JP2705541B2 - Printing apparatus and method of creating conversion table used for the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing apparatus, and more particularly to a printing apparatus suitable for printing characters or images by using a dot matrix.

[0002]

2. Description of the Related Art In a conventional color printing apparatus, a color original is read after being separated by a CCD line sensor or the like, and is converted into a signal of a color material such as color toner or ink by color masking and printed. .

In color masking, color separation signals R (Red: Red), G (Green: Green), B
(Blue: blue), a predetermined operation is performed, and color material signals C (Cyanine: cyan) and M (Magent)
a: magenta) and Y (Yellow: yellow) to control the color tone at the time of color reproduction and to improve the saturation while maintaining the color balance.

As a calculation method for obtaining a CMY value from an RGB value, a complementary color of the RGB value is simply set to a CMY value,
The full black method, in which all Y values overlap, is black, or the skeleton black, in which only CMY values are replaced by K (black or black), in order to eliminate dark-colored clicks, where only CMY values exceed a certain threshold. The law is often used.

However, CM of a color material used in a printing apparatus
That the Y value is not in a correct complementary color relationship with the RGB value, that the gradation is not linear, that the hue changes when the gradation is changed, that a correct color mixing result cannot be obtained even when the colors are superimposed, etc. Due to the problem described above, there is a problem that the result printed by this method is too different from the color of the original image data, so that it has not been used for purposes other than business graphs.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 2-118680, RG obtained by some form of rule of thumb or the like is used.
Using a conversion table from B value to CMY value,
The signal of K is determined from the minimum value of the CMY values of the color material (full black method) or from the converted value in which the difference between the maximum value and the minimum value is taken into consideration for the minimum value, and the CM is determined from the conversion table by that amount.
The under color is removed by reducing the Y signal or the like.

Further, linear masking theory and Neugebauer theory are used, and conversion from RGB values to CMYK values is used as a black box, and a conversion table is obtained from measurement of output for a large number of color samples.

[0008]

However, in the above conventional example, it is difficult to quickly obtain an accurate CMYK value based on the RGB values of the color image data. Has the disadvantage that the color reproducibility is insufficient.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a printing apparatus which can solve the disadvantages of the prior art and can perform high-speed printing with excellent color reproducibility in color printing.

[0010]

SUMMARY OF THE INVENTION Accordingly, a stamp according to the present invention is provided.
In the printing apparatus, a data input unit for inputting image data, a conversion table storing correspondence between RGB values and CMYK values created using a uniform color space as an intermediary, and referring to the conversion table, It is provided with a driver unit for converting the RGB values of the image data from the input unit into CMYK values to create print data, and a print unit for printing using print data from the driver unit . Moreover, the driver
The unit refers to the conversion table and performs an interpolation operation on the image.
An interpolation operation unit that converts RGB values of data into CMYK values
It has a configuration of being provided. This aims to achieve the above-mentioned object. According to the invention
The conversion table used in the printing apparatus is the conversion table according to the present invention.
It is good to make by the method of making a cable. According to the invention
In the method of creating the conversion table, the RG input to the input unit
CMYK value mark printed on the B value image data by the printing unit
To character data. That is, a predetermined image of RGB values
Displaying the data (S1) on the monitor display unit (S2)
(S3) a step of measuring colors in a uniform color space, and this step
Based on the result of the color measurement by (S3), RGB and uniform colors
Steps for creating a mutual conversion table (S4, S5)
The predetermined print data (S6) of the CMYK value is
(S7) and colorimetry in a uniform color space (S7).
8) Based on the result of the colorimetry in the step (S8) and the step
And create a mutual conversion table for the CMYK and uniform colors.
(S9, S10) steps. Furthermore, RG
B and uniform color mutual conversion table and CMYK and uniform color
The conversion table of RGB and CMYK
The step (S11) of creating a conversion table is provided. Also,
The process of creating the RGB and CMYK conversion tables is
A combination of RGB and CMYK that minimizes the color difference in the uniform color
It is preferable to select and combine the combinations (S11).

[0011]

When the image data is input from the data input unit,
The driver unit searches the conversion table the RGB values of the image data as a key, to together is converted into CMYK values,
Interpolation is performed to create print data and output it to the print unit.

The printing unit converts print data from the driver unit into image data and performs printing processing.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

The embodiment shown in FIG. 1 includes a data input unit 3 for inputting image data, an image memory unit 4 for holding image data from the data input unit 3, and an image data stored in the image memory unit 4. A monitor display unit 5 for displaying, a conversion table 2 storing the correspondence between RGB values and CMYK values created using a uniform color space as an intermediary, and stored in the image memory unit 4 with reference to the conversion table 2. A driver unit 1 that converts the RGB values of the image data into CMYK values to create print data, a print unit 6 that prints using print data from the driver unit 1, and an operation panel unit where the operator inputs various instructions And 7.

As shown in FIG. 2, the data input unit 3 optically reads a color original, separates the color original, and performs RGB separation.
A CCD line sensor 3A for converting the image data into values, a reading device 3B adapted to various storage media for inputting image data created by another image processing device, and an interface 3C for downloading image data by data communication. I have.

However, the data input section 3 does not need to include all of the above.

The image memory unit 4 may be provided with a storage means such as a hard disk for storing image data.

As the monitor display section 5, a CRT display is generally used for performing color display, but the present invention is not limited to this. However, a high-resolution one is desirable.

The driver unit 1 includes, as shown in FIG.
A conversion unit 1A that converts the RGB values into CMYK values with reference to the conversion table 2, an interpolation operation unit 1B that performs an interpolation operation on the RGB values not described in the conversion table 2 to calculate the CMYK values, and a conversion unit 1A or A gradation conversion unit 1C for converting a CMYK value having a gradation from the interpolation calculation unit 1B into a gradation number suitable for the printing unit 6, and CMYK values from the conversion unit 1A, the interpolation calculation unit 1B, or the gradation conversion unit 1C. A code conversion unit 1D that converts the value into code data and outputs the code data to the printing unit 6.

As shown in FIG. 4, the printing section 6 includes a printing buffer 6B for temporarily storing printing image data and a printing buffer for converting code data from the code conversion section 1D into image data. An image conversion unit 6A for developing the image data into a print buffer 6B and a print unit 6C for printing the image data stored in the print buffer 6B are provided.

Next, the operation of this embodiment will be described.

(1). When copying a color original:

[0023] The operator sets the color document at a predetermined position, and instructs reading of image data via the operation panel unit 7.

[0024] The CCD line sensor 3A decomposes the image data of the document into RGB values according to an instruction from the operation panel unit 7, and stores the RGB values in the image memory unit 4.

The image data stored in the image memory unit 4 is displayed on the monitor display unit 5.

Here, the operator can perform image processing such as trimming, enlargement, and reduction through the operation panel unit 7 if necessary. Further, it is also possible to store the image data in a storage means such as a hard disk or a floppy disk.

[0027] When the operator instructs printing via the operation panel unit 7, the conversion unit 1A reads image data from the image memory unit 4 and converts the RGB values of the image data into CMYK values with reference to the conversion table 2.

RGB not described in conversion table 2
As for the values, the interpolation calculation unit 1B performs an interpolation calculation based on the CMYK values for the preceding and following RGB values described in the conversion table 2 to calculate the CMYK values.

Further, the gradation conversion section 1C outputs a C signal having a gradation.
A gradation conversion process is performed to set the MYK value to the number of gradations (mostly binary) corresponding to the printing unit 6.

[0030] The code conversion unit 1D converts the CMYK values from the conversion unit 1A, the interpolation calculation unit 1B, and the gradation conversion unit 1C into code data, and outputs the code data to the printing unit 6.

[0031] The image conversion unit 6A converts the code data from the code conversion unit 1D into image data and develops the image data in the print buffer 6B.

The printing section 6C includes a printing buffer 6B.
Prints the image data stored in.

(2). When printing RGB data created by another device 1:

[0034] The operator sets a medium storing an image data file created by another device in the reading device 3B, and instructs reading of image data via the operation panel unit 7.

[0035] The reading device 3 </ b> B reads out image data according to an instruction from the operation panel unit 7,
To be stored.

The image data stored in the image memory unit 4 is displayed on the monitor display unit 5.

Here, if necessary, the operator can perform image processing such as trimming, enlargement, and reduction via the operation panel section 7. Further, it is also possible to store the image data in a storage means such as a hard disk or a floppy disk.

[0038] When the operator instructs printing via the operation panel unit 7, the conversion unit 1A reads image data from the image memory unit 4 and converts the RGB values of the image data into CMYK values with reference to the conversion table 2.

RGB not described in conversion table 2
As for the values, the interpolation calculation unit 1B performs an interpolation calculation based on the CMYK values for the preceding and following RGB values described in the conversion table 2 to calculate the CMYK values.

Further, the gradation conversion section 1C outputs a C signal having a gradation.
A gradation conversion process is performed to set the MYK value to the number of gradations (mostly binary) corresponding to the printing unit 6.

[0041] The code conversion unit 1D converts the CMYK values from the conversion unit 1A, the interpolation calculation unit 1B, and the gradation conversion unit 1C into code data, and outputs the code data to the printing unit 6.

[0042] The image conversion unit 6A converts the code data from the code conversion unit 1D into image data and develops the image data in the print buffer 6B.

The printing section 6C includes a printing buffer 6B.
Prints the image data stored in.

(3). When printing RGB data created by another device 2:

[0045] The operator connects a communication cable from another device holding the image data file to the interface 3C, and instructs reading of image data via the operation panel unit 7.

[0046] The interface 3 </ b> C receives image data from another device according to an instruction from the operation panel unit 7 and stores the image data in the image memory unit 4.

The image data stored in the image memory unit 4 is displayed on the monitor display unit 5.

Here, the operator can perform image processing such as trimming, enlargement, and reduction through the operation panel section 7 if necessary. Further, it is also possible to store the image data in a storage means such as a hard disk or a floppy disk.

[0049] When the operator instructs printing via the operation panel unit 7, the conversion unit 1A reads image data from the image memory unit 4 and converts the RGB values of the image data into CMYK values with reference to the conversion table 2.

RGB not described in conversion table 2
As for the values, the interpolation calculation unit 1B performs an interpolation calculation based on the CMYK values for the preceding and following RGB values described in the conversion table 2 to calculate the CMYK values.

Further, the gradation conversion section 1C outputs a C signal having a gradation.
A gradation conversion process is performed to set the MYK value to the number of gradations (mostly binary) corresponding to the printing unit 6.

[0052] The code conversion unit 1D converts the CMYK values from the conversion unit 1A, the interpolation calculation unit 1B, and the gradation conversion unit 1C into code data, and outputs the code data to the printing unit 6.

[0053] The image conversion unit 6A converts the code data from the code conversion unit 1D into image data and develops the image data in the print buffer 6B.

The print section 6C includes a print buffer 6B.
Prints the image data stored in.

Here, the operation of each unit can be controlled by a CPU operating according to a program stored in the ROM.

Next, a method of creating a conversion table will be described in detail with reference to the flowchart of FIG.

[0057] R value using graphic software, etc.
Set appropriate values for the G value and the B value (step S in FIG. 5).
1) The color having the RGB values is displayed on the monitor display unit 5 (step S2 in FIG. 5).

[0058] The color is measured by bringing a color difference meter or the like into contact with the monitor display unit 5 to determine the L ^* value, a ^* value, and b ^* value (FIG. 5).
Step S3).

[0059] The above process is repeated for various RGB values, and the RGB
RGB → L ^* a for calculating L ^* a ^* b ^* value from B value
^* b ^* conversion table (step S4 in FIG. 5) and L ^* a
L ^* a ^* b ^* → R for calculating RGB values from ^* b ^* values
A GB conversion table (step S5 in FIG. 5) is created.

[0060] In the printing unit 6, C value, M value, Y value
Value and K value (step S6 in FIG. 5)
Printing is performed in a color having the CMYK value (step S7 in FIG. 5).

[0061] The printed paper is contacted with a colorimeter or the like to measure the color, and the L ^{* '} value, a ^*' value, and b ^{* '} value are obtained (step S8 in FIG. 5).

[0062] The above process is repeated for various CMYK values, and C
CMYK for obtaining L ^{* '} a ^*' b ^{* '} value from MYK value →
L ^{* '} a ^*' b ^{* '} conversion table (step S9 in FIG. 5);
^{L * 'a *' b *} ' for determining the CMYK values from the values L ^*' a ^* '
b ^{* '} → CMYK conversion table (Step S10 in FIG. 5)
Create

[0063] R for obtaining the CMYK values from the RGB values by combining the conversion tables created in the above and
Create a GB → CMYK conversion table.

However, an L ^* a ^* b ^* value group obtained by measuring the RGB display colors and an L ^{* '} a ^*' b ^{* '} value group obtained by measuring the CMYK print colors Are not the same.

Therefore, the L ^* a ^* b ^* value group and L ^{* '} a ^*' b ^{* '}
An RGB → CMYK conversion table (FIG. 5) is selected and combined so as to minimize the color difference from the value group.
Step S11) is created.

Further, in order to correct the point that the color expression range of the original image and the color range that can be expressed by the printing unit 6 do not match, the white color in the RGB space is matched with the color of the printing paper (Y = M = C = K = 255), and by matching black in the RGB space with the solid color in the printing unit 6 (Y = M = C = 0 and K = solid), the gray axis in the RGB space is changed to CMYK. The rotation and compression of the axis is performed during the transformation to coincide with the gray axis in space. Here, the adaptation function of human vision is considered.

As described above, according to the present invention, the conversion formulas obtained from the colorimetric results are combined by a simple method of combining colors so as to minimize the color difference in a uniform color space.
A GB → CMYK conversion table can be created.

Since the RGB → CMYK conversion table is created so that the color difference in human vision is minimized, accurate color reproduction can be performed.

Further, by including conversion for rotating and compressing the color space by applying the visual color adaptation function, preferable color reproduction without discomfort can be achieved.

That is, since the RGB → CMYK conversion table created through the CIE-L ^* a ^* b ^* uniform color space capable of expressing a color space close to human visual perception is used, the color reproducibility is high. Excellent printing can be performed.

Further, when the CMYK values are obtained from the RGB values, the interpolation calculation is performed with reference to the RGB → CMYK conversion table, so that the processing time can be reduced.

[0072]

The present invention is constructed and functions as described above. According to this, when calculating the CMYK values from the RGB values, the RGB → CMY created through the uniform color space.
The use of the K conversion table and the use of the interpolation calculation process allow conversion taking into account the human visual function, thereby enabling high-speed printing with excellent color reproducibility. It is possible to provide an unprecedented excellent printing apparatus.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram for describing a detailed configuration of a data input unit in FIG. 1;

FIG. 3 is an explanatory diagram for describing a detailed configuration of a driver unit in FIG. 1;

FIG. 4 is an explanatory diagram for describing a detailed configuration of a printing unit in FIG. 1;

FIG. 5 is a flowchart illustrating a method for creating a conversion table.

[Explanation of symbols]

 Reference Signs List 1 driver section 1A conversion section 1B interpolation calculation section 1C gradation conversion section 1D code conversion section 2 conversion table 3 data input section 3A CCD line sensor 3B reader 3C interface 4 image memory section 5 monitor display section 6 printing section 6A image conversion section 6B Printing buffer 6C Printing section 7 Operation panel section

Claims (4)

(57) [Claims] A data input unit for inputting image data;
RGB values and CMYK created using a uniform color space as an intermediary
A conversion table that stores the correspondence between the
Image data from the data input unit with reference to the conversion table.
Convert the RGB values of the data to CMYK values and create print data.
And the print data from this driver
Ri equipped with a printing portion for printing, the driver unit, characterized in that it comprises an interpolation calculator for converting the RGB values of the image data into CMYK values by referring to the interpolation operation the conversion table Printing device. 2. The image data of RGB values input to an input unit.
Data into CMYK value print data to be printed by the print unit
In a method of creating a conversion table, predetermined image data of the RGB values is displayed on a monitor display unit.
And colorimetry in a uniform color space.
Conversion between RGB and uniform colors based on colorimetric results
And a predetermined printing of the CMYK values.
Data is printed on the printing unit and colorimetrically measured in a uniform color space
Based on the result of the colorimetry in this step
Creating a mutual conversion table for CMYK and uniform colors;
Provided with a, the said RGB and uniform color interconversion table CMYK
RGB and CM
A step of creating a YK conversion table is provided.
How to create a conversion table. 3. The conversion table for RGB and CMYK is
The step of creating an RG that minimizes the color difference in the uniform color
Select and combine a combination of B and CMYK
3. The method of creating a conversion table according to claim 2, wherein 4. The conversion table for RGB and CMYK is
3. The method according to claim 2 , wherein the creating step matches the gray axis of the RGB space with the gray axis of the CMYK space.
How to create the described conversion table.