is an example of the saturation calculation, and when another calculation formula is used, a formula including a parameter representing brightness such as lightness for each monochromatic light is used. Further, it has a threshold value generation unit 6, and as shown in FIG. 5, a threshold value that increases linearly in response to an increase in a parameter representing brightness such as lightness is input to the determination unit 5. The threshold in FIG. 5 may not be a straight line but may be a curve that increases in response to an increase in brightness. The characteristics of the image reading apparatus, the characteristics of the image reproducing apparatus, the application of the output image, etc. It is possible to set the threshold value according to.

FIG. 4 shows the detection result of the chromatic area detection unit 2 shown in FIG. 2 for the original image of the gradation image which changes from Green to Red in the horizontal direction and changes from Blue to Yellow in the vertical direction. Shown in contrast. Figure 1
The detection result of the conventional chromatic area detection unit 2 shown in FIG.
As shown in, the Green / Red axis and Blue
An isotropic achromatic region X is formed at the center of the coordinates of the / Yellow axis, and a chromatic region Y is formed around the achromatic region X. In this embodiment, as a result of calculating the saturation by performing the different weighting described above, a flat achromatic region X having a long shape in the Green / Red axis direction is formed at the center as shown in FIG. 4B. It In the areas of Yellow and Blue where the saturation value tends to be low and there is a high possibility that the chromatic color is mistakenly determined to be an achromatic color, the width of the achromatic color is narrowed to make the characters of these colors black characters. The possibility of making a false decision is low.

In the present embodiment, the threshold generator 6 supplies the threshold K shown in FIG. That is, the threshold value generation unit 6 sets a threshold value that increases linearly, for example, as the brightness increases. As a result, in the detection result of the chromatic area detection unit 2, as shown in FIG. 6B, the width of the achromatic area X decreases from the low lightness portion to the high lightness portion. As a result, the possibility of misjudgment in the low lightness portion, which greatly affects the character quality due to misjudgment of chromatic color / achromatic color, is reduced.

As shown in FIG. 7, the area expansion unit 7 determines the adjacent pixel p for one pixel based on the pixel PX determined to be chromatic.
Processing for expanding x1 to px8 into a chromatic color area is performed. In addition, two or more adjacent pixels may be expanded.

FIG. 3 shows an image formed by the image data processed by the area expansion unit 7.

FIG. 3A is an original image, in which the chromatic color character portion YM is formed in the background portion G, but the chromatic color character portion YM is formed.
Has an edge portion E between the background portion G and the chromatic character portion YM. As described above, in the conventional image area discrimination, the area mm determined to be the achromatic character portion is scattered corresponding to the edge portion E, but by the processing of the area expansion portion 7, the area mm is processed.
As shown in (c), the area mm disappears, and a character image composed of a straight line with a clear boundary between the chromatic character area ym and the background portion g is formed.

Further, the chromatic color detection and threshold generation unit 6 by the calculation in which the weighting is changed in the saturation calculation unit 4 is performed.
By the chromatic color detection using the variable range value by, the discrimination accuracy of the chromatic color character / achromatic color character is further improved and it becomes possible to form a higher quality character image.

In the above-described embodiment, the area expansion unit 7 executes the processing for expanding the chromatic color area.
The area expansion unit 7 may be configured to expand the achromatic area. That is, by processing the periphery of the achromatic pixel detected by the chromatic area detection unit 2 as an achromatic color, it is possible to prevent the disturbance of the edge portion of the black character.

The output of the black character area detection unit 3 is input to an image processing means (not shown) and used for processing image data. As is well known, in image processing means, character data is subjected to a hardening process to generate image data for forming a hard image, and for images other than character images, emphasis is placed on reproduction of halftones. Image processing is performed.

The image processing apparatus described above has an image reading means and an image processing apparatus, and has an image reading apparatus and an image reading means for reading an image to generate digital image data, an image processing apparatus and an image forming means. It is used in an image forming apparatus that reads an image and forms an image on a recording material.

In the image forming means, as is well known, an image is formed by using yellow, magenta, cyan and black inks or toners for a chromatic image, and an image is formed by using black inks or toners for an achromatic color. Is formed.

[0041]

According to the present invention, erroneous discrimination of chromatic color / achromatic color at the edge portion of a character image is prevented, so that a character image with a well-defined contour is formed and a high quality character image is formed. Can be formed.

In the edge portion of the character image, the chromatic area detection unit may erroneously distinguish the chromatic color character from the achromatic color character. However, the invention of claim 3 effectively prevents such erroneous judgment. .

According to the invention of claim 4, by expanding the achromatic region, it is possible to effectively prevent the quality of the character image from being deteriorated due to the erroneous discrimination of the image region discriminating section.

According to the invention of claim 6, proper image processing is performed on each of the character image and the image other than the character, so that an image of high image quality can be formed.

According to the invention of claim 7 or 8, since erroneous discrimination between chromatic color and achromatic color is further reduced, it is possible to form an image of higher image quality.

According to the invention of claim 9, a high quality image,
In particular, an image reading apparatus that generates image data that enables an image including a color character image to be formed is realized.

According to the tenth aspect of the invention, an image forming apparatus capable of forming an image of high image quality, particularly an image including a color character image is realized.

[Brief description of drawings]

FIG. 1 is a block diagram of a conventional image processing apparatus.

FIG. 2 is a block diagram of an image processing apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing an original image and a reproduced image.

FIG. 4 is a diagram showing a chromatic / achromatic color discrimination result of a color gradation image.

FIG. 5 is a graph showing a variable threshold.

FIG. 6 is a diagram showing a chromatic / achromatic color discrimination result of a color gradation image.

FIG. 7 is a diagram showing region expansion.

[Explanation of symbols]

1 Character area detector 2 Chromatic area detector 3 Black character area detector 4 Saturation calculator 5 Judgment section 6 Threshold generator 7 Area extension D image data

Claims (10)

[Claims] 1. A character region detection unit for discriminating a character region from a region other than a character, a chromatic region detection unit for discriminating a chromatic color region from an achromatic color region, an region expansion unit for extending a chromatic color region or an achromatic color region, and An image processing apparatus having a black character area detection unit. 2. The chromatic region detection unit, a saturation calculation unit that calculates saturation from image data, a threshold generation unit that generates a threshold value, and a determination unit that determines chromatic color / achromatic color using the threshold value. The image processing apparatus according to claim 1, further comprising: 3. The image processing apparatus according to claim 1, wherein the area expansion unit sets a pixel around the target pixel to a chromatic color when the target pixel is a chromatic color. . 4. The image processing apparatus according to claim 1, wherein the area expansion unit sets the pixels around the target pixel to an achromatic color when the target pixel is an achromatic color. . 5. The black character area detection unit determines that the character is a black character when it is determined that the character is a character and the color is achromatic, and otherwise determines the color area. The image processing device according to any one of 1 to 4. 6. The image processing device according to claim 1, further comprising image processing means for performing image processing, which is different from image processing on an area other than the character area, on an area determined to be a character by the character area detecting unit. The image processing device according to claim 1. 7. The saturation calculating section calculates the saturation using an arithmetic expression including B image data, G image data and R image data, and calculates the saturation using the B image data and the G image in the arithmetic expression.
7. The image processing apparatus according to claim 2, wherein at least one of the weighting factors of the image data and the R image data has a value different from other values. 8. The threshold value generation unit inputs a variable threshold value to the determination unit.
The image processing device according to item. 9. An image reading apparatus comprising the image processing apparatus according to claim 1. Description: 10. An image forming apparatus comprising the image processing apparatus according to claim 1. Description: