JP5108373B2 - Image reading apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image reading apparatus and an image forming apparatus using the image reading apparatus.

  2. Description of the Related Art Document reading units (image reading apparatuses) such as digital copying machines, facsimile machines, and image scanners form an image of a document image on a photoelectric conversion element, which is a light receiving element, by an optical system to convert the document image into an electrical signal. Here, in order to read document information in color, the illumination system is provided with a plurality of light sources having different wavelength regions, and the light source is sequentially turned on to convert the color information of the document into a signal. A so-called three-line CCD in which line sensors having green and blue filters are arranged in three rows on one chip is used, and a color image is separated into three primary colors by forming an original image on this light receiving element. There is a method to signal.

  In an image reading apparatus of a digital copying machine, when a line drawing such as a photograph, a halftone dot image, or a character is mixed in the document information, a pseudo halftone process is performed on the photograph portion in order to improve the image quality of the copy. In addition, it is known that moire removal processing is performed on halftone dots, and sharpening processing with emphasis on resolution is performed on line drawings such as characters. Also in the case of transmitting an image, an optimal encoding method is selected for each region in order to improve the compression rate of the image. In an image reading apparatus of a digital copying machine, in order to realize such processing, so-called image area separation that separates a character area and a picture area (photograph area, halftone dot area) in an image with high accuracy as preprocessing. It has image processing called processing.

  In addition, a reading lens used in such an image reading apparatus is generally required to have high contrast in a high spatial frequency region on the image plane and to have an aperture efficiency close to 100% up to the periphery of the angle of view. Yes. Furthermore, in order to read a color original satisfactorily, it is necessary to make the image forming positions of red, green and blue colors coincide with the optical axis direction on the light receiving surface, and the chromatic aberration correction of each color must be corrected very well. . For this reason, it is necessary to design the reading lens to be used so that the curvature of field is very small and the imaging performance at each image height from the vicinity of the optical axis to the periphery is uniform.

  Furthermore, in order to meet the demand for improving the productivity of copying in recent years, a bright lens of about F4.2 is required for the reading lens. As an imaging lens for satisfying these performances and specification values, it is relatively A Gauss type of 4 elements in 6 groups is used, which suppresses the occurrence of coma flare even when the aperture is large and has high chromatic aberration correction capability.

  Here, in order to satisfactorily correct axial chromatic aberration using a Gaussian type, at least one of the third and fourth lenses, which are negative lenses, has a property that the partial dispersion deviation has a positive property. An invention for obtaining good performance using an anomalous dispersion glass is disclosed (see Patent Documents 1 to 6).

  However, since the Gauss type has a large number of lenses of six, the outer diameter of the lens becomes large, and there is a limit to miniaturization and cost reduction of the lens and a device using the lens. Furthermore, anomalous dispersion glass having a relatively high dispersion (Abbe number in the vicinity of 40 to 45) generally used for a negative lens has a problem in processing such as faintness and has a demerit that increases processing cost. It was.

  On the other hand, a telephoto type invention with a four-group, four-element configuration and a small number of lenses has been disclosed (see Patent Documents 7 and 8), but the F number is as dark as 6 or more, which supports high speed. It was impossible. Patent Documents 9 and 10 disclose an invention that achieves a large aperture with a telephoto type, but the invention described in Patent Document 9 has an F number of 4.5 and a relatively large aperture. The amount of aberration is very large, and it does not have imaging performance that can be used for high density reading such as 600 dpi. Further, although the invention described in Patent Document 10 has an F number of 4 and a large aperture, the axial chromatic aberration in both the blue and red regions is very large, and it does not have a performance that can be used for full color.

Japanese Patent No. 2729039 Japanese Patent No. 2790919 JP-A-9-304696 Japanese Patent Laid-Open No. 10-253881 JP-A-11-109221 JP 2001-166359 A JP 2002-31753 A JP 2001-166359 A Japanese Patent No. 3856258 Japanese Patent Application Laid-Open No. 9-101452

  The present invention has been made in view of the above-described circumstances, and has a good image area separation process using an imaging lens that can obtain a sufficient angle of view and brightness at a low cost with a small number of lenses. An object of the present invention is to provide a low-cost, compact and high-quality image reading apparatus having performance and an image forming apparatus using the same.

The present invention provided to solve the above problems is as follows.
(1) An illumination system that irradiates an original with illumination light, an image forming element that forms an image of light (reflected light) reflected by the original with the illumination light, and the light imaged by the image forming element In the image reading apparatus having a light receiving element that performs photoelectric conversion to a signal and an image processing unit that performs image processing for determining document information of a target area of the document using an electrical signal of the document image, the illumination system or the imaging element In any optical path of the imaging optical system using the optical element, the illumination light or the reflected light is transmitted through the first wavelength region , the blue wavelength region , the second wavelength region , the green wavelength region , The image forming element includes color separation means for color-separating into light of three types of wavelength regions of the red light wavelength region that is the third wavelength region , and the imaging element has optical characteristics that satisfy the following formula (1): The light receiving element has a wavelength region separated by the color separation means. And photoelectrically converting it into an electrical signal of the original image, and the image processing unit converts the signal (first color signal) based on the light in the first wavelength region out of the electrical signal of the original image and the second wavelength region. An image reading apparatus that performs image processing to determine whether or not the document information is a halftone dot region using a signal (second color signal) based thereon.
| Bf1-Bf2 | <| Bf3-Bf2 | (1) (however,
Bf1: distance from the rear end of the imaging element to the imaging position for light of an arbitrary wavelength in the first wavelength region, Bf2: imaging element for light of an arbitrary wavelength in the second wavelength region Bf3: distance from the rear end of the imaging element to the imaging position for light of an arbitrary wavelength in the third wavelength region. )
(2 ) In the image reading apparatus according to (1 ), the image forming element is an image forming lens that reduces and forms an original image.
( 3 ) The image reading apparatus according to ( 2 ), wherein the focal length of the imaging element satisfies the following expressions (2) and (3).
| F1-f2 | <| f3-f2 | (2) Equation 0.003 <| f3-f2 | / f2 <0.0045 (3) (however,
f1: Focal length at F line (486.13 nm)
f2: Focal length at reference wavelength e-line (546.07 nm)
f3: focal length at C line (656.27 nm). )
( 4 ) In the image reading apparatus according to ( 3 ), the imaging element includes, in order from the document side, a positive power first lens, a negative power second lens, a positive power third lens, and a negative power. An image reading apparatus comprising the fourth lens.
( 5 ) In the image reading apparatus according to ( 4 ), the first lens is a meniscus lens having a convex surface facing the object side, the second lens is a biconcave lens, the third lens is a biconvex lens, and the fourth lens is a document. An image reading apparatus comprising: a meniscus lens having a concave surface directed toward the side, wherein the imaging element has a diaphragm between the second lens and the third lens.
( 6 ) The image reading apparatus according to ( 4 ) or ( 5 ), wherein the imaging element satisfies the following expressions (4) and (5).
0.05 <n convex-n concave <0.25 (4) Formula 25.0 <ν convex-ν concave <36.5 (5) (However,
n-convex: the total refractive index of the positive lens (first lens, third lens) at d-line (587.56 nm),
n-concave: the total refractive index of d-line (587.56 nm) of the negative lens (second lens, fourth lens),
ν-convex: the sum of the Abbe numbers in the d-line (587.56 nm) of the positive lens (first lens, third lens),
v-concave: Total of Abbe numbers of d-line (587.56 nm) of negative lenses (second lens and fourth lens). )
( 7 ) The image reading apparatus according to any one of ( 4 ) to ( 6 ), wherein the imaging element satisfies the following expression (6).
31.0 <fL1 × ν1 / f2 <37.0 (6) (however,
fL1: focal length of the first lens at the e-line (546.07 nm),
ν1: Abbe number of the first lens,
f2: focal length at reference wavelength e-line (546.07 nm). )
( 8 ) The image reading apparatus according to any one of ( 3 ) to ( 7 ), wherein the imaging element is a lens made of a glass material that does not contain a harmful substance. .
( 9 ) The image reading apparatus according to any one of ( 3 ) to ( 8 ), wherein the imaging elements are all formed of a spherical surface.
( 10 ) As means for reading a document image in full color and outputting an image signal, the image reading apparatus according to any one of (1) to ( 9 ) is provided, and an image corresponding to the image signal is written. An image forming apparatus for forming an image.
( 11 ) The image forming apparatus according to ( 10 ), wherein the image corresponding to the image signal is written by optical writing.
( 12 ) The image forming apparatus according to ( 11 ), wherein an electrostatic latent image corresponding to an image to be formed is formed on a photoconductive photosensitive member by optical writing.

According to the image reading apparatus of the present invention, a compact and low-cost image formation in which the number of components is reduced as the image forming element by determining the halftone dot region using the B signal and the G signal without using the R signal. Even if a lens is used, it is possible to detect halftone dots satisfactorily, and high-precision image reading can be performed without causing image quality degradation such as moire.
Further, according to the image forming apparatus of the present invention, by using the image reading apparatus of the present invention, it is possible to read the original satisfactorily without deteriorating the image area separation performance. It is possible to form a good image without any problem.

The configuration of the image forming apparatus using the image reading apparatus according to the present invention will be described below.
An image forming apparatus according to the present invention has an image reading apparatus according to the present invention, which will be described later, as means for reading a document image in full color and outputting an image signal, and forms an image by writing an image corresponding to the image signal. It is characterized by doing. In this image forming apparatus, the image signal can be written by various known methods such as an ink jet method, an ink ribbon method, a heat sensitive method, and the like. “The image corresponding to the image signal is written by optical writing. Is preferred. Further, in this case, writing by optical writing may be performed on a silver salt film or the like, but “an optical writing is performed on a photoconductive photoreceptor to form an electrostatic latent image corresponding to an image to be formed. Is preferred.

FIG. 1 shows a configuration example of a digital full-color copying machine which is an embodiment of an image forming apparatus.
An image forming apparatus according to the present invention includes an image reading unit including a scanner 1 serving as a document reading unit located at an upper portion of the apparatus, and a first image processing unit including a scanner correction unit (not shown) and a compression processing unit (not shown). And an “image forming unit” positioned below the apparatus.

Here, an image reading apparatus according to the present invention includes an illumination system that irradiates a document with illumination light, an imaging element that forms an image of light (reflected light) reflected by the document, and the imaging element. A document reading unit including a light receiving element that photoelectrically converts the imaged light into an electrical signal of a document image, and an image processing unit that performs image processing for determining document information of a target area of the document using the electrical signal of the document image In the image reading apparatus having the above, in the optical path of the imaging optical system using the illumination system or the imaging element, the illumination light or the reflected light, the first wavelength region, the second wavelength region, A color separation unit that separates light into at least three types of wavelength regions including a third wavelength region; and the imaging element includes an imaging element for light of an arbitrary wavelength in the first wavelength region. The distance from the rear end to the imaging position is Bf1, the first The distance from the rear end of the imaging element to the imaging position for light of an arbitrary wavelength in the wavelength region of Bf2 is from the rear end of the imaging element for light of an arbitrary wavelength in the third wavelength region. When the distance to the image forming position is Bf3, the light receiving element has an optical characteristic that satisfies the following expression (1), and the light receiving element converts the electric power of the original image for each light in the wavelength region separated by the color separation means. The image processing unit performs photoelectric conversion to a signal, and the image processing unit outputs a signal based on light in the first wavelength region (first color signal) and a signal based on light in the second wavelength region (first color signal) of the electrical signal of the document image. The image reading apparatus performs image processing for discriminating the document information using a second color signal.
| Bf1-Bf2 | <| Bf3-Bf2 | (1) Also, at this time, light of an arbitrary wavelength in the first wavelength region is blue light (blue (B)), and in the second wavelength region. It is preferable that light of an arbitrary wavelength is green light (green (G)) and light of an arbitrary wavelength in the third wavelength region is light of three primary colors of red light (red (R)).
Furthermore, it is preferable that the image processing unit determines whether or not the document information is a halftone dot region using the first color signal and the second color signal.

FIG. 2 shows an example in which a so-called three-line CCD is used as a light receiving element as a configuration example of the scanner 1 which is an image reading apparatus according to the present invention.
In the scanner 1, the document 102 is disposed on the contact glass 101, and the document 102 is illuminated by an illumination optical system 107 disposed below the contact glass 101. The illumination reflected light L of the document 102 is reflected by the first mirror 103 a of the first traveling body 103, and then reflected by the first mirror 104 a and the second mirror 104 b of the second traveling body 4, to the reduction imaging lens 105. The light is guided and formed on the line sensors 106R, 106G, and 106B of the line sensor unit 106 by the imaging lens 105.
When the longitudinal direction of the document 2 is read, the first traveling body 103 moves from the left end in the drawing to the right at a speed of V to the position (103 ′) on the right end in the drawing. From the left end in the figure, the document moves to the position (104 ′) in the center in the figure at a speed of 1/2 V, which is half the speed of the first traveling body 103, and reads the entire original.

  The line sensor unit 106 includes line sensors 106R, 106G, and 106B, which are line CCDs, arranged in parallel in three rows on one chip so that the longitudinal direction of the line sensor is the sub-scanning direction (vertical direction in the drawing). (So-called 3-line CCD), and filters (R, G, B filters (R, G, B) for separating the illumination reflected light L into light of three types of wavelength regions corresponding to the line sensors 106R, 106G, 106B. A filter that separates the illumination reflected light L into light in the red (R) wavelength region, a filter that separates the illumination reflected light L into light in the green (G) wavelength region, and the illumination reflected light L as blue (B). A filter for color separation into light in the wavelength region)) is arranged in front of the sensor.

FIG. 3 shows an example of the output of the line sensor unit 106. Here, a case where general white light enters the line sensor unit as illumination reflected light L is shown, where the horizontal axis indicates the wavelength and the vertical axis indicates the spectral sensitivity.
In the figure, the curve of R corresponds to the line sensor 6R, and shows a high transmittance for red light. The G curve corresponds to the line sensor 6G and shows a high transmittance for green light, and the B curve corresponds to the line sensor 6B and shows a high transmittance for blue light. Each wavelength region of the R, G, and B curves is as follows in the visible region of 400 nm to 700 nm, for example. That is, the wavelength region of R is a region having spectral sensitivity in the range of 550 to 700 nm with a peak wavelength in the vicinity of 650 nm. The G wavelength region is a region having spectral sensitivity in a range of 450 to 650 nm with a peak wavelength of 550 nm. The B wavelength region is a region having spectral sensitivity in the range of 400 to 550 nm with 450 nm as the peak wavelength.

  As a color separation method, a color separation prism or filter is selectively inserted between the imaging lens 5 and the line sensors 106R, 106G, and 106B to separate the colors into R, G, and B, or R, G There is a method of illuminating the original 102 by sequentially turning on the B light source, but any method can be used as long as it can be decomposed into a predetermined wavelength region. As the image reading optical system, in addition to the above-described method, as shown in FIG. 4, the optical path is folded back by a plurality of mirrors (the number is arbitrary), and the imaging lens 105 and the line sensor unit 106 are integrated. It is also possible to employ a method in which the document information is read by holding the unit 108 and moving the entire unit 108.

  When a color image (original image) is formed on the light receiving surface of the line sensor unit 106, the line sensors 6R, 6G, and 6B are color-separated into R, G, and B3 light original images by the filters described above. , G, and B light original images are photoelectrically converted to R, G, and B color electrical signals (R signal, G signal, and B signal, also referred to as RGB image data, respectively). It is output to the image processing unit. At this time, the B signal is an electric signal in the wavelength region showing a high transmittance in the curve B shown in FIG. 3, the G signal is an electric signal in the wavelength region showing a high transmittance in the curve G shown in FIG. 3, and the R signal is FIG. 4 is an electric signal in a wavelength region showing a high transmittance in the curve of R shown in FIG.

  Next, in the first image processing unit, predetermined image processing is performed on the RGB image data from the line sensor unit 106, and a "write image signal (signal for writing each color of yellow, magenta, cyan, and black). C, M, Y, Bk data, which is a signal converted into “)”. Details of this will be described later. Next, the C, M, Y, Bk data is compressed by the compression processing unit.

The image forming unit in FIG. 1 includes a second image processing unit and an image output unit.
The second image processing unit includes an expansion processing unit and a printer correction unit. First, the decompression processing unit decompresses the compressed image data (the C, M, Y, and Bk data) to the original multi-value data, and then the printer correction unit 7 performs printer γ (gamma) correction processing and gradation. Processing is performed, and image data is quantized and output by error diffusion processing or dither processing according to the gradation characteristics of the image output unit and the image area separation result, and correction processing of the light and dark characteristics of the subsequent image output unit To do. The first image processing unit and the second image processing unit may be combined into an image processing unit 1200 shown in the drawing.
Next, the image output unit writes the image data to form an image.

  Here, as shown in FIG. 1, the image output unit includes a photoconductive photoconductor 1100 formed in a cylindrical shape as a “latent image carrier”, and a charging roller 1110 as a charging unit around the photoconductive photoconductor 1100. A revolver type developing device 1130, a transfer belt 1140, and a cleaning device 1150 are provided. As the charging means, a “corona charger” can be used instead of the charging roller 1110. Further, the optical scanning device 1170 that receives a signal for writing from the image processing unit 300 and writes on the photosensitive member 1100 by optical scanning performs optical scanning of the photosensitive member 1100 between the charging roller 1110 and the developing device 1130. It has become. Reference numeral 1160 denotes a fixing device, reference numeral 1180 denotes a cassette, reference numeral 1190 denotes a registration roller pair, reference numeral 1220 denotes a paper feed roller, reference numeral 1210 denotes a tray, and reference numeral P denotes a transfer sheet as a “recording medium”.

  When image formation is performed, the photoconductive photosensitive member 1100 is rotated at a constant speed in the clockwise direction in the drawing, the surface thereof is uniformly charged by the charging roller 1110, and exposure by optical writing of the laser beam of the optical scanning device 1170 is performed. In response, an electrostatic latent image is formed. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed.

  “Image writing” is performed in the order of a yellow image, a magenta image, a cyan image, and a black image in accordance with the rotation of the photoconductor 1100, and the formed electrostatic latent image is stored in each developing unit Y ( Development with yellow toner), M (development with magenta toner), C (development with cyan toner), K (development with black toner) are sequentially reversed and visualized as a positive image. The respective color toner images are sequentially transferred onto the transfer belt 1140 by the transfer voltage application roller 114A, and the respective color toner images are superimposed on the transfer belt 1140 to form a color image.

  The cassette 1180 containing the transfer paper S is detachable from the main body of the image forming apparatus, and the uppermost sheet of the stored transfer paper S is fed by the paper feed roller 1220 when mounted as shown in the figure. The leading edge of the fed transfer paper S is caught by the registration roller pair 1190. At this time, the registration roller pair 1190 feeds the transfer sheet S to the transfer unit at the timing when the “color image by toner” on the transfer belt 1140 moves to the transfer position. The transferred transfer paper S is superimposed on the color image at the transfer portion, and the color image is electrostatically transferred by the action of the transfer roller 114B. The transfer roller 114B presses the transfer sheet S against the color image during transfer.

  The transfer sheet S on which the color image is transferred is sent to the fixing device 1160, where the color image is fixed in the fixing device 1160, passes through a conveyance path by a guide means (not shown), and is discharged onto the tray 1210 by a pair of paper discharge rollers (not shown). The Each time each color toner image is transferred, the surface of the photoreceptor 1100 is cleaned by a cleaning device 1150 to remove residual toner, paper dust, and the like.

Next, an image processing system in the digital full-color copying machine of FIG. 1 will be described.
FIG. 5 is a block diagram showing a schematic configuration of an image processing system in the digital full-color copying machine.
Here, referring to FIG. 5, the configuration of each part of the image processing system and the process for copying the original, that is, the process of reading the original image, accumulating the read image, and outputting the print using the accumulated image are performed. The outline of the contents will be described along the processing flow of image data at the time of copying.

  When operating as a full-color copying machine, the scanner 1 reads the original image as an analog image signal that is color-separated into R (red), G (green), and B (blue) by the line sensor unit 106, and digitally converts the obtained image signal. Convert to data and output.

  The scanner correction unit 2 performs image processing such as scanner γ correction processing and filter processing on the RGB image data (digital data) read by the scanner 1 to correct the characteristics of the scanner. In the image processing performed here, the original image is separated into a plurality of different image areas (image areas are separated into characters, line drawings, patterns, etc.) and adapted to the image type (for example, the character portion of the image is emphasized and the pattern is emphasized). Part is subjected to a smoothing filter process). Note that the processing related to image area separation in the scanner correction unit 2 is an element characterizing the present invention, and details will be described later.

  The compression processing unit 3 compresses the multivalued image data after the scanner correction, and sends the data to the general-purpose bus 10. The compressed image data is sent to the controller 4 through the general-purpose bus 10. The controller 4 has a semiconductor memory (not shown) and accumulates transmitted data. Data stored in the semiconductor memory is written to a hard disk drive (HDD) 5 which is a large capacity storage device as needed. This is because even when paper is jammed at the time of print output and the output does not end normally, to avoid rereading the document again, to perform electronic sorting to rearrange multiple document image data, or to store the read document This is to re-output when necessary. Although the compression processing unit 3 compresses the image data here, the data may be handled in an uncompressed state if the bandwidth of the general-purpose bus 10 is sufficiently wide and the capacity of the HDD 5 to be stored is large. .

  Next, the controller 4 sends the image data stored in the HDD 5 to the expansion processing unit 6 via the general-purpose bus 10. The decompression processing unit 6 decompresses the compressed image data to the original multi-value data and sends it to the printer correction unit 7.

  The printer correction unit 7 performs printer γ (gamma) correction processing and gradation processing, and according to the light / dark characteristic correction processing of the plotter 8 (the image output unit at the subsequent stage), the gradation characteristics of the plotter 8 and the image area separation result. The image data is quantized by error diffusion processing or dither processing.

  The plotter 8 is a laser beam writing type transfer paper printing unit that drives a laser with image data to draw an image as a latent image on a photosensitive member, and after image formation / transfer processing with toner, a copy image is printed on the transfer paper. Form.

The operation when the image processing system shown in FIG. 5 operates as a distribution scanner, that is, when image data is distributed via the network to the PC 11 as an external apparatus using the scanner input image data will be described.
Also in this case, the original image is read from the scanner 1 and is sent to the controller 4 through the processing of the scanner correction unit 2 and the compression processing unit 3 as in the case of operating as a copying machine.
The controller 4 reduces the load on the network and performs a format process for converting the image data into data in a format that takes into account the usability of the PC 11 as an external device, and then performs the PC 11 via the NIC (Network Interface Controller) 9. Deliver to. In the format processing, for example, conversion into a JPEG (Joint Photographic Experts Group), TIFF (Tagged Image File Format), or BMP (Bit Map) format used as a general-purpose image format is performed.

The internal configuration of the scanner correction unit 2 in the image processing system (FIG. 5) is shown in the block diagram of FIG.
As shown in FIG. 6, the scanner correction unit 2 reads a document with the scanner 1 and converts a digital value of RGB image data based on the characteristics of the scanner into a digital value proportional to lightness based on the input RGB image data. The γ (gamma) correction unit 21 determines whether each pixel (region) of the RGB image data belongs to a different image type such as a character, halftone character, or design, and sets the image region (image region) of the document. An image area separation unit 22 that separates into image type regions, a filter processing unit 23 that applies sharpening processing or smoothing processing to image data based on the result of the image region separation, and a color in the RGB color space The separated image data is recorded color information of C (cyan), M (magenta), Y (yellow), and Bk (black), which are other color spaces (hereinafter “Bk” may be simply referred to as “K”). (black A color correction unit 25 which converts the color image data including the point) ", with a scaling section 27 and outputs the scaling the size of the main scanning direction in the input image as a component.
The image processing unit 22 and the related processing unit using the image region separation result in the scanner correction unit 2 are elements that characterize the present invention, and will be described in detail below.

FIG. 7 is a block diagram showing the internal configuration of the image area separation unit 22.
As shown in FIG. 7, the image area separation unit 22 includes a filter unit 221, a white region extraction unit 222, a halftone dot separation unit 223, an edge extraction unit 224, a halftone dot edge extraction unit 225, a color determination unit 226, and a comprehensive determination unit. 227, and based on the input RGB image data, a C / P signal (pattern, character, halftone character, halftone dot region) and B / C signal (image region) representing an image area separation result (image type) A chromatic area / achromatic area).
The C / P and B / C signals are input in synchronization with the image data expressed in the RGB or CMYK color space input to each processing unit of the scanner correction unit 2 according to the processing flow, and if necessary. Referenced. After the compression / decompression process is performed together with the image data, it is also input to the printer correction unit 7 and is referred to as necessary in each processing unit of the printer correction unit 7.
Hereinafter, each processing unit of the image area separation unit 22 will be described in detail.

  The filter unit 221 receives G image data, and outputs G image data in which the deterioration of the MTF characteristic is corrected by emphasizing the edge of the image data in order to mainly extract the edge of the character. This filter processing can be performed by using an existing technique. For example, the processing of the filter unit described in Japanese Patent Laid-Open No. 2003-46772 (see the publications [0069] to [0077]). It is possible to apply. The G image data processed by the filter unit 221 is output to the edge extraction unit 224.

  In the edge extraction unit 224, the G image data in which the edge is enhanced by the filter unit 221 is input, a character edge region is determined based on the continuity of each of the high level density black pixels and the low level density white pixels, The “1” edge signal is output to the pixel determined to belong to the region, and the “0” edge signal is output to the pixel determined to belong to the non-edge region. This edge extraction processing can be performed by using an existing technique. For example, the edge extraction processing described in Japanese Patent Laid-Open No. 2003-46772 (see the above publications [0078] to [0083]). ) Can be applied. The edge signal generated by the edge extraction unit 224 is output to the halftone dot extraction unit 225 and the overall determination unit 227.

In the white area extraction unit 222, the input RGB image data and the G image data in which the edge is enhanced by the filter unit 221 are input, and a “1” wh signal is output to a pixel determined to belong to the white area. A “0” wh signal is output to a pixel determined not to belong to the region.
The wh signal indicating the final white background separation result includes a non-white background boundary region with respect to the white background and the boundary portion. In other words, the area is larger than the actual white background on the document. This white area extraction process can be performed by using an existing technique. For example, the white area extraction unit described in Japanese Patent Application Laid-Open No. 2003-46772 (the same publication [0084] to [0126]). ]) Can be applied. The wh signal generated by the white area extraction unit 222 is output to the comprehensive determination unit 227.

The halftone dot separation unit 223 in the image area separation unit 22 receives the G image data (G signal) and the B image data (B signal), and outputs a halftone dot detection signal peak and a halftone dot region signal ht.
FIG. 8 is a block diagram showing an internal configuration of the halftone separator 223 according to the present embodiment.
As shown in FIG. 8, the halftone dot separation unit 223 includes a first halftone dot peak detection unit 2231, a second halftone dot peak detection unit 2232, a peak signal generation unit 2234, a halftone dot region detection unit 2236, and a halftone dot total determination unit. 2238.

  G image data and B image data are input to the first halftone peak detector 2231 and the second halftone peak detector 2232. The G image data is image data sensitive to the black density of the color image, and it is not necessary to convert the image data into a luminance signal or the like. However, the G image data is not sensitive to Y (yellow: yellow), and the peak detection based on it is a leak of the Y peak. On the other hand, since B image data is sensitive to Y, peak detection based on it compensates for leakage of peak detection using the G signal. Therefore, by detecting both G and B, the accuracy of halftone dot detection can be increased.

The first halftone dot peak detection unit 2231 uses G image data to form a pixel (“halftone peak”) that forms part of a halftone dot from pixel density information in a local area having a predetermined size in two dimensions. (Referred to as “pixel”).
The second halftone peak detection unit 2232 receives a B image signal instead of the G image signal input by the first halftone peak detection unit 2231. Internal peak pixel detection processing is performed in exactly the same manner as the first halftone peak detection unit 2231. Similarly, when the detection process is performed and the center pixel of the area is detected as a halftone peak pixel, the second halftone peak detection unit 2232 generates a halftone peak detection signal bpk = 1, otherwise , Bpk = 0 is generated.
That is, the first halftone dot peak detection unit 2231 outputs a binary signal gpk as the detection result, and the second halftone dot peak detection unit 2232 outputs bpk. The gpk and bpk are input to the peak signal generator 2234, and a logical sum is output as peak.

The halftone dot detection unit 2236 receives detection signals gpk and bpk from the first and second halftone peak detection units 2231 and 2232, and generates a binary signal ami as a halftone dot region detection result.
Specifically, the halftone dot region detection unit 2236 detects a binary halftone dot region detection signal by the following detection method based on the halftone dot peak detection signals gpk and bpk that are input. That is, when a pixel with a halftone dot detection signal gpk = 1 or a halftone dot detection signal bpk = 1 is input as a halftone dot peak pixel, the number of pixels is two-dimensionally assigned to each small region. Counting is performed, and the sum of halftone dot peak pixels of peaks and valleys is taken as a count value P. When the count value P is larger than the threshold value Pth, all the pixels in the small area (or only the central pixel of the small area in the case of pixel unit processing) are determined as the halftone dot area.
When the halftone dot region is determined by such a method, the halftone dot region detection signal ami = 1 of the corresponding pixel is output. Otherwise, ami = 0 is output.
Note that halftone dot peak pixels that are actually in the halftone dot region of the document are detected as clusters having a certain size. If a pixel with a halftone dot detection signal gpk = 1 or bpk = 1 is detected in isolation, there is a high probability that it is due to characters or simply due to image noise. Therefore, by increasing the threshold value Pth, it is possible to reduce the probability that a pixel with isolated gpk = 1 or a pixel with isolated bpk = 1 is determined as a halftone dot region.
The halftone dot region detection signal ami detected as described above is input to the halftone dot total determination unit 2238.

Next, the halftone dot comprehensive determination unit 2238 receives the detection signal ami from the halftone dot region detection unit 2236, and outputs a binary signal ht indicating the final halftone dot separation result.
That is, the halftone dot total determination unit 2238 finally determines a halftone dot region based on the input halftone dot region detection signal ami and generates a halftone dot detection signal ht. Output to H.227.
When the pixel of the halftone dot area detection signal ami = 1 is input as a pixel of the halftone dot area in the small area having a predetermined size of interest, the halftone dot total determination unit 2238 counts the number of pixels. To do. When the total value AmiP is larger than a predetermined threshold value Amith, the halftone dot total determination unit determines that the focused small area is finally in the halftone dot area, and the halftone dot detection signal ht = 1. Is output. Otherwise, it is determined as a non-halftone area and a halftone detection signal ht = 0 is output.

  The halftone dot extraction unit 225 in the image area separation unit 22 receives the edge signal of the character from the edge extraction unit 224 and the peak signal from which the halftone dot peak is detected from the halftone separation unit 223, and receives the halftone dot signal hted. Output.

The color determination unit 226 receives R, G, and B image data and determines whether the pixel of interest is a chromatic pixel or an achromatic pixel. If chromatic, iro = 1, or achromatic In this case, a binary signal with iro = 0 is output. This color determination process can be performed by using an existing technique. For example, the process of the color determination unit described in Japanese Patent Application Laid-Open No. 2003-46772 (see the publications [0158] to [0205]). ) Can be applied.
The iro signal indicating the chromatic / achromatic pixel determination result determined by the color determination unit 226 is output to the comprehensive determination unit 227.

  The comprehensive determination unit 227 in the image area separation unit 22 includes a wh signal indicating a white area from the white region extraction unit 222, an ht signal indicating a halftone detection result from the halftone separation unit 223, and an edge signal from the edge extraction unit 224. Then, the hted signal from the halftone dot extraction unit 225 and the iro signal indicating the determination result of the chromatic / achromatic pixel from the color determination unit 226 are input, and the C / P signal representing the result of image area separation (image type) (Picture, character, halftone character, halftone dot regions) and B / C signals (representing chromatic / achromatic regions) are generated and output.

  As a result of the image area separation by the image area separation unit 22, C / P signals (picture, character, halftone character, halftone dot areas) and B / C signals (representing chromatic / achromatic areas) are obtained. In order to perform processing according to the image type of the separated area, as shown in FIG. 6, the filter processing unit 23, the color correction unit 25, the scaling processing unit 27, the printer that processes the image data, Each part of the correction unit 7 is cascaded in synchronization with the image data.

  The filter processing unit 23 is a filter that corrects the MTF of the RGB image data, and includes a coefficient matrix corresponding to an N × N pixel matrix and logic that multiplies each coefficient by each image data to obtain a weighted average value. Yes. When the C / P signal indicates 1 (character area) or 2 (halftone character area), the coefficient matrix for sharpening processing is used to indicate 0 (picture area) or 3 (halftone area) In such a case, a weighted average value is derived using a coefficient matrix for smoothing processing and output to the color correction unit 25.

  The color correction unit 25 converts R, G, and B image data into C, M, and Y data by a primary masking process or the like, and further performs UCR (Under Color Removal) processing. By this UCR processing, color reproduction of image data can be improved. In the UCR process, a common part of C, M, and Y data is subjected to additive color removal processing to generate Bk data, whereby the color correction unit outputs C, M, Y, and Bk data. Here, when the C / P signal is 1 (character area) or 2 (halftone character area), full black processing is performed. Further, when the C / P signal is 1 or 2 and the B / C signal is 0 (achromatic region), the C, M, and Y data are erased. This is because black characters are expressed only by the black component.

  At the time of image formation, the printer correction unit 7 decompresses the compressed data stored in the HDD 5 through the processing on the scanner input side by the decompression processing unit 6, and changes the frequency characteristics of the plotter 8 to the restored CMYK image data. Accordingly, γ (gamma) correction is performed, quantization such as dither processing and error diffusion processing is performed, and the obtained image data C "M" Y "K" is synchronized with the image data writing operation to obtain a plotter. 8 is output.

  As described above, according to the present embodiment, the character region and the halftone character portion are separated using the image region separation result by the image region separation unit 22, and the image processing is switched between the two. The image quality can be improved by performing the image processing. In particular, it is possible to ensure the correspondence to the halftone dot character area on the white ground.

Here, the basis for using the G image data (G signal) and the B image data (B signal) among the input RGB image data in the halftone dot separation unit 223 of the image area separation unit 22 will be described in detail. .
FIG. 9 shows an example of spectral reflectance of general ink used for printing an original.
Usually, in a wavelength region where the reflectance of ink is high, the change in the amount of received light due to the presence or absence of ink is small and there is no difference in intensity, making it difficult to detect document information. For example, when attention is paid to yellow ink (yellow plot in the figure) which is a complementary color of the B signal, the reflectance is high in the wavelength region corresponding to the R / G signal, and the reflectance is substantially in the wavelength region corresponding to the B signal. 0%. That is, when there is information printed with yellow ink on a document, and when the document is read by the document reading unit as shown in FIG. 1, the intensity of the B signal becomes very small, and there is no information printed with yellow ink. Since the intensity increases, the presence or absence of information printed with yellow ink can be detected by using the B signal. For this reason, in order to satisfactorily detect the document information of the portion printed with yellow ink, imaging performance in a wavelength region corresponding to the B signal is required.

  Further, in the case of magenta ink (magenta plot in the figure) that is a complementary color of the G signal, the reflectance is high in the wavelength range corresponding to the R signal, but in the wavelength range corresponding to the G signal that is the complementary color. The reflectance is almost 0%, and the presence or absence of information printed with magenta ink can be detected by using the G signal which is a complementary color. However, since the reflectance is low even in the wavelength region corresponding to the B signal, the magenta ink can also detect the B signal.

  When attention is paid to cyan ink (cyan plot in the figure) that is a complementary color of the R signal, the reflectance is high in the wavelength region corresponding to the B signal, but the reflectance is almost 0 in the wavelength region corresponding to the R signal. Thus, it is possible to detect document information printed with cyan ink using an R signal which is a complementary color. However, since the reflectance is low even in the wavelength region corresponding to the G signal, it is possible to detect the cyan ink even with the G signal.

  As can be seen from the above, for yellow ink, a complementary B signal is necessary for detection, but for cyan ink and magenta ink, signals other than complementary colors can also be detected. Note that the black ink has a low reflectance in the wavelength range corresponding to any of the R, G, and B signals, and therefore can detect any of the R, G, and B signals.

In image processing, in order to simplify processing and perform processing with as little memory as possible, it is better to perform processing with as little data as possible.
Here, the G signal has the highest sensitivity in human visual sensitivity. When the R, G, and B signals are converted into a luminance signal and a color difference signal, the G signal has the greatest influence. The signal becomes an essential signal during image processing. In order to detect yellow ink information, only the B signal can be detected as described above, so the B signal is also required. As described above, the intensity of the cyan ink can be detected even with the G signal. Therefore, in the image processing in the image reading apparatus of the present invention, image processing related to image area separation is performed using the two signals of the B signal and the G signal.

  In the present invention, image processing for determining a halftone dot region is executed using these two signals (B signal and G signal). Here, a halftone document is a representation of a printed photographic image or a lightly painted image as a collection of small dots, and is used to express smooth shading. For this reason, when the detection of the halftone dot area fails, moire occurs in the image formed based on the result. Moire is very conspicuous with human eyes, and is therefore regarded as a significant deterioration in image quality. In addition, since it is an aggregate of small points, it needs an imaging performance of a relatively high spatial frequency (usually a region of 1/2 or more of the Nyquist frequency) as an imaging element. Therefore, by using the B signal and the G signal without using the R signal for halftone dot detection, it is possible to reduce the imaging performance in the high spatial frequency region of the R optical element.

  The conditional expression necessary to obtain an image reading apparatus with reduced R signal performance is the expression (1), and is a third wavelength region (R signal) that is a wavelength region not used for image processing. And the difference between the distance from the rear end of the imaging element to the imaging position in the reference second wavelength region (G signal), the first wavelength region (B signal) used in image processing and the reference second wavelength region It is necessary to increase the difference in distance from the rear end of the imaging element (G signal) to the imaging position.

  With this configuration, even when a compact and low-cost imaging lens with a reduced number of components is used as the imaging element 105 in the scanner 1 of FIG. Therefore, highly accurate image reading can be performed without causing image quality degradation such as moire. This also makes it necessary to improve the imaging performance in the wavelength region corresponding to the G signal and the B signal for the imaging element (imaging lens) used in the image reading apparatus. The performance in the wavelength region corresponding to the R signal not used for processing can be kept low, and the degree of freedom in optical design is greatly expanded.

  The imaging element 105 used in the image reading apparatus of the present invention is preferably an imaging lens that forms a reduced original image. As an image forming element used in the image reading apparatus, there are a reduction optical system for reducing image formation of original information and an equal magnification image formation optical system for forming original information at the same magnification. The image reading apparatus of the present invention is compatible with either optical system, but the reduction optical system ensures good performance even when the document surface is deep and the document floats on the contact glass. Is possible. For this reason, a more accurate image reading apparatus can be obtained.

At this time, the focal length of the imaging element 105 at the F line (486.13 nm) is f1, the focal length of the e line (546.07 nm) is f2, and the focal length of the C line (656.27 nm) is f3. It is preferable to satisfy the conditions of the following formulas (2) and (3).
| F1-f2 | <| f3-f2 | (2) Equation 0.003 <| f3-f2 | / f2 <0.0045 (3) Equation

  In the case of using a reduction optical system in which the image forming element 105 is an image forming lens for reducing the original image, the conditional expression of the image forming lens for satisfying the expression (1) is defined as (2 ) And (3).

  The expression (2) defines the so-called axial chromatic aberration of the imaging lens corresponding to the range of the expression (1). The wavelength of the axial chromatic aberration of the imaging lens corresponding to the R signal is defined as the C-line (656. 27 nm), the wavelength of the axial chromatic aberration of the imaging lens corresponding to the G signal is e line (546.07 nm), the wavelength of the axial chromatic aberration of the imaging lens corresponding to the B signal is F line (486.13 nm), When the reference wavelength of the lens design is the e-line (546.07 nm) corresponding to the G signal, the F-line (486.13 nm) corresponding to the B signal necessary for ensuring performance in addition to the G signal necessary for the image reading apparatus. ) Axial chromatic aberration amount (| f1-f2 |) is required to be smaller than the axial chromatic aberration amount (| f3-f2 |) of the C line (656.27 nm) corresponding to the R signal. .

  Further, the expression (3) defines the amount of chromatic aberration on the axis of the C line (656.27 nm). By setting the chromatic aberration on the axis of the C line within this range, the number of lenses can be reduced and the lens can be made compact. Therefore, a low-cost imaging lens can be obtained. If the lower limit of the expression (3) is not reached, the chromatic aberration of the C line is in a good state, but in order to achieve this, good color correction is required, and the number of lens components increases and the total length of the lens becomes long. On the contrary, if the upper limit is exceeded, the chromatic aberration of the C line becomes too large and the imaging performance of the R signal is greatly deteriorated, so that the image processing cannot be performed satisfactorily and the read image quality is greatly deteriorated.

  The imaging element 105, which is an imaging lens for reducing the original image defined by the equations (2) and (3), has a positive power first lens and a negative power in order from the object side. It is preferable that the lens is composed of a second lens, a positive power third lens, and a negative power fourth lens (Configuration A).

  Further, in addition to the configuration A, the first lens has a meniscus lens with a convex surface facing the object side, the second lens has a biconcave lens, the third lens has a biconvex lens, and the fourth lens has a concave surface facing the object side. It is a meniscus lens, and it is preferable to have a stop between the second lens and the third lens (Configuration B).

  By forming the imaging element 105 with these configurations A and B, what has been achieved with a so-called Gauss type lens having a four-group six-lens configuration is also good as a so-called telephoto type lens having a four-group four-lens configuration. Imaging performance can be obtained.

The imaging element 105 having configurations A and B has a total refractive index of the positive lens (first lens, third lens) d-line (587.56 nm) of n convex, negative lens (second lens, fourth lens). ) Of the refractive index of the d-line (587.56 nm) is n-concave, and the sum of the Abbe numbers of the positive lens (first lens and third lens) of the d-line (587.56 nm) is ν-convex, negative lens (second lens) When the sum of the Abbe numbers on the d-line (587.56 nm) of the fourth lens) is ν concave, it is preferable that the conditions of the following formulas (4) and (5) are satisfied (configuration C).
0.05 <n convex-n concave <0.25 (4) Formula 25.0 <ν convex-ν concave <36.5 (5) Formula

  In the image reading apparatus according to the present invention, the R signal is not used for detection of document information (halftone dot information), so that the image formation position of the R region is farther from the B region than the reference G region. be able to. However, with respect to other imaging performance, performance equivalent to that of a general image reading apparatus is required. In other words, it is required to have a uniform and high contrast from the vicinity of the optical axis to the periphery in the high spatial frequency region. For this reason, the imaging lens needs to correct field curvature well, particularly in the sub-scanning direction. In order to make the contrast uniform, it is necessary to satisfactorily correct the field curvature in the sagittal direction and suppress the coma flare.

  In addition, in order to read the G signal and the B signal satisfactorily, it is necessary to match the image forming positions of green and blue colors on the light receiving surface in the optical axis direction. The on-axis chromatic aberration must be corrected very well. Furthermore, it is required that the aperture efficiency is close to 100% up to the periphery of the angle of view.

  The conditions of the expressions (4) and (5) define the material used for the imaging lens in order to satisfy the above-described performance, and the expression (4) constitutes the imaging lens. The range of the refractive index of the convex lens and the concave lens is determined. If the upper limit is exceeded, the Petzval sum becomes too small, and the image plane falls to the positive side and the field curvature increases. On the contrary, if the value falls below the lower limit, the Petzval sum becomes too large, the image surface falls to the negative side, and the astigmatic difference becomes large.Under these conditions, good imaging performance can be obtained over the entire screen. Disappear.

Equation (5) is a condition for satisfactorily correcting axial chromatic aberration. If the upper limit is exceeded, the axial chromatic aberration will be overcorrected, and the axial chromatic aberration will become larger on the positive side at shorter wavelengths than the reference wavelength. Below the lower limit, the axial chromatic aberration becomes insufficiently corrected, and the axial chromatic aberration becomes larger on the negative side on the shorter wavelength side than the dominant wavelength.
As described above, if the conditions of the expressions (4) and (5) are not satisfied, the performance required for the imaging lens cannot be satisfied.

In the imaging elements 105 having the configurations A, B, and C, the focal length of the first lens at the e-line (546.07 nm) is fL1, the Abbe number of the first lens is ν1, and the reference wavelength is at the e-line (546.07 nm). When the focal length is f2, it is preferable to satisfy the condition of the following formula (6) (Configuration D).
31.0 <fL1 × ν1 / f2 <37.0 (6)

  The condition for satisfying the conditions of the configurations A, B, and C, further satisfying the image processing performance and read image quality, and reducing the cost of the imaging lens is the conditional expression (6). If the value falls below the lower limit of the expression (6), the power of the first lens becomes too strong, so the coma flare increases and the axial chromatic aberration becomes too large. It is too far from the imaging position. On the other hand, when the upper limit is exceeded, the power of the first lens becomes too loose, the entire lens becomes large, and it becomes impossible to achieve cost reduction and size reduction.

The imaging element 105 is a glass lens, and the glass material does not contain a harmful substance such as lead or arsenic (Configuration E). All lenses are made of optical glass that is chemically stable and does not contain harmful substances such as lead and arsenic, so that materials can be recycled and there is no water pollution due to waste liquid during processing, saving resources and processing. It is possible to reduce CO _{2 and the} like that are sometimes generated, and to obtain a small and low-cost reading lens in consideration of the global environment.

  In addition, it is preferable that the imaging elements having the configurations B, C, D, and E are all formed of spherical surfaces, which is a reading lens. Currently, aspherical lenses are used in digital cameras and the like. However, if the outer diameter of the aspherical lens is increased, it takes time for molding, and the processing cost increases and the surface shape cannot be kept good. Therefore, the reading lens according to the present invention can be a lens having a good workability and surface shape accuracy without any size limitation by constituting all surfaces with spherical surfaces.

Examples of the image reading apparatus according to the present invention will be described below. Here, the configuration and specifications of the reading lens that is the imaging element 105 were changed, and the optical characteristics were verified.
Further, as shown in FIG. 10, the reading lens is arranged on the optical axis from the object side with the first lens L1, the second lens L2, the aperture I, the third lens L3, and the fourth lens. The radius of curvature of the i-th lens surface counted from ri, the surface interval on the optical axis between the i-th and i + 1-th lens surfaces di, and the material of the j-th lens counted from the object side The refractive index and Abbe number are nj and νj, respectively (specifically, the refractive indexes for the d-line, e-line, F-line, and C-line are ndj, nej, nFj, and nCj, respectively). Note that i = 5 for the diaphragm I provided between the second lens L2 and the third lens L3. For the contact glass 101 and the CCD cover glass 106c of the line sensor unit 106 in the image reading apparatus, the radius of curvature of the i-th glass plate surface counted from the object side is rci, and the i-th and i + 1-th glass plate surfaces. The distance between the surfaces on the optical axis is dci, the refractive index and Abbe number of the glass plate material of the contact glass 101 are nc1 and νc1, respectively (specifically, the refractive indices for the d-line, e-line, F-line, and C-line) , Ndc1, nec1, nFc1, and nCc1), and the refractive index and Abbe number of the glass plate material of the CCD cover glass 106c are nc3 and νc3, respectively (specifically, d line, e line, F line, and C line) As the refractive indices of ndc3, nec3, nFc3, and nCc3).

The meanings of symbols in each example are as follows.
f: Composite focal length FNo of entire system FNo: F number m: Reduction ratio ω: Half angle of view (degrees)
Y: object height ri (i = 1-9): radius of curvature of i-th lens surface counted from the object side di (i = 1-8): i-th surface interval nj (j = 1) counted from the object side 4): Refractive index νj (j = 1 to 4) of the material of the j-th lens counted from the object side: Abbe number rc1 of the material of the j-th lens counted from the object side: Curvature of the contact glass on the object side Radius rc2: curvature radius rc3 on the image side of the contact glass rc4 radius of curvature rc4 on the object side of the CCD cover glass: curvature radius dc1 on the image side of the CCD cover glass: thickness dc3 of the contact glass: nc1 thickness of the CCD cover glass: CCD cover glass refractive index nc3: Contact glass refractive index νc1: Contact glass Abbe number νc3: CCD cover glass Abbe number nd: d-line (587.56 nm) refractive index ne: e-line (546.07 nm) refractive index nF: F Refractive index of line (486.13nm) nC: Refractive index of C line (656.27nm)

(Examples 1-5)
FIG. 11 (Example 1), FIG. 13 (Example 2), FIG. 15 (Example 3), FIG. 17 (Example 4), and FIG. Shown in 5). Tables 1 to 5 show the specifications of the reading lenses and the names of the used glasses in the order of Examples 1 to 5. These aberration diagrams are shown in FIG. 12 (Example 1), FIG. 14 (Example 2), FIG. 16 (Example 3), FIG. 18 (Example 4), and FIG. 20 (Example 5). In the aberration diagrams, e, F, and C are related to the e-line (546.07 nm), the F-line (486.13 nm), and the C-line (656.27 nm), respectively. In the spherical aberration diagram, the wavy line indicates the sine condition, and in the astigmatism graph, the solid line indicates the sagittal ray and the dotted line indicates the meridional ray.

(Conventional example)
For comparison, a conventional example of a Gauss type with four groups and six elements was examined.
FIG. 21 shows the configuration (schematic shape and arrangement relationship) of the reading lens, and Table 6 shows the specifications of the reading lens and the material name of the glass used. The symbol is the same as in the embodiment, but only the surface number is increased by the difference in the number of components. FIG. 22 shows aberration diagrams of the conventional example. The notation in this aberration diagram is the same as in the example.

  Here, in Examples 1 to 5 and the conventional example, the distance Bf1 from the rear end of the imaging element of the F line to the imaging position, the distance Bf2 from the rear end of the imaging element of the e line to the imaging position, and the C line Table 7 shows the distance Bf3 from the rear end of the imaging element to the imaging position, the focal length f1 of the F line, the focal length f2 of the e line, and the focal length f3 of the C line. Table 8 shows values of the expressions (1), (2), and (3) obtained using the values in Table 7.

  Table 9 shows values of the expressions (4), (5), and (6) in Examples 1 to 5 and the conventional example.

As is apparent from the values of the conditional expressions (Tables 8 and 9) and the aberration diagrams (FIGS. 12, 14, 16, 18, 20, and 22), this embodiment is compared with the conventional example. In this case, the chromatic aberration on the axis of the C line (656.27 nm) corresponding to the R signal is increased. As a result, the distance from the rear end (final surface of the imaging lens) of the imaging element to the light receiving element in the actual use state. The difference with respect to the e-line (546.07 nm) corresponding to the G signal having a reference wavelength is large. However, in the present invention, since the R signal is not used to detect the halftone dot of the image area separation process, there is no influence on the image area separation performance.
Focusing on other aberrations, although the half angle of view exceeds 19 degrees, distortion is suppressed to as small as about ± 0.1%, and field curvature, particularly sagittal field curvature, is extremely low. Despite being small and coma has a large aperture of F4.2, the flare component is corrected well and has the same performance as the conventional example. It can be seen that it has excellent performance. Further, the chromatic aberration of magnification is suppressed to be smaller than that of the conventional example, although the axial chromatic aberration is large, and the pixel shift for each color in the final image hardly occurs.

  Although the present invention has been described with the embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. Can be changed within the range that can be conceived, and any embodiment is included in the scope of the present invention as long as the effects and advantages of the present invention are exhibited.

1 is a configuration diagram of a digital full-color copying machine that is an aspect of an image forming apparatus according to the present invention. FIG. It is sectional drawing which shows the structure (1) of the scanner which is an image reading apparatus which concerns on this invention. It is an example of an output of a line sensor unit. It is sectional drawing which shows the structure (2) of the scanner which is an image reading apparatus which concerns on this invention. FIG. 2 is a block diagram showing a schematic configuration of an image processing system in the digital full-color copying machine of FIG. 1. FIG. 6 is a block diagram illustrating an internal structure of a scanner correction unit in the image processing system illustrated in FIG. 5. FIG. 7 is a block diagram showing an internal structure of an image area separation unit in the scanner correction unit shown in FIG. 6. It is a block diagram which shows the internal structure of the halftone dot separation part in the image area separation part shown in FIG. It is a figure which shows the spectral reflection characteristic of the general ink used for original printing. It is the schematic which shows the lens structure of the image formation element in an Example. FIG. 3 is a diagram illustrating a schematic shape and an arrangement relationship of lenses of the imaging element according to the first embodiment. FIG. 3 is an aberration curve diagram of Example 1. 6 is a diagram illustrating a schematic shape and an arrangement relationship of lenses of an imaging element according to Embodiment 2. FIG. FIG. 6 is an aberration curve diagram of Example 2. 6 is a diagram illustrating a schematic shape and an arrangement relationship of lenses of an imaging element according to Embodiment 3. FIG. FIG. 6 is an aberration curve diagram of Example 3. 6 is a diagram illustrating a schematic shape and an arrangement relationship of lenses of an imaging element according to Embodiment 4. FIG. FIG. 6 is an aberration curve diagram of Example 4. FIG. 10 is a diagram illustrating a schematic shape and an arrangement relationship of lenses of an imaging element according to a fifth embodiment. FIG. 6 is an aberration curve diagram of Example 5. It is a figure which shows schematic shape and arrangement | positioning relationship of the lens of the image formation element of a prior art example. It is an aberration curve figure of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Scanner 2 Scanner correction | amendment part 3 Compression processing part 4 Controller 5 HDD
6 Decompression processing unit 7 Printer correction unit 8 Plotter 9 NIC
DESCRIPTION OF SYMBOLS 11 External PC terminal 21 Scanner gamma correction part 22 Image area separation part 23 Filter processing part 25 Color correction part 27 Scaling processing part 101 Contact glass 102 Original 103,103 '1st traveling body 103a, 104a, 104b Mirror 104,104' Second traveling body 105 Imaging element 106 Line sensor unit 106R, 106G, 106B Line sensor 106c CCD cover glass 107 Illumination optical system 108 Integrated unit 221 Filter unit 222 White area extraction unit 223 Halftone separation unit 224 Edge extraction unit 225 Network Point edge extraction unit 226 Color determination unit 227 General determination unit 1100 Photoconductor 1110 Charging roller 1130 Development device 1140 Transfer belt 114A Transfer potential application roller 114B Transfer roller 1150 Cleaning device 1160 Fixing device 1 170 Optical scanning device 1180 Cassette 1190 Registration roller pair 1200 Image processing unit 1210 Tray 1220 Paper feed roller 2231 First halftone peak detection unit 2232 Second halftone peak detection unit 2234 Peak signal generation unit 2236 Halftone dot region detection unit 2238 Halftone dot Comprehensive judgment part I Aperture L1, L2, L3, L4, L5, L6 Lens S Recording medium

Claims (12)

An illumination system that irradiates an original with illumination light, an imaging element that forms an image of light (reflected light) reflected from the original by the illumination light, and photoelectrically converts the light imaged by the imaging element into an electrical signal of the original image In an image reading apparatus having a light receiving element for conversion and an image processing unit for performing image processing for determining document information of a target area of the document using an electrical signal of the document image,
In the optical path of the imaging optical system using the illumination system or the imaging element, the illumination light or the reflected light is a first wavelength region of blue light wavelength region , a second wavelength region . The imaging element includes color separation means for color-separating into light of three types of wavelength regions, a wavelength region of green light and a wavelength region of red light which is the third wavelength region , and the imaging element satisfies the following expression (1) With optical properties
The light receiving element photoelectrically converts each light in the wavelength region color-separated by the color separation means into an electrical signal of an original image, and the image processing unit emits light in the first wavelength region of the electrical signal of the original image. Image processing for determining whether the document information is a halftone dot region using a signal based on the first color signal (first color signal) and a signal based on the second wavelength region (second color signal). A characteristic image reading apparatus.
| Bf1-Bf2 | <| Bf3-Bf2 | (1) (however,
Bf1: distance from the rear end of the imaging element to the imaging position for light of an arbitrary wavelength in the first wavelength region, Bf2: imaging element for light of an arbitrary wavelength in the second wavelength region Bf3: distance from the rear end of the imaging element to the imaging position for light of an arbitrary wavelength in the third wavelength region. ) The image reading apparatus according to claim 1 ,
The image reading device, wherein the image forming element is an image forming lens for forming a reduced image of an original image. The image reading apparatus according to claim 2 .
An image reading apparatus characterized in that a focal length of the imaging element satisfies the following expressions (2) and (3).
| F1-f2 | <| f3-f2 | (2) Equation 0.003 <| f3-f2 | / f2 <0.0045 (3) (however,
f1: Focal length at F line (486.13 nm)
f2: Focal length at reference wavelength e-line (546.07 nm)
f3: focal length at C line (656.27 nm). ) The image reading apparatus according to claim 3 .
The imaging element includes a first lens having a positive power, a second lens having a negative power, a third lens having a positive power, and a fourth lens having a negative power in order from the document side. Image reading device. The image reading apparatus according to claim 4 .
The first lens is a meniscus lens with a convex surface facing the object side, the second lens is a biconcave lens, the third lens is a biconvex lens, and the fourth lens is a meniscus lens with a concave surface facing the document side,
The image reading device, wherein the imaging element has a stop between the second lens and the third lens. The image reading apparatus according to claim 4 or 5 ,
The image reading device is characterized in that the imaging element satisfies the following expressions (4) and (5).
0.05 <n convex-n concave <0.25 (4) Formula 25.0 <ν convex-ν concave <36.5 (5) (However,
n-convex: the total refractive index of the positive lens (first lens, third lens) at d-line (587.56 nm),
n-concave: the total refractive index of d-line (587.56 nm) of the negative lens (second lens, fourth lens),
ν-convex: the sum of the Abbe numbers in the d-line (587.56 nm) of the positive lens (first lens, third lens),
v-concave: Total of Abbe numbers of d-line (587.56 nm) of negative lenses (second lens and fourth lens). ) The image reading apparatus according to any one of claims 4 to 6 ,
The image forming device satisfies the following expression (6).
31.0 <fL1 × ν1 / f2 <37.0 (6) (however,
fL1: focal length of the first lens at the e-line (546.07 nm),
ν1: Abbe number of the first lens,
f2: focal length at reference wavelength e-line (546.07 nm). ) The image reading apparatus according to any one of claims 3 to 7 ,
The image reading device, wherein the imaging element is a lens made of a glass material not containing a harmful substance. The image reading apparatus according to any one of claims 3 to 8 ,
An image reading apparatus characterized in that all of the imaging elements are formed of spherical surfaces. A means for reading a document image in full color and outputting an image signal includes the image reading apparatus according to any one of claims 1 to 9 , and writing an image corresponding to the image signal to form an image. An image forming apparatus. The image forming apparatus according to claim 10 .
An image forming apparatus, wherein an image corresponding to the image signal is written by optical writing. The image forming apparatus according to claim 11 .
An image forming apparatus, wherein an electrostatic latent image corresponding to an image to be formed is formed on a photoconductive photosensitive member by optical writing.

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