JP2005098935A - Spectroscopic analyzer and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spectroscopic analyzer capable of analyzing spectroscopic characteristics of an image precisely with a reduced number of light sources, and an image forming device equipped with the such spectroscopic analyzer. <P>SOLUTION: The spectroscopic characteristics for expressing a relation between a wavelength of light and intensity of the light are approximated using a summation function comprising a summation of semi-basic functions added respectively with weight factors onto a plurality of basic functions having the same shape. The each weight function is determined to bring the weight factors having the light number or less of the light sources out of the weight factors into the weight factors independent each other and to bring the weight factors other than the the independent weight factors into the weight factors dependent on the independent weight factors, so as to determine the spectroscopic characteristic. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a spectral analysis device that analyzes spectral characteristics of an image and an image forming apparatus that includes the spectral analysis device.

  In image forming apparatuses such as printers and copiers, it has become common to form color images using color materials such as Y (yellow), M (magenta), C (cyan), and K (black). ing. For example, in a printer to which an electrophotographic method is applied, the surface of a charged photoreceptor is exposed to form a latent image, the latent image is developed with toner of each color to form a toner image, and the toner image is A color image is formed by transferring the image onto a recording medium directly or via an intermediate transfer member. In an image forming apparatus that forms such a color image, an attempt has been made to improve the color reproducibility of the color image. The sensitivity to human color differences is extremely high, and if the target level of color reproduction accuracy is set below the human color difference recognition limit, the required value of color reproduction accuracy for the image forming apparatus is the L * a * b * color system. It becomes very high such as ΔE = 3 or less. Actually, the color reproducibility of the image forming apparatus is likely to fluctuate due to environmental conditions such as temperature and humidity, and deterioration over time of the photoconductor and developer. Therefore, in order to keep the color reproducibility of a color image optimal, for example, at the beginning of a day's work, the color patch is output by the image forming apparatus so that the color of the color patch approaches the target color. In addition, for example, controlling exposure and development is widely performed.

  As a method for measuring the color of a color patch, many methods using an image reading unit such as a scanner incorporated in an image forming apparatus have been proposed (for example, Patent Document 1, Patent Document 2, Patent Document 3, And Patent Document 4). However, according to these methods, in order to measure the color of the color patch, it is necessary for the operator to transfer the image once output to the image reading unit and then read the image, and these operations are performed on a daily basis. There is a problem that this is very annoying. In addition, the colorimeter used for off-line measurement is a post-spectral type that measures the color density by spectroscopically analyzing the reflected light reflected from the light emitted from the white light source on the image with a diffraction grating or many filters. If a post-spectral color sensor is used to measure the color of an image in a printer that has a color sensor and is not originally equipped with a scanner, etc., the size of the device will increase and it will take considerable costs. There is also a difficulty.

Light emitting diodes (hereinafter referred to as LEDs) of B (blue), G (green), and R (red) colors corresponding to single colors of Y, M, and C color materials for the post-spectral color sensor In addition, a kind of pre-spectral color sensor that measures the color density of an image by receiving reflected light of light emitted sequentially from the LEDs has been proposed (for example, Patent Document 5 and Patents). Reference 6). Since this pre-spectral color sensor does not require an expensive white light source or diffraction grating, there is an advantage that it can be realized in a small size and at a low price even when incorporated in a printer or the like.
JP-A 62-296669 JP-A 63-185279 Japanese Patent Laid-Open No. 01-169467 JP-A-5-199407 JP-A-9-171279 JP-A-63-020956

  However, the emission spectrum of the LED has a narrower band than the spectrum obtained by the RGB filter used in the post-spectral color sensor, and the wavelength distribution in the commercial LED is limited. It is difficult to disperse the color gamut with high accuracy. In a pre-spectral type color sensor that uses R, G, and B three-color LEDs as light sources, a so-called primary color patch that is formed of a single color of C, M, and Y, which are complementary colors of R, G, and B. The color density can be accurately measured. The methods of Patent Document 5 and Patent Document 6 described above are far more limited in cost and size than conventional post-spectral color sensors, with limited applications for measuring the color density of the primary color patch. It is an object of the present invention to provide a pre-spectral color sensor that is advantageous for the above.

  However, in order to measure not only primary colors but also secondary colors and tertiary colors by overlaying primary colors, measure colors in a wide color gamut within the color reproduction range that can be output by the image forming device. There is a need.

  Therefore, by adding several additional light sources to R, G, and B and irradiating the color patches with light from each of the light sources, the reflectance of each color is expressed by a color such as an L * a * b * value. It is possible to convert it to a value. The conversion relationship between the reflectance of each color and the color value is stored in advance in the database, and when color value conversion is performed, conversion processing is performed based on the conversion relationship stored in this database. In the case of this method, if the color material or paper constituting the color patch is equivalent to the correlation stored in the database, the reflectance of each color is accurately converted to a color value. be able to. However, if the color material, the paper, the image forming method, and the like are different, the spectral characteristics of the formed color patch are also affected by the influence thereof, so that the conversion accuracy may be deteriorated.

  In order to accurately measure the spectral characteristics of color patches using a pre-spectral color sensor without depending on conditions such as paper and color materials, it is necessary to divide the visible wavelength range into many channels and perform measurement. In theory, 30 or more channels may be required every 10 nm. If you try to prepare all this number of LEDs with different wavelength ranges, it will be an obstacle to cost reduction and downsizing, and it is a reality that all these LEDs can be covered with commercial products. There is a problem that it is impossible.

  In view of the above circumstances, the present invention is a spectroscopic analysis apparatus that can accurately analyze spectral characteristics of an image with a small number of light sources, regardless of paper or color materials, and an image including such a spectroscopic analysis apparatus. The present invention relates to a forming apparatus.

The spectral analysis apparatus of the present invention that achieves the above object includes a light source that sequentially emits each of a plurality of lights having different wavelength distributions,
A light receiving unit that measures each intensity of the light obtained from the image when each of the plurality of lights emitted from the light source is sequentially irradiated on the image;
Spectral characteristics representing the relationship between the wavelength of light emitted to an image and the intensity of light obtained from the image, which are more than the number of light emitted from the light source, each having the same shape, with the wavelength as a variable Approximate with a sum function consisting of the sum of a plurality of quasi-basic functions with each weighting factor added to each of the basic functions whose wavelength regions are shifted from each other, and the wavelength of each of the plurality of lights emitted from the light source. The spectral characteristics are analyzed by determining each weighting factor so that the calculated light intensity obtained from the distribution matches each light intensity measured by the light receiving unit. In determining each weighting factor, Among the weighting factors, predetermined weighting factors equal to or less than the number of lights emitted from the light source are independent weighting factors, and weighting factors other than these independent weighting factors are weights dependent on these independent weighting factors. Characterized by comprising an analysis unit for determining as a coefficient.

The intensity R (λ) of the light acquired from the image when the light whose wavelength distribution is represented by S (λ) is irradiated onto the image is represented by P (λ) as the spectral characteristic of the image.
R (λ) = S (λ) * P (λ) (1)
(1) The spectral characteristic P (λ) is expressed by a plurality of quasi-basic elements in which a plurality of basic functions F (λ) having the same shape and wavelength distributions are shifted from each other, and weighting factors k _x independent from each other are added. When approximated by a sum function P ′ (λ) consisting of the sum of functions,
P ′ (λ) = k ₁ * F ₁ (λ) + k ₂ * F ₂ (λ) +... K _i * F _i (λ) (2)
(2) is obtained. In this formula (2), 0 <i, and the approximation accuracy increases as i increases. When this summation function P ′ (λ) is applied to equation (1) instead of the spectral characteristic P (λ),
R (λ) = S (λ) * {k ₁ * F (1) + k ₂ * F (2) +... K _i * F (i)} (3)
(3) is obtained. Here, since the integrated value of the light intensity is a value that can be actually measured by the light receiving unit, the light S _j (λ) of j types of wavelengths where i ≦ j is applied to the image, and then By measuring the integral value of the intensity R _j (λ), the value of the weight coefficient k _x included in the equations (2) and (3) is uniquely determined.

  Here, the more the number i of basic functions prepared in Equation (3), the more accurately the spectral characteristic P (λ) of the image can be approximated. However, the number of necessary light types j increases accordingly. End up. For example, in the case of commercially available LEDs, the wavelength distribution is limited to several types, and there is a problem that it is insufficient to create an accurate approximate function.

By the way, the spectral characteristic P (λ) of an actual image created using a color material as described above has a characteristic that, for example, there is almost no intensity change in any color on the long wavelength region side. The weighting factors k _x on the long wavelength region side included in the summation function P ′ (λ) in which P (λ) is approximated are almost the same. In this way, since some weighting factors k _x have a strong correlation, several weighting factors can be substituted with other weighting factors. The spectroscopic analysis apparatus of the present invention utilizes this property, instead of formula (2),
_{P'(λ) = {k 1} * F 1 (λ) + ... k m * F m (λ)} + {k'm + 1 * F m + 1 (λ) + ... k'j * F j ( λ)} (4) where 0 <m ≦ i ≦ j
As shown in Equation (4), Equation (4) is used which includes an independent part to which a mutually independent weight coefficient k _x is attached and a dependent part to which a dependent weight coefficient k ′ _x is attached. Here dependent weighting factor _k'x is a coefficient relationship predetermined subordinate to one or more independent weighting factor k _x, for example, becomes like a constant multiple of the coefficient of independent coefficients k _x Yes. By applying the equation (4) to the equation (3) and using it, it is possible to reduce the types of required light wavelengths without reducing the approximation accuracy of the summation function P ′ (λ). Therefore, it is possible to accurately analyze the spectral characteristics of the image with a small number of light sources.

In the spectroscopic analysis apparatus of the present invention,
"The light receiving unit measures the reflection intensity of the light irradiated on the image,
The analysis unit analyzes the spectral characteristics representing the spectral reflectance of the image. ''
This form is suitable.

  The reflection intensity of an image formed on a sheet or the like can be easily measured by a light receiving unit such as a CCD that has been widely used in the past, so the light reflection unit measures the light reflection intensity and the analysis unit displays an image. It is preferable to analyze the spectral characteristics representing the spectral reflectance of the light.

  In the spectroscopic analysis apparatus of the present invention, the analysis unit preferably uses a spline function as a basic function.

  The spline function is a function that can create a desired smooth curve like a so-called free ruler (see Noboru Ota, “Basics of Color Reproduction Optics”, Corona, 240P). Therefore, the spectral characteristic of the image can be accurately approximated by the sum function obtained by applying this spline function as a basic function.

  In the spectroscopic analysis apparatus of the present invention, it is also preferable that the analysis unit uses a plurality of basic functions whose wavelength regions are evenly shifted.

  In the spectral analysis apparatus of the present invention, it is preferable that the analysis unit uses a plurality of basic functions for each wavelength region of blue, green, and red.

  As color materials for forming an image, color materials of three colors of cyan (C), magenta (M), and yellow (Y) are generally used. Therefore, by using a plurality of basic functions for each wavelength region of red (R), green (G), and blue (B), which are complementary colors of these C, M, and Y colors, analysis can be performed efficiently. .

  In the spectroscopic analysis apparatus of the present invention, it is also preferable that the analysis unit uses a plurality of basic functions for each wavelength region of 400 to 500 nm, 500 to 600 nm, and 600 to 700 nm.

  400 to 500 nm is a blue wavelength distribution region, 500 to 600 nm is a green wavelength distribution region, and 600 to 700 nm is a red wavelength distribution region.

  In the spectroscopic analysis apparatus of the present invention, it is preferable that the plurality of light emitting diodes are provided and the plurality of light emitting diodes emit light sequentially.

  The light emitting diode has an advantage that it is less expensive than a white light source that has been widely applied as a light source. According to the spectroscopic analysis apparatus of the present invention, it is possible to analyze the spectral characteristics of an image with sufficient accuracy by using a small number of light emitting diodes that emit a small number of colors.

An image forming apparatus of the present invention that achieves the above object includes an image forming unit that forms an image using a plurality of color materials having different colors, and
An image fixing unit for fixing the image on a recording medium;
A light source that sequentially emits each of a plurality of lights having different wavelength distributions;
A light receiving unit that measures each intensity of light obtained from the image when each of the plurality of light emitted from the light source is sequentially irradiated onto the image formed by the image forming unit;
Spectral characteristics representing the relationship between the wavelength of light emitted to an image and the intensity of light obtained from the image, which are more than the number of light emitted from the light source, each having the same shape, with the wavelength as a variable Approximate with a sum function consisting of the sum of multiple quasi-basic functions with each weighting factor attached to each of the basic functions whose wavelength regions are shifted from each other, and the wavelength distribution of each of the light emitted from the light source and the sum function The spectral characteristics are analyzed by determining each weighting factor so that the calculated light intensity obtained from the above matches each light intensity measured by the light receiving unit. Predetermined weighting factors that are equal to or less than the number of light emitted from the light source are independent weighting factors, and weighting factors other than these independent weighting factors are weighting factors dependent on these independent weighting factors. And analysis unit that determines as shall,
And a correction control unit that corrects the color of the image by controlling the image forming unit based on spectral characteristics of the image analyzed by the analysis unit.

  By providing the image forming apparatus with the spectral analysis apparatus as described above and performing correction based on the analysis result, an image with good color reproducibility can be obtained.

  In the image forming apparatus of the present invention, it is preferable that the light receiving unit measures light intensity in an image formed by the image forming unit and fixed on the recording medium.

  Various inconveniences that occur during image formation, such as the transfer process, by measuring the light intensity in the image fixed on the recording medium, which is the final stage of image formation, and performing correction based on the measurement result Can be corrected. Therefore, the color image reproduction accuracy can be further improved.

  In the image forming apparatus according to the aspect of the invention, the image forming unit may form an image by using at least two color materials among yellow, cyan, magenta, and black as a plurality of color materials. Is preferred.

  The image forming apparatus of the present invention is particularly effective when the color of the image measured by the light receiving unit is a color.

  According to the present invention, a spectral analysis device that can accurately analyze the spectral characteristics of an image with a small number of light sources without depending on the type of paper or color material, and an image including such a spectral analysis device. A forming apparatus can be provided.

  Hereinafter, embodiments of the present invention will be described.

  FIG. 1 is a schematic configuration diagram showing a main part of a printer to which an embodiment of a spectral analysis apparatus and an image forming apparatus of the present invention is applied.

  As shown in FIG. 1, the printer 1 includes four image forming units 10Y, 10M, 10C, and 10K. Each image forming unit 10 includes a photoconductor 11Y, 11M, 11C, 11K, and Chargers 12Y, 12M, 12C, 12K, exposure units 13Y, 13M, 13C, 13K, developing units 14Y, 14M, 14C, 14K, primary transfer members 15Y, 15M, 15C, 15K, cleaning devices 16Y, 16M, 16C, 16K Is provided. The printer 1 is an embodiment of the intermediate transfer belt 30, the intermediate transfer belt cleaner 31, the secondary transfer body 32, the fixing device 33, the tension roller 34, the control unit 35, and the spectral analysis apparatus of the present invention. A color measuring device 36 is also provided. The image forming units 10Y, 10M, 10C, and 10K are examples of the image forming unit in the image forming apparatus of the present invention, and include the intermediate transfer belt 30, the intermediate transfer belt cleaner 31, the secondary transfer member 32, and the fixing device 33. This corresponds to an example of an image forming unit in the image forming apparatus of the present invention.

  The printer 1 is capable of full-color printing, and the symbols Y, M, C, and K added to the end of each of the above components are yellow, magenta, cyan, and black images, respectively. It is a component for formation.

  A basic operation of the printer 1 in image formation will be described.

  First, as preparations for forming an image, the photoconductors 11Y, 11M, 11C, and 11K for each color are rotated in the direction of arrow A, and contact type chargers are formed on the surfaces of the photoconductors 11Y, 11M, 11C, and 11K. Predetermined charges are applied by 12Y, 12M, 12C, and 12K, respectively.

  Subsequently, an input image signal representing a color separation image obtained by separating the image into yellow, magenta, cyan, and black is given to the corresponding image forming units 10Y, 10M, 10C, and 10K by the control unit 35.

  Next, toner image formation by the yellow image forming unit 10Y is started, and exposure light corresponding to a yellow color separation image is irradiated onto the surface of the photoconductor 11Y by the exposure device 13Y, so that an electrostatic latent image (electrostatic potential) is generated. Latent image) is formed. The electrostatic latent image is developed by a developing voltage applied to a developing position between the developing device 14Y and the photosensitive member 11Y with yellow toner contained in the developer circulated and supplied by the developing device 14Y. A yellow toner image is formed on the body 11Y. The toner image is transferred to the intermediate transfer belt 30 by the primary transfer body 15Y.

  The intermediate transfer belt 30 circulates in the direction of arrow B, and is synchronized with the timing at which the yellow toner image transferred onto the intermediate transfer belt 30 reaches the primary transfer body 15M of the next color image forming unit 10M. The magenta image forming unit 10M forms a toner image so that the next color magenta toner image reaches the primary transfer body 15M. The magenta toner image formed in this way is transferred onto the primary transfer body 15M by being superimposed on the yellow toner image on the intermediate transfer belt 30. Here, when the toner images on the photoconductors 11Y, 11M, 11C, and 11K are transferred onto the intermediate transfer belt 30, the photoconductors 11Y, 11M, 11C, and 11K are cleaned by the cleaning devices 16Y, 16M, 16C, and 16K. Waste toner remaining on the top is removed.

  Subsequently, toner image formation by the cyan and black image forming units 10C and 10K is performed at the same timing as described above, and is sequentially superimposed on the yellow and magenta toner images of the intermediate transfer belt 30 in the primary transfer bodies 15C and 15K. Is transcribed.

  In this way, the multicolor toner image transferred onto the intermediate transfer belt 30 is secondarily transferred onto the paper 200 by the secondary transfer body 32, and the multicolor toner image is conveyed along with the paper 200 in the direction of arrow C, and the fixing device 33. As a result, the color image is formed by being fixed on the sheet 200.

  Also, a series of correction processes for maintaining the color reproducibility of the color image is performed, for example, after the end of a day's work.

  FIG. 2 is a functional block diagram of the printer shown in FIG. Hereinafter, for convenience of explanation, various elements provided in the cyan image forming unit 10C shown in FIG. 1 will be used as representatives.

  FIG. 2 shows the color measuring device 36, the control unit 35, and the image forming unit 10C that are also shown in FIG.

  The control unit 35 uses a color conversion profile stored in the memory 37, a color conversion unit 351 that converts the color of the image into a beautifully visible color, a color conversion control unit 352 that controls the color conversion unit 351, an image An image density control unit 353 for controlling the color density, a reference signal generation unit 354 for generating an image signal representing a plurality of color patches having different color values, and a CPU 356 for controlling access to the memory 37. Yes. The control unit 35 is an example of a correction control unit in the image forming apparatus of the present invention.

  For example, when the start of the correction process is instructed by the operator, the reference signal generator 354 generates image signals representing a plurality of color patches. The generated image signal is sent to the image forming unit 10C, and a color patch is formed on the paper 200 in FIG. 1 by the series of image forming processes described above.

  When the color patch is formed, the color measurement device 36 calculates the color value (L * a * b * value) of each color patch formed on the paper 200 by a measurement process described later. The calculated color value is transmitted to the control unit 35.

  The image density control unit 353 corrects the difference based on the difference between the calculated color value and the target value of the color value stored in the memory 37 in advance, the charge amount, the exposure amount, and the development bias. The number of rotations of the developing roll, the toner supply coefficient, and the like are calculated. The image density control unit 353 transmits these calculated values to the image forming unit 10C.

  In addition to the charger 12C, the exposure device 13C, the developing device 14C, and the photoconductor 11C also shown in FIG. 1, the image forming apparatus 10C includes a grid power source 12C ′ that supplies power to the charger 12C, and the exposure device 12C. An exposure controller 13C ′ for adjusting the exposure, a development controller 14 ′ for adjusting the developing device 14C, and a photoconductor controller 11C ′ for adjusting the rotation of the photoconductor 11C and the like are provided.

  The grid power supply 12C ′ of the image forming unit 10C adjusts the power supplied to the charger 12C according to the charge amount value transmitted from the image density control unit 353. The exposure controller 13C ′ adjusts the exposure amount in the exposure unit 13C according to the calculated exposure amount value. The development controller 14C ′ adjusts the development bias of the developing unit 14C, the rotation speed of the development roll, the amount of discharged toner, and the like according to the development bias, the rotation speed of the development roll, and the toner supply coefficient transmitted from the image density control unit 353.

  By such a series of correction processes, the color value of the color patch output from the printer 1 is brought close to the target value, and the color reproducibility of the color image is maintained.

  Here, in the present embodiment, correction processing is performed by adjusting the charge amount, exposure amount, development bias, rotation speed of the developing roll, toner supply coefficient, and the like. For example, the number of rotations of the photoconductor 11C may be changed, or the color conversion control unit 352 may correct the color conversion profile used in the color conversion unit 351. Good.

  Here, the feature of the present invention in the printer 1 resides in the color measuring device 36. Hereinafter, the color measuring device 36 and the measurement process performed by the color measuring device 36 will be described in detail.

  FIG. 3 is an internal configuration diagram of the color measuring device, and FIG. 4 is an enlarged view of the vicinity of the lens shown in FIG.

  The color measuring device 36 includes a light receiving element 361, a lens 362, an LED 363, an irradiation unit 364, and an analysis unit 365.

  The LED 363 has n LEDs 363 that emit light having different wavelength distributions (described later), and FIG. 4 shows four LEDs 363 (363_1,... 363_4) among them. The LED 363 emits light from each LED one by one toward the color patch 201 on the paper 200. The LED 363 corresponds to an example of a light source according to the present invention. Light emitted from the LED 363 is irradiated on the color patch 201 by the irradiation unit 364.

  The light irradiated on the color patch 201 is reflected on the color patch 201. This reflected light is condensed on the light receiving element 361 by the lens 362.

  When the reflected light is received by the light receiving element 361, the reflection intensity of the reflected light is measured. The light receiving element 361 corresponds to an example of a light receiving unit according to the present invention. The reflection intensity measured by the light receiving element 361 is transmitted to the analysis unit 365.

  The analysis unit 365 calculates the reflectance from the reflection intensity measured by the light receiving element 361 and the amount of light emitted from the LED 363, and analyzes the spectral characteristics of the color patch 201 using the reflectance. The analysis unit 365 further calculates the color value of the color patch 201 using the analyzed spectral characteristics. The analysis unit 365 corresponds to an example of the analysis unit referred to in the present invention.

  Hereinafter, a method for analyzing the spectral characteristics will be described.

  When the i-th (0 <i ≦ n) LED 363_i having a light emission amount Si (λ) emits light, the reflection intensity Ri of the reflected light reflected by the color patch 201 is measured by the light receiving element 361. . The reflection intensity Ri is transmitted to the analysis unit 365, and the reflectance Pi = Ri / Si is calculated from the light emission amount Si and the reflection intensity Ri.

  Here, the relationship between the reflectance Pi and the spectral characteristic Q (λ) of the color patch 201 is as follows.

Pi = {∫Q (λ) * Si (λ) dλ} / ∫Si (λ) dλ (5)
The spectral characteristic Q (λ) corresponds to an example of the spectral characteristic referred to in the present invention, and represents the spectral reflectance here.

  In order for the color measuring device 36 to accurately analyze the spectral characteristics of mixed color patches such as secondary colors and tertiary colors, it is possible to use the LEDs 363_1,. It is necessary to compensate for light having a wavelength in the region.

  FIG. 5 is a diagram showing an emission spectrum of main commercially available LEDs.

  In the color measuring device 36 of the form shown in FIG. 3, the reflectance can be accurately measured only in the vicinity of the peak wavelength of the LEDs 363_1,. Therefore, when eight types of LED_L1 to LED_L8 as shown in FIG. 5 are applied as the LED 363_i of the light source, the reflectance can be accurately measured in the high wavelength region by the LED_L5 to LED_L8, but in the vicinity of 550 nm to 600 nm, etc. There is a problem that the accuracy of the measurement result is lowered.

Here, the spectral characteristic Q (λ) of the color patch 201 will be replaced using a plurality of spline functions. The spline function C (λ) is
C (λ) = {w ³ + 3w ² (w− | λ |) + 3w (w− | λ |) ² −3 (w− | λ |) ³ } / 6w ³ (when | λ | ≦ w)
C (λ) = (2w− | λ |) ³ / 6w ³ (when w ≦ | λ | ≦ 2w)
C (λ) = 0 (when 2w <| λ | w)
By using a plurality of spline functions having different wavelength regions, an arbitrary smooth curve can be created like a free ruler.

  FIG. 6 is a diagram illustrating an example of a spline function.

FIG. 6 shows a plurality of spline functions S _{1 to} S ₁₆ whose wavelength regions are evenly shifted. Spectral characteristics Q (λ) can be approximated by preparing a plurality of such spline functions in the visible region and adding them to each other by adding independent weighting coefficients. If m spline functions are prepared, and the j-th spline function is C _j (λ) and the weighting coefficient is x _l , the approximate function S (λ) of the spectral characteristic Q (λ) is
S (λ) = Σx _j * C _j (λ) = x ₁ * C ₁ + x ₂ * C ₂ +... X _m * C _m (6)
(Where Σ represents the sum of j from 1 to m)
Can be expressed as The weight coefficient x _j is an example of the weight coefficient referred to in the present invention, and the spline function C _j (λ) is an example of the basic function referred to in the present invention. The weight coefficient x _j and the spline function C _j (λ) are The product corresponds to an example of a quasi-basic function according to the present invention. Further, the approximate function S (λ) represented by the equation (6) corresponds to an example of the summation function referred to in the present invention. By applying this approximate function S (λ) to the spectral characteristic Q (λ) part of equation (5) and substituting equation (6),
Pi = {∫Σx _j * C _j (λ) * Si (λ) dλ} / ∫Si (λ) dλ (7)
(I is 1 ≦ i ≦ n and LED number, j is 1 ≦ j ≦ m and spline function number). Since part of ∫Si (λ) dλ is a fixed value for each LED363_i, it will be described here replaced by a constant 1 / T _i. Further, in order to simplify the formula, it is abbreviated as C _j (λ) = C _j and Si (λ) = Si. At this time, the equation (7) becomes
Pi = {∫ (x ₁ * C ₁ + x ₂ * C ₂ +... X _m * C _m ) * Si (λ) dλ} * T _i (8)
It can be rewritten as In Expression (8), Pi is a value calculated based on the reflection intensity Ri actually measured by the light receiving element 361 shown in FIG. 3, and Si (λ) is the emission wavelength characteristic of the i-th LED. So it is a function that is known in advance. Therefore, the unknown is only the weighting factor x _j , and theoretically, the LED Pi is measured by irradiating the color patch 201 with n LEDs where j ≦ n, thereby identifying the weighting factor x _j . Thus, the approximate function S (λ) of the spectral characteristic Q (λ) can be uniquely determined.

  FIG. 7 is a diagram showing the spectral characteristic Q (λ) and its approximate function S (λ).

  A curve P shown in FIG. 7 indicates the spectral characteristic Q (λ). In order to bring the curve formed by Expression (6) closer to the curve P, it is preferable to use as many spline functions as possible. However, increasing the number of spline functions requires increasing the types of LEDs as shown in equation (8). However, there is a limit to the type of LED.

  FIG. 8 is a diagram showing the wavelength region distribution of the spline function prepared in this embodiment.

  FIG. 8 shows B (400 to 500 nm: short wavelength region Rs), G (500 to 600 nm: medium wavelength region Rm), R (600 to 700 nm: long) corresponding to the complementary colors of the Y, M, and C toners. Three spline functions (S_s1 to S_s3, S_m1 to S_m3, S_l1 to S_l3) are prepared for each region of the wavelength region Rl), and one spline function (1 to both ends) ( The distribution of the wavelength region of a total of 11 spline functions when S_Smax, S_Lmax) is prepared is shown.

  A curve Ps shown in FIG. 7 shows a curve formed by the approximate function S (λ) when the spectral characteristic Q (λ) is approximated using the 11 spline functions shown in FIG. The spline functions S1 to S11 illustrated in FIG. 7 are functions in which a weighting coefficient is added to the spline function illustrated in FIG. In this manner, the spectral characteristic Q (λ) can be approximated with sufficient accuracy by using 11 spline functions. That is, if at least 11 LEDs are prepared, the spectral characteristic Q (λ) can be uniquely determined.

  However, as shown in FIG. 5, there are about 8 types of commercially available LEDs, and there is a problem that even 11 LEDs are still too many. Here, the spline function is reduced.

  FIG. 9 is a diagram showing spectral reflection curves in various color patches mixed with Y, M, and C colors.

  As shown in FIG. 9, the spectral reflectance of the actual color patch is characterized in that there is almost no intensity change in any color on the long wavelength region side of 650 nm or more. Therefore, the weighting factors of some spline functions can be replaced with constants, or the weighting factors of adjacent spline functions can be substituted.

  FIG. 10 is a diagram showing a correlation between weight coefficients of adjacent spline functions in the long wavelength region. The horizontal axis in FIG. 10 represents the weighting coefficient of one spline function in the long wavelength region, and the vertical axis represents the weighting coefficient of another spline function close to the spline function.

  In the case of a spline function on the long wavelength region side, as shown in FIG. 10, it becomes a straight line in which the slope of the correlation graph of the weighting coefficients between adjacent spline functions is approximately 1. Therefore, on the long wavelength region side, the weighting factor can be replaced with a nearby weighting factor.

  FIG. 11 is a diagram illustrating a correlation between weight coefficients of adjacent spline functions in a short wavelength region. The horizontal axis in FIG. 11 represents the weighting coefficient of one spline function in the long wavelength region, and the vertical axis represents the weighting coefficient of another spline function close to the spline function.

  In the case of the spline function on the short wavelength region side, as shown in FIG. 11, the correlation graph of the weighting coefficients between the adjacent spline functions becomes a straight line having a predetermined slope. By using this slope, the weighting coefficient is calculated. Can be substituted.

For example, the weight coefficient of _two spline functions C ₁ and C ₂ on the short wavelength side is replaced with a coefficient k * x ₃ that is subordinate to the weight coefficient x ₃ of the third spline function with a constant k, and When the three spline functions C ₉ , C ₁₀ , and C ₁₁ are replaced with x _{8 as} the weight coefficients of the _eighth spline function, Expression (6) can be expressed by, for example,
S (λ) = (x ₃ * C ₃ +... X ₈ * C ₈ ) + (k * x ₃ * C ₁ + k * x ₃ * C ₂ + x ₈ * C ₇ + x ₈ * C ₁₀ + x ₈ * C ₁₁ ) ... (9)
Equation (8) is expressed as
Pi = {∫ {(x ₃ * C ₃ +... X ₈ * C ₈ ) + (k * x ₃ * C ₁ + k * x ₃ * C ₂ + x ₈ * C ₇ + x ₈ * C ₁₀ + x ₈ * C ₁₁ )} * Si (λ) dλ} * T (10)
It is expressed as As a result, the number of unknowns is six from x ₃ to x _8, and the number of LEDs necessary to identify them is also six or more. Therefore, these weighting factors can be uniquely determined even using only commercially available LEDs as shown in FIG.

  As the LED 363_n illustrated in FIG. 4, six or more LEDs having different emission wavelength regions are applied, and the reflection intensity R with respect to the light emitted from the LEDs is measured by the light receiving element 361. The analysis unit 365 shown in FIG. 3 calculates the weighting coefficient by applying the reflectance P calculated based on the measurement result to the equation (10), and determines the approximate function S (λ). This approximate function S (λ) is an approximation of the spectral characteristic Q (λ) of the color patch 201, and this approximate function S (λ) is used as the spectral characteristic Q (λ).

  The analysis unit 365 further calculates a color value using the analyzed spectral characteristic Q (λ).

  FIG. 12 is a diagram showing color matching functions in the XYZ color system.

  Using the three color matching functions X (λ), Y (λ), Z (λ) and the spectral characteristic Q (λ) shown in FIG. 12, the tristimulus values X, Y, Z of the image are It is expressed as follows.

X = t * ∫ {X (λ) * Q (λ)} dλ
Y = t * ∫ {Y (λ) * Q (λ)} dλ
Z = t * ∫ {Z (λ) * Q (λ)} dλ
The tristimulus values X, Y, and Z thus obtained are converted into the above-described L * a * b * values by a predetermined conversion formula. This L * a * b * value is transmitted to the control unit 35 shown in FIG. 2, and the correction processing described above is performed.

  As described above, according to the color value measuring apparatus of the present invention, the spectral characteristic Q (λ) can be accurately measured with a small number of types of light sources. Measurement can be performed regardless of the type of color material or paper and the image forming method.

  Here, in the above description, the spectral analysis device that measures the color value of the color patch formed on the paper has been described, but the spectral analysis device of the present invention measures the color value of the image during the image forming process. It may be a thing. By measuring the color value of the color patch formed on the paper, it is possible to perform correction with high accuracy including defects in the transfer process.

  In the above description, an example in which a spline function is applied as a basic function has been described. However, the basic function referred to in the present invention is, for example, a normal distribution function with a wavelength as a variable, a 2n-order function (n is a natural number), It may be a function such as a sine function or cosine function.

  In the above description, an example in which three basic functions are used for each wavelength region of blue, green, and red in the analysis unit has been described. However, the analysis unit according to the present invention is, for example, about the red region. May use a different number of basic functions for each wavelength region, such as using one basic function.

  In the above description, an example in which a dependent weight coefficient is replaced with an independent weight coefficient or a coefficient having a linear relationship with an independent weight coefficient has been described. For example, a nonlinear correlation with an independent weight coefficient It may be replaced with a coefficient having

  In the above description, the image forming apparatus including the correction unit that corrects the charge amount, the exposure amount, and the like based on the result measured by the spectroscopic analysis apparatus has been described. For example, a process of outputting a message to an operator may be performed.

  In the above description, the image forming apparatus to which the electrophotographic system is applied has been described. However, the image forming apparatus of the present invention may be an apparatus to which, for example, an ink jet system or a thermal film system is applied.

1 is a schematic configuration diagram illustrating a main part of a printer to which an embodiment of a spectral analysis device and an image forming apparatus of the present invention is applied. It is a functional block diagram of a printer. It is an internal block diagram of a spectroscopic analyzer. FIG. 4 is an enlarged view of the vicinity of the lens shown in FIG. 3. It is a figure which shows the emission spectrum of main commercially available LED. It is a figure which shows the example of a spline function. It is a figure which shows spectral characteristic Q ((lambda)) and its approximation function S ((lambda)). It is a figure which shows distribution of the wavelength range of a spline function. It is a figure which shows the spectral reflection curve in the color patch of a mixed color of YMC. It is a figure which shows the correlation between the weighting coefficients of the adjacent spline function in a long wavelength area | region. It is a figure which shows the correlation between the weighting coefficients of the adjacent spline function in a short wavelength area | region. It is a figure which shows the color matching function in an XYZ color system.

Explanation of symbols

10Y, 10M, 10C, 10K Image forming unit 11Y, 11M, 11C, 11K Photoconductor 12Y, 12M, 12C, 12K Charger 13Y, 13M, 13C, 13K Exposure unit 14Y, 14M, 14C, 14K Developer 15Y, 15M, 15C, 15K Primary transfer member 16Y, 16M, 16C, 16K Cleaning device 30 Intermediate transfer belt 31 Intermediate transfer belt cleaner 32 Secondary transfer member 33 Fixing device 34 Tension roller 35 Control unit 351 Color conversion unit 352 Color conversion control unit 353 Image density Control unit 354 Reference signal generation unit 356 CPU
36 Spectroscopic analysis device 361 Light receiving element 362 Lens 363 LED
364 Irradiation unit 365 Analysis unit 37 Memory 200 Paper

Claims (10)

A light source that sequentially emits each of a plurality of lights having different wavelength distributions;
A light receiving unit that measures each intensity of light obtained from the image when each of the plurality of lights emitted from the light source is sequentially irradiated on the image;
Spectral characteristics representing the relationship between the wavelength of light applied to the image and the intensity of light obtained from the image, each of which is greater than the number of light emitted by the light source, each having a wavelength as a variable. Approximate with a sum function consisting of the sum of a plurality of quasi-basic functions each having a weighting factor attached to each of the basic functions having the same shape and wavelength regions shifted from each other, and the sum function and each of the plurality of lights emitted from the light source The spectral characteristics are analyzed by determining each weighting factor so that the calculated light intensity obtained from the wavelength distribution of each matches the intensity of the light measured by the light receiving unit. Among the weighting factors, the predetermined weighting factors equal to or less than the number of light emitted from the light source are independent weighting factors, and the weighting factors other than the independent weighting factors are independent weighting factors. Spectroscopic analysis apparatus characterized by comprising an analysis unit for determining as being dependent weighting factors. The light receiving unit measures the reflection intensity of light irradiated on the image,
The spectral analysis apparatus according to claim 1, wherein the analysis unit analyzes a spectral characteristic representing a spectral reflectance of the image.   The spectral analysis apparatus according to claim 1, wherein the analysis unit uses a spline function as the basic function.   The spectroscopic analysis apparatus according to claim 1, wherein the analysis unit uses a plurality of basic functions whose wavelength regions are evenly shifted.   2. The spectral analysis apparatus according to claim 1, wherein the analysis unit uses a plurality of basic functions for each wavelength region of blue, green, and red.   The spectral analysis apparatus according to claim 1, wherein the analysis unit uses a plurality of basic functions for each wavelength region of 400 to 500 nm, 500 to 600 nm, and 600 to 700 nm.   2. The color measuring apparatus according to claim 1, wherein the light source includes a plurality of light emitting diodes, and sequentially emits the plurality of light emitting diodes. An image forming unit that forms an image using a plurality of color materials having mutually different colors;
An image fixing unit for fixing the image on a recording medium;
A light source that sequentially emits each of a plurality of lights having different wavelength distributions;
A light receiving unit that measures each intensity of light obtained from the image when each of the plurality of lights emitted from the light source is sequentially irradiated onto the image formed by the image forming unit;
Spectral characteristics representing the relationship between the wavelength of light applied to the image and the intensity of light obtained from the image, each of which is greater than the number of light emitted by the light source, each having a wavelength as a variable. Approximate with a sum function consisting of the sum of a plurality of quasi-basic functions each having a weighting factor attached to each of the basic functions having the same shape and wavelength regions shifted from each other, and the sum function and each of the plurality of lights emitted from the light source The spectral characteristics are analyzed by determining each weighting factor so that the calculated light intensity obtained from the wavelength distribution of each matches the intensity of the light measured by the light receiving unit. Among the weighting factors, the predetermined weighting factors equal to or less than the number of light emitted from the light source are independent weighting factors, and the weighting factors other than the independent weighting factors are independent weighting factors. An analysis unit for determining as being dependent weighting factors,
An image forming apparatus comprising: a correction control unit that corrects the color of the image by controlling the image forming unit based on spectral characteristics of the image analyzed by the analyzing unit.   The image forming apparatus according to claim 7, wherein the light receiving unit measures light intensity in an image formed by the image forming unit and fixed on the recording medium.   8. The image according to claim 7, wherein the image forming unit forms an image using at least two color materials of yellow, cyan, magenta, and black as the plurality of color materials. Forming equipment.

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