JP2014153078A - Spectral characteristic acquisition device, image evaluation device, and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spectral characteristic acquisition device which is capable of acquiring average spectral characteristics within an array pitch in a plurality of measurement positions of an object.SOLUTION: The spectral characteristic acquisition device includes: first imaging means for imaging light beams in a plurality of positions from an object; a first opening array including a plurality of openings through which the light beams in the plurality of positions which are imaged on the first imaging means pass; an imaging means array in which a plurality of second imaging means on which the light beams passing through the first opening array are imaged are arrayed; a diffraction element 43 which diffracts the light beams passing through the plurality of second imaging means in the imaging means array; a second opening array including a plurality of openings through which the light beams diffracted by the diffraction element pass; and an imaging element which receives the light beams passing through the second opening array. An optical distance between the first opening array and the imaging means array is shorter than an object-side focal distance of the imaging means array, and an optical distance between the imaging means array and the second opening array is equal to an image-side focal distance of the imaging means array.

Description

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

  In recent years, full-color image forming apparatuses (printers, copiers, etc.) such as electrophotographic systems and inkjet systems have demanded high image quality for color images printed on image-bearing media such as paper, and color reproduction. The improvement of safety is one of the important technical issues. In order to cope with such a technical problem, it is desirable to mount a spectral sensor for measuring a color after image formation and adjust the image forming apparatus based on information of the spectral sensor.

  Furthermore, it is more desirable to install a spectroscopic sensor array in which a large number of spectroscopic sensors are arrayed in a direction orthogonal to the feed direction of the image carrier, because color information at an arbitrary position can be acquired from an arbitrary image.

  An example of such a spectroscopic sensor array is “ImSpector” released by JFE Techno-Research (Non-Patent Document 1), which is spatially sampled by a slit, collimated by a first lens, The light is split by the prism-diffraction grating-prism, and further imaged on the surface of the two-dimensional image sensor by the second lens behind. By splitting the light in the short direction of the slit, light at different positions in the longitudinal direction of the slit is split in the short direction of the slit and imaged. Thereby, the spectral characteristics at a plurality of positions are measured.

  However, such a spectroscopic sensor array requires a certain distance between the slit and the image sensor, and spectrally converts wavelength information into position information. Therefore, the slit is subject to vibration, thermal expansion, change with time, etc. If the relative positional relationship between the lens and the image sensor deviates even a little, this becomes a factor that deteriorates the measurement accuracy. Therefore, for example, it is not suitable for an application that is mounted on an image forming apparatus and performs inline measurement.

  As another example of a spectroscopic sensor array, a light receiving unit receives reflected light from an object via a first lens array, a diaphragm having a plurality of apertures, a second lens array, a diffraction grating, and a third lens array. Thus, there is a spectroscopic sensor array that measures the wavelength spectrum of reflected light. The spectroscopic sensor array having such a configuration can also be used for applications such as in-line measurement (for example, see Patent Document 1).

  However, in the example of Patent Document 1, in a spectroscopic sensor that outputs spectroscopic information corresponding to each point of the spectroscopic sensor array, light is sampled using an aperture that is smaller than the array pitch of the spectroscopic sensors. It will output a very narrow range of colors. However, in most cases, what is desired to be obtained is an average color (average spectral characteristic) within the pitch width of the measurement positions with respect to a plurality of measurement positions. For example, a halftone dot is used to express a halftone in a printed matter or the like, so that if the measurement range on the object is small, the output signal varies due to the influence of the halftone dot.

  On the other hand, in the direction orthogonal to the arrangement direction of the spectroscopic sensor array, since the image sensor is exposed for a finite time, the image carrier moves during the exposure time, so a moving average depending on the exposure time is taken. Is the same as Therefore, an optical system that measures a sufficiently narrow range statically is suitable for this direction.

  This invention is made in view of said point, and makes it a subject to provide the spectral characteristic acquisition apparatus which can acquire the average spectral characteristic within an arrangement pitch about several measurement position of a target object. .

  The spectral characteristic acquisition apparatus includes: a first imaging unit that images light beams at a plurality of positions from an object; and a plurality of openings through which the light beams at a plurality of positions imaged on the first imaging unit pass. Including a first aperture row, an imaging means row in which a plurality of second imaging means for imaging a light beam that has passed through the first aperture row, and a plurality of second connections in the imaging means row. A diffractive element that splits the light beam that has passed through the image means, a second aperture row that includes a plurality of apertures that allow the light beam split by the diffractive element to pass through, and a light beam that has passed through the second aperture row are received. An imaging element, wherein an optical distance between the first aperture row and the imaging means row is shorter than an object-side focal length of the imaging means row, and the imaging means row and the second The optical distance of the aperture row is required to be equal to the image side focal length of the imaging means row.

  According to the disclosed technology, it is possible to provide a spectral characteristic acquisition device that can acquire an average spectral characteristic within an arrangement pitch for a plurality of measurement positions of an object.

It is a perspective view which illustrates the spectral characteristic acquisition device concerning a 1st embodiment. It is sectional drawing which illustrates the spectroscopy means which concerns on 1st Embodiment. It is a top view which illustrates the slit array of a spectroscopy means, a lens array, and a diagonal slit array. It is a figure which illustrates the relationship between an image sensor and a diagonal slit array. It is a figure explaining the positional relationship of a slit array, a lens array, and a diagonal slit array. It is a top view which shows the other example of a diagonal slit array. It is sectional drawing which illustrates the spectral characteristic acquisition apparatus which concerns on 2nd Embodiment. It is a figure which illustrates the spectral characteristic acquisition apparatus which concerns on 3rd Embodiment. It is a figure which illustrates the image forming apparatus which concerns on 4th 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.

<First Embodiment>
FIG. 1 is a perspective view illustrating a spectral characteristic acquisition apparatus according to the first embodiment. Referring to FIG. 1, the spectral characteristic acquisition apparatus 10 includes a line illumination light source 20, a reduced imaging lens 30, a spectral unit 40, and a line sensor 50. Reference numeral 90 denotes an image bearing medium such as paper which is a reading target (hereinafter, referred to as a target 90). In FIG. 1, a reading object 90 is conveyed in the Y-axis direction at a constant speed. The spectral characteristic acquisition device 10 can simultaneously acquire spectral characteristics at a plurality of positions in the measurement region 90 a of the object 90.

  The line illumination light source 20 is a direction in which a measurement region 90 a extending in a direction (X-axis direction) perpendicular to the conveyance direction (Y-axis direction) of the object 90 is inclined by about 45 degrees with respect to the normal direction of the object 90. Illuminate from. As the line illumination light source 20, for example, a white LED (Light Emitting Diode) array having intensity over substantially the entire visible light region can be used. As the line illumination light source 20, a fluorescent lamp such as a cold cathode tube or a lamp light source may be used.

  However, it is preferable that the line illumination light source 20 emits light in a wavelength region necessary for spectroscopy and can be illuminated uniformly over the entire observation region. In addition, you may add the collimating lens which has a function which collimates and irradiates the light emitted from the line illumination light source 20 to the target object 90 (as parallel light).

  The reduction imaging lens 30 is arranged so that its optical axis coincides with the normal direction of the object 90, and forms an image of reflected light (light beam) from the object 90 on the incident surface of the spectroscopic means 40 at a predetermined magnification. It has a function. Here, by adding the image side telecentric characteristic to the reduction imaging lens 30, the principal ray of the light beam incident on the image plane becomes substantially parallel to the optical axis. The reduction imaging lens 30 may be composed of a plurality of lenses. The reduction imaging lens 30 is a typical example of the first imaging means according to the present invention.

  In addition, by adding the image side telecentric characteristic to the reduction imaging lens 30, the principal ray of the light beam incident on the image plane can be easily made substantially parallel to the optical axis. However, the reduction imaging lens 30 has the image side telecentric characteristic. It is not necessary to add it. In that case, the positional relationship between each aperture 41x (each slit) of the slit array 41 (described later) and each lens 42a of the lens array 42 is adjusted according to the inclination of the principal ray at each position on the image plane. Thus, the same effect can be obtained.

  Specifically, for example, each lens of the lens array 42 so that the principal ray of the light beam transmitted through each opening 41x (each slit) of the slit array 41 passes through the center of each lens 42a corresponding to the lens array 42. The position of 42a is adjusted. Further, the position of each opening 45x (each slit) of the oblique slit array 45 to be described later may be similarly adjusted according to the inclination of each principal ray.

  The principal ray at each position on the image plane is made parallel to the optical axis so that the optical axis of each spectroscopic optical system of the subsequent spectroscopic means 40 is parallel to the optical system of the reduction imaging lens 30. Because it is. As a result, in each spectroscopic optical system of the spectroscopic means 40, the light beam emitted from each opening 41 x of the slit array 41 enters the opening of each lens 42 a of the lens array 42.

  The spectroscopic means 40 has a function of spectroscopically diffusing and reflecting diffused light of light irradiated on the object 90. The spectroscopic means 40 will be described in detail separately.

  The line sensor 50 includes a plurality of pixels having a light receiving region whose longitudinal direction is the Y-axis direction, arranged in the X-axis direction, and acquires an amount of light in a predetermined wavelength band incident through the spectroscopic unit 40. It is. As the line sensor 50, for example, a metal oxide semiconductor device (MOS), a complementary metal oxide semiconductor device (CMOS), a charge coupled device (CCD), or the like can be used.

  In the optical system illustrated in FIG. 1, the illumination light emitted from the line illumination light source 20 is incident on the object 90 at an angle of approximately 45 degrees, and the line sensor 50 is diffusely reflected from the object 90 in the vertical direction. This is a so-called 45/0 optical system that receives light. However, the configuration of the optical system is not limited to that illustrated in FIG. 1. For example, the illumination light emitted from the line illumination light source 20 is perpendicularly incident on the object 90, and the line sensor 50 is moved from the object 90. A so-called 0/45 optical system that receives light diffusing in the 45-degree direction may be used.

  2 is a cross-sectional view illustrating the spectroscopic means according to the first embodiment. FIG. 2A is a cross-section parallel to the XZ plane of FIG. 1, and FIG. 2B is the YZ plane of FIG. Each of the cross-sections is shown in parallel. FIG. 3 is a plan view illustrating a slit array, a lens array, and an oblique slit array of the spectroscopic means, and all of FIGS. 3A, 3B, and 3C are seen through from the line sensor direction. Indicates the state.

  2 and 3, the spectroscopic means 40 according to the first embodiment includes a slit array 41, a lens array 42, a diffraction element 43, a cylinder lens 44, and an oblique slit array 45. .

  The slit array 41 is an aperture row in which a plurality of openings 41x (slits) whose longitudinal direction is the X-axis direction are arranged in a row in the X-axis direction, and light fluxes at different measurement positions in the plurality of apertures 41x. It has the function to acquire. The slit array 41 is disposed on the image plane of the reduction imaging lens 30.

  In the slit array 41, the opening 41x is a portion through which light is transmitted, and the periphery of the opening 41x is a light shielding portion through which light is not transmitted. In addition, in FIG. 3A, the part shown with the satin pattern is a light shielding part. The slit array 41 is a typical example of the first opening row according to the present invention. In FIG. 3A, the planar shape of the opening 41x is rectangular. However, the planar shape of the opening 41x is not limited to this, and the planar shape of the opening 41x may be an elliptical shape whose major axis is the X-axis direction, It is good also as a polygon shape which makes an axial direction a longitudinal direction, and another complicated shape which makes an X-axis direction a longitudinal direction.

  The lens array 42 includes a plurality of lenses 42 a arranged in a line in the X-axis direction. Each lens 42 a of the lens array 42 weakly diffuses each diffused light beam that has passed through each opening 41 x of the slit array 41. It has a function of converting into a luminous flux. The lens 42a is a typical example of the second imaging means according to the present invention, and the lens array 42 is a typical example of the imaging means row according to the present invention.

  The weakly diffused light beam refers to a diffused light beam that is closer to a parallel light beam than the incident diffused light beam. In other words, it is a diffused light beam that is less diffused (weakened) than the incident diffused light beam.

  Each lens 42a constituting the lens array 42 is arranged at a position corresponding to each opening 41x constituting the slit array 41, and each lens 42a has such a diameter that all light transmitted through each opening 41x is incident thereon. Has been. However, the planar shape of each lens 42a may not be circular.

  In the present embodiment, the slit array 41 and the lens array 42 are disposed on the incident surface and the exit surface of one glass substrate 46, but the present invention is not limited to this. The thickness of the glass substrate 46 is determined so that the optical path lengths of the slit array 41 and the lens array 42 are shorter than the object-side focal length of each lens 42 a of the lens array 42. In order to eliminate stray light in the lens array 42, it is preferable to shield portions other than the openings of the lenses 42a. In addition, in FIG.3 (b), it is a suitable part if the part shown with the satin pattern is light-shielded.

  The light (weakly diffused light beam) that has passed through the lens array 42 enters the diffraction element 43 and further enters the cylinder lens 44. The diffractive element 43 has a function of dispersing the light beam transmitted through each lens 42a of the lens array 42 in the Y-axis direction. That is, the diffraction axis direction of the diffraction element 43 is the Y-axis direction.

  As the diffraction element 43, it is preferable to use a blazed diffraction grating with enhanced diffraction efficiency of the first-order diffracted light. By using the blazed diffraction grating as the diffractive element 43, it becomes possible to increase the diffraction efficiency of only the first-order diffracted light, so that the light utilization efficiency of the optical system can be increased, and a signal of sufficient quality can be obtained in a short time. Can be acquired (measurement time can be shortened).

  The cylinder lens 44 is a bowl-shaped lens arranged with its longitudinal direction oriented in the X-axis direction, and has a function of condensing each weakly diffused light beam transmitted through the diffraction element 43 in the Y-axis direction. The cylinder lens 44 is a typical example of the asymmetric imaging unit according to the present invention. In the present embodiment, the diffractive element 43 and the cylinder lens 44 are arranged on the incident surface and the exit surface of one glass substrate 47, but the present invention is not limited to this.

  The light transmitted through the cylinder lens 44 enters the oblique slit array 45. The oblique slit array 45 is an opening row in which a plurality of openings 45x (slits) whose longitudinal direction is inclined with respect to the X-axis direction are arranged in the X-axis direction. In the oblique slit array 45, the opening 45x is a portion through which light is transmitted, and the periphery of the opening 45x is a light-blocking portion through which light is not transmitted. In addition, in FIG.3 (c), the part shown with the satin pattern is a light-shielding part.

  The inclination angle of each opening 45x with respect to the X-axis includes the arrangement pitch of the slit array 41 and the lens array 42, the grating pitch of the diffraction element 43, the vertical and horizontal sizes of the pixels of the line sensor 50, and the line sensor used in each spectroscopic sensor. It can be set as appropriate according to the number of pixels of 50.

  The oblique slit array 45 is arranged in the X-axis direction with respect to diffracted light of a predetermined order (first order in the present embodiment) dispersed by the diffraction element 43 out of the light flux that has passed through each opening 41x of the slit array 41. Each has a function of passing components in different wavelength bands. The oblique slit array 45 is a typical example of the second opening row according to the present invention.

  The arrangement pitch in the X axis direction of the openings 45x of the oblique slit array 45 is substantially the same as the arrangement pitch in the X axis direction of the openings 41x of the slit array 41. The size of the opening 45x in the Y-axis direction is the same as the width of the wavelength band to be measured (for example, visible light) in the first-order diffracted light B.

  The oblique slit array 45 is disposed at the image side focal position of the lens array 42. A line sensor 50 is disposed immediately after the oblique slit array 45, and a plurality of pixels arranged in the X-axis direction of the line sensor 50 receive light beams that have passed through the openings 45 x of the oblique slit array 45. Convert to electrical signal.

  In this way, the light beam that has passed through each opening 41x of the slit array 41 is converted into weakly diffused light by the lens array 42, and becomes convergent light only in the Y-axis direction by the cylinder lens 44. As a result, the light beams that have passed through the openings 41x of the slit array 41 are mixed on the surface of the oblique slit array 45 to form a linear image that is long in the X-axis direction.

  Since this linear image that is long in the X-axis direction is dispersed in the Y-axis direction by the diffraction element 43, it has a width in the X-axis direction and is dispersed in the Y-axis direction at a position shifted from the optical axis in the Y-axis direction. A first-order diffraction image is formed. Then, the light beam that has passed through each opening 45x of the oblique slit array 45x enters the line sensor 50, is photoelectrically converted by a plurality of pixels, and is converted into a signal corresponding to the amount of light.

  FIG. 4 is a diagram illustrating the positional relationship between the oblique slit array and the line sensor, and shows a state seen through from the line sensor direction. In FIG. 4, A indicates transmitted light (0th-order diffraction image), B indicates a first-order diffraction image, and D indicates a second-order diffraction image.

  Referring to FIG. 4, each opening 45x extends obliquely with respect to the X-axis direction (since the direction inclined with respect to the X-axis direction is the longitudinal direction). The light beam incident on the line sensor 50 becomes light having different spectral characteristics for each pixel 50a. Thereby, spectral information corresponding to each opening 41x of the slit array 41 can be measured based on a signal received by a predetermined pixel column on the line sensor 50.

  The output signal of the line sensor 50 is divided into signals of pixel columns corresponding to the respective openings 41x of the slit array 41, and spectral information such as spectral reflectance is calculated from the signals of each pixel column. Spectral information was calculated using the multiple regression analysis shown in, for example, “Tokumichi Tsumura et al.“ Estimation of spectral reflectance from multiband images by multiple regression analysis ”Optics 27, 7 (1998) 384-391”. Existing methods such as methods can be used.

  Incidentally, one opening 41x of the slit array 41, one lens 42a of the lens array 42 corresponding thereto, a part of the diffraction element 43 (light beam transmitting part), a part of the cylinder lens 44 (light beam transmitting part), this With one opening 45x of the oblique slit array 45 corresponding to 1 and a part of the pixel array of the line sensor 50, it optically has the function of one spectrometer. Therefore, a part having the function of one spectroscope may be referred to as a spectroscopic sensor. In addition, since the spectral sensors are substantially arranged in one row, the spectral sensors arranged in one row may be referred to as a spectral sensor array.

  Here, the positional relationship among the slit array, the lens array, and the oblique slit array will be described with reference to FIG. In FIG. 5, P indicates the image side focal point, and Q indicates the object side focal point. In FIG. 5, the optical path length, which is the optical distance between the slit array 41 and the lens array 42, is shorter than the object side focal length of the lens array 42. The optical path length, which is the optical distance between the lens array 42 and the oblique slit array 45, is equal to the image-side focal length of the lens array 42.

  A slit array 41 is arranged on the image plane of the reduction imaging lens 30 having image side telecentric characteristics. Therefore, the light beam passing through an arbitrary point in the opening 41x of the slit array 41 has a principal ray parallel to the optical axis and a constant object side numerical aperture corresponding to the image side numerical aperture of the reduction imaging lens 30. It becomes a diffused light beam (divergent light beam) that diffuses (diversifies).

  In FIG. 5, the light flux passing through the central portion and both end portions of the opening 41x is illustrated. The light passes through the lens surface of the lens array 42 to become weakly diffused light, and the principal ray (indicated by a one-dot chain line) is bent toward the optical axis O. All principal rays intersect on the optical axis O on the oblique slit array 45 arranged at the image side focal point.

  Further, it is preferable that the length in the X-axis direction of each opening 41x of the slit array 41 and the optical path length from the slit array 41 to the lens array 42 are made appropriate in accordance with the image-side numerical aperture of the reduction imaging lens 30. . Thereby, vignetting due to the opening of each lens 42x of the lens array 42 can be reduced.

  Therefore, on the oblique slit array 45, the light beam widths are substantially the same, and the chief ray becomes the optical axis. That is, all the light passing through the openings 41x of the slit array 41 is mixed and overlapped. Thereby, the spectral information acquired from the predetermined pixel column of the line sensor 50 becomes the average spectral characteristic of the light beam transmitted through each opening 41x of the slit array 41.

  Strictly speaking, since the length in the X-axis direction of each opening 41x of the slit array 41 is smaller than the pitch, an average spectral characteristic in a range slightly narrower than the arrangement pitch of the spectroscopic sensor array is obtained in view of the measured surface. Will be. However, since the influence of the imaging characteristics of the optical system is added, an average spectral characteristic in a range substantially equal to the pitch between the measurement points on the object of the spectral sensor array can be actually acquired.

  By the way, each opening 45x of the oblique slit array 45 shown in FIG. 3C is formed with a constant width. However, the present invention is not limited to this, and the width of each opening 45x is partially different. Also good. For example, when the spectral radiance distribution of illumination differs depending on the wavelength band, increasing the width of a part of the slit corresponding to the wavelength band with relatively low radiance can increase the signal in the wavelength band with a small amount of illumination. it can.

  An example is shown in FIG. Each opening 45y of the oblique slit array 45 shown in FIG. 6 is formed so that the width gradually becomes narrower in the X axis plus direction. For example, when a light source having a light amount in a blue wavelength band smaller than that of red, such as a halogen light source, is used as the line illumination light source 20, each opening 45y of the oblique slit array 45 is offset so as to cancel out the bias of the spectral distribution. The width of can be adjusted.

  Thereby, even when the spectral distribution of the line illumination light source 20 is biased, for example, the bias of the light amount can be corrected by increasing the light amount in the wavelength band where the light intensity is weak. As a result, a signal with sufficient quality can be acquired from the entire wavelength band measured from the line sensor 50, and a spectral characteristic acquisition device with higher measurement accuracy can be realized.

  As described above, according to the first embodiment, in the spectral characteristic acquisition device that acquires the spectral characteristics of the plurality of measurement points on the measurement target surface of the object, the spectral characteristic output of each measurement point is converted to the array of measurement points. An output indicating an average color within a width substantially equal to the direction pitch can be obtained. Thereby, for example, in measurement of a printed image using halftone screening, it is difficult to be affected by halftone dots, and stable spectral characteristics can be measured, which is industrially useful.

<Second Embodiment>
In the second embodiment, an example using a spectroscopic unit different from that in the first embodiment will be described. Note that in the second embodiment, the same components as those described in the above embodiments are denoted by the same reference numerals, and the description thereof may be omitted.

  FIG. 7 is a cross-sectional view illustrating the spectroscopic means according to the second embodiment, and FIGS. 7A and 7B are cross-sectional views corresponding to FIGS. 2A and 2B. Respectively. Referring to FIG. 7, the spectral characteristic acquisition apparatus according to the second embodiment is different from the spectral characteristic acquisition apparatus 10 according to the first embodiment in that the spectral unit 40 is replaced with the spectral unit 40A (FIG. 1). , See FIG. 2 etc.).

  The spectroscopic means 40 </ b> A includes a slit array 41, a toric lens array 48, a diffraction element 43, and an oblique slit array 45. Unlike the spectroscopic means 40, the spectroscopic means 40A does not have the cylinder lens 44.

  The toric lens array 48 is formed by arranging a plurality of toric lenses 48 a corresponding to the respective openings 41 x of the slit array 41 in the X-axis direction. The toric lens 48a has different refractive power in the X-axis direction and the Y-axis direction, converts the diffused light beam that has passed through the opening 41x of the slit array 41 into a weakly diffused light beam in the X-axis direction, and converges the light beam in the Y-axis direction. It has the function of converting (condensing) into The toric lens 48a is a typical example of the asymmetric imaging means according to the present invention, and the toric lens array 48 is a typical example of the asymmetric imaging means row according to the present invention.

  In FIG. 7, the light beam transmitted through each opening 41 x of the slit array 41 is incident on the lens surface of each corresponding toric lens 48 a of the toric lens array 48. In the toric lens array 48, the curvature of the lens surface of each toric lens 48a differs between the XZ plane and the YZ plane. Thereby, each light beam becomes weakly diffused light on the XZ plane and convergent light on the YZ plane. Thereby, the functions of the lens array 42 and the cylinder lens 44 shown in FIG. 2 can be achieved by one optical functional surface. As a result, the cylinder lens 44 can be deleted.

  Since the toric lens array 48 can be manufactured by a transfer process using a mold, the complexity of the lens surface shape of each toric lens 48a does not have a large effect on the cost in the mass production process. Therefore, by using the toric lens array 48 in which the functions of the lens array 42 and the cylinder lens 44 are combined, one lens surface can be reduced, which is effective in reducing the size and cost of the spectral characteristic acquisition device. .

  As described above, according to the second embodiment, the spectroscopic means includes the toric lens array that combines the functions of the lens array and the cylinder lens, so that it is possible to reduce the lens surface, and Miniaturization and cost reduction can be realized.

<Third Embodiment>
In the third embodiment, an example of an image evaluation apparatus having a spectral characteristic acquisition apparatus is shown. Note that, in the third embodiment, the same components as those described above may be denoted by the same reference numerals, and the description thereof may be omitted.

  FIG. 8 is a diagram illustrating an image evaluation apparatus according to the third embodiment. Referring to FIG. 8, the image evaluation device 60 includes a spectral characteristic acquisition device 10, a transport unit 61, and an image evaluation unit 62. The transport unit 61 has a function of transporting the object 90 having the measurement region 90a in the Y-axis direction.

  The image evaluation unit 62 has a function of controlling the transport unit 61 and the spectral characteristic acquisition device 10 and operating them in conjunction to acquire the spectral characteristic of the entire surface of the object 90. Further, based on the acquired spectral characteristics, the colorimetric results such as tristimulus values XYZ and CIELAB are calculated, and the color of the image formed on the object 90 with a plurality of colors is evaluated.

  The image evaluation unit 62 includes, for example, a CPU, a ROM, a main memory, and the like, and various functions of the image evaluation unit 62 are performed by reading a program recorded in the ROM or the like into the main memory and executing it by the CPU. realizable. However, part or all of the image evaluation unit 62 may be realized only by hardware. Further, the image evaluation unit 62 may be physically configured by a plurality of devices.

  With such a configuration, the image evaluation apparatus 60 can be used on the object 90 on which a print image or the like is formed based on speed information from an encoder sensor or the like that is known or attached to a conveyance unit (not shown). It is possible to acquire spectral characteristics at a plurality of positions, for example, color information.

  In FIG. 8, the transport unit 61 may move the object 90 and the spectral characteristic acquisition apparatus 10 relatively in a predetermined direction (Y-axis direction in the case of FIG. 8). Therefore, in FIG. 8, the transport unit 61 fixes the spectral characteristic acquisition device 10 and moves the object 90. However, unlike FIG. 8, the conveyance unit 61 may fix the target object 90 and move the spectral characteristic acquisition apparatus 10. .

  When the object 90 can be bent, for example, like paper, the conveying means 61 may be configured to rotate, for example, with a rotating drum after the object 90 is attached to the surface thereof.

  As described above, according to the third embodiment, it is possible to realize an image evaluation apparatus that can independently evaluate the spectral characteristics of the entire surface of the object. That is, since the spectral characteristic and color at an arbitrary position in the image of the object 90 can be measured, color unevenness within the surface of the object 90, color differences between predetermined positions of the plurality of objects 90, and the like are evaluated. It becomes possible. For example, when the object 90 is a printed material, it is possible to manage color changes during the printing process by periodically extracting the printed material during printing and evaluating it with the image evaluation device 60. Adjustments can be made.

<Fourth embodiment>
In the fourth embodiment, an example of an image forming apparatus having the image evaluation apparatus according to the third embodiment is shown. FIG. 9 is a diagram illustrating an image forming apparatus according to the fourth embodiment.

  Referring to FIG. 9, the image forming apparatus 80 includes an image evaluation apparatus 60, a paper feed cassette 81a, a paper feed cassette 81b, a paper feed roller 82, a controller 83, a scanning optical system 84, and a photoreceptor 85. An intermediate transfer member 86, a fixing roller 87, and a paper discharge roller 88. The image forming apparatus 80 is, for example, a full color image forming apparatus such as an electrophotographic system or an inkjet system.

  In the image forming apparatus 80, an object 90 conveyed by a guide (not shown) and a paper feed roller 82 from paper feed cassettes 81a and 81b is exposed to a photosensitive member 85 by a scanning optical system 84, and a color material is applied and developed. The The developed image is transferred onto the intermediate transfer member 86 and then from the intermediate transfer member 86 onto the object 90. The image transferred onto the object 90 is fixed by the fixing roller 87, and the object 90 on which the image is formed is discharged by the paper discharge roller 88. The image evaluation device 60 is installed at the subsequent stage of the fixing roller 87.

  As described above, according to the fourth embodiment, an object 90 after printing (an image after printing) is measured in-line, and an image forming apparatus that can adjust the printing process based on the measurement is realized. it can. That is, by installing the image evaluation apparatus 60 including the spectral characteristic acquisition apparatus 10 at a predetermined position of the image forming apparatus 80, it is possible to acquire spectral characteristics at an arbitrary position of the printed image. Further, based on the acquired spectral characteristics, color measurement results such as tristimulus values XYZ and CIELAB can be calculated. Therefore, use the colorimetric results from any image to monitor the printing process, and if there is a change, interrupt the printing process or adjust the printing process to offset the printing process change. This makes it possible to stably produce more accurate color images.

  The preferred embodiment has been described in detail above. However, the present invention is not limited to the above-described embodiment, and various modifications and replacements are made to the above-described embodiment without departing from the scope described in the claims. Can be added.

DESCRIPTION OF SYMBOLS 10 Spectral characteristic acquisition apparatus 20 Line illumination light source 30 Reduction imaging lens 40, 40A Spectroscopic means 41 Slit array 41x, 45x, 45y Aperture 42 Lens array 42a Lens 43 Diffraction element 44 Cylinder lens 45 Diagonal slit array 46, 47 Glass substrate 48 Toric lens array 48a Toric lens 50 Line sensor 50a Pixel 61 Conveying means 62 Image evaluation means 80 Image forming apparatus 81a Paper feeding cassette 81b Paper feeding cassette 82 Paper feeding roller 83 Controller 84 Scanning optical system 85 Photoconductor 86 Intermediate transfer body 87 Fixing roller 88 Discharge roller 90 Object 90a Measurement area A Transmitted light (0th order diffraction image)
B First-order diffraction image D Second-order diffraction image P Image-side focus Q Object-side focus

JP 2008-256594 A

Susumu Moriya "ImSpector" Imaging Spectrometer = Basic Characteristics and Applications = "Optical Alliance Vol.10, no.11 1999, p.4-9

Claims (10)

First imaging means for imaging light beams at a plurality of positions from the object;
A first aperture row including a plurality of openings through which light beams at a plurality of positions imaged on the first imaging means pass;
An imaging means row in which a plurality of second imaging means for imaging a light beam that has passed through the first aperture row is arranged;
A diffractive element that splits a light beam that has passed through a plurality of second imaging means in the imaging means row;
A second aperture array including a plurality of apertures through which the light beam dispersed by the diffraction element passes;
An image sensor that receives the light flux that has passed through the second aperture row, and
The optical distance between the first aperture row and the imaging means row is shorter than the object side focal length of the imaging means row, and the optical distance between the imaging means row and the second aperture row is the A spectral characteristic acquisition device characterized by being equal to an image-side focal length of an imaging means row. The first aperture row is arranged on the image plane of the first imaging means, and a plurality of apertures having a first direction as a longitudinal direction are arranged in the first direction,
The imaging means row is arranged with a plurality of second imaging means corresponding to a plurality of openings included in the first aperture row in the first direction,
The diffractive element splits a light beam imaged by a plurality of second imaging means of the imaging means row in a second direction orthogonal to the first direction,
Asymmetric imaging means for condensing the light beam dispersed by the diffraction element in the second direction;
The second opening row has a plurality of openings arranged in the first direction, the longitudinal direction being a direction inclined with respect to the first direction,
2. The spectral characteristic acquisition apparatus according to claim 1, wherein the imaging element arranges a plurality of pixels having a light receiving region whose longitudinal direction is the second direction in the first direction. The diffused light beam that has passed through the openings of the first aperture row is incident on the second imaging means,
3. The spectral characteristic acquisition apparatus according to claim 1, wherein the second imaging unit converts the diffused light beam into a weakly diffused light beam that is closer to a parallel light beam than the diffused light beam. In place of the imaging means row and the asymmetric imaging means, an asymmetric imaging means row is provided,
The asymmetric imaging means row has different refractive powers in the first direction and the second direction, and a plurality of asymmetric imaging means corresponding to a plurality of openings of the first opening row are arranged in the first direction. 3. The spectral characteristic acquisition apparatus according to claim 1, wherein the spectral characteristic acquisition apparatus is arranged in a direction. A diffused light beam that has passed through the opening of the first aperture row is incident on the asymmetric imaging unit,
The asymmetric imaging means converts the diffused light beam into a weak diffused light beam that is closer to a parallel light beam than the diffused light beam in the first direction, and converts the diffused light beam into a convergent light beam in the second direction. The spectral characteristic acquisition apparatus according to claim 4.   The spectral characteristic acquisition apparatus according to claim 1, wherein the first imaging unit has an image-side telecentric characteristic.   7. The spectral characteristic acquisition apparatus according to claim 1, wherein the diffraction element is a blazed diffraction grating, and the predetermined order is a first order.   8. The spectral characteristic acquisition apparatus according to claim 1, wherein the widths of the openings of the second opening row are partially different. 9. The spectral characteristic acquisition device according to any one of claims 1 to 8,
Transport means for relatively moving the spectral characteristic acquisition device and the object;
An image evaluation apparatus comprising: an image evaluation unit configured to operate the spectral characteristic acquisition device and the transport unit in conjunction with each other to acquire the spectral characteristic of the entire surface of the object.   An image forming apparatus comprising the spectral characteristic acquisition device according to claim 1, wherein the spectral characteristics at the plurality of positions of the object after image formation are acquired.

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