JP2002112036A - Image processing device - Google Patents

Abstract

(57) [Summary] [Problem] To reduce the supply amount of toner (ink) without canceling the effect of a spatial filter, and to enable recording of an image without bleeding or protrusion. An edge area filter (18a) sequentially enhances the density value of each pixel in an image portion of an edge area, and when the total density value of one pixel exceeds a threshold value, the total density value of the pixel becomes less than the threshold value. Up to this point, the selection of a filter having a lower emphasis degree is repeated to emphasize the density value of the pixel, and the selection of the filter when the total density value of the pixel falls below the threshold is maintained. This makes it possible to emphasize the density value of the pixel while suppressing the total density value below the threshold value for all the pixels in the image portion of the edge region. The toner supply amount becomes excessive, so that the toner does not scatter or protrude.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an image processing apparatus for processing image data.

[0002]

2. Description of the Related Art In recent years, digitalization of office automation equipment has been rapidly progressing, and image recording apparatuses such as digital color copying machines and color printers for printing color images have been widely and generally used. In this type of image recording apparatus, one of a character mode, a photograph mode, a text / photograph mixed mode, and the like is manually selected, or an image is divided into an edge area, a halftone dot area, and a photograph area. Accordingly, the processing contents of the image data can be changed by switching the color conversion table, the spatial filter, the dither method, and the like.

The image data input to the image recording apparatus is an RGB (red, green and blue) signal.
CMY corresponding to the three primary colors of the additive color mixture of printing the GB signal
(Cyan, magenta, and yellow) signals and further improve the character representation by
A (black) signal is generated, and a cyan image, a magenta image, a yellow image, and a black image are sequentially printed on a recording sheet in accordance with the CMYK signals to form a color image.

[0004]

By the way, the images of each color are formed by sequentially superimposing and attaching the toners (inks) of the respective colors to the recording paper. On the recording paper, the later the superposition, or the greater the total amount of supply of the toner of each color to one pixel, the lower the toner adhesion rate, and the greater the amount of toner scattered or protruding. Especially when recording fine lines on recording paper,
When the toner scattered or ran out, dirt around the fine line was conspicuous, and the image quality was significantly deteriorated.

[0005] Therefore, in the "color image forming method" described in Japanese Patent No. 2608262, the sum of the ink amounts of the respective colors is obtained, and when the sum exceeds a certain value,
While maintaining the ratio of the ink amount of each color, the total sum of the ink amount of each color is reduced, thereby preventing the bleeding and scattering of the ink and preventing the image quality from deteriorating.

Further, in the "image processing apparatus" described in Japanese Patent Application Laid-Open No. 9-200588, the dust (ink bleeding and scattering) characteristic inherent to the image forming apparatus is stored.
With reference to this dust characteristic, the amount of ink of each color is corrected, for example, at the edge of the image, thereby preventing ink bleeding and scattering.

However, in the processing of an image, there is a processing of enhancing the image using the spatial filter described above. When this spatial filter is used, the above-mentioned Patent No. 26
As described in Japanese Patent Application Laid-Open No. 08262, when the sum of the ink amounts of the respective colors exceeds a certain value, the sum of the respective ink amounts is reduced,
Alternatively, if the amount of ink of each color is corrected at the edge of the image as in JP-A-9-200558, the enhancement of the image by the spatial filter is canceled.

When a spatial filter is used, the entire image is uniformly processed by the spatial filter, or the image is divided into an edge area, a halftone dot area, and a photographic area, and these areas are processed by the respective spatial filters. In the edge region, a spatial filter having a characteristic of enhancing characters and symbols clearly and easily is applied. In the halftone dot region, a spatial filter having a characteristic of performing moiré removal or a spatial filter having a characteristic of not blurring an edge of an image is applied. Further, in the photographic area, a spatial filter having a characteristic of favorably expressing gradation or a spatial filter having a characteristic of not blurring the edge of an image is applied.

Alternatively, one of a character mode, a photograph mode, and a text / photograph mixed mode is manually selected, and the entire image is uniformly processed by a spatial filter corresponding to the selected mode. Further, only when the text / photo mixed mode is selected, the image is divided into the edge area, the halftone dot area, and the photograph area as described above, and these areas are processed by the respective spatial filters.

For example, when attention is paid to the edge region, a spatial filter having a characteristic that emphasizes characters and symbols clearly and easily is used. Is particularly emphasized. In this case, the total supply amount of the cyan, magenta, and yellow toners and the supply amount of the black toner become extremely large, so that the toner adhesion rate decreases, and the toner scatters or runs off.

[0011] However, the above-mentioned patent No. 2608262
If the amount of toner supplied is reduced by applying the technology described in Japanese Patent Application Laid-Open No. Hei 9-200558 and Japanese Patent Application Laid-Open No. 9-200558, the effect of the spatial filter is canceled out, and characters and symbols are not emphasized.

In view of the foregoing, the present invention has been made in view of the above-mentioned conventional problems, and has been made to reduce the supply amount of toner (ink) without canceling out the effect of a spatial filter, and to reduce the amount of an image without bleeding or protrusion. It is an object of the present invention to provide an image processing apparatus capable of recording.

[0013]

According to the present invention, there is provided an image processing apparatus for processing images of respective colors which are superimposed on each other to represent a color image.
Used to emphasize the density values of the pixels of each color image,
Using a plurality of spatial filter means having different emphasis levels from each other and one of the respective spatial filter means, the density values of the pixels of each color superimposed on each other were emphasized, and the density values of the respective pixels were totaled. When the total density value is equal to or larger than a preset threshold value, the image processing apparatus further includes control means for re-emphasizing the density value of each pixel by using another spatial filter means having a low emphasis degree.

According to the present invention having such a configuration, the density value of each color pixel is emphasized using one of the spatial filter means, and the total density value obtained by summing the density values of each pixel is equal to or larger than the threshold value. In some cases, the density value of each pixel is emphasized again using another spatial filter having a low degree of emphasis. Therefore, the processing by the spatial filter means is repeated until the total density value of each pixel becomes less than the threshold value. If a density value corresponding to the maximum supply amount of toner (ink) that can adhere to the recording paper is set as the threshold value, the supply amount of the toner of each color corresponding to the total density value of the pixels of each color is set to the maximum supply amount. It is possible to prevent the toner from being scattered or protruding, because the amount is suppressed to less than the amount, and the toner adhesion rate is not reduced.

According to the present invention, there is provided an image processing apparatus for processing a black image and a color image which are superimposed on each other to represent a color image. A plurality of spatial filter means, each of which is used to emphasize a density value, and each of which has a different degree of emphasis, and a density value of a black pixel and a color value of each color which are superimposed on each other by selectively using each spatial filter means. If the density value of the pixel is emphasized and the density value of the black pixel is equal to or greater than a first threshold value set in advance, the density value of the black pixel is reduced When the emphasis is performed again and the total density value obtained by summing the density values of the pixels of the respective colors is equal to or more than a second threshold value set in advance,
And control means for re-emphasizing the density value of each color pixel by using another spatial filter means having a low emphasis degree.

Here, the black processing and the processing for each color are separately performed in parallel. This is a color that is specially extracted from cyan, magenta, and yellow in order to achieve the purpose of emphasizing black characters, and existing devices treat black as distinct from each color. In order to match practical use.

In the present invention, the lowest level is set in advance as the degree of enhancement of each spatial filter means for enhancing the density value of a pixel.

Alternatively, a minimum level is set in advance as the degree of emphasis of each spatial filter means for emphasizing the density value of a black pixel, and each spatial filter means for emphasizing the density value of each color pixel. As the degree, a minimum level is set in advance.

If the lowest level is set as the degree of emphasis of each spatial filter means, the emphasis of pixels can be guaranteed regardless of the total density value.

In the present invention, the density value of each color pixel representing the pixel of the color image is emphasized by the spatial filter means for each pixel of the color image, and the total density value of the pixels of each color is less than the threshold value. If, the pixel of the color image is excluded from the target of processing by the spatial filter means.

Alternatively, for each black pixel, the density value of the black pixel is emphasized by the spatial filter means. If the density value of the black pixel is less than the first threshold value, the black pixel is filtered by the spatial filter. The density value of the pixel of each color representing the pixel of the color image is emphasized by the spatial filter means, excluding from the target of the processing by the means, and for each pixel of the color image,
If the total density value of the pixels of each color is less than the second threshold, the pixels of the color image are excluded from the processing by the spatial filter.

As described above, when the total density value of the pixels of each color falls below the threshold value, when the density value of the black pixel falls below the first threshold value, the total density value of the pixels of each color falls below the second threshold value. When this happens, since the purpose of the processing for the pixel has been achieved, this pixel is excluded from the processing target. As a result, redundant processing is not performed, and the processing can be speeded up.

Further, the image processing apparatus of the present invention is used for enhancing the density value of a pixel of an image, and comprises a plurality of spatial filter means having different emphasis levels and one of the spatial filter means. To emphasize the density value of the pixel, and when the density value of the pixel is equal to or higher than a preset threshold value, the emphasis of the density value of the pixel is re-emphasized using another spatial filter means having a low emphasis degree. Control means for performing the control.

Also in the present invention, the density value of the pixel can be suppressed below the threshold value, the supply amount of the toner is suppressed below the maximum supply amount, the reduction of the toner adhesion rate is prevented, and the scattering of the toner is prevented. Extrusion can be prevented. That is, the present invention may be applied to only black among cyan, magenta, yellow, and black.

[0025]

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

FIG. 1 is a block diagram showing a first embodiment of the image processing apparatus of the present invention. In FIG. 1, a color image input device 10 irradiates a document with light from a light source, condenses reflected light from the document with an optical element, and reads a formed color image with an image sensor (eg, a CCD). And outputs RGB (red, green, and blue) signals indicating a color image.

Here, the pre-scan and the main scan are performed by the color image input device 10, that is, the reading of the document is repeated twice, and each time these scans are performed, an RGB signal indicating the image of the document is output to the image processing device 11. Is input to

In the image processing apparatus 11 according to the present embodiment, R representing a color image from the color image input apparatus 10 is used.
The GB signal is input to the A / D converter 12. The A / D converter 12 converts the RGB signals into digital signals and outputs the digital signals to the shading corrector 13. The shading correction unit 13 converts various distortions caused by the characteristics of the light source for irradiating the original in the color image input device 10, the characteristics of the optical element for condensing the reflected light from the original, and the characteristics of the image sensor for capturing a color image with RGB. From the signal, this RGB
The signal is output to the input tone correction unit 14. The input tone correction unit 14 adjusts the color balance of the RGB signals,
Since the RGB signals indicate the levels (reflectances) of the red, green and blue reflected lights from the original, the RGB signals are converted into CMY (cyan, magenta, and yellow) signals corresponding to the three primary colors of additive color mixing in printing. Output a signal.

At the time of pre-scanning, the CMY signals generated by the input tone correction section 14 are stored in the storage section 15. The area separation processing section 16 divides the image indicated by the CMY signal in the storage section 15 into an edge area, a halftone dot area, and a photograph area, and outputs the image portions of these areas to the spatial filter coefficient selection section 17. For example, the image is divided by comparing the sum of the density values of the respective colors indicated by the CMY signals with respective threshold values preset for the edge area, the halftone dot area, and the photograph area.

As shown in FIG. 2, the spatial filter processing unit 18
Has, for example, an edge area filter 18a, a halftone area filter 18b, and a photograph area filter 18c. The spatial filter coefficient selecting unit 17 determines the edge of the spatial filter processing unit 18 for each region so that appropriate spatial filtering is performed on each image portion of the edge region, the halftone dot region, and the photograph region. It is set which of the area filter 18a, the halftone area filter 18b and the photographic area filter 18c processes the CMYK signal.

The CMY signal generated by the input tone correction section 14 is input to the color correction section 19. The color correction unit 19 performs a process for removing color turbidity based on the spectral characteristics of the cyan, magenta, and yellow toners from the CMY signal, and outputs the CMY signal subjected to this process to the black generation under color removal unit 20. I do. The black generation and under color removal unit 20
The region separation processing unit 16 notifies the edge region, the halftone dot region, and the photograph region, and extracts, for example, an image portion of the edge region from the image indicated by the CMY signal. Is generated, the K signal is subtracted from the CMY signal,
Generate a new CMY signal. Similarly, the K signal and the new C
Generate the MY signal.

Since the image portion of the edge area represents characters, symbols, etc., it is necessary to generate a K signal. Further, it is not always necessary to generate the K signal for the image portion of the other halftone dot region and the photograph region.

The CMYK signal thus generated is output to the spatial filter processing section 18. The spatial filter processing unit 18 is designated with the image portion of the edge region from the spatial filter coefficient selecting unit 17, and as will be described in detail later, the enhancement of the edge region filter 18a suitable for enhancing the density value of the image portion. Set the degree.

That is, in the pre-scan, the original image is divided into an edge area, a halftone dot area, and a photograph area.
The filters 18a, 18b, and 18c of the spatial filter processing unit 18 are appropriately assigned to the image portions of these regions. Further, the degree of enhancement of the edge area filter 18a of the spatial filter processing unit 18 is appropriately set.

Next, at the time of the main scan, the processing up to the generation of the K signal indicating the image portion of each area and the new CMY signal by the black generation and under color removal unit 20 is exactly the same as that of the pre-scan. Storage unit 15, area separation processing unit 1
6 and the processing by the spatial filter coefficient selection unit 17 are not performed.

The processing up to the black generation and under color removal unit 20 is as described above. CMY from the black generation and under color removal unit 20
The K signal is processed by a spatial filter processing unit 18, an output gradation correction unit 21, and a gradation reproduction processing unit 22 for each of an edge region, a halftone dot region, and a photograph region.
3 is output.

The spatial filter processing section 18 corrects the spatial frequency of the image to correct the blur, graininess, moiré, etc., of the CMYK signal. The output gradation correction unit 21 adjusts the CMYK to match the recording method of controlling the dot area ratio of the color image output device 23.
Transform the signal. The tone reproduction processing unit 22 outputs a C
A signal indicating each pixel is generated from the MYK signal, and the signal of each pixel is processed so that the gradation of each pixel is expressed.

For example, the edge area filter 18a is set with a high degree of emphasis at the time of pre-scanning. In order to improve the reproducibility of characters, symbols, and the like included in the image area of the edge area, the edge area filter 18a has a high level with respect to the CMYK signal. A sharpness enhancement process for enhancing the band frequency is performed. Then, the tone reproduction processing unit 22 converts the CMYK signal into a signal suitable for high resolution.
Perform value conversion or multi-value processing.

The halftone dot filter 18b removes a halftone dot component from the image portion of the halftone dot region.
A low-pass filter (smoothing filter) process is performed on the signal. Then, the tone reproduction processing unit 22 performs binarization or multi-value processing on the CMYK signals with emphasis on tone reproducibility.

When the CMYK signal is input, the color image output device 23 records a color image on recording paper by an electrophotographic method or an ink jet method.

Next, the processing by the region separation processing section 16 in the image processing apparatus 11 of the present embodiment will be described in more detail.

The image division processing by the area separation processing unit 16 is described in, for example, a document “Method for identifying halftone pictures” (Transactions of the Institute of Electronics, Information and Communication Engineers 1987/2 Vol.2 J70-B No.2 p.222)
~ P.232.) "Block separation conversion method"
(Block Separate Transformation Method: BSTM)
Can be applied. This method divides an image into blocks, and distinguishes non-halftone areas (characters and photographs) from halftone areas based on density changes in the blocks. In the halftone dot region, since the halftone dots are periodically arranged, pixels having a high density are dispersed, and the dot region is extracted by focusing on this feature. The following is a series of procedures. (1) The image indicated by the CMY signal is divided into blocks each consisting of u × v pixels. (2) The level of a signal indicating an image portion in a block is detected, and a maximum level Lmax, a minimum level Lmin, and a difference (Lmax-Lmin) are obtained. (3) The difference (Lmax-Lmin) is compared with a preset reference value P, and if (Lmax-Lmin) <P, the block is determined to be a non-dot area (photographic area). Also, (Lma
If (x−Lmin) ≧ P, the process proceeds to (4) and subsequent steps. (4) An average value of the signal level indicating the image portion in the block is obtained, and using this average value as a threshold, the signal level of each pixel is identified, and each pixel is binarized into “0” and “1”. . (5) The number of times KH at which the value of each pixel changes in the main scanning direction of the image portion in the block is obtained. In the sub-scanning direction,
The number of times KV at which the value of each pixel changes is determined. (6) Each of the times KH and KV is compared with a preset reference value T, and if KH ≧ T and KV ≧ T, the block is determined to be a halftone dot area. If KH <T or KV <T, the block is determined as a non-dot area (edge area).

Further, such a series of processes is accompanied by a correction process for suppressing erroneous determination. For example, since the identification accuracy of a coarse halftone dot region is reduced, if there are many other blocks in the halftone dot region around the block, the reference value T is reduced, and the determination accuracy of the halftone dot region is improved.

Next, the processing by the spatial filter processing section 18 in the image processing apparatus 11 of the present embodiment will be described in more detail.

In the spatial filter processing section 18, the dot area filter 18b and the photographic area filter 18c are each a single unit, and the edge area filter 18a
Includes at least a first filter 181, a second filter 182, a third filter 183, and a fourth filter 184 as shown in FIG. 3, and includes first to fourth filters 181 to 184.
Is selectively used.

Accordingly, at the time of pre-scanning, the edge area filter 18a, the halftone area filter 18b, and the photographic area filter 18c are assigned to the edge area, the halftone area, and the photographic area of the image. One of the first to fourth filters 181 to 184 of the edge area filter 18a is selected.

As described above, the edge area filter 18a is used for improving the reproducibility of characters and symbols.
This emphasizes the high frequency range of the signal. The first filter 181 has the highest degree of enhancement, and has an MTF (Modulation Transfer Function; MTF) as shown in the graph of FIG.
It has a frequency characteristic of the spatial filter's frequency characteristic (amplitude ratio) = 3.0, and converts the density value of each pixel using the coefficients of the table 31 as shown in FIG. 4B. The second filter 182 has the second highest degree of enhancement, and has a frequency characteristic of MTF = 2.5 as shown in the graph of FIG.
The density value of each pixel is converted using the coefficients of the table 32 as shown in FIG. Third filter 183
Has the third highest degree of emphasis, has a frequency characteristic of MTF = 2.0 as shown in the graph of FIG. 6A, and uses the coefficients of the table 33 as shown in FIG. This is to convert the density value of the pixel. The fourth filter 184 has the lowest emphasis degree, and has an MTF = 1.1 as shown in the graph of FIG.
It has a frequency characteristic of 5 and converts the density value of each pixel using the coefficients of the table 34 as shown in FIG. 7B.

The dot area filter 18b performs a low-pass filter (smoothing filter) process on the CMYK signal in order to remove a dot component from the CMYK signal, and has a frequency of MTF = 1.0. Has characteristics.
The photographic region filter 18c also performs, for example, a low-pass filter (smoothing filter) process on the CMYK signal, and has a frequency characteristic near MTF = 1.0.

As described above, at the time of pre-scan,
The degree of emphasis of the edge area filter 18a is appropriately set.
That is, one of the first to fourth filters 181 to 184 is selected according to the image portion of the edge area.

Here, attention is paid to a group of pixels, for example, as shown in FIGS. 8A and 8B included in the image portion of the edge area.
FIG. 8A shows a cyan color, a magenta color,
It shows the density value of the yellow color (hereinafter referred to as C color, M color, Y color). Here, for the sake of simplicity, it is assumed that the density values of the respective colors are the same. FIG. 8 (b)
Indicates the density value of black (hereinafter referred to as K color) of each pixel.

When the density value of each color of the pixel 41 in FIGS. 8A and 8B is processed by each of the first to fourth filters 181 to 184 of the edge area filter 18a, FIG.
In the chart 51 shown in (c), MTF = 3.0, 2..
5, 2.0, 1.5 (first to fourth filters 181 to 1)
84, C, M, Y
The density values of the colors are 62, 57, 51, and 46, and the density values of the K color are 228, 205, 179, and 156. Furthermore,
The total density of the C, M, and Y colors is 186, 171, 15
3, 138, and the total density values of C, M, Y, and K are 414, 376, 332, and 294.

However, the density value of the pixel is assumed to be in the range of 0 to 255, and if the result of the conversion by the spatial filter processing unit 18 includes a numerical value below the decimal point, the value after the decimal point is rounded off. I have.

As in FIGS. 8A, 8B and 8C, FIGS. 9A, 9B and 9C also illustrate a pixel group, a pixel 42 and a chart 52. ing.

Here, the total density value of each color of the pixel is 765.
When (= 255 × 3) is exceeded, the total supply amount of the toner (ink) of each color to the pixel becomes too large, the toner adhesion rate decreases, and the toner scatters or runs off. Therefore, the threshold value is set to 765, and when the total density value of each color exceeds the threshold value, the filter used for the spatial filtering process is switched, the spatial filtering process is performed again, and the total density value is suppressed below the threshold value.

At the time of pre-scanning, the edge area filter 18a uses the first filter 18 having the highest emphasis degree.
1 is selected first, and the first filter 181 starts emphasizing the density value of the pixel. For example, the first filter 181
When the density values of the pixels 41 in FIGS. 8A and 8B are emphasized, the total density values of the C, M, Y, and K colors are calculated as shown in FIG.
MTF = 3.0 in the chart 51 of FIG.
414 corresponding to 1) is obtained, and this density total value 414 is obtained.
Is less than the threshold value 765, the total supply amount of the toner of each color to the pixel is an appropriate amount. Therefore, the first filter 1
The selection of 81 is maintained.

Thereafter, when the first filter 181 emphasizes the density values of the pixels 42 in the pixel group shown in FIGS. 9A and 9B, the density of the C, M, Y, and K colors is increased. The total value is a value 820 corresponding to MTF = 3.0 (first filter 181) in the chart 52 of FIG. 9C, and the total density value 820 is equal to or larger than the threshold value 765. At this time, in the edge area filter 18a, instead of the first filter 181, the second filter 182 having the second highest degree of enhancement is used.
Is selected, and the density value of the pixel 42 is emphasized again by the second filter 182. As a result, the total density of the C, M, Y, and K colors was MTF = 2.5 in the chart 52 of FIG. 9C.
(733) corresponding to (second filter 182)
This total density value 733 is less than the threshold value 765. Therefore, the selection of the second filter 182 is maintained.

Similarly, the density value of each pixel in the image portion of the edge area is sequentially emphasized, and when the total density value of one pixel exceeds the threshold value 765, the total density value of the pixel becomes the threshold value 765.
The selection of a filter having a lower emphasis degree is repeated until the value becomes less than 5, and the density value of the pixel is repeatedly emphasized, and the selection of the filter when the total density value of the pixel becomes less than the threshold value 765 is maintained. .

At the point in time when the enhancement of all the pixels in the image portion of the edge area has been completed, one filter has been selected. The selected filter is used at the time of the main scan. This makes it possible to emphasize the density value of the pixel while suppressing the total density value of the C color, M color, Y color, and K color below the threshold value 765 for all the pixels in the image portion of the edge area. In the above, in the image portion of the edge region, the total supply amount of the toner of each color to the pixel becomes excessive, so that the toner does not scatter or protrude.

By the way, in this type of image processing,
The K color component of a pixel is often distinguished from other C, M, and Y color components of the pixel. For this reason, in the pre-scan, a filter for enhancing the density value of the K color of the pixel,
It is more practically preferable to separately select filters for enhancing the density values of the C, M, and Y colors of the pixels.

For this purpose, it is necessary to separately set a first threshold value for the density value of the K color of the pixel and a second threshold value for the total density value of the C, M, and Y colors of the pixel. Here, the first threshold is set to 255, and the second threshold is set to 510.
(= 255 × 2).

At the time of pre-scanning, the first filter 181 is selected first, and the first filter 181 starts enhancing the density value of the pixel. For example, when the density value of the pixel 41 in FIGS. 8A and 8B is emphasized by the first filter 181, the total density value of the C color, the M color, and the Y color is calculated in the chart 51 of FIG. 186 corresponding to MTF = 3.0 (first filter 181) is obtained, and this total density value 1
86 is less than the second threshold value 510 and the density value of the K color is 228, and since this density value 228 is less than the first threshold value 255, the supply of the C, M, and Y toner to the pixels is performed. The total amount is appropriate.

Thereafter, when the first filter 181 emphasizes the density value of the pixel 42 shown in FIGS. 9A and 9B, the total density value of the C, M, and Y colors becomes as shown in FIG. ) Corresponding to MTF = 3.0 (first filter 181) in the chart 52 of FIG.
10 or more, and the density value of K color is 274,
This density value 274 is equal to or greater than the first threshold value 255. At this time, in the edge area filter 18a, instead of the first filter 181, the second filter having the second highest enhancement degree is used.
The filter 182 is selected, and the density value of the pixel 42 is emphasized again by the second filter 182. As a result, the K color density becomes a value 250 corresponding to MTF = 2.5 (the second filter 182) in the chart 52 of FIG. 9C, and the total density value 250 becomes less than the first threshold value 255. . Also, C color,
The density sum value of the M color and the Y color is MT in the chart 52 of FIG. 9C.
Value 483 corresponding to F = 2.5 (second filter 182)
Thus, the total density 483 becomes smaller than the second threshold 510. Therefore, the selection of the second filter 182 is maintained.

Similarly, each pixel in the image portion of the edge area is sequentially emphasized, and when the total density of C, M, and Y colors of one pixel exceeds the second threshold 510, the total density of the pixel is reduced. Until the value becomes less than the second threshold value 510, a filter with a lower emphasis degree is selected and the processing is repeated. Until the value becomes less than 255, a filter having a lower emphasis degree is selected, the processing is repeated, and when emphasis of all the pixels in the image portion of the edge area is completed, at least 1
Select one filter.

The selected filter is used at the time of the main scan. Thus, for all the pixels in the image portion of the edge area, the total density of the C, M, and Y colors is kept below the second threshold 510, and the density of the K color is kept below the first threshold 255. The density value of the pixel can be emphasized, so that the toner does not scatter or protrude on the recording paper.

FIG. 10 shows a spatial filter processing section in a second embodiment of the image processing apparatus of the present invention. The spatial filter processing unit 61 of the present embodiment is inserted between the black generation and under color removal unit 20 and the output gradation correction unit 21 instead of the spatial filter processing unit 18 of FIG. A fifth filter 185 and a sixth filter 186 are provided in addition to the first to fourth filters 181 to 184 of the edge area filter 18a, the halftone area filter 18b, and the photographic area filter 18c shown in FIG. The fifth and sixth filters 185 and 186 can enhance the density value of each image portion of the edge area, the halftone dot area, and the photograph area.

The fifth filter 185 has the fifth highest degree of enhancement among the first to sixth filters 181 to 186, and
It has a frequency characteristic of MTF = 1.2 as shown in the graph of FIG. 11A, and converts the density value of each pixel using the coefficients of the table 35 as shown in FIG. 11B. . The sixth filter 186 includes first to sixth filters 181-1 to 181-1.
86 has the lowest emphasis degree, has a frequency characteristic of MTF = 1.1 as shown in the graph of FIG.
The density value of each pixel is converted using the coefficients of the table 36 as shown in FIG.

When the density values of the respective colors of the pixel 43 in FIGS. 13A and 13B are processed by the first to sixth filters 181 to 186, respectively, the MTF = 3. 0, 2.5, 2.0, 1.5, 1.
As described corresponding to 2.1.1 (first to sixth filters 181 to 186), C, M, and Y density values, K color density values, C color, and M color , Y color density sum, C
The total density value of the colors M, Y, and K is obtained.

Here, the threshold value is set to 555, and C color, M
When the total density of the color components of Y, K, and K exceeds the threshold value 555, the filter is switched, the spatial filter processing is performed again, and the total density value is suppressed below the threshold value.

At the time of prescan, the first filter 181 having the highest emphasis degree is selected first, and the first filter 181 is selected.
, The density value of each pixel is sequentially emphasized. For example, the first
13A and 13B by the filter 181.
When the density value of 3 is emphasized, the total density value of the C, M, Y, and K colors is MTF = 3.0 in the chart 53 of FIG.
1072 corresponding to (first filter 181),
This total density value 1072 is equal to or greater than the threshold value 555. Therefore, instead of the first filter 181, the second filter 182 having the second highest enhancement degree is selected, and the density value of the pixel 43 is emphasized again by the second filter 182.

Thereafter, similarly, until the total density of the pixels 43 becomes less than the threshold value 555, a filter with a lower emphasis degree is selected, and the density values of the respective colors of the pixels 43 are repeatedly emphasized. The filter when the total value is less than the threshold value 555 is selected.

Here, as is clear from the chart 53 of FIG. 13C, the only way to make the total density value of the pixels 43 less than the threshold value 555 is to select the sixth filter 186. However, the degree of enhancement of the fifth and sixth filters 185 and 186 is too low to enhance the image portion in the edge region.

Therefore, the spatial filter processing section 61 of the present embodiment prohibits the application of the fifth and sixth filters 185 and 186 when enhancing the image portion of the edge area. Thus, when the fourth filter 184 is selected, even if the total density of the pixels 43 is equal to or greater than the threshold 555, the selection of the fourth filter 184 is maintained thereafter.

The selected filter is used at the time of the main scan. For this reason, the enhancement of the density value in the image portion of the edge region does not have to be lost.

Next, in the image processing apparatus shown in FIG.
The processing procedure is modified so that the first to fourth filters 181 to 18 of the edge area filter 18a are used at the time of the main scan.
4 is selected, and the image portion of the edge area is emphasized using the selected filter.

That is, up to now, any one of the first to fourth filters 181 to 184 of the edge area filter 18a has been selected at the time of the pre-scan, and the selected filter has been used at the time of the main scan. , The image portion of the edge region is emphasized. Here, at the time of the main scan, any one of the first to fourth filters 181 to 184 is selected, and the image of the edge region is selected using the selected filter. Emphasize parts.

For this purpose, the spatial filter processing section 61 shown in FIG. 10 first selects the first filter 181 having the highest emphasis degree in the main scan, and emphasizes the density value of the pixel by the first filter 181. Start. Then, when the total density of one pixel is equal to or greater than a preset threshold, until the total density of the pixel becomes less than the threshold,
The selection of a filter with a lower degree of emphasis is repeated to emphasize the density value of the pixel, and the selection of the filter when the total density value of the pixel falls below the threshold is maintained. Here, it is assumed that the first to sixth filters 181 to 186 can be selected.

When the total density of the pixels is less than the threshold value, the CMYK signal processed by the filter is immediately output to the output gradation correction section 21 at the subsequent stage.

For example, in a pixel group as shown in FIG. 14A, while sequentially selecting each main scanning line along the sub-scanning direction, each pixel on the selected main scanning line is aligned along the main scanning direction. Process sequentially. Here, assuming that the processing for the pixel 45 has been performed, a filter is selected such that the density value of the pixel 45 is less than the threshold value, and the CMYK signal processed by this filter is output to the output gradation correction unit 21. Is output. In addition, for each pixel that has already been processed (lightly shaded), processing by a filter in which the emphasized density value is less than the threshold value is performed first, and CMYK
The signal is output to the output gradation correction unit 21 first. Further, for each of the pixels that have not been processed yet (lightly shaded) shown in FIG. 14B, processing by a filter in which the emphasized density value is less than the threshold value is performed later, and the CMYK signal Is output to the output gradation correction unit 21 later.

As described above, at the time of the pre-scan, the first to sixth filters 181 to 18 of the edge area filter 18a are used.
Even without selecting 6, the selection of the filter and the processing and output of the CMYK signal can be performed at the time of the main scan. This speeds up the processing.

The present invention is not limited to the above embodiments, but can be variously modified. For example,
Although a filter that processes a matrix having a size of 3 × 3 is exemplified as the spatial filter, the size of this matrix can be changed as appropriate.

[0081]

As described above, according to the present invention, the density value of each color pixel is emphasized using one of the spatial filter means, and the total density value obtained by summing the density values of each pixel is equal to the threshold value. In the case described above, the density value of each pixel is emphasized again by using another spatial filter having a low emphasis degree.
Therefore, the processing by the spatial filter means is repeated until the total density value of each pixel becomes less than the threshold value. If a density value corresponding to the maximum supply amount of toner (ink) that can adhere to the recording paper is set as the threshold value, the supply amount of the toner of each color corresponding to the total density value of the pixels of each color is set to the maximum supply amount. It is possible to prevent the toner from being scattered or protruding, because the amount is suppressed to less than the amount, and the toner adhesion rate is not reduced.

According to the present invention, the black processing and the processing for each color are separately performed in parallel. This is because black serves the purpose of emphasizing black characters, cyan,
This is a color that is specially extracted from the magenta color and the yellow color. In existing devices, black is often treated separately from each color, so that it is suitable for practical use.

According to the present invention, the minimum level is set as the degree of emphasis of each spatial filter means.
Regardless of the total density value, it is possible to guarantee the enhancement of the pixel.

According to the present invention, when the total density value of the pixels of each color becomes less than the threshold value, when the density value of the black pixel becomes less than the first threshold value, the total density value of the pixels of each color becomes When the value becomes smaller than the second threshold value, the purpose of the processing for the pixel has been achieved, and this pixel is excluded from the processing target. Accordingly, redundant processing is not performed, and the processing can be speeded up.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a first embodiment of an image processing apparatus according to the present invention.

FIG. 2 is a block diagram showing a configuration of a spatial filter processing unit in the device of FIG.

FIG. 3 is a block diagram illustrating an edge area filter in a spatial filter processing unit in FIG. 2;

4A is a graph showing a frequency characteristic of a first filter in the edge area filter of FIG. 3, and FIG. 4B is a diagram showing a table of the first filter.

5A is a graph showing a frequency characteristic of a second filter in the edge area filter of FIG. 3, and FIG. 5B is a diagram showing a table of the second filter.

6A is a graph showing a frequency characteristic of a third filter in the edge area filter of FIG. 3, and FIG. 6B is a diagram showing a table of the third filter.

7A is a graph illustrating a frequency characteristic of a fourth filter in the edge area filter of FIG. 3, and FIG. 7B is a diagram illustrating a table of the fourth filter.

8A and 8B are diagrams showing a pixel group processed by the edge area filter of FIG. 3, and FIG. 8C is a table showing a result of processing by the edge area filter.

FIGS. 9A and 9B are diagrams showing another pixel group processed by the edge area filter of FIG. 3, and FIG.
9 is a chart showing a result of processing by an edge region filter.

FIG. 10 is a block diagram illustrating a spatial filter processing unit according to a second embodiment of the image processing apparatus of the present invention.

11A is a graph illustrating a frequency characteristic of a fifth filter in the spatial filter processing unit in FIG.
(B) is a figure which shows the table of a 5th filter.

12A is a graph illustrating a frequency characteristic of a sixth filter in the spatial filter processing unit in FIG.
(B) is a figure which shows the table of a 6th filter.

13A and 13B are diagrams illustrating another pixel group processed by the first to fifth filters of the spatial processing filter unit in FIG. 10, and FIG. 13C is a diagram illustrating first to fifth filters. 6 is a table showing the results of the processing according to FIG.

14A is a diagram showing each pixel already processed and a pixel being processed along the main scanning direction and the sub-scanning direction, and FIG. 14B is a diagram showing each pixel that has not been processed yet. is there.

[Explanation of symbols]

 Reference Signs List 10 color image input device 11 image processing device 12 A / D conversion unit 13 shading correction unit 14 input tone correction unit 15 storage unit 16 area separation processing unit 17 spatial filter coefficient selection unit 18 spatial filter processing unit 19 color correction unit 20 black Generation and Undercolor Removal Unit 21 Output Tone Correction Unit 22 Tone Reproduction Processing Unit 23 Color Image Output Device

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/46 H04N 1/46 Z F term (Reference) 2C262 AA04 AA24 AB13 AC02 AC04 BA09 BA12 BC07 DA06 5B057 CA01 CA08 CA12 CB01 CB08 CB12 CC02 CE16 CH18 DB02 DB06 DB09 DC16 5C077 LL17 LL19 MP02 MP07 MP08 PP03 PP27 PP28 PP33 PP38 PP47 PQ08 PQ20 TT03 TT05 5C079 HB03 KA15 LA15 LA31 MA11 NA02 NA11 NA25

Claims (7)

[Claims] 1. An image processing apparatus for processing images of respective colors which are superimposed on each other to represent a color image, wherein the image processing apparatus is used for enhancing a density value of a pixel of the image of each color,
Using a plurality of spatial filter means having different emphasis levels from each other, and using any of the respective spatial filter means, the density values of the pixels of each color superimposed on each other are emphasized, and the density values of the respective pixels are summed. When the total density value is equal to or more than a preset threshold value, the image processing apparatus further comprises control means for re-emphasizing the density value of each pixel by using another spatial filter means having a low emphasis degree. Processing equipment. 2. An image processing apparatus for processing a black image and an image of each color which are superimposed on each other to represent a color image, wherein a density value of a pixel of the black image and a density value of a pixel of the image of each color are enhanced. A plurality of spatial filter means, each having a different degree of emphasis, and a density value of a black pixel and a density value of a pixel of each color which are superimposed on each other by selectively using each spatial filter means. Is emphasized, and when the density value of the black pixel is equal to or larger than the first threshold value set in advance, the density value of the black pixel is emphasized again by using another spatial filter having a low emphasis degree. In addition, if the total density value obtained by summing the density values of the pixels of each color is equal to or more than a second threshold value set in advance, the other spatial filter means having a low emphasis degree is used to calculate the density value of the pixel of each color. Re-emphasis system The image processing apparatus characterized by comprising a means. 3. The image processing apparatus according to claim 1, wherein a minimum level is set in advance as an emphasis degree of each spatial filter means for emphasizing a density value of a pixel. 4. A minimum level is set in advance as the degree of emphasis of each spatial filter means for emphasizing the density value of a black pixel, and each spatial filter means for emphasizing the density value of a pixel of each color. 3. The image processing apparatus according to claim 2, wherein a minimum level is set in advance as the degree. 5. The density value of each color pixel representing a pixel of the color image is emphasized by a spatial filter means for each pixel of the color image, and if the total density value of the pixels of each color is less than a threshold value, The image processing apparatus according to claim 1, wherein the pixel of the image is excluded from a target to be processed by the spatial filter unit. 6. The spatial filter means emphasizes the density value of the black pixel for each black pixel. If the density value of the black pixel is less than a first threshold value, the black pixel is filtered by a spatial filter. The density value of the pixel of each color representing the pixel of the color image is emphasized by the spatial filter means for each pixel of the color image, and the total density value of the pixel of each color is equal to the second threshold value. 3. The image processing apparatus according to claim 2, wherein if the number is less than the pixel, the pixel of the color image is excluded from processing by the spatial filter unit. 7. A method of emphasizing the density value of a pixel of an image, wherein a plurality of spatial filter means having different emphasis levels from each other, and using any one of the spatial filter means, the density value of the pixel is calculated. Control means for emphasizing, when the density value of the pixel is equal to or greater than a preset threshold value, using another spatial filter means having a low degree of emphasis, and re-emphasizing the density value of the pixel. Characteristic image processing device.