JPH07264409A - Image processing device - Google Patents

Abstract

(57) [Summary] [Purpose] By using image area separation information and color information, the background removal threshold value is made to follow the density level of the background continuously and is switched with high accuracy to remove the background. The image area separation unit 5 separates the scanner data into a halftone dot area, a line drawing area, a photographic area, and a fluorescent color area. The background removing unit 6 includes a threshold updating unit 7 and a density converting unit 8. Based on the result of separation by the image area separation unit 5, the threshold updating unit 7
The background removal threshold of is updated for each pixel. The density conversion unit 8 obtains the removal amount based on the background removal threshold and the image data. When the separation result is the above area, the image data is output as it is, and when the separation result is not any area, the image data is output. The removal amount is subtracted from the output.

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 which controls background removal in accordance with the result of image area separation and the result of color information detection.

[0002]

2. Description of the Related Art Generally, in an image processing apparatus such as a copying machine, when a target document is read by an image reading device such as a scanner and the read multi-valued image is output to a printer or a display, the gray level of the background of the document is also reduced. Since it is reproduced as it is, the dirt on the background is not noticeable in the output image. Therefore, conventionally, before outputting an image, a threshold value corresponding to the density level of the background of the document is set, the background is detected based on this threshold, and the stain on the background of the document is removed.

By the way, in a manuscript in which a plurality of manuscripts are pasted together, for example, papers having a high background density such as newspapers and papers having a low background density such as high-quality paper are mixed, and the background density levels have different values. It will be. Therefore, for example, if the background is removed from high-quality paper in accordance with the background density level of newspapers, the highlights and low-contrast characters in the pattern of high-quality paper are removed, or the characters become thin and deteriorate. However, it becomes difficult to read. On the contrary, if a threshold value suitable for the background density level of high-quality paper is applied, there is a problem that the background of newspaper is not removed.

Therefore, when a plurality of background density levels exist in a document, in order to detect the background with high accuracy, it is determined which background density level the paper is, and the threshold value suitable for each is appropriately switched. Is required.

[0005]

As a conventional example as described above, there is a background removing method described in Japanese Patent Laid-Open No. 4-37259. This is related to a background removal method for a bonded original having a plurality of background density levels. The original is pre-scanned and divided into a plurality of representative background density areas corresponding to the respective areas. Then, it is determined which density region the pixel of interest belongs to during the main scan by observing the density change of a pixel row of a certain length from the pixel of interest, and based on the result of this determination, the threshold value applied to the background removal is switched. Control.

However, the above-mentioned conventional method has the following problems. That is, (1) When the number of originals to be bonded is large, or when the ratio of the background to the originals is small, the features of the background are less likely to appear in the histogram, and therefore the threshold cannot be switched with high accuracy. (2) Since the histogram is created by focusing only on the density level, it is impossible to distinguish the background of the newspaper from the highlight pattern of the same density level. (3) In order to divide into a plurality of representative background density regions with high accuracy, it is necessary to create a histogram during prescan, which requires a considerable processing time.

An object of the present invention is to use the image area separation information and the color information to continuously and accurately switch the background removal threshold value to the background density level, and when there are a large number of bonded originals. Another object of the present invention is to provide an image processing apparatus that removes the background by switching with high accuracy even when the ratio of the background area to the original is small.

Another object of the present invention is to provide an image processing apparatus which can improve the detection accuracy of the background by using the image area separation information and the color information and can distinguish the background of the newspaper from the highlight of the pattern. To do.

Still another object of the present invention is to provide an image processing apparatus for performing background removal processing in real time without performing prescan.

[0010]

In order to achieve the above object, in the present invention, in order to remove the background of the newspaper and maintain the picture highlight and the reproducibility of the characters, the first embodiment separates the image areas. Technology (halftone dot area separation, line drawing area separation, photographic area separation, fluorescent color area separation) is used, and color information detection technology (density level detection, saturation detection) is used in the second embodiment. It is characterized in that the image area separation technology and the color information detection technology are used to identify the background having a particularly high density level, such as newspapers, and the pattern highlights and characters, and to control the background removal according to the identification result. The third embodiment is characterized in that the removal calculation of the density conversion section forming the background removal section is performed on the signal after the edge enhancement processing. The fourth embodiment is
The fifth embodiment is characterized in that the undercolor removal and the background removal are processed by a common circuit, and the fifth embodiment is characterized in that the background removal image area separation unit and the filtering processing image area separation unit are shared. .

[0011]

The image area separating section separates the RGB density signals from the scanner into a halftone dot area, a line drawing area, a photographic area and a fluorescent color area. The background removing unit is composed of a threshold updating unit and a density converting unit, and when the separation result in the image area separating unit is not any of the regions, the threshold updating unit updates the background removing threshold by following the background density level. Then, when the separation result is the region, the threshold updating unit updates the value to a value equivalent to the background density level.
The density conversion amount of the density conversion unit is determined based on the background removal threshold value, and when the separation result is not one of the areas, the background density of the original is converted and output. In this way, since the background removal is controlled using the image area separation result, the reproducibility of the image is improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to the drawings. <Embodiment 1> FIG. 1 shows the configuration of Embodiment 1 of the present invention.
In the figure, the scanner 1 has a photoelectric conversion device such as a CCD sensor, and reads an original (not shown) to read R (red),
The color separation signals of three colors G (green) and B (blue) are output. C
The CDs are arranged in a line in the main scanning direction, and the originals are read by moving CCDs, mirrors, etc. along the originals in the sub-scanning direction. The A / D converter 2 converts the R, G, B analog signals into, for example, 8-bit digital signals. The shading correction unit 3 corrects the light distribution of the exposure light source that illuminates the document and the variation of the CCD sensor. log
The (logarithmic) converter 4 converts the reflectance linear data into density linear data (RGB density signal). For example,
When each pixel is converted into an 8-bit digital signal, the RGB density signal of each pixel takes a value of 0-255. Therefore, white is (R, G, B) = (0,0,0), and black is (R, G, B) = (255,255,255).

When the values of R, G and B are linear reflectance, 255 is the brightest color and 0 is the darkest color.
Further, the reflectance is a ratio (= Ir / Io) of the intensity of the light illuminating the original and the intensity of the light reflected from the original, and the common logarithm of the reflectance is the density (= log (Ir / Io)). ).

In the present embodiment, the data obtained by converting the reflectance signal read by the scanner into the RGB density signal as described above is targeted, but the present invention is not limited to this, and for example, L *. u * b * signal, L * a * b * signal,
It can also be applied to other color systems such as Y (yellow), M (magenta), and C (cyan) signals after color conversion.

The image area separating section 5 separates the RGB density signal into any one of a halftone dot area, a line drawing area, a photographic area and a fluorescent color area, and an area other than the area (background of the original). The background removing unit 6 of the present invention includes a threshold updating unit 7 that updates the background removing threshold for each pixel, and a density converting unit 8 that performs density conversion based on the background removing threshold. The unit 8 is controlled by the image area separation result, converts the density of the background portion of the document, and outputs it to a printer or the like. As the printer, for example, a color printer capable of outputting 256 gradations per dot is used. Further, in the case of a color printer having a gradation degree lower than this, gradation processing is performed by multi-value dither processing or multi-value error diffusion processing.

Each part will be described in detail below. Image area separation unit: As described above, the image area separation unit separates each pixel in the input image into four kinds of areas, that is, a halftone dot area, a line drawing area, a photographic area, and a fluorescent color area, and an area that is neither of them. First, the separation of the halftone dot area and the line drawing area will be described. In the description of FIG. 1, the data input to the image area separation unit is density linear, but the present embodiment is not limited to this and may be reflectance linear data.

As a method for determining a halftone dot area, the paper “Image area separation method for mixed image of characters / pictures (halftone dots, photographs)” previously proposed by the present applicant (The Institute of Electronics, Information and Communication Engineers, Vol.
J75-DII No.1 pp39-47 1992 1
The technique of halftone dot area detection described in "Moon" is used.
That is, the detection of the halftone dot area detects the pixels at the top and the bottom of the halftone dot in the local area. Specifically, FIG.
As shown in, in the 3 × 3 block, the density level L of the central pixel is higher than that of all the surrounding pixels,
Alternatively, the density levels (a, b) of the pair of pixels which are low and diagonally across L and the center pixel are all four pairs,
When | 2 × L−a−b |> TH (fixed threshold),
The central pixel is a halftone dot area pixel.

For the determination of the line drawing (edge) area, for example, the technique described in the above-mentioned paper (see FIG. 10 on p42) is used. FIG. 3 is a block configuration diagram of the line drawing (edge) area detection unit. In the ternarization circuit 11, after the input image data is edge-emphasized, two types of fixed thresholds (TH
, TH2) is used for ternarization. That is, white pixels <
TH1, TH1 ≦ intermediate density pixel <TH2, TH3 <black pixel. The black pixel continuity detecting unit 12 and the white pixel continuity detecting unit 13 detect the regions where the black pixels and the white pixels after the ternarization are continuous by pattern matching.

FIG. 4 shows a pattern for detecting continuity of black pixels, and FIG. 5 shows a pattern for detecting continuity of white pixels. When the white pixel and the black pixel which are matched with these patterns are continuously detected, the AND circuit 14 outputs the center pixel as a line drawing (edge) area when the AND circuit 14 matches these patterns.

The method of determining the photographic area is as follows. In this embodiment, 8 pixels near the pixel of interest have an intermediate density and a density change, and pixels other than the halftone dot area and line drawing area are determined as the photographic area. FIG. 6 is a block configuration diagram for determining a photo area.

The MAX (r, g, b) circuit 20 determines the density level MAX (r, g, b) of the input pixel (r, g, b). The 8-pixel buffer 21 holds the MAX (r, g, b) values of the pixel of interest and the 7 pixels processed before that. Note that the length of this buffer is not limited to 8 pixels as long as it can detect the density change. The maximum value pixel detection unit 22 detects the maximum value 1 of the values held in the 8-pixel buffer 21, and the minimum value pixel detection unit 23 detects the minimum value 2 of the values held in the 8-pixel buffer 21. To do.

The intermediate density determination unit 25 is provided in the 8-pixel buffer 2
It is determined whether the maximum value 1 of 1 is an intermediate density. The determination method is an intermediate density when TH4 <maximum value 1 <TH5.
However, TH4 and 5 are predetermined threshold values. The density variation determination unit 26 determines whether the density varies more than a predetermined variation amount in the 8-pixel width. The determination method is the difference device 2
In 4, the difference between the maximum value 1 and the minimum value 2 is obtained, and when the difference is larger than a predetermined value, it is determined that the variation amount is large.

The image area separating units 27 and 28 detect the halftone dot pixels and the line drawing pixels, respectively, as described above. In the comprehensive determination unit 29, when the intermediate density determination unit 25 determines that it is an intermediate density, the density variation determination unit 26 determines that the variation amount is large, and the image area separation units 27 and 28 determine that it is not a halftone dot or line drawing. , It is determined to be a photograph area and output.

In the present embodiment, the image area separation technique described in the above-mentioned paper is used for explanation, but the image area separation circuit and method used in the present embodiment are not limited to this. Basically, any character / design (halftone dot, photograph) may be separated from the image.

Next, separation of fluorescent color areas will be described.
The method for identifying fluorescent colors described below uses the method described in Japanese Patent Application No. 5-151982 previously proposed by the present applicant.

The fluorescent color in this embodiment is, for example, a color applied to the paper surface with a fluorescent pen or the like. Organic fluorescent substances are widely used in commercial fluorescent pens, and they are stimulated by light in the ultraviolet to visible short wavelength range (purple, blue, blue-green),
It has the characteristic of emitting fluorescence (red, yellow, etc.) of a wavelength different from that of the stimulating light. The color of general printed matter is determined only by the reflected light of the irradiated light, whereas the fluorescent color is determined by the reflected light of the irradiated light and the light of the emitted fluorescence. Is different.

Then, as fluorescent colors, red, brown, pink,
When a fluorescent material with high fluorescence emission such as orange and yellow is used, since these fluorescent colors have high fluorescence in the wavelength range from green to red, the reflectance of R or G is compared with that of the white part of the document. And takes a very high value. Therefore, when there is not much difference in reflectance between the originals, it is possible to distinguish whether the color is a fluorescent color or not by determining the input values of R and G with a threshold value.
Further, since almost no fluorescence is emitted in the blue wavelength range, the reflectance of the B component becomes a relatively low value, similar to ordinary red and orange.

Therefore, if the color signal from the scanner of the pixel of interest (in the case of linear reflectance) is [r, g, b], then (r ≧ Th1 or g ≧ Th2) and (b ≦ Th
The fluorescent color can be identified by the determination based on the thresholds Th1, Th2, and Th3 in 3). FIG. 6 shows the configuration of the fluorescent color identifying section when the above determination is used. Comparator 31
Compares the input r with Th1, outputs 1 when r ≧ Th1, outputs 0 otherwise, and the comparator 32
Compares the input g with Th2, outputs 1 when g ≧ Th2, outputs 0 otherwise, and the comparator 33
Compares the input b with Th3, outputs 1 when b ≦ Th3, and outputs 0 otherwise. Comparator 33
Outputs 1 and the comparator 31 or 32 outputs 1 via the OR circuit 34, the AND circuit 35 outputs 1, that is, a fluorescent color identification signal. The identification of the fluorescent color by the threshold value determination described above can be applied not only to the color signal of the image input unit but also to other color signals such as the RGB density signal after gradation correction and the YMC density signal after color conversion. is there.

Threshold updating unit: FIG. 8 shows the configuration of an embodiment in which the threshold updating unit is controlled based on the information of the separation result (halftone dot area, line drawing area, photographic area, fluorescent color area) of the image area separating unit.
In the figure, a minimum value density detection circuit 41 obtains and outputs a minimum value NewTH of the density of pixels in a 3 × 3 block in the vicinity of the pixel of interest for the input density linear r, g, b data. The comparator 42 includes the background removal threshold value holding circuit 4
4. The background removal threshold value TH and the minimum value density Ne held in No. 4
Compare with wTH and output the smaller value. The minimum value density NewTH and the output from the comparator 42 are input to the selection circuit 43, and one of them is selected according to the separation result of the image area separation unit 45.

That is, as a result of the separation by the image area separation unit 45,
When it is determined to be a halftone dot (line drawing, photograph, fluorescent color) area, the selection circuit 43 selects the output value from the comparator 42, and the value is set in the background removal threshold value holding circuit 44. As described above, the output value of the comparator 42 is the background removal threshold value holding circuit 4
The background removal threshold value TH is always smaller than or equal to the background removal threshold value TH set to 4, and as a result, the background removal threshold value TH in the halftone dot (line drawing, photograph, fluorescent color) area is low (low density side). ), But not to high values (high density side).

When it is determined that the image area separation result is not the halftone dot (line drawing, photograph, fluorescent color) area, the selection circuit 43 selects the minimum value density NewTH, and the value is sent to the background removal threshold value holding circuit 44. Is set. Background removal threshold value holding circuit 44
Holds a background removal threshold value according to the image area separation result, and this threshold value TH is given to the density conversion unit as described later.

The above processing is performed for each pixel, and the background removal threshold value is updated and controlled according to the image area separation result. The above-described operation is the result of image area separation, which is a line drawing area, a photographic area,
The same applies to the fluorescent color region. Further, the minimum value density detection circuit of the above-described embodiment is another circuit as long as it has a function of detecting the value corresponding to the background density level of the pixel of interest, for example, the average of the densities of the pixels of interest pixel neighborhood. It can be configured with a circuit that detects a value, a median value, a maximum value, and the like.

Density converter: FIG. 9 shows the structure of the density converter. The maximum density determination circuit 51 uses a linear density r,
The maximum value MAX (r, g, b) of the g, b data is obtained.
The removal amount determination circuit 52 uses the background removal threshold value TH set in the background removal threshold value holding circuit and the maximum value MAX (r, g,
The removal amount SUB is determined based on b). The removal amount SUB is
The following conversion formula is used. That is, SUB = TH * M-MAX (r, g, b) For example, when MAX (r, g, b) is the r component, S
UB = TH × M−r. In the above example, when the removal amount SUB is determined, the concentration maximum value determination circuit uses r,
Although the maximum values of g and b are used, the present invention is not limited to this, and one component in the r, g, and b data may be used.

The removal arithmetic circuit 53 inputs the input image data IN
The removal amount SUB is subtracted from (r, g, b), respectively, and O
UT (r-SUB, g-SUB, b-SUB) is output. However, when the subtraction result is a negative value, 0 is output. FIG. 10 shows an input IN and an output OU of the removal arithmetic circuit 53.
The conversion characteristic of T is shown. A method of switching the value of M according to the value of TH can be considered, but in the present embodiment, a constant value (see FIG.
In the case of 0, the gradient M = 2). In FIG. 10, MA
X (r, g, b) = IN. Therefore, OUT = IN
-SUB = IN- (TH * 2-IN) = 2 (IN-T
H).

When the value of M is switched according to the value of TH, the fluctuation of the input / output characteristics before and after the background removal becomes large. As a result, the image quality deteriorates, such as the occurrence of pseudo contours in a smoothly changing image. By setting the value of M to a fixed value regardless of the value of TH, the fluctuation of the input / output characteristics is reduced, and an image with no discomfort can be obtained. Further, when the input / output characteristics are configured in a table, the table configuration becomes simple because M has a fixed value.

The image area separating unit 55 determines whether or not the pixel of interest is a halftone dot (line drawing, photograph, fluorescent color) area, and the selection circuit 54 determines that the separation result of the image area separating unit 55 is a halftone dot (line drawing). , Photograph, fluorescent color), the output result (OUT = IN-SUB) of the removal calculation circuit 53 is selected and the image data after the background removal is output. In the halftone dot (line drawing, photograph, fluorescent color) area, the selection circuit 54 selects the input image data and outputs it as it is. The density conversion is not limited to the above-described one, and for example, the maximum value MAX of each pixel (r, g, b)
If (r, g, b) is lower than the background removal threshold set by the threshold update unit, it is converted to (0,0,0), and otherwise, the original signal (r, g, b) is output. You may do it.

The operation of this embodiment will be described using a specific example. As an original for which the background is to be removed, an example in which two types of originals, a newspaper original and a high-quality original, are pasted together is used. FIG. 11 shows the maximum value MAX (r, g, b) data of the image data before the background removal on the main scanning line, and the image area separation result thereof. The image area separating section 5 separates the newspaper pattern portion of the above-mentioned newspaper manuscript as a halftone dot area and the picture highlight portion of the high quality paper manuscript as a halftone dot area. The newspaper background portion and the fine paper background portion are separated as non-dotted areas (non-photographic, non-line drawing, non-fluorescent color) areas. In the example of FIG. 11, the density level of the newspaper background is high, and the density level of the picture highlight portion is the same as or lower than the density level of the newspaper background, and both cannot be distinguished only by the density level. In the embodiment, the newspaper background and the picture highlight portion are identified by the image area separation, so that the background control for the newspaper background becomes possible.

Now, assuming that the main scanning is performed from left to right in FIG. 11, first, the image data A is input to the image area separation unit 5 and also to the threshold value updating unit 7. The image area separation unit 5 performs image area separation on the image data A, and outputs a non-halftone dot (non-photograph, non-line drawing, non-fluorescent color) area (newspaper background) as a result of the separation. In the threshold updating unit 7, the detection circuit 41 (FIG. 8) detects the density level of the input image data A, and the background removal threshold TH1 corresponding to the background of the newspaper is set in the holding circuit 44.

FIG. 12 is a diagram for explaining an example of updating the background removal threshold value, which will be described below with reference to FIGS. 11 and 12. Next, the image data B is sequentially input, and the image area separating section 5 outputs a halftone dot area (newspaper pattern) as the separation result. Since the separation result of the image area separation unit 5 is a halftone dot area,
The selection circuit 43 of the threshold update unit 7 selects the output of the comparator 42. That is, in this case, the holding circuit 44 has the threshold value TH.
Since 1 is held, the comparator 42 compares the threshold value TH1 with the minimum value density of the image data B sequentially input. In the picture area of the newspaper, only pixels having a higher density than the threshold TH1 exist, so the comparator 42 outputs the threshold TH1 having a smaller value and writes it in the holding circuit 44. That is, in the picture area of the newspaper, the threshold TH1 set for the background of the newspaper is kept held, and the value is not updated.

When the process proceeds to the pattern highlight portion (image data C) of the high-quality paper, the low density (TH
The pixel of 2) appears. Since this area is a halftone dot area, the comparator 42 outputs TH2 and updates TH1 currently set in the holding circuit 44 to TH2. When the processing of the pattern highlight portion of the high-quality paper is completed, the background (image data D) of the high-quality paper is then processed. Since this area is a non-dot area (non-photograph, non-line drawing, non-fluorescent color) area,
The selection circuit 43 of the threshold value updating unit selects the output of the detection circuit 41, writes it in the holding circuit 44, and updates the threshold value. The background removal threshold TH3 corresponding to the background of the high-quality paper is a value lower than the currently set threshold TH2, and the holding circuit 44.
Is updated to TH3.

With respect to the threshold value updating process of the present invention, when processed from the high-quality paper side (assuming that the main scanning is performed from right to left), the process is as follows. In the background portion of the high-quality paper, the threshold value is first set to the value TH3. Since only pixels having a higher density than the threshold TH3 exist in the picture highlight portion and the picture area of the newspaper, the threshold is not updated. Further processing,
When entering the background area of a newspaper, halftone dots (photographs, line drawings, fluorescent colors)
Since it is not a region, the threshold value is updated to TH1.

As described above, the background removal threshold according to the present invention follows the background density level in the background portion and is updated to a value equal to or lower than the background density level in the pattern portion, and thus the background is removed and the pattern is removed. Is updated and set to a threshold value that does not remove. Then, the background removal is performed by using the background removal threshold set as described above.

That is, first, the background removal threshold value holding circuit 4
The threshold value TH1 from 4 is the removal amount determination unit 52 of the density conversion unit 8.
The removal amount SUB is obtained, and the removal amount SUB is supplied to the removal calculation circuit 53. The removal arithmetic circuit 53 is I
Output N-SUB. Since the separation result of the image area separation is a non-halftone dot (non-photograph, non-line drawing, non-fluorescent color) area (newspaper background), the selection circuit 54 selects the output of the removal calculation circuit 53, and the background density is converted ( That is, it is removed). In the next newspaper picture area and picture highlight, since the separation result is the halftone dot area, the selection circuit 54 selects the input image data and outputs the original images B and C as they are. In the background portion of the high-quality paper, SUB is obtained based on the threshold value TH3, and the separation result is a non-halftone dot (non-photograph, non-line drawing, non-fluorescent color) region (newspaper background), so the output of the removal calculation circuit 53 is The background density is selected and converted. FIG. 13 shows image data after the background removal.

According to the present invention, as described above, halftone dots, line drawings, photographs and fluorescent color areas are detected using the image area separating means, and the threshold value updating section and the density converting section are controlled accordingly. There is an effect explained in. That is, in a general background detection method, attention is paid to the density level, and a density area lower than a predetermined threshold is detected as the background. However, the highlight color of the picture (that is, the halftone dot area) and the background of the newspaper may have the same density level as shown in FIG. 11, and cannot be identified only by the density level.

On the other hand, the image area separating means of the present invention is
Since the picture highlight is detected as a halftone dot area, it can be distinguished from the background of the newspaper and the background detection accuracy is improved. Further, the background removal threshold value is switched with high accuracy by continuously following the background density level. As a result, the background of the newspaper is removed, but the highlight portion of the pattern having the same (or lower) density level is not removed.

Similarly, if attention is paid only to the density level in the line drawing area, the photographic area, and the fluorescent color area, it may be confused with the background of the newspaper, but like the picture highlight color, the image area separating means (line drawing, By using (photograph, fluorescent color), the line drawing, photograph, and fluorescent color can be distinguished from the background of the newspaper, and the detection accuracy of the background is improved.

<Second Embodiment> FIG. 14 shows a second embodiment of the present invention.
Shows the configuration of. The second embodiment is the image area separating unit 5 of the first embodiment.
Is replaced with the color information detection unit 9, and the other components are the same as those described in the first embodiment. The background removing unit 6 is configured similarly to the first embodiment, and controls updating of the background removing threshold according to the color information detection result. That is, for example, when the density level is high (chromatic color) in the color information detection result, the output value of the comparator 42 in FIG. 8 is selected, and when not, the value of the minimum value density detection unit 41 is selected. , The background removal threshold value holding circuit 44. Then, the density conversion unit 8 of the background removal unit converts the density of the background portion of the document of the scanner data and outputs it to a printer or the like. Similar to the first embodiment, the density conversion unit is controlled according to the color information detection result. For example, when the color information detection result indicates that the density level is high (that is, when the color is chromatic), the selection circuit 54 selects the input image data, and otherwise the output of the removal calculation circuit 53 is selected.

The color information detector 9 will be described below.
The color information detection unit 9 detects pixels having the following characteristics in the image data read by the scanner. That is, (1) a pixel having a high density level and (2) a chromatic color pixel are detected.

The detection of color information when the RGB density signals are targeted will be described. Pixel density [r, g, b]
And As a first method of detecting a pixel having a high density level, when the maximum value MAX (r, g, b) of RGB signals is higher than a predetermined threshold value, a pixel having a high density level is set.
In the second method, L = C1 × r + C2 × g + C3 × b is defined, and when L is higher than a predetermined threshold value, a pixel having a high density level is defined. Here, C1, C2, C3 are constants,
For example, values such as C1 = 0.1, C2 = 0.6, and C3 = 0.3 are taken (the reason why C2, that is, the weight of the g signal is made high is that the characteristics are likely to appear in the luminance signal). .
Although an example of detecting a pixel with a high density level is given,
The present embodiment is not limited to this, and other concentration level determination methods may be used.

On the other hand, in the detection of chromatic color pixels, S = MAX (r, g, b) -MIN (r,
g, b), and when S is a pixel higher than a predetermined level, it is a chromatic pixel. In the second embodiment, the color information detection unit detects the density level and the saturation, but it is also possible to detect the brightness, hue, or luminance information, and use the result to control the background removal.

<Third Embodiment> FIG. 15 shows a third embodiment of the present invention.
Shows the configuration of. In this embodiment, the edge emphasizing circuit 1 is provided before the removal arithmetic circuit that constitutes the background removal unit described in FIG.
0 is provided (the density maximum value determination circuit is omitted from this figure). Then, the threshold updating unit and the removal amount determination circuit process the signal before the edge enhancement processing, and the removal calculation circuit processes the signal after the edge enhancement processing. In the edge enhancement circuit 10, for example, as shown in FIG.
Edge enhancement processing is performed using a filter as shown in. That is, the value of the pixel of interest is determined by performing the convolution operation on the pixel of interest and the pixels around it with the coefficient of the filter.

As a result, since the threshold updating unit uses data close to the original image before the edge enhancement processing, the accuracy of the threshold is improved, and since the removal calculation is performed on the signal after the edge enhancement processing, the density is increased. The boundary between the background and the non-background that occurs at the time of conversion is not edge-emphasized, and the deterioration of image quality is prevented.

<Fourth Embodiment> FIG. 17 shows a fourth embodiment of the present invention.
Shows the configuration of. In this embodiment, the undercolor removal and the background removal are commonly used to simplify the hardware configuration (note that the maximum density determination circuit is omitted from this figure).
In the figure, a color correction unit 61 converts a density linear RGB signal into a complementary color YMC signal. Such color correction is based on the following equation, for example.

C = a0 + a1 × R + a2 × G + a3 × B M = b0 + b1 × R + b2 × G + b3 × B Y = c0 + c1 × R + c2 × G + c3 × B where a0 to a3, b0 to b3, and c0 to c3 are color correction coefficients. .

The undercolor removal amount determining unit 62 calculates Min (Y, M, C) from the Y, M, C signals and outputs it as the K signal to the adder 65. Undercolor removal (UCR)
Is a process of calculating Min (Y, M, C) from Y, M, C signals to create a K (black) signal and subtracting K signals from the signals of the respective color materials, that is, Y−K = Y ′. , M−K = M ′,
CK = C '.

On the other hand, as described above, SUB is output from the removal amount determination unit, and K + SUB is output by the undercolor removal unit 63,
Given to 64. Further, the separation result from the image area separation unit is given to the undercolor removal units 63 and 64, and when the separation result is a halftone dot, line drawing, photograph, or fluorescent region, the undercolor removal unit 63 operates, When the separation result is not in any area, the under color removal unit 64 operates. That is, in the undercolor removal unit 63, S
When UB = 0, Y−K = Y2, M−K = M2, C−K
= C2, K is output. In the undercolor removal unit 64, Y1 = Y
-(K + SUB), M1 = M- (K + SUB), C1 =
C- (K + SUB), K is output. In the case of a single color, for example, in the case of a Y single color, the undercolor removal amount K is 0 (K = Min
(Y, 0,0) = 0), and the under color removal unit 63 outputs Y and the under color removal unit 64 outputs Y-SUB. Then, the output γ conversion unit performs density conversion processing suitable for the characteristics of the output device, and sends the image data to an image output device such as a printer.

As described above, in this embodiment, the circuit of the density conversion unit (removal calculation circuit) for background removal and the undercolor removal unit are made common, and the value obtained by adding the removal amount of background removal and the undercolor removal amount is reduced. It is subtracted in the color removal section.

<Fifth Embodiment> FIG. 18 shows a fifth embodiment of the present invention.
Shows the configuration of. The figure shows the image area separation unit used for background removal,
The configuration of an embodiment in which the image area separation unit used for filtering processing (smoothing, edge enhancement) is shared and the circuit scale is reduced is shown. This is an example of the configuration applied to a color copying machine, for example. In the smoothing processing unit, filtering processing for smoothing is performed on an area other than the line drawing (character) area where the image area separation result of the image area separation unit is. By such filtering processing, moire in the pattern area is removed. FIG. 19
Shows an example of a smoothing filter.

The color correction unit converts the RGB signals into YMC signals of complementary colors, as described in the fourth embodiment (FIG. 17).
In the edge emphasis processing unit 72, the image area separation result is a line drawing (character).
When it is a region, filtering processing for edge enhancement, that is, resolution processing is performed. As the edge emphasis filter, for example, the filter described in the third embodiment is used. In the undercolor removal unit, Min (Y, M,
C) to obtain a K (black) signal, and Y ′ = Y−K,
Outputs M ′ = M−K and C ′ = C−K, K. In the background removal unit, the update amount and the removal amount of the background removal threshold are controlled according to the image area separation result, as described in the first embodiment and the like. Then, the output γ conversion unit performs density conversion processing suitable for the characteristics of the output device, and reproduces and outputs the image to a printer or the like.

[0060]

As described above, according to the invention described in claim 1, since the background is detected by using the image area separation technique, the accuracy of the background detection is improved and the image area separation result is improved. Since the background removal of the document is controlled in real time by using, the background removal processing most suitable for the background of the document type is performed, and the image reproducibility is improved.

According to the second and third aspects of the present invention, the threshold applied to the background removal is switched with high accuracy in accordance with the background density level, and the value is equal to or lower than the background density level in a pattern portion or the like. Since they are switched, the threshold value is updated and set so that the background is removed and the pattern is not removed. Therefore, the background can be removed with the threshold value corresponding to each background density. Further, the threshold value can be switched with high accuracy even when the number of bonded originals is large or the ratio of the background area to the originals is small, so that the background can be removed with the threshold value corresponding to each background density. .

According to the fourth and fifth aspects of the present invention, the background having a high density level such as a newspaper, the pattern (halftone dot area) highlight area and the character (line drawing) having the same density level as the background.
Since the area, the photographic highlight area, and the area formed by the fluorescent color are accurately detected and the density is converted, the reproducibility of each area is improved.

According to the sixth aspect of the invention, since the background is detected by using the color information detecting technique, the background detection accuracy is improved, and the background of the original is removed by using the detection result of the color information. Since the control is performed in real time, the background removal processing most suitable for the background of the document type is performed, and the image reproducibility is improved.

According to the seventh and eighth aspects of the present invention, the threshold value applied to the background removal is switched with high accuracy in accordance with the background density level, and in a pixel with a high density level, the threshold value is equal to or lower than the background density level. Since I switched to the value of
The background is removed, and the threshold value is updated and set so as not to remove pixels having a high density level. Therefore, the background can be removed with the threshold value corresponding to each background density.

According to the ninth and tenth aspects of the present invention, the background, the pixel having a high density level, and the pixel having a high saturation are accurately discriminated and the density is converted. The reproducibility of colored pixels is improved.

According to the eleventh, twelfth and thirteenth aspects of the present invention, it is possible to detect a pixel having a high density level and a pixel having a high saturation with high accuracy and with a simple means.

According to the fourteenth aspect of the present invention, even if adjacent pixels having the same density level have different background removal threshold values applied to the respective pixels, the input / output characteristics do not change. The difference in the amount does not increase, so that a reproduced image with smooth image quality and no discomfort can be obtained.

According to the fifteenth aspect of the present invention, the image data before the edge enhancement processing is closer to the original image in the image data before the edge enhancement processing, so that the accuracy of the threshold value obtained by the threshold value updating unit is improved. In addition, by performing the density conversion after the edge enhancement processing, it is possible to prevent the discontinuity between the background and the non-background that occurs during the density conversion from being emphasized.

According to the sixteenth aspect of the present invention, the undercolor removing section and the background removing section can be shared, and the image processing apparatus can be downsized.

According to the seventeenth aspect of the present invention, the image area separation unit used for the filtering processing and the image area separation unit used for the background removal processing can be made common, and the hardware scale of the image processing apparatus can be increased. It can be reduced.

[Brief description of drawings]

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

FIG. 2 is a diagram illustrating halftone dot pixels.

FIG. 3 is a block configuration diagram of a line drawing area detection unit.

FIG. 4 is a pattern for detecting continuity of black pixels.

FIG. 5 is a pattern for detecting continuity of white pixels.

FIG. 6 is a block configuration diagram for determining a photographic area.

FIG. 7 is a block configuration diagram of a fluorescent color region identification unit.

FIG. 8 is a block configuration diagram of a threshold updating unit.

FIG. 9 is a block configuration diagram of a density conversion unit.

FIG. 10 shows input / output conversion characteristics of a removal arithmetic circuit.

FIG. 11 shows an example of image data before background removal.

FIG. 12 shows an example of updating a background removal threshold value.

FIG. 13 shows an example of image data after background removal.

FIG. 14 shows a configuration of a second embodiment of the present invention.

FIG. 15 shows a configuration of a third embodiment of the present invention.

FIG. 16 shows an example of an edge enhancement filter.

FIG. 17 shows a configuration of a fourth embodiment of the present invention.

FIG. 18 shows the configuration of Example 5 of the present invention.

FIG. 19 shows an example of a smoothing filter.

[Explanation of symbols]

 1 Scanner 2 A / D Converter 3 Shading Corrector 4 Log Converter 5 Image Area Separator 6 Background Remover 7 Threshold Update 8 Density Converter

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G06T 9/20 // G06T 1/00 7459-5L G06F 15/70 335 Z 15/64 400 C

Claims (17)

[Claims] 1. A means for digitally reading an original,
A unit that separates the read image data into image areas, a unit that removes the background component of the document included in the image data,
In an image processing apparatus having means for outputting image data after background removal, the background removal means controlled by the image area separation means is means for updating a threshold value applied to background removal, and based on the threshold value. An image processing apparatus comprising means for converting the density of the image data. 2. The image processing apparatus according to claim 1, wherein the threshold value updating means includes means for controlling the updating of the threshold value by following the background density level. 3. The update control means includes means for detecting a density in the vicinity of a pixel of interest, means for holding a first threshold value applied to background removal, and the detected density and the first threshold value. The output of the comparison means is selected when the separation result of the image area separation means is any one of a halftone dot area, a line drawing area, a photographic area, and a fluorescent color area. 3. The means for selecting the output of the detecting means and setting it in the holding means when the separation result of the image area separating means is not one of the areas.
The image processing device described. 4. The separation result is a halftone dot area, a line drawing area,
When it is either a photographic area or a fluorescent color area, the density conversion means controls so as not to perform density conversion on the image data, and when the separation result is not any of the areas, the density conversion means uses the threshold value. The image processing apparatus according to claim 1, further comprising means for controlling to perform density conversion of the image data based on a threshold value of the updating means. 5. The density conversion control means determines a removal amount based on a threshold value set in the threshold value updating means and image data, means for subtracting the removal amount from the image data, and The separation result of the image area separation means is a halftone dot area,
When it is one of the line drawing area, photographic area, and fluorescent area,
The image processing apparatus according to claim 4, further comprising means for selecting the image data and selecting an output of the subtraction means when the separation result is not in any of the areas. 6. Means for digitally reading an original,
In an image processing apparatus comprising means for detecting predetermined color information from the read image data, means for removing a background component of a document included in the image data, and means for outputting the image data after the background removal. The background removal unit controlled by the color information detection unit includes a unit for updating a threshold value applied to the background removal and a unit for converting the density of the image data based on the threshold value. Image processing device. 7. The image processing apparatus according to claim 6, wherein the threshold value updating unit includes a unit that controls the updating of the threshold value in accordance with the background density level. 8. The updating control means includes means for detecting a density in the vicinity of a pixel of interest, means for holding a first threshold value applied to background removal, and the detected density and the first threshold value. A means for outputting a smaller value by comparison, and when the detection result of the color information detecting means is a pixel with a high density level or a pixel with high saturation, the output of the comparing means is selected, and the detection result is 8. The image processing apparatus according to claim 7, further comprising means for selecting an output of the detection means and setting it in the holding means when the pixel is not one of the pixels. 9. When the detection result is a pixel having a high density level or a pixel having a high saturation, the density conversion means controls the image data so as not to perform density conversion, and the detection result is one of the pixels. The image processing apparatus according to claim 6, wherein the density conversion means includes means for controlling the density conversion of the image data based on the threshold value of the threshold value updating means. 10. The density conversion control means determines a removal amount based on a threshold value set in the threshold value updating means and image data, a means for subtracting the removal amount from the image data, and When the detection result is a pixel having a high density level or a pixel having a high saturation, the image data is selected, and when the detection result is not any of the pixels, a means for selecting the output of the subtraction means is provided. The image processing apparatus according to claim 9, wherein 11. The pixel having a high density level is a pixel in which at least one component of the n component signal values of the pixel of interest is higher than a predetermined threshold value. Image processing device. 12. The pixel having a high density level is a pixel in which a weighted average value of n-component signal values of a pixel of interest is higher than a predetermined threshold value. Image processing device. 13. The high-saturation pixel is n of a target pixel.
11. The image processing apparatus according to claim 8, wherein the difference between the maximum value and the minimum value of the component signal values is a pixel higher than a predetermined threshold value. 14. The means for subtracting the removal amount outputs M (IN-TH) when the input to the means is IN and the threshold of the updating means is TH, and the gradient M is different at different thresholds TH. The image processing apparatus according to claim 5, wherein the image processing apparatus has a constant input / output conversion characteristic. 15. A unit for digitally reading an original, and a unit for separating the read image data into image areas.
In the image processing apparatus, which comprises means for applying edge enhancement to the image data, means for removing a background component of a document included in the image data, and means for outputting the image data after the background removal, The background removing means controlled by the separating means updates the threshold applied to the background removal, determines a removal amount based on the threshold and image data, and subtracts the removal amount from the image data. The removal amount determining means determines the removal amount using the image data before the edge enhancement processing is performed, and the subtraction means uses the image data after the edge enhancement processing is performed. An image processing device characterized by performing subtraction. 16. A means for reading an original document as R, G, B digital image signals, a means for converting the R, G, B signals into Y, M, C signals of complementary colors, and the Y, M, C signals. Means for generating an undercolor removal amount corresponding to a K (black component) signal from the minimum value of, a means for separating the read R, G, B signals from the image area, and a means included in the Y, M, C signals. In the image processing apparatus provided with a means for removing the background component of the original document and a means for outputting the image data after the background removal, the background removal means controlled by the image area separating means is a threshold applied to the background removal. For updating the threshold value and the Y,
An image processing apparatus comprising: a means for determining a removal amount based on M and C signals; and a means for subtracting the undercolor removal amount and the removal amount from the Y, M and C signals. . 17. A unit for digitally reading a document, and a unit for separating the read image data into image areas.
An image processing apparatus comprising: means for switching filtering processing for the image data; means for removing a background component of a document included in the image data after the filtering processing; and means for outputting the image data after the background removal,
The image processing apparatus, wherein the switching unit and the background removing unit are controlled by the image area separating unit.