JP2000184210A - Color.black/white image conversion method and image processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically convert a color image mainly consisting of characters and symbols into a black/white image where the characters and the symbols do not disappear in the background. SOLUTION: A color.black/white conversion function section 13 converts all pixels of a color image file 12 into black/white pixels by using conversion functions F1-Fn to obtain black/white pixels from combinations of color components of color pixels and stores the black/white pixels to black/white image files 1-n. An image compression function section 16 compresses the black/ white images of each file and stores the compressed image to compressed image files 1-n. An image selection function section 18 selects the compressed image with a maximum file size and transmits the selected compression image to a print signal output device 2. The output device 2 restares the received compression image into the black/white image and outputs it into a printer 3. Thus, recognition of characters or the like can be optimized by selecting black/white image data that are converted by using any of the conversion functions F1-Fn so as to obtain a largest difference between pixels of characters or the like and pixels of the background.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing system for converting a color image into a black and white image, and more particularly, to an image processing method and apparatus suitable for black and white conversion of color characters and symbols.

[0002]

2. Description of the Related Art With the development of image processing technology, the output of color images created by computers has become commonplace, and natural images such as TV images and photographs have been taken in and processed and edited as desired. I have. However, black and white images are still often used. For example, when outputting a computer-processed color image, if the printing apparatus is a black and white printer, the color image must be converted to a black and white image.

In order to convert a color image into a black and white image, a conversion function F for obtaining a black and white pixel value from a combination of the color component values of the color pixels is prepared, and all the pixels of the color image are converted into black and white pixel values. . In order to determine the conversion function F, for example, Japanese Patent Application Laid-Open No. 5-75847 discloses a method of obtaining weighted addition of all components according to the specific gravity of the color components input by the user. That is, assuming that the specific gravity of RGB is Kr: Kg: Kb, the function formula is F = Kr × R + K
g × G + Kb × B. In addition, Japanese Patent Application Laid-Open No. 10-63833
Discloses a method of analyzing the frequency distribution of each color component for each image and dynamically changing the weighting of the color components.

[0004] In these conventional conversion techniques, natural images represented by TV images, photographs, paintings and the like are targeted, so realism is emphasized. Since the object of the natural image is recognized from the image of the whole image, such as the outline, the pattern, and the relation with other objects, the color / black-and-white conversion has a feature in that the intermediate color of the color is expressed by the black and white gradation. .
When an appropriate conversion function is determined according to the characteristics of the target color image or the characteristics expected of the converted black-and-white image, the conversion function is dedicated.

[0005]

As described above, the conventional color / black-and-white conversion technique is applicable to natural images, and attention is paid to the problem of color / black-and-white conversion of an image mainly including characters and symbols. Not. At first glance, color / black and white conversion of characters and the like seems to be simpler than natural images, but since interpolation cannot be expected as in the recognition of natural images, important words, sentences, or symbols in figures and tables are completely lost. May be unrecognizable.

For example, in a plant monitoring device, an operator can easily monitor a system diagram, a data transition diagram, and the like.
Characters, symbols, and the like are color-coded and displayed on a monitor by changing the display color during a state transition such as an abnormality.
When this color chart is converted to black and white for printing, characters and symbols of a certain color become the same color as the background after conversion,
In some cases, words, sentences, or symbols of a certain color are all lost in the background. In particular, when a character or the like of an intermediate color is converted, the difference between the monochrome pixel value and the background often does not become a recognizable size.

Of course, if an appropriate function expression can be determined by the method disclosed in Japanese Patent Application Laid-Open No. 5-75847, the character and the background after conversion can be differentiated from the background. However, determining the function formula by changing the weight of the color component for each color combination of the target image requires trial and error time and skill, which imposes a heavy burden on the operator. In the method of changing the weighting according to the frequency distribution of the color components as in Japanese Patent Application Laid-Open No. 10-63833, the importance of characters and the like in figures and tables has no direct relationship with the frequency distribution.
It is not suitable for converting characters and the like.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problem. When a color image including characters and symbols is converted into a black-and-white image, the converted characters and the like are buried in the background. It is an object of the present invention to provide a color / monochrome image conversion method capable of avoiding the above, and an image processing apparatus capable of automatically executing the color / monochrome conversion.

[0009]

According to the present invention, there is provided a color / monochrome image conversion method for obtaining a monochrome pixel value for a combination of color component values of a color pixel by a conversion function. A plurality of conversion functions corresponding to a plurality of colors of a character and a background or a character and a figure and a background to be used are prepared in advance so that a character or a character and a figure after black and white conversion can be identified as a background.
A plurality of black-and-white image data is obtained by performing a conversion using a plurality of the above-described conversion functions on all the pixels of the target color image. It is characterized in that the largest monochrome image data is selected.

[0010] Further, each of the black and white image data is compressed to obtain the same number of compressed image data, and an image having the largest data amount is selected from the compressed image data and restored to a black and white image. I do.

An image processing apparatus to which the method of the present invention is applied includes:
Color image storage means for storing a target color image, conversion method storage means for storing a plurality of conversion methods for converting a color image into a black and white image, and color for performing conversion on the target image by the plurality of conversion methods / Black and white image conversion means, black and white image storage means for storing the same number of black and white images as the conversion method, image compression means for compressing black and white image data, and compressed image storage for storing the same number of compressed image data as the black and white images Means, an image selecting means for selecting the one having the largest data amount among the compressed image data, and a compression restoring means for restoring a monochrome image from the selected compressed image data.

According to the present invention, a plurality of methods for converting a color image into a black and white image are stored in advance, so that a conversion method for increasing the difference in pixel value between a character or the like and the background becomes large. You can select from the characteristics of the data. In other words, when a plurality of black-and-white image data after black-and-white conversion is compressed, the larger the difference between the pixel values of characters and the like in the black-and-white image and the background, the larger the information amount of the black-and-white image (the lower the compression ratio). By using this, black-and-white image data in which characters and the like can be best recognized with respect to the background is selected.

In addition, if a conversion function capable of recognizing characters and the like after black-and-white conversion is defined in advance in correspondence with the color arrangement of various color images used on a monitor screen or the like, an optimum black-and-white image for the target color image can be obtained. Conversion can be performed automatically.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a color / black and white conversion method according to the present invention is executed by a dedicated image processing apparatus according to a first embodiment.
And a second embodiment applied to a monitoring system will be described in detail.

[First Embodiment] FIG. 1 is a functional block diagram showing an image processing apparatus according to one embodiment. The hardware configuration of this apparatus includes a computer 1 for performing color / black and white image conversion, a print signal output device 2 for outputting a black and white image transferred from the computer 1 to a printer, and a black and white printer device 3.

The computer 1 has a color image reading function unit 11, a color / monochrome conversion function unit 13, an image compression function unit 16, and an image selection function unit 18. A color image file 1 for storing the read color image
2, a conversion function file 14 for storing the conversion functions F1 to Fn, a black and white image file 15 for storing the converted black and white image, and a compressed image file 17 for storing a black and white compressed image.

The conversion function file 14 includes a conversion function F for obtaining a black and white pixel value from a combination of color component values of a color pixel.
As described above, all the pixels of the color image are converted into monochrome pixel values. The contents of the n types of conversion functions F1 to Fn may be function expressions or conversion tables. Each of the monochrome image file 15 and the compressed image file 17 has n files corresponding to the conversion function Fi (i = 1 to n).

Inside the print signal output device 2, a compression / decompression function unit 21 for decompressing one compressed image selected by the image selection function unit 18, and an output function unit for outputting the restored monochrome image to the printer 3 23, and a monochrome image file 22 for storing the restored monochrome image.

FIG. 2 shows a flowchart of the color / monochrome image conversion process. The computer 1 first reads color image data from the outside by the color image reading function unit 11, decomposes the color image data into R, G, and B color components and stores them in the color image file 12 (S11). Then, the initial value = 1 is substituted for the loop variable i (S12), and thereafter, i is repeated from 1 to n.

Next, color / monochrome image conversion is performed by the color / monochrome conversion function unit 13 using the function Fi stored in the conversion function file 14 (S13). That is,
The conversion function F is applied to each pixel of the color image file 12 to obtain a black and white pixel value, which is stored in the file i in the black and white image file 15. The black-and-white pixel value V is obtained by Expression (1), where R is the value of the red component of the color pixel, G is the value of the green component, and B is the value of the blue component.

[0021]

V = F (R, G, B) (1) FIG. 3 is a conversion table showing one embodiment of the conversion function. The conversion functions F1 to Fn correspond to all combinations of the color pixel values (R, G, B) (in this example, R, G, and B each correspond to the second floor) so as to adapt to the combination of the background color and the character color of the color image. The black and white pixel value corresponding to the tone is set.

For example, a conversion function F1 can be used to convert a color image having a yellow background and red characters into a monochrome image having a white background and black characters. However, when the function F2 is used for this color image, both the background and the characters become black,
When the function Fn is used, both the background and the character become white.

On the other hand, when the conversion function F2 is used for a color image with a white background and purple characters, and when the conversion function F3 is used for a color image with a red background and black characters, the background is white and the characters are white. It can be converted to a black and white image. In each case, the application of other functions results in the background and text being the same color.

Next, the image compression function unit 16 performs file compression on the black-and-white image file i, and stores the compression result in the file i in the compressed image file 17 (S1).
4). The processes of S13 and S14 are repeated until i = n, and conversion and compression processing by the conversion functions F1 to Fn are performed and stored in the compressed files 1 to n.

If i = n, the conversion and compression processing ends. Here, the larger the difference between the pixel values of the background and characters in the converted monochrome image, that is, the smaller the number of characters buried in the background of the monochrome image, the greater the amount of information after compression. As a result, the file size of the compressed image increases as the difference between the pixel values of the background and the character in the black-and-white image increases, in other words, as the degree of adaptation of the applied conversion function Fi increases.

Then, the image selecting function unit 18 selects the compressed image file having the largest file size from the compressed image files 1 to n obtained in step S14 (S1).
7). That is, a black-and-white image file is selected in which the difference between the pixel value of the character in the black-and-white image and the background is estimated to be the largest. Here, the selected compressed image file is stored in file k
(1 ≦ k ≦ n). Finally, the selected compressed image file k is transferred to the print signal output device 2, and the process is terminated (S18).

FIG. 4 shows a flowchart of the monochrome image printing process. In the print signal output device 2, first, the compression / decompression function unit 21 reads the compressed image file k transferred from the computer 1, sequentially compresses and decompresses the compressed image file k, and stores it in the monochrome image file 22 (S21). Next, monochrome image data is output to the printer device 3 by the monochrome image output function unit 23 (S22).

As described above, according to the present embodiment, of the black-and-white images converted by the conversion function Fi (i = 1 to n), the black-and-white image having the largest pixel value difference between the character and the background is selected. You can select and output.

In this embodiment, equation (1) is applied to each pixel, but the present invention is not limited to this. Any number of conversion methods may be prepared in advance, and any method may be used as long as an optimum conversion method is selected from the conversion results using the conversion methods.

In this embodiment, an example in which the computer 1 performs the sequential processing has been described.
Can be processed in parallel, the processing can be speeded up.
For example, by performing steps S13 and S14 in FIG. 2 in parallel with n processors, S12 to S16
Is unnecessary for n times of loop processing.

Further, when the monochrome image file i is compressed in S14, the size of the compressed file i-1 is compared with the size of the previous compressed file i-1 so that a large compressed file is left.
The number of compressed files is n / 2. Further, the computer 1 and the print signal output device 2 in FIG. 1 can be realized by the same computer.

[Second Embodiment] Next, an example in which the color / black and white image conversion of the present invention is applied to a black and white hard copy of a power system monitoring system will be described.

FIG. 5 shows a schematic configuration of the power system monitoring system. The main computer 4 that processes the online information of the power system is connected to m man-machine computers (hereinafter, referred to as MM computers) 501 to 503 that exchange information with the user via the LAN 6. The black-and-white printer device 3 is a print signal output device 2 equivalent to that shown in FIG.
Is connected to the LAN 6 via. The main computer 4 calculates the substation, transmission line,
The state of the switch and the like, the measured value of the current and the like are analyzed, and the result information is transferred to the m MM computers 501 to 503 via the LAN 6.

FIG. 6 is a functional block diagram showing the internal configuration of the MM computer. The MM computer 5 includes a LAN input / output function unit 51 for exchanging information with the LAN 6, a system information processing function unit 52 for processing power system information into a color image in a display form requested by the user, and a color holding the processed image. Image memory 53, which outputs a color image to CRT 7
An RT output function unit 54 and a user input function unit 55 that receives a user request from the input device 8 are provided.

In the system information processing function unit 52, the main computer 4
The power system information transferred from the LAN via the LAN 6 is processed into a color image in a display form requested by the user and stored in the color image memory 53.

The computer 1 starts the color / monochrome image conversion processing of FIG.
The processing of steps S12 to S18 is performed on the color image stored in the printer, and the selected compressed image is transferred to the print signal output device 2 via the LAN 6. In these image conversion processes, a color / monochrome conversion function unit 13, a conversion function file 14, a monochrome image file 15, an image compression function unit 16, a compressed image file 17, The image selection function unit 18 is used.

FIGS. 7 to 9 show display examples of color images processed and displayed by the MM computer. FIG. 7 is a color image showing a power system diagram, in which the operating state of a power generating / substation (working, overload, etc.), the state of a transmission line between substations (during a power outage), and the like are displayed in different colors. In the screen of this example, the background is green, the characters are all black, and the squares of the substations and power stations are displayed in yellow when there is a fault, and in the background color (green) when there is no fault. Also, figures representing transmission lines and switches are color-coded and displayed in white, red, and black according to the state of charge.

FIG. 8 is a color image showing the state and measured values of devices and electric wires in a substation. In this example, the background color is green, the measured values are red and black depending on the degree of risk such as overload,
All other characters are black. Figures such as devices and electric wires are displayed in white, yellow, red, and black according to states such as charging, power failure (ON / OFF), and work.

FIG. 9 is a tabular color image showing time-series data showing a state change occurring in the entire power system. In this example, the background is gray, and the data display rectangle is displayed in blue and gray depending on the presence or absence of the latest data.
The character string representing the state change is displayed in white, yellow, or red according to the importance. There are no figures on this screen.

FIG. 10 shows an embodiment of the conversion function applied to FIGS. In the present embodiment, a color intermediate color such as gray is represented by RGB multi-tones (each component of R, G, B has three or more values). As shown, when the function F1 is used for the color image in FIG. 7, it can be converted to a black and white image with a white background and black characters and symbols.

On the other hand, if the function F2 or the function F3 is used in FIG. 7, the yellow in the square at the time of the occurrence of the fault, such as a substation, is converted to black, and characters cannot be identified. As a result, in the conversion functions F1 to F3, the converted image amount of the monochrome image converted by the function F1 is the largest, and the compressed image file of the maximum size is selected by the image selection function unit 18.

Similarly, a monochrome image converted using the function F2 is selected for the color image shown in FIG. 8, and a monochrome image converted using the function F3 is selected for the color image shown in FIG. Will be.

The conversion functions F1 to Fn of this embodiment include MM
For all display forms in the computer 5, the characters and symbols are not buried in the background by the black and white conversion.
A correspondence table between combinations of color pixel values and black and white pixel values is prepared in advance. As a result, the execution of the main image conversion is automatically processed, and it is possible to provide a black-and-white image in which characters and graphics are identified as the background.

As described above, according to the present embodiment, a black-and-white hard copy in which characters and symbols are not buried in the background can be output in all power system display modes. In this embodiment, a conversion function is provided that allows all of the characters and graphics in the color image to be identified in the converted black and white image. However, even if there are many combinations of colors in the target image and a conversion function that can identify all characters and figures cannot be defined, the object of the present invention is achieved to some extent by preparing a suboptimal conversion function. it can.

According to this embodiment, the MM computers 501 to 501
The monochrome image data transferred from the print signal output device 503 to the print signal output device 2 is always compressed data, and also has the effect of shortening the LAN transfer time. Further, the function of compressing and decompressing is provided in the print signal output device 2, and since the decompression is synchronized with the print output, the processor occupation time of the MM computer is reduced as compared with the case where the compression decompression function is held in each MM computer. It also has the effect of suppressing.

In this embodiment, an example in which the present invention is applied to a power system monitoring system has been described. However, the present invention is widely applied to other plant and machine monitoring systems, and further to general-purpose computers, for example, computer systems that perform arbitrary processing such as CAD. it can.

[0047]

According to the present invention, when a color image mainly composed of characters and the like is converted to a black and white image, conversion to a black and white image in which the characters and the like are not buried in the background can be realized, and the converted monochrome image can be realized. This has the effect of improving the quality of the product.

In addition, for all display modes used in the system, a conversion function that prevents characters and symbols from being buried in the background by black-and-white conversion is prepared, so that the optimum conversion mode for each display mode is automatically selected. Since the conversion is performed, the user's burden can be greatly reduced.

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing one embodiment of a color / monochrome image conversion process according to the present invention.

FIG. 3 is an explanatory diagram showing a plurality of conversion functions according to one embodiment.

FIG. 4 is a flowchart illustrating an example of a printing process.

FIG. 5 is a schematic configuration diagram of a power system monitoring system to which the present invention is applied.

FIG. 6 is a functional block diagram showing a man-machine computer of a power system monitoring system according to another embodiment of the present invention.

FIG. 7 is a display example diagram of a color image showing a power system diagram.

FIG. 8 is a display example diagram of a color image showing states and measured values of devices and electric wires in a substation.

FIG. 9 is a display example of a data table showing a state change occurring in the entire power system.

FIG. 10 is an explanatory diagram showing a conversion function applied to FIGS. 7 to 9;

[Explanation of symbols]

1, 101, 102, 103: Computer, 11: Color image reading function unit, 12: Color image file, 13: Color / monochrome conversion function unit, 14: Conversion function file, 15:
Black and white image file, 16: Image compression function unit, 17: Compressed image file, 18: Image selection function unit, 2: Print signal output device, 21: Compression and decompression function unit, 22: Black and white image file, 23: Black and white image output function Unit, 3 printer device, 4
... Main computer, 5,501,502,503 ... Man-machine computer, 51 ... LAN input / output device, 52 ... System information processing function unit, 53 ... Color image memory, 54 ... CRT output function unit, 55 ... User input function unit , 6 ... LAN, 7 ... CR
T, 8: Input device.

Continued on front page F term (reference) 5B057 AA19 CA01 CA08 CA12 CA16 CB02 CB06 CB12 CB16 CH01 CH04 CH07 CH11 DA15 DA16 DA17 DB02 DB06 DB09 DC02 5C079 HA13 HB01 LA02 LA06 LA07 LA26 LA31 LB15 MA01 MA02 MA04 MA11 MA17 NA06 NA00

Claims (5)

[Claims] 1. A color / monochrome image conversion method for obtaining a monochrome pixel value for a combination of color component values of color pixels by a conversion function, wherein a plurality of colors of a character or a character and a graphic used in a target color image and a background are used. A plurality of conversion functions defined so that characters or characters and graphics after black-and-white conversion can be identified as a background are prepared in advance, and the conversion is performed by performing conversion using the conversion function for all pixels of the target color image. Color / black and white, wherein the same number of black and white image data as the function is obtained and black and white image data having the largest pixel value difference between a character and a background or a character or a figure and a background is selected from the black and white image data. Image conversion method. 2. The monochrome image data according to claim 1, wherein each of the monochrome image data is compressed to obtain the same number of compressed image data, and an image having the largest data amount is selected from the compressed image data and restored to a monochrome image. A color / black-and-white image conversion method. 3. An image processing apparatus for converting a color image into a black and white image and outputting the same, wherein a color image storage means for storing a target color image and a plurality of conversion methods for converting the color image into a black and white image are stored. Conversion method storage means, color / black and white image conversion means for performing conversion on the target color image by the plurality of conversion methods, black and white image storage means for storing the same number of black and white images as the conversion methods, Image compression means for compressing, compressed image storage means for storing the same number of compressed image data as the black-and-white image, image selection means for selecting the largest data amount among the compressed image data, An image processing apparatus, comprising: a compression / decompression unit for decompressing a monochrome image from image data. 4. The method according to claim 3, wherein the conversion method is a conversion function for obtaining a black-and-white pixel value for a combination of color component values of a color pixel, wherein the conversion method includes a character or a character and a graphic used for a target color image. An image processing apparatus which stores a plurality of conversion functions corresponding to a plurality of color arrangements with a background and defined so that a character or a character and a figure after black and white conversion can be identified as a background in the conversion method storage means. 5. An image processing apparatus connected to a network of a monitoring system and provided in a computer for outputting online monitoring information to a display device or a printing device, wherein the image processing device stores a plurality of color images for a monitoring screen. When,
Means for storing a plurality of conversion methods for converting the characters or characters and figures to black and white so as to be identifiable, corresponding to a plurality of colors of a character or characters and figures and a background reflecting the monitoring information in each color image; Means for selecting black and white image data having the largest pixel value difference between the character or the character and the figure and the background from the plurality of converted black and white images, and outputting the selected black and white image to the printing apparatus An image processing apparatus comprising means.