JPH1188712A - Image processing method and image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a boundary between graphics and characters whose lightness is approximated clear at the time of converting color image data into monochromatic image data and to obtain the monochromatic image whose content is easily discriminated. SOLUTION: When the image processor 200 outputs color image data as monochromatic image data, a monochromatic data conversion part 205 is provided. The monochromatic data conversion part 205 obtains image element value change quantity between the picture elements of color image data, converts data into monochromatic image data corresponding to the picture element value of color image data when picture element value change quantity is within a prescribed range and substitutes it for monochromatic image data different from the picture element value of color image data when picture element value change quantity is out of the prescribed range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing method and an image processing apparatus, and more particularly to an image processing method and an image processing apparatus for converting or replacing color image data from a computer or the like as grayscale monochrome image data and outputting the same. .

[0002]

2. Description of the Related Art When a color image displayed on a color CRT screen of a host computer or the like is output to a monochrome hard copy device, or when output from a color hard copy device in a monochrome mode, the color image data is converted to monochrome image data. Need to be converted and output.

In such a case, the image processing apparatus converts the color image data into grayscale monochrome image data in a series of image processing steps.

[0004]

In an image processing apparatus for converting color image data into monochrome image data as described above, the image data is uniquely converted to gray scale by the brightness information and the like included in the color image data. For this reason,
Even if the color image includes a region where the hue changes rapidly, if the change in brightness is small, only a monochrome image with a small dynamic range may be obtained when converted to monochrome image data.

For example, a “blue character” on a “red background” is easy to discriminate as a color image, but when this is converted into a grayscale monochrome image, the “red background” and the “blue Since "characters" are converted to almost the same gray scale, it is almost impossible to determine the contents.

FIG. 6 shows the theoretical color gamut of Munsell hue. The lightness of a pure color at the intersection of the chroma limit line and the color density limit line differs for each hue, but if the V value (lightness) is the same for different hues, the same gray scale is obtained by converting the color image data to gray scale. It will be selected. As a result, the original color cannot be distinguished at all from the gray scale.

[0007] In addition, it is almost impossible to discriminate a combination of colors having similar lightness such as "bright orange" and "yellow green", "dark gray" and "purple" after gray scale conversion. There are many combinations.

As described above, depending on color image data including a combination of colors that are converted to close or equivalent gray scales, when color image data is converted to monochrome image data and output, there is a lack of image information especially for a figure. Often it can be severe.

The present invention solves such a problem. When converting color image data into monochrome image data and outputting the same, the boundaries of figures, characters, and the like having similar lightness are clarified, and the contents are changed. It is an object of the present invention to provide an image processing method and an image processing apparatus capable of obtaining a monochrome image in which the image can be easily determined.

[0010]

Accordingly, the invention as a means for solving the problem is described in the following (1) to (11).

(1) The invention according to claim 1 is an image processing method for outputting color image data as monochrome image data, wherein a pixel value change amount between pixels of the color image data is obtained, and the pixel value change amount is calculated. Is within a predetermined range, the image data is converted into monochrome image data corresponding to the pixel value of the color image data. If the pixel value change amount is outside the predetermined range, the pixel value is different from the pixel value of the color image data. This is an image processing method characterized by replacing the image data with monochrome image data.

In the invention of this image processing method, first, a pixel value change amount between pixels of color image data is obtained, and a color boundary is obtained. If the change at the color boundary is within a predetermined range, conversion to normal monochrome image data is performed. If the change at the color boundary is outside the predetermined range, replacement with monochrome image data different from the pixel value of the original color image data is performed.

As a result, at a color boundary where the amount of change in pixel value falls outside a predetermined range, a boundary line is formed by replacing the original color image data with monochrome image data different from the pixel value.

Therefore, when converting color image data into monochrome image data and outputting it, it is possible to clarify the boundaries of figures, characters, and the like having similar lightness and obtain a monochrome image whose contents can be easily discriminated. .

(2) The invention according to claim 2 is characterized in that (1)
Wherein the amount of change in pixel value is calculated based on a color difference, a hue angle difference, and a lightness difference. According to the invention of this image processing method, the color difference, the hue angle difference, and the lightness difference are calculated to calculate the pixel value change amount between the pixels of the color image data. This makes it possible to clarify the boundaries of characters and the like and obtain a monochrome image whose contents can be easily determined.

(3) The invention according to claim 3 is characterized in that (1)
In the above, when the pixel value change amount is out of a predetermined range,
It is characterized in that monochrome image data different from the pixel value is replaced based on the pixel value of the pixel to be replaced.

According to the invention of this image processing method, when replacing with monochrome image data different from the pixel value of the original color image data, the replacement is executed based on the pixel value of the pixel to be replaced.

That is, the pixel value of the pixel to be replaced is determined by referring to the pixel value of the pixel to be replaced, and the pixel value of the monochrome to be replaced is determined. , The boundaries of figures, characters, and the like with similar lightness are clarified, and it is possible to obtain a monochrome image whose contents can be easily distinguished.

(4) The invention according to claim 4 is characterized in that:
In (3), when the pixel value change amount is out of the predetermined range, the pixel value is converted into monochrome image data corresponding to the pixel value of the color image data, or is converted into monochrome image data different from the pixel value of the color image data. It is characterized in that it can be replaced or one of them can be selected.

According to the invention of this image processing method, whether the monochrome image data is replaced with another pixel value at the boundary,
Either monochrome image data converted at the boundary or selected is output.

As a result, it is possible to select whether or not to form a boundary line by replacement at a color boundary with a small change in which the pixel value change amount is outside a predetermined range. Therefore, it is possible to obtain a monochrome image in which the boundaries between figures and characters with similar lightness are clear and the content is easy to determine, and a monochrome image in which figures and characters with similar lightness are kept as they are.

(5) The invention according to claim 5 is characterized in that:
In (3), a result of conversion into monochrome image data corresponding to the pixel value of the color image data is selected and output irrespective of the pixel value change amount between pixels of the color image data.

In the invention of this image processing method, monochrome image data converted based on the pixel values of the color image data is selected and output regardless of the pixel value change amount. In this case, the state becomes suitable for processing color image data such as a photograph.

(6) An image processing apparatus for outputting color image data as monochrome image data according to a sixth aspect of the present invention, wherein: a determination unit for determining a pixel value change amount between pixels of the color image data; A conversion unit that converts the pixel value of the color image data into monochrome image data according to the pixel value of the color image data when the value change amount is within a predetermined range; A replacement unit for replacing with monochrome image data having a different value.

In the invention of the image processing apparatus, first, a pixel value change amount between pixels of color image data is obtained, and a color boundary is obtained. If the change at the color boundary is within a predetermined range, conversion to normal monochrome image data is performed. If the change at the color boundary is outside the predetermined range, replacement with monochrome image data different from the pixel value of the original color image data is performed.

As a result, at a color boundary where the amount of change in pixel value falls outside a predetermined range, a boundary line is formed by replacing the original color image data with monochrome image data different from the pixel value.

Therefore, when converting color image data into monochrome image data and outputting it, it is possible to clarify the boundaries of figures, characters, and the like having similar lightness and obtain a monochrome image whose contents can be easily discriminated. .

(7) The invention according to claim 7 is characterized in that:
Wherein the determination means calculates the pixel value change amount based on a color difference, a hue angle difference, and a brightness difference. According to the invention of this image processing apparatus, by calculating the pixel value change amount between the pixels of the color image data by paying attention to the color difference, the hue angle difference, and the lightness difference, it is possible to obtain a graphic having an approximate lightness while having a hue angle difference or a color difference. This makes it possible to clarify the boundaries of characters and the like and obtain a monochrome image whose contents can be easily determined.

(8) The invention according to claim 8 is characterized in that:
Wherein the replacement means replaces, based on the pixel value of a pixel to be replaced, monochrome image data different from the pixel value, when the pixel value change amount is outside a predetermined range.

According to the invention of the image processing apparatus, when replacing the original color image data with the monochrome image data different from the pixel value, the replacement is executed based on the pixel value of the pixel to be replaced.

That is, the pixel value of the pixel to be replaced is determined with reference to the pixel value of the pixel to be replaced, and the pixel value of the monochrome to be replaced is determined. , The boundaries of figures, characters, and the like with similar lightness are clarified, and it is possible to obtain a monochrome image whose contents can be easily distinguished.

(9) The invention according to claim 9 is characterized in that:
In (8), when the pixel value change amount is out of a predetermined range, the pixel value is converted into monochrome image data according to the pixel value of the color image data, or the monochrome image data is different from the pixel value of the color image data. Or replace
It is characterized by comprising a selection means for selecting either one.

According to the invention of this image processing apparatus, whether the monochrome image data is replaced with another pixel value at the boundary,
Either monochrome image data converted at the boundary or selected is output.

As a result, it is possible to select whether or not to form a boundary line by replacement at a color boundary with a small change in which the pixel value change amount is outside a predetermined range. Therefore, it is possible to obtain a monochrome image in which the boundaries between figures and characters with similar lightness are clear and the content is easy to determine, and a monochrome image in which figures and characters with similar lightness are kept as they are.

(10) In the invention according to claim 10, in the above (6) to (8), the result of conversion into monochrome image data corresponding to the pixel value of the color image data is obtained irrespective of the pixel value change amount. A selection means for selecting and outputting is provided.

In the invention of this image processing apparatus, the monochrome image data converted based on the pixel values of the color image data is selected and output regardless of the pixel value change amount. In this case, the state becomes suitable for processing color image data such as a photograph.

(11) The invention according to claim 11 is characterized in that, in the above (6) to (9), the setting can be changed in a predetermined range of the pixel value change amount. According to the invention of this image processing apparatus, it is possible to change a predetermined range (threshold) of a pixel value change amount for determining a pixel to be processed as a color boundary by a user operation.

Therefore, when converting color image data into monochrome image data and outputting the monochrome image data, the boundary between figures and characters with similar lightness is clarified under the conditions set by the user, and a monochrome image whose contents are easy to determine is obtained. It is possible to obtain.

[0039]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating an example of the overall configuration of an image processing apparatus that performs an image processing method according to an embodiment of the present invention. FIG. 3 is a block diagram showing a main part of FIG. 1 in detail.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, reference numeral 100 denotes an example of an external device such as a host computer, which outputs color image data. Reference numeral 200 denotes an image forming apparatus according to the present embodiment, which converts color image data into monochrome image data. Reference numeral 300 denotes a unit for forming an image of monochrome image data and printing out the recording image on recording paper.

Image data (RGB color image data) and control commands input from the host computer 100 through the image data input unit 202 are stored in the program RO.
The image memory 2 is processed by the CPU 207 that operates according to the image data processing program stored in the M203 and is in a format that can be processed by the image processing apparatus.
08 is stored.

The image data stored in the image memory 208 may be data of the entire image or data of a part of the image. The operation panel 206 changes the settings of the image processing apparatus, and notifies the operator of the state of the image processing apparatus on a display unit (not shown) in the operation panel 206.

Generally, RGB image data of 256 gradations (8 bits each) is used for color image data, and the present embodiment will be described in accordance with this. A part of the image data in the RGB format which is temporarily stored in the image memory 208 and can be processed by the image processing apparatus is processed by the region extracting unit 204 so that the distribution change of the pixel value can be easily calculated for each pixel. It is cut out as shown in FIG. 2 in the form of a rectangular area centering on the pixel to be processed (pixel of interest).

In the example shown in FIG. 3, an example of a rectangular area of a total of 9 pixels including 8 pixels around the pixel to be processed is shown. However, this example shows an example of a data processing unit. It does not necessarily have to be the same as this state.

The RGB image data of each pixel in the rectangular area is subjected to the following processing by the monochrome image data conversion unit 205. The processing of the monochrome image data conversion unit 205 will be described in detail with reference to FIG.

[RGB → XYZ Conversion] The RGB image data in the rectangular area described above is once converted to the XYZ color system by the color conversion unit 401 in FIG.

[0047]

(Equation 1)

Here, (XR, YR, ZR), (XG, Y
(G, ZG) and (XB, YB, ZB) are coordinate values of R, G, and B in the XYZ space. Γ = 2.2 (normal gamma value of CRT).

[XYZ → L * a * b * conversion] and XY
The coordinate values in the Z space are furthermore perceptually substantially uniform in the color conversion unit 401 by the following equation (2).
a * b * is converted to uniform color space coordinates, and the L * value of each pixel, a *
Get the value, b * value.

[0050]

(Equation 2)

Here, Xo, Yo and Zo are X, Y and Z in a standard light source. However, Y / Yo is 0.008
In the case of 856 or less, L * = 903.29 (Y / Yo), and any of X / Xo, Y / Yo and Z / Zo is 0.00
In the case of 8856 or less, each cubic root is set to “7.778
(A / Ao) +16/116 ". This C
In the IE L * a * b * uniform space, any section having the same size matches the change in the perceived color of the same size, so that there is an advantage that the pixel value change amount can be quantitatively represented. .

[Calculation of color difference, hue angle difference, and lightness difference] Here, the pixel value change amount between two arbitrary pixels m and n is calculated based on the color difference (ΔEmn), the hue angle difference (Δθmn), and the lightness difference. (ΔVmn) is calculated as follows.

[0053]

(Equation 3)

However, the brightness difference calculated here (ΔVmn
Bk) is a lightness difference in a gray scale converted between two pixels. Further, f (x) is a gray scale conversion function of the image processing apparatus, and f (Lx *) represents a converted gray level.

Since the actual operation in the apparatus is converted in the form of reference to a gray scale table, the brightness difference (ΔVmn · Bk) is calculated as the difference between the index values of the table. The color difference (ΔEmn) / hue difference (Δθm) between these pixels m and n
n) The change in pixel value of the brightness difference (ΔVmn)

[0056]

(Equation 4)

When the expression (4) is satisfied, when the color image data is converted into monochrome image data as it is and outputted, the pixel e and the pixel e have the same color difference and hue difference between the pixels mn. a is displayed in a gray scale similar to each other.

In this case, the degree of similarity gray scale determination can be adjusted by adjusting the set values of α1, α2, and α3. [Calculation of Pixel Change Amount] For the pixel e to be processed located at the center of the rectangular area in FIG. 3, the pixel value change amount with respect to the pixel a located at the upper left is calculated.

First, the RGB values of the pixel e are converted into L * a * b * values by the color conversion unit 401 in FIG.
Stored in register 402. At the same time, the hue angle of the pixel e calculated by the hue angle calculation unit 404 and the index number of the pixel e referred to in the conversion gray scale table 405 are stored in the third register 408.

Next, the RGB values of the pixel a are input, converted into L * a * b * values by the color conversion unit 401, and the values are stored in the second register 403. At the same time, the hue angle calculator 40
The hue angle of the pixel a calculated by 4 and the index number of the pixel a referred to in the conversion gray scale table 405 are stored in the fourth register 409.

The subtractor 411 subtracts the hue angle and the index number of the pixel a stored in the fourth register 409 from the hue angle and the index number of the pixel e stored in the third register 408, respectively. To the comparator 412.

The L * a * b of the pixel e stored in the first register 402 and the second register 403, respectively.
The * value and the L * a * b * value of the pixel a are calculated by the color difference calculator 407 as L * a *.
The distance (ΔE) in the b * space is obtained, and the value is sent to the comparator 412.

The comparator 412 sets the input distance (ΔE), hue angle difference (Δθ) and index number difference (ΔV) in the L * a * b * space in the condition setting section 410. The value (α1, α2, α3) is compared, and a flag reflecting the comparison result is stored in the flag register 413.

The threshold value set in condition setting section 410 can be changed externally. For example, when there is a setting change instruction from the operation panel 206 by the user, the CPU 207 sets the threshold data held by the condition setting unit 410 as new threshold data.

The comparison by the comparator 412 is for judging whether or not the pixel value change amount between the pixels a and e satisfies the above equation (4). In this case, the above equation (4) is replaced by the following equation (5) Becomes

[0066]

(Equation 5)

When the expression (5) is satisfied, a flag a indicating that the amount of change in the pixel value between the pixels a and e satisfies the condition is set and stored in the flag register 413. Subsequently, the pixel e to be processed is calculated as follows in terms of a pixel value change amount with respect to the pixel b located immediately above the pixel e.

The RGB values of the pixel b are input to the color conversion unit 401, and the converted L * a * b * values of the pixel b are stored in the second register 403. At the same time, the hue angle of the pixel b calculated by the hue angle calculation unit 404 and the index number of the pixel b referred to in the conversion grayscale table 405 are stored in the register 4 (409).

The L * a * b * value of the pixel e stored in the first register 402 and the hue angle and index number of the pixel e stored in the third register 408 are left as they are.

The subtractor 411 subtracts the hue angle and the index number of the pixel b stored in the register 4 (409) from the hue angle and the index number of the pixel e stored in the third register 408, respectively. To the comparator 412.

The L * a * b of the pixel e stored in the first register 402 and the second register 403, respectively.
The * value and the L * a * b * value of the pixel b are calculated by the color difference calculation unit 407 using L * a * b *.
The distance (ΔE) in the a * b * space is determined, and the value is sent to the comparator 412.

The comparator 412 sets the input distance (ΔE), hue angle difference (Δθ) and index number difference (ΔV) in the L * a * b * space in the condition setting section 410. Compare with the values (α1, α2, α3).

The comparison by the comparator 412 is for judging whether or not the pixel value change amount between the pixels b and e satisfies the above equation (4). In this case, the above equation (4) is replaced by the following equation (6) Becomes

[0074]

(Equation 6)

When the expression (6) is satisfied, a flag b indicating that the pixel value change between the pixels be satisfies the condition is set, and is additionally stored in the flag register 413.
Subsequently, the pixel e to be processed is the pixel d located on the left side.
Is calculated in the same manner as above, and the pixel d−
It is determined whether or not the pixel value change amount between e satisfies the above equation (4). In this case, the above equation (4) becomes the following equation (7).

[0076]

(Equation 7)

When the equation (7) is satisfied, a flag d indicating that the amount of change in pixel value between the pixels d and e satisfies the condition is set, and is additionally stored in the flag register 413.
If at least one of the flags a, b, and d is set, the color difference change flag He of the pixel e is set.

The same operation as that for the pixel e is also performed for the pixels f.hi.i in the rectangular area of three pixels each in the vertical and horizontal directions. The pixel e obtains the color difference change flag H by obtaining the pixel value change amount with the pixels a, b, and d located on the upper left, right above, and left, while the pixel f obtains the color difference change flag H.
The color difference change flag Hf is obtained by obtaining the amount of change in the pixel value between the pixels b, c, and e located on the left.

Similarly, the pixel h obtains the color difference change flag Hh by calculating the pixel value change amount with the pixels d, e, g located at the upper left, right above, and left. The pixel i obtains the color difference change flag Hi by calculating the pixel value change amount with the pixels e, f, and h located at the upper left, right above, and left.
In this way, the flag register 413 stores the hue change flags He, Hf, Hh, and Hi of the four pixels, that is, the pixel e to be processed and the right, bottom, and bottom right pixels f, h, and i. Is done.

[Determination / Conversion / Replacement] Depending on the states of these four hue change flags, the selector 414 determines whether to use the conversion grayscale table 405 for converting the color image data into the normal grayscale as the grayscale conversion table. Is switched to use the replacement grayscale table 406 for performing replacement to generate a boundary line.

One of the four flags He, Hf, Hh, Hi
When the 3 flag is set, the selector 414 selects the replacement grayscale table 406. in this case,
The monochrome image data conversion unit 205 converts (replaces) the pixel value of the pixel e into the gray scale for the boundary instead of the gray scale that should be originally converted, and converts the pixel value into the frame memory 20.
Write 9

On the other hand, when the 0 flag or the 4 flags among the 4 flags of He, Hf, Hh, Hi are set, the selector 414 selects the conversion gray scale table 405. In this case, the pixel value of the pixel e is converted into a normal gray scale and written to the frame memory 209.

When the 0 flag or 4 flag is set, the normal gray scale is used instead of the boundary gray scale. When the 0 flag is set, there is not much change in hue around the target pixel e, and the boundary gray scale is not used. This is because it is not necessary to clarify.

When the 4 flag is set, the target pixel e
Means that the hue change is relatively large around the image, and it is presumed that the data is image data such as a photographic image. Therefore, a normal gray scale is used.

The replacement gray scale table 406 has a plurality of density levels, and it is determined which gray level to use in accordance with the pixel value of the pixel e.
In this case, the density level of the gray scale table for replacement 406 simply suffices if it is roughly classified into dark, medium, and light. For example, when the pixel value of the pixel e is relatively low, the color image data is expressed as a medium density level, when the pixel value is medium, a dark or light density level, and when the pixel value is relatively high, a light density level. Even if the monochrome conversion is performed, it is sufficient that the boundary of the color difference change can be recognized.

When the series of processing for the pixel e is completed, the area extracting unit 204 cuts out a new rectangular area of three pixels each in the vertical and horizontal directions centering on another pixel from the image memory 208, and performs a series of processing for the pixel e. The same operation as is performed.

By the above operation, the color image as shown in FIG. 4A is not a monochrome image with unclear boundaries as shown in FIG. 4B, but the boundary portion as shown in FIG. Is replaced with another density to obtain a clear monochrome image.

In a graphic in which several groups of areas overlap, there is also an advantage that a sense of depth can be obtained by replacing the image part which is a boundary part and exists in the back.

[Image formation] This operation is performed by the image memory 208.
This is continued until all pixels of the image data stored in are completed. When all or part of the data that can be printed by the image forming apparatus 300 is formed in the frame memory 209, the CPU 207 issues a print command to the image forming apparatus 300, and the image forming apparatus 300 performs printing.

When the image forming apparatus 300 is a line printer or the like, the CPU 207 issues a print command to the image forming apparatus 300 when a part of printable data is formed. If the image forming apparatus 300 is a page printer or the like, the CPU 207 issues a print command to the image forming apparatus 300 when all printable data has been formed.

[Other Embodiments] (1) Although FIG. 3 has a configuration in which processing is performed for each pixel for the sake of simplicity, pixel operations are performed, for example, in line units or band units. A configuration in which the processing speed such as performing the processing may be considered. In that case, it is necessary to configure hardware and software suitable for it. Further, the image processing may be performed only by software.

(2) In the above example, the boundary of the image data is determined from the change in the distribution of the pixel values of the image data, and the gray scale value of the monochrome image data on the boundary is determined as necessary so that the boundary becomes clear. Although the replacement data is taken from the grayscale table for the boundary in order to perform the replacement, the same result can be obtained by the replacement in which the pixel value of the pixel to be processed is calculated by addition or subtraction to obtain the replacement data. Can be

(4) The above-described image data conversion is an example of an image processing apparatus connected to a host computer or the like. However, the same conversion processing function is provided to the printer driver so that the image data can be converted in the host computer. Similar image data conversion processing may be performed.

(5) The image processing apparatus is set by a control command input from the operation panel 206 or the image data input unit 202 so that only normal gray scale conversion is performed without using the boundary gray scale. It is possible to put.

In this case, as shown in FIG.
Command register 4 based on the command setting from
15, the selector 414 may be fixed to the conversion gray scale table. Thus, the selector 41
4 is fixed to the conversion gray scale table 405, only the conventional monochrome conversion operation is performed. In this case, the state becomes suitable for processing color image data such as a photograph.

Similarly, the command register 415 releases the fixed state of the selector 414 based on the command setting, so that the replacement gray scale table is used in the case of a predetermined change amount.

[0097]

As described in detail above, according to the inventions described in this specification, the following effects can be obtained.

(1) In the image processing method according to the first aspect, first, the amount of change in pixel value between pixels of color image data is obtained, and the color boundary is obtained. If the change at the color boundary is within a predetermined range, conversion to normal monochrome image data is performed. If the change at the color boundary is outside the predetermined range, replacement with monochrome image data different from the pixel value of the original color image data is performed.

As a result, at a color boundary where the amount of change in the pixel value falls outside the predetermined range, a boundary line is formed by replacing the original color image data with monochrome image data different from the pixel values. Therefore, when converting color image data into monochrome image data and outputting the monochrome image data, it is possible to clarify the boundaries of figures, characters, and the like having similar lightness and obtain a monochrome image whose contents can be easily discriminated.

(2) In the image processing method according to the second aspect, the pixel value variation between the pixels of the color image data is obtained by paying attention to the color difference, the hue angle difference, and the lightness difference. It is possible to clarify the boundaries of figures, characters, and the like having similar lightness while having a color difference, and to obtain a monochrome image whose contents can be easily distinguished.

(3) In the image processing method according to the third aspect, when replacing with monochrome image data different from the pixel value of the original color image data, based on the pixel value of the pixel to be replaced. Performing a replacement.

That is, since the pixel value of the monochrome to be replaced is determined with reference to the pixel value of the pixel to be replaced and the replacement is performed, the pixel value of the pixel to be replaced is clearly different. , The boundaries of figures, characters, and the like with similar lightness are clarified, and it is possible to obtain a monochrome image whose contents can be easily distinguished.

(4) In the image processing method according to the fourth aspect, either one of the monochrome image data replaced at the boundary with another pixel value and the monochrome image data converted at the boundary is selected. Output.

As a result, it is possible to select whether or not to form a boundary line by replacement at a color boundary with a small change in which the pixel value change amount is outside a predetermined range. Therefore, it is possible to obtain a monochrome image in which the boundaries between figures and characters with similar lightness are clear and the content is easy to determine, and a monochrome image in which figures and characters with similar lightness have the same brightness.

(5) In the image processing method according to the fifth aspect, the monochrome image data converted based on the pixel values of the color image data is selected and output regardless of the pixel value change amount. In this case, the state becomes suitable for processing color image data such as a photograph.

(6) In the image processing apparatus according to the sixth aspect, first, the amount of change in pixel value between pixels of the color image data is obtained, and the color boundary is obtained. If the change at the color boundary is within a predetermined range, conversion to normal monochrome image data is performed. If the change at the color boundary is outside the predetermined range, replacement with monochrome image data different from the pixel value of the original color image data is performed.

As a result, at a color boundary where the pixel value change amount is outside the predetermined range and the change is small, a boundary line is formed by replacing the original color image data with monochrome image data different from the pixel value. Therefore, when converting color image data into monochrome image data and outputting the monochrome image data, it is possible to clarify the boundaries of figures, characters, and the like having similar lightness and obtain a monochrome image whose contents can be easily discriminated.

(7) In the image processing apparatus according to the seventh aspect, the pixel value change amount between pixels of the color image data is obtained by paying attention to the color difference, the hue angle difference, and the lightness difference. It is possible to clarify the boundaries of figures, characters, and the like having similar lightness while having a color difference, and to obtain a monochrome image whose contents can be easily distinguished.

(8) In the image processing apparatus according to the eighth aspect, when replacing the original color image data with monochrome image data different from the pixel value of the original color image data, based on the pixel value of the pixel to be replaced. Performing a replacement.

That is, since the pixel value of the monochrome to be replaced is determined with reference to the pixel value of the pixel to be replaced and the replacement is performed, the pixel value of the pixel to be replaced is clearly different. , The boundaries of figures, characters, and the like with similar lightness are clarified, and it is possible to obtain a monochrome image whose contents can be easily distinguished.

(9) In the image processing apparatus according to the ninth aspect, either one of monochrome image data replaced at the boundary with another pixel value and monochrome image data converted at the boundary is selected. Output.

As a result, it is possible to select whether or not to form a boundary line by replacement at a color boundary with a small change in which the pixel value change amount falls outside a predetermined range. Therefore, it is possible to obtain a monochrome image in which the boundaries between figures and characters with similar lightness are clear and the content is easy to determine, and a monochrome image in which figures and characters with similar lightness have the same brightness.

(10) In the image processing apparatus according to the tenth aspect, irrespective of the pixel value change amount, the monochrome image data converted based on the pixel value of the color image data is selected and output. In this case, the state becomes suitable for processing color image data such as a photograph.

(11) In the image processing apparatus according to the eleventh aspect, a predetermined range (threshold) of a pixel value change amount for determining a pixel to be processed as a color boundary is changed by a user operation. It is possible to do.

Therefore, when converting color image data into monochrome image data and outputting the monochrome image data, the boundary between figures and characters with similar lightness is clarified under the conditions set by the user, and the monochrome image whose contents can be easily discriminated is determined. It is possible to obtain.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing, by function, a circuit configuration of an entire image processing apparatus according to an embodiment of the present invention;

FIG. 2 is an explanatory diagram showing how a pixel to be processed is cut out according to the embodiment of the present invention;

FIG. 3 is a functional block diagram showing, by function, a circuit configuration of a main part of the image processing apparatus according to the embodiment of the present invention;

FIG. 4 illustrates an image processing according to an embodiment of the present invention.
FIG. 4 is an explanatory diagram illustrating a state where a color image is converted into a monochrome image.

FIG. 5 is a functional block diagram showing, by function, a circuit configuration of a main part of an image processing apparatus according to another embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a theoretical color gamut of Munsell hue.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 host computer 200 image processing device 202 image data input unit 203 program ROM 204 area extraction unit 205 monochrome data conversion unit 206 operation panel 207 CPU 208 image memory 209 frame memory 300 image forming device

Claims (11)

[Claims] 1. An image processing method for outputting color image data as monochrome image data, wherein a pixel value change amount between pixels of the color image data is obtained, and the pixel value change amount is within a predetermined range. Is converted into monochrome image data according to the pixel value of the color image data, and when the pixel value change amount is outside a predetermined range, the pixel value is replaced with monochrome image data different from the pixel value of the color image data. Characteristic image processing method. 2. The method according to claim 1, wherein the pixel value change amount is a color difference, a hue angle difference,
2. The image processing method according to claim 1, wherein the calculation is performed based on a brightness difference. 3. The method according to claim 1, wherein when the pixel value change amount is outside a predetermined range, the pixel value is replaced with monochrome image data different from the pixel value based on the pixel value of the pixel to be replaced. The image processing method described in the above. 4. When the pixel value change amount is out of a predetermined range, the pixel value is converted into monochrome image data according to the pixel value of the color image data, or is converted into monochrome image data different from the pixel value of the color image data. 4. The image processing method according to claim 1, wherein replacement or one of the replacement is selectable. 5. The method according to claim 1, wherein a result of conversion into monochrome image data corresponding to the pixel value of the color image data is selected and output irrespective of a pixel value change amount between pixels of the color image data. The image processing method according to claim 3. 6. An image processing apparatus for outputting color image data as monochrome image data, comprising: a determination unit for determining a pixel value change amount between pixels of the color image data, wherein the pixel value change amount is within a predetermined range. A conversion unit that converts the pixel value of the color image data into monochrome image data according to the pixel value of the color image data in a case where the pixel value change amount is out of a predetermined range; An image processing apparatus comprising: 7. The image processing apparatus according to claim 6, wherein the determination unit calculates the pixel value change amount based on a color difference, a hue angle difference, and a brightness difference. 8. The method according to claim 1, wherein when the pixel value change amount is out of a predetermined range, the replacement unit replaces the image data with monochrome image data different from the pixel value based on a pixel value of a pixel to be replaced. The image processing apparatus according to claim 6, wherein 9. When the pixel value change amount is out of a predetermined range, the pixel value is converted into monochrome image data according to the pixel value of the color image data, or is converted into monochrome image data different from the pixel value of the color image data. 9. The image processing apparatus according to claim 6, further comprising a selection unit for performing replacement or selecting one of the replacement. 10. A system according to claim 6, further comprising a selection unit that selects and outputs a result of conversion into monochrome image data according to the pixel value of the color image data, regardless of the pixel value change amount. An image processing apparatus according to claim 8. 11. The image forming apparatus according to claim 6, wherein a setting can be changed in a predetermined range of the pixel value change amount.