JPWO2011048743A1 - Color densitometer and density measuring method - Google Patents

Abstract

In the color densitometer 10 and the density measuring method according to the present invention, the non-polarized spectral reflectance coefficient of the sample 1 of the printed matter is measured using the first illumination light receiving system, and the geometry approximates that of the first illumination light receiving system. And the third illumination light receiving system, the non-cross-polarized reflectance coefficient and the cross-polarized reflectance coefficient of the sample 1 are measured, respectively, and the measured non-cross-polarized reflectance coefficient and the cross-polarized reflectance coefficient are The surface reflectance coefficient of the sample 1 is obtained from the difference between the two, and the obtained surface reflectance coefficient is uniformly subtracted from the non-polarized spectral reflectance coefficient at each wavelength to thereby remove the spectral reflectance of the sample from which the surface reflection has been removed. A reflectance coefficient is determined.

Description

  The present invention relates to measurement of reflection characteristics of printed matter, and more particularly, to a color densitometer and a density measuring method for obtaining ink density and color value of the printed matter from the measurement result.

  With respect to the printed matter, the operator appropriately removes the printed matter from the printing press, and measures the reflection characteristics of the CMYK test patch formed outside the original printing area of the printed matter with a color densitometer, thereby controlling the print quality. For example, a defective product is identified. The print quality is managed by ink density, and the density is measured according to ISO5-4.

  FIG. 11 is a diagram for explaining the measurement method. As shown in FIG. 11, the ink density illuminates the sample surface Is with illumination light Il from a direction of 45 degrees with respect to the normal line of the sample surface Is, and the reflected light in the normal direction is received by the light receiving system D. Measured by 45: 0 geometry. Alternatively, the ink density is measured by a 0:45 geometry in which the illumination light I1 and the light receiving system D are interchanged.

  Here, FIG. 11A shows a state immediately after printing, and FIG. 11B shows a state after sufficient time has passed. Immediately after printing, as shown in FIG. 11A, the ink layer Ik is not dried, and the ink layer Ik compensates for the irregularities on the surface Ps of the paper P. The surface Is) becomes smooth. Therefore, the reflected light Ss on the surface of the ink layer Ik (the sample surface Is) is specularly reflected in the direction of −45 degrees with respect to the normal line, and does not have a component incident on the light receiving system D in the normal direction. On the other hand, the component of the illumination light incident on the ink layer Ik reaches the paper P and is diffused therein, and then a part is diffused and radiated from the surface Ps, and again passes through the ink layer Ik and passes through the surface (the sample). Diffuse radiation (indicated by dashed arrows) is emitted from the surface Is). This diffused light is colored by ink, and its normal component Dp is incident on the light receiving system D.

  On the other hand, when the ink layer Ik is dried, the surface Is of the ink layer Ik is uneven along the surface Ps of the paper P as shown in FIG. For this reason, irregular reflection occurs on the surface of the ink layer Ik (the sample surface Is), and the normal component Ds of irregularly reflected light (indicated by a two-dot chain line arrow) from the surface not colored by the ink is colored diffused light. The normal component Dp is incident on the light receiving system D. That is, the reflected light from the printed surface after drying has the spectral characteristics of the illumination light Il from the surface of the ink layer Ik as well as the colored diffused light (indicated by the dashed arrows) from the inside of the ink layer Ik. Almost maintained irregularly reflected light is superimposed. Thus, the density after drying is lower than the density immediately after printing, and this phenomenon is called dry down or dry back.

  Therefore, in order to respond quickly to the density change during printing and suppress the occurrence of the defective product, it is necessary to measure the density immediately after printing. It cannot be directly compared with the concentration of the reference sample in the dry state.

  Therefore, in order to eliminate the influence of the dry down and compare the density immediately after printing with the density of the reference sample, a polarizing filter having polarization characteristics orthogonal to each other is inserted in the optical path between the illumination system and the light receiving system. Measurement is conventionally performed in, for example, Patent Document 1 and Patent Document 2. This is because the normal component Dp of the colored diffused light, which has been depolarized by diffusion in the paper P, is approximately half of the normal component Dp that passes through the polarization filter of the light receiving system and is received. Since the polarization characteristic is maintained, it is utilized that the light is blocked by a polarizing filter of the light receiving system. Thus, irrespective of the state of the surface of the ink layer Ik (the sample surface Is), it is possible to eliminate the influence of the surface reflected light and obtain a density comparable to the dry state even immediately after printing.

However, the transmittance of the polarizing filter is about 40% at the highest, and the decrease in S / N (SN ratio) due to the light loss and the decrease in the repeatability caused by it are at best 1 / 6 or less ((0.4) ^{2 with two} filters on the light emitting side and the light receiving side).

  On the other hand, the color value that should be correlated with the visual evaluation of the printed product after drying needs to be measured in consideration of the surface reflected light as in the case of the visual evaluation. Therefore, a color densitometer that measures both the density and the color value. After drying, it is necessary to attach and detach the polarizing filter depending on whether the surface reflection light is removed or the surface reflection light is added. This includes a type that is manually attached and detached, and a type that incorporates a drive mechanism for attachment and detachment, but the former places a burden on the user, and the latter is expensive. Further, in order to suppress the influence of the surface anisotropy, in the 45a (a: annular): 0 illumination that illuminates in a ring shape from all directions, the polarizing filter becomes a ring shape and costs increase.

U.S. Pat. No. 4,961,646 JP 2001-158083 A

The present invention has been made in view of the above circumstances, and its object is to provide a color densitometer and a density capable of measuring a spectral reflectance coefficient by removing or taking into account surface reflected light with a simple and low-cost configuration. It is to provide a measurement method.
In the color densitometer and the density measuring method according to the present invention, the non-polarized spectral reflectance coefficient of the sample of the printed matter is measured using the first illumination light receiving system, and the second and second geometries approximate to the first illumination light receiving system are measured. Using a three-illumination light receiving system, the non-cross-polarized reflectance coefficient and the cross-polarized reflectance coefficient of the sample were measured, respectively, and the difference between the measured non-cross-polarized reflectance coefficient and the cross-polarized reflectance coefficient The surface reflectance coefficient of the sample is obtained from the sample, and the obtained surface reflectance coefficient is uniformly subtracted from the non-polarized spectral reflectance coefficient at each wavelength, thereby removing the spectral reflectance of the sample. A coefficient is determined. For this reason, the color densitometer and the density measuring method according to the present invention can measure the spectral reflectance coefficient with the surface reflection light removed or added with a simple and low-cost configuration.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

It is a block diagram which shows the structure of the color densitometer which concerns on the 1st Embodiment of this invention. It is a flowchart for demonstrating the measurement process of the spectral reflectance coefficient which removed the influence of the surface reflected light of the sample by the color densitometer shown in FIG. It is a graph which shows the relationship between the spectral reflectance coefficient containing surface reflection of the magenta printing surface, and the spectral reflectance coefficient which removed surface reflection. It is a graph which shows the light emission characteristic of white LED and purple LED. It is a block diagram which shows the structure of the color densitometer which concerns on the 2nd Embodiment of this invention. It is a front view of the incident end of the optical fiber in the color densitometer shown in FIG. FIG. 6 is an optical path diagram of first to third illumination light receiving systems in the color densitometer shown in FIG. 5. It is an optical path diagram in the color densitometer which concerns on the 3rd Embodiment of this invention. It is a figure of the illumination light-receiving system in the color densitometer which concerns on the 4th Embodiment of this invention. It is a figure of the illumination light-receiving system in the color densitometer which concerns on the 5th Embodiment of this invention. It is a figure for demonstrating the incident reflected light of the printing sample surface.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted suitably.

(Embodiment 1)
FIG. 1 is a block diagram showing the structure of a color densitometer 10 according to the first embodiment of the present invention. 1A shows the front of the optical system, and FIG. 1B shows the side. As shown in FIG. 1, the color densitometer 10 includes a drive circuit 2d and a white LED 2, a cylindrical mirror 3, a reflecting mirror 4a and an objective lens 4, a drive circuit 5d, a purple LED 51 and a polarizing filter 51f, a spectral filter The apparatus 6, the arithmetic control unit 7, the external IF 8, the polarizing filter 9 f, the light receiving element 9, and the IV conversion circuit 9 d are provided, and the specimen 1 of the printed material is irradiated with illumination light and its spectral reflection characteristics are measured. The ink density and the color value are obtained. For this purpose, first, the emitted light 2a of the white LED 2 is reflected by a cylindrical mirror 3 formed by cutting out a part thereof, and the measurement surface 1s of the sample 1 is reflected from the surface normal by the reflected emitted light 2a. Illuminated from almost all directions at an angle of 45 degrees. The component 2b in the normal direction in the reflected light from the measurement surface 1s due to this illumination is incident on the spectroscopic device 6 via the reflecting mirror 4a and the objective lens 4, and the non-polarized spectral distribution Inp (λ ) Is measured. The non-polarized spectral distribution Inp (λ) is converted into a non-polarized spectral reflectance coefficient Rnp (λ) including diffuse reflected light from the inside of the ink and paper and surface (scattered) reflected light.

  On the other hand, in order to eliminate the influence of dry-down after ink drying, the spectral reflectance coefficient Rse (λ) of the sample from which the surface reflection is removed is obtained (estimated) from the measured non-polarized spectral reflectance coefficient Rnp (λ). For this purpose, polarized light is used. In order to use this polarized light, the color densitometer 10 of the present embodiment does not give the measurement system for measuring the spectral reflection characteristic a polarization characteristic, but a polarization characteristic in a measurement system of a specific wavelength provided separately. Is given.

  That is, the first measurement unit is configured to measure the non-polarized spectral reflectance coefficient Rnp (λ). There are provided second and third measurement units each including a first illumination light receiving system in the first measurement unit and second and third illumination light receiving systems that approximate a geometric relationship (geometry) with respect to the measurement surface 1s. More specifically, the angles from the surface normal of the measurement surface 1s between the illumination light flux of the second and third measurement units and the received measurement surface reflected light flux are respectively the values of the first measurement unit. The second and third measurement units are provided so as to approximate the angle from the surface normal to the illumination light beam and the received measurement surface reflected light beam, and the second measurement unit has a predetermined wavelength, for example, a single color. The non-crossed polarization intensity Inx of the sample 1 is measured at the wavelength of the LED, and this is converted into a non-crossed polarization reflectance coefficient Rnx. The third measurement unit has polarization characteristics in which the illumination system and the light reception system in the third illumination light receiving system are orthogonal to each other, and the cross polarization intensity Ix of the sample 1 is measured at the same wavelength as the second measurement unit. It is converted into a cross polarization reflectance coefficient Rx.

  More specifically, the first illumination light receiving system forms a 45a: 0 geometry, and neither the illumination system nor the light receiving system includes a polarizing filter. On the other hand, in the second illumination light receiving system of the second measurement unit, for example, the radiated light 51a of the purple LED 51 having a center wavelength of 410 nm passes through the polarizing filter 51f and passes through the measurement surface 1s at an angle of 45 degrees from the surface normal. Illuminated from the azimuth direction, the component 51b in the normal direction in the reflected light from the measurement surface 1s is received by the spectroscopic device 6 from the notched portion of the cylindrical surface mirror 3 via the reflecting mirror 4a and the objective lens 4, The cross polarization intensity Inx is measured.

  Further, in the third illumination light receiving system of the third measurement unit, the radiated light 51a of the purple LED 51 passes through the polarizing filter 51f and illuminates the measurement surface 1s from one direction at an angle of 45 degrees from the surface normal to measure the measurement surface 1s. The component 51c in the vicinity of the normal line in the reflected light from the light is received by the light receiving element 9 through the polarizing filter 9f, and the current generated by this light reception is converted into a voltage value by the IV conversion circuit 9d, and the cross polarization intensity Ix is measured.

  Accordingly, the second illumination light receiving system reaching the spectroscopic device 6 forms a 45: 0 geometry, and the third illumination light receiving system reaching the light receiving element 9 forms a geometry approximate to 45: 0. The polarization filter 9f disposed in front of the light receiving element 9 of the third illumination light receiving system is orthogonal to the polarization filter 51f, and the second illumination light receiving system measures the non-crossing reflectance coefficient Rnx. The third illumination light receiving system measures the cross reflectance coefficient Rx.

  Thus, the cost can be reduced by using the monochrome purple LED 51 as the light emitting element in the second and third illumination light receiving systems. The second illumination light receiving system includes an illumination system of the third illumination light receiving system and a light receiving system of the first illumination light receiving system that does not have the polarizing filter 9f, and the illumination system is shared with the third illumination light receiving system. By sharing the light receiving system with the light receiving system of the first illumination light receiving system, the configuration becomes simpler and the cost can be reduced. In this case, the 410 nm wavelength region portion of the first illumination light receiving system is the second illumination light receiving system.

  The arithmetic control unit 7 controls the white LED 2 and the purple LED 51 and the spectroscopic device 6 via the drive circuits 2d and 5d, respectively. In addition, the arithmetic control unit 7 sets the non-polarized spectral distribution Inp (λ), the non-cross polarized intensity Inx, and the cross-polarized intensity Ix by the first, second, and third illumination light receiving systems to the non-polarized spectral reflectance, respectively. The coefficient Rnp (λ), the non-cross polarization reflectance coefficient Rnx, and the cross polarization reflectance coefficient Rx are respectively converted. Further, the arithmetic control unit 7 converts the non-polarized spectral reflectance coefficient Rnp (λ) into a spectral reflectance coefficient Rse (λ) from which surface reflection has been removed as described later, and further the spectral reflectance coefficient Rnp. (Λ) and Rse (λ) are converted into color values and densities, and communicated with an external device such as a personal computer through an external interface (external IF) 8.

The calculation method of the density and the color value is as follows. First, the tristimulus values X, Y, and Z that serve as a reference for the color value are the sum of products of the spectral reflectance coefficient R (λ) of the sample, the spectral distribution I (λ) of the illumination light, and the spectral sensitivity s (λ). S;
S = ∫I (λ) · R (λ) · s (λ) dλ
And the product sum Sw similarly obtained for the spectral reflectance coefficient rw (λ) of the white reference surface;
Sw = ∫I (λ) · Rw (λ) · s (λ) dλ
And the ratio R;
R = S / Sw
It is requested from.

  Here, the standard observer color matching functions x (λ), y (λ), and z (λ) defined by the CIE are used for the spectral sensitivity s (λ). , Y, Z are obtained. In addition, it is recommended that the standard illuminant D50 defined by the CIE be used as illumination light for the color measurement of a printed sample.

On the other hand, the density D is obtained from Rs similarly obtained using the non-printing surface of the printing paper as a white reference.
D = −log (1 / Rs)
Sought by. Here, spectral sensitivities r (λ), g (λ), b (λ), and v (λ) defined by ISO 5-33 or the like are used as the spectral sensitivities s (λ). Dr, Dg, Db, and Dv are obtained. For measuring the density of a printed sample, it is recommended that the standard illuminant A defined by the CIE is used as illumination light.

  FIG. 2 is a flowchart for explaining the process of measuring the spectral reflectance coefficient Rse (λ) from which the influence of the surface reflected light of the sample 1 is removed by the color densitometer configured as described above. The arithmetic processing unit 7 first turns on the white LED 2 via the drive circuit 2d (# 1), and the spectroscopic device 6 removes the component 2b in the normal direction of the sample reflected light illuminated by the first illumination light receiving system. Measured as a polarized spectral distribution Inp (λ) (# 2), and converted into a non-polarized spectral reflectance coefficient Rnp (λ) using the spectral distribution of the white reference surface reflected light by the white LED 2 illumination light measured in advance. (# 3), the white LED 2 is turned off (# 4).

  Subsequently, the arithmetic control unit 7 turns on the purple LED 51 via the drive circuit 5d (# 5), and converts the components 51b and 51c in the normal direction of the sample reflected light illuminated by the second illumination light receiving system into the spectroscopic device. 6 and the light receiving element 9 respectively measure the non-cross polarization intensity Inx and the cross polarization intensity Ix of the sample in the vicinity of 410 nm (# 6) (# 7). And the arithmetic processing part 7 uses the intensity | strength of the white reference surface reflected light by purple LED51 illumination light previously measured by the 2nd and 3rd illumination light reception system with non-cross polarization intensity | strength Inx and cross polarization intensity | strength Ix, Conversion into the non-cross polarization reflectance coefficient Rnx and the cross polarization reflectance coefficient Rx is performed (# 8) (# 9), and the purple LED 51 is turned off (# 10). Further, the arithmetic processing unit 7 obtains the surface reflectance coefficient Rs in the vicinity of 410 nm (Rs = Rnx−Rx) (# 11) from the difference between the non-cross polarization reflectance coefficient Rnx and the cross polarization reflectance coefficient Rx.

  Finally, the arithmetic processing unit 7 obtains and outputs the spectral reflectance coefficient Rse (λ) obtained by removing the surface reflection by uniformly subtracting the surface reflectance coefficient Rs from the non-polarized spectral reflectance coefficient Rnp (λ) (Rse). (Λ) = Rnp (λ) −Rs) (# 12).

  Here, the surface reflectance coefficient Rs depends on the reflectance of the interface (1s) between the air and the sample 1 and the scattering characteristics of the reflected light due to the surface roughness. However, when the sample 1 is a printing surface, the reflection at the interface is Fresnel reflection depending on the refractive index of the ink, and the wavelength dependency in the visible region is very small. Further, the wavelength dependence of scattering due to surface roughness of several microns to several tens of microns on the ink surface is also small. For this reason, as a result, the wavelength dependence of the surface reflectance coefficient Rs can be ignored. FIG. 3 is a graph showing the spectral reflectance coefficient including the surface reflection of the magenta printing surface (indicated by a solid line) and the spectral reflectance coefficient after removing the surface reflection (indicated by a plot of ■). As understood from FIG. 3, the difference between the two corresponding to the spectral surface reflectance coefficient Rs (λ) is substantially constant, indicating that the wavelength dependency is extremely small.

  Therefore, if the geometries of the first, second, and third illumination light receiving systems are close to each other, the surface reflection near 410 nm obtained by the difference between the reflectance coefficients Rnx, Rx by the second and third illumination light receiving systems. The spectral reflectance coefficient Rse (λ) is obtained by uniformly reducing the rate coefficient Rs from the non-polarized spectral reflectance coefficient Rnp (λ) including the surface reflected light by the first illumination light receiving system as described above to remove the surface reflection. Even so, the error is small.

  Therefore, using the measured non-polarized spectral reflectance coefficient Rnp (λ) as it is, it is possible to obtain the color value after drying the ink in consideration of the surface reflected light in the same manner as the visual evaluation, and the non-polarized spectral reflectance coefficient Rnp. Using spectral reflectance coefficient Rse (λ) obtained by removing surface reflectance coefficient Rs from (λ), it is possible to obtain densities that can be compared with each other before and after ink drying. Thus, the non-polarized spectral reflectance coefficient Rnp (λ) including the surface reflected light and the spectral reflectance obtained by removing the surface reflected light depending on the purpose without causing a light amount loss due to the polarizing filter in the first illumination light receiving system. The coefficient Rse (λ) can be measured. Moreover, although the polarization filters 5f and 9f are used in the second and third illumination light receiving systems, the color densitometer 10 of the present embodiment realizes a simple and low-cost configuration without a complicated configuration for attaching and detaching. be able to.

  In the second illumination light receiving system, the spectral reflectance coefficient Rnx (λ) of non-cross-polarized light in the vicinity of 410 nm is measured by the spectroscopic device 6, but the non-polarized spectral reflectance coefficient Rnp (λ) by the first illumination light receiving system is measured. λ) has a low accuracy in the vicinity of 410 nm where the emission intensity of the white LED 2 is low, and thus the non-polarized spectral reflectance coefficient Rnx (λ) in the vicinity of 410 nm is replaced with the spectral reflectance coefficient Rnx (λ) of non-cross-polarized light. May be.

  That is, as shown in FIG. 4, the white LED 2 includes a light emitting diode that generates blue light and a yellow phosphor that converts the blue light into broadband light centered at 550 to 600 nm. The emission intensity is low at around 410 nm. On the other hand, as described with reference to FIG. 3, the reflectance coefficient including the surface reflection (non-cross polarization reflectance coefficient Rnx) and the reflectance coefficient from which the surface reflection is removed (cross polarization reflectance coefficient Rx). , That is, the wavelength dependency of the surface reflectance coefficient Rs is extremely small, and the surface reflectance coefficient Rs is not limited to the purple LED 51 and may be obtained at any wavelength. However, the light source for obtaining the surface reflectance coefficient Rs is supplemented to the light emission intensity of the light source (white LED 2) for obtaining the non-polarized spectral reflectance coefficient Rnp (λ) as described above. Thus, the measurement accuracy of the non-polarized spectral reflectance coefficient Rnp (λ) by the first measurement unit is improved, which is preferable.

(Embodiment 2)
FIG. 5 is a block diagram showing the structure of the color densitometer 20 according to the second embodiment of the present invention. The color densitometer 20 is similar to the above-described color densitometer 10, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. Here, in the color densitometer 20 according to the present embodiment, the incident end 6a of the optical fiber 6g connected to the spectroscopic device 6 is disposed at the focal position of the objective lens 4 and adjacent to the light receiving element 9. The optical fiber 9g, 9h incident ends 9i, 9j (see FIG. 6) are connected in common.

  The reflected light 2b or 51b in the normal direction of the sample 1 illuminated by the white LED 1 or the purple LED 51 is incident on the incident end 6a by the lens 4 and the reflecting mirror 4a, and is guided to the incident slit of the spectroscope 6 by the optical fiber 6g. Reflected lights 51g and 51h (see FIG. 7 described later) near the normal line of the sample 1 illuminated by the purple LED 51 enter the incident ends 9i and 9j, and are guided to the light receiving element 9 by the optical fibers 9g and 9h, respectively. .

  6 is a front view of the incident ends 6a; 9i, 9j of the optical fibers 6g; 9g, 9h, and FIG. 7 is an optical path diagram of the first to third illumination light receiving systems. Here, on the focal plane of the lens 4, a light receiving system polarization filter 9 f having a polarization direction orthogonal to the second and third illumination light receiving system illumination filters 51 f is disposed. . Here, since an opening is provided in the portion facing the incident end 6a of the optical fiber 6g of the first illumination light receiving system, the light enters the optical fibers 9g and 9h of the third illumination light receiving system and is received by the light receiving element 9. Only the light beam passes through the polarizing filter 9f. Accordingly, as in the first embodiment of FIG. 1, the arithmetic control unit 7 turns on the white LED 2 and the first illumination light receiving system from the white LED 2 to the spectroscopic device 6 performs non-polarized spectral reflectance coefficient Rnp (λ ), The purple LED 51 is turned on, and the non-crossed polarization reflectance coefficient Rnx is obtained by the second illumination light receiving system from the purple LED 51 to the spectroscopic device 6, and at the same time, the first light reaching the light receiving element 9 through the polarizing filter 9f. The cross-polarized spectral reflectance coefficient Rx is obtained by the three illumination light receiving system, and further, the spectral reflectance coefficient Rse (λ) of the sample 1 from which the surface reflection Rs is removed is obtained by the same processing as in the embodiment of FIG.

  In this case, as shown in FIG. 7, the optical fibers 9g and 9h have the light beams 51h and 51g from the region 51m, and the optical fiber 6g has the light beam 2b from the region 1m and the common mask 4b and the lens 4. After incident. Since the incident ends 6a; 9i and 9j are adjacent to each other, the region 1m and the region 51m substantially coincide with each other, and the first, second, and third illumination light receiving systems have high geometric approximation. Therefore, the approximation between the surface reflectance coefficient included in the non-polarized spectral reflectance coefficient Rnp (λ) by the first illumination light receiving system and the surface reflectance coefficient by the second and third illumination light receiving systems becomes high. The spectral reflectance coefficient Rse (λ) of the sample 1 from which the surface reflection is removed can be obtained with high accuracy.

  The optical fibers 6g; 9g, 9h are arranged in a single line as viewed from the incident end 6a; 9i, 9j side (FIG. 6), but may be triangular.

(Embodiment 3)
FIG. 8 is an optical path diagram in the color densitometer 30 according to the third embodiment of the present invention. The configuration of the color densitometer 20 shown in FIGS. 5 to 7 can be used for this color densitometer. Here, in the color densitometer 30 according to the present embodiment, the polarizing filter 9f is placed only in front of the incident end 9i of the optical fiber 9g, comparing FIG. 7 with FIG. 8, and the incident end of the optical fiber 9h. It is not placed before 9j. Similarly to the second embodiment, the optical fiber 9g on which the light beam that has passed through the polarizing filter 9f enters is guided to the light receiving element 9 to form the third illumination light receiving system, but the light beam that does not pass through the polarizing filter enters. The optical fiber 9h is guided to a second light receiving element (not shown) to form a second illumination light receiving system.

  Therefore, the light beam 51h from the region 51n enters the optical fiber 9h, the light beam 51g from the region 51m enters the optical fiber 9g, and the light beam 2b from the region 1m enters the optical fiber 6g through the common mask 4b and the lens 4, respectively. . With this configuration, the second illumination light receiving system for obtaining the non-cross polarization reflectance coefficient Rnx and the third illumination light receiving system for obtaining the cross polarization reflectance coefficient Rx are not only the geometry but also the system leading to the light receiving element. Since all the elements are approximated, when the surface reflectance coefficient Rs is obtained by the difference between the non-crossing and crossed polarization reflectance coefficients Rnx and Rx, errors due to time or temperature change are offset, and the accuracy is increased.

(Embodiment 4)
FIG. 9 is a diagram of the second and third illumination light receiving systems in the color densitometer 40 according to the fourth embodiment of the present invention. Although not shown, the color densitometer 40 includes the same first illumination light receiving system as the color densitometer 10 of the first embodiment, and is emitted from the surface normal by the radiated light 51a of the purple LED 51 that has passed through the polarizing filter 51f. Illuminated from one direction at 45 degrees, the component 51b in the vicinity of the normal line of the sample surface reflected light is received by the light receiving element 9 through the polarizing filter 9f whose polarization direction is orthogonal to the polarizing filter 51f, and the cross polarization reflectance coefficient Rx Is provided with a third illumination light receiving system. Here, in the color densitometer 40 in the present embodiment, the sample surface is illuminated at 45 degrees from the surface normal by the radiated light 52a of the second purple LED 52 that does not pass through the polarizing filter, from a different direction from the radiated light 5a. A component 52b in the vicinity of the normal line is received by the light receiving element 9 through the same polarizing filter 9f, and a second illumination light receiving system for obtaining a non-crossed polarization reflectance coefficient Rnx is provided. That is, in this color densitometer 40, the second illumination light receiving system emits illumination light having the same spectral distribution as the light receiving system of the third illumination light receiving system and the illumination system of the third illumination light receiving system, and the polarization filter And an illumination system having no.

  Even in this configuration, as in the third embodiment, the second illumination light receiving system for obtaining the non-cross polarization reflectance coefficient Rnx and the third illumination light reception system for obtaining the cross polarization reflectance coefficient Rx are geometrical. In addition, since all elements of the system reaching the light receiving element 9 are approximated, when the surface reflectance coefficient Rs is obtained by the difference between the non-crossing and crossing polarization reflectance coefficients Rnx and Rx, the error is offset and the accuracy is improved. Get higher. In addition, since the second illumination light receiving system shares the light receiving system with the third illumination light receiving system, the color densitometer 40 according to the present embodiment has a simple configuration and can reduce costs.

(Embodiment 5)
FIG. 10 is an optical path diagram in the color densitometer 50 according to the fifth embodiment of the present invention. Although not shown, this color densitometer 50 also includes the same first illumination light receiving system as the color densitometer 10 of the first embodiment, and the emitted light 51a of the purple LED 51 that has passed through the polarizing filter 51f and the polarizing filter 51f. And the radiated light 53a of the red LED 53 that has passed through the polarizing filter 53f of the same polarization direction as above, respectively, is illuminated from one direction at 45 degrees from the surface normal, and the components 51b and 53b in the vicinity of the normal of the sample surface reflected light are polarized by the polarizing filter 9f. The light receiving element 9 passes through the third illumination light receiving system for obtaining the cross polarization reflectance coefficient Rx, and the normal direction component of the reflected light is received by the light receiving system of the first illumination light receiving system, and the non-cross polarization reflectance is received. And a second illumination light receiving system for obtaining the coefficient Rnx. Here, in the color densitometer 50 in the present embodiment, the common illumination system of the second and third illumination light receiving systems is two sub illumination systems of a purple LED 51 having a center wavelength of 410 nm and a red LED 53 having a center wavelength of 660 nm. The sample surface is illuminated through the polarizing filters 51f and 53f from the same 45 degrees from the surface normal and different orientations.

  In the measurement of the sample 1, the arithmetic control unit 7 turns on the white LED 2 and obtains the non-polarized spectral reflectance coefficient Rnp (λ) by the first illumination light receiving system, and then turns on the purple LED 51. And the non-cross polarization reflectance coefficient Rnx (λ1) and the cross polarization reflectance coefficient Rx (λ1) are measured by the third illumination light receiving system, and the first surface reflectance coefficient Rs (λ1) in the vicinity of the wavelength of 410 nm is obtained. Further, the red LED 53 is turned on, and similarly, the non-cross polarization reflectance coefficient Rnx (λ2) and the cross polarization reflectance coefficient Rx (λ2) are measured, and the second surface reflectance coefficient Rs (λ2) near the wavelength of 660 nm is measured. ) The arithmetic control unit 7 further linearly interpolates the first and second surface reflection coefficients Rs (λ1) and Rs (λ2) in the vicinity of wavelengths 410 nm and 660 nm, and thereby the spectral surface reflection coefficient Rs (λ) in a predetermined wavelength region. And the spectral reflectance coefficient Rse (λ) of the sample 1 obtained by subtracting from the non-polarized spectral reflectance coefficient Rnp (λ) and removing the surface reflection is obtained.

  With this configuration, even if the surface reflectance coefficient Rs has some wavelength dependence, the error due to this is reduced, and the spectral reflectance coefficient Rse (λ of the sample 1 from which surface reflection is removed with high accuracy. ).

  The present specification discloses various aspects of the technology as described above, and the main technologies are summarized below.

  A color densitometer according to one aspect is a color densitometer that measures a reflection characteristic of a sample of a printed matter and obtains an ink density and a color value. The color densitometer includes a first illumination light receiving system and has a predetermined wavelength range, for example, a visible range. A first measurement unit for measuring the non-polarized spectral reflectance coefficient (Rnp (λ)) of the sample, and a second illumination light receiving system whose geometrical relationship with respect to the sample surface approximates that of the first illumination light receiving system. A second measuring unit that measures the non-cross-polarized reflectance coefficient (Rnx) of the sample in a predetermined wavelength, for example, a wavelength region of a monochromatic LED, and a geometric relationship with the sample surface approximates that of the first illumination light receiving system, A third measuring unit for measuring a cross-polarized reflectance coefficient (Rx) of the sample at the same wavelength as that of the second illumination receiving system; Measured non-cross-polarized reflectance coefficient The surface reflectance coefficient (Rs) of the sample is obtained from the difference between Rnx) and the cross polarization reflectance coefficient (Rx), and the obtained surface reflectance coefficient (Rs) is determined as the non-polarized spectral reflectance coefficient ( And an arithmetic control unit that obtains the spectral reflectance coefficient (Rse (λ)) of the sample from which surface reflection has been removed by uniformly subtracting from Rnp (λ)).

  A density measuring method according to another aspect is a density measuring method for determining the ink density by measuring the reflection characteristics of a sample of printed matter, and using a first illumination light receiving system, for example, a visible wavelength range, for example, visible. Measuring a non-polarized spectral reflectance coefficient (Rnp (λ)) of the sample in a region, and using a second illumination light receiving system whose geometrical relationship to the sample surface approximates that of the first illumination light receiving system. The step of measuring the non-cross-polarized reflectance coefficient (Rnx) of the sample at a predetermined wavelength, for example, the wavelength range of a monochromatic LED, and the geometric relationship with the sample surface approximate to the first illumination light receiving system, and the illumination system and light receiving Measuring a cross polarization reflectance coefficient (Rx) of the sample at the same wavelength as the second illumination light receiving system using a third illumination light receiving system having polarization characteristics orthogonal to each other; and the second illumination Measured using light receiving system The surface reflectance coefficient (Rs) of the sample is obtained from the difference between the non-cross polarization reflectance coefficient (Rnx) and the cross polarization reflectance coefficient (Rx) measured using the third illumination light receiving system. Then, the surface reflectance coefficient (Rs) is uniformly subtracted from the non-polarized spectral reflectance coefficient (Rnp (λ)) at each wavelength measured using the first illumination light receiving system. Obtaining a spectral reflectance coefficient (Rse (λ)) of the sample from which is removed.

  According to the above configuration, in a color densitometer that irradiates a sample of printed matter with illumination light, measures its spectral reflection characteristics, and obtains ink density and color value, illumination in a predetermined wavelength range such as the visible range. Eliminates the effect of dry-down after drying ink from diffused light from inside the ink and paper measured by irradiating light and non-polarized spectral reflectance coefficient (Rnp (λ)) including surface (scattered) reflected light Therefore, polarized light is used to obtain (estimate) the spectral reflectance coefficient Rse (λ) of the sample from which the surface reflection is removed. When using this polarized light, the measurement system for measuring the spectral reflection characteristic in the predetermined wavelength range does not have the polarization characteristic as in the background art, but in the above configuration, the measurement of a specific wavelength provided separately is performed. The system has polarization characteristics.

  That is, the configuration for measuring the non-polarized spectral reflectance coefficient (Rnp (λ)) is the first measurement unit, and the first illumination light receiving system in the first measurement unit and the geometric relationship (geometry) with respect to the sample surface. ) Are provided, the second and third measurement units respectively including the second and third illumination light receiving systems are provided. In the second measurement unit, the non-cross polarization reflectance coefficient (Rnx) of the sample is measured at a predetermined wavelength, for example, the wavelength of a monochromatic LED. In the third measurement unit, the illumination system and the light reception in the third illumination light receiving system are measured. The system has polarization characteristics orthogonal to each other, and the cross-polarized reflectance coefficient (Rx) of the sample is measured at the same wavelength as the second measurement unit.

  The surface reflectance coefficient (Rs) depends on the reflectance at the interface between the air and the sample and the scattering characteristics of the reflected light due to the surface roughness. The Fresnel reflection depends on the refractive index of the light, and the wavelength dependence in the visible range is very small, and the wavelength dependence of scattering due to the surface roughness of the ink surface is also small, so that the wavelength dependence can be ignored as a result. Then, Rs = Rnx−Rx is obtained by the arithmetic control unit, and further Rse (λ) = Rnp (λ) −Rs is obtained.

  Therefore, the color densitometer and the density measuring method with such a configuration use the measured non-polarized spectral reflectance coefficient (Rnp (λ)) as it is, and after drying the ink in consideration of the surface reflected light as in the visual evaluation. Ink drying is performed using the spectral reflectance coefficient (Rse (λ)) obtained by removing the surface reflectance coefficient (Rs) from the non-polarized spectral reflectance coefficient (Rnp (λ)). Concentrations comparable to each other before and after can be obtained. In this way, without causing light loss due to the polarizing filter in the first illumination light receiving system, the non-polarized spectral reflectance coefficient (Rnp (λ)) including the surface reflected light and the spectrum from which the surface reflected light is removed depending on the purpose. The reflectance coefficient (Rse (λ)) can be measured. In the second and third illumination light receiving systems, although a polarizing filter is used, a simple and low-cost configuration without a complicated configuration for attaching and detaching the filter can be realized.

  In another aspect, the color densitometer described above preferably further includes a lens that collects reflected light from the sample, and in each of the first to third illumination light receiving systems, An optical fiber is provided, and an incident surface of the optical fiber is arranged adjacent to a focal point of the lens.

  According to the above configuration, the geometric relationship is approximated by bundling the optical fibers and arranging the incident surface adjacent to the vicinity of the focal point of the lens that collects the reflected light from the sample. Can do.

  Therefore, the approximation between the surface reflectance coefficient included in the non-polarized spectral reflectance coefficient Rnp (λ) by the first illumination light receiving system and the surface reflectance coefficient by the second and third illumination light receiving systems becomes high, The spectral reflectance coefficient Rse (λ) of the sample from which the surface reflection is removed can be obtained with high accuracy.

  In another aspect, in the color densitometer described above, preferably, the third illumination light receiving system removes the surface reflected light that maintains the polarization characteristics of the illumination light, and the cross-polarized reflectance coefficient (Rx). In order to measure, a polarizing filter having polarization directions orthogonal to each other is provided as a polarizing element interposed in each light flux of the illumination system and the light receiving system.

  In this case, the second illumination light receiving system is preferably configured to include an illumination system of the third illumination light receiving system and a light receiving system having no polarization filter.

  According to the above configuration, since the illumination system in the second illumination light receiving system is shared with the third illumination light receiving system, the color densitometer having such a configuration is simplified and the cost can be reduced.

  In another aspect, in the above color densitometer, preferably, the light receiving system that does not have the polarizing filter is a light receiving system of the first illumination light receiving system.

  According to the above configuration, not only the illumination system is shared with the third illumination light receiving system, but also the light reception system is shared with the first illumination light receiving system, so that the color densitometer having such a configuration is easier to configure. Therefore, the cost can be reduced.

  In another aspect, in the above color densitometer, preferably, the second illumination light receiving system has the same spectral distribution as the light receiving system of the third illumination light receiving system and the illumination system of the third illumination light receiving system. And an illumination system that does not have a polarizing filter.

  According to the above configuration, since the second illumination light receiving system shares the light reception system with the third illumination light receiving system, the configuration of the color densitometer configured as described above is simplified and the cost can be reduced.

  In another aspect, in the color densitometer described above, preferably, the illumination system of the third illumination light receiving system includes two sub illumination systems that emit illumination lights having different wavelengths (λ1, λ2). The arithmetic control unit sequentially drives the two sub illumination systems, and the non-cross polarization reflectivity coefficients (Rnx (λ1), Rnx (λ2)) and the cross polarization reflectivities in each sub illumination system. Coefficients (Rx (λ1), Rx (λ2)) are measured, and from the surface reflectance coefficients (Rs (λ1), Rs (λ2)) at the two wavelengths (λ1, λ2) obtained from them, Interpolation of spectral surface reflectance coefficient (Rs (λ)) at each wavelength (λ) and subtraction from the non-polarized spectral reflectance coefficient (Rnp (λ)), respectively, thereby removing the surface reflection of the sample. A spectral reflectance coefficient (Rse (λ)) is obtained.

  According to the above configuration, the spectral surface reflectance coefficient (Rs (λ)) at each wavelength (λ) is approximately obtained and subtracted from the non-polarized spectral reflectance coefficient (Rnp (λ)), respectively. Since the spectral reflectance coefficient (Rse (λ)) of the sample from which the surface reflection is removed is obtained, the spectral reflectance coefficient (Rse (λ)) is accurate even for a sample whose surface reflectance coefficient (Rs) is wavelength-dependent. You can ask well.

  In another aspect, in the color densitometer described above, preferably, the light emitting element in the first illumination light receiving system is a white LED, and the light emitting element in the second and third illumination light receiving systems is the white color. This is a monochromatic LED that emits light of a wavelength component with low emission intensity in the LED.

  According to the above configuration, when measuring the non-polarized spectral reflectance coefficient (Rnp (λ)) using the white LED in the first illumination light receiving system, the light of the wavelength component having a low emission intensity in the white LED is The wavelength components are supplemented by the light emitting elements in the second and third illumination light receiving systems.

  Accordingly, since the monochromatic LED is used as the light emitting element, the second and third measuring units for measuring the non-cross polarization reflectance coefficient (Rnx) and the cross polarization reflectance coefficient (Rx) of the sample in a specific wavelength range can be simply and While being able to comprise at low cost, the measurement precision of the non-polarization spectral reflectance coefficient Rnp by a 1st measurement part can also be raised.

  This application is based on Japanese Patent Application No. 2009-244848 filed on Oct. 23, 2009, the contents of which are included in this application.

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not covered by the claims. To be construed as inclusive.

  According to the present invention, a color densitometer and a density measuring method can be provided.

Claims (9)

A color densitometer that measures the reflection characteristics of a sample of a printed matter to obtain ink density and color value,
A first measurement unit comprising a first illumination light receiving system and measuring a non-polarized spectral reflectance coefficient of the sample;
A second measuring unit comprising a second illumination receiving system whose geometrical relationship to the sample surface approximates that of the first illumination receiving system, and measuring a non-cross-polarized reflectance coefficient of the sample at a predetermined wavelength;
A third measurement for measuring a cross-polarized reflectance coefficient of the sample at the same wavelength as that of the second illumination light receiving system, comprising a third illumination light receiving system whose geometrical relation to the sample surface approximates that of the first illumination light receiving system; And
The surface reflectance coefficient of the sample is determined from the difference between the measured non-cross-polarized reflectance coefficient and the cross-polarized reflectance coefficient, and the determined surface reflectance coefficient is determined from the non-polarized spectral reflectance coefficient at each wavelength. A color densitometer comprising: an arithmetic control unit that obtains a spectral reflectance coefficient of a sample from which surface reflection has been removed by subtracting uniformly. The third illumination light receiving system includes polarizing filters whose polarization directions are orthogonal to each other as polarizing elements interposed in the respective light fluxes of the illumination system and the light receiving system in order to measure the cross polarization reflectance coefficient. The color densitometer according to claim 1. A lens for collecting the reflected light from the sample;
2. The first to third illumination light receiving systems according to claim 1, wherein each light receiving system has an optical fiber, and an incident surface of the optical fiber is disposed adjacent to a focal point of the lens. The described color densitometer. The color densitometer according to claim 2, wherein the second illumination light receiving system includes an illumination system of the third illumination light receiving system and a light receiving system having no polarization filter. The color densitometer according to claim 4, wherein the light receiving system having no polarizing filter is a light receiving system of the first illumination light receiving system. The second illumination light receiving system includes a light receiving system of the third illumination light receiving system and an illumination system that emits illumination light having the same spectral distribution as the illumination system of the third illumination light receiving system and does not have a polarization filter. The color densitometer according to claim 3, wherein the color densitometer is configured. The illumination system of the third illumination light receiving system is composed of two sub-illumination systems that emit illumination light having different wavelengths,
The arithmetic control unit sequentially drives the two sub-illumination systems, measures the non-cross-polarized reflectance coefficient and the cross-polarized reflectance coefficient in each sub-illuminated system, and calculates the 2 obtained from them. By interpolating the spectral surface reflectance coefficient at each wavelength from the surface reflectance coefficients at one wavelength and subtracting each from the non-polarized spectral reflectance coefficient, the spectral reflectance coefficient of the sample from which the surface reflection has been removed is calculated. The color densitometer according to claim 1, wherein the color densitometer is obtained. The light emitting element in the first illumination light receiving system is a white LED, and the light emitting element in the second and third illumination light receiving systems is a monochromatic LED that emits light of a wavelength component with low emission intensity in the white LED. The color densitometer according to claim 1. A density measurement method for measuring the reflection characteristics of a sample of a printed material to obtain an ink density,
Measuring a non-polarized spectral reflectance coefficient of the sample using a first illumination light receiving system;
Measuring a non-cross-polarized reflectance coefficient of the sample at a predetermined wavelength using a second illumination receiver system whose geometric relationship to the sample surface approximates the first illumination receiver system;
Measuring a cross-polarized reflectance coefficient of the sample at the same wavelength as the second illumination light receiving system using a third illumination light receiving system whose geometrical relationship to the sample surface approximates that of the first illumination light receiving system;
From the difference between the non-cross-polarized reflectance coefficient measured using the second illumination receiving system and the cross-polarized reflectance coefficient measured using the third illumination receiving system, the surface reflectance coefficient of the sample is calculated. Seeking steps,
The surface reflectance coefficient of the sample from which the surface reflection is removed is obtained by uniformly subtracting the surface reflectance coefficient from the non-polarized spectral reflectance coefficient at each wavelength measured using the first illumination light receiving system. A concentration measuring method comprising the steps of:

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