JP3496887B2 - Digital color image processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital reproduction of a color image using recording signals C (cyan), M (magenta), Y (yellow) and K (black). The present invention relates to a digital color image processing device for outputting. 2. Description of the Related Art As a color image reproducing apparatus capable of achieving both the image quality of black characters and the image quality of pictures, for example, Japanese Patent Laid-Open No.
There is an apparatus described in Japanese Patent No. 14378. In the device described in the publication, whether or not a pixel of interest belongs to a black character area is determined and output as “0” to “1” based on local image information, and for a pixel determined to be a black character area,
For example, high-resolution reproduction processing (for example, 100% UC
R processing) and image reproduction processing (for example, 50% UCR processing) suitable for a picture is performed on the other pixel areas. More specifically, black generation processing and UCR processing are adaptively switched. By the way, the present applicant has already made some proposals on a so-called image area separation method for determining to which area a pixel of interest belongs based on local image information. (For example, "Character / Picture (dots,
Photo) Image Area Separation Method of Mixed Image "IEICE Transactions on Electronics, Vol.J75-DI1 No.1 pp39-471
See January 992). In such an image area separation method, there is naturally a limit in the separation accuracy due to the use of local information. Therefore, in the current image area separation technology, for example, in adaptive processing using black character separation, a picture pattern is not used. The presence of an erroneous separation area determined as a black character area cannot be avoided. As a result, there is an area in the picture where 100% UCR processing is performed (or an area where a single black color is applied with ink in a full range), which is related to the deterioration of the reproduction image quality. In other words, a discontinuous gap caused by a difference between a 100% UCR-processed area and the surrounding area (for example, a 50% UCR-processed area) is noticeable.
This is the main cause of image quality deterioration. The present invention has been made in view of the above points, and an object of the present invention is to control the amount of black generation stepwise according to the amount of black edge to reduce a sudden change in the UCR rate. An object of the present invention is to provide a digital color image processing apparatus for reproducing a high-quality image. Another object of the present invention is to provide a digital color image processing apparatus for reproducing a high-quality image by controlling the amount of CMY erasure in multiple stages according to the amount of black edge. In order to achieve the above object, according to the first aspect of the present invention, an original is read as r, g, b digital image signals, and recording signals C, M, Y, and generates K, in a digital color image processing apparatus for digitally printed, the
From the r, g, b signals or the C, M, Y signals,
Means for calculating an edge amount, and the r, g, b signals or
A method for calculating the amount of white background around the pixel of interest from the C, M, and Y signals
And r, g, and r in accordance with the step and the calculated black edge amount.
Outputs multi-step K signal from b signal or C, M, Y signal
Means for subtracting the K signal from the C, M, Y signals
Means for outputting C ′, M ′, Y ′ signals after subtraction,
With the calculated black edge amount and the division amount corresponding to the white background amount,
Means for dividing the C ', M', and Y 'signals after the subtraction.
It is characterized by comprising. The black edge amount calculation section is composed of a blackness calculation circuit and an edge amount calculation circuit, calculates the black edge amount n of the pixel of interest, and outputs it to the black generation circuit. K = α × m
The generation of black is controlled in multiple stages according to in (C, M, Y). The correspondence between the black edge amount n and α is constituted by a table, and the black amount K changes in multiple stages according to the output n from the black edge amount calculation unit. As a result, a sudden change in the UCR rate in the image is suppressed, and the image quality is improved. An embodiment of the present invention will be specifically described below with reference to the drawings. Embodiment 1 FIG. 1 is a block diagram of a first embodiment of the present invention. In this embodiment, multi-stage black generation control is performed. The apparatus shown in FIG. 1 is roughly composed of two parts, that is, an image reproducing unit and a black edge amount calculating unit. In accordance with the output (3 bits in this embodiment) from the black edge amount calculating unit, the apparatus shown in FIG. Change the amount of production. This makes it possible to suppress a sudden change in the UCR rate in an image. Hereinafter, the configuration of the embodiment will be described in detail. In the image reproducing section, the scanner 1
It has a photoelectric conversion element such as a D camera, reads an original (not shown), outputs three color separation signals of red, green, and blue, and A / D converts the r, g, b digital signals of the color separation signals Output a signal (8 bits). The Log conversion circuit 2 includes a table for converting the characteristics of the signal from the reflectance space to the density space, and the signals C ′, M ′,
Y ′ is output. The color correction circuit 3 removes the turbid component of the color separation filter in the scanner 1 and the turbid component of the ink. Generally, color correction is performed by a masking method, a memory map method (also referred to as an interpolation method), and the like. In the present embodiment, the former masking method will be described. The masking is performed by, for example, the following equation (1). C = k11 × C ′ + k12 × M ′ + k13 × Y ′ + k14 M = k21 × C ′ + k22 × M ′ + k23 × Y ′ + k24 Y = k31 × C ′ + k32 × M ′ + k33 × Y ′ + k34. . . Equation (1) Here, k11 to k34 are constants, and are determined based on experiments. Generally, in a color image processing apparatus such as a color copying machine, a black generation circuit 4 is provided, and a part of C, M, and Y after the above masking is replaced with K (black ink). That is, min (C,
M, Y) is calculated, and a black signal is generated using this as a black signal, and the added K is subtracted from C, M, and Y. As described above, the amount of 100% of min (C, M, Y) is changed to C,
100% UCR processing to reduce each from M and Y, and instead generate a considerable amount of K, and min (C, M, Y)
50% of C, M, and Y respectively reduced from C,
50 that generates M, Y and K corresponding to the reduced amount.
There is a% UCR process. As a result, effects such as reducing the ink consumption, expanding the reproduction range of the dark part in terms of image quality, and improving the tightness of the picture can be obtained. In the present embodiment, the generation of black (black ink) is controlled according to equation (2). K = α × min (C, M, Y) Equation (2) Here, α (%) changes according to an output n (3 bits) from a black edge amount calculation unit described later. The correspondence between the output n and α is constituted by a table, and FIG. 2 is a diagram showing an example thereof. The black amount K changes in eight stages according to the output n from the black edge amount calculation unit. When n is 0, α becomes 50%, and n
Is 7, when α becomes 100%, the rate of α, that is, the black amount K changes stepwise during that time. The subtraction circuit (UCR circuit) 5 calculates C ", M", Y "(printer launch signal) after inking according to the equation (3). C" = CKM "= M- KY "= Y-K (3) For the sake of simplicity, the color printer 6 is assumed to be a color printer capable of outputting 256 gradations per dot in this embodiment. In the case of a color printer having a gradation lower than this, gradation processing is performed by multi-value dither processing or multi-value error diffusion processing. The black edge amount calculation section 7 includes a blackness calculation circuit 8 and an edge amount calculation circuit 9. The blackness calculation circuit 8 is a circuit that calculates how close the target pixel is to black. 3 and 4 show the configuration of the blackness calculation circuit 8 according to two embodiments. The blackness calculation circuit 8 shown in FIG. 3 calculates the maximum value s of the linear reflectance image data from the scanner 1.
This is equivalent to calculating the minimum value after converting the linear reflectance data into linear density data by the Log conversion circuit. The output blackness is an integer from 0 to 255. The blackness calculating circuit 8 shown in FIG. 4 calculates the maximum value s of the linear reflectance image data. Further, the data r, g, and b from the scanner 1 are calculated by the following equation (4). The calculation shown by is performed by the calculation circuit. That is, p = max (| r−g |, | g−b |, | br |) Expression (4) Then, after calculating p + s, the blackness is output. The output blackness is an integer from 0 to 255 (however, 0
Less than 0 and 256 or more 255). The edge amount calculation circuit 9 is a circuit for determining the edge amount of the pixel of interest. That is, in the 3 × 3 mask, matching is performed for the four patterns shown in FIG. 5 to calculate the edge amount n. That is, Th1> T
When h2> 0, if (all pixels xi> Th1) then n1 = 2 else if (all pixels xi> Th2) then n1 = 1 else then n1 = 0. The density level of the pixel of interest is L, the pixel A is
When the density level of A is A, the contrast is LA
It becomes. Tha>Thb>Thc>Thd>The> 0
Then, if (LA> Tha) then n2 = 5 else if (LA> Thb) then n2 = 4 else if (LA> Thc) then n2 = 3 else if (LA> Thd) ) Then n2 = 2 else if (LA> Then) then n2 = 1 else then n2 = 0 is calculated. The edge amount calculation circuit 9 adds the calculated n1 and n2 (the edge amount n = n1 + n).
2) The maximum value among n of the four patterns is set as the edge amount n (0 ≦ n ≦ 7) of the target pixel. The edge amount is
It can also be calculated by using a mask operation such as a first derivative (a), (b), or a second derivative (c) as shown in FIG. In this case, the relationship between n and α as shown in FIG. 2 is set again by experiments or the like, but it is necessary to include a condition in which α increases as n increases. Since the first embodiment is configured as described above, the black generation circuit 4 corresponds to n with reference to the table of FIG. 2 according to the detected black edge amount (black character degree) n. Then, a black amount K is generated by calculating α, and a stepwise UCR process is performed. Second Embodiment FIG. 7 shows a configuration of a second embodiment in which multi-stage black generation control and multi-stage C, M, Y erase processing are performed. In the second embodiment, in addition to the reduction of the abrupt change in the UCR rate of the first embodiment, the following effect can be obtained. That is, the image quality is improved when black characters are reproduced in a single black color. However, if a black single color portion exists in a picture due to erroneous separation, the black characters are conspicuous as if they are mismatched with the surroundings, causing deterioration in image quality. Therefore, in the present embodiment, even when a black monochrome region is formed, the above-described deterioration in image quality is avoided by performing the processing stepwise. For this purpose, in this embodiment, a division amount calculating circuit 10 and a dividing circuit 11 are provided in addition to the configuration of the first embodiment. C ″, after the subtraction according to the above equation (3),
The division circuit 11 divides the M ″ and Y ″ signals. The division amount calculation circuit 10 changes the division amount (β) in the division circuit 11 according to the output n (3 bits) from the black edge amount calculation unit 7. The correspondence between the output n and β is constituted by a table, and FIG. 8 shows an example thereof. Note that if n is equal to or more than a predetermined value (for example, 6), it is effective to forcibly set the C ", M", and Y "signals to 0. <Embodiment 3> FIG. 3 shows the configuration of the third embodiment, which performs black generation control and multi-stage C, M, Y erase processing.
Since it is effective to perform the erasing process on black characters on a white background (that is, it is not necessary to perform the C, M, and Y erasing processes on other characters), in the third embodiment, in the third embodiment, Is calculated, and this white background amount is used as information for the CMY erase process. For this reason, in this embodiment, in addition to the configuration of the second embodiment, a white pixel detection circuit 13 and a white background amount calculation circuit 14
Is provided. The white pixel detection circuit 13 is a circuit that determines whether a target pixel is a white pixel. FIG. 10 shows an example of the white pixel detection circuit 13, in which the minimum value of linear reflectance data from the scanner is calculated (this is equivalent to calculating the maximum value for linear density data). The output value q (0 to 255) is binarized at a predetermined threshold th. That is, if q> th, an ON signal representing a white pixel is output. The white background amount calculation circuit 14 is a circuit for calculating how many white pixels exist around the target pixel (the output value is m). For example, as shown in FIG. 11, the number of white pixels after binarization is counted on both sides of the target pixel,
The amount of white background is determined according to the number. Then, as shown in FIG. 11, the amount of white background m corresponding to the number of white pixels is output in multiple stages (real number output of [0, 1]) by using a table,
Alternatively, as shown in (2), it is also possible to output a white background amount m according to the number of white pixels in binary. In this embodiment, in order to simplify the description, the white background amount m is output as a binary output. The division amount calculation circuit 10 performs an AND operation on the above-described black edge amount n and white background amount m, and outputs a division amount β in accordance with the table shown in FIG. As shown in FIG. 11, when the white background amount m is a multi-step output, for example, a value obtained by multiplying n and m is input to the division amount calculation circuit 10, and the division amount β is determined according to the multiplied value. You may make it output. As described above, according to the present invention,
Then, the following effects can be obtained. (1) Since the black edge amount of the pixel of interest in the image is calculated and the amount of black generation is controlled in multiple stages according to the black edge amount,
An abrupt change in the UCR rate is reduced, and in particular, an abrupt change in the UCR rate in a picture is reduced, thereby enabling high-quality image reproduction. (2) The black edge amount of the pixel of interest in the image is calculated, and the black generation amount and the C, M, and Y erasure amounts are controlled in multiple stages according to the black edge amount. Even if there is a black single-color part in the picture, the black single-color area is processed step by step, so the black single-color part in the picture stands out as if it were raised, eliminating image quality degradation and enabling high-quality image reproduction Become. (3) The amount of black edge of the pixel of interest in the image and the amount of white background near the pixel of interest are calculated, and the amount of black generation and the amount of erasure of C, M, and Y are increased according to the amount of black edge and the amount of white background. Since the control is performed in stages, the black character on the white background is subjected to a single-color, high-resolution reproduction process, so that a high-quality image can be reproduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a first embodiment of the present invention. FIG. 2 is a table storing correspondence between black edge amounts n and α. FIG. 3 is a configuration of a first embodiment of a blackness calculation circuit. FIG. 4 is a configuration of a second embodiment of a blackness calculation circuit. FIG. 5 is a pattern for detecting an edge amount. FIGS. 6A, 6B, and 6C show examples of masks for detecting an edge amount. FIG. 7 is a block diagram of a second embodiment of the present invention. FIG. 8 is a table in which the correspondence between the black edge amount n and the division amount β is stored. FIG. 9 is a block diagram of a third embodiment of the present invention. FIG. 10 is a diagram illustrating an example of a white pixel detection circuit. FIG. 11 is a diagram illustrating calculation of a white background amount. FIG. 12 is a table storing correspondences between a black edge amount n, a white background amount m, and a division amount β. [Description of Signs] 1 Scanner 2 Log conversion circuit 3 Color correction circuit 4 Black generation circuit 5 Subtraction circuit 6 Color printer 7 Black edge amount calculation unit 8 Blackness calculation circuit 9 Edge amount calculation circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/46 H04N 1/40

Claims (1)

(57) [Claims 1] An original is read out as r, g, b digital image signals, and recording signals C, M,
In a digital color image processing apparatus for generating Y and K and printing digitally, the r, g and b signals
Alternatively, calculate the black edge amount of the target pixel from the C, M, and Y signals
And the r, g, b signal or the C, M, Y signal
Means for calculating the amount of white background around the pixel of interest from
The r, g, b signals or
Means for outputting a multi-stage K signal from the C, M, and Y signals;
The K signal is subtracted from the C, M, and Y signals,
Means for outputting C ', M', Y 'signals;
After the subtraction, the divided amount corresponding to the black edge amount and the white background amount
Means for dividing the C ', M', and Y 'signals .