JP3129590B2 - Image processing circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing circuit used in a digital full-color electronic copying machine having a forgery prevention function.

[0002]

2. Description of the Related Art Conventionally, digital full-color electronic copiers with a forgery prevention function have been used to track the copy (specifically, such as the machine that made the copy and the date of copying, etc.) in order to prevent forgery of bills and the like by color copying. For example, tracking information such as a machine number and a date of copying is added at the time of copying. The addition of such tracking information needs to be performed at a density that is not visually recognizable so that deterioration of the output image (reproduced image) due to the addition of the tracking information is minimized.
In practice, a method of adding tracking information using yellow color image data that is difficult to visually recognize is employed.

[0003]

By the way, in such a method of adding tracking information, a predetermined value (a value as small as possible so that visual recognition is impossible) is always applied to yellow color image data obtained by reading a document. In the case where the tracking information is added by adding the yellow color image data, for example, in a low-density area (white background) of a document having almost no yellow color image data, the added tracking information is added. There is a possibility that the density of the toner becomes too low, and reading with a color scanner for follow-up investigation becomes impossible.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and the tracking information is added so that the deterioration of the output image due to the addition is minimized, and the tracking information is read by a color scanner for tracking investigation. It is an object of the present invention to provide an image processing circuit for performing the operation reliably.

In order to achieve the above object, the present invention provides:
In an image processing circuit provided with tracking information adding means for adding tracking information based on yellow color image data to yellow, magenta, and cyan color image data obtained by reading, the tracking information adding means includes:
Yellow image data in the low density range below the set threshold
Is replaced by replacing it with yellow color image data of a certain value.
Adds trace information and reads the yellow color image data
Yellow in the high density range where the data exceeds the set threshold
Add tracking information by adding a predetermined value to the color image data of
Addition.

[0006]

[0007]

According to this configuration, for example, in a low-density yellow area of a document, the additional density of yellow as tracking information is set as high as possible so that the tracking information can be reliably read by a color scanner for tracking investigation. In addition, in the other density areas of the document, the additional density of yellow as tracking information can be made as low as possible in order to minimize the effect on image quality due to the addition of tracking information.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the present invention, an image processing circuit in a digital full-color electronic copying machine will be described below with reference to the drawings. In this embodiment, the additional density of yellow as the tracking information in the yellow low density area of the document is set to be higher than the yellow additional density in the yellow high density area.

More specifically, as shown in FIG. 2, in a yellow high-density region of a document in which the yellow color image data read from the document exceeds a set threshold, a predetermined value (in this case, The tracking information is added by adding a B value as small as possible so as to make it impossible to view the image. In this case, the tracking information is added by replacing the image data with yellow color image data having an A value larger than the B value) so that the image can be read by a scanner for tracking investigation.

In this way, it is possible to surely read the tracking information added to all the density regions of the copy by the color scanner while minimizing the deterioration of the copy image quality due to the addition of the tracking information. Here, FIG.
Of Y ₀ denotes a case where the output as not the concentration added as tracking information to the color image data of yellow 8-bit read from the document (256 gradations), Y
Reference numeral ₁ denotes a case in which density is added as tracking information and output, and the threshold value is set to, for example, about 30 gradations.

FIG. 1 shows an example of an image processing circuit adopting such an additional system, and 1 outputs color image data in the form of three primary colors (R, G, B) of light by reading a color original to be copied. Color scanner 2 and color scanner 1
Is a color conversion circuit that converts color image data in the form of three primary colors of light output from the printer into three color image data of yellow, magenta, and cyan representing toner density.

Reference numeral 3 denotes color correction (such as correction to match the characteristics of human eyes) on 8-bit (256 gradations) yellow, magenta, and cyan color image data output from the color conversion circuit 2.
And a color correction / black generation circuit 4 for generating black color image data therefrom. Reference numeral 4 denotes a color correction / black generation circuit 3 for reading yellow, magenta, cyan, and black colors obtained by reading a color original. This is a color selector that sequentially outputs four color image data for each color image data.

Reference numeral 5 denotes an additional circuit for adding density (gradation) as tracking information to the yellow color image data from the color selector 4 as shown in FIG. In the low-density yellow region where the value of the tone is 30 or less, the yellow color image data read from the original is replaced with the yellow color image data of the tone A that can be read by the color scanner for tracking investigation. In the yellow high-density region where the data value exceeds the gradation 30, a gradation B as low as possible is added to the value of the yellow color image data from the color selector 4 so as not to deteriorate the image quality. I have.

Reference numeral 6 denotes a memory in which position data for specifying a density addition position as tracking information is stored, and a machine number, a copy date, and the like can be specified by the density addition position. 7 outputs the magenta, cyan, and black color image data from the color selector 4 as it is, but outputs the yellow color image data from the color selector 4 or the additional circuit 5 based on the position data from the memory 6. When the addition of density as tracking information is instructed by the position data from the memory 6 with a selector for selecting whether to output the color image data of the color, the yellow color image data from the color selector 4 is replaced with the tracking information as the tracking information. The yellow color image data from the adding circuit 5 to which the density has been added is output.

For example, tracking information having a unit information size of 2 pixels (dots) and 4 pixels in the main scanning direction and the sub-scanning direction, respectively, is stored in the main scanning direction and the sub-scanning direction in accordance with the position data from the memory 6. Are instructed to add (16-2) pixels to (16-4) pixels, respectively, the selector 7 outputs yellow color image data as shown in FIGS. 3 and 4, for example. Will be.

Reference numeral 8 denotes an intermediate processing circuit for performing gradation processing by a multi-value dither method for reproducing halftones. Reference numeral 9 denotes a pulse for controlling on / off of a laser beam output in accordance with an output from the intermediate processing circuit 8. This is a pulse width modulation circuit that changes the width to make one pixel multi-valued, and supplies the pulse width modulation signal to a subsequent laser scanner unit.

FIG. 5 is a schematic view of a digital full-color electronic copying machine provided with an image processing circuit for adding such tracking information.
Color original 1 placed so as to be pressed by
2 is scanned by a scanning optical system 13 constituting a color scanner unit, and the image information is guided from a condenser lens 14 to a light receiving element 15 such as a CCD using light as a medium, and is converted into an electric signal. Signal processing necessary for image processing such as addition of tracking information and color conversion is performed by the processing circuit section 16, and thereafter, a latent image is drawn on the photosensitive drum 18 by the laser scanner unit 17. Prior to this, the surface of the photosensitive drum 18 is
Charged by

When a color image is formed, first, a photosensitive member is output by a laser beam output based on a PWM signal of yellow color image data which has been subjected to signal processing necessary for image processing such as addition of tracking information and color conversion. A latent image is formed on the drum 18, and the latent image is developed by the Y developing device 20. The Y developing device 20 has a yellow toner, and develops the latent image on the photosensitive drum 18 with the yellow toner. Then, the image on the photosensitive drum 18 developed and formed with the yellow toner is transferred onto a sheet wound around the surface of the transfer drum 21. The paper is supplied from the paper feed cassette 22 or 23 through a paper feed path.

Then, this sheet is transferred to the transfer drum 2 as it is.
It is mounted on one surface and provided for the next color transfer. That is, after the residual toner is wiped off by the cleaning unit 24 and the charge of the photosensitive drum 18 is removed by the charge removing unit (not shown),
The photosensitive drum 18 is formed by a laser beam output which is charged again by the main charger 19 and which performs a latent image writing operation based on a PWM signal of magenta color image data which has been subjected to signal processing required for image processing. The latent image corresponding to the magenta image is developed by the M developing unit 25. At this time, the M developing device 25 is
It is brought to a position facing the photosensitive drum 18 instead of 0, and is developed with magenta toner.

In this embodiment, a developing device is a Y developing device 20 for developing yellow and an M developing device 2 for developing magenta.
5. A C developing device 26 for developing cyan and a BK developing device 27 for developing black are sequentially mounted on a moving body 28 that moves vertically as shown in the figure,
It is alternatively brought to a developing position (a position facing the photosensitive drum 18) in accordance with the color image data for writing a latent image by the laser beam output.

The image on the photosensitive drum 18 developed with the magenta toner is transferred to a sheet on the surface of the transfer drum 21 (a sheet on which a yellow image has been previously formed). In the same manner, cyan and black images are further transferred to the paper, and a color image is formed. afterwards,
The sheet on which the color image has been formed is separated from the transfer drum 21 and fixed by the fixing unit 29, and then discharged from the electronic copying machine.

In this embodiment, the case where the threshold is set to the gradation 30 has been described. However, the present invention is not limited to this, and the threshold can be finely adjusted by the maker according to the copying state. Is also good.

[0023]

As described above, according to the present invention, in an image processing circuit for adding tracking information based on yellow color image data, it is possible to minimize the influence of the tracking information addition on the image quality while minimizing the effect on the image quality. Since the reading by the color scanner can be reliably performed irrespective of the density range of the added copy, the tracking performance can be greatly improved without deteriorating the image quality as far as the left.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an example of adding density as the tracking information.

FIG. 3 is a diagram showing an output example of yellow color image data in a main scanning direction from the selector.

FIG. 4 is a diagram showing an output example of yellow color image data in the sub-scanning direction from the selector.

FIG. 5 is a schematic diagram of a digital full-color electronic copier embodying the present invention.

[Explanation of symbols]

 1 color scanner 2 color selector 3 additional circuit 4 memory 5 selector

Claims (1)

(57) [Claims] 1. An image processing circuit comprising: tracking information adding means for adding tracking information based on yellow color image data to yellow, magenta, and cyan color image data obtained by reading; is read in the low density region color image data following set threshold yellow perform additional tracking information by replacing the color image data of yellow predetermined value, the set threshold value color image data of yellow read An image processing circuit for adding tracking information by adding a predetermined value to the read yellow color image data in a high density region exceeding the threshold value.