JPH0418767B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides information on C (cyan), M (magenta), and Y for printing based on color information obtained by optically measuring a color sample. (yellow) or C,
The present invention relates to a device for determining the halftone area ratio of each color separation plate of M, Y, and BK (black).

[Technical background of the invention 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.

In printing factories, the most common multi-color printing method is a four-color printing method that uses C, M, Y, and BK color separation plates. , M, Y, and BK color separation plates are determined at what percentage of dot area should be used for printing, and the color separation plates are produced under these conditions.

Conventionally, the above-mentioned work involved preparing a color chart, which is a collection of many printed matter, in which the halftone area ratio of each C, M, Y, and BK color separation plate was changed at intervals of about 10%. Visually compare the sample and each color in the color chart and select the color closest to the color sample from the color chart. Using the fact that the dot area ratio is listed, find out the dot area ratio of each color separation plate required to print the selected color above, and create each color separation plate with that dot area ratio. to print,
Reproduces the color specified in the color sample.

However, this method requires manual work, and since there are a huge number of colors in the color chart, it takes time to compare it with color samples.
Another disadvantage is that the colors selected from the color chart vary depending on the operator, which tends to cause variations in the reproduced colors.

The present applicant has solved these shortcomings and developed accurate dot area ratios for each color separation when reproducing the colors specified in the color sample by overprinting Y, M, C, and BK color inks, for example. Japanese Patent Application No. 57-205217 (Japanese Patent Laid-open No. 59-94759) has proposed a device that can obtain
It was proposed in This inventive device irradiates light onto a color sample and converts the reflected light into R (red), G (green),
The light is received by the light receiving element through each B (blue violet) filter, and the color density is calculated, and the measured color density is compared with the color density of the color density-dot area ratio conversion table created in advance. The Y, M, C, and BK halftone dot area ratios corresponding to the color densities in the table that match or are most similar to the measured color densities are extracted, and these are sent to an output device such as a liquid crystal display. By outputting it, it is possible to determine the halftone area ratio of Y, M, C, and BK that can reproduce the color specified in the color sample.

In this dot area ratio determining device, in order to measure the color density of a color sample, reflected light from the color sample illuminated by a light source is received by a light source conversion element via a filter, and converted into an electrical signal. Obtaining color density. The filter usually has three color separation filters, a red (R) filter, a green (G) filter, and a blue-violet (B) filter, installed in a switchable manner, and configured to be switched manually or automatically. There is.

By the way, the filter actually used does not exhibit ideal spectral characteristics, and is a commonly used R, G, B color separation filter, Ratsuten No.
25, 58, and 47, they have ideal spectral characteristics as shown in Figure 4, that is, F _B has a transmittance of 100% only between 400 nm and 500 nm, and a transmittance of 100 only between 500 nm and 600 nm.
%F _G , transmittance 100% only between 600nm and 700nm
It is far from _FR . For this reason, there is a gap between the spectral characteristics of the filter, that is, around 500 nm and
The problem is that colors whose spectral characteristics change around 600 nm, such as pale yellow and orange, are difficult to capture, making it difficult to calculate accurate reflected color density.

For example, as shown in Figure 4, G filter and R filter
Consider four orange colors with a rising spectral reflection curve near 600 nm in the valley of the filter. In terms of color, its reflection intensity can be easily detected by a G filter. However, when it comes to colors, it is difficult to capture the reflected light by both the G filter and the R filter, and the colors cannot be differentiated and are measured as colors with similar densities. When it becomes colored, a reflection curve enters the spectral characteristic range of the R filter, making it easier to detect again. In addition, even if there is a slight difference in wavelength between a color whose reflection curve is attracted to the spectral characteristics of a color separation filter and a color whose reflection curve is not attracted to it, the density can be measured depending on whether or not it can be detected. There is a big difference. What I said above
The same can be said for light yellowish colors with a rising reflection curve near 500 nm.

For the reasons stated above, the dot area ratios obtained by measuring pale yellow and orange colors in the valleys of filter spectral characteristics using conventional dot area ratio determination devices have large errors and are difficult to reproduce the colors of the color samples. There was a drawback.

[Purpose of the invention]

The present invention solves the above-mentioned problems, and allows colors such as pale yellow and orange to be difficult to detect with the conventional three color separation filters between the spectral filters.
It is an object of the present invention to provide a halftone dot area ratio determination device that has sufficient measurement accuracy even for a color system corresponding to a wavelength and can determine a halftone dot area ratio that allows accurate color reproduction.

[Summary of the invention]

The present invention, which has been made to achieve the above object, irradiates a color sample with light and converts the reflected light from the color sample into R, G,
Through a total of five filters: a B color separation filter and an auxiliary filter that has a narrow spectral range with transmittance peaks in the valleys of the spectral characteristics of these color separation filters, that is, around 500 nm and 600 nm. Color information measurement means 2 for measuring color information
0, the measured R, G, and B color information stored in the second storage means 30, and the first color information created in advance.
The dot area ratio corresponding to the color information in the table that matches or most closely matches the measured color information by comparing the color information stored in the storage means 10 and the color information in the dot area ratio conversion table. halftone area ratio extraction means 40 for extracting combinations from the table;
and a determination means 50 for determining whether or not the determined combination of halftone area ratios is a color that falls within a predetermined range of values and corresponds to a wavelength between the valleys of the spectral characteristics, and a determination unit 50 that performs correction. If necessary, based on the reflected color density value obtained through the auxiliary filter,
A correction means 60 for correcting the halftone dot area ratios of R, G, and B, and is capable of determining the halftone dot area ratio of each color separation plate with high accuracy to reproduce the color of the color sample in printing. This is a dot area ratio determination device that can

[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, in which a first storage means 10 stores in advance a network corresponding to a combination of R, G, and B color information and a combination of color information of a plurality of color separation plates. A color density-dot area ratio conversion table indicating the correspondence with combinations of dot area ratios is stored, and a color density-dot area ratio conversion table indicating a correspondence relationship with a combination of dot area ratios is stored, and is
The color information combination data obtained by the color information measuring means 20 is temporarily stored in the second storage means 30. Color information includes color density, chromaticity, and the like. In the following description, color density will be used as an example of color information, but chromaticity is also acceptable. The combination data of color densities stored in the first storage means and the second storage means 30 includes, for example, three types of color data obtained by passing the color densities of color samples through R, G, and B filters. concentration and as shown in Figure 4.
This is a combination of color densities obtained through filters having transmittance peaks around 500 nm and 600 nm. The latter two filters were added for the purpose of compensating for the gaps in the spectral characteristics of the R, G, and B filters, and will hereinafter be referred to as the B-G auxiliary filter and the G-R auxiliary filter, respectively. These filters include
It is preferable to use a filter having so-called narrow band properties, which has a narrow spectral wavelength range but high peak transmittance, such as an interference filter.

Next, the color density selection means 40 selects a combination of color densities in the color density-dot area ratio conversion table stored in the first storage means 10 and the colors of the measured R, G, and B color samples. From among the combinations of densities, one that matches or is closest to the combination of color densities of the color sample is selected by performing distance calculations. A combination of halftone area ratios corresponding to the selected combination of color densities is calculated from the conversion table.

Next, the color determination means 50 determines whether the color of the color sample has a wavelength
Check whether the color is pale yellow or orange with a rising spectral reflection curve near 500 nm or 600 nm. For example, a method of checking is to define the upper and lower limits of the R, G, and B halftone dot area ratio values for orange color, and then select the combination of the halftone dot area ratios determined by the color density selection means. If it falls within this range, it is considered to be an orange color, and correction is applied by the dot area ratio correction means described below. The same applies to the judgment of pale yellow color. Although the following description will be made regarding orange colors, the same applies to pale yellow colors.

When the color check means determines that the color is orange, the halftone area ratio correction means 60 selects G-R stored in the second storage means 30.
Based on the color density measured by the auxiliary filter,
Each of the C, M, and Y halftone dot area ratios is corrected according to a certain stored correction formula.

To specifically explain the orange color shown in Figure 3,
After measuring color density and converting to halftone area ratio for color ~, this value falls within the range of C≦10%, M=50-100%, Y≧60 using a color check means, and is judged to be an orange color. and G stored in the second storage means.
The color density obtained through the -R auxiliary filter is read into the dot area ratio correction means. By the way, G-
The stronger the reflected light of the color sample that has passed through the R auxiliary filter, the lower the density is, closer to yellow, and conversely, the weaker the reflected light, the lower the density is, closer to red. Among the above colors, the color is the strongest and the reflected light is transmitted, and the color decreases in order, and the reflected light that is the most transmitted is the weakest. Therefore, a correction is made to slightly increase the halftone area ratio of the Y plate in the order of color, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,,,,,,, 90, 00, 10, 1, , , , , , , , , , , , , , , , , , , , , ,,,,,,,, Or, make corrections such as slightly reducing the halftone area ratio of the M plate in the order of color, , etc. The correction amount is determined according to a correction formula, and there is no need to particularly store a correction amount table.

As a correction formula, if the color density obtained through the auxiliary filter is d, then for example, ΔC=α ₁ d+β ₁ ΔM=α ₂ d+β ₂ ΔY=α ₃ d+β ₃ However, α ₁ , α ₂ , α ₃ The coefficients β ₁ , β ₂ , β ₃ are expressed by constants, etc.

The dot area ratio correction amount calculated as described above is stored in the second storage means 30.
It is added to each halftone dot area ratio and displayed by the halftone dot area ratio display means 70.

Regarding light yellow color, for example, if it falls within the following ranges: C≧40%, M≦10%, Y≧75%, it can be determined that the color is light yellow.

The above is an explanation based on a conceptual diagram of the apparatus of the present invention, and an example of the configuration of the optical system and signal processing system of the apparatus of the present invention will be explained based on FIG.

That is, the light source 2 serves as the reflected color density measuring means 20.
5, a group of filters 31 for R, G, B, etc., a photoelectric conversion element 23, an amplifier 24, a log amplifier 105, and an analog-digital converter 106. The reflected light is received by the photoelectric conversion element 23 by sequentially replacing each color filter such as R, G, B, B-G auxiliary filter, and G-R auxiliary filter. The photoelectric conversion element 23 outputs an electric signal of a magnitude corresponding to the amount of received light, and after amplifying it with the amplifier 24,
A log amplifier 105 performs logarithmic conversion to obtain a color density, and an analog-digital converter 106 converts this into a digital signal.

The combination of color densities obtained by measuring the color samples through each filter is stored in a predetermined area of the RAM 111 set as the second storage means 30 under the control of the CPU 110.

On the other hand, the first storage means 10 is EEPROM, UV
It is set in a predetermined area of the ROM 112 such as erasable PROM. The reflected color density to halftone dot area ratio conversion table stored in the first storage means 10 is used to obtain the color density by actually measuring a color chart as described above, and calculate the halftone dot area ratio corresponding to the color chart. The table is created by inputting information using the keyboard 102, performing the above operations and processing on all color charts, and sequentially storing them in a predetermined area of the ROM 112.

Further, the processing in the color density selection means 40, the color determination means 50, and the correction means 60 is performed by the ROM 1, which will be described later.
According to the program stored in 12, the CPU
This is executed at 110. The results are sent to the output means 70 consisting of the display unit controller 103 and the display unit 101, and are output. Note that AB is an address bus and DA is a data bus.

Next, the color density selection means 4 in the CPU 110
0. The processing procedure including the color determining means 50 and the correcting means 60 will be explained based on FIG.

A second storage unit stores the R, G, and B color densities obtained as a result of measuring the color sample as the object to be measured, and the color densities obtained through the B-G auxiliary filter and the G-R auxiliary filter. R, G, from the storage means 30 of
Read the color density of B (step S1), and
The color densities of R, G, and B are sequentially read from the color density-dot area ratio conversion table stored in the storage means 10, and the distance between the two is calculated, and the color density matches or is most similar to the color density of the color sample. Find out the color density in the table (steps S2 to S7)
The halftone area ratio corresponding to the color density is extracted (step S8).

Next, it is determined whether the measured color is pale yellow or orange. In addition to the above-mentioned expression, any other expression that takes into consideration the characteristics can be used as the expression.

If it is determined in step S9 that the color is pale yellow,
The color density of the B-G auxiliary filter is read from the second storage means, the correction amount is calculated using, for example, the above formula, and this is added to the halftone area ratio obtained in step 8. When it is determined that the color is orange, the color density of the G-R auxiliary filter is read from the second storage means, the correction amount is calculated in the same way, and this is added to the halftone area ratio obtained in step 8. By doing this, it is possible to correct the dot area ratio of pale yellowish or orange colors (steps S9 to S14), thereby adjusting the dot area ratio that can reproduce that color in all colors. It becomes possible to find it accurately.

In order to obtain the dot area ratio with higher accuracy, it is possible to interpolate the color density - dot area ratio conversion table, but this is described in Japanese Patent Application No. 57-205217 filed by the applicant. This method is explained in "Dot Area Ratio Determining Device," and if the color specified in the color sample cannot be reproduced by overprinting ink, it is also possible to quantitatively know to what extent it cannot be reproduced. This is explained in detail in ``Color Reproducibility Determination Method'' in Japanese Patent Application No. 58-249665, and these ideas can be applied to the present invention.

By the way, in the above explanation, after converting the measured color density to a halftone area ratio using a conversion table, corrections were made for pale yellow and orange colors, but another method is to convert the measured R, G, After adding the correction amount from the auxiliary filter to the B color density, the halftone area ratio may be calculated using a conversion table. In such a case, color determination and color density correction may be performed before processing by the color density selection means.

〔Effect of the invention〕

According to the dot area ratio determination device according to the present invention,
When the color to be reproduced in printing is specified as the actual printed color, as in the case of a color sample, it is extremely easy for even non-experienced people to easily and quickly determine each separation in which the specified color should be reproduced. The dot area ratio of the plate can be determined. In particular, the dot area ratio can be determined with sufficient measurement accuracy even for pale yellow and orange colors, which conventionally had low accuracy and difficulty in color reproducibility due to the spectral characteristics of color separation filters. .

Next, according to the device of the invention of this application, the halftone area ratio of each plate is always determined in a standardized form, unlike the conventional method in which humans judge it, so it is possible to stabilize the quality of printed matter. becomes.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram of the present invention, Figure 2 is a block diagram of the optical system and signal processing system of the present invention, Figure 3 is a flowchart of the processing in the present invention, and Figure 4 is a diagram of each filter in the visible light range. It is an explanatory diagram showing spectral characteristics. DESCRIPTION OF SYMBOLS 10... First storage means, 20... Color density measurement means, 30... Second storage means, 50... Color check means, 60... Halftone area ratio correction means, 40... Color density selection means, 70... Halftone dot area Rate display means.

Claims (1)

[Scope of Claims] 1. Color information measurement means for obtaining color information by optically measuring a color sample; A color information-dot area ratio conversion table in which halftone area ratios corresponding to the color information are stored in advance; and extracting means for extracting a halftone dot area ratio corresponding to the color information measured by the color information measuring means from the color information to halftone dot area ratio conversion table, the color specified by the color sample being reproduced by printing. In the apparatus for determining the halftone dot area ratio of each color separation plate, the color information measuring means includes R, G, and B color separation filters and a B filter having a transmittance peak near a wavelength of 500 nm.
-Equipped with a G auxiliary filter and a G-R auxiliary filter with a transmittance peak around 600 nm, and checks whether the color information input through the R, G, B color separation filter is within a preset range. a determination means for determining whether or not correction of the color information is necessary based on the color information; and a color input through an R, G, B color separation filter when the determination means determines that correction is necessary. correction means for correcting the halftone area ratio determined based on the information or the color information input via the R, G, B color separation filter, using the color information obtained via the auxiliary filter; A dot area ratio determining device characterized by: