JP2848558B2 - Color image processing equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a color image processing apparatus.

[Prior Art] Conventionally, an image processing apparatus that controls black output and color output in order to form a black character portion of an image visually well has been devised.

[Problems to be Solved by the Invention] However, when a black character is determined when a black character is determined, an erroneous determination may occur between a character region and a halftone dot region having similar characteristics. However, the determination accuracy was not always good.

Also, if there is a black character part that is also colored in the black character part,
There are black character parts with almost no saturation, but the measures were not sufficient for these various black character parts.

In view of the above, the present invention provides an image processing apparatus capable of identifying black characters in consideration of achromatic chromaticity, character areas and halftone areas in order to improve the above problems. Aim.

[Means for Solving the Problems] To achieve the above object, a color image processing apparatus of the present invention has the following configuration. That is, a color image processing apparatus that has a generating unit that generates a plurality of color component signals representing a color image, and performs a color image formation using the plurality of color component signals. First output means for outputting a signal corresponding to the above, second output means for outputting an achromatic chromaticity signal representing the saturation based on the plurality of color component signals, and a signal corresponding to the luminance and the null signal. Means for determining a black character using a chromaticity signal, outputting data for identifying a character area and a halftone area, identifying means for identifying a black character other than the halftone area, and identification by the identification means Control means for controlling the output of the black component and the color component according to the result.

[Operation] With the above configuration, a signal corresponding to luminance and an achromatic chromaticity signal representing chroma are output from a plurality of color component signals representing a color image, and a signal corresponding to the luminance and the achromatic chromaticity signal are used. And outputs data for identifying a character region and a halftone dot region to identify a black character outside the halftone dot region, and controls the output of a black component and a color component according to the identification result. .

[Description of Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of a digital color copying apparatus according to an embodiment. In the figure, reference numeral 101 denotes an input image, which is, for example, a color document image in which a character image, a photographic image and the like are mixed. Reference numeral 102 denotes a reader, which converts the color original image 101 into R, G, B
The readout signal is A / D converted and digital image signals (luminance signals) R, G, and B (each 8 bits) are output. 103 is a logarithmic conversion circuit, and a luminance signal
R, G, and B are logarithmically converted and the resulting density signals C ₁ , M ₁ , and Y ₁ are output. Reference numeral 104 denotes a minimum value extraction circuit, and the input density signal C ₁ ,
While passing M ₁ and Y ₁ as they are, the minimum value signal min (Y ₁ , M ₁ , C ₁ ) among them is detected and output. 105 is an inking / UCR circuit, which is the minimum input signal min (Y ₁ , M ₁ , C ₁ )
To test and to produce a black (black) signal K ₂ based on, outermost minimum value signal min (Y _1, M _1, C ₁₎ density signals C ₁ of the input based on, M _1, Y
Generate and output density signals C ₂ , M ₂ , and Y ₂ from ₁ under color removal (UCR). Reference numeral 106 denotes a masking circuit, which performs a known masking matrix operation in order to match the density signals C ₂ , M ₂ , and Y ₂ with the ink or the like in accordance with the characteristics of the ink (toner or the like) of the printer. Reference numeral 107 denotes a gradation correction circuit that corrects the density signals C ₃ , M ₃ , Y _3, and K ₃ after masking according to the gradation of the printer. Thus, the output signal for normal printer printing
C ₄ , M ₄ , Y ₄ and K ₄ are obtained. Reference numeral 113 denotes a gate circuit which receives the above-mentioned transmission signals C ₄ , M ₄ , Y ₄ , and K ₄ as inputs, and receives only a black signal K ₅ according to a black pixel determination signal S described later (in the case of a black pixel determination). ) Or four primary color signals C ₅ , M ₅ , Y ₅ , K ₅ (in the case of judging that the pixel is not a black pixel) and outputs it. A laser beam printer 114 forms a color image in accordance with the four primary color signals C ₅ , M ₅ , Y ₅ , and K ₅ . 115 is an output image.

On the other hand, reference numeral 108 denotes a matrix conversion circuit which converts the input luminance signals R, G, B into NTSC which is a general color television signal.
Convert to standard y, i, q signal. This matrix conversion formula is, for example, as in formula (1). , Here, y is a luminance signal (8 bits) corresponding to the brightness of the image, and i and q are color difference signals (8 bits each). A lookup table 109 receives the above color difference signals i and q as input and outputs an achromatic chromaticity signal W representing the degree of achromatic color by table conversion. The achromatic chromaticity signal W of this embodiment is set to be maximum when the input is achromatic (i = q = 0). That is, the achromatic chromaticity signal W of the embodiment is related to the color difference signals i and q according to, for example, equation (2).

W = 255 × exp [− (i / 1024) ² − (q / 1024) ² ]
(2) In the above equation (2), the term (exp) on the right side has a maximum value of 1 when the input is an achromatic color (i = q = 0). Therefore, the achromatic chromaticity signal W has a maximum value of 255. (8 bits). 116
Is a multiplier, which converts the luminance signal y and the content of the achromatic chromaticity signal W to convert to an achromatic luminance signal V. Specifically, V = (255−y) × w / 255 (3)

In the above equation (3), the luminance signal y on the right side is introduced in the form of (255-y) so as to take a large value in a low luminance portion. Accordingly, the term (255-y) is minimum when the input image is bright (white portion), and is maximum when the input image is dark (black portion). On the other hand, the term (W / 255) is 1 when the color is achromatic, and takes a value of 1 or less when the color is chromatic. Therefore, the achromatic luminance signal V becomes the maximum value 255 when the input is achromatic and black by taking the product of the two, and becomes a small value when the achromatic color is white or gray. It is not always necessary to take the product of the two as in the case of the achromatic luminance signal V described above.
For example, it is clear that an appropriate threshold value is set, a dark condition is determined from (255-y), and a substantially achromatic condition is determined from (W).

Reference numeral 110 denotes a line buffer which stores four lines of achromatic luminance signals V necessary for Hadamard transform described later.
The determination of a black pixel based on the achromatic color luminance signal V may be performed independently for each pixel. However, in general, an image such as a black character is distributed over a considerably large area compared to the size of one pixel (for example, 16 pel). Therefore, it is much better to make a judgment taking into account the properties of the image around the pixel (character, line image area or photographic image area, etc.) rather than making a judgment for each pixel alone. Stable black pixel determination and control can be performed.
Therefore, in this embodiment, 4 × 4 pixels for determining 4 × 4 pixels are determined.
A line buffer for the line was prepared. Reference numeral 111 denotes a Hadamard transform circuit, which includes, for example, a 4 × 4 pixel Hadamard transform matrix.

FIG. 2 is a diagram for explaining the Hadamard transform processing of the embodiment. In the figure, the value of the achromatic luminance signal V of each pixel is represented by a
and _ij, the pixel of interest is a pixel a ₂₂ of a suitable intermediate position.
Then, the Hadamard transform y _kl in this block area is expressed by equation (4).

Where C _kl (i, j) is the order (k, l) of the Hadamard transform
Are obtained as follows.

The Hadamard transform y _{kl in} the above equation (4) represents the spatial structure of the black image in the block of interest, and if the order (k,
If the value of the Hadamard transform y _kl of small l) is large, the block of interest is an image with flat luminance, and if the value of the Hadamard transform y _kl of large order (k, l) is large, the image contains edge components. I understand.

Returning to FIG. 1, reference numeral 112 denotes a determination circuit which determines whether or not the block of interest belongs to a character or diagram area by the following determination method, for example.

FIG. 3 is a diagram showing an array of the Hadamard transform y _kl of the embodiment. In FIG., Y ₁₁ represents an average value in the block, edge component is detected in the horizontal direction when the increasing order k. When the order 1 increases, an edge component in the vertical direction is detected. When the orders k and 1 increase, edge components (halftone dots and the like) in the horizontal and vertical directions are detected. Therefore, in the present embodiment, the following value is obtained from the obtained Hadamard transform y _kl .

Y _V = y ₁₂ + y ₁₃ + y ₁₄ Y _H = y ₂₁ + y ₃₁ + y ₄₁ Y _S = y ₄₄ + y ₃₄ + y ₄₃ (5) Accordingly, when Y _V is large, a vertical edge exists in the block of interest when Y _V is large. and, when Y _H is large and there is lateral edge when Y _S is large so that the complex pattern such as dot exists. Therefore, predetermined thresholds T ₁ , T ₂ , and T ₃ are set, and when the following condition is satisfied, the block of interest is determined to be a black character and black line area.

(Y _V > T ₁ or Y _H > T ₂ ) and Y _S <T ₃ (6) That is, a vertical edge or a horizontal edge exists and is not a complicated pattern such as a halftone dot. Incidentally, the detection of the area of the black flat portion can be performed by detecting from the start to end of detection of Y _V > T ₁ or Y _H > T ₂ or directly examining y ₁₁ with a predetermined threshold value. As described above, when an achromatic black character area or the like is determined, the signal S of the determination result is output from the gate circuit.
113, and normally output the density signals C ₄ , M ₄ , Y ₄ , and K _{4 as} they are as the density signals C ₅ , M ₅ , Y ₅ , and K ₅ , whereas the above-described black area determination is reduced. Then, the constituent gate circuits of each color are turned ON / OFF so that the density signals C ₅ = O, M ₅ = O, Y ₅ = O and the density signals K ₅ = K ₄ . Thus, the above control sets the target pixel to 1
This is performed based on the Hadamard transform for the block of interest of the peripheral pixel at each point in time while shifting the pixel by pixel.

In the above embodiment, the Hadamard transform is adopted, but the present invention is not limited to this. For example, another orthogonal transformation or the maximum value and the minimum value of the signal V in the block of interest may be detected, and edge judgment may be performed based on the magnitude of the difference.

Also, the method of obtaining the achromatic signal W and the method of obtaining the luminance signal Y are not limited to those in the above embodiment.

[Effects of the Invention] As described above, according to the present invention, it is means for determining a black character using a signal corresponding to luminance and an achromatic signal, and is used for distinguishing a character region from a halftone dot region. It has an identification means for outputting data and identifying black characters other than the halftone dot area, and a means for controlling the output of the black component and the color component according to the identification result by the identification means. Thus, it is possible to identify a black character in consideration of a halftone dot region having similar characteristics to a character region.

[Brief description of the drawings]

FIG. 1 is a block diagram of the digital color copying apparatus of the embodiment, FIG. 2 is a diagram for explaining the Hadamard conversion process of the embodiment, and FIG. 3 is a diagram showing an array of the Hadamard conversion _ykl of the embodiment. In the figure, 101: input image, 102: reader, 103: logarithmic conversion circuit, 104: minimum value extraction circuit, 105: black ink / UC
R circuit, 106 masking circuit, 107 gradation correction circuit, 108 matrix conversion circuit, 109 look-up table, 110 line buffer, 111 Hadamard conversion circuit, 112 decision circuit, 114 …… Printer, 115…
... This is an output image.

Claims (1)

(57) [Claims] 1. A color image processing apparatus, comprising: generating means for generating a plurality of color component signals representing a color image, wherein the color image processing apparatus forms a color image using the plurality of color component signals. First output means for outputting a signal corresponding to luminance from a signal; second output means for outputting an achromatic chromaticity signal representing chroma based on the plurality of color component signals; and a signal corresponding to the luminance. Means for determining a black character using the achromatic signal, outputting data for identifying a character area and a halftone area, and identifying means for identifying a black character other than the halftone area; Control means for controlling output of a black component and a color component in accordance with a result of identification by the means.