JP2684376B2 - Color image processing equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image processing apparatus for obtaining an image in which a background color is removed from a read color original.

[Background of the Invention]

The color copying apparatus captures the image data of the read color original by color-separating each color of R (red), G (green), and B (blue), and the RGB color data for image formation (for recording).
Of the complementary colors of Y (yellow), M (magenta), and (C) cyan, or from these, BK (black)
Color data is also created, a toner image is formed in the image forming unit by the converted image data, and the toner images of the respective colors are superposed to obtain a copy image.

[Problems to be solved by the invention]

However, when copying a color original having a line drawing original such as characters and symbols or a mixed drawing original in which line drawings are mixed in a photographic image, when the background of the line drawing part of the original is colored, the background color remains the same. The toner is copied and the toner consumption increases. Further, this base is often unnecessary and it is desirable to remove it.

In view of such circumstances, an object of the present invention is to be able to remove the background color of a read image.

[Means for solving the problem]

To this end, the present invention, means for creating a histogram of the read RGB image data, means for setting the threshold for background removal by the shape of each histogram,
A means for converting data having a density higher than the above threshold value in the read image data into maximum density data is provided.

〔Example〕

Hereinafter, examples of the present invention will be described. FIG. 2 is a block diagram of a copying machine equipped with an image processing apparatus according to an embodiment of the present invention. A is an image reading device for reading a document image, and B is
Is an image processing apparatus that performs various processes on the read image data, and C is an image forming apparatus that forms a color image from the image data that has undergone image processing.

The image reading apparatus A scans a document placed on the document table 1 with the light source 2, guides the reflected light image of the document to the lens 6 via the mirrors 3 to 5, and the dichroic mirror 7 converts the reflected light image to RGB.
Separated into 3 colors and input to each different CCD8R, 8G, 8B.

The image forming apparatus C reflects the laser beam modulated by the image data transferred from the image processing apparatus B by the polygon mirror 9, passes through the mirror 10, and exposes the photosensitive drum 12 charged in advance by the band electrode 11. A latent image is formed on the surface, and the latent image is developed by a developing device 13Y having a yellow toner, a developing device 13M having a magenta toner, 13C having a cyan toner,
Develop with a developer selected from 13BK with black toner. These latent image formation and development are performed four times in total according to the color of the image data, and after the toner image of YMCBK is formed on the photosensitive drum 12 in a superimposed manner, the toner image is transferred to the transfer pole 14.
Is transferred to the transfer sheet. This transfer sheet is separated by the separation pole 15 by the photosensitive drum 12, fixed by the fixing unit 16 and discharged.

The image processing apparatus B described above includes the configuration shown in FIG. RGB image signals input from CCD8R, 8G, 8B are A / D
The signals are converted into digital signals by the converters 17R, 17G, and 17B, and at the same time subjected to shading correction, and input to a background removal unit 18 that performs the processing described later. Then, the RGB signal output from the background removal unit 18 is converted into image data of a complementary color by a color correction circuit 19 using a CCM (computer color matching) table in consideration of the characteristics of the image reading apparatus A and the image forming apparatus C. To be converted. And from here, those complementary colors YMCBK
Density data and color code data indicating their colors YMCBK are input to the color ghost removing circuit 20 to remove the color ghost in the scanning direction and the sub-scanning direction. Then, the resolution of the image data output therefrom is corrected by the MTF correction circuit 21, the image data of the color to be currently recorded is selected by the color data selector 22, and the image data is input to the multi-value quantization circuit 23. The multi-valued circuit 23 receives a preset fixed threshold value from the threshold value setting circuit 24, multi-values it, and transfers it as recorded image data to the image forming section C.

The background removal unit 18 prescans the document before the image reading unit A reads for recording, and creates a threshold for background removal based on the density data of the image data of each color at that time. To do. When a histogram is created from the RGB density data of each color read by the prescan, for example, it becomes as shown in FIG. The density threshold for background removal set by this histogram is TH. Therefore, in the background removing unit 18, the density threshold TH of each color set in this way is compared with the read image data of each color read thereafter, and data above the density threshold is determined to be the background, Convert them all to the highest density (lightest density: white). 4th
The figure is a diagram showing a histogram of image data subjected to the background removal processing in this manner. The image data obtained here is line drawing data such as characters or symbols.

FIG. 5 shows an example of the above-mentioned threshold setting method. Here, first, the highest density part of the histogram intersecting the line a having a frequency of 10% of the total number of samples in the read data is set.
D _max , the minimum density is D _min , the high density part is the density difference between D _max and the most frequent density D _P, and the density difference A
Concentrations higher than D _P by 0.2 times and 0.5 times are defined as D ₁ and D ₂ , respectively, and other concentrations D ₃ and D _{4 having} frequencies similar to those of D ₁ and D ₂
Ask for. Then, a straight line b passing through the densities D ₃ and D ₄ is drawn, and the density at the point of frequency 0 on the straight line b is defined as D ₅ . next,
The density difference between this density D ₅ and the minimum density D _min is defined as B, and the density D ₅
The density threshold value TH is a density D ₆ which is lower by 0.4 B than. As a result, in this example, all the data having the density of D ₆ or more are regarded as the background data and are converted to white.

The image data that has been subjected to the background removal processing as described above is converted into image data for YMCBK image formation by the color correction circuit 19 and is multivalued by the multivalued circuit 23. At this time, the multi-valued threshold value is multi-valued by the threshold value from the threshold value setting circuit 24 in consideration of the characteristics of the image forming apparatus C so that the color balance is not lost.

〔The invention's effect〕

As described above, according to the present invention, the background color of the read image is removed, so that the toner consumption can be reduced, and at the same time, the character or symbol portion can be made more prominent.

[Brief description of the drawings]

FIG. 1 is a block diagram of an image processing unit according to an embodiment of the present invention,
FIG. 2 is an explanatory view showing the structure of the copying apparatus, FIG. 3 is a histogram of RGB colors obtained by prescan, FIG. 4 is a histogram of RGB colors after background removal processing, and FIG. FIG. 6 is an explanatory diagram of threshold value determination for. A: image reading unit, B: image processing unit, C: image forming unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Yamamoto, 2970 Ishikawa-cho, Hachioji, Tokyo Konica Corporation (72) Masahiko Matsunawa, 2970 Ishikawa-cho, Hachioji, Tokyo Konica Corporation

Claims (4)

(57) [Claims] 1. A means for creating a histogram of read image data of each RGB color, a means for setting a threshold value for background removal according to the shape of each histogram, and a density higher than the threshold value of the read image data. And a means for converting the above data into maximum density data. 2. A means for converting the image data obtained from the converting means into image forming color data, and a means for converting the image data obtained from the means into a multi-valued image with a fixed threshold value. The color image processing apparatus according to claim 1. 3. The color image processing apparatus according to claim 2, wherein the threshold value of the multi-value quantization means is set to a threshold value that does not disturb the color balance. 4. The color image processing apparatus according to claim 1, wherein the image data for creating the histogram is obtained by pre-scanning.