JPH05260293A - Color converting circuit - Google Patents

Abstract

PURPOSE:To provide a color converting circuit where color conversion is processed in accordance with an individual document without collectively color- converting a ground part when excessively thin color in an area except the ground part of the color document is designated as color to be converted. CONSTITUTION:The histogram of the document is generated from color picture data of a Magenta, which is read at the time of scanning so as to be inputted to an input terminal 2 for M by a histogram generating circuit 34 under control from CPU 7, the ground part of the document is judged from the generation histogram by CPU 7 and density (multilevel) in the border of the ground part is read so as to be used as a lower-limit limiting value limiting the lower-limit value of a conversion range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color conversion circuit used in an image forming apparatus such as an electronic copying machine.

[0002]

2. Description of the Related Art Conventionally, for example, in a digital color electronic copying machine as an image forming apparatus, a color on a color original designated by a user (that is, a conversion target color) is changed to another color desired by the user (that is, a conversion color). ), And has a color conversion function that can be copied (copied). Specifically, each of the three colors of yellow, magenta, and cyan obtained by reading a color original to be copied with a color scanner. When performing predetermined signal processing on the image data in the image processing circuit unit, the image data of each color of the conversion target color is converted from the image data of each color input by the color conversion circuit in the image processing circuit unit. After the data is converted and output to a laser scanner unit for forming a latent image in the subsequent stage, a color-converted color image is formed.

[0003]

By the way, the conversion of each color image data in such a color conversion circuit can be performed in accordance with the variation of each color image data of the conversion target color caused by the reading variation of the color scanner or the like. In this manner, that is, in order to ensure that the designated color conversion processing is performed, it is considered to perform conversion with a predetermined width (that is, conversion range). However, in such a color conversion method, when the density on the color original is extremely low as the color to be converted, that is, when the color close to the density of the background portion of the original is specified, the specified color is set depending on the setting of the conversion range. Besides, even the background portion of the document may be erroneously subjected to the conversion process as the conversion target color. For example, if you specify a light pink with a density close to the background part of the document (generally white or light gray achromatic color) as the conversion target color, the background part of the document other than the pink specified by the setting of the conversion range There is also a risk that the color conversion processing will be performed together as the conversion target color.

The present invention has been made in view of such a point. When an extremely light color is designated as a conversion target color in a region other than the background portion of the document, the background portion is also colored. It is an object of the present invention to provide a color conversion circuit adapted to perform color conversion processing according to an individual document so as not to perform conversion.

[0005]

In order to achieve the above-mentioned object, according to the present invention, the color image data of the conversion target color is converted from the input color image data into the color image data of the converted color, and the color is output. In the conversion circuit, a histogram creating means for creating a histogram from the input color image data, and when setting the conversion range of the color image data, the lower limit value of the conversion range does not fall below a predetermined value set based on the histogram. A limiting means for limiting the above is provided. Specifically, the histogram creating means creates a histogram from color image data of any one of yellow, magenta, and cyan that is read and input during prescan, and the limiting means is a conversion that is read during prescan. Calculation means for calculating the average value of each color image data of yellow, magenta, and cyan of the target color, and addition and subtraction of a predetermined set value to each of the average values of yellow, magenta, and cyan calculated by this calculation means. Setting means for setting the upper and lower limits of the conversion range, and the respective lower limit values set by subtraction by the setting means are equal to or less than the predetermined lower limit value set based on the histogram. It comprises a lower limit limiting means for determining whether or not and setting the lower limit limit value as the lower limit value when the value is less than that. It is those containing a micro-computer for image processing.

[0006]

With this configuration, when setting the conversion range of the color image data, the lower limit limit value for limiting the conversion range not to include the background portion of the document is set based on the histogram of the document. As a result, the conversion range is restricted according to the background portion of each original.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A color conversion circuit in a digital color electronic copying machine as an embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numerals 1, 2, and 3 denote image data (digital data) of three colors of yellow (Y), magenta (M), and cyan (C) obtained by reading a color original to be copied with a color scanner. Each is input with an 8-bit structure (256 gradations), that is, color image data in the form of the three primary colors (R, G, B) of light obtained from a color scanner is converted into image data of yellow, magenta, and cyan representing toner density. After that, the Y, M, and C input terminals 4, 5 and 6 are read during the pre-scan performed before the copy scan and input to the Y, M and C input terminals 1, 2 and 3, respectively. Y, M, and C memories for storing the respective color image data of the conversion target colors, and 7 is a microcomputer used for image processing in the image processing circuit section (hereinafter referred to as “CPU”). ), The CPU 7 calculates the average value of the yellow, magenta, and cyan color image data of the conversion target colors stored in the Y, M, and C memories 4, 5, and 6 respectively, and then calculates the calculated yellow and magenta. , The average value of cyan is added and subtracted with a predetermined set value to set the upper and lower limit values of the conversion range, respectively, and the lower limit value set by subtracting at that time is the predetermined lower limit value. It is determined whether or not it is below, and if it is less than that, the lower limit value is set as the lower limit value in the Y, M, C upper limit and lower limit setting units described later. Specifically, the conversion target color is designed to be read at the time of prescan by the user by designating one point of any color on the color original on the tablet. For example, the conversion target color is designated as the conversion target color at the time of prescan. Image data for each color of 1 mm square on the manuscript (where 16 dots (pixels) / m
If m, 256 dots of each color image data) are read and stored in the Y, M, and C memories 4, 5, and 6 (in this case, each memory capacity is 256 bytes), and then the stored conversion target is stored. The average values A1, A2 and A3 of the respective color image data of yellow, magenta and cyan are expressed by the following equation: A1 = (sum of 256 color image data of yellow) / 256 A2 = (magenta of 256 dots) (Sum of color image data) / 256 A3 = (sum of 256 color image data of cyan)
It is designed to be calculated at / 256. For example, the average values of the color image data of the three colors of magenta, cyan, and yellow in the conversion target color region read and calculated during the prescan are “tone 35, tone 20, and tone 200”, respectively. The set value for addition and subtraction from the average value “gradation 35, gradation 20, gradation 200” is gradation 20, and the lower limit value of each color image data is “gradation 20, gradation 20, gradation 20”, respectively. In this case, the upper limit and the lower limit of the conversion range obtained by addition and subtraction by the CPU 7 are the upper limit “tone 55, tone 40, tone 220” and the lower limit “tone 15, tone 0, tone”, respectively. 180 "
Therefore, the lower limit value of yellow (gradation 180) is larger than the lower limit value (gradation 20) and is set as it is, and the lower limit value of magenta and cyan (gradation 15, 0) is set to the lower limit value (gradation 20). ) Or less, the lower limit value (gradation 20) is set as each lower limit value. Here, the lower limit value is set on the basis of the histogram so that the color conversion does not reach the background portion of the document (in this case, gradation 20). That is, under the control of the CPU 7, the histogram creation circuit 45 creates a histogram (density distribution table) from the magenta color image data read during the prescan and input to the M input terminal 2, and the created histogram is created. From the CPU 7, the density (gradation) of the boundary of the background portion is read out by the CPU 7 as a portion where the number of data (the number of pixels) exceeds the determination threshold of the background is the background portion, and is used as the lower limit value. Become. For example,
As shown in FIG. 3, the magenta color image data of the entire document or a predetermined area read and input during the pre-scan is distributed by 25 to 20 gradations under the control of the CPU 7 at intervals of 25 gradations. If such a histogram is obtained, it is assumed that the portion having a larger amount of data than the determination threshold value X of the background is the background portion, and the density of the boundary of the background portion (in this case, gradation 50) is read and used as the lower limit value. become. 8 is a memory (for example, a program ROM) in which a control program of the CPU 7 is stored,
9A, 10A, 11A and 9B, 10B, 11B are Y, M, and C for which the upper and lower limits of the conversion range of each color image data of yellow, magenta, and cyan are set by the CPU 7.
Upper and lower limit setting units (for example, 8-bit input / output registers), 12, 13, and 14 are Y, M, and C conversion color setting units in which image data of respective conversion colors desired by the user are set by the CPU 7. , These setting units 9A, 9B, 10A,
The setting of each data in 10B, 11A, 11B and 12, 13, 14 is performed between the prescan and the copy scan under the control of the CPU 7.
The conversion colors include standard colors preset in the copying machine, registered colors set by the user, and designated colors designated by the user on the color original document. It is stored in the memory (not shown) for the controlled conversion color. 15, 16, and 17 are read at the time of the copy scan after the prescan, and Y,
The upper limit and lower limit of the yellow, magenta, and cyan color image data input to the M, C input terminals 1, 2, and 3 are set in the upper limit and lower limit setting sections 9A, 9B, 10A, 10B, 11A, and 11B. Y, M, C comparators for comparing the respective values with the respective comparators 15, 16, 17 for the upper limit of each color image data input from the Y, M, C input terminals 1, 2, 3 respectively. The color image data located within the conversion range defined by the lower limit value is, that is, Y lower limit value ≦ Y color image data ≦ Y upper limit value, M lower limit value ≦ M color image data ≦ M upper limit value, C
Each of the image data that satisfies the three conditions of color image data for lower limit value ≤ C ≤ upper limit value for C is output as an H level control signal as color image data of the conversion target color. The respective control signals are applied to the Y, M, and C selectors described later through the AND circuit 18. 19, 20, 21 are Y based on each control signal,
Image data of each color input from the M, C input terminals 1, 2, 3 or Y, M, C conversion color setting units 12, 13, 14
The selectors for Y, M and C which selectively output any of the color image data set to
21 is Y, only when an H level control signal is input.
Instead of the color image data from the M, C input terminals 1, 2, 3 the color image data from the Y, M, C conversion color setting sections 12, 13, 14 are output to the Y, M, C output terminals 22, 23, 2
It is designed to output to 4 and output terminals 22 and 2
The color image data output from the reference numerals 3 and 24 are supplied to the laser scanner unit in the subsequent stage after being subjected to signal processing such as generation of black color image data and data correction.

Therefore, when the user selects the color conversion mode and designates the color to be converted and the color to be converted on the color original and then operates the copy button, a prescan is first carried out for Y, M and C. After reading the image data of each color of yellow, magenta, and cyan of the conversion target colors designated by the memories 4, 5, 6 and the CPU 7 and calculating their respective average values, the conversion range is calculated from the respective calculated average values. The upper and lower limits are calculated respectively, and the Y, M, and C upper and lower limit setting units 9 are calculated.
A, 9B, 10A, 10B, 11A, 11B are set, and the conversion color setting units 12, 13, 1 for Y, M, C color image data of conversion colors yellow, magenta, and cyan are set.
4 will be set. Then, during the copy scan after the prescan, the Y, M, and C comparators 15, 16, 1
Comparing detection of each color image data of conversion target color by 7,
Output selection by the Y, M, C selectors 19, 20, 21 is performed, and color images within the conversion range are selected from the respective color image data input to the Y, M, C input terminals 1, 2, 3. Assuming that the data is the color image data of the conversion target color, it is converted into each color image data of the conversion color and output.

Next, the control operation for setting the upper and lower limits by the CPU will be described with reference to the flowchart of FIG. FIG. 2 is a flowchart showing a case in which the lower limit value set by subtraction is limited to the lower limit value set based on the histogram regardless of whether the conversion target color is a chromatic color or an achromatic color, First, prescan in the color conversion mode is performed, and the average value of each color image data of yellow, magenta, and cyan of the conversion target colors stored in the Y, M, and C memories 4, 5, and 6 is calculated. , Step #
The upper limit of the conversion range by adding / subtracting a predetermined set value to / from each of the average values of yellow, magenta, and cyan calculated in 5
Find the lower limit. Then, in step # 10, it is determined whether each lower limit value obtained by the subtraction is equal to or less than a predetermined lower limit value set based on the histogram. In the following case, the lower limit value is set as the lower limit value. If it is not below, the lower limit value subtracted is used as it is. Then, the procedure proceeds to step # 15, where the upper and lower limits obtained are Y, M, and C.
Upper and lower limit setting parts 9A, 9B, 10A, 10B, 11
The control operation is ended by setting A and 11B.

FIG. 4 is a schematic view of a digital color electronic copying machine having such a color conversion function. The color original 27 placed on the contact glass 25 so as to be pressed by the original presser 26 is a color scanner section. Is pre-scanned and then copy-scanned by the scanning optical system 28, and image information thereof is guided from a condenser lens 29 to a light-receiving element 30 such as a CCD using light as a medium, where it is converted into an electric signal and then color conversion The image processing circuit unit 31 including a circuit performs signal conversion necessary for color conversion processing and other image processing such as generation of black color image data, and thereafter, a latent image is formed on the photosensitive drum 33 by the laser scanner unit 32. Depicted as. Prior to this, the surface of the photosensitive drum 33 is charged by the main charger 34. When forming a color image, first, a latent image is formed on the photosensitive drum 33 by a laser beam based on the yellow color image data that has been subjected to signal processing such as color conversion, and the latent image is formed by the Y developing device. 35 to develop. The Y developing device 35 has yellow toner and develops the latent image on the photoconductor drum 33 with this yellow toner. Then, the image developed on the photoconductor drum 33 with the yellow toner is transferred onto the paper wound around the surface of the transfer drum 36. This paper is supplied from the paper feed cassette 37 or 38 through the paper feed path. Then, this paper is directly transferred onto the transfer drum 36.
It is mounted on the surface and used for image transfer of the next color. That is,
The photoconductor drum 33 is wiped of residual toner by a cleaning unit 39 and discharged by a charge eliminating unit (not shown), then charged again by the main charger 34, and this time magenta subjected to signal processing such as color conversion. The latent image corresponding to the magenta image on the photoconductor drum 33 formed by the laser beam that performs the latent image writing operation based on the color image data is developed by the M developing device 40. At this time, the M latent image portion 40 is brought to a position facing the photoconductor drum 33 instead of the Y developing portion 35, and is developed with magenta toner. In this embodiment, the developing device is a Y developing device 35 for developing yellow, an M developing device 40 for developing magenta, a C developing device 41 for developing cyan, and a BK developing device 42 for developing black. Is sequentially mounted on the moving body 43 that moves in the vertical direction as described above, and the developing position (the position facing the photoconductor drum 33) is alternatively selected corresponding to the color image data of the latent image writing by the laser beam. ) Is being brought to. Now, the image developed on the photosensitive drum 33 with the magenta toner is transferred onto the paper on the surface of the transfer drum 36 (the paper on which the yellow image has been previously transferred and formed). In the same manner, cyan and black images are further transferred onto the paper, and a color image subjected to color conversion processing is formed. After that, the sheet on which the color image is formed is separated from the transfer drum 36, fixed by the fixing unit 44, and then discharged from the electronic copying machine.

As described above, in the present embodiment, the case where the color conversion processing is performed in the state of the color image data of the three colors of yellow, magenta and cyan before the generation of the black color image data has been described. Color conversion processing may be performed after the generation. Further, the lower limit value set based on the histogram is set to the gradation 20.
However, the present invention is not limited to this, and the lower limit value may be finely adjusted by the user according to the copy state. Further, in the present embodiment, the histogram is created from the magenta color image data, but the histogram may be created from the yellow or cyan color image data, and the lower limit value obtained from the magenta histogram can be set. Although the lower limit limit values for yellow and cyan are used, the lower limit limit values obtained from the respective histograms may be used by creating histograms for magenta, yellow, and cyan, respectively.

[0012]

As described above, according to the color conversion circuit of the present invention, when the conversion range of color image data is set, the lower limit of the conversion range is restricted so as not to fall below a predetermined value. When an extremely light color is designated as a conversion target color in a region other than the background part, the desired color conversion can be performed without performing the color conversion on the background part. Further, since the predetermined value used for the lower limit of the conversion range is set based on the histogram, when it is applied to a color electronic copying machine, for example, it corresponds to the histogram of each color original, that is, each color The lower limit value matching with the background portion of the document can be performed, and the color conversion process without erroneous conversion can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a color conversion circuit for realizing the present invention.

FIG. 2 is a flowchart for explaining the control operation.

FIG. 3 is a diagram showing an example of creating the histogram.

FIG. 4 is a schematic diagram of a digital color electronic copying machine embodying the present invention.

[Explanation of symbols]

7 CPU 8 memory 9A, 9B, 10A, 10B, 11A, 11B Y,
M, C upper / lower limit setting unit 12, 13, 14 Y, M, C conversion color setting unit 15, 16, 17 Y, M, C comparator 19, 20, 21 Y, M, C selector 45 Histogram creation circuit

Claims (4)

[Claims] 1. A color conversion circuit for converting color image data of a color to be converted from input color image data into color image data of a converted color and outputting the color image data, and creating a histogram from the input color image data. Histogram creation means,
A color conversion circuit, comprising: a limiter for limiting the lower limit of the conversion range of the color image data so that the lower limit of the conversion range does not fall below a predetermined value set based on the histogram. 2. The histogram creating means is configured to read yellow, magenta, and
The color conversion circuit according to claim 1, wherein a histogram is created from any one of the color image data of cyan. 3. The limiting means is a calculating means for calculating an average value of each color image data of yellow, magenta, and cyan of conversion target colors read at the time of prescan, and yellow calculated by the calculating means. , Magenta,
Setting means for adding and subtracting a predetermined set value to each average value of cyan to set an upper limit and a lower limit of the conversion range, respectively.
It is determined whether or not each lower limit value set by subtraction by the setting means is less than or equal to a predetermined lower limit value set based on the histogram, and when it is less than that, the lower limit value is set as the lower limit value. The color conversion circuit according to claim 1, further comprising: a lower limit limiting unit for performing the above. 4. The color conversion circuit according to claim 3, wherein each of the means includes a microcomputer used for image processing in an image processing circuit section.