JP2000196871A - Method and device for image processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the recording quality of achromatic characters by not recording color dots in the periphery of achromatic characters. SOLUTION: A character part included in an image signal is discriminated by a character detection part 112, and a chromatic part, and an achromatic part of the inputted image signal are discriminated by a color discriminating part 111. The inputted image signal is subjected to color conversion by an LOG conversion means 104, an output gamma part 107, etc., in matching with image output characteristics in an image output part 110. A quantization part 108 quantizes the signal of each color subjected to gamma correction to output it to a black character reflecting part 109, and this part 109 converts the color converted chromatic signal into an achromatic signal in the black character part detected by the character detection part 112 and the color discriminating part 111 and outputs the result to the color image output part 110.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image processing method and apparatus for outputting an image by performing image area separation based on a color image signal.

[0002]

2. Description of the Related Art Conventionally, a copying machine or the like reads an original image and performs image area separation processing for distinguishing a character portion, a background, a halftone dot, and the like from the read image signal, and corresponds to each image area. Image processing is performed to obtain a good image.

In such a copying machine, there is a printer which records an image, for example, adopts an ink jet printer or the like. Further, among such inkjet printers, there are products that use dark and light inks and perform ternary output on input image data to improve the gradation of an output image.

[0004]

In the above-described copying machine,
Good image reproduction is possible for black characters by performing black area processing to determine the image area separation for distinguishing the character part from the background and halftone dots, and to record the black part in a single black color. . However, when a color pixel is present around a black character, color dots other than black are hit around the black character, and the image quality of the recorded black character is degraded. This has been particularly noticeable in ink jet printers and the like that have inks (colorants) of a plurality of colors and have those dark and light inks.

The present invention has been made in view of the above-mentioned conventional example, and provides an image processing method and apparatus in which the recording quality of achromatic characters is improved by preventing color dots from being recorded around the achromatic characters. The purpose is to:

It is another object of the present invention to provide an image processing method and apparatus for improving the recording quality of achromatic characters by preventing color dots from being recorded around achromatic characters even when dark and light inks are used. Is to do.

[0007]

In order to achieve the above object, an image processing apparatus according to the present invention has the following arrangement.
That is, character identification means for identifying a character part included in an image signal, pixel color identification means for identifying a chromatic part and an achromatic part of the image signal, and an image output characteristic of an image output device. A color conversion unit that performs color conversion together, and a color portion that is converted by the color conversion unit in correspondence with an image portion that is identified as a character portion by the character identification unit and that is identified as an achromatic color portion by the pixel color identification unit. Achromatic color conversion means for converting the chromatic portion into an achromatic color. In order to achieve the above object, an image processing apparatus according to the present invention has the following configuration. That is, image signal input means for inputting an image signal, color image forming means for forming a color image, character identification means for identifying a character portion included in the image signal input by the image signal input means, A pixel color identification unit that identifies a chromatic portion and an achromatic portion of an image signal; a color conversion unit that performs color conversion on the image signal in accordance with image forming characteristics of the color image forming unit; Achromatic color conversion means for converting the chromatic color part converted by the color conversion means into an achromatic color, corresponding to the image part identified as a part and identified as an achromatic color part by the pixel color separation means. The image data converted by the achromatic color conversion unit is output to the color image forming unit to form a color image. The image processing method of the present invention comprises the following steps. That is, a character identification step for identifying a character part included in an image signal, a pixel color identification step for identifying a chromatic color part and an achromatic color part of the image signal, and the image signal to an image output characteristic in an image output device. A color conversion step of performing color conversion together, and corresponding to an image part identified as a character part in the character identification step and identified as an achromatic color part in the pixel color weave separation step, and converted in the color conversion step. An achromatic color conversion step of converting the chromatic portion into an achromatic color.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[First Embodiment] FIG. 1 is a block diagram showing a functional configuration of a color copying machine according to a first embodiment of the present invention.

Reference numeral 101 denotes a color image input unit, which includes, for example, an image reader and an image scanner, and reads an image of a color original and inputs it as an image signal, or in a broad sense, an image input unit for inputting image data from a computer. It also has functions. This color image input unit 1
Reference numeral 01 outputs three-color separation signals R1, G1, and B1 which are separated into RGB for each pixel of the color image. 3 of the color image signal output from the color image input unit 101
The G1 signal, which is one of the color separation signals R1, G1, and B1, is input to the character detection unit 112, and the corresponding pixel is a pixel of a line image such as a character or a thin line or a continuous image such as a photographic image or a print image. It is determined whether or not the pixel is included in the gradation image. Then, the determination result is output to the black character signal generation unit 114 as a character determination signal MJ.

FIG. 2 is a diagram showing the configuration of the character judging section 112. As shown in FIG.

In the image signal input 201, an 8-bit G1
A signal is input, and a determination input signal D is output. In the present embodiment, G1 of the color image signal from the color image input unit 101 is used as an input.

That is, D [V] [H] = G1 [V] [H]. ([V] [H] is the coordinates of the pixel of interest in the image) In the 5 × 5 average density calculation 204, area processing is performed on a 5 × 5 pixel range, and the average of the input data (D [V] [H]) is obtained. A value is obtained, and the average value is output as AVE5. That is, AVE5 [V] [H] = (〓〓D [V + x] [H + y]) / 25 (each range of Σ〓 is x, y, and is “−2” to “2”)
Becomes

The edge component extraction 202 is a pre-process for performing the edge enhancement process 203, and extracts an edge component based on the G1 signal.

FIG. 3 shows an example of a 5 × 5 filter used in the present embodiment, which is used for extracting an edge component (EDD 55). That is, EDD55 = 〓〓 (D [V + x] [H + y] × KM0 [x] [y]) Here, each range of ｘ is x, y, and “−2” to
"2", and KM0 [x] [y] indicates a filter coefficient at the position (x, y).

In the next edge enhancement process 203, the edge of the target pixel is enhanced based on the edge components calculated in the edge component extraction 202. In the process, as shown by the following equation, EDGE1 is output as a result of the edge enhancement.

EDGE1 [V] [H] = D [V] [H] + EDD55 × EDKYD
1 Here, “EDKYD1” is 0, 1/1, 1/2, 1 /
Any one of 4, 1/8 can be selected, and the edge enhancement amount is adjusted according to this value.

The density difference calculation 205 is based on the edge emphasis processing 20
The output value “EDGE1” from the third and the output value “AVE5” from the 5 × 5 average density calculation 204 are input, these are binarized, and the result is output as a character signal “MJ”.

The details of the density difference calculation process will be described below.

When AVE5 [V] [H] −EDGE1 [V] [H]> NOUDO, MJ [V] [H] = 1, otherwise, MJ [V] [H] = 0. Here, “NOUDO” is a threshold value for determining an edge portion.

By the above-described method, the image area of the character edge portion and the other image portion is determined, and the result is output to the black character signal generation section 114.

Further, the character determination signal MJ is input to the spatial filter storage unit 113. When the corresponding pixel is a character, the character spatial filter coefficient shown in FIG. Selects the image spatial filter coefficients shown in FIG. Thus, depending on whether the target image is a character or an image, the corresponding spatial filter coefficient Kij
Is output to the filtering unit 102.

The color determination unit 111 receives the three-color separation signals R1, G1, and B1 of a color image and determines whether the pixel is monochrome (achromatic) or color (chromatic). And a chromatic / achromatic color determination signal “CO
LOR "is output.

In this embodiment, the determination method is as follows.
The following formula shall be followed.

Max (R1, G1, B1) -Min (R1,
When (G1, B1) <COL1, COLOR indicates an achromatic color, and Max (R1, G1, B1) -Min (R1, G1, B1)
When ≧ COL1, COLOR indicates a chromatic color.

Here, “COL1” is a chromatic color,
This is a threshold value for determining achromatic color.

The determination of a chromatic color or an achromatic color in the color determination unit 111 may be a determination based on a Lab space or other various color determination methods.

The black character signal generation unit 114 is provided with the character detection unit 1
12 character determination signal MJ (1 bit) and the color determination unit 11
The chromatic / achromatic color determination signal COLOR (1 bit) from 1 is input, and a black character signal KM1 = 1 is output to the black character signal scaling section 115 for a pixel which is a character portion and is determined to be achromatic. The other pixels are output as black character signal KM1 = 0.

In the filtering unit 102, the three-color separation signals R1, G1, and B1 of the color image are output based on the character or image spatial filter coefficient Kij output from the spatial filter storage unit 113 in response to the MJ signal. , A filtering process such as edge enhancement and smoothing is performed.

The signals R2, G2, B2 output from the filtering
Are input to the image scaling unit 103 and are scaled. The image scaling unit 103 performs scaling processing such as enlargement and reduction by linear interpolation, and also performs resolution conversion when the resolution of the input image is different from that of the output image. For example, if the resolution of the scanner in the color image input unit 101 is 300 dpi and the resolution of the color image output unit 110 is 600 dpi, linear output is performed so that both the vertical and horizontal directions are doubled when outputting at the same magnification. Also, 200%
When performing the enlargement process, linear interpolation is performed so that the image is quadrupled both vertically and horizontally.

The black character signal KM1 output from the black character signal generation unit 114 is subjected to scaling processing and resolution conversion by the black character signal scaling unit 115, and is output as a scaled black character signal KM2. Here, since the input black character signal KM1 is a binary signal, enlargement and reduction are performed using the logical sum method.

Reference numeral 104 denotes a LOG conversion unit which converts color luminance signals R3, G3, and B3 of three primary colors into a color image output unit 110.
Are converted into density signals of cyan C1, magenta M1, and yellow Y1 for output at. This conversion formula is as follows.

C = (− 255 / 1.60) × log 10 (R / 255) M = (− 255 / 1.60) × log 10 (G / 255) Y = (− 255 / 1.60) × log 10 ( B / 255) When this conversion is performed by hardware, for example, a memory of a look-up table is used to store the values after logarithmic conversion in a memory address corresponding to the input data, and these RGB values are stored in the memory. A configuration may be adopted in which data is input as an address, and at that time, data output from the memory becomes CMY values after LOG conversion.

The black generator 105 outputs cyan C1, magenta M1, and yellow Y1 output from the LOG converter 104.
, And outputs the lowest value among the three colors as black K2. Note that C2, M2 and Y2 are respectively C1 and M2.
The values are equivalent to M1 and Y1.

The output masking section 106 includes the black generation section 10
5, the respective values of the signals C2, M2, Y2, and K2 output from the color image output unit 110
, And outputs the result as C3, M3, Y3, and K3.

The output gamma unit 107 converts the signals C3, M3, Y3 and K3 output from the output masking unit 106 into
A color image signal C converted according to a preset density conversion characteristic curve and adjusted for density and color balance.
4, M4, Y4, and K4.

The quantization unit 108 performs quantization, such as a ternary error diffusion method, on the multi-valued C4, M4, Y4, and K4 input from the output gamma unit 107, and performs C dark / light (dark C5, dark C5).
Light C5), M dark / light (dark M5, light M5), Y dark / light (dark Y5, light Y5), K dark / light (dark K5, light K5) I do.

FIG. 6 shows details of the quantization section 108.

FIG. 7 is a diagram showing another example of the configuration of the quantization unit 108. Here, the configuration is shown in which the color image output unit 110 does not have black ink separately for dark and light. . In this case, the black signal K4 is quantized in the binary error diffusion unit by a binarization process such as a binary error diffusion method, and is output as one black signal (dark K5).

The black character reflecting unit 109 outputs the binary image data dark C5, light C5, dark M5, light M5,
The color image output signals dark C6 and light C6 which receive the dark Y5, the light Y5, the dark K5 and the light K5, and the black character signal KM2 (1 bit) from the black character signal scaling section 115 and output to the color image output section 110. , Dark M6, light M6, dark Y6, light Y
6, dark K6 and light K6 are output.

In the black character reflection section 109, when the black character signal KM2 = 0 (other than the black character portion), the dark C5 and dark M
5, dark Y5, dark K5, light C5, light M5, light Y5, light K5
Signals are directly used as dark C6, dark M6, dark Y6, dark K6,
Output as light M6, light Y6, and light K6.

When the black character signal KM2 = 1 (black character portion), at the color image output section 110, any one of the deep C5, dark M5, dark Y5, and dark K5 signals is one. If the data is "1", the color signal is replaced by a dark black single color signal (dark K) regardless of the color.
6) and output. The color image output unit 11
At 0, if any one of the light C5, light M5, light Y5, and light K5 is at least one color, the color signal is converted to a light black single color signal (light K6) regardless of the color. And output.

By such processing, in the black character portion, the dark ink portion is made of dark black monochromatic ink (dark K6), and the light ink portion is made of pale black monochromatic ink (light K).
An image is output according to 6), whereby high quality black character output can be realized without color dots appearing around the black character.

The color image output unit 110 has two types of inks of cyan, magenta, yellow, and black, each of a dark ink (dark ink) and a light color ink (light ink). The dark C6, the light C6, the dark M6,
Based on the light M6, dark Y6, light Y6, dark K6, and light K6 signals, a binary printer (e.g., an inkjet method) that discharges ink of a corresponding color prints on paper, or
It is output to a file or the like as value image data. As described with reference to FIG. 7, the color image output unit 11
For 0, only black ink may be used.

[Second Embodiment] FIG. 8 is a block diagram showing a configuration of a color copying machine according to a second embodiment of the present invention. Portions common to FIG. 1 described above are denoted by the same reference numerals, and description thereof is omitted. I do.

The quantization unit 150 according to the second embodiment corresponds to the case where the color image output unit 110 does not have dark and light black ink, and the configuration of the quantization unit 150 is as follows. As shown in FIG.

In this case, the black character reflecting unit 151 receives the dark C5 / light C5, dark M5 / light M5, dark Y5 / light Y5, and dark K5 from the quantizing unit 150, and
5 is converted according to the value of the black character signal KM2 from the following. That is, when the black character signal KM2 = 0 (other than the black character portion), dark C5, dark M5, dark Y5, dark K5, light C5,
The signals of light M5, light Y5, and light K5 are used as they are, and dark C6, dark M6, dark Y6, dark K6, light C6, light M6, light Y6, light K
Output as 6.

When the black character signal KM2 = 1 (black character portion), any one of the dark C5, dark M5, dark Y5, dark K5, light C5, light M5, and light Y5 is one color. If (corresponding data is "1" data), the color signal is converted into a dark black single color (dark K6) regardless of the color and output.

By such a conversion process, in a black character portion, color dots around the black character are replaced with black dots, and the black character portion is output in a single black color, thereby realizing high quality black character output.

[Embodiment 3] FIG. 9 is a block diagram showing a configuration of a color copying machine according to Embodiment 3 of the present invention. Portions common to the above-mentioned drawings are denoted by the same reference numerals, and description thereof is omitted. I do.

The color image output unit 110 according to the third embodiment
Indicates that each of the C, M, and Y inks is specially dark (particularly dark)
There are four types of dark / light / special colors (especially light) (a total of 16 types), and it can output 5 values for each color. It has two types of black ink, dark and light. It is assumed that an ink jet recording apparatus capable of performing ternary output is provided.

The quantizing section 160 according to the present embodiment is based on the assumption that such a color image output section 110 is used, and its configuration is as shown in FIG.

In the black character reflecting section 161, the quantization section 160
Tono C5, Tono C5, Tono C5, Tono C5, Tono M5
・ Dark M5 ・ Dark M5 ・ Dark M5 、 Dark Y5 ・ Dark Y5 ・ Light Y
5. The input of the special color Y5, the dark K5, and the light K5, and the following conversion according to the value of the black character signal KM2 (1 bit) from the black character signal scaling section 115.

Now, when the black character signal KM2 = 0 (other than the black character portion), the special dark C5, dark C5, light C5, special light C5,
Tokuno M5, Toku M5, Toku M5, Toku M5, Tokuno Y5, Toku Y
5, Light Y5 / Toku Y5, Dark K5, Light K5 signals are used as they are, and Tono C6 / C6 / Light C6 / Toku C6 and Tono M6 ・
Dark M6 / Light M6 / Light Y6, Tono Y6 / Light Y6 / Light Y6
-Output as special light Y6, dark K6, and light K6.

When the black character signal KM2 = 1 (black character portion), the special density C5, the special density C5, the special density M5, the density M5, and the special density Y
If any one of the 5, dark Y5, and dark K5 signals has a color for recording a dot (becomes "1"), the color signal is converted to a dark black single color (regardless of the type of color). (Concentration K6) and output.

Further, light C5, special light C5, light M5, special light M
5, if there is any color to be recorded among any of the light Y5, the special light Y5, and the light K5, the color signal is converted to a light black single color (light K6) regardless of the color. Output.

By such a conversion, in the black character portion, the color dots around the black character are replaced with black dots, and the black character portion is output as a single black color, thereby realizing high quality black character output.

In the above embodiment, the case where a color ink jet recording apparatus is used in the color image output section has been described as an example. However, the present invention is not limited to this. A similar effect can be obtained if the printer device can perform multi-value (n-value) printing using a printer or toner.

The color image output section 110 is not limited to a printer or the like, and the same effects can be obtained by using image data or a display.

Although the above-described various images and processing such as color conversion have been described as being realized by hardware, the present invention is not limited to this. The effect of is obtained.

Even if the present invention is applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), an apparatus (for example, a copying machine, a facsimile) including one device Device).

Another object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or apparatus, and to provide a computer (or CPU) of the system or apparatus.
Or MPU) reads and executes the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) running on the computer based on the instruction of the program code. ) Performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instructions of the program code, The case where the CPU of the function expansion board or the function expansion unit performs part or all of the actual processing, and the function of the above-described embodiment is realized by the processing.

As described above, according to the present embodiment, it is said that, by determining image area separation for distinguishing a character portion from a background or a halftone dot portion, processing is performed so that a black character portion is struck with a single black color. Also, black character processing can be performed by a multi-valued printer using dark and light inks, eliminating color dots around black characters and achieving good reproduction of black characters.

[0068]

As described above, according to the present invention, the recording quality of achromatic characters can be improved by preventing color dots from being recorded around the achromatic characters.

According to the present invention, even when dark and light inks are used, there is an effect that color dots are not recorded around achromatic characters, thereby improving the recording quality of achromatic characters.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a functional configuration of an image processing apparatus according to Embodiment 1 of the present invention.

FIG. 2 is a block diagram illustrating a functional configuration of a character detection unit according to the present embodiment.

FIG. 3 shows 5 used in the edge component extraction unit of the embodiment.
It is a figure showing an example of a × 5 filter coefficient.

FIG. 4 is a diagram illustrating an example of a filter coefficient for characters used in black character processing in the filtering unit according to the present embodiment.

FIG. 5 is a diagram illustrating an example of filter coefficients used in image signal processing in the filtering unit according to the present embodiment.

FIG. 6 is a functional block diagram illustrating a functional configuration of a quantization unit according to the present embodiment.

FIG. 7 is a functional block diagram illustrating a functional configuration of another quantization unit according to the present embodiment.

FIG. 8 is a block diagram showing a functional configuration of an image processing apparatus according to Embodiment 2 of the present invention.

FIG. 9 is a block diagram illustrating a functional configuration of an image processing apparatus according to Embodiment 3 of the present invention.

FIG. 10 is a block diagram illustrating a functional configuration of a quantization unit according to Embodiment 3 of the present invention.

Continued on front page F term (reference) 2C262 AA02 AA24 AB13 AC11 BA02 BA10 BA20 BB16 DA03 EA07 EA08 5B057 AA11 BA28 CA01 CA08 CA12 CA16 CB01 CB06 CB08 CB12 CB16 CC03 CE03 CE11 CE12 CE17 CE18 CH01 DC16 5C077 PP06 MP07 MP06 PP31 PP32 PP33 PP43 PP46 PP47 RR02 RR05 TT05 5C079 HB01 HB02 HB12 KA12 KA15 LA03 LA06 LA10 LA12 LA13 LA15 LA33 LA34 LB02 MA11 NA02

Claims (12)

[Claims] 1. A character identifying means for identifying a character part included in an image signal; a pixel color identifying means for identifying a chromatic part and an achromatic part of the image signal; Color conversion means for performing color conversion in accordance with output characteristics; and the color conversion means corresponding to an image part identified as a character part by the character identification means and identified as an achromatic color part by the pixel color identification means. An achromatic color conversion unit for converting the chromatic color part converted by the above into an achromatic color. 2. The character discriminating means includes an average density calculating means for calculating an average density of a predetermined area of the image signal, and an edge emphasizing means for performing edge emphasis in the predetermined area. 2. The image processing apparatus according to claim 1, wherein a character portion is identified based on a density difference between the obtained average density and the edge-emphasized portion. 3. The image processing apparatus according to claim 2, wherein the color conversion unit includes at least a LOG conversion unit that converts an RGB signal into a YMC signal, and a gamma conversion unit that performs a color conversion corresponding to an image output characteristic of the image output device. Claim 1
Or the image processing device according to 2. 4. The image output device is an ink jet recording device, wherein the ink jet recording device is a multi-color ink, and performs recording by using dark and light multi-color inks, respectively. 2. The image processing device according to 1. 5. The image processing apparatus according to claim 1, wherein the color conversion unit converts the chromatic portion into multi-valued data and converts the achromatic portion into binary data. 6. An image signal input unit for inputting an image signal, a color image forming unit for forming a color image, and a character identification unit for identifying a character portion included in the image signal input by the image signal input unit A pixel color identification unit that identifies a chromatic portion and an achromatic portion of the image signal; a color conversion unit that performs color conversion on the image signal in accordance with image forming characteristics of the color image forming unit; Means for converting the chromatic color part converted by the color conversion means into an achromatic color corresponding to the image part identified as a character part by the means and identified as an achromatic part by the pixel color separation means Means for outputting color image data converted by the achromatic color conversion means to the color image forming means to form a color image. . 7. The color image forming means includes an ink jet recording apparatus, wherein the ink jet recording apparatus records using a plurality of inks of a plurality of colors, each of which is dark and light. Item 7. The image processing device according to Item 6. 8. A character identification step for identifying a character part included in an image signal; a pixel color identification step for identifying a chromatic color part and an achromatic color part of the image signal; A color conversion step of performing color conversion in accordance with an output characteristic; and a color conversion step corresponding to an image part identified as a character part in the character identification step and identified as an achromatic color part in the pixel color weave separation step. An achromatic color conversion step of converting the chromatic portion converted in step (a) into an achromatic color. 9. The character identification step includes a step of calculating an average density of a predetermined area of the image signal; and an edge enhancement step of performing edge enhancement in the predetermined area, wherein the average density and the edge-enhanced portion are included. 9. The image processing method according to claim 8, wherein a character portion is identified based on a density difference between the character portion and the character portion. 10. In the color conversion step, at least RG
The image processing according to claim 8, further comprising: a LOG conversion step of converting a B signal into a YMC signal; and a gamma conversion step of performing color conversion in accordance with an image output characteristic of the image output device. Method. 11. The image output device is an ink jet recording device, and the ink jet recording device is a plurality of color inks, and performs recording using a plurality of dark and light color inks, respectively. 9. The image processing method according to 8. 12. The image processing method according to claim 8, wherein in the color conversion step, the chromatic portion is converted into multi-value data, and the achromatic portion is converted into binary data.