JPS61123844A - Color density converting device - Google Patents

Abstract

PURPOSE:To stabilize the quality of printed matter by standardizing the transmission color density of each color separation plate for a gravure process on the basis of reflection color information obtained by measuring a color sample optically. CONSTITUTION:The transmission color density of the color separation plate and the reflection color information obtained by measuring optically printed matter printed actually by using the color separation plate are obtained in various combinations to generate a reflection color information-transmission color density conversion table. The color sample, on the other hand, is measured optically to obtain reflection color information on a color in which a print is to be made and compared with the reflection color information in said table to find a combination of the measured reflection color information and transmission color density corresponding to reflection color information coincident with or closest to the measured reflection color information in said table, thereby determining the transmission color density of the color sample in a print according to the combination of the transmission color density. Therefore, this color density converting device calculates the transmission color density of the continuous tone positive of each plate in standardized form, so the quality of printed matter is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention provides color information for C (cyan) and M (cyan) for conventional gravure printing based on reflected color information obtained by optically measuring a color sample. The present invention relates to an apparatus for determining the transmitted color density of each color separation plate of magenta), Y (yellow), or C, M, Y, and Bk (black).

[Prior art and its problems]

2. Description of the Related Art Conventionally, a small piece of paper called a color sample for specifying a color is sometimes attached to a printing layout sheet for the purpose of an orderer specifying in advance the color of a certain part of a printed matter.

For example, when it is desired to uniformly fill the background of a picture with a certain color, a small piece of paper having the color of the background is attached as a color sample and brought to a printing factory.

At the printing factory, in conventional gravure printing, a four-color printing method using C, M, Y, and Bk separation plates is used, and in order to print a designated area in the same color as the color sample, The sum of the transmitted color densities of the M, Y, and Bk color separation plates is determined to determine the value that should be used for printing, and continuous tone positive color separation plates are prepared and printed under these conditions.

Conventionally, the above-mentioned work involves preparing a color chart, which is a collection of many printed matter, printed by changing the transmitted color density of C, M, Y, and B approximate color separation plates at intervals of about 0.1, and then manually Visually compare each color in the color sample and this color chart, select the color from the color chart that is closest to the color sample,
The color chart contains the transmission color density of each color separation required to print each color in the color chart.Using this fact, calculate the transmission color density of each color separation required to print the selected color above. After knowing the color density, each color separation plate with that transmitted color density is created and printed to reproduce the color specified in the color sample.

However, this method requires manual work;
In addition, since there are a huge number of colors in the color chart, it takes time to compare them with color samples, and since it depends on the visual judgment of the worker, the colors selected from the color chart vary depending on the worker, making it difficult to reproduce. The disadvantage is that the colors tend to vary.

On the other hand, various densitometers for optically measuring a measured object are commercially available. Such conventionally known densitometers have different reflection color densities and
Alternatively, only the transmitted color density is measured, which is extremely inconvenient when trying to find out the transmitted color density of each color separation plate from a color sample that is a reflective original.

Further, the conventionally known densitometer cannot accurately determine the transmitted color density of each color separation plate for reproducing the color of the color sample for the following reason.

In other words, C, M, and Y printing inks are not ideal;
C ink contains M and Y components, M ink contains C and Y components, and Y ink contains C and M components. Can be mentioned. For example, assume that solid printing is performed using only C ink from a certain ink manufacturer. The C, M, and Y reflection densities of this printed matter are calculated through the R filter, G filter, and B filter, and are respectively 1.53.0.52.0.17.
Even though it was printed using only C ink, a value containing M and Y components was obtained, making it impossible to determine the correct transmitted color density to reproduce the color specified in the color sample. This phenomenon becomes even more complicated in the case of printed matter in which inks of multiple colors are overprinted.

[Purpose of the invention]

The present invention eliminates the various drawbacks mentioned above, and can produce conventional gravure using ink of each color of YlM, C or ink of each color of Y, M, C, Bk for any color. It is an object of the present invention to provide an apparatus that can easily determine how to combine the transmitted color densities of each color separation plate when expressed by printing.

[Summary of the invention]

The present invention, which was made to achieve the above object, provides various combinations of the transmitted color density of a color separation plate and the reflected color information obtained by optically measuring a printed matter actually printed with the color separation plate. Create a reflection color information-transmission color density conversion table.
The color sample is optically measured to obtain reflected color information of the color to be printed, and this reflected color information is compared with reflected color information of a previously created reflected color information-transmitted color density conversion table,
A combination of transmitted color densities corresponding to the reflected color information in the table that matches or most closely matches the measured reflected color information is extracted from the table, and the color of the color sample is printed using this combination of transmitted color densities. It can be determined as the transmitted color density of each color separation plate that can be reproduced.

[Embodiments of the invention]

The present invention will be described in detail below based on embodiments shown in the drawings. FIG. 1 is a conceptual diagram of the apparatus of this application, and a first storage means 01 stores in advance a combination of reflection color information and a combination of transmission color density corresponding to the combination of reflection color information of a color separation plate of a plurality of colors. A reflection-transmission color density conversion table showing the correspondence relationship between the two is stored, and the combination data of the reflection color information obtained by the reflection color information measurement means (2) for obtaining the combination data of the reflection color information of the object to be measured is The information is temporarily stored in the storage means of the computer. Color information includes color density and i. In the following description, reflected color density will be taken as an example of reflected color information, but there is no problem with reflected chromaticity. Second storage means■
As the combination data of reflected color densities stored in , for example, the reflected color densities of the object to be measured are
A set of combinations of different color densities, or even an amber filter or ND filter in addition to the above-mentioned filters.
This is a set of four types of reflected color densities including the reflected color densities obtained through the filter.

Next, the transmitted color density calculation means (4 (l) is a combination of the reflected color density of the reflected color density-transmitted color density conversion table stored in the first storage means fllll and the reflected color density stored in the second storage means From among the combinations of reflected color densities of the object to be measured, one that matches or is closest to the combination of reflected color densities of the object to be measured is selected.

Next, the combination of transmitted color densities corresponding to the combination of reflected color densities selected from the reflected color density-transmitted color density conversion table as matching or closest to the combination of reflected color densities of the object to be measured is calculated. and is displayed by the transmitted color density display means σ. As described above, when expressing the color of an object to be measured (for example, a color sample) by printing with printing ink, it is easily determined at what transmission color density each color of ink should be printed.

FIG. 2 shows an example of the reflected color density-transmitted color density conversion table 01. On the left side, the combinations of reflected color densities obtained through each of the R filter, G filter, and B filter are shown. The right side shows combinations of transmitted color densities that correspond to the combinations of reflected color densities shown on the left.

To create such a table,
1. When actually measuring reflected color density using the color chart shown below.
It is preferable to obtain the reflected color density by measuring in the □ column, and then input the corresponding transmitted color density using a keyboard or the like to create a table.

Although it is common to measure the hair reflection color density using the R, G, B, amber or ND filters mentioned above,
An interference filter having a peak at the absorption portion of the spectral reflection curve of the printing ink may be used, or a spectral dispersion means such as a prism or a diffraction grating may be used. Here, the same filter used when creating the reflected color density-transmitted color density conversion table must be used when measuring the reflected color density of the object to be measured. Reflection color density -
The data of the transmission color density conversion table is stored in the first storage means, and such storage means may be an appropriate storage means such as a magnetic disk, a floppy disk, or a ROM.

As described above, the reflection color density-transmission color density conversion table is stored in advance in the first storage means.

The reflected color density measuring means section is for measuring the reflected color density of the object to be measured, and FIG. 3 shows an embodiment thereof.
, 7 diagrams are shown. In the example shown in Fig. 3, the object to be measured (1) such as a color sample is illuminated by a light source &l+, and the reflected light is input to a photoelectric conversion element (23) through a filter, where it is converted into an electrical signal. The filters are the same as those used when creating the reflected color density - transmitted color density conversion table, R filter, G filter
Three types of filters, B filters, or four types of filters, including an amber filter or an ND filter, are installed convertably. In this case, the filter may be switched electrically or manually. In addition, in the example shown in Figure 3, the light from the light source is emitted from an angle of 45 degrees and is received directly above. You may also do so. The electrical signal generated by the photoelectric conversion element is amplified by the amplifier (24), the necessary correction is made by the correction circuit, the logarithmic conversion process is performed by the logarithmic converter (to), and the analog signal is converted to an analog signal by the A/D converter. is converted into a digital signal and inputted and stored in the second storage means as a reflected color density.

The value of the electrical signal that has been logarithmically converted by the logarithmic converter (a) can be checked on the display meter (support). The display meter may be placed after the A/D converter fin to provide a digital display.

By measuring the object to be measured for each filter in the manner described above, a combination of reflected color densities of the object to be measured is obtained, and this is stored in the second storage means as described above. As the second storage means (2), an appropriate one such as a RAM can be selected. In the transmitted color density calculation means (4 (I), the transmitted color density is calculated according to a program stored in advance. An example of this is calculated based on the flowchart shown in FIG. The th reflected color density is read (step 83).Next, the distance between the reflected color density of the object to be measured and the reflected color density read from the first storage means (101) is calculated (step Sa). Expressing the distance calculation in a general formula, the first storage means (101 reflection color densities?TBfnl, To(nl, TRfn
l, the distance 3 A (nl is C5Afnl ]" = [TB, (nl - DB) 2+
(To(nl-Do)2+(TR(nl-DR')2
It can be obtained from the relational expression.

Since the distance SA fl between the reflected color density of the object to be measured and the first reflected color density in the table has not been determined so far, in step S4, the number and distance are assumed to be the minimum value. The information is stored at a predetermined address in the memory (step 85).

It is determined whether or not the value of this distance is 0 (step S6), and if it is 0, the distance calculation with other reflected color densities is stopped at that point, and the transmitted color density corresponding to that number is calculated. Call from the reflection color density-transmission color density conversion table (step Ss). If the distance is not 0, read the second reflection color density combination from the transmission color density conversion table and perform the same distance calculation to find the distance to the reflected color density of the object to be measured. A comparison is made with the first distance (step S4), and the number and distance of the smaller distance are stored. (Step Ss).

In this way, unless the distance becomes 0, the reflected color density of the object to be measured is calculated by calculating the distance from all the combinations of reflected color densities in the reflected color density → transmitted color density conversion table. A combination number with a small reflected color density is found. Next, by extracting the combination of transmitted color density corresponding to that number from the reflected color density and transmitted color density conversion table, the combination of Y, M, and C
The transmitted color density of each 1Bk separation plate can be determined.

Transparent color density determined in this way? Transparent color density display means such as CRT liquid crystal, printer, etc. (Y, M, C, Bk versions that can reproduce the specified color of the object to be measured by printing by displaying on 701) It may be possible to inform the operator of the transmitted color density, but this is explained in Japanese Patent Application No. 57-205217 filed by the present applicant entitled "Dot Area Ratio Determination Apparatus". If the color specified in the sample cannot be reproduced by overprinting ink, it is possible to quantitatively know to what extent it cannot be reproduced.
This is explained in detail in "Determination Method with Color Reproduction" published by No. 49665, and these ideas can be applied to the present invention as well.

Further, in this embodiment, a software-based processing using a microcomputer is described as the transmitted color density calculation means, but it goes without saying that a hardware configuration or an achievement Ij constant circuit may be used.

〔Effect of the invention〕

According to the color density conversion device of the present invention, when the color to be reprinted in conventional gravure printing is specified as the actual printed color, such as a color sample, even an inexperienced person can easily print the color. Moreover, in a short period of time, it is possible to determine the transmitted color density of the continuous-tone photodiode of each separation plate that should reproduce the designated color.

Next, according to the apparatus of the invention of this application, the continuous tone positive transmission color density of each plate is always determined in a standardized form, unlike the conventional method in which humans judge it, so the quality of printed matter is improved. It is possible to stabilize the

[Brief Description of the Drawings] Fig. 1 is a conceptual diagram of the present invention, Fig. 2 is an explanatory diagram of a reflected color density-transmitted color density conversion table, and Fig. 3 is an explanatory diagram of one embodiment of the reflected color density measuring means. , FIG. 4 is a flowchart for determining transmitted color density. 1... Color sample 21... Light source 22...
Filter 23...Photoelectric conversion element 24...Reflector 25...Correction circuit 26...Logarithmic converter 27...A/D converter 28...Display meter Patent filed by Toppan Printing Co., Ltd. Representative Kazuo Suzuki Figure 1 Figure 3 Figure 2 t5 h゛, 1] Medium `` '' I) 4 + Rem 4 Beam and Serum A (Figure ↓

Claims (1)

[Claims] 1) a first storage means storing a reflection color information-transmission color density conversion table indicating a relationship between combinations of reflection color information and combinations of transmission color densities in a continuous tone positive color separation plate of a plurality of colors; a reflective color information measuring means for determining a combination of reflective color information of the object to be measured; a second storage means for storing the combination of reflective color information determined by the reflective color information measuring means; and the first storage means. The reflected color information-transmitted color density conversion table stored in the storage means is compared with the combination of reflected color information of the object to be measured stored in the second storage means, and the combination of the reflected color information-transmitted color density conversion table stored in the second storage means is compared. Select the one that matches or is closest to the combination of reflected color information of the object to be measured from among the combinations of reflected color information, and calculate the combination of transmitted color densities that correspond to the selected combination of reflected color information. A color density conversion device comprising: a calculation means; and a transmission color density display means for displaying the calculated combination of transmission color densities.