JP2015036659A - Spectroscopic characteristic acquisition device, image evaluation device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spectroscopic characteristic acquisition device that can acquire spectral characteristics of an object under the optimal measurement conditions according to the purpose, an image evaluation device using the same, and an image forming apparatus.SOLUTION: A spectroscopic characteristic acquisition device 100 includes light irradiation means 101 for irradiating an object 10 with light, diffraction means 105 for diffracting reflection light from the object to form a diffraction image, light receiving means 106 for receiving the diffraction image on a light receiving surface and outputting a signal according to the intensity of the received light, first moving means 107 for moving the diffraction means in the vertical direction with respect to the light receiving surface, and calculation means 121 for performing estimation calculation of the spectroscopic characteristics of the object by using a conversion matrix in the signal.

Description

  The present invention relates to a spectral characteristic acquisition device, an image evaluation device, and an image forming device.

  In production printing, for example, by using an electrophotographic or ink jet printer, it has become possible to provide a printed matter with a small lot and a short delivery time. A printer used for such production printing is required to output image quality equivalent to that of a conventional offset printing press.

  In order to improve the color stability and color reproducibility of the image, some printers measure the color of the printed image and optimize the image forming conditions based on the color measurement result. In order to perform color measurement of a printed image in a printer, for example, a full width array spectrophotometer for full width scanning color analysis of a printed printing medium sheet has been proposed (for example, see Patent Document 1).

  Here, color measurement in a printer may require high-speed processing, for example, to ensure productivity, or may require high-resolution measurement to optimize image forming conditions. It is desirable that the measurement conditions can be changed according to the purpose. However, in the full width array spectrophotometer according to Patent Document 1 described above, it is necessary to change the configuration of the lens, the image sensor, and the like in order to change the measurement conditions, and it is difficult to change the measurement conditions as appropriate.

  The present invention has been made in view of the above, and an object of the present invention is to provide a spectral characteristic acquisition device that can acquire the spectral characteristics of an object under optimal measurement conditions according to the purpose.

  According to the spectral characteristic acquisition device of one aspect of the present invention, a light irradiation unit that irradiates light on a target, a diffraction unit that diffracts reflected light from the target to form a diffraction image, and the diffraction image A light receiving unit that receives light on the light receiving surface and outputs a signal corresponding to the intensity of the received light, a first moving unit that moves the diffraction unit in a direction perpendicular to the light receiving surface, and a conversion matrix from the signal Calculating means for estimating and calculating the spectral characteristics of the object.

  According to the embodiment of the present invention, it is possible to provide a spectral characteristic acquisition device that can acquire the spectral characteristics of an object under an optimal measurement condition according to the purpose.

It is a figure which illustrates schematic structure of the spectral characteristic acquisition apparatus which concerns on 1st Embodiment. It is a figure explaining the relationship between a diffraction element and a line sensor. It is the photograph (1) which illustrates the incident light to the line sensor seen from the entrance plane side. It is a figure (1) explaining the relationship between a line sensor and a diffraction image. It is the photograph (2) which illustrates the incident light to the line sensor seen from the incident surface side. It is a figure which illustrates the spectral distribution of the toner image used for simulation. It is a figure which illustrates a simulation result. It is a figure (2) explaining the relationship between a line sensor and a diffraction image. It is a figure which illustrates a mode that a line sensor moves according to the position of a diffraction image. It is a figure which illustrates a light shielding member. It is a figure which illustrates the flowchart of the spectral characteristic acquisition process in 1st Embodiment. It is a figure which illustrates a stair-like diffraction element. It is a figure which illustrates schematic structure of the image evaluation apparatus which concerns on 2nd Embodiment. It is a figure which illustrates schematic structure of the image forming apparatus which concerns on 3rd Embodiment.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted. In the present application, the spectral characteristic refers to the amount of diffuse reflected light expressed as a function of wavelength, and the spectral characteristic includes spectral reflectance.

[First embodiment]
FIG. 1 is a schematic diagram illustrating a configuration example of a spectral characteristic acquisition apparatus 100 according to the first embodiment. In the following description, the X direction indicates the pixel arrangement direction of the line sensor 106, the Y direction indicates a direction orthogonal to the X direction on the light receiving surface of the line sensor 106, and the Z direction indicates a direction perpendicular to the light receiving surface of the line sensor 106.

  As shown in FIG. 1, the spectral characteristic acquisition apparatus 100 includes a line illumination light source 101, a first imaging optical system 102, an aperture array 103, a second imaging optical system 104, a diffraction element 105, a line sensor 106, and a first movement. Means 107, second moving means 108, and control means 120 are provided.

  Below, the spectral characteristic acquisition apparatus 100 demonstrates the example which measures the spectral reflectance of the target object 10. FIG. The object 10 is, for example, a sheet-like printed material, and an image is formed on the surface of the object 10.

  In addition, the broken line shown in FIG. 1 has shown typically the typical optical path after the light irradiated to the target object 10 diffusely reflected. In the following description, the specularly reflected light is the same angle as the incident angle of the irradiation light irradiated from the line illumination light source 101 to the object 10 and is reflected light that is reflected to the opposite side of the incident direction (that is, the incident angle). Is the reflected light having a reflection angle of π−θ). Diffuse reflected light refers to reflected light other than regular reflected light. The spectral reflectance is a ratio of the amount of diffuse reflected light from the measurement object to the amount of diffuse reflected light from a reference plate (white plate or the like) as a function of wavelength.

  The line illumination light source 101 is an example of a light irradiating unit, and irradiates light to a region that extends in a line shape in the width direction (X direction) of the object 10. The line illumination light source 101 is, for example, a white LED (Light Emitting Diode) array having intensity over almost the entire visible light range. The line illumination light source 101 is not limited to a white LED, but may be a fluorescent lamp such as a cold cathode tube, a lamp light source, or the like.

  On the optical path from the line illumination light source 101 to the target object 10, the light emitted from the line illumination light source 101 is collimated (substantially as parallel light) on the target object 10 or condensed and irradiated in a line shape. You may arrange | position the collimating lens which has.

  The first imaging optical system 102 images the diffuse reflected light in the Z direction of the light irradiated on the object 10 on the openings of the aperture array 103. Note that the first imaging optical system 102 does not necessarily have to accurately image the diffuse reflected light on the openings of the aperture array 103, and may be in a defocused state or an infinite system.

  As the first imaging optical system 102, for example, a condensing lens array in which a plurality of lenses are arranged in the X direction can be used. The first imaging optical system 102 may be an imaging optical system including a gradient index lens array such as a SELFOC (registered trademark) lens array, a microlens array, or a mirror.

  The aperture array 103 is an example of a region dividing unit, and has a plurality of apertures formed in a row, for example, and a portion other than the apertures of the aperture array 103 is a light shielding unit that blocks light. The aperture array 103 divides the reflected light from the object 10 into regions by apertures.

  The opening array 103 is, for example, a pinhole array or a slit array, and may be an opening formed in a metal or black resin material. Alternatively, a light shielding part may be formed by patterning a metal film, a black resin, or the like on glass or transparent resin, and a part other than the light shielding part may be used as an opening. The opening has a circular shape, a rectangular shape, an elliptical shape, or any other shape.

  The aperture array 103 divides the diffusely reflected light from the object 10 into a plurality of apertures, thereby shielding unnecessary portions of light. Thereby, only the light of the focal plane which passed each opening part is detected, and mixing of the reflected light from an adjacent area | region is suppressed.

  The second imaging optical system 104 is an example of imaging means, and is composed of, for example, a plurality of lenses. The reflected light that has passed through the aperture array 103 is coupled to the light receiving surface of the line sensor 106 via the diffraction element 105. Image. The second imaging optical system 104 is, for example, a lens used for a general scanner optical system or a line sensor lens used industrially.

  The diffractive element 105 is an example of diffracting means, and forms a diffraction image by diffracting the reflected light of the light irradiated on the object. More specifically, the diffractive element 105 divides the diffusely reflected light collected by the second imaging optical system 104 after being divided into regions by each aperture of the aperture array 103 and propagates it in different directions depending on the wavelength. A diffraction image corresponding to each opening is formed. The diffraction element 105 is, for example, a prism, a transmission diffraction grating, or a combination thereof.

  The line sensor 106 is an example of a light receiving unit, and is a multiband spectral sensor array in which a plurality of spectral sensors composed of a plurality of pixels are provided in parallel on the light receiving surface. The line sensor 106 acquires a light amount for each predetermined wavelength band from a diffraction image incident on the light receiving surface via the diffraction element 105, and converts the acquired light amount into an electrical signal. The electrical signal converted by the line sensor 106 is sent to the control means 120.

  The line sensor 106 is, for example, a MOS (Metal Oxide Semiconductor Device), a CMOS (Complimentary Metal Oxide Semiconductor Device), a CCD (Charge Coupled Device), a CIS (Contact Image Sensor), a PDA (Photo Diode Array), or the like.

  The first moving means 107 can change the distance between the diffractive element 105 and the line sensor 106 by moving the diffractive element 105 in the direction perpendicular to the light receiving surface of the line sensor 106 (Z direction). When the distance between the diffraction element 105 and the line sensor 106 changes, the size of the diffraction image on the light receiving surface of the line sensor 106 changes.

  The second moving means 108 moves the line sensor 106 in the diffraction direction of the diffraction image formed by the diffraction element 105 in a plane parallel to the light receiving surface of the line sensor 106, and the positional relationship between the spectroscopic sensor and the diffraction image is obtained. Optimize.

  The control unit 120 includes a calculation unit 121 and a storage unit 122, controls the first moving unit 107 and the second moving unit 108, and determines the spectral characteristics of the object 10 based on the electric signal sent from the line sensor 106. Ask.

  The control unit 120 includes, for example, a CPU, a ROM, a main memory, and the like, and various functions of the control unit 120 are realized by reading a program recorded in the ROM or the like into the main memory and executing it by the CPU. However, part or all of the control means 120 may be realized only by hardware. Further, the control means 120 may be physically configured by a plurality of devices.

  The calculating means 121 estimates and calculates the spectral characteristics of the object 10 from the electrical signal sent from the line sensor 106 using a conversion matrix. A method of estimating spectral characteristics by the calculation unit 121 will be described later.

  The storage unit 122 is, for example, a ROM, a RAM, or the like, and stores a conversion matrix used for spectral characteristic estimation calculation in the calculation unit 121.

  In the optical system illustrated in FIG. 1, for example, the illumination light emitted from the line illumination light source 101 is incident on the object 10 at an angle of approximately 45 degrees, and the line sensor 106 diffuses from the object 10 in the Z direction. A so-called 45/0 optical system that receives reflected light can be obtained. In addition, a so-called 0/45 optical system in which illumination light emitted from the line illumination light source 101 is perpendicularly incident on the object 10 and the line sensor 106 receives light diffusely reflected from the object 10 in a 45 degree direction. It is good.

  The spectral characteristic acquisition apparatus 100 shown in FIG. 1 configured as described above can be operated at high speed by the line sensor 106 and can acquire the spectral characteristics of the object 10 at a high speed at a time. It is applicable to the field where high speed measurement is required.

  FIG. 2 is a diagram illustrating the relationship between the diffraction element 105 and the line sensor 106.

  As shown in FIG. 2, the line sensor 106 has a plurality of pixels arranged in a line in the X direction on the light receiving surface. The line sensor 106 is a spectroscopic sensor array in which a plurality of first spectroscopic sensors 106 a, second spectroscopic sensors 106 b, third spectroscopic sensors 106 c, and the like, each of which includes a group of N pixels arranged in a row, are arranged. The first spectroscopic sensor 106a, the second spectroscopic sensor 106b, the third spectroscopic sensor 106c, and the like have N pixels that receive light having different spectral characteristics. Note that the N pixels included in the line sensor 106 may be arranged in two or more columns.

  The light from one aperture of the aperture array 103 is incident on N pixels of one spectroscopic sensor of the line sensor 106, and the N of the spectroscopic sensors of the aperture array 103 and the line sensor 106 are aligned. The pixel is in an imaging relationship.

The diffractive element 105 is preferably formed by, for example, a sawtooth shape formed on a transparent substrate at a predetermined interval, since it can enhance the + 1st order diffracted light, but may have other shapes such as a stepped shape. When the interval of the sawtooth shape of the diffractive element 105 is p, light having a wavelength λ incident on the diffractive element 105 at an angle θ _in is diffracted to an angle θ _m expressed by the equation (1). In Expression (1), m is the diffraction order by the diffraction element 105, and can take a positive or negative integer value.

Due to the wavelength dependence of the diffraction angle θ _m expressed by the equation (1), it is possible to make light having different spectral characteristics incident on the N pixels of each spectral sensor of the line sensor 106.

  Here, when the diffraction element 105 diffracts light in the arrangement direction (X direction) of the plurality of pixels of the line sensor 106, the diffracted light has transmitted through the 0th order light, the second order diffraction image, and the adjacent opening. In some cases, diffraction images and the like overlap on the line sensor 106. In such a case, the crosstalk shown in FIG. 3 occurs, making it difficult to obtain accurate spectral characteristics.

  Therefore, as shown in FIGS. 4 and 5, for example, the diffraction element 105 is rotated in the XY plane, or the tooth angle of the diffraction element 105 is appropriately set, and the diffraction direction of the diffracted light and the arrangement of the pixels of the line sensor 106 are set. The direction is configured to have a predetermined angle α.

  With such a configuration, as shown in FIGS. 4 and 5, only the + 1st order diffraction image B of each aperture of the aperture array 103 is formed on the line sensor 106. Unnecessary non-diffracted image A (0th order diffracted image), −1st order diffracted image C, + 2nd order diffracted image D, −2nd order diffracted image E and the like are formed at positions away from the pixels of the line sensor 106. Therefore, the spectral characteristic acquisition apparatus 100 can obtain the spectral characteristic of the object 10 from the + 1st-order diffraction image B without the crosstalk of the diffraction image. In the following description, the + 1st order diffraction image B may be simply referred to as a diffraction image.

  As described above, the line sensor 106 according to the first embodiment further includes a plurality of first spectral sensors 106a, second spectral sensors 106b, third spectral sensors 106c, and the like, each of which includes a group of N pixels arranged. Multiband spectroscopic sensor.

  In multiband spectroscopy, the resolution of the spectral characteristics measured increases as the number N of pixels of each spectral sensor increases. However, the number of pixels provided in the line sensor 106 has an upper limit, and the number of spectral sensors that can be arrayed decreases as the number of pixels of the spectral sensor increases. Therefore, it is preferable that the spectral characteristic acquisition apparatus 100 has processing (spectral estimation processing) in which the spectral distribution is estimated by estimation means such as Wiener estimation while minimizing the number of pixels of the spectral sensor. Many methods have been proposed for the spectral estimation processing, and are described in detail, for example, in “Non-patent literature“ Analysis and evaluation of digital color images: University of Tokyo Press: p154-157 ””.

  An example of a technique for estimating the spectral distribution from the output vi of one spectroscopic sensor is shown below. From the row vector v storing the signal outputs vi (i = 1 to N) from the N pixels constituting one spectroscopic sensor and the conversion matrix G, the spectral reflectance (for example, 400 to 700 nm) of each wavelength band. (31 of 10 nm pitch) is stored as a row vector r expressed by the equation (2).

As shown in the equations (3) to (5), the conversion matrix G includes a matrix R that stores the spectral distributions of a large number (n) of samples whose spectral distributions are known in advance, and the spectral samples obtained by the spectral characteristic acquisition apparatus 100. It is obtained by minimizing the square norm ‖ · ‖ ² of the error using the least square method from the matrix V storing v when measured.

The regression transformation matrix G of the regression equation from V to R, where V is the explanatory variable and R is the objective variable, is expressed by the equation (6) using the Moore-Penrose generalized inverse matrix that gives the least-square norm solution of the matrix V. Is calculated as follows.

The superscript T represents the transpose of the matrix, and the superscript -1 represents the inverse matrix. By storing G obtained by Expression (6), the spectral distribution r of an arbitrary object 10 is estimated by taking the product of the transformation matrix G and the signal output v during actual measurement. As described above, the calculation unit 121 of the spectral characteristic acquisition apparatus 100 estimates the spectral characteristic of the object 10 using the conversion matrix G based on the electrical signal output from each pixel of the spectral sensor included in the line sensor 106. Calculate by calculation.

  Here, the spectral distribution of the toner image output by the electrophotographic image forming apparatus is estimated by the spectral characteristic acquisition apparatus 100 according to the first embodiment, and a color difference that is an estimation error is calculated from the estimated spectral distribution. A simulation was performed. In the simulation, the color difference (ΔE) between the side color result when the value of the number N of pixels of the spectroscopic sensor is changed and the side color result obtained from a more detailed spectroscopic device is obtained.

  FIG. 6 is a diagram illustrating the spectral distribution of the toner image used in the simulation, and FIG. 7 is a diagram illustrating the simulation result. From the results shown in FIG. 7, it can be seen that the color difference (ΔE) decreases as the number N of pixels of the spectroscopic sensor increases, and the spectral characteristics are required with high accuracy.

  Next, the relationship between the diffraction image and the pixel of the spectral sensor in the line sensor 106 will be described with reference to FIG.

FIG. 8 shows a state in which light incident on one opening is incident on the diffraction element 105 and a + 1st order diffraction image B is formed on the light receiving surface of the line sensor 106. Diffraction angle theta _i +1 order diffraction image B by the diffraction element 105 is determined from the above equation (1), +1 imaging position of order diffraction image of the wavelength lambda _i by the diffraction element 105 relative to 0-order diffraction images A The distance s between the diffraction element 105 and the line sensor 106 is used to obtain s × tan θ _i . Here, if the wavelength region to be measured is λ ₀ ≦ λ ≦ λ _n , the width j of the + 1st order diffraction image B can be expressed as j = s × (tan θ _n −tan θ ₀ ). Therefore, the width j of the + 1st order diffraction image B is proportional to the distance s between the diffraction element 105 and the line sensor 106.

The shape of the + 1st order diffraction image B is defined by the grating pitch p of the diffraction grating, the distance s to the imaging surface, the imaging characteristics of the imaging optical system, and the shape of the aperture. The first-order diffraction image B has a shape in which the effect of blurring by the imaging optical system and the diffraction grating is superimposed, and is defined as a region that attenuates to 1 / e ^{2 with} respect to the peak intensity of each wavelength, for example.

  In the spectral characteristic acquisition apparatus 100 according to the present embodiment, since light having different wavelengths is split and incident in the pixel arrangement direction of the line sensor 106, the wavelength of each spectral sensor is determined by the shape of the + 1st order diffraction image B on the line sensor. Resolution is determined. The degree to which the wavelength resolution is set is determined by the purpose of use of the spectral characteristic acquisition device 100, and the width of the aperture and the imaging performance of the imaging optical system are designed according to the required wavelength resolution.

  When each pixel of the line sensor 106 has a width w and a height h, and the spectral sensor 106n has N pixels, for example, the diffraction element 105 is arranged with respect to the arrangement direction (X direction) of the pixels of the line sensor 106. , And an inclination angle α obtained by the following equation (7).

In such a configuration, for example, when the width w of the pixel of the line sensor 106 is 10 μm, the period p of the diffraction element 105 is 10 μm, and the distance s between the diffraction element 105 and the line sensor 106 is 2 mm, the spectral sensor A + 1st order diffraction image B is formed on 6 pixels of 106n.

  When the diffractive element 105 is moved in the Z direction by the first moving means 107, the width j of the + 1st order diffraction image B changes. For example, when the distance s is 1 mm, the + 1st order diffraction image B is added to 3 pixels of the spectroscopic sensor 106n. Forms an image. For example, when the distance s is 3 mm, the + 1st order diffraction image B is formed on nine pixels of the spectroscopic sensor 106n.

  Here, when the diffraction element 105 is moved in the Z direction by the first moving means 107, the position of the diffraction image formed on the light receiving surface of the line sensor 106 changes. For example, as shown in FIG. 9, when the distance s between the diffraction element 105 and the line sensor 106 changes from 3 mm (FIG. 9A) to 2 mm (FIG. 9B), the + 1st order diffraction image B and + 2nd order diffraction are obtained. The image C is displaced so as to approach the non-diffracted image A (0th-order diffraction image) along the diffraction direction Dd.

  As described above, when the first moving unit 107 brings the diffraction element 105 close to the line sensor 106, the + 1st order diffraction image B may deviate from the pixels of the line sensor 106. Therefore, in the spectral characteristic acquisition apparatus 100 according to the first embodiment, as illustrated in FIG. 9B, the second moving unit 108 allows the + 1st order diffraction image B to be within the pixels of the line sensor 106. The line sensor 106 is moved along the diffraction direction Dd. The second moving means 108 moves the line sensor 106 according to the distance s between the diffraction element 105 and the line sensor 106, so that the + 1st order diffraction image B is within the pixel of the line sensor 106, and the line sensor 106 is always + 1st order diffraction image B can be received.

  When the second moving unit 108 moves the line sensor 106, for example, as shown in FIG. 9B, the + 2nd order diffraction image C may be incident on the pixels of the line sensor 106. In such a case, in the spectral characteristic estimation calculation, the electrical signal output from the pixel on which the + 2nd-order diffraction image C is incident is discarded without being used. Spectral characteristics can be obtained without the need. Alternatively, as shown in FIG. 10, a light shielding member 109 that blocks the + second order diffraction image C may be provided between the diffraction element 105 and the line sensor 106. The light shielding member 109 is provided so as to shield the diffracted images other than the + 1st order diffracted image B used for spectral characteristic estimation calculation among the diffracted images incident on the line sensor 106.

  Here, when the distance s between the diffractive element 105 and the line sensor 106 is increased, the number of pixels on which the + 1st order diffraction image B is incident is increased in each spectroscopic sensor of the line sensor 106, the resolution of the wavelength to be measured is increased, and the spectrum is increased. The characteristic estimation accuracy is improved. However, when the diffraction image is dispersed over a wide range and acquired by many pixels, the amount of light that can be acquired by each pixel of the line sensor 106 decreases. Therefore, a sufficient exposure time is required to ensure measurement accuracy, and a corresponding time is required until the spectral characteristics are acquired.

  Further, when the distance s between the diffraction element 105 and the line sensor 106 is reduced, the number N of pixels on which the + 1st order diffraction image B is incident on each spectral sensor of the line sensor 106 is reduced. In this case, although the estimation accuracy of the spectral characteristics decreases, the amount of light incident on one pixel of the line sensor 106 increases, so that the spectral characteristics can be obtained at high speed.

  Here, in the spectral characteristic acquisition apparatus 100 according to the first embodiment, the spectral characteristic of the object 10 is estimated in three modes, that is, the high accuracy mode, the high speed mode, and the normal mode.

  In the high accuracy mode, for example, the distance s between the diffractive element 105 and the line sensor 106 is set to 3 mm, and a diffracted image is incident on nine pixels in each spectroscopic sensor of the line sensor 106, so that the spectral characteristics can be estimated with high accuracy. In the high-speed mode, for example, the distance s between the diffractive element 105 and the line sensor 106 is set to 1 mm, and a diffraction image is incident on three pixels in each spectroscopic sensor of the line sensor 106, so that spectral characteristics can be estimated at high speed. In the normal mode, for example, the distance s between the diffractive element 105 and the line sensor 106 is set to 2 mm, and a diffraction image is incident on 6 pixels in each spectral sensor of the line sensor 106. Spectral characteristics can be estimated at higher speed. Note that the setting of each mode is not limited to the above example, and can be appropriately set according to the purpose.

  In each of the above-described modes, the number of pixels on which the diffraction image is incident is different in each spectroscopic sensor of the line sensor 106, so that a corresponding conversion matrix is obtained in advance and stored in the storage unit 122. When obtaining the spectral characteristics of the object 10, the calculation means 121 acquires a conversion matrix corresponding to the mode from the storage means 122, and performs spectral characteristic estimation calculation using the acquired conversion matrix.

  FIG. 11 illustrates a flowchart of spectral characteristic acquisition processing in the first embodiment.

  In the case where the spectral characteristic acquisition apparatus 100 acquires the spectral characteristic of the object 10, first, in step S101, the mode is selected by the user. In step S102, the first moving unit 107 moves the diffraction element 105 in the Z direction based on the selected mode, and sets the distance s between the diffraction element 105 and the line sensor 106 to a predetermined distance. Subsequently, in step S103, the second moving unit 108 moves the line sensor 106 along the diffraction direction Dd of the diffraction image as necessary so that the diffraction image is within the pixel of the spectroscopic sensor.

  In step S104, the transformation matrix corresponding to the mode selected by the computing means 121 is acquired from the storage means 122. Next, in step S105, the calculation means 121 performs an estimation calculation of the spectral characteristics of the object 10 using the acquired conversion matrix, and then ends the process.

  As described above, according to the spectral characteristic acquisition apparatus 100 according to the first embodiment, the first moving unit 107 moves the diffraction element 105 and changes the distance s between the diffraction element 105 and the line sensor 106. It is possible. Accordingly, the distance s between the diffractive element 105 and the line sensor 106 can be changed according to the required accuracy, time, etc., and the spectral characteristics of the object 10 can be acquired under optimum measurement conditions according to the purpose.

  The diffraction element 105 may be a stepped diffraction element 110 as shown in FIG. The stepped diffraction element 110 is a kind of blazed diffraction element, and all blazed surfaces are perpendicular to the optical axis, and a predetermined step is formed at a predetermined pitch.

  The stair-like diffraction element 110 emits a first-order diffraction image having a predetermined wavelength parallel to the optical axis by appropriately providing a grating pitch and a step. Therefore, even if the distance s between the stepped diffraction element 110 and the line sensor 106 is changed, the first-order diffraction image is not displaced, so the line sensor 106 is moved according to the distance s with the stepped diffraction element 110. There is no need to let them. Therefore, it is not necessary to provide the second moving means 108, and the apparatus configuration can be simplified.

  Further, the stepped diffraction element 110 has high diffraction efficiency of the first-order diffracted light having a predetermined wavelength and its peripheral wavelength, and has low diffraction efficiency of other orders. Accordingly, the stepped diffraction element 110 can increase the amount of light incident on the line sensor 106 and can obtain a sufficient amount of light with a shorter exposure time, and is therefore suitable for speeding up the estimation of spectral characteristics. In addition, since the amount of diffracted light of other orders is reduced, stray light components that deteriorate the measurement system are reduced, and the spectral characteristics can be estimated with higher accuracy.

[Second Embodiment]
In the second embodiment, an image evaluation apparatus 200 including the spectral characteristic acquisition apparatus 100 will be described. Note that in the second embodiment, the same components as those already described in the embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 13 is a diagram illustrating a schematic configuration of an image evaluation apparatus 200 according to the second embodiment. As illustrated in FIG. 13, the image evaluation apparatus 200 includes a spectral characteristic acquisition apparatus 100 according to the first embodiment, an image evaluation unit 201, and a conveyance unit (not illustrated) that conveys the object 10.

  The spectral characteristic acquisition apparatus 100 includes a line illumination light source 101, a first imaging optical system 102, an aperture array 103, a second imaging optical system 104, a diffraction element 105, a line sensor 106, and a control means 120.

  The image evaluation apparatus 200 evaluates an image formed on the object 10 by, for example, an electrophotographic image forming apparatus over the entire width. 13 illustrates an example in which the image evaluation apparatus 200 includes one spectral characteristic acquisition apparatus 100. For example, a plurality of spectral characteristic acquisition apparatuses 100 may be arranged in parallel in the width direction of the object 10. Good.

  The image evaluation unit 201 includes, for example, a CPU, a ROM, a main memory, and the like, and various functions of the image evaluation unit 201 are realized by a program recorded in the ROM or the like being read into the main memory and executed by the CPU. The However, part or all of the image evaluation unit 201 may be realized only by hardware. Further, the image evaluation unit 201 may be physically configured by a plurality of devices.

  The conveying means conveys the object 10 in the direction of the arrow in FIG. The image evaluation apparatus 200 is configured to move the object 10, but the image evaluation apparatus 200 may be configured to move relative to the object 10. For example, a conveyance roller or a conveyance belt can be used as the conveyance unit. The image evaluation unit 201 can calculate spectral image data over the entire image forming unit of the object 10 based on speed information from an encoder sensor that is known or attached to the conveyance unit.

  The image evaluation apparatus 200 preferably compares the colorimetric result obtained by the line sensor 106 with the master image in the image evaluation unit 201, extracts the difference from the master image, and displays it. As a result, the operator can easily perform comparison with the master image. Further, the master image may be configured so that a digital master image can be input from the outside, and the measurement result of an arbitrary object 10 measured by the image evaluation apparatus 200 may be set as the master image.

  As described above, according to the second embodiment, by configuring the image evaluation apparatus 200 using the spectral characteristic acquisition apparatus 100, the color of an image or the like formed on the object 10 to be conveyed can be changed. An image evaluation apparatus 200 capable of performing evaluation at high speed can be realized.

[Third embodiment]
In the third embodiment, an image forming apparatus 300 including the image evaluation apparatus 200 according to the second embodiment will be described. Note that in the third embodiment, identical symbols are assigned to components that are the same as in the previously described embodiments and descriptions thereof are omitted.

  FIG. 14 is a diagram illustrating an image forming apparatus 300 according to the third embodiment. As shown in FIG. 14, the image forming apparatus 300 includes an image evaluation apparatus 200 according to the second embodiment, a paper feed cassette 301a, a paper feed cassette 301b, a paper feed roller 302, a controller 303, a scanning optical system 304, a photosensitive device. A body 305, an intermediate transfer body 306, a fixing roller 307, and a paper discharge roller 308. The object 10 is a recording medium such as paper.

  In the image forming apparatus 300, the object 10 conveyed by the guide (not shown) and the paper feed roller 302 from the paper feed cassettes 301 a and 301 b is exposed to the photoconductor 305 by the scanning optical system 304, and a color material is applied and developed. The The developed image is transferred onto the intermediate transfer member 306 and then secondarily transferred from the intermediate transfer member 306 onto the object 10. The image transferred onto the object 10 is fixed by the fixing roller 307, and the object 10 on which the image is formed is discharged by the paper discharge roller 308. The image evaluation apparatus 200 is installed at the subsequent stage of the fixing roller 307.

  According to the image forming apparatus 300 according to the third embodiment, by providing the image evaluation apparatus 200 according to the second embodiment, the color information within the surface of the recording medium is synchronized with the conveyance of the recording medium. Can be obtained. When the image forming apparatus 300 is, for example, an image product based on an electrophotographic method, based on the obtained image color evaluation result, the adjustment unit performs one-scan control or printing within the light source output of the writing scanning optical system. By adjusting the image forming conditions such as the previous gamma correction, the color unevenness of the image formed on the recording medium can be reduced.

  Further, when the image forming apparatus 300 is an image product using, for example, an ink jet method, color unevenness of an image formed on a recording medium can be reduced by directly controlling the ink discharge amount according to the head position.

  In addition, since the image evaluation apparatus 200 according to the second embodiment can acquire spectral characteristics having different spatial resolutions two-dimensionally over the entire image, if there is a color chart, it is possible to evaluate the spectral characteristics suitable for the color chart. It becomes. Further, when there is no color chart, it is possible to evaluate spectral characteristics suitable for an arbitrary position of an arbitrary image of the user. Then, by adjusting the image forming conditions based on the respective evaluations, the image forming apparatus 300 with higher color stability and color reproducibility can be realized.

  The spectral characteristic acquisition apparatus 100 is not limited to the above-described embodiment, and can be mounted on various apparatuses other than the image evaluation apparatus and the image forming apparatus. For example, the spectral characteristic acquisition apparatus 100 may be provided in an inspection apparatus that inspects authenticity such as banknotes and credit cards.

  The spectral characteristic acquisition device, the image evaluation device, and the image forming device according to the embodiments have been described above, but the present invention is not limited to the above embodiments, and various modifications and improvements can be made within the scope of the present invention. It is.

10 Object 101 Line illumination light source (light irradiation means)
105 Diffraction element (Diffraction means)
106 Line sensor (light receiving means)
107 first moving means 108 second moving means 109 light shielding means 110 stepped diffraction element 121 computing means 100 spectral characteristic acquisition apparatus 200 image evaluation apparatus 201 image evaluation means 300 image forming apparatus

JP 2005-315883 A

Claims (8)

A light irradiation means for irradiating the object with light;
Diffraction means for diffracting reflected light from the object to form a diffraction image;
A light receiving means for receiving the diffraction image on a light receiving surface and outputting a signal corresponding to the intensity of the received light;
First moving means for moving the diffraction means in a direction perpendicular to the light receiving surface;
An apparatus for obtaining spectral characteristics, comprising: an arithmetic unit that estimates and calculates spectral characteristics of the object using a conversion matrix from the signal. 2. The spectral characteristic acquisition apparatus according to claim 1, further comprising a second moving unit configured to move the light receiving unit in a diffraction direction of the diffraction image within a plane parallel to the light receiving surface of the light receiving unit. 3. The calculation means according to claim 1, wherein the calculation means estimates and calculates the spectral characteristics of the object using different transformation matrices in accordance with a position of the diffraction means in a direction perpendicular to the light receiving surface. The spectral characteristic acquisition apparatus described. 4. The spectral characteristic acquisition apparatus according to claim 1, wherein the light receiving unit is a spectral sensor array in which a plurality of spectral sensors each including a plurality of pixels are arranged on the light receiving surface. 5. . 5. The light-shielding unit that shields light other than the diffraction image used for the calculation calculation of the spectral characteristic by the calculation unit among the diffraction images of the reflected light incident on the light-receiving unit. The spectral characteristic acquisition apparatus as described in any one of Claims.   6. The spectral characteristic acquisition apparatus according to claim 1, wherein the diffraction unit is a step-like diffraction element. The spectral characteristic acquisition device according to any one of claims 1 to 6,
An image evaluation apparatus comprising: an image evaluation unit that evaluates an image of the object based on the spectral characteristic obtained by the spectral characteristic acquisition apparatus.   An image forming apparatus comprising the image evaluation apparatus according to claim 7.