JP3133409B2 - Digital color copier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital color copying apparatus which reads an original, performs digital signal processing, and forms an image on a transfer medium.

[0002]

2. Description of the Related Art Generally, in a digital color copying apparatus, red, green, and blue RGB signals read by a scanner are converted into yellow, magenta, cyan, and black YMCBs.
It is configured to perform color conversion to k signals. In this conversion process, an additive color system composed of light elements is converted to a subtractive color system composed of dyes such as toner and ink, and the spectral characteristics of color materials such as toner on the recording side and the scanner RG
The spectral characteristics and the like of the B decomposition filter are considered. in this case,
The conversion process is determined as a color conversion coefficient. The color conversion coefficient is obtained by sampling the saturation and brightness of a certain color range, for example, a color ranging from red to blue or a color ranging from white to black. The tens of representative colors are determined in a well-balanced manner, so that the errors are uniformly distributed.

FIG. 5 is an explanatory diagram showing the color conversion coefficients. The axes of R, G, B, Y, M, and C indicate correction targets, and the lengths of the axes indicate saturation. In FIG. 5, the coefficients of R, G, B, Y, M, and C are all “1” as indicated by black dots.
A total of thirteen coefficients of "0", "5", and "0" are shown. Therefore, as the distance from the center point increases, the correction in the direction of higher color saturation of the color is appropriately performed, and all the colors are appropriately corrected by the coefficient of the center point.

Conventionally, this type of digital color copying apparatus has one color conversion table in which correction coefficients for all colors are determined in a well-balanced manner, and converts RGB signals read by a scanner into the one color conversion table. YMCB
It is configured to perform color conversion to k signals.

[0005]

However, in the above-mentioned conventional digital color copying apparatus, color conversion is performed by one color conversion table, so that almost satisfactory color conversion can be performed in a normal document. In the case of originals that are represented by a slight difference in saturation or lightness in a specific range, such as originals with many colors or special tones with many blue tones, it is possible to reproduce color originals with similar subtle hues in close proximity. There is a problem that can not be. In the case of such a special document, a method of manually adjusting the color balance is known. However, it is impossible to finely adjust a subtle color having the same hue.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a digital color copying apparatus capable of improving the reproducibility of a color original in which subtle same hues are close to each other.

[0007]

Since SUMMARY OF THE INVENTION The present invention to achieve the above object, a plurality of color conversion table corresponding to the hue of the original, a optimal hue of a document automatically discriminated by the hue of the original color and selecting means for selecting one of the conversion tables, reading
Converts the scanned image of the original into a digital signal
Digital color copier for forming color image on body
In the above, the selecting means may determine that each of the RGB values is equal to or greater than a predetermined
Pixels whose difference between RGB values is equal to or greater than a predetermined value
Counted by representing the color with the large value
The hue barycenter and color distribution are calculated from the
Select the color conversion table closest to the mind

[0008]

[0009]

[0010]

According to the present invention , the comparator and the counter have the above configuration.
Calculate the center of gravity with a simple circuit such as
The color conversion table closest to the hue centroid of the manuscript is selected
Therefore, it is possible to improve the reproducibility of a color original in which delicate same hues are close to each other with a simple circuit .

[0011]

[0012]

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a block diagram showing an image processing circuit of one embodiment of a digital color copying apparatus according to the present invention.
3B is a block diagram showing a detailed configuration of the color conversion circuit of FIG. 1A, FIG. 2 is a side view showing an image scanner, and FIG.
FIG. 4 is a block diagram showing an overall configuration of a reading processing unit including the image processing circuit of FIG. 1, and FIG. 4 is an explanatory diagram showing an operation of the image processing circuit of FIG.

First, the schematic configuration of the image scanner 1 of the digital color copying apparatus according to the present embodiment will be described with reference to FIG. The image scanner 1 includes a contact glass 10 on which a document is placed, a light source 11, a first scanning mirror 12, a second scanning mirror 13, and an imaging lens 14.
And a photoelectric conversion unit 15 that reads a document image by photoelectrically converting reflected light 19 of the document. Light source 11
And the first scanning mirror 12 are supported by a first carriage C1, and the second scanning mirror 13 is supported by a second carriage C2. The image scanner 1 also includes a light source 1
And a DC motor 17 for the first carriage C1 and the second carriage C2 to perform sub-scanning.
And a video processing circuit 2 and the like.

The image scanner 1 is configured to scan a document while fixing the document so as to cope with the variety of the document, and to make the optical path length of the reflected light 19 constant when sub-scanning the document. Then, the first carriage C1 and the second carriage C2 are moved in the sub-scanning direction by the DC motor 17 at a speed ratio of 2: 1.

As shown in FIG. 3, the photoelectric conversion unit 15 includes CCDs 15R, 1R for reading R, G, and B colors.
5G and 15B, and each color signal is converted into an 8-bit digital signal by the A / D converter 21, for example. These digital signals are output to the CCDs 15R and 15R.
The correction is performed by the shading correction circuit 22 in accordance with the variation in the sensitivities of G and 15B, and then output to an image processing circuit 30 shown in detail in FIG.

In FIG. 3, the rotational angular speed of the DC motor 17 for driving the first carriage C1 and the second carriage C2 is detected by the rotary encoder En and fed back to the speed signal generating circuit 23, and is output to the next stage. The sub-scanning speed control circuit 24 performs constant speed control and speed control such as starting and stopping. The reading by the image scanner 1 is sequence-controlled by the scanner control circuit 25.

Next, the image processing circuit 30 of this embodiment will be described in detail with reference to FIG. The R, G, and B digital signals corrected by the shading correction circuit 22 shown in FIG. 3 are first converted by the color conversion circuit 31 into Y, M, and C color signals. As shown in detail in FIG. 1B, the color conversion circuit 31 includes a hue determination circuit 3 for determining the hue of the document.
1a, a selection circuit 31b and a color conversion table 31c for selecting the most optimal color conversion table according to the determination result of the hue determination circuit 31a. The color conversion table 31c has six types of color conversion tables as an example.

Next, the operation of the color conversion circuit 31 will be described with reference to FIG. FIGS. 4A and 4B are examples.
A color distribution state of a certain document (shown by oblique lines) is shown.
The signal is obtained by statistical processing. Here, the statistical result is R =
10, G = 6, B = 2, Y = 8, C
= 4, M = 6, and an area shown by a broken line is obtained. In this area, a red correction coefficient R5 or a yellow correction coefficient Y5 close to the center of gravity is obtained.

Next, the operation in the case where the hue determination circuit 31a determines the hue of a document will be described. The reading by the image scanner 1 is started from the upper left end of the document and moves rightward (the number of pixels k) as shown in FIG. 4C, and is sequentially read in the sub-scanning direction (the number of lines n). The reading density is, for example, 400 dpi, that is, 16 dots / mm.
Thus, 8-bit data for each of RGB is obtained for each dot, and the range of this data is "0" to "255".

The hue discriminating circuit 31a first discriminates whether each value of RGB is equal to or more than "30", and does not count if it is equal to or less than "30". Further, the difference between each value of RGB is "1".
No counting is performed even in the case of "5" or less. When each of the RGB values is “30” or more, and when the difference between the RGB values is “1”
5 ”or more, the largest value f of RGB
(R), f (G) and f (B) are counted. That is, when the read values are R = 60, G = 180, and B = 90, the G value f (G) is counted. As described above, each pixel is represented by the color having the largest value, and this count is performed for all the pixels (= k × n).

The reason why counting is not performed when the values of RGB are equal to or less than "30" is that no color tendency appears even if the area is near the background or an image area. The reason why counting is not performed when the difference between the RGB values is less than “15” is that the color is achromatic gray, black characters, or no color tendency appears. Therefore, when each of the RGB values is “30” or more, and when the difference between the RGB values is “15” or more, the color tone is an important halftone area in which there is no saturation difference. Since it is an area, it is most suitable for determining a color tone.

Next, the count value g thus obtained is obtained.
The center of gravity is determined from the ratio of (R), g (G), and g (B). In this case, the positions of the RY axis, the GY axis, and the BY axis are obtained by subtracting the RY, GY, and BY, and the center of gravity is obtained from these positions. If the total ratio of the count value is indicated in the range of “0” to “10”, a color distribution as shown in FIG. 4A is obtained, and therefore, the selection circuit 31b operates the color conversion table closest to the center of gravity. Can be selected from the table 31c.

In FIG. 1A, the color conversion circuit 31
Are corrected by the gamma correction circuit 32, the difference between the ideal spectral distribution of the YMC and the spectral reflection density of the used toner is corrected by the masking processing circuit 33, and then the UCR circuit 34, the black component BK
Is extracted. Then, the smoothing filter processing circuit 35,
Edge emphasis filter processing circuit 36, density pattern circuit 3
7. Each process is performed by the multi-value processing circuit 38 and output to a printer (not shown). These circuits 32-38
It is controlled by the main body control circuit 39 and the synchronization control circuit 40.

Therefore, according to the above embodiment, the color conversion circuit 31c has, for example, six types of color conversion tables according to the hue of the document, the hue determination circuit 31a determines the hue of the document, and the selection circuit 31b Since the optimum color conversion table is selected, the reproducibility of a color document can be improved.
According to the above-described embodiment, the hue determination circuit 31a is configured to determine the hue of the document and automatically select the color conversion table. However, the user may determine the hue of the document and manually select the color conversion table. May be configured.

[0026]

As described above, according to the present invention, RGB
Is greater than or equal to a predetermined value, and the difference between the RGB values is
Pixels above the value are represented by the color with the largest value.
Count, and the center of hue and
Find the color distribution and select the color conversion table closest to this center of gravity.
Since-option can Rukoto improve the reproducibility of subtle color original same hue are close with a simple circuit.

[0027]

[0028]

[Brief description of the drawings]

FIG. 1 is a block diagram showing an image processing circuit of an embodiment of a digital color copying apparatus according to the present invention.

FIG. 2 is a side view showing the image scanner.

FIG. 3 is a block diagram illustrating an overall configuration of a reading processing unit including the image processing circuit of FIG. 1;

FIG. 4 is an explanatory diagram illustrating an operation of the image processing circuit of FIG. 1;

FIG. 5 is an explanatory diagram showing general color conversion coefficients.

[Explanation of symbols]

 31 color conversion circuit 31a hue determination circuit 31b selection circuit 31c color conversion table

Continuation of the front page (56) References JP-A-2-16874 (JP, A) JP-A-63-64479 (JP, A) JP-A-1-114266 (JP, A) JP-A-62-92074 (JP, A) JP-A-2-194773 (JP, A) JP-A-1-166670 (JP, A) JP-A-1-166667 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB Name) H04N 1/60 G06T 1/00 510 H04N 1/46

Claims (1)

(57) [Claims] A plurality of color conversion tables corresponding to the hue of a document.
Le and optimal Irohen hue of a document automatically discriminated by color of the document
Selection means for selecting one of the conversion tables, wherein the selection means converts each value of RGB into a digital image by forming a color image on a transfer medium by converting the read image of the original into a digital signal. Is not less than a predetermined value and R
Pixels in which the difference between each value of GB is equal to or greater than a predetermined value are set to the largest value
The color is representatively represented by a color having a color, and the center of gravity and color distribution of the hue are calculated from the ratio of the count value.
A color conversion table closest to the center of gravity .