JP2002232704A - Image processor and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processor and an image forming device which can precisely determine the background region of characters and line drawings as a plurality of regions of different properties, and can perform image processing on adequate conditions corresponding to the determination. SOLUTION: In this system, the regions of characters and line drawings are determined, and their backgrounds are determined by distinguishing them into a plurality of different patterns of a white background detector 61, a halftone region detector 62, or the like, so that different image processings can be performed in response to characters, line drawings, or determined background regions. This enables the optimal image processing, based on the correct determination of the properties of background of characters and line drawings, therefore, leading to the improvement of the quality of output images.

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 detecting characteristics of an input image and performing image processing on an image to be output based on the detection result, and an image forming apparatus equipped with the image processing apparatus. .

[0002]

2. Description of the Related Art In an image processing apparatus used in a digital copying machine or the like, when reproducing an image in which a pattern and a character such as a halftone dot or a solid color (photograph) are mixed, a high quality reproduced image is obtained. It is desirable to perform high-gradation image processing on a picture, and to perform image processing emphasizing resolution on characters and line drawings. Further, when reproducing black characters using a color copying machine, it is considered that eliminating coloration is important for improving character quality. Therefore, it is required to automatically identify a character area and a picture area, and to perform undercolor removal (UCR) processing suitable for each area.

[0003] In general documents, characters often exist on a white background (a character area having a white background area). However, in a table or the like published in a catalog or the like, characters are present.
In many cases, a character has a halftone dot (a character having a halftone dot background).

For characters on a white background, 100% undercolor removal processing of replacing Min (cyan C, magenta M, yellow Y) with black K toner is, of course, optimal. In letters, it is not necessarily 1
Undercolor removal processing of 00% is not preferred. In the halftone portion, since the undercolor removal processing is performed with an emphasis on gradation, for example, 50%, the difference in the undercolor removal rate between the halftone portion and the character portion around the character causes image distortion and white spots. Appear. as a result,
Reproducing the character portion with high ink makes the image rather unsightly. Therefore, in the so-called image area separation processing, it is general that characters in a halftone dot area are regarded as a picture part and image processing for a picture is performed similarly to the halftone part, and an output device having a large pixel displacement is generally used. In, the coloring of the characters in the halftone dot area is a major problem. That is, at present, it is not possible to reproduce both a character having a white background as a background and a character having a halftone dot as a background with high image quality.

[0005] For this reason, as described in Japanese Patent Application Laid-Open No. H6-152945, image processing in which a background region of a character is determined as a background degree and black character processing is performed in accordance with the background degree. A device has been proposed. This is to perform black character processing according to the background. Specifically, when the background is a white background, the UCR amount is increased to make the characters clear, and when the background is a halftone dot or a solid color, the UCR amount is reduced. It is intended to reproduce the original image faithfully by weakly applying it.

[0006]

However, the background of a character includes a white background, a halftone dot, and a solid color (photograph), and the density varies from highlight to dark.
As described in Japanese Patent Publication No. 152945, there is a limit to performing optimal image processing in accordance with the background region even if the determination is made based on only one reference pattern, that is, the background degree. Further, in the embodiment of the publication, it is described that the periodicity in the main scanning direction is added to the determination element when the background degree is determined, but the halftone dot changes its cycle when the document is slightly inclined. The conditions worsen.

A first object of the present invention is to provide an image processing apparatus capable of accurately determining a background area of a character or a line drawing as a plurality of areas having different properties and performing image processing under appropriate conditions according to the determination. It is to be.

A second object of the present invention is to provide an image processing apparatus capable of outputting a low-density bold character without borders and clear.

[0009]

According to a first aspect of the present invention, there is provided an image processing apparatus comprising: a character / line drawing area determining unit for determining a character or line drawing area of an input document image; Background area determining means for distinguishing the background of the determined character / line drawing area into a plurality of different patterns, and a character or line image determined by the character / line drawing area determining means and a background area determined by the background area determining means Image processing switching means for performing different image processing according to the image processing.

Therefore, it is possible to correctly determine the nature of the background area of the character or the line drawing, and it is possible to perform image processing under appropriate conditions in accordance with the property of the character or the line drawing and the correctly determined background area. .

According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the character / line drawing area determining means includes:
The determination is made based on the detection result of the edge amount detection.

Therefore, it is possible to output characters and line drawings which are hardly affected by color misregistration.

According to a third aspect of the present invention, in the image processing apparatus according to the first aspect, the character / line image area determining means includes:
The determination is made based on the detection result of the fine line detection.

Therefore, it is possible to output low-density thick characters clearly.

According to a fourth aspect of the present invention, in the image processing apparatus according to the first aspect, the character / line image area determining means includes:
The determination is made based on the detection results of both the edge amount detection and the fine line detection.

Therefore, it is possible to output a character or a line image clearly while obtaining the advantages of both the edge amount detection and the fine line detection.

According to a fifth aspect of the present invention, in the image processing apparatus of the first aspect, the background area determination means makes a determination based on a detection result including a white background area detection and a halftone dot area detection.

Therefore, by determining the nature of the background area of a character or a line drawing on the basis of the detection results including the white background area detection and the halftone dot area detection, the properties of both of the contradictory highlight and dark areas can be determined. It is possible to make a correct determination.

According to a sixth aspect of the present invention, in the image processing apparatus of the fifth aspect, the background area determination means makes a determination based on a detection result including a solid area detection.

Therefore, the nature of the background region of a character or a line drawing is determined by the detection result including the white background region detection, the halftone dot region detection, and the solid region detection, so that the nature of the background region can be more finely determined. It becomes possible. This makes it possible to set the image processing conditions corresponding to the background area more precisely.

According to a seventh aspect of the present invention, in the image processing apparatus according to the first aspect, the image processing performed by the image processing switching means is an under color removal process that applies an under color removal amount according to the background area. is there.

Therefore, for a character or a line drawing having a background such as a halftone dot as a background, it is possible to suppress the drawbacks caused by the reproduction of the edge with high black, and to reproduce a character or a line drawing having a background as a white background without coloring. Becomes possible.

According to an eighth aspect of the present invention, in the image processing apparatus according to the first aspect, the image processing performed by the image processing switching means is a filter processing according to the background area.

Therefore, with respect to characters and line drawings having a background such as a halftone dot, defects are suppressed by using a filter having relatively low sharpness at edges, and characters and line drawings having a white background as a background are used. Can be reproduced sharply.

According to a ninth aspect of the present invention, in the image processing apparatus according to the first aspect, the image processing performed by the image processing switching means is a gamma correction process according to the background area.

Therefore, with regard to characters and line drawings having a background such as a halftone dot as a background, a defect is suppressed by performing a gamma correction process using a table having a relatively gentle gamma characteristic at the edge, and the background is reduced. Characters and line drawings that are to be white background areas can be reproduced sharply.

An image forming apparatus according to a tenth aspect includes the image processing apparatus according to the first to ninth aspects, and a printing unit.

Accordingly, there is provided an image forming apparatus capable of correctly determining the nature of the background area of a character or a line drawing and performing image processing under appropriate conditions in accordance with the properties of the character or line drawing and the correctly determined background area. It becomes possible.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. First, a schematic configuration of an image processing circuit A as an image processing device will be described with reference to FIG. In the present embodiment, the image processing circuit A is mounted on a digital copying machine as an example of an image forming apparatus, but is not limited thereto, and may be connected to an interface (not shown) such as a color scanner or a network. It may be connected.

The image processing circuit A includes a filter processing section 1, a color correction section 2, an under color removal (UCR) / black generation section 3, a gamma correction section 4, and a character / line drawing area of a document. It has a character area detecting section 5 as a character / line image area determining means, a background area detecting section 6 as a background area determining means for determining a background area of a character area of a document, and a lookup table (LUT) 7. The present invention provides a "character / line drawing area" for applying to either a character area or a line drawing area.
However, in the present embodiment, a “character area” will be described to simplify the description.

In the present embodiment, the character area detection by the character area detection unit 5 and the background area detection by the background area detection unit 6 use the G signal of the input image signal RGB from the interface. To detect, but Max
The detection may be performed using a luminance signal or a brightness signal obtained from the (R, G, B) signal or the RGB signal. The method of determining the character area and the background area will be described later.
Filter processing unit 1 based on the output of the
Processing, under color removal (UCR) / black generator 3
The parameters of image processing such as under color removal processing by the gamma correction unit 4 and gamma correction processing by the gamma correction unit 4 are to be determined by a look-up table (LUT) 7. The look-up table 7 functions as an image processing switching unit for performing different image processing according to the character area and the background area. The different image processing is, for example, a processing with a different undercolor removal rate in the case of undercolor removal processing. This will be described later.

Next, FIG. 2 is a block diagram showing an electrical configuration of the background area detecting section 6 shown in FIG.
Will be described. The background area detection unit 6 performs a white area detection by the white area detection unit 61 to determine whether or not the pattern is a white area pattern.
The halftone dot area detection unit 62 detects a halftone dot area to determine whether or not it is a halftone dot pattern, and the determination unit 63 makes a determination based on the output that is the result of both detections. The determination unit 63 outputs (0) having a meaning as a white background region when it is determined as a white background region by the output of the white background region detection unit 61 and is determined to be not a halftone region by the output of the halftone region detection unit 62. (1) is output in the case of other determination (in the case of a dot area or a solid area).

Here, the white background area detecting section 61 shown in FIG.
Will be described in more detail with reference to FIG. FIG. 3 is a block diagram showing the white background area detection unit 61. The white area detection in the present embodiment is performed by a method similar to a known method described in, for example, Japanese Patent Application Laid-Open No. 4-14378, and thus will only be briefly described.

First, the G signal of the input image signal is converted to a binary
2 for white / non-white pixels according to the threshold determined in 11
Value. Next, the white pixel detection unit 612 detects a white pixel by comparing a local two-dimensional pattern formed by the binarized signal with a previously prepared white pixel pattern. As an example of a white background pixel pattern in this case, it is simplest that all pixels are white pixels in a 5 × 5 mask. When this condition is satisfied, it is assumed that the target pixel is a white background pixel. judge. Subsequently, when the expansion processing unit 613 recognizes that one or more white background pixels detected in the previous process exist in a block of a certain size around the target pixel, the target block is determined to be a temporary white background neighboring area. Subsequently, when the correction processing unit 614 recognizes that a white background exists in the left / right or up / down direction of the target block, it is determined that the target block is a white background. At this time, the correction process may be performed based on the presence of a white background on only one side in the left-right direction or only one side in the up-down direction of the block of interest. However, by referring to the presence or absence of the white background on both sides, bold characters are detected as white background characters. You can manipulate whether or not.

The presence or absence of the white background on both sides can be checked as follows. Here, the presence / absence of the white background on both the left and right sides of the target block is checked. The same applies to the case of checking the white background on both the top and bottom sides. N blocks are referred to the left side and N + 1 blocks are referred to the right side with respect to the target block. At this time, the left side is the L-th block (L
≦ N) and the right side of the area near the temporary white background appears at the Mth block (M ≦ N), the width of the non-white background area (this is considered as the character width) is (L−1).
+ (M−1) +1 block ”. That is, by referring to the left and right sides of the target block, the distance between a white background and a white background = character width can be known. If it exceeds, it is also possible to perform control such that it is determined as a non-white background area and processing for a picture portion is performed.

Next, a description will be given of the dot area detection processing by the dot area detection section 62 shown in FIG. The dot area detection in the present embodiment is described in, for example, IEICE Transactions Vol. J75-D2 1992-1 “Image Area Separation Method for Character / Picture (Dot, Color) Mixed Image”. Since the method is performed in the same manner as the method, only a brief description will be given. The dot area detection in this example is a method based on peak pixel detection. This is to determine whether or not the target pixel is an extreme point indicating the peak of the density change based on the density relationship with surrounding pixels. Specifically, in the block of M × M pixels (see FIGS. 4A and 4B), the density level of the central pixel is set to be higher than the density levels of all other pixels by a series of calculation formulas shown below or Is high or low, it is determined whether or not it is an extreme point.

FIG. 4A is a schematic diagram for explaining the detection of peak pixels in a block of M × M pixels = 3 × 3, and FIG. 4B is a diagram showing the detection of peak pixels of M × M pixels = 5 × 5. FIG. 3 is a schematic diagram illustrating peak pixel detection in a block. m ₀ corresponds to the density level of the central pixel.

A series of formulas when M × M = 3 × 3 | 2m ₀ −m ₁ −m ₈ | ≧ Δm _TH and | 2m ₀ −m ₂ −m ₇ | ≧ Δm _TH and | 2m ₀ −m _3- m ₆ | ≧ Δm _TH and | 2m ₀ −m ₄ −m ₅ | ≧ Δm _TH A series of calculation formulas in the case of M × M = 5 × 5 | 2m ₀ −m ₃ −m ₂₂ | ≧ Δm _TH and | 2m ₀ −m ₈ −m ₁₇ | ≧ Δm _TH and... | 2m ₀ −m ₁ −m ₂₄ | ≧ Δm _TH and | 2m ₀ −m ₇ −m ₁₈ | ≧ Δm _TH Although the calculation formula in the middle is omitted, in short, the absolute value of the difference between the average value of the density levels of the two pixels located symmetrically with respect to the center pixel and the density level of the center pixel is smaller than the threshold value Δm _TH. When larger, the central pixel is detected as a peak. Then, it is determined whether or not the area is a halftone area based on the information of the peak pixel. For example, in the simplest case, halftone pixels are counted for each block of a predetermined size, and if the counted value is equal to or larger than a predetermined number, it is determined that the halftone area is a halftone area.

Next, a description will be given of the character area detecting process by the character area detecting section 5 shown in FIG. In the present embodiment, when the edge amount is detected, the area is determined as a character area. The edge amount is used to determine whether or not an edge is multi-valued.
This shall include value judgment. The character area detection processing based on the edge amount detection will be described with reference to FIG. FIG. 5 is a block diagram of edge amount detection processing for character area detection.

In this example, the G signal of the input image signal is filtered. Specifically, for the G signal, a first edge amount detection filter 511, a second edge amount detection filter 512, a third edge amount detection filter 513, a fourth
Masking using the edge amount detection filter 514 of
The absolute values of the four detection outputs at that time are converted into absolute value
5, 516, 517, and 518, the one having the largest absolute value is selected by the maximum value selection unit 519, and is set as the edge amount. 7
× 7 first to fourth edge amount detection filters 511, 51
2, 513, 514 are shown in FIGS. 6 (a), (b), (c), and (d).
Are different filters as shown in FIG.

Next, an image processing switching means for performing different image processing on the image of the character area according to the background area determined by the background area detection unit 6 will be described. Means under color removal (UCR)
Any one of the under color removal processing in the black generation unit 3, the filter processing in the filter processing unit 1, and the gamma correction processing in the gamma correction unit 4 may be used. Hereinafter, description will be made in order.

First, the undercolor removal (UCR) / undercolor removal processing in the black generator 3 will be described. Under color removal (UCR)
When the background area is determined to be the maximum with the edge amount being the white background area, the black generation unit 3 shown in FIG.
(K of black determined by 100% undercolor removal rate)
A signal is generated, and when it is determined that the edge amount is the maximum in a halftone dot region or a solid color region (photo region), a K signal determined by the black generation table-1 is generated,
If determined to be non-edge (the edge amount is zero), a K signal determined by the black generation table-2 is generated.
In the case of an intermediate edge amount, when it is determined that the area is a white background area, a K signal corresponding to the area between the black generation table-0 and the black generation table-2 is generated, and the halftone area or the solid area is determined. At this time, a K signal corresponding to the range between the black generation table-1 and the black generation table-2 is generated.
Under color removal processing is performed according to the value of. Note that the black generation table in FIG. 7 is an example of data defined in a look-up table 7 (see FIG. 1) that determines image processing parameters based on detection results of the character region detection unit 5 and the background region detection unit 6.

Next, a case where the image processing performed by the image processing switching means is a filter processing in the filter processing section 1 will be described. The filter processing unit 1 performs the strongest edge enhancement processing when it is determined that the character is on a white background area,
When it is determined that the character is on a halftone dot region or a solid color region, a slightly weak edge enhancement process is performed. If it is determined to be a non-character part, weaker edge processing is performed.

In this case, the adjustment of the edge emphasis strength may be performed by directly switching the parameters of the filter, or a means for switching the coefficient by which the output of the Laplacian filter 8 is multiplied as shown in FIG. Conceivable.
Here, adaptive edge enhancement generally performed is briefly described. Assuming that the original signal is G, the output of the Laplacian filter 8 is L (G), and the signal after edge enhancement is G ', the edge enhancement is represented by G' = G + L (G). This calculation is performed by the adder 9 in FIG. This is the same as multiplying the original signal G by changing the value at the center of the Laplacian filter 8 of FIG. FIG. 9 shows a 5 × 5 Laplacian filter 8.
Is an explanatory diagram showing an example in which the target pixel component and the Laplacian filter 8 are separated and shown.

From the above equation, it can be seen that the output L (G) of the Laplacian filter 8 corresponds to the enhancement component.
Therefore, the coefficient for adjusting the intensity of the Laplacian filter 8 (output from the LUT 7) is P, and G ′ = G + L (G) × P is calculated. This calculation is performed by the multiplier 10 in FIG. At this time, the P to be multiplied can adjust the edge enhancement adaptively.

The filter processing in the filter processing unit 1 includes edge smoothing in addition to edge enhancement. In the case of smoothing, contrary to the case of edge emphasis, a smooth-through filter is used for characters on a white background area, and a stronger smoothing filter and non-characters are used for characters on a halftone area or solid area. A stronger filter may be used for the section.

Further, a case where the image processing performed by the image processing switching means is the gamma correction processing in the gamma correction unit 4 will be described. The gamma correction process prepares a gamma table as shown in FIG. The gamma correction unit 4 uses the steepest gamma table-0 when it is determined to be a character on a white background area, and uses a slightly gentle gamma table when it is determined to be a character on a halftone area or a solid area. 1 is used, and if it is determined to be a non-character portion, processing is performed using gamma table-2. The gamma table is an example of data defined in a look-up table 7 (see FIG. 1) that determines image processing parameters based on detection results of the character area detection unit 5 and the background area detection unit 6.

As described above, according to the present invention, when the background area is detected, the detection of the white background area and the detection of the picture area such as a halftone dot different from the white background area detection are performed. The most suitable image processing can be performed in accordance with the characteristics of.

Next, a second embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. In the present embodiment and other embodiments following this, the same parts as those in the above-described first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the first embodiment, the edge amount is detected, and a portion where the edge amount is high is regarded as a character area. In the present embodiment, not the edge amount but the fineness is used as an index representing the character area. .

Here, the concept of the edge amount is shown in FIG.
FIG. 11B shows the concept of fineness. FIG. 11 shows a case where each of the edge amount and the fine line degree is determined in three values. The black portion indicates the maximum value 2, the intermediate gray portion indicates the intermediate ground 1, and the lightest gray portion indicates the minimum value. 0
Area. The edge amount in FIG. 11A is a feature amount representing “distance from the edge”, and the fineness in FIG. 11B is a feature amount representing “fine line width”. In the case where the character area is determined based on the edge amount in FIG. 11A, the gap between the lightest gray portion (the portion in the character) and the edge portion of the black portion is conspicuous and gives an uncomfortable feeling. On the other hand, FIG.
When the character area is determined based on the fineness of 1 (b), the same processing is performed between the edge portion and the middle of the character when viewed in the horizontal direction on the paper, and the processing is switched in the vertical direction on the paper having different line widths. However, the switching at the thin line portion is less noticeable than the switching at the thick line portion, and the discomfort is hardly felt.

Referring to FIG. 12, a description will be given of the character area detection processing based on the fine line degree detection. FIG. 12 is a block diagram of the fine line degree detection processing for character area detection. First, the binarization unit 5
At 21, the G signal of the input image signal is binarized into black pixels and white pixels, and then the number of continuous black pixels is counted by a continuous black pixel counting unit 522.
23 outputs fineness "2""1""0". “2”
Is the maximum value that is detected as an area where the number of continuous black pixels is 1 to 14 and determined as a character.
An intermediate value determined as an area of ~ 30, and "0" is a minimum value detected as an area having a number of continuous black pixels of 31 or more and determined as a non-character.

By counting the number of continuous black pixels not only in the main scanning direction but also in the sub-scanning direction, the precision of fineness can be further improved. Further, the fine line degree detection is not limited to the detection of the number of continuous black pixels, but can be applied to the detection of the distance between a white background and a white background, the detection of the distance between edges, and the like.

Next, a third embodiment of the present invention will be described with reference to FIG.
It will be described based on. FIG. 13 is a block diagram showing an electrical connection structure of the character area detection unit 5. In the first embodiment, the edge amount detection is used to determine the character area, and in the second embodiment, the fine line degree detection is used. In the present embodiment, the edge amount is detected from the G signal. The fine line degree is detected by the thin line degree detecting section 52, and the output of the edge amount detecting section 51 and the output of the fine line degree detecting section 52 are multiplied by the multiplier 53 to obtain a character area determination result. is there. The edge amount detection processing by the edge amount detection unit 51 is the same as the processing described in the first embodiment,
The fine line degree detection processing is the same as the processing described in the second embodiment.

If the character area is determined based on the edge amount, there is a merit that the influence of color misregistration at the time of outputting an image is reduced, and if the character area is determined based on the fineness, it is effective for high-quality reproduction of low-density thick characters. There are benefits.

Although the multiplier 53 is used to extract the output of the edge amount detecting section 51 and the output of the fine line degree detecting section 52, another element may be used instead of the multiplier 53.

Further, a fourth embodiment of the present invention is shown in FIG.
4 and FIG. FIG. 14 is a block diagram of the background area detection unit 6. In the first embodiment, the background region detection unit 6 shown in FIG. 1 is configured by the white background region detection unit 61, the halftone dot region detection unit 62, and the determination unit 63 as shown in FIG. In the embodiment, the white area detection unit 61
In addition to the detection result by the dot region detection unit 62 and the detection result by the solid region (photo region) detection unit 64, whether the background of the character is a white background region or a dot region is determined. The determination unit 65 determines whether the area is a solid color area.

In this embodiment, the background of a character or a line drawing is
The determination can be made separately for a white background area, a halftone dot area, and a solid color area, and optimal image processing can be performed for each determined area.

Thus, in the undercolor removal processing, for example, in a document in which a human face is shown in a solid color area, the high-black reproduction of the contour of the face further deteriorates the image quality as compared with the halftone dot area. Even if the undercolor removal rate is optimal for characters and line art on the halftone dot area, the undercolor removal rate is often still high in the outline of the face. Is good. However, in the present embodiment, the region other than the white background region is determined by dividing it into a halftone region and a solid region, so that image processing suitable for the background region can be performed.

The processing in the solid area detection section 64 is the same as the intermediate level pixel detection method described in, for example, Japanese Patent Application Laid-Open No. 7-298074, and will be briefly described with reference to FIG. FIG. 15 is a block diagram of the solid area detection unit 64 (see FIG. 14). That is, G of the input image signal
The signal is ternarized by two thresholds in a ternarization unit 641, and the pattern matching unit 64
2, pattern matching is performed. This is 3x
If all the pixels in the block 7 are intermediate level pixels, the pixel of interest is output as a photographic pixel. Subsequently, the counter 643 counts the number of photo pixels for each block of a predetermined size, and when the count value is equal to or larger than the predetermined number, the determination unit 644 outputs a signal indicating that the area is a colored area.

This method of detecting a solid color region is a detection method which focuses on the property that a photographic original contains many intermediate level pixels and these intermediate level pixels have a certain amount of clumps. Without using the solid area detection unit 64,
Although it can be determined as a solid area with non-dots and non-white background, as in the present embodiment,
By providing the solid area detection unit 64, it is possible to further easily recognize a highlight or a dark part that is difficult to recognize as a solid area.

[0062]

According to the image processing apparatus of the first aspect,
In addition to determining the character or line drawing area, the background of the character or line drawing is determined by differentiating into a plurality of different patterns, and different image processing is performed according to the character or line drawing and the determined background area. After properly determining the nature of the background area of the line drawing, optimal image processing can be performed,
Therefore, the quality of the output image can be improved.

According to the second aspect of the present invention, in the image processing apparatus according to the first aspect, the character / line image area determining means determines based on the detection result of the edge amount detection.
Characters and line drawings that are not easily affected by color shift can be output.

According to the third aspect of the present invention, in the image processing apparatus according to the first aspect, the character / line image area determination means makes the determination based on the detection result of the thin line detection, so that the low-density bold character can be clearly seen. Can be output.

According to the fourth aspect of the present invention, in the image processing apparatus according to the first aspect, the character / line image area determination means makes a determination based on both detection results of edge amount detection and fine line detection. Characters and line drawings can be output clearly while obtaining the advantages of both edge amount detection and fine line detection.

According to the fifth aspect of the present invention, in the image processing apparatus according to the first aspect, the background area determination means performs the determination based on the detection result including the white background area detection and the halftone dot area detection. It is possible to correctly determine the properties of both the highlight area and the dark area of the background area.

According to the sixth aspect of the present invention, in the image processing apparatus according to the fifth aspect, the background area determination means performs the determination based on a detection result including a solid area detection, so that the background area is defined as a white area and a halftone area. Correct determination can be made separately for the point area and the solid area, whereby the image processing conditions according to the background area can be set more precisely.

According to the seventh aspect of the present invention, in the image processing apparatus according to the first aspect, the image processing performed by the image processing switching means is an under color removal process for applying an under color removal amount according to a background area. Therefore, for a character or a line drawing having a background such as a halftone dot as a background, it is possible to suppress a defect caused by the high-black reproduction of the edge and to reproduce a character or a line drawing having a background as a white background without coloring. .

According to the eighth aspect of the present invention, in the image processing apparatus according to the first aspect, the image processing performed by the image processing switching means is a filter processing according to the background area.
For characters and line drawings with a background such as a halftone dot, use a filter with relatively low sharpness at the edges to suppress defects, and for characters and line drawings with a white background as a background, play them sharply. can do.

According to the ninth aspect of the present invention, in the image processing apparatus according to the first aspect, since the image processing performed by the image processing switching means is a gamma correction processing according to the background area, a picture pattern such as a halftone dot is formed. For characters and line drawings with a background as a background, defects are suppressed by performing gamma correction using a table with relatively gentle gamma characteristics at edges, and for characters and line drawings with a white background as a background, It can be reproduced sharply.

According to a tenth aspect of the present invention, since the image forming apparatus includes the image processing apparatus according to the first to ninth aspects and a printing unit, it is possible to correctly determine the nature of the background area of a character or a line drawing, and It is possible to provide an image forming apparatus capable of performing image processing under appropriate conditions in accordance with the properties of a background area that is correctly determined.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an image processing circuit as an image processing device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a background area detection unit.

FIG. 3 is a block diagram illustrating a white background area detection unit.

FIG. 4A is a schematic diagram illustrating peak pixel detection in a 3 × 3 pixel block, and FIG. 4B is a schematic diagram illustrating peak pixel detection in a 5 × 5 pixel block.

FIG. 5 is a block diagram of edge amount detection processing for character area detection.

FIG. 6 is an explanatory diagram of a masking processing filter used for edge amount detection.

FIG. 7 is an explanatory diagram showing data of a black generation table used for image processing in an under color removal / black generation unit.

FIG. 8 is an explanatory diagram of edge enhancement processing in a filter processing circuit.

FIG. 9 is an explanatory diagram illustrating an example in which a Laplacian filter is used in a filtering process performed by a filtering circuit.

FIG. 10 is an explanatory diagram showing gamma table data used for image processing in a gamma correction unit.

FIG. 11 shows a second embodiment of the present invention.
(A) is a conceptual diagram of an edge amount, (b) is a conceptual diagram of a fine line degree.

FIG. 12 is a block diagram of a fine line degree detection process for character area detection.

FIG. 13 is a block diagram illustrating an electrical connection structure of a character area detection unit according to a third embodiment of the present invention.

FIG. 14 is a block diagram of a background area detection unit according to a fourth embodiment of the present invention.

FIG. 15 is a block diagram of a solid area detection unit.

[Explanation of symbols]

 5 Character / line drawing area determining means 6 Background area determining means 7 Image processing switching means

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/46 H04N 1/46 Z (72) Inventor Koji Kobayashi 1-3-6 Nakamagome, Ota-ku, Tokyo No. F-term in Ricoh Co., Ltd. LA06 LA07 LA12 LA14 LA21 LA31 MA04 MA11 NA01 NA29 PA02 5L096 AA02 AA06 DA01 FA06 FA43 FA44 GA02

Claims (10)

[Claims] 1. A character / line drawing area determining means for determining a character or line drawing area of an input document image, and a background of the character / line drawing area determined by the character / line drawing area determining means is set to a plurality of different patterns. A background region determining unit that determines by distinction; an image processing switching unit that performs different image processing according to the character or line image determined by the character / line image region determining unit and the background region determined by the background region determining unit; An image processing apparatus comprising: 2. The image processing apparatus according to claim 1, wherein the character / line image area determination unit determines based on a detection result of edge amount detection. 3. The image processing apparatus according to claim 1, wherein the character / line image area determination unit makes a determination based on a detection result of fine line detection. 4. The image processing apparatus according to claim 1, wherein said character / line image area determining means determines based on both detection results of edge amount detection and fine line detection. 5. The image processing apparatus according to claim 1, wherein said background area determination means makes a determination based on a detection result including white background area detection and halftone dot area detection. 6. The image processing apparatus according to claim 5, wherein the background area determination unit performs the determination based on a detection result including a solid area detection. 7. The image processing apparatus according to claim 1, wherein the image processing performed by the image processing switching means is an undercolor removal process that applies an undercolor removal amount according to the background area. 8. The image processing performed by the image processing switching means is a filtering process according to the background area.
The image processing apparatus according to any one of the preceding claims. 9. The image processing apparatus according to claim 1, wherein the image processing performed by the image processing switching means is a gamma correction process according to the background area. 10. An image forming apparatus comprising: the image processing apparatus according to claim 1; and a printing unit.