JP2954230B2 - Image processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for processing input color image data.

[Prior Art] Conventionally, a device has been devised for simultaneously outputting a photographic image and a character image and outputting each image beautifully.

[Problems to be Solved by the Invention] However, there are black characters of various densities in an input image, and these cannot be processed as black characters.

Further, when color image data is input, the density is detected to be low around black characters in the image, and as a result, a color shift is likely to occur. As a result, a chromatic color may be erroneously determined around a black character that should be an achromatic color.

The present invention has been made in view of such a problem, and can perform black character processing on black characters having various densities.Furthermore, even if a color shift occurs between the respective color components, the pixel of interest and its The purpose of the present invention is to provide an image processing apparatus capable of reducing erroneous determination of color misregistration by correcting the achromatic color determination result for a target pixel using the achromatic color determination result for peripheral pixels, and performing good processing on a black character portion. is there.

[Means for Solving the Problems] An image processing apparatus of the present invention for solving the problems has the following configuration. That is, input means for inputting color image data having a plurality of color components, determination means for determining whether or not a target pixel in the color image data input by the input means is included in an achromatic region, Correction means for correcting the determination result of the determination means for the pixel of interest using the determination result of the determination means for the peripheral pixels of the pixel of interest; and processing for black characters according to the determination result corrected by the correction means. And control means for controlling whether or not to enable.

Embodiment An embodiment according to the present invention will be described below in detail with reference to the accompanying drawings. In the embodiment, a color copying machine will be described as an example.

<Description of Apparatus Configuration (FIG. 1)> FIG. 1 is a block diagram of an image processing system of a color copying machine according to the present embodiment. Hereinafter, an outline of the processing will be described.

An image reading unit (for example, a CCD) 800 reads an original image and outputs data (8 bits each) for each of R, G, and B color components. Each of the RGB data passes through a next logarithmic conversion unit 801 and a masking calculation unit 802, and then Y ₀ (yellow) and M ₀
(Magenta), converted to C ₀ (cyan) signal, then UCR section
In step 803, the signals Y ₁ , M ₁ , C ₁ , and B _K1 (black) after the undercolor removal are output.

Data Y output from the UCR unit _{803 1, M 1, C 1} , B K1 are simultaneously input respectively to the edge enhancement circuit 804 and a smoothing circuit 805.

The edge emphasizing circuit 804 includes, for example, a 3 as shown in FIG.
Using a × 3 matrix, a Laplacian filter operation is performed based on the data of the pixel of interest and its surrounding pixel group to generate each data of Y ₂ , M ₂ , C ₂ , and _BK2 . The edge enhancement itself is a well-known technique, and will not be described in detail.

Also, in the smoothing circuit 805, 3 × shown in FIG.
Filter operation is performed using a matrix of ₃ and Y ₃ , M ₃ ,
Outputs C ₃ and B _K3 .

On the other hand, the R, G, B output from the image reading unit 800
Are passed through the smoothing circuits 104 to 106, and are passed through the black area determination unit 80.
Entered in 6. The black area determination unit 806 determines whether or not the target pixel belongs to the black area based on the input R, G, B data, and outputs the determination result to the selector 807.

When the selector 807 receives a signal indicating that the pixel of interest is a black area, the data Y ₂ , M ₂ , C ₂ ,
Select and output B _K2 . Also, the target pixel is outside the black area,
That is, when a signal indicating a chromatic color area is received, the data of the data Y ₃ , M ₃ , C ₃ , and _{BK 3} from the smoothing circuit 805 are selected.

Accordance connexion, black character portion will be output as image data _{Y 4, M 4, C 4} , B K4 which is edge emphasis processing. Then, after the data Y ₄ , M ₄ , C ₄ , and _{BK 4} are input to the error diffusion circuit 808, they are output to an image forming unit (not shown) to form a visible image.

In the error diffusion route 808, binary data for the target pixel is determined from the input data Y ₄ , M ₄ , C ₄ , and _BK4 for the target pixel and the data allocated to the target pixel so far. The error generated at this time is distributed to peripheral pixels (pixel groups to be processed later) around the target pixel (the position of the “*” mark in the figure) according to the matrix elements shown in FIG.

<Description of Black Region Determining Unit (FIGS. 5 and 6)> FIG. 5 shows a configuration near the black region determining unit 806 in the embodiment.

R, G, B data from the smoothing circuits 104 to 106 (8 bits each)
Are input to the maximum value detection circuit 107 and the minimum value detection circuit 108, respectively. The maximum value detection circuit 107 is a circuit that detects the maximum value A in each of the input data of R, G, and B, and is a circuit that calculates the following equation if it is expressed by an equation.

A = max (R, G, B) The minimum value detection circuit 108 is a circuit that detects the minimum value B in each of the input R, G, B data. In a formula, B = min (R, G, B).

Now, these maximum value detection circuit 107 and maximum value detection circuit 1
Maximum value data A of each RGB component of the target pixel obtained in 08
And the minimum value data B are input to the next subtraction circuit 109, which calculates a subtraction value D (= A−B) and outputs it to the comparison circuit 110.

The comparison circuit 110 compares the subtraction value D with a preset value a and outputs a comparison result of the following equation.

D <a: output “1” D ≧ a: output “0” ... The output data A of the maximum value detection circuit 107 is
11 and is compared with a preset value b. The comparison circuit 111 outputs a comparison result of the following equation.

A <b: output “1” A ≧ b: output “0”... The AND circuit 112 ANDs the result signals from the comparison circuits 110 and 111 and outputs the result to the line buffer 115 as a signal 114. The line buffer 115 has a buffer for three lines, from which a data group corresponding to a total of 9 pixels of 3 × 3 is output to an OR circuit 113. OR circuit 113
The line buffer 115 constitutes a correction circuit for correcting a signal output from the AND circuit 112. Then, the OR circuit 113 calculates the logical sum of the input pixel of interest and the data of the surrounding pixel group, and outputs a signal indicating whether or not the pixel of interest is a black area.

In this embodiment, the higher the lightness, the larger the value of the input color signals 101-103. Therefore, D = max (R, G,
B) The value of -min (R, G, B) is smaller than the constant a, and A
If the value of = max (R, G, B) is smaller than the constant brightness for the constant b, that is, if the input signal in the shaded area shown in FIG. 6 is not included, the output from the AND circuit 112 “0”
Is output to the OR circuit 113.

Accordingly, by appropriately setting the values of the constant values (threshold values) a and b, it is possible to identify the black area of the input image from the other chromatic areas and the bright original background.

However, there is a possibility that an erroneous determination may occur in a portion around the black region due to the influence of a color shift error of the input color signal. The OR circuit (black area correction circuit) 113 corrects this erroneous determination.

FIG. 7 shows a line buffer 115 and an OR circuit 1 in the embodiment.
13 shows the relationship.

The black area determination signal 114 output from the AND circuit 112 is stored as a 1-bit signal in a line buffer (constituted by three lines of FIFO) 115. The OR circuit 113 inputs, from the line buffer 115, data of a total of 9 bits of the black area data "e" for the pixel of interest and the adjacent pixel groups "ad" and "fi". When the bit state is "1" (meaning that it is determined to be within the shaded area in FIG. 6), the level of the corrected black area determination signal 116 is output as "1". In other words, the corrected black area determination signal 116 becomes “0” only when all of a to i are “0”.

 The correction result will be described based on the signal arrangement shown in FIG.

FIG. 8 (b) shows that a, b, d, e, g, and h of a to i are "0".
This is the case where c, f, i are “1”. In this case, even if the value of the target pixel position e before correction is “0”, the value of e after correction is “1”.

FIG. 8 (c) shows a case where only b is "1" and all others are "0". In this case, too, the value of the target pixel position e before correction is "0". Becomes “1” after the correction.

FIG. 9 is a diagram for explaining from the black characters in the document to the reproduction of the corrected black area.

In the figure, reference numeral 601 denotes an original black character, 602 denotes an input image, 604 denotes a black area before correction, and 605 denotes a black area after correction.

As shown in the figure, the original black character 601 is read, and the determined black area signal 114 is determined to be smaller than the original black character 601 as indicated by 604 due to the color shift error 603 of the input color signal generated when reading around the original black character. . Therefore, the correction circuit (OR circuit) 13 corrects the black character signal 114 and outputs the judgment signal 116.
Output, the thicker corrected black area 60
5 can be reproduced.

Before and after the description, the configuration of the smoothing circuit 104 is shown in FIG. The other smoothing circuits 105 and 106 have exactly the same configuration.

In the figure, reference numeral 301 denotes a line buffer for storing input color component data (R component data), and has a capacity to store three lines of 8-bit data per pixel. Reference numeral 302 denotes a smoothing operation unit which inputs R component data of peripheral pixels j, k, l, and m including the pixel n to be smoothed from the line buffer 301 and smoothes the R component value of the pixel n.

 This smoothing value is calculated based on the following equation.

n ← (4n + j + k + 1 + m) / 8 That is, a smoothed color signal is obtained by taking a weighted average.

FIGS. 11 (a) and 11 (b) show experimental results of a computer. FIG. 11C shows an example of a black character original.

FIG. 11 (a) shows the distribution of max (R, G, B) -min (R, G, B) of the input color current signal before performing the smoothing process.
FIG. 11 (b) shows the distribution after the smoothing process. As shown, when the smoothing process is performed,
Experiments show that the variation of max (R, G, B) -min (R, G, B) is reduced, and that it is effective to use a smoothed color signal for the judgment processing for extracting the black area. Was confirmed. In particular, a remarkable effect is seen in a character having a large number of strokes as shown in FIG.

<Explanation of Second Embodiment (FIG. 12)> FIG. 12 is a block diagram of the second embodiment.

The description of the same reference numerals (numbers) as in FIG.

In the illustrated configuration, when the black area is determined by the black area determination unit 806, the selector 813 selects Y ₂ , M ₂ , C ₂ , and _{BK 2} from the 0 data unit 810. The value of the data Y ₂ , M ₂ , C ₂ is “0”
Stipulated. Accordingly, the values of the outputs Y ₄ , M ₄ , and C ₄ of the selector 813 at this time also become “0”. Also, B _K2 is after logarithmic transformation of the signal of the G component among the input color signals, is obtained by the density correction in LUT (look up table) 810.
The reason for employing the G component is that it is closest to the neutral density image as compared with the other components.

If it is determined that the color is chromatic, the data Y ₁ , M ₁ ,
Data Y ₃ , M ₃ , C ₃ , B _{K3 obtained} by performing smoothing processing on C ₁ , B _K1
Select

<Description of Third Embodiment (FIG. 13)> FIG. 13 shows a block diagram of the third embodiment.

In the example shown in the figure, after moiré is removed by the smoothing process, an edge emphasizing circuit for correcting the deterioration of the sharpness due to the smoothing process is inserted, so that a sharp image of the chromatic portion can be obtained. .

As described above, according to the present embodiment, it is possible to reduce a determination error by separating an achromatic color, that is, a black character portion and a chromatic color region. And
An image close to a binary image can be obtained by edge emphasizing a black character portion, and an image from which moiré has been removed can be obtained by performing a smoothing process on a chromatic color portion.

[Effects of the Invention] As described above, according to the present invention, black characters having various densities can be subjected to black character processing, and even if a color shift occurs between the respective color components, the pixel of interest By correcting the achromatic color determination result for the target pixel using the achromatic color determination results for the peripheral pixels and the surrounding pixels, erroneous determination of color misregistration can be reduced, and good processing can be performed for black character portions.

[Brief description of the drawings]

FIG. 1 is a block diagram of the image processing apparatus of the first embodiment, FIG. 2 is a diagram showing matrix elements used for edge enhancement, and FIG. 3 is a diagram showing matrix elements used for smoothing. FIG. 4 is a diagram showing matrix elements used for error diffusion processing, FIG. 5 is a diagram showing the internal configuration of a black region determination unit, FIG. 6 is a diagram showing the distribution of black regions in an input color signal, 7 is a diagram showing details of the vicinity of the OR circuit shown in FIG. 5, FIG. 8 (a) is a diagram showing a matrix used in the correction circuit, and FIGS. 8 (b) and (c) are examples of execution of the correction process. FIG. 9 is a diagram showing a transition until a corrected black area is reproduced, FIG. 10 is a block diagram of a smoothing circuit, and FIGS. 11 (a) to 11 (c) show processing outlines of the smoothing circuit. FIG. 12 is a block diagram of an image processing apparatus according to a second embodiment. , FIG. 13 is a block diagram showing the arrangement of an image processing apparatus in the third embodiment. In the figure, 104 to 106: smoothing circuit, 107: maximum value detection circuit, 108: minimum value detection circuit, 109: subtraction circuit, 110 and 111: comparison circuit, 112: AND circuit, 113 ... OR circuit,
115 ... Line buffer, 800 ... Image reading unit, 801 ...
Logarithmic conversion unit, 802: Masking operation unit, 803: UCR
804: Edge emphasizing circuit, 805: Smoothing circuit, 806: Black area determination unit, 807: Selector, 808 ...
It is an error diffusion circuit.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (2)

(57) [Claims] An input unit for inputting color image data having a plurality of color components; and a determination unit for determining whether a pixel of interest in the color image data input by the input unit is included in an achromatic region. Correction means for correcting the determination result of the determination means for the pixel of interest using the determination result for the pixel of interest and the surrounding pixels of the pixel of interest; and a black character according to the determination result corrected by the correction means. An image processing apparatus comprising: a control unit configured to determine whether or not a process for use is to be enabled. 2. The image processing apparatus according to claim 1, wherein said determining means further determines whether or not the target pixel has a predetermined density or more.