JPH0650390B2 - Halftone dot area ratio determination device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to C (cyan), M (magenta), and Y for printing based on color information obtained by optically measuring a color sample. The present invention relates to a device for determining the dot area ratio of each color separation plate of (yellow) or C, M, Y, Bk (black).

[Technical background of the invention and its problems]

2. Description of the Related Art Conventionally, for the purpose of pre-designating a color of a portion of a printed matter by a purchaser, a small piece of paper for color designation called a color sample may be attached to a printing layout sheet.

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

In a printing factory, the most common multicolor printing method is the four-color printing method using C, M, Y, and Bk color separation plates. To print the designated part in the same color as the color sample, use the C ,
The percentage of the halftone dot area of each color separation plate of M, Y, and Bk is determined to determine the printing rate, and the color separation plate is produced and printed under the conditions.

Conventionally, the above-mentioned work involves preparing a color chart, which is an aggregate of a large number of printed matters, in which the dot area ratios of C, M, Y, and Bk color separation plates are changed at intervals of about 10%, and Visually compare the color sample and each color in this color chart, select the color closest to the color sample from the color chart, and in the color chart, separate each color required to print each color in the color chart. Knowing the halftone dot area ratio of each color separation plate necessary for printing the selected color by utilizing the fact that the halftone dot area ratio of the plate is described, It is produced and printed to reproduce the colors specified in the color sample.

However, this method requires manual work,
In addition, since the number of colors in the color chart is enormous, it takes time to compare with the color sample, and the color selected from the color chart differs depending on the operator, and the reproduced color tends to vary. There are drawbacks.

The applicant of the present invention has solved such drawbacks and, when reproducing a color designated by a color sample, for example, by overprinting inks of respective colors Y, M, C, and Bk, an accurate halftone dot area of each color separation plate. A device capable of obtaining the rate was proposed in Japanese Patent Application No. 57-205217 (Japanese Patent Laid-Open No. 59-94759). This invention device is
The color sample is irradiated with light, and the reflected light is R (red), G
The color density is calculated by receiving light on the light receiving element through each of the (green) and B (blue violet) filters, and the measured color density and the color of the previously prepared color density-halftone dot area ratio conversion table. The density is compared, the halftone dot area ratios of Y, M, C, and Bk corresponding to the color density in the table that is the same as or closest to the measured color density are extracted, and this is output to an output device such as a liquid crystal. By outputting, it is possible to determine the Y, M, C, and Bk halftone dot area ratios capable of reproducing the color designated by the color sample.

According to such an apparatus, the halftone dot area ratio of the Y, M, C, and Bk printing plates capable of reproducing the color designated by the color sample can be determined extremely easily and accurately, and the work load can be significantly reduced. It becomes possible to reduce.

Thus, in this halftone dot area ratio determination device, in order to measure the color density of the color sample, the reflected light from the color sample illuminated by the light source is received by the photoelectric conversion element through the filter and converted into an electrical signal. To obtain the color density. Normally, a red (R) filter, a green (G) filter, a blue violet (B) filter and the like are switchably attached to the filter, and the filter is configured to be manually or automatically switched.

The electric signal photoelectrically converted by the photoelectric conversion element passes through an amplifier and a correction circuit, undergoes logarithmic conversion processing by a logarithmic converter, and then A
Each color density is obtained by converting the analog signal into a digital signal by the / D converter.

In such a configuration, the filter is switched to R,
Since G, B and other color densities are obtained, manual switching,
Any automatic switching takes time, and the device becomes large in order to make several kinds of filters variable, and since there are moving parts, maintenance of the device is troublesome. ing.

In addition, the filter actually used does not exhibit ideal spectral characteristics, and is the currently known best result R, G, B color separation filter, which is Ratten NO, 25, 5
As shown in FIG. 3, even if it is 8 or 47, the ideal spectral characteristic, that is, F _B , 50 with a transmittance of 100% only between 400 nm and 500 nm,
The transmittance of 100% only between 0nm~600nm F _G, 600nm~700
It is far from F _R, which has 100% transmittance only between nm. For this reason, there remains a problem that it is difficult to capture a color whose spectral characteristic changes in the valley between the filters and the spectral characteristic of the filter, that is, near 500 nm or 600 nm in this example, for example, a color such as pale yellow or orange.

Furthermore, when an interference filter is used as the filter, there is no problem, but the color separation filters made of gelatin such as the Ratten filter described above show fading over time, which changes the spectral characteristics and adversely affects the measurement results. It also includes the drawbacks that it brings.

[Object of the Invention]

The present invention solves the above-mentioned problems of the prior art, and Y, M, C or Y, M, C, Bk capable of reproducing the color of an object to be measured (hereinafter referred to as a color sample) such as a color sample by printing. Not only can the halftone dot area ratio of each color separation plate of such colors be easily determined, but higher measurement accuracy can be obtained, the measurement time can be significantly shortened, and maintenance management becomes easier. It is an object of the present invention to provide a halftone dot area ratio determination device which is capable of maintaining a high measurement accuracy without any change over time.

[Outline of Invention]

The present invention made to achieve the above object does not use a color separation filter in irradiating a color sample with light and separating the reflected light from the color sample, and the reflected light is spectrally dispersed by a prism or a diffraction grating. The light is spectrally dispersed using a means, the spectrally dispersed light is received by a linear photoelectric conversion element, an electric signal from the photoelectric conversion element is processed, and measured through, for example, ideal R, G, and B filters. The color density equal to the color density obtained is compared with the color density of the previously prepared color density-halftone dot area ratio conversion table, and the table is the same or closest to the color density measured. A combination of dot area ratios corresponding to the color density of is extracted from the table,
This makes it possible to determine the halftone dot area ratio of each color separation plate that can reproduce the color of the color sample by printing by combining this halftone dot area ratio.

Example of Invention

The present invention will be described below in detail based on the embodiments shown in the drawings. FIG. 1 is an explanatory diagram showing an optical system and a signal processing system of a halftone dot area ratio determining device according to the present invention.

(1) is a color sample, which is placed on a plain white plate. A light source (21) is provided to illuminate the color sample (1). As for the installation position of the light source (21), a plurality of light sources may be provided at a slanting angle of 45 ° as shown in the figure, or may be provided right above and the reflected light may be taken in from a slanting direction of 45 °. There is no particular limitation. The reflected light from the color sample is guided to the slit (123) via the mirror (122), for example. The reflected light whose width is limited by the slit (123) is incident on the spectral dispersion means. In this embodiment, the prism (124) is used as the spectral dispersion means, but it may be a diffraction grating or the like. The reflected light incident on the prism (124) is spectrally dispersed, and a linear photoelectric conversion element (125) is arranged at a position where the visible light region (400 nm to 700 nm) of the spectrally dispersed light can be received. As the line-shaped photoelectric conversion element (125), a CCD
Type, MOS type, array sensor such as photocell, and the like are applicable. The number of photoelectric conversion elements (125) can be variously selected according to need. For example, if the wavelength range of 400 nm to 700 nm is dispersed with a wavelength resolution of 1 nm, 300 or more elements will suffice.

This photoelectric conversion element (125) is driven by a sensor control circuit (126), and the sensor control circuit (126) is a cpu described later.
It operates according to the command from (138).

The electric signal from the photoelectric conversion element (125) for each pixel in the wavelength region of 400 nm to 700 nm is led to the switching circuit (130) via the amplification circuit (127) and the analog / digital conversion circuit (129).

The output signal from the photoelectric conversion element (125) contains errors such as variations in the wavelength characteristics of the light source and the characteristics of the photoelectric conversion element, and these errors must be removed. For this reason, in this device, three line buffers (131), (132), (1
33) and a correction circuit (134) are provided. That is, the line buffer 1 (131) measures the reference white paper instead of the color sample (1), stores the output signal of each pixel from the line sensor (125) of this spectrally dispersed light, and stores it in the line. Buffer 2 (13
Similarly, the reference signal for black paper is stored in 2), and the measurement signal for the color sample is stored in the line buffer 3 (133). The switching of the inputs to the three line buffers is performed by receiving a command from CPu (138).
0).

FIG. 2 shows an example of the output signal for each wavelength stored in each line buffer. The horizontal axis represents wavelength and the vertical axis represents signal level. The reference white curve is W, the reference black curve is B, and the color sample curve is O. As is clear from FIG. 2, it is understood that W and B are not at the same level for each wavelength, and therefore the color sample curve O also contains an error rather than an accurate spectral curve.

In order to remove this error, a signal for each pixel is input to the correction circuit (134) from each line buffer (131), (132), (133). The timing is the memory control circuit (14
It is controlled by 2). In the correction circuit (134), the signal levels Wλ of white, black, and color samples for a certain pixel, that is, a certain wavelength,
Assuming Bλ and Oλ, the following equation for taking the ratio of the signal level difference between white and the color sample and the signal level difference between white and black, Roλ = (Wλ-Oλ) / (Wλ-Bλ), is executed. It is possible to obtain the spectral signal Roλ of the removed color sample. Ro for each pixel
By obtaining λ, it is possible to obtain a set of color sample output signals from which errors have been removed in all wavelength bands received by the photoelectric conversion element (125), that is, a spectral signal Ro. The spectral signal Ro obtained in this way is indicated by the broken line R in FIG.
Denote by o.

Next, based on the corrected spectral signal Ro of the color sample, color information such as color density and chromaticity for the color shown in the color sample is obtained.

For this purpose, the correction circuit (134) is connected to the integration circuit (135), and the integration circuit (135) further includes a spectral characteristic signal memory (13
6) is connected, and the ideal color separation spectral characteristic shown by the broken line in FIG.
A signal for one or several color specifications of the spectral characteristics of the three stimulus values of the IE, arbitrarily created spectral characteristics, etc. is stored,
One of these is used to obtain color information. In this embodiment, the following description will be made assuming that the above-mentioned ideal color separation spectral characteristics F _B , F _G , and F _R are used.

In the integrating circuit (135), the ideal color separation read out from the color sample spectral signal Ro input from the correction circuit (134) and the spectral characteristic signal memory (136) by a command from the memory control circuit (142). The color density corresponding to B, G, and R can be obtained by sequentially performing integral calculation with the characteristics F _B , F _G , and F _R, and then performing logarithmic conversion in the logarithmic conversion circuit (137).

For example, for the color density for B, the reflectance I _B of the color sample for _B is first obtained by the integral calculation of the ideal color separation characteristic F _B and the spectral signal Ro, I _B = ∫Roλ · F _B λdλ further color density D _B can be determined by performing a D _{B =} log 1 / I B becomes the formula in logarithmic converter (137). Similarly, for G and R, ideal color separation spectral characteristics
F _G , F _R from the spectral characteristic signal memory (136) to the integration circuit (135)
Read in and perform integral calculation with the spectral signal Ro of the color sample,
Further, by performing logarithmic conversion in the logarithmic conversion circuit (137), each color density D _G , D _R can be obtained.

As a result, it is equivalent to obtaining the color density by performing color separation using a color separation filter having ideal color separation characteristics F _B , F _G , and F _R, and it is possible to obtain accurate results for colors such as pale yellow and orange. It can offer its characteristics.

According to the present invention, the means for obtaining the color information as described above is used not only when measuring the color sample but also when creating the color information-halftone dot area ratio conversion table. That is, Y, M, C, and Bk inks are used on the printing paper, and the halftone dot area ratio is 0.
% To 100% at appropriate intervals, for example Y, M,
The C and Bk plates are sequentially changed at 10% intervals and printing is actually performed to create a color chart. Such combinations when using Y, M, C, and each version of Bk, 11 ⁴ = 1464
It becomes 1 way, and you can get the color chart of 14641 sheets.

With respect to all of the color charts created in this way, the color information (color density in this example) is measured by the above-mentioned means for measuring color information in exactly the same manner as in the case where the DUT is a color sample. Then, the obtained color information is sent to the cpu (138). The cpu (138) executes the pre-stored program shown in FIG. 4 and inputs the color density of the color chart (step Sa). Then, the color chart of Y, M, C, and Bk is input. Since the halftone dot area ratio of each plate is described, the halftone dot area ratio of each plate of the color chart whose color information is measured is input by using the keyboard (138) (step Sb).

By performing such an operation on all color charts, for example, the relationship between the combinations of halftone dot area ratios in which the Y, M, C, and Bk plates are sequentially changed by 10% and the color information corresponding to the respective combinations. Is created, that is, a color information-halftone dot area ratio conversion table is created, and a table memory (139)
Is stored in the predetermined address (step Sc).

The color information referred to here is the color density, chromaticity, etc. as described above, and, of course, the color information is stored in the spectral characteristic memory (13) when the color information-halftone dot area ratio conversion table is created.
4) Ideal color separation spectral characteristics F _B , F _G , F _R read out from 4)
When the color density is obtained by using, it is necessary to similarly set the color information as the color density at the time of measuring the color sample.

An example of the color density-halftone dot area ratio conversion table created in this way is shown in FIG.

Logarithmic conversion circuit obtained by measuring the color sample (13
The color densities D _B , D _G , and D _R output from 7) are input to the cpu (138), and the cpu (138) calculates the halftone dot area ratio according to a program stored in advance.

An example of this will be described with reference to the flowchart shown in FIG. 5. The color densities D _B , D _G , and D _{R of} the color sample are input (step S ₁ ), and color information (in this case, the color information from the table memory 139) is input. color density) - 1st color density dot percent table is read (step S _3). Then, distance calculation color density read from the color concentration and memory (139) of the color samples is performed (step S _4). If Shimese distance computation in general formula, memory color density from _{(139) T B (n)} , T G (n), T
If it is _R (n), the distance S _A (n) is [S _A (n)] ² = [T _B (n) −D _B ] ² + [T _G (n) −D _G ] ² + [ T
It can be obtained from the relational expression of _R (n) −D _R ] ² .

Since the distance S _A (1) between the color density of the color sample and the first color density in the table has not been obtained by then,
In step S ₄ , the number and the distance are stored in a predetermined address of the internal memory as the minimum value (step
S ₅ ).

For this distance, it is determined whether or not the value is O (step S ₆ ), and if it is O, the distance calculation with other color densities is stopped at that point, and the halftone dot area ratio corresponding to that number is stopped. Color density −
Called from the halftone dot area ratio conversion table (step S _8).
If the distance is not O, the second color density combination is read from the color density-halftone dot area ratio conversion table, the same distance calculation is performed, and the distance from the color density of the color sample is calculated. comparison between the distance is carried out (step S ₄₎ number and distance towards smaller distance is stored (step
S ₅ ).

In this way, unless the distance becomes O, the distance between the color density of the color sample and all the combinations of the color density of the color density-halftone dot area ratio conversion table is calculated. The combination number is required.
Next, by extracting the combination of the halftone dot area ratios corresponding to the number from the color density-halftone dot area ratio conversion table, the Y, M, C and Bk color separation versions corresponding to the measured color samples are extracted. The dot area ratio can be obtained.

By displaying the halftone dot area ratio obtained in this way on an output device (141) such as a liquid crystal or printer, the color designated by the color sample can be reproduced by printing Y,
It is possible to inform the operator of the dot area ratio of each of M, C, and Bk plates. It is also possible to directly input the determined halftone dot area ratio into a scanner and use it as color separation data.

In order to obtain the halftone dot area ratio with higher accuracy, it is conceivable to interpolate a color density-halftone dot area ratio conversion table, which is described in Japanese Patent Application No. 57-2.
In detail in No. 05217, it is also possible to quantitatively know how much color cannot be reproduced if the color specified in the color sample cannot be reproduced by overprinting ink,
For more details, see Japanese Patent Application No. 58-249665.
Since these are not the subject of the present invention, their description is omitted here.

In the above description, the calculated dot area ratio is Y,
It is a color separation version of 4 colors of M, C, Bk, but 3 of Y, M, C
Even when it is desired to reproduce colors by color printing, the halftone dot area ratios of the Y, M, and C3 plates can be obtained in the same manner with this apparatus. That is, a color chart is printed in three colors of Y, M, and C, color information of this color chart is obtained, and the halftone dot area ratios of Y, M, and C are input from the keyboard, so that the color information and Y, M , A C3 plate halftone dot area ratio table is created and stored in the table memory, and the measured color sample color information and the color information in the table are sequentially compared to correspond to the matched or closest color information. By extracting the halftone dot area ratio from the table, it is possible to determine the halftone dot area ratio of the Y, M and C3 plates that can reproduce the color of the color sample.

〔The invention's effect〕

As described above, the halftone dot area ratio determining device according to the present invention spectrally disperses the reflected light from the object to be measured, such as a color sample or a color chart, by the spectral dispersal means, and forms a linear photoelectric conversion element. By receiving the output signal at each wavelength, that is, a spectral characteristic signal by receiving light, and obtaining color information by performing an integral operation of the spectral characteristic signal and the signal for color specification, it is possible to obtain specific color information as in the prior art. The deficiency that colors are difficult to capture has been resolved, the halftone dot area ratio can be accurately determined for any color, and since there is no need to switch filters, the time required for measurement can be shortened and filter switching is possible. Since the moving parts of can also be eliminated, maintenance management is easy, and the measurement accuracy does not change over time as when using a gelatin filter. In which excellent effects such as can be maintained have measurement accuracy.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a halftone dot area ratio measuring device of the present invention, FIGS. 2 and 3 are explanatory diagrams showing spectral characteristics in a visible light region,
4 and 5 are flowcharts of a program for determining the halftone dot area ratio, and FIG. 6 is an explanatory diagram showing an example of the color information-halftone dot area ratio conversion table. 1-color sample, 21-light source 122-mirror, 123-slit 124-prism, 125-line sensor 135-integrator circuit, 136-spectral characteristic memory 138-cpu, 139-table memory

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A 61-51509 (JP, A) JP-A 59-94759 (JP, A) JP-A 52-6581 (JP, A) JP-A 53- 49486 (JP, A) JP 57-52806 (JP, A) JP 53-52183 (JP, A) JP 54-14290 (JP, A) Actual development 58-65538 (JP, U)

Claims (1)

[Claims] 1. A color sample is optically measured to obtain color information, and a color designated by the color sample is obtained based on this color information and a color information-halftone dot area ratio conversion table created and stored in advance. In a device that determines the dot area ratio of each color separation plate that can be reproduced by printing, a means for spectrally dispersing the reflected light from the measured object such as a color sample and a color chart, and a device for spectrally dispersed light. A line-shaped photoelectric conversion element that receives the visible light wavelength range and decomposes the visible light wavelength range into an electrical signal by converting it to an electrical signal, and a spectral signal output from the line-shaped photoelectric conversion element and a color A means for obtaining color information of the object to be measured by integrating the spectral characteristic signal, and the color information measured together with the corresponding halftone dot area ratio separately input when the object to be measured is a color chart. Data of halftone dot area ratio conversion table Then, when the object to be measured is a color sample, the measured color information is compared with the color information in the table, and the color in the table that matches or is closest to the color information in the color sample is stored. Means for extracting the halftone dot area ratio corresponding to the information as the halftone dot area ratio of each color separation plate capable of reproducing the color specified by the color sample by printing. Rate determining device.