JP2650239B2 - Color image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method of replacing yellow, magenta, cyan and black by replacing a portion where three color image data of yellow, magenta and cyan overlap with each other with black color image data. The present invention relates to a color image forming apparatus which forms a color image in color.

[0002]

2. Description of the Related Art Conventionally, in a digital color electronic copying machine as a color image forming apparatus, in order to improve the reproducibility of black color of a color original to be copied read by a color scanner, yellow, Rather than superimposing the toners of the three colors magenta and cyan to reproduce the black color (that is, the result is a pale black with a blue tint), the toner overlaps the toners of the three colors. Is replaced with a black toner, that is, a color image is formed using four color toners.

More specifically, a yellow document obtained by reading a color original to be copied with a color scanner,
The portion where the three color image data of magenta and cyan overlap is replaced with the color image data of black, that is, the data of the three color image data of yellow, magenta and cyan is replaced for each pixel. The data values are compared and the minimum data value is taken out as black color image data, and the three color values of yellow, magenta and cyan are obtained by the data value of the black color image data. The color image data of the color is subjected to a subtraction process (removal of a lower color component) to generate three color image data of yellow, magenta, and cyan of the pixel, and based on each of the color image data. The amount of toner of four colors is determined for each pixel, and the color is determined.
An image was formed.

[0004]

However, if the black color image data is subtracted from yellow, magenta, and cyan as a lower color component as it is, the subtraction is too large and the color reproducibility deteriorates (especially. The problem is that black is too effective in the light-colored portion). Further, in a case where predetermined color correction processing is further performed on the yellow, magenta, and cyan color image data from which the undercolor component has been removed, if the undercolor component to be subtracted is too large, the color is reduced accordingly. Since the color image data input to the correction circuit is small, an error in color correction particularly in light colors (colors in which the color image data is originally small) is likely to occur, and the color reproducibility is further deteriorated.

An object of the present invention is to provide a novel image forming apparatus which can solve such a problem simply.

In order to achieve the above object, according to the present invention, a portion where three color image data of yellow, magenta and cyan overlap is replaced with black color image data, and The yellow, magenta, and cyan color image data are obtained by subtracting the overlapping portions from the color image data.
Magenta, cyan, and 4 of the replaced black
In a color image forming apparatus configured to form a color image with color image data of colors, the yellow, magenta,
A means for reducing the data value of the overlapping portion to be subtracted from the cyan color image data is made smaller than the black color image data.

[0006]

According to this structure, since the undercolor component subjected to the undercolor removal processing is smaller than the black color image data actually used as the black component, each of the yellow, magenta and cyan color image data is processed. The ink will remain as large as that amount, and the effect of black in light-colored portions will be prevented. Further, in the case of performing color correction on the yellow, magenta, and cyan color image data after removing the undercolor, errors in color correction hardly occur.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to a digital color.
The electronic copying machine will be described with reference to the drawings. FIG. 1 shows four color image data of yellow, magenta, cyan and black.
1 shows a data generation circuit block for generating data;
Is input with color image data Y, M and C of three colors of yellow, magenta and cyan obtained by reading a color original to be copied by a color scanner in an 8-bit configuration (256 gradations). The input terminal unit 2 compares the data values of the three color image data of yellow, magenta and cyan inputted for each pixel and compares the data values with the minimum data value (Min).
(Y, M, C)) is a minimum data value selection circuit that takes out (ie, replaces) it in an 8-bit configuration, and outputs a FIFO (fast-first data) as black color image data BK.
The data is output from the data generation circuit block via the (in-first-out) memory 5. In the subsequent circuit, the toner amount of black is determined based on the black image data BKout.

Reference numeral 3 denotes a conversion circuit having input / output characteristics as shown in FIG. 2. The black color image data BK output from the minimum data value selection circuit 2 is converted by the conversion circuit 3.
Black data BK 'whose tone is kept low by
Is supplied to the subtractor 4 at the next stage. The conversion circuit 3
Is a RAM for converting data values by a look-up table method
It consists of. The subtractor 4 receives the yellow, magenta, and cyan color image data Y, M,
The output BK ′ of the conversion circuit 3 is subtracted from C (under color component removal). The three color image data subjected to the subtraction processing by the subtracter 4 is output from the data generation circuit block via the FIFO memory 5. These three color image data Yo
Based on ut, Mout, and Cout, the toner amounts of the three colors yellow, magenta, and cyan are determined.

Next, in the embodiment of FIG. 3, a RAM 6 is connected after the minimum data value selection circuit 2. The RAM 6 converts the black color image data BK taken out from the minimum data value selection circuit 2 into a look-up table system based on conversion characteristics as shown in FIG. 4 corresponding to the data values. A RAM for converting data values, and a RAM 6 for converting data corresponding to the data value of the black color image data BK input from the minimum data value selection circuit 2 based on the conversion characteristics; The data values are stored in a look-up table format and the minimum data
When black color image data is input from the data value selection circuit 2, the CPU is controlled to output a conversion data value corresponding to the data value in an 8-bit configuration.

Due to the presence of the RAM 6, in the embodiment shown in FIG. 3, the minimum data values of the input three color image data of yellow, magenta and cyan are small, and the minimum data value selection circuit 2 If the data value of the black color image data BK outputted from the RAM becomes smaller than the gradation 65, the RAM
3 is converted to 0 data value and no black color image data is generated, and the input three color image data of yellow, magenta and cyan are directly inputted from the subtractor 4 to the FIFO memory 5. And the black color is reproduced by the three color image data Y, M and C.

The minimum data value of the input three color image data of yellow, magenta and cyan is large, and the black color image data output from the minimum data value selection circuit 2 is large. If the data value of the data BK is equal to or higher than the gradation 65 and the data value is increased to a certain degree or more, the RAM
6, the data is converted into large data values, and yellow, magenta,
From cyan color image data to black color image data
The rate at which the data BK1 is generated increases, and the black color image data BK1 reproduces the black color. This is similarly performed in the case where the data values of the input three color image data are the same and complete black color reproduction is performed.

On the other hand, the lower color component BK supplied to the subtractor 4
Reference numeral 1 'denotes a RAM by a conversion circuit 3 having a characteristic as shown in FIG. 5 (the conversion circuit 3 is constituted by a RAM, for example).
The output of the subtractor 4 is further reduced as a whole
Led to. Therefore, also in this case, the amount of subtraction is as small as possible, and the same effect as in FIG. 1 is produced.

In FIG. 3, for example, in the case of a light color original having a small data value of three color image data of yellow, magenta and cyan, a black color appears. In this case, the black color is reproduced by the three color image data so that the color image data of the three color image data has a large data value. Thus, the black color is reproduced by the black color image data BK1 in which the high gradation portion is emphasized so that the black color is clearly displayed.

Next, in the embodiment shown in FIG. 6, the output BK 'of the conversion circuit 3 (composed of a RAM) having the conversion characteristics shown in FIG. 2 is also used as black color image data. The output BK 'of the circuit 3 is passed through a relative luminous efficiency correction circuit 7 having characteristics as shown in FIG. That is, when the black color image data is reduced by the conversion circuit 3 so as not to remove the undercolor excessively, if the black color image data is used as it is, the portion that should become the original black has sufficient black. Therefore, the relative visibility correction circuit 7 is used to correct this. It should be noted that the relative luminosity correction circuit 7 is also formed of, for example, a RAM, like the conversion circuit 3.

As clearly shown in the above three embodiments, in the present invention, the black color image data used for removing the undercolor is made smaller than the black color image data. I have.

FIG. 8 is a schematic diagram of a digital color electronic copying machine having a circuit block for generating color image data of four colors as in each of the above embodiments. The color original placed so as to be pressed is scanned by a scanning optical system constituting a color scanner, and the image information is guided from a condenser lens 10 to a light receiving element 11 such as a CCD using light as a medium. After being converted into an electric signal, the image signal is subjected to signal processing in the image processing circuit 12, and thereafter, the laser-scanner unit 13
Is drawn as a latent image on the photosensitive drum 14. Prior to this, the surface of the photosensitive drum 14 is charged by the main charger.

When a color image is formed, a latent image is first formed on the photosensitive drum 14 by a laser beam based on yellow color image data, and the latent image is formed into a Y image. The image is developed by the developing device 15. The Y developing device 15 has a yellow toner, and forms a latent image on the photosensitive drum 14 in yellow.
Is developed with an amount of yellow toner determined based on the color image data. The image on the photosensitive drum 14 developed and formed by the yellow toner is transferred to the transfer drum 16.
The image is transferred to a sheet wound around the surface.

This sheet is mounted on the surface of the transfer drum 16 as it is, and is subjected to the next transfer. That is, the photosensitive drum 1
Reference numeral 4 denotes a main charger again after the residual toner is wiped off by the cleaning unit and the charge is removed by the charge removing unit (not shown).
The latent image corresponding to the magenta image on the photosensitive drum 14 formed by the laser beam which is charged by the jaw and performs a latent image writing operation based on the magenta color image data is M The image is developed by the developing device 17. At this time, the M developing unit 17 is brought to a position facing the photosensitive drum 14 in place of the Y developing unit 15, and an amount of magenta toner determined based on magenta color image data.
Will be developed.

In this embodiment, the developing units are a Y developing unit 15 for developing yellow, an M developing unit 17 for developing magenta, a C developing unit 18 for developing cyan, and a BK developing unit for developing black. A device 19 is vertically mounted on a moving body 20 which moves in the vertical direction as shown in the figure, and is selectively provided in correspondence with color image data for writing a latent image by a laser beam. The toner is brought to a developing position (a position facing the photosensitive drum 14), and is developed with an amount of toner determined based on each color image data.

The image on the photosensitive drum 14 developed with the magenta toner is transferred to a sheet on the surface of the transfer drum 16 (a sheet on which a yellow image has been previously formed). In the same manner, cyan and black images are further transferred to the sheet, and a full color image is formed. Thereafter, the sheet on which the color image is formed is separated from the transfer drum 16 and is fixed by a fixing unit, and then discharged from the electronic copying machine.

[0021]

As described above, according to the present invention, since the undercolor component subjected to the undercolor removal processing is smaller than the black color image data actually used as the black component, yellow, magenta, and cyan are used. The image data of each color remains large by that amount, so that black is not excessively effective in a light color portion. Further, in the case of performing color correction on the yellow, magenta, and cyan color image data after removing the under color, an effect that an error in color correction hardly occurs can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a digital color copying machine embodying the present invention.

FIG. 2 is a partial characteristic diagram thereof.

FIG. 3 is a main part block diagram of another embodiment of the present invention.

FIG. 4 is a partial characteristic diagram thereof.

FIG. 5 is another characteristic view of the same.

FIG. 6 is a main part block diagram of still another embodiment of the present invention.

FIG. 7 is a partial characteristic diagram thereof.

FIG. 8 is a schematic view of a digital color copying machine embodying the present invention.

[Explanation of symbols]

 Reference Signs List 1 input terminal section 2 minimum data value selection circuit 3 conversion circuit 4 subtracter 5 FIFO memory 6 RAM 7 relative visibility correction circuit

Claims (2)

(57) [Claims] 1. A portion where three color image data of yellow, magenta and cyan overlap with each other by black color image data, and a portion where color image data of yellow, magenta and cyan overlap each other. And a color image forming apparatus for forming a color image with the color image data of the four colors of black replaced with yellow, magenta, and cyan, respectively. Of overlapping parts to be subtracted from the color image data of
A color image forming circuit comprising means for making the data value smaller than the black color image data. 2. The color image according to claim 1, wherein the color image data of yellow, magenta, and cyan from which the data value of the overlapping portion has been subtracted are subjected to color correction. Forming equipment.