JP3281391B2 - Full-color image reproducing apparatus and full-color image reproducing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a full-color image reproducing apparatus and a full-color image reproducing method.

[0002]

2. Description of the Related Art Conventionally, as a full-color image reproducing apparatus,
A color original is decomposed into a plurality of color signals and read, and after performing appropriate image processing, a copy output is formed using a plurality of colors. In order to express a color, it is sufficient to obtain a color separation signal based on three basic primary colors, as is well known. When a document is read, three colors of red (R), green (G), and blue (B) are used. Decomposition is common. On the other hand, when an image on a recording medium is formed based on the obtained color separation signal, it is basically to use three colors of ink or toner of cyan (C), magenta (M), and yellow (Y). However, actually, in many cases, the image is output in four colors obtained by adding black (BK) to the three colors.
When reproducing achromatic color such as black, C, M, Y
When the three colors are superimposed and expressed, turbidity is generated and the quality is not good. In addition, undercolor removal is performed to improve problems such as misalignment when colors are superimposed and color fringing around black. This is a technique commonly used in printing.

However, even if the undercolor removal is performed in this way,
In a full-color copying apparatus, for example, for a document with black characters, the read signal usually does not represent perfect black, so that the color of the characters does not become black without 100% under-color removal, Therefore, there is a problem that color bleeding occurs around the character, and it is difficult to reproduce the character with good quality. In order to improve this problem, a method of detecting a black character area present in the original image and switching the image processing method to improve the character reproducibility rather than the normal processing for the area,
For example, it has been devised as Japanese Patent Application No. 2-295348.

According to this method, black pixels and pixels constituting characters are extracted from a color separation signal of a color original image, and black character portions are printed with pure black toner to improve the reproducibility of character portions. It is.

[0005]

However, in the above-mentioned conventional example, in order to detect black characters as effectively as possible, the pixels around the pixel determined to be black in the color determination are chromatic. Had ignored this. Because the color blur at the time of image reading always occurs around the black character on the image signal, if the chromatic pixel around the black pixel is determined to be a colored part, the black character processing is not applied around the character. This is because Because of this determination method, if there is a character composed of halftone dots in the document, if it is a chromatic color that is clearly not black when viewed with the naked eye, it will be recognized as a black character, and as a result it will be black The inconvenience of being reproduced occurred. Regarding the halftone dot portion, a configuration is adopted in which a relatively large area is excluded, but a small halftone area is easily determined as a character area,
Further, as a result of the overlapping of the halftones of the respective colors, the number of pixels determined to be black increases, and it is easy to determine that the character is a black character. Similarly, blue-colored characters with low saturation are liable to be erroneously determined due to the presence of pixels that are determined to be black due to noise components included in blue signals with poor S / N.

According to the present invention, a chromatic color conventionally determined to be black is used.
Halftone characters are prevented from being erroneously determined to be black characters,
Full-color image playback device that can perform highly accurate black character determination
And that Ru <br/> to the purpose of providing a full color image reproducing method.

[0007]

In order to achieve the above object, a full-color image reproducing apparatus according to the present invention comprises: an image reading means for scanning a color original to generate a color separation signal;
Specific to a particular color judging means for chromatic signal and the black signal generating <br/>, the chromatic signal generated by a dot region of the color original of the chromatic signal with live color separation signals Means, and a character area of the color original based on the color separation signal.
A character region determining means for generating a character region signal in the area, and the generated chromatic color signal
The color source obtained by masking a black signal.
A black signal from which the black signal generated in the halftone dot region has been removed,
Using the character area signal, black characters of the color original
Generate black character area signal for black character processing of area
And having a black character area determining means. In order to achieve the above object, a full-color image reproducing method according to the present invention generates a color separation signal by scanning a color original.
Particular an image reading step, a color determination step of generating a chromatic signal and a black signal using the generated color separation signals, a chromatic signal generated by a dot region of the color original of the chromatic signal A specific step to perform , based on the color separation signal
Generates a character area signal in the character area of the color original
A character area determining step of the chromatic signal the specific
By masking the generated black signal using
The black signal generated in the halftone dot area of the color original is
Using the removed black signal and the character area signal,
Black text to process black text in black text area of color original
Characterized the this <br/> having a black character area determining step of generating a character area signal.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a full-color copying machine will be described as an embodiment. However, the present invention can be implemented as long as it reads a color original and reproduces it with a plurality of separation colors including black, such as a color facsimile machine and a color facsimile machine. It goes without saying that the present invention can also be implemented in a desktop publishing (DTP: electronic desktop printing) device or the like.

FIG. 1 is a schematic configuration diagram showing an image processing circuit of a full-color copying apparatus according to the present embodiment. In the figure, 101 is a line sensor, 102 is an A / D converter, 103 is a shading correction circuit, 104 is a density conversion circuit, 105 is a UCR / masking correction circuit, 106
Is a two-dimensional filtering circuit, 107 is a gamma correction circuit, 1
08 is a laser driver, 109 is a color judgment circuit, 110 is an isolated point removal circuit, and 111 is a character area judgment circuit.

In the above configuration, the light reflected or transmitted from the document is separated into red (R), green (G), and blue (B) color components by the line sensor 101, and is converted into an electric signal. . In addition, the line sensor 1
01 and the line sensor 101 with respect to the readout direction 01.
, The image on the entire surface of the document can be read. Here, the read image signal is A
The digital signal is converted into a digital signal quantized by the / D converter 102, the shading correction circuit 103 corrects the sensitivity unevenness in the reading direction of the line sensor 101, and the density data (C ′, M ′,
Y ′ signal). Next, the converted density data is subjected to under color removal and masking correction in the UCR / masking correction circuit 105, and each signal of cyan (C), magenta (M), yellow (Y), and black (BK) is obtained. Becomes

Then, each output color is selected by switching the masking correction coefficient, and C, M,
Image formation is performed in the order of Y and BK in a plane-sequential manner.
The formed C, M, Y, and BK signals are subjected to edge enhancement and smoothing processing by a two-dimensional filtering circuit 106, and a γ correction circuit 107 corrects non-linearity at the time of printing. The semiconductor laser is driven to form an electrostatic latent image on the photosensitive drum. Then, the image is developed with toner and transferred onto a recording medium to form a final copied image.

Next, the operation of the entire apparatus in the present embodiment will be described. FIG. 2 is a diagram showing a configuration of a main part of the digital full-color copying apparatus of the present embodiment. Referring to FIG. 1, reference numeral 201 denotes an image scanner which reads a document and performs digital signal processing. Reference numeral 202 denotes a printer unit, which can print out image data corresponding to a document image read by the image scanner unit 201 in full color on recording paper.

In the image scanner section 201, 20
Reference numeral 0 denotes a mirror pressure plate, and the original 25
1 is illuminated by an illumination lamp 252,
07, 208, and an image is formed on the line sensor 101 by the lens 209. As a result, the signal components are sent to the signal processing unit 211 as R, G, and B signal components of full color information. The line sensor 101 has three R, G, and B components.
Photoelectric conversion element (101-1, 1
01-2, 101-3).

The lamp 252 and the mirror 206 have a speed V,
The mirrors 207 and 208 are connected to the line sensor 101 at 1 / 2V.
Mechanical scanning in the direction perpendicular to the electrical scanning direction, the entire surface of the original is scanned while keeping the optical path length between the reading portion on the original 251 and the line sensor 101 constant. The signal processing unit 211 electrically processes the read signal, separates the read signals into M, C, Y, and BK color components, and sends the signals to the printer unit 202. In addition, for one document scan (scan) by the image scanner unit 201, one component of M, C, Y, and BK is sent to the printer unit 202, and one print is performed by a total of four document scans. Out is completed.

The M, C, Y and BK image signals sent from the image scanner unit 201 are transmitted to the laser driver 1.
08. Then, the laser driver 108 modulates and drives the semiconductor laser 254 according to these image signals, and the laser light is transmitted to the polygon mirror 214 and the f-θ lens 2.
15. Scan the photosensitive drum 217 via the mirror 216 to form an electrostatic latent image.

The electrostatic latent image formed on the photosensitive drum 217 is connected to the magenta developing unit 21
9, a developing unit of a rotary developing unit 218 composed of a cyan developing unit 220, a yellow developing unit 221, and a black developing unit 222. Then, the recording paper fed from the recording paper cassette 224 or 225 is wound around the transfer drum 223, and the image formed on the photosensitive drum 217 is transferred to the recording paper. After the four colors M, C, Y, and BK are sequentially transferred in this manner, the recording paper passes through the fixing unit 226 and is discharged.

Next, details of processing for a black character area in the present embodiment will be described below.

The circuit for determining the necessary black color for detecting the black character image area is the color determination circuit 109 described above. The circuit 109 is configured as shown in FIG. 3, and performs an operation of comparing the input maximum value and minimum value of R, G, and B to determine whether the pixel is a chromatic color or an achromatic color. First, a correction process is performed in the color shift correction circuit 301 in order to correct the R, G, and B color shifts caused by the difference in the MTF of the line sensor 101 and the vibration at the time of reading. The color misregistration correction process is a smoothing process in both the main scanning and sub-scanning directions, and the configuration thereof is a known two-dimensional filter. A maximum value / minimum value detection circuit 302 obtains the maximum value and the minimum value from the R, G signals and the B signals subjected to the color misregistration correction. It is determined whether it is colored. That is,
If the difference between the maximum value and the minimum value is larger than a predetermined range, the color is determined to be chromatic, and if the difference is smaller than the predetermined value, the color is determined to be achromatic, and the determination condition is that all the following expressions (1) are satisfied. is there.

Max−16 <Min × 2, Max−38 <Min, Max−72 <Min ÷ 2 (1) where Max = max (R, G, B), Min = min (R, G, B ). In addition, the numerical values and mathematical expressions described here do not necessarily have to be exactly as described above, and preferable determination conditions can be appropriately used according to the properties of the image signal. Further, the result of the comparison circuit 305 that determines that the minimum value is equal to or smaller than a certain threshold value set in the register 304 and the AND of the achromatic signal
By taking D, an achromatic pixel having a certain density or higher is determined to be black. Thus, the color determination circuit 109 generates a black signal and a chromatic color signal.

However, the determined chromatic signal is not necessarily detected only in a colored region, but is also detected in a black edge portion or a halftone dot region. Therefore, a circuit for removing unnecessary noise components from the chromatic signal is the isolated point removal circuit 110. This circuit 110 expands the input signal by 3 × 3 pixels as shown in FIG.
It is configured to shrink by 5 pixels. That is,
The input signal is delayed by a FIFO memory (first-in-first-out memory) 401, the signal of three lines is ORed by an OR 402, further delayed by a D flip-flop 403 and then ORed to obtain a 3 × 3 pixel. Inflate. Subsequently, the expanded signal is delayed by the FIFO 401, and the logical product of 5 lines is obtained by the AND 404, and the logical product of 5 clocks is obtained.
Shrink by 5 pixels. This circuit 110 expands and contracts the input chromatic signal to remove extra noise. If the chromatic signal is a chromatic signal generated in a halftone dot area, the circuit 110 shown in FIG.
As shown in (A) of FIG.
The chromatic signal remains without disappearing even when contracted. On the other hand, when a chromatic signal exists for only a few pixels, such as a character outline having color fringing, the chromatic signal disappears upon expansion and contraction as shown in FIG. The black signal is masked by the chromatic signal from which noise has been removed as described above, and a black determination signal that is erroneously generated in a halftone dot portion can be removed.

FIG. 6 is a diagram showing a configuration of the above-described character area determination circuit 111. As shown in FIG. In the figure, 600 is a minimum value detection circuit, 601 is a FIFO, 602 is a 5 × 5 pixel averaging circuit, 603 is a 3 × 3 pixel averaging circuit, 604 and 6
05 is a binarization circuit, 606 is a halftone dot detection circuit, 607 is a reduction circuit, and 608 is an expansion circuit.

In the above configuration, first, the signal of the darkest color is selected from the R, G, and B signals input by the minimum value detection circuit 600, and the line is delayed by the FIFO 601. Next, the average values of 3 × 3, 5 × 5 pixels are calculated by the averaging circuits 602, 603, respectively, and the average values of 5 × 5 pixels are respectively referred to by the binarization circuits 604, 605, and 3 × 3 The average value of the pixels and the original signal that is not averaged are binarized. Then, the halftone dot detection circuit 606 detects a portion printed by halftone dots in the document, and a logical sum of a signal indicating the halftone dot area and the other binarized signal is obtained. The extra noise is removed by the expansion circuit 608, the image area and the character area are separated, and a character area signal is generated.

The black character area and color determination signals generated by the above processing are input to the UCR / masking correction circuit 105, the two-dimensional filtering circuit 106, and the γ correction circuit 107 in FIG. First, the UCR / masking correction circuit 105 is configured as shown in FIG. 7, and the minimum value detection circuit 701 generates a minimum value based on the C ′, M ′, and Y ′ signals input from the density conversion circuit 104. A black component BK ′ is obtained by multiplication, a multiplication circuit 702 multiplies each color component by a weighting coefficient set in a register 704, and adds the resultant components by an addition circuit 705 to perform masking correction. And the register 70
4 is a set of weighting coefficients stored in C,
When printing M, Y, and BK, different combinations are set by a micro computer (not shown). For each color masking correction factor,
There are two sets of registers 704 so that two kinds of coefficients for normal processing and black character processing can be set.
Selector 703 selects which set of coefficients to use for that pixel. For example, when performing black character processing, register setting is such that all coefficients for outputting C / M / Y are set to “0”, and appropriate values are set only when outputting the BK component, and the image is set in image sequence. Perform formation.

Next, the two-dimensional filtering circuit 106
Is configured as shown in FIG. As shown, the input image signal is delayed in the sub-scanning direction by the FIFO memory 801, and the edge component in the sub-scanning direction for the pixel of interest is calculated by the adding circuit 802. Further, an edge component in the main scanning direction with respect to the pixel of interest is added from the pixel data delayed by the D flip-flop 804 to the addition circuit 8.
05. Then, the multiplication circuits 806 and 8
At 07 and 808, the adder 811 multiplies the edge component in the sub-scanning direction, the pixel component of interest, and the edge component in the main scanning direction by the multiplication coefficient read from the register 809.
To perform a two-dimensional filtering process. As the multiplication coefficient at that time, a normal coefficient and a coefficient for black character processing are selected by the selector 810 according to the black character determination signal 812. This two-dimensional filtering circuit 106
According to the multiplication coefficient stored in the register 809, not only edge enhancement but also smoothing processing can be performed.

As described above, according to this embodiment,
By masking the black signal of the color determination signal with a chromatic signal from which noise has been removed, it is possible to improve the color determination accuracy for chromatic halftone characters and blue-based characters that were conventionally determined to be black. This makes it possible to perform more preferable black character processing.

[0026]

[Other Embodiments] In the above-described embodiment, the noise removal of the chromatic signal after the color determination is performed by expansion and contraction by the isolated point removal circuit 110. However, other than this method, a majority decision method may be used. It is possible. As shown in FIG. 9, the chromatic color signal and the black signal from the color determination circuit 109 are respectively counted in a window of M × N pixels centering on the pixel of interest.
By comparing the numbers of pixels with each other with a comparison circuit, the configuration of determining the property of the pixel of interest also makes it possible to remove unnecessary noise and perform black determination. More specifically, a chromatic signal and a black signal are input to a FIFO9.
01, the number of pixels is counted in the sub-scanning direction by the pixel number counting circuits 902 and 903, and further summed up in the main scanning direction by the main scanning direction summing circuit 904, and then compared by the comparison circuit 905. Determines whether the pixel of interest is black.

Here, the size of the window is appropriately 5 × 5 pixels, for example, but is not necessarily limited to this.

As described above, the case of realizing the full color copying apparatus by hardware has been described as an example. However, the same processing can be realized by software in a color desktop publishing (DTP) apparatus or the like. That is, it is necessary to take an image from a scanner once, combine it with desired data such as text data on a processor (usually a personal computer or the like), create final data, and output this to a full-color printer. Although it is possible, the processing described in the above-described embodiment is performed on the captured image data,
It can also be executed as software on a processor.

The method of realizing the image determination processing by software is the same as the known image processing method, and although not described in detail, the detection of a black character area in the image data read in the above-described embodiment is not described. Can be done by programming the processor to simulate the hardware. After performing the image determination process, only the determination signal may be supplied to the printer in addition to the image data, and the character portion may be processed inside the printer. Alternatively, masking after the determination process may be performed on the processor. A configuration may be adopted in which all processing up to the character portion including the processing and the two-dimensional filtering processing is performed by software.

The present invention may be applied to a system constituted by a plurality of devices or to an apparatus constituted by a single device. Needless to say, the present invention can also be applied to a case where the above is achieved by supplying a program to a system or an apparatus.

[0031]

As described above, according to the present invention,
Chromatic halftone characters that were previously determined to be black are mistaken for black characters.
Prevention from being judged, and highly accurate black character judgment
As a result, black character reproducibility is improved
Can be

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an image processing circuit of a full-color copying apparatus according to an embodiment.

FIG. 2 is a diagram illustrating an overall configuration of a full-color copying apparatus according to the embodiment.

FIG. 3 illustrates a color determination circuit according to the present embodiment.

FIG. 4 shows a noise removing circuit according to the present embodiment.

FIG. 5 is a diagram illustrating a processing state of a determination signal in the embodiment.

FIG. 6 illustrates a character area determination circuit according to the present embodiment.

FIG. 7 shows a UCR / masking correction circuit according to the present embodiment.

FIG. 8 shows a two-dimensional filtering circuit according to the present embodiment.

FIG. 9 is a diagram illustrating a noise determination circuit for a color determination signal according to another embodiment.

[Explanation of symbols]

 Reference Signs List 101 Line sensor 102 A / D conversion circuit 103 Shading correction circuit 104 Density conversion circuit 105 UCR / masking circuit 106 Two-dimensional filtering circuit 107 γ correction circuit 108 Laser driver 109 Color judgment circuit 110 Isolated point removal circuit 111 Character area judgment circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46-1/64 G06T 11/60 120

Claims (2)

(57) [Claims] And 1. A image reading means for scanning a color original to generate <br/> color separation signals, a color determination means for generating a chromatic signal and a black signal using the generated color separation signals, said generated in halftone dot region of the color original of the chromatic signal
Specifying means for specifying a chromatic signal which, in the character area of the color document based on the color separation signals
Character area determining means for generating a character area signal in the image signal, and the generated black signal using the specified chromatic signal.
No. of the color document obtained by masking the
A black signal from which a black signal generated in a halftone dot region has been removed;
Using a character area signal, a black character area of the color original
A black sentence that generates a black character area signal for processing black characters
A full-color image reproducing apparatus comprising: a character area determining unit. 2. A scanning a color original read image generating <br/> color separation signals step, a color determination step of generating a chromatic signal and a black signal using the generated color separation signals, said generated in halftone dot region of the color original of the chromatic signal
A specifying step of specifying a chromatic signal to be performed, and a character area of the color original based on the color separation signal.
A character area determining step of generating a character area signal in the image signal; and the generated black signal using the specified chromatic signal.
No. of the color document obtained by masking the
A black signal from which a black signal generated in a halftone dot region has been removed;
Using a character area signal, a black character area of the color original
A black sentence that generates a black character area signal for processing black characters
A full-color image reproduction method characterized by having a shaped area determining step.