JPS63174472A - Color image processing device - Google Patents

Abstract

PURPOSE:To realize a color image including a color character with simple processing constitution and with fidelity, by performing different signal processings by identifying a halftone part from a character part out of one kind of signal common to the signals of three colors of red, green, and blue. CONSTITUTION:Inputted R, G, and B, after being balance-corrected to gray by an equivalent neutral density conversion circuit(END)12, are inputted to a color correction processing circuit 13. The color correction processing circuit 13 converts them to END density signals of yellow, magenta, and cyan so as to reproduce desired colors at a color image output device 9. Meanwhile, the inputted R, G, and B are inputted to a luminance signal generation circuit 10, and area identification whether the input image is the character part or the halftone part is performed from a luminance signal I at an area identification circuit 11. The above area identified result is sent to a data conversion circuit 14, and when it is the character part, a data from the color correction processing circuit 13 is binarized with a single threshold value, and is sent to a UCR circuit 15.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a document reading device used in digital color copying machines, color facsimiles, etc. The present invention relates to a color image processing apparatus that, after reading a color document containing a mixed image area, identifies both areas and performs appropriate processing on each area.

[Conventional technology and its problems]

Many common documents contain a mixture of binary images such as characters and halftone images such as photographs and prints.

If such a document is converted into a pure binary and recorded, the quality of the text will be good, but the quality of the photo will deteriorate; conversely, if it is converted into a binary and recorded using halftone generation methods such as dithering, the quality of the photo will deteriorate. Although the results are good, the quality of the characters deteriorates. In order to obtain good quality for each of text and photographs, it is necessary to identify two different types of areas; for example, it is necessary to perform pure binarization for characters and dither processing for photographs.

As shown in Japanese Unexamined Patent Publication No. 58-22 (1563), as a method for identifying the character area and the halftone area, the focus value, which is the contrast value data of the pixel of interest, and the There is a method of taking the absolute value of the difference between the defocus values, which are the average values of pixels, and determining that it is a text area when this value exceeds a certain darkness value.

Additionally, as shown in Japanese Patent Application Laid-Open No. 58-3374,
Some methods make determination based on the difference between the maximum and minimum gray values of pixels within the window.

Areas that are determined to be text are converted into binary values using a single darkness value, and areas that are determined to be photographs are converted into binary values using dither processing.
By converting it into values, it is possible to faithfully reproduce the manuscript to some extent.

Conventionally, circuit configurations shown in FIGS. 6 and 7 are known for performing such area determination processing on color originals.

Figure 6 shows the red obtained by the color separation filter.

A region identification circuit 1, a binarization circuit 2, and a dither processing circuit 3 are provided independently for each of the three color signals R, G, and B of green and blue, and processing is performed for each color to produce a binarized output. Signals r, g,
b. However, this method has the disadvantage that the hardware scale becomes large because each circuit must be provided for each color.

Further, in FIG. 7, the area is identified in the area identification circuit 1 using only one specific type of signal, for example, the luminance signal Y obtained by matrix calculation from the three color signals R, G, and B. The result is then supplied to a binarization circuit 2 provided in common for the three color signals R, G, and B, and the output of the binarization circuit 2 is supplied to a dither processing circuit 3. . That is, in the circuit shown in FIG. 7, the area identification results are divided into three color signals R, G, and B, binarized, and dithered. However, in this circuit, it is necessary to provide a character color determination circuit 4 in order to handle colored characters, and the processing circuit is also complicated.

The present invention was devised to solve the above-mentioned problems, and an object of the present invention is to faithfully reproduce color images containing color characters with a simple processing configuration.

[Means for solving problems]

In order to achieve the above object, the present invention provides an apparatus for reading and recording a color original in which a character area and a halftone area coexist. a circuit that generates one type of signal common to the same three color signals; an area identification circuit that identifies an area of the color original based on the one type of signal;
a color correction processing circuit that obtains yellow, magenta, and cyan three-color signals from the blue three-color signal; and a color correction processing circuit that obtains yellow, magenta, and cyan signals from the color correction circuit when the area identification circuit determines that the color document is a character area. The present invention is characterized in that it is provided with a data conversion circuit that converts cyan three-color signals into predetermined binary values.

[Effect]

In the present invention, color correction processing is performed on three color signals of red, green, and blue obtained by color separation of the color original, and three color signals of yellow, magenta, and cyan are generated. At the same time, one type of signal common to the three color signals of red, green, and blue,
For example, a luminance signal is generated, and based on this signal, halftone areas and text areas are identified. If it is identified as a character part, the three colors of yellow, magenta, and cyan after color correction processing are
The color signal is compared with the darkness value and converted into binary values of predetermined maximum and minimum values. At this time, since binarization is performed after the color correction process, the latitude with respect to the dark value is widened and colors are not misidentified. Furthermore, if it is identified as a halftone portion, the signal after color correction processing is output as is, so that the color original is faithfully reproduced.

〔Example〕

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, features of the present invention will be specifically described based on examples with reference to the drawings.

FIG. 2 shows a block diagram of the entire image processing device.

5 in the figure is a color image input device, which inputs color document information at approximately 160 dots/cm (400 dots/inch).
The signals are separated into red, green, and blue signals R, G, and B at a resolution of

Reference numeral 6 denotes an image memory, which has a capacity capable of storing image data for three colors of red, green, and blue of a read color document one page at a time in A4 size. In addition, instead of the red, green, and blue image data, Y, which is used in the color television system,
, I, and Q signals may be stored.

A color image processing device 7 generates a specific type of signal from the red, green, and blue signals from the image memory 6 or the color image input device 5, and performs area identification based on this signal. Then, based on this result, data conversion is performed on the yellow, magenta, and cyan signals after color correction processing, and this is subjected to dither processing. This dithering process generates a signal for reproducing a halftone image in the color image output device 9, which can only express binary values of 0.1.

8 is a control device, which performs signal control of the entire device.

The color image output device 9 records a binary image at a resolution of about 160 dots/cm, and although an electrophotographic laser beam printer is taken as an example here, a thermal printer, an inkjet printer, etc. can also be used. It is also possible.

Next, details of the color image processing device 7 will be explained.

FIG. 1 is a block diagram showing the configuration of a color image processing device.

In the figure, reference numeral 10 indicates a luminance signal generation circuit, and reference numeral 11 indicates a region identification circuit. These circuits 10 and 11 perform region identification as to whether the input image is a character portion or a halftone portion.

In the luminance signal generation circuit 10, as shown in equation (1), by multiplying the input signals R, G, and B by weights and adding them together, one type of signal that is common to the input signals R, G, and B is generated. A luminance signal I is obtained as follows.

1=a-R+b-G+c-B...(11 where a,
b and c are weighting coefficients, which may be changed depending on the character color you want to identify, but if you want to appropriately identify characters in the seven colors of yellow, magenta, cyan, black, blue, green, and red, use the weighting coefficients. For example, a, b, and c are 0.30.0.59.
O, Ll are used.

Next, the area identification circuit 11 uses this luminance signal I to
Areas are identified by detecting concentration gradients in the document.

Here, as shown in the above-mentioned Japanese Patent Laid-Open No. 58-3374, a method is used in which when the difference between the maximum value and the minimum value in a block is larger than a predetermined threshold th, it is used as a character, and when it is smaller, it is used as a halftone. The six-area discriminating circuit 11, which employs this method, may detect the concentration gradient using other methods, and sends the determination result obtained through the above processing to the data converting circuit 14.

When the data conversion circuit 14 receives information from the area identification circuit 11 that the image is a halftone part, the data conversion circuit 14 directly converts the data from the color correction processing circuit 13 to the undercolor removal circuit (
15 (shown as a UCR circuit in the figure).

In addition, in the case of a character part, the single darkness value 8th is compared with the shading data from the color correction processing circuit 13, and if the threshold value Bth is larger, the shading data is set to the minimum level (usually 0). , if smaller, the maximum level (2 for 8 bits)
25). By converting only the character part into data in this way, the character part is also outputted with a color ratio of 2 (color ratio) by the dither processing of the dither processing circuit 17, which will be described later.

In addition, the human input signals R, G, and B are converted to an equivalent neutral concentration conversion circuit (
After the gray balance is corrected by an END conversion circuit (indicated by an END conversion circuit in the figure) 12, the signal is input to a color correction processing circuit 13. The color correction processing circuit 13 receives the color separation output ER of the original image from the equivalent neutral density conversion circuit 12.

Ec, F++, the first yellow and magenta that can reproduce the desired color in the color image output device 9.

Cyan’s END? It is converted into M-degree signals yl, m, ,c,.

The color correction processing circuit 13 is composed of, for example, a circuit that performs the calculation shown in (2).

Note that in formula (2), a4. H(i:1~3.j:1
-3) are coefficients determined from the color reproduction characteristics of the color image output device 9 and the color separation characteristics of the input.

The first yellow converted by the color correction processing circuit 13.

The magenta and cyan signals V l+mI,CI are inputted to the data conversion circuit X4, subjected to the above-described processing divided into the halftone part and the character part, and then inputted to the undercolor removal circuit 15.

The undercolor removal circuit 15 generates 1 as a first black signal from the first yellow, magenta, and cyan signals)'++ffl++C+. Further, by subtracting an amount corresponding to 1 from the first yellow, magenta, and cyan signals y++m, ,C, to the generated first black signal, the second yellow, magenta, and cyan signals y
Convert to 2+ m2+ C2.

FIG. 3 shows a block diagram of the undercolor removal circuit 15.

In the figure, 18 indicates the first yellow, magenta, and cyan signals.
/1+m1+C1 This is a minimum value calculation circuit that calculates the minimum value from the signal, and the black signal generation circuit 19 generates a first black signal corresponding to the minimum value.

The black signal generation circuit 19 is composed of, for example, a look amplifier table, and when the minimum value is the maximum level (255 in the case of 8 pips 1-), the first black signal K is always at the maximum level. In this way, the black text of human power is reproduced in black.

The first black signal generated in the black signal generation circuit 19 is connected to an under color removal amount generation circuit (indicated by a tJcR amount generation circuit in the figure) 20 and the next stage gradation reproduction control shown in FIG. The signal is input to a circuit (indicated by a TRC circuit in the figure) 1G. The under color removal amount generation circuit 20 generates an under color removal amount to be filtered from the first yellow, magenta, cyan yl, m, , c corresponding to the first black signal Kl, and supplies it to the subtracter 21. . 1st
If 1 is the maximum level for the black signal of It is possible to reproduce the black characters in black as described above.

The second level of each temperature level supplied to the gradation reproduction control circuit 16
The yellow, magenta, and cyan signals 3'z+mz+Cz and 1 for the first black signal are the third yellow, magenta, and cyan Y 3+ m 3+ corresponding to the area ratio that matches the characteristics of the output color material.
The C3 signal and the second black signal are converted into 2 and input to the dither processing circuit 17.

In the dither processing circuit 17, faithful reproduction of a color original can be achieved by performing color correction processing or the like by the color correction processing circuit 13 described above for pixels determined to be halftone portions by the area identification circuit 11. Furthermore, for pixels determined to be character areas, the first yellow, magenta, and cyan signals Yl
+ ” l + By simply binarizing CI, it is possible to reproduce colored characters.

Next, an example of color character processing will be explained based on actual experimental data.

Table 1 shows the primary 5 secondary printing process inks.

This is an example of the densities obtained by reading tertiary colors using red, green, and blue color separation filters, and here the densities 0 to 2 are converted to 8-bit signals (0 to 255).

Table 1 When reading a color original with such density, if a single darkness value of 8th is set for the area determined to be a text area after performing area identification processing as in the past, color text may be incorrectly displayed. It may be judged. For example, to improve the reproducibility of low density black characters, the density is 0.5 (=2X64/255
), for colored characters shown in Table 1, the density levels of green, magenta, and blue will be higher than the threshold Bth, as shown in Figure 4, so magenta will become red. , and blue is incorrectly determined as gray. Also, green,
There were cases in which very uncertain judgments were made even for cyan color characters. This is because some colored characters have a high unnecessary absorption density, and in particular, the latitude of blue and green density with respect to the dark value is narrow.

Here, in this embodiment, the conversion of the signal for the character part after the area identification process is performed using the first yellow, magenta, and cyan signals Y1+ after passing through the color correction processing circuit 13.
By applying this to m++ C1, it is possible to widen the latitude with respect to the darkness value of color characters, as described below, and it is possible to freeze the misjudgment of color characters to a large extent.

Table 2 shows the output values E* after END conversion for the colors shown in Table 1.
, E6. Ell and the first yellow, magenta, and cyan signals y++ff generated using the color correction coefficient shown in equation (3)
An example of l++C+ is shown.

Table 2 In this case, as shown in Figure 5, the first yellow, magenta,
It can be seen that the latitude of color character determination for the cyan signal Y l + ml + CI widens widely, and even when the threshold value Bth is 64, no erroneous determination occurs for color characters.

〔Effect of the invention〕

As mentioned above, in the present invention, red and green are used.

One type of signal is generated from the three blue color signals to perform area identification, and data conversion of the three color signals of yellow, magenta, and cyan after color correction processing is performed according to the result of this area identification. . In this way, since data conversion is performed after color correction processing, color text can be reproduced by simply binarizing pixels determined to be text areas. At this time, since the latitude with respect to the darkness value is widened by the color correction process, the color will not be erroneously determined. Therefore, although area identification is performed using a common signal, it is possible to output color characters without having to judge the character color for each color, and it is possible to faithfully reproduce color originals with a simple device configuration. Characters can be reproduced clearly.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a color image processing device according to the present invention, FIG. 2 is a schematic block diagram of the entire image processing device according to the present invention, FIG. 3 is a block diagram of a UCR circuit, and FIG. FIG. 5 is an explanatory diagram showing the latitude of conventional color character determination. FIG. 5 is an explanatory diagram showing the latitude of color character determination according to an embodiment of the present invention. FIGS. 6 and 7 are block diagrams of a conventional color image processing device. shows. Patent applicant Fuji Xerox Co., Ltd. Agent
Masu Koita (and 2 others) 4th Decoy Red Green Blue Figure 5

Claims (1)

[Claims] 1. In a device that reads and records a color original in which a character area and a halftone area coexist, from the three color signals of red, green, and blue obtained by color-separating the color original, a common color signal of the same three color signals is extracted. an area identification circuit that identifies an area of the color original based on the one type of signal; and an area identification circuit that identifies an area of the color document based on the one type of signal;
a color correction processing circuit that obtains three color signals of cyan; and a color correction processing circuit that receives three color signals of yellow, magenta, and cyan from the color correction circuit when the area identification circuit determines that the color document is a character area. A color image processing device comprising a data conversion circuit for converting into binary data.