JP5674131B2 - Color measuring device and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a colorimetric device for measuring a colorimetric value indicating the color of an object to be measured, such as a colorimetric value of various color systems defined by the CIE (International Lighting Commission), and an image forming apparatus provided with the same. is there.

  Color management such as color stability and color reproducibility is one of the important technical problems in image forming apparatuses such as printing apparatuses and printers. In recent years, a spectrocolorimeter, which is a color measuring apparatus, is used to control the image forming apparatus. Color tone management has been performed (for example, Patent Document 1). Specifically, for example, the diffuse reflection light of the output image (measurement object) is measured with a spectrocolorimeter to obtain the spectral reflectance, and from there, the RGB color system, XYZ color system, L * defined by CIE Colorimetric values used in the a * b * color system and the like are calculated, and the color tone inspection of the output image is performed using this result, and the image forming conditions are adjusted.

FIG. 8 is an explanatory diagram for explaining an example of a spectrocolorimeter.
The spectrocolorimeter illuminates from the illumination device 2 from a direction inclined by 45 ° from the normal direction of the surface to be measured 1 of the measurement object. Diffuse reflected light reflected in the normal direction from the surface to be measured passes through the first lens 3 and is condensed on the slit 4. The light beam that has passed through the slit 4 becomes substantially parallel light by the second lens 5 and enters the diffraction element 6 that is a spectroscopic means. The light beams having the respective wavelengths diffracted and separated by the diffraction element 6 are transmitted through the third lens 7 and are condensed in different light receiving regions on the light receiving element array 8 as the light receiving means. Then, photoelectric conversion is performed by the light receiving element in each light receiving region, and an output signal indicating the amount of light received in each light receiving region is output. Therefore, it is possible to detect light intensity signals in different wavelength bands in each light receiving region. By using such a spectrocolorimeter, for example, it is possible to acquire 16 channel output signals with a wavelength of 400 to 700 [nm] at a pitch of 20 [nm]. The acquired output signal is sent to the arithmetic unit 9, where the spectral reflectance distribution, tristimulus values XYZ (colorimetric values) of the XYZ color system, L * a * b * L of the color system * A * b * values (colorimetric values) are calculated.

The spectral reflectance is a ratio between the detected output signal and the output signal (reference output signal) when a complete diffuse reflection surface is used as the surface to be measured. Usually, a standard white surface (magnesium oxide vapor deposition surface, etc.) is used as the perfect diffuse reflection surface, and after measuring this and storing the reference output signal, the output signal when measuring the measurement object is this The value divided by the reference output signal is calculated as the spectral reflectance. Since the reflectance of the standard white surface is approximately 99% in the visible wavelength region, the measured value is substantially equal to the spectral product that is the spectral characteristic of the entire optical system. Considering this as a matrix, the spectral reflectance vector r, which is a column vector for storing the spectral reflectance distribution, is the transformation matrix G in which the inverse of the spectral product is entered at the diagonal of the matrix and the output signal of the spectrocolorimeter. Using the output signal vector v which is the stored column vector, it can be obtained from the following equation (1).

For example, when the tristimulus value XYZ (colorimetric value of the XYZ color system) indicating the color of the measurement object is calculated from the spectral reflectance distribution thus obtained, the tristimulus value XYZ is equal to the spectral reflectance distribution or the like. It can be obtained by convolution integration of the color function. Considering this calculation as a matrix, a colorimetric value vector T, which is a column vector for storing tristimulus values XYZ, is a color matching function matrix H in which three color matching functions are discretized and stored, a spectral reflectance vector r, and Can be obtained from the following equation (2).

Therefore, from the above equations (1) and (2), the tristimulus value XYZ of the measurement object is a product sum using the product of the conversion matrix G and the color matching function matrix H as a weight matrix, and the following equation (3 )become that way.

  A conventional spectrocolorimeter using a xenon lamp or the like as the illumination means has poor light utilization efficiency and takes about 1 second for measurement time. For this reason, it has been difficult to perform high-speed measurement that can be incorporated into an image forming apparatus such as a printing press to perform in-line colorimetric surveys of printed images. Accordingly, the present inventors have focused on white LED light sources that have both high stability and long life, and have recently been improved in brightness and efficiency, and perform high-speed measurement using white LED light sources as illumination means. Research and development of a colorimetric device that can be realized. A general white LED light source has, for example, a configuration in which a blue LED and a phosphor that absorbs blue light and emits yellow light are combined.

FIG. 9 is a graph in which three color matching functions in the XYZ color system and the spectral luminance distribution of the white LED light source are superimposed.
This white LED light source is a combination of a blue LED and a yellow phosphor, and its spectral luminance distribution shows a relatively sharp blue band peak (about 460 [nm]) as shown in FIG. It has a peak of a comparatively gentle yellow band (about 570 [nm]). Here, as shown in the above equation (3), the tristimulus value XYZ (colorimetric value vector) of the measurement object is obtained from the output signal (output signal vector v) when the measurement object is measured with the spectrocolorimeter. When calculating (T), the product sum of the weight matrix obtained by the product of the conversion matrix G storing the reciprocal of the spectral product and the color matching function matrix H and the output signal vector v of the light receiving element array is taken. Therefore, an output signal corresponding to a wavelength band having a large color matching function value is greatly amplified. For this reason, when the S / N ratio of the output signal corresponding to the wavelength band having a large color matching function value is small, the influence of the noise component becomes large, and the error of the calculated tristimulus value XYZ becomes large. Conversely, even in a wavelength band where the value of the color matching function is large, if the S / N ratio of the output signal is large, the influence of the noise component is small, and the calculated tristimulus value XYZ has a small error. In the wavelength band where the value of the color matching function is small, even if the S / N ratio of the output signal is small, the influence of the noise component is small and the calculated tristimulus value XYZ has a small error. Therefore, in order to suppress the error of the calculated tristimulus values XYZ, it is important to increase the S / N ratio of the output signal as much as possible for the wavelength band where the value of the color matching function is large.

  Here, a random error (random noise) is superimposed on the output signal of each light receiving element of the light receiving element array due to the influence of dark current or the like. From the law of error propagation, it is known that the error of the sum of a plurality of signals having uncorrelated random errors is the square root of the sum of squares. Such an error (noise) is irrelevant to the magnitude of the signal component included in the output signal. Therefore, if the signal component included in the output signal is sufficiently large, the S / N ratio can be sufficiently large even if such noise is included. However, if the signal component included in the output signal is small, the S / N ratio is small.

  In order to increase the signal component included in the output signal, it is effective to increase the luminance of the light emitted from the illumination means. For example, when the white LED light source having the spectral luminance distribution shown in FIG. 9 is used as the illumination means, the illumination luminance is very high in the vicinity of the blue band peak (near 440 to 480 [nm]). Since this wavelength band (near 440 to 480 [nm]) is a wavelength band where the Z value of the color matching function is large, the output signal is greatly amplified. Therefore, the noise contained in the output signal is greatly amplified. However, since the illumination brightness in that wavelength band is sufficiently large, a large signal component can be taken in the output signal. Therefore, for this wavelength band (near 440 to 480 [nm]), although the Z value of the color matching function is large, the S / N ratio can be made sufficiently large. The effect on it is kept small.

  However, when FIG. 9 is seen, since this white LED light source has a small luminance near 430 [nm], the S / N ratio of the output signal in this wavelength band is small. As shown in FIG. 9, this wavelength band is a wavelength band in which the Z value of the color matching function is large. For this reason, in this wavelength band (near 430 [nm]), the S / N ratio of the output signal cannot be increased even though the Z value of the color matching function is large. Therefore, the output signal in this wavelength band has a great influence on the calculated tristimulus value XYZ.

FIG. 10 is a graph showing the ratio of each color matching function to the spectral luminance distribution of the illumination means.
It can be said that the ratio of the color matching function to the spectral brightness distribution of the illumination means indicates whether or not the lighting brightness is sufficient according to the value of each color matching function in each wavelength band. Therefore, this ratio is an index value indicating the magnitude of the effect on the calculated tristimulus value XYZ error. Referring to FIG. 10, in the vicinity of 430 [nm], which is a wavelength band in which the value of the color matching function (Z value) is large but the illumination luminance is insufficient (that is, the S / N ratio of the output signal is small). The index value is increasing. This indicates that an output signal in the vicinity of 430 [nm] greatly affects the error of the calculated tristimulus value XYZ.

  When an illumination unit having insufficient luminance in a part of the wavelength band having a large color matching function (near 430 [nm]), such as a white LED light source having a spectral luminance distribution shown in FIG. 9, the wavelength band is used. This greatly affects the error of the calculated tristimulus value XYZ, resulting in a problem that the measurement accuracy of the tristimulus value XYZ is lowered. This problem is not limited to measuring tristimulus values XYZ as colorimetric values, but is calculated using output signals output from the light receiving element array, spectral luminance distribution data of illumination means, and color matching function data. If it is a colorimetric value, it can occur in the same way even when other colorimetric values are measured. The same applies to the case of measuring other colorimetric values (for example, L * a * b * values in the L * a * b * color system) obtained by converting such colorimetric values.

  For example, it is conceivable to use a blue LED constituting a white LED light source whose peak wavelength is shifted to a lower wavelength side than 460 [nm] with respect to the above problem. In this case, in the vicinity of 430 [nm], it is possible to reduce the influence on the error of the calculated tristimulus value XYZ. However, since the peak waveform of the spectral luminance distribution of the blue LED is narrow, that is, the half-value width of the spectral luminance distribution of the blue LED is narrow, instead, the higher wavelength side (for example, 470) of the wavelength band where the Z value of the color matching function is large. In the vicinity of [nm], there is a situation where the illumination brightness is insufficient. As a result, the output signal in this wavelength band greatly affects the error of the calculated tristimulus value XYZ, and as a result, the measurement accuracy of the calculated tristimulus value XYZ is low. Also, if the blue LED peak wavelength is shifted and adjusted in this way, the luminous efficiency of the blue LED is lowered, so the overall luminance of the blue LED is lowered, the overall S / N ratio is deteriorated, and the measurement time is reduced. Incurs problems such as a long time.

  In addition, the said problem is not restricted to the case where the white LED light source mentioned above is used as an illumination means. Specifically, the spectral luminance distribution has a peak in the vicinity of the wavelength at which the color matching function data shows a peak, and the half width (spectral luminance distribution half width) of the peak of the spectral luminance distribution is the color matching function data. In the case of using a white light source that is narrower than the half-value width (color matching function half-value width) of the peak, it can occur similarly. In this way, when the spectral luminance distribution half-value width of the white light source is narrower than the color matching function half-value width, the wavelength band corresponding to the spectral luminance distribution half-value width does not overlap among the wavelength bands corresponding to the color matching function half-value width This is because a portion (white light source luminance insufficiency band) occurs, and the illumination luminance by the white light source can be insufficient in such a wavelength band portion.

  The present invention has been made in view of the above background, and the object of the present invention is to perform colorimetry with high measurement accuracy of colorimetric values calculated using a color matching function even when such a white light source is used. An apparatus and an image forming apparatus including the same are provided.

In order to achieve the above object, the invention of claim 1 is directed to an illuminating means for illuminating a measurement object, a spectroscopic means for dispersing a reflected light beam from the measurement object, and receiving each of the dispersed light beams for each wavelength. Using light receiving means for outputting an output signal indicating the amount of light received in the band, each output signal output from the light receiving means, spectral luminance distribution data of light illuminated by the illumination means, and color matching function data, In the colorimetric apparatus comprising a calculation means for calculating a colorimetric value indicating the color of the measurement object, the illumination means has a peak of spectral luminance distribution in the vicinity of the wavelength at which the color matching function data shows a peak, A white light source whose spectral luminance distribution half-value width corresponding to the half-value width for the peak of the spectral luminance distribution is narrower than the color matching function half-value width corresponding to the half-value width for the peak of the color matching function data; The minute in To the peak of the luminance distribution, the peak value than the peak value of the peak is low and wavelength wavelength band corresponding to the spectroscopic intensity distribution half-width of the wavelength band corresponding to the equal color function half-width not overlap The measurement object is illuminated with another light source having a spectral luminance distribution having a peak shifted in wavelength on the side where the band portion exists.
According to a second aspect of the present invention, in the colorimetric apparatus according to the first aspect, the white light source uses a light emitting diode having a light emission wavelength at a wavelength indicating the peak of the spectral luminance distribution. To do.
The invention according to claim 3 is the colorimetric device according to claim 1 or 2, wherein the other light source uses a light emitting diode having a light emission wavelength at a wavelength showing the peak of the spectral luminance distribution. It is characterized by.
According to a fourth aspect of the present invention, in the colorimetric apparatus according to the first aspect, the calculation means calculates a tristimulus value of an XYZ color system as the colorimetric value. All of the light sources use light emitting diodes whose emission wavelengths are the wavelengths showing the peak of the spectral luminance distribution, and the white light source is 450 [nm] or more and 470 [nm] or less as the light emitting diode. The first blue light-emitting diode that emits light at the emission wavelength of the light-emitting diode and includes a phosphor that emits light by receiving light from the first blue light-emitting diode, and the other light source is the light-emitting diode, Using a second blue light emitting diode that emits light at an emission wavelength of 430 [nm] or more and 450 [nm] or less and separated from the emission wavelength of the first blue light emitting diode by 10 [nm] or more. It is characterized in that.
According to a fifth aspect of the present invention, in the colorimetric apparatus according to the fourth aspect, the illuminating means includes a single unit of the first blue light emitting diode and the phosphor that constitute the white light source, and the second blue light emitting diode. It is characterized by being modularized.
According to a sixth aspect of the present invention, in the colorimetric device according to any one of the first to fifth aspects, the light receiving means outputs output signals for three to fifteen wavelength bands. It is a feature.
According to a seventh aspect of the present invention, there is provided an image forming apparatus for forming an image composed of a plurality of colors on an image carrying medium, a color measuring apparatus for measuring a colorimetric value of the image formed on the image carrying medium, 7. The color measurement device according to claim 1, further comprising: an image formation condition adjustment unit configured to adjust an image formation condition based on a color measurement value measured by the color measurement device. An apparatus is used.

According to the white light source of the illumination means of the present invention, since the spectral luminance distribution has a peak in the vicinity of the wavelength at which the color matching function data shows a peak, it is possible to illuminate with high luminance in the wavelength band where the value of the color matching function is large. Is possible. However, since the half-value width of the spectral brightness distribution of this white light source is narrower than the half-value width of the color matching function, the wavelength band corresponding to the half-value width of the spectral brightness distribution does not overlap among the wavelength bands corresponding to the half-value width of the color matching function. A portion, that is, a white light source luminance deficiency band in which illumination luminance due to the white light source is insufficient occurs.
In the present invention, using such a white light source and another light source having a peak shifted to the wavelength side where the white light source luminance deficiency band exists with respect to the peak of the spectral luminance distribution of the white light source, Illuminate the measurement object. Thereby, the illumination brightness | luminance about the white light source brightness | luminance insufficient zone | band where the illumination brightness | luminance by a white light source is insufficient can be supplemented with said other light source. As a result, the S / N ratio of the output signal in the white light source luminance deficiency band can be made larger than when the white light source alone is illuminated. Therefore, it is possible to increase the measurement accuracy of the colorimetric values calculated by the calculation means.
In addition, in the present invention, the lack of illumination brightness in the white light source brightness shortage band is solved by adding another light source, so that the white light source emits light without considering the lack of illumination brightness in the white light source brightness shortage band. A highly efficient one can be used. Therefore, a high S / N ratio can be maintained for the other wavelength bands excluding the white light source luminance insufficient band. On the other hand, the other light source is an auxiliary light source for making up for the lack of illumination brightness in the white light source brightness shortage band. That is, a light source having a spectral luminance distribution having a peak value lower than that of a white light source is sufficient for the other light sources.

  As described above, according to the present invention, even when the white light source as described above is used, it is possible to obtain an excellent effect that the colorimetric value calculated using the color matching function can be measured with high accuracy.

It is a functional block diagram of the spectral colorimeter in the embodiment. It is explanatory drawing which shows schematic structure of the spectral colorimeter. 3 is a graph showing three color matching functions in the XYZ color system and spectral luminance distributions of a first white LED light source and a second white LED light source that constitute an illumination device of the spectrocolorimeter. It is the graph which took the ratio of each color matching function with respect to the spectral luminance distribution of the illumination device. It is a graph which shows the result of numerical simulation. It is explanatory drawing which shows schematic structure of the light source which comprises the illuminating device in the modification 1. It is explanatory drawing which shows an example of the image forming apparatus carrying the same spectral colorimeter. It is explanatory drawing for demonstrating an example of the conventional spectral colorimeter. 3 is a graph showing three color matching functions in an XYZ color system and a spectral luminance distribution of a white LED light source that constitutes an illumination device of a conventional spectrocolorimeter. It is the graph which took ratio of each color matching function with respect to the spectral luminance distribution of the illuminating device of the conventional spectrocolorimeter.

Hereinafter, an embodiment of a spectrocolorimeter as a colorimetric device according to the present invention will be described with reference to the drawings.
First, the configuration and operation of the spectrocolorimeter will be described along the flow of measuring the tristimulus values XYZ that are the colorimetric values of the measurement object by the colorimetry method using the spectrocolorimeter.

FIG. 1 is a functional block diagram of the spectrocolorimeter in the present embodiment.
FIG. 2 is an explanatory diagram showing a schematic configuration of the spectrocolorimeter.
In the spectrocolorimeter of the present embodiment, the illumination device 20 illuminates the surface (measurement surface) 1 of the measurement object, and diffused light reflected by the measurement surface 1 is reflected by the diffraction element 6 to m wavelength bands. Spectroscopy to (wavelength band). Then, the light intensity signal (luminance signal) of each wavelength band obtained thereby is detected in each light receiving region (one or more light receiving elements on the light receiving element array 8) corresponding to each wavelength band, and these lights are detected. The intensity signal is output as an output signal. The basic configuration of the spectrocolorimeter in the present embodiment is the same as that of the conventional spectrocolorimeter shown in FIG. 8, but in the present embodiment, as will be described later, the illumination device 20 and the conventional illumination device 2 are combined. Is different. An output signal output from the light receiving element array 8 is input to the spectral reflectance calculation unit 102 configured by the arithmetic unit 9.

  The spectral reflectance calculation unit 102 calculates the product of the output signal vector v based on the output signal output from the light receiving element array 8 and the conversion matrix G stored in the conversion matrix storage unit 103 according to the above equation (1). The calculation result is output as a spectral reflectance vector r indicating the spectral reflectance of the measurement object.

The conversion matrix storage unit 103 stores the conversion matrix G used in the spectral reflectance calculation unit 102. To describe an example of a method for calculating the transformation matrix G, by preparing a plurality of color samples having a known spectral reflectance, a sample showing their respective spectral reflectance vector r ₁ ~r _n of the equation (4) below Stored as a spectral reflectance matrix R. Then, an output signal (sample output signal) is obtained from the light receiving element array 8 for these color samples. After that, based on the sample output signal of each color sample, sample output signal vectors v _{1 to} v _n are generated. A group of the sample output signal vectors v _{1 to} v _n is a sample output signal matrix V shown in the following equation (5). Then, using this sample extended sensor response matrix V and the stored sample spectral reflectance matrix R, using the generalized inverse matrix of Moore-Penrose, the transformation matrix G is obtained from the following equation (6). Is calculated. The transformation matrix G calculated in this way is set in the transformation matrix storage unit 103. Here, the superscript “t” indicates transposition of a vector or a matrix, and the superscript “−1” indicates an inverse matrix. For calculating the inverse matrix, a generally known singular value decomposition method or the like can be used.

  The colorimetric value calculation unit 101 calculates the spectral reflectance vector r output from the spectral reflectance calculation unit 102 and the color matching function matrix H stored in the color matching function data storage unit 104 according to the above equation (2). The product is calculated, and the calculation result is output as a colorimetric value vector T that stores the tristimulus values XYZ of the measurement object.

Next, the structure of the illuminating device 20 which is the characterizing part of this invention is demonstrated.
The illumination device 20 of the present embodiment includes a first white LED light source 21 including a blue LED having a center wavelength (emission wavelength) of 460 [nm] and a yellow phosphor, and a center wavelength (emission wavelength) of 440 [nm]. ] Of the second white LED light source 22 as another light source composed of a blue LED and a yellow phosphor, and a collimating lens 23 for converting the white light emitted from the white LED light sources 21 and 22 into a substantially parallel light beam. Become.

FIG. 3 is a graph in which three color matching functions in the XYZ color system and the spectral luminance distributions of the first white LED light source 21 and the second white LED light source 22 are superimposed.
The first white LED light source 21 is the same as the one having the spectral luminance distribution shown in FIG. That is, a blue peak is present at 460 [nm] in the vicinity of the wavelength (about 450 [nm]) at which the color matching function of the Z value shows a peak, and the half-value width (spectral luminance distribution half-value width) of the blue peak. Is narrower than the half value width of the Z value color matching function (color matching function half value width). Therefore, when this is illuminated alone, as described above, the luminance in the vicinity of 430 [nm], which is a wavelength band where the Z value of the color matching function is large, decreases, and this wavelength band becomes a white light source luminance insufficient band. . Therefore, the S / N ratio of the output signal in this wavelength band is small, and the influence on the error of the calculated tristimulus value XYZ is large.

  Therefore, in the illumination device 20 of this embodiment, the first white LED light source 21 and the second white LED light source 22 described above are used in combination to illuminate the surface to be measured 1. As shown in FIG. 3, the second white LED light source 22 has a peak value lower than the blue peak (460 [nm]) of the first white LED light source 21 and a color matching function half of the Z value. The wavelength band portion (approximately 425 to 445 [nm]) in which the wavelength band (approximately 445 to 475 [nm]) corresponding to the half width of the spectral luminance distribution does not overlap among the wavelength bands (approximately 425 to 475 [nm]) corresponding to the value width. ) Has a blue peak (440 [nm]) with a shifted wavelength. According to the present embodiment, the second white LED light source 22 can supplement the illumination luminance of the white light source luminance insufficient band where the illumination luminance of the first white LED light source 21 is insufficient. As a result, the S / N ratio of the output signal in the white light source luminance deficiency band can be increased and the measurement accuracy of the calculated tristimulus values XYZ can be increased as compared with the case of illuminating with only the first white LED light source 21. be able to.

FIG. 4 is a graph showing the ratio of each color matching function to the spectral luminance distribution of the illumination device 20 in the present embodiment.
As described above, this ratio is an index value indicating the magnitude of the effect on the calculated tristimulus value XYZ error. When the graph of this embodiment shown in FIG. 4 is compared with the conventional graph shown in FIG. 10 (graph when illuminated only by the first white LED light source 21), according to this embodiment, the graph of FIG. The peak around 430 [nm] that appeared was reduced, and the index value could be kept low over the entire visible light wavelength range.

Next, a numerical simulation performed to confirm the effect of adding another light source to the first white LED light source 21 as in the present embodiment will be described.
In this numerical simulation, as another light source used in combination with the first white LED light source 21, the peak value is half of the blue peak of the first white LED light source 21, and the center wavelengths are 430 [nm], 435 [nm], The colorimetric accuracy when using blue LEDs having 440 [nm], 445 [nm], 450 [nm], and 455 [nm], respectively, was estimated. For comparison, the same simulation was performed for a conventional light source illuminated only by the first white LED light source 21.

  Before carrying out the numerical simulation, first, color patches of 24 colors of ColorChecker made by X-Rite were used as color samples, and this was measured with a reflection spectrodensitometer (X-Rite 939) made by X-Rite, and spectrally analyzed. A reflectance (31 channels with a wavelength of 400 to 700 [nm] and a pitch of 10 [nm]) was obtained. A reference L * a * b * value (reference L * a * b * value) was calculated from the spectral reflectance distribution of each color patch thus obtained. On the other hand, in the numerical simulation, a pseudo sensor signal is generated by adding the spectral product to the spectral reflectance distribution of each color patch obtained as described above, and then a random value of 0.2 [%] of the maximum value of the pseudo sensor signal is generated. After the noise was superimposed, the pseudo spectral reflectance measurement result was calculated by dividing by the spectral product, and the L * a * b * value was calculated therefrom. The spectral radiance distribution of the light source was used for the spectral product of the spectroscopic sensor optical system. This numerical simulation is performed 10 times, the standard deviation of the color difference between the L * a * b * value as the simulation result and the reference L * a * b * value is calculated, and the color difference ΔE * ab for the 24 color patches is calculated. The average value and the maximum value of the variation (3σ) were obtained.

FIG. 5 is a graph showing the results of the numerical simulation described above.
As shown in this graph, when the peak wavelength is 455 [nm], the maximum value of the variation (3σ) of the color difference ΔE * ab is slightly decreased as compared with the conventional light source, and the color measurement accuracy is improved. However, since the peak wavelength (455 [nm]) is close to the blue peak wavelength 460 [nm] of the first white LED light source, the effect is relatively small.
On the other hand, from the case where the peak wavelength is 450 [nm], the peak wavelength of the other light source gradually shifts to the low wavelength side (that is, the side away from the blue peak wavelength 460 [nm] of the first white LED light source). The effect increased and the measurement accuracy increased. When the peak wavelength of the other light source is 435 [nm], the variation (3σ) in the color difference ΔE * ab is about 1/4 on the average and about 1/5 on the maximum as compared with the conventional light source. It became.

In the present embodiment, the conversion matrix G multiplied by the color matching function matrix H is a weight for the tristimulus values XYZ of the optical system including the light source. A second white LED light source 22 as a light source is added to reinforce the spectral distribution of the lighting device 20. For example, when the light receiving region of the light receiving element array 8 is divided into 6 to obtain 6 channel output signals, the spectrum width per channel is about 50 [nm]. When illuminated with the conventional illumination device shown in FIG. 9 (illuminated with only the first white LED light source 21), the weight for the tristimulus value Z of one channel in charge of the wavelength of 400 to 450 [nm] is large. Thus, this noise component is excessively enlarged, and it can be seen that sufficient accuracy cannot be obtained. On the other hand, in the illumination device according to the present embodiment, the weight of the channel is reduced and the weight bias is reduced, so that noise of a specific channel is not enlarged and high accuracy is obtained.
In multiband spectroscopy, since the number of channels can be reduced, the amount of light received per channel increases, so the exposure time of the light receiving element can be shortened, and it is suitable for spectral colorimetry that acquires color information at a higher speed. is there.

As a result of the study by the present inventors, the main white light source (first white LED light source 21) has a blue peak in the range of 450 to 470 [nm] capable of realizing high luminous efficiency. Preferably, on the other hand, as an auxiliary light source (other light source) that compensates for the white light source luminance deficiency band, it has a blue peak in the range of 430 to 450 [nm], and the blue color of the main white light source Those having a central wavelength difference of 10 nm or more from the peak are preferable.
Further, here, for the sake of simplicity of explanation, a case where the first blue LED 31 as the main first light source and the second blue LED 32 as the auxiliary second light source are arranged one by one will be described. However, the number of these light sources may be two or more, and the number is appropriately set.

[Modification 1]
Next, a modification of the illumination device in the spectrocolorimeter of the above embodiment (hereinafter, this modification is referred to as “modification 1”) will be described.
FIG. 6 is an explanatory diagram showing a schematic configuration of a light source that constitutes the illumination device according to the first modification.
The illumination device according to the first modification includes a first blue LED 31 having a center wavelength (emission wavelength) of 460 [nm] and a second blue LED 32 having a center wavelength (emission wavelength) of 440 [nm], and a yellow phosphor. A multichip module is formed together with the fluorescent material 34 included. In this light source, a first blue LED 31 having an emission wavelength of 460 [nm] and a second blue LED 32 having a wavelength of 440 [nm] are mounted on a substrate 35, and the fluorescent material 34 covers them. Yes. The luminous flux emitted from the first blue LED 31 and the second blue LED 32 is transmitted through the fluorescent material 34, and the yellow phosphor in the fluorescent material 34 absorbs the blue luminous flux and emits yellow fluorescence.

  By using such a multi-chip modularized light source, the two blue LEDs 31 and 32 can be arranged close to each other. As a result, the difference in spectral distribution depending on the illumination position is reduced, and uniform illumination can be realized. And

[Modification 2]
Next, another modified example of the illumination device in the spectrocolorimeter of the above embodiment (hereinafter, this modified example is referred to as “modified example 2”) will be described.
The illumination device according to the second modification includes a first blue LED 21 having a center wavelength (emission wavelength) of 460 [nm], a second blue LED 22 having a center wavelength (emission wavelength) of 440 [nm], and a yellow phosphor. Composed. However, at present, a blue LED having a light emission wavelength of about 440 [nm] has lower light emission efficiency than a blue LED having a light emission wavelength of about 460 [nm], and it is difficult to ensure the same luminance. Therefore, in the second modification, a blue LED having an emission wavelength of 440 [nm], which is a main first light source, is used to irradiate yellow fluorescent material with yellow light to cause yellow fluorescence. The second power source is configured to irradiate the surface 1 to be measured without irradiating the yellow phosphor. As a result, for a blue LED having an emission wavelength of 440 [nm] with poor emission efficiency, there is no reduction in the amount of light due to the fluorescence of the yellow phosphor, so that it is easy to ensure the luminance of the auxiliary second power supply. Become.

In the present embodiment (including each modification, the same applies hereinafter), a 16-channel spectrocolorimeter has been described. For example, a 3-15-channel spectroscope using a known multiband spectroscopic technique is used. The same effect can be obtained even with this.
Moreover, although this embodiment demonstrated the case where the white LED light source which consists of blue LED and yellow fluorescent substance was used as a 1st main light source, this invention is not limited to this, For example, blue LED Similar effects can be obtained by using white LED light sources having other configurations, such as white LED light sources using green and red phosphors.
In the present embodiment, the case where a diffractive element is used as the spectroscopic means has been described. However, the present invention is not limited to this. For example, the same applies to a case where a plurality of color filters having different spectral transmittances are used. An effect can be obtained.

The spectral characteristic measuring apparatus described above is mounted on the image forming apparatus, and there is a utilization method such as adjusting the image forming conditions based on the spectral characteristic of the output image measured by the spectral characteristic measuring means. Hereinafter, this example will be described with reference to FIG.
As shown in FIG. 7, the image forming apparatus 80 includes the above-described spectral characteristic measuring apparatus denoted by reference numeral 60. In addition, the image forming apparatus 80 includes a paper feed cassette 81a, a paper feed cassette 81b, a paper feed roller 82, a controller 83, a writing optical system 84, a photosensitive member 85, an intermediate transfer member 86, a fixing roller 87, and a paper discharge roller 88. And so on. Reference numeral 90 denotes an image bearing medium (paper or the like).

  In the image forming apparatus 80, when the four photoconductors 85 are exposed by the writing optical system 84 based on the image data, an electrostatic latent image corresponding to each color is formed on each photoconductor 85. Development processing is performed by attaching a color material such as toner of a color corresponding to the electrostatic latent image. Each color toner image formed on each photoconductor 85 by this development processing is transferred onto the intermediate transfer body 86 so as to overlap each other. Thereafter, the toner image on the intermediate transfer body 86 is transferred from the paper feed cassettes 81 a and 81 b to the image carrier medium 90 conveyed by a guide (not shown) and the paper feed roller 82. The toner image transferred onto the image bearing medium 90 in this manner is fixed by the fixing roller 87, and the image bearing medium 90 is ejected by the ejection roller 88. In the present embodiment, the spectral characteristic measuring device 60 is installed at the subsequent stage of the fixing roller 87.

  In this image forming apparatus, the spectral characteristic measurement device 60 measures (estimates) the spectral characteristics (spectral reflectance, etc.) of the output image (measurement target) at a predetermined timing, and sends the measurement results to the controller 83. The controller 83 functions as an image forming condition adjusting unit, and adjusts the image forming condition based on the measurement result. As a result, since automatic color calibration is possible, it is possible to continuously provide a high-quality image with little color variation, and to stably operate the image forming apparatus.

As described above, the color measurement device according to the present embodiment includes the illumination device 20 as the illumination unit that illuminates the measurement target surface 1 that is the measurement target, and the spectroscopic unit that splits the reflected light beam from the measurement target surface 1. , The light receiving element array 8 as a light receiving means for receiving the dispersed light beam and outputting an output signal indicating the amount of light received in each wavelength band, and each output signal output from the light receiving element array 8 (Output signal vector v), spectral luminance distribution data (conversion matrix G) of light illuminated by the illuminating device 20, and color matching function data (color matching function matrix H) are used to change the color of the surface 1 to be measured. And an arithmetic unit 9 as arithmetic means for calculating tristimulus values XYZ, which are colorimetric values to be shown. And the illuminating device 20 has the peak of spectral luminance distribution in the wavelength vicinity where the color matching function data shows a peak, and the half value width (spectral luminance distribution half value width) about the peak of the spectral luminance distribution is the same color. The first white LED light source 21 that is the first light source as the white light source that is narrower than the half-value width (the half-value width of the color matching function) for the peak of the function data (in the first modification, the first blue LED 31 and the phosphor 34) The light source unit) and the peak of the spectral luminance distribution in the first light source have a peak value lower than this and correspond to the spectral luminance distribution half-value width in the wavelength band corresponding to the color matching function half-value width. The second white LED light source 22 as the second light source as another light source having a spectral luminance distribution having a peak shifted in wavelength on the side where there is a wavelength band portion where the wavelength bands to be overlapped do not exist (in the above modification 1) Using a light source portion) and composed of the second blue LED32 and the fluorescent material 34 to illuminate the surface to be measured 1. With such a configuration, the second light source can supplement the illumination brightness for the white light source brightness insufficient band where the illumination brightness by the first light source is insufficient. As a result, the S / N ratio of the output signal in the white light source luminance deficiency band can be made larger than when the first light source (white light source) is illuminated alone. Therefore, the measurement accuracy of the tristimulus values XYZ calculated by the calculation device 9 can be increased.
Moreover, since the 1st light source in this embodiment uses blue LED which is LED which made the wavelength which shows the said peak of the said spectral luminance distribution the light emission wavelength, generally the white light source marketed is used as the 1st light source. Can be used as
Moreover, since the 2nd light source in this embodiment uses blue LED which is LED which made the wavelength which shows the said peak of the said spectral luminance distribution the light emission wavelength, generally used blue LED or white light source is used. It can be used as a second light source.
In the present embodiment, the first light source uses a first blue LED that emits light with an emission wavelength of 450 [nm] or more and 470 [nm] or less, and emits light by receiving light from the first blue LED. The second light source is a second light source that emits light having an emission wavelength of 430 [nm] or more and 450 [nm] or less and that is 10 nm or more away from the emission wavelength of the first blue LED. A blue LED is used. Thereby, the measurement accuracy of the tristimulus values XYZ calculated by the calculation device 9 can be effectively increased.
In addition, the lighting device 20 in the first modification is a multichip module in which the first blue LED 31 and the fluorescent material 34 that is a phosphor and the second blue LED 32 constituting the first light source are formed as a single module. The one light source and the second light source can be arranged close to each other, and the difference in the spectral distribution depending on the illumination position is reduced, so that uniform illumination can be realized.
Further, as described in the above embodiment, the light receiving element array 8 may be configured to output output signals for 3 to 15 wavelength bands. In this case, even in the configuration of the present embodiment using the first light source and the second light source having different spectral distributions and luminances, it is possible to reduce the bias of the spectral distribution depending on the position, and to provide a more stable spectral colorimetric apparatus. It becomes possible.

DESCRIPTION OF SYMBOLS 1 Measuring surface 2,20 Illuminating device 3 1st lens 4 Slit 5 2nd lens 6 Diffraction element 7 3rd lens 8 Light receiving element array 9 Arithmetic device 21 1st white LED light source (1st light source)
22 Second white LED light source (second light source)
23 Collimating lens 31 First blue LED
32 Second blue LED
34 Fluorescent material 35 Substrate 60 Spectral characteristic measuring device 80 Image forming device

JP 2007-208708 A

Claims (7)

Illumination means for illuminating the measurement object;
A spectroscopic means for splitting the reflected light beam from the measurement object;
A light receiving means for receiving the split luminous flux and outputting an output signal indicating the amount of light received in each wavelength band;
Calculation means for calculating a colorimetric value indicating the color of the measurement object using each output signal output from the light receiving means, spectral luminance distribution data of light illuminated by the illumination means, and color matching function data In a color measuring device equipped with
The illumination means has a spectral luminance distribution peak in the vicinity of a wavelength at which the color matching function data shows a peak, and the spectral luminance distribution half-value width corresponding to the peak of the spectral luminance distribution is the same color. A white light source that is narrower than the half-value width of the color matching function that is the half-value width of the peak of the function data, and the peak value of the spectral luminance distribution in the white light source is lower than the peak value of the peak , and Other than the wavelength band corresponding to the half-value width of the color matching function, a spectral brightness distribution having a wavelength shifted peak on the side where the wavelength band portion where the wavelength band corresponding to the half-value width of the spectral brightness distribution does not overlap exists. A colorimetric apparatus for illuminating the measurement object using a light source. The colorimetric apparatus according to claim 1,
The color measurement apparatus according to claim 1, wherein the white light source uses a light emitting diode whose emission wavelength is a wavelength indicating the peak of the spectral luminance distribution. The color measuring device according to claim 1 or 2,
The color measuring apparatus according to claim 1, wherein the other light source uses a light emitting diode having a light emission wavelength as a wavelength showing the peak of the spectral luminance distribution. The colorimetric apparatus according to claim 1,
The calculation means calculates a tristimulus value of an XYZ color system as the colorimetric value,
Each of the white light source and the other light source uses a light emitting diode whose emission wavelength is the wavelength showing the peak of the spectral luminance distribution,
The white light source uses, as the light emitting diode, a first blue light emitting diode that emits light with an emission wavelength of 450 [nm] or more and 470 [nm] or less, and emits light by receiving light from the first blue light emitting diode. With a phosphor,
The other light source is a second blue light emitting that emits light having a light emission wavelength of 430 [nm] or more and 450 [nm] or less, which is 10 nm or more away from the light emission wavelength of the first blue light emitting diode. A colorimetric apparatus using a diode. The colorimetric apparatus according to claim 4, wherein
The colorimetric device, wherein the illuminating means comprises a single module of the first blue light emitting diode, the phosphor and the second blue light emitting diode constituting the white light source. The colorimetric apparatus according to any one of claims 1 to 5,
An output signal for 3 to 15 wavelength bands is output from the light receiving means. In an image forming apparatus for forming an image composed of a plurality of colors on an image bearing medium,
A colorimetric device for measuring the colorimetric values of the image formed on the image bearing medium;
Image forming condition adjusting means for adjusting image forming conditions based on colorimetric values measured by the color measuring device;
An image forming apparatus using the color measuring device according to claim 1 as the color measuring device.

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