JP5020904B2 - Image reading apparatus, control method therefor, and image forming apparatus - Google Patents

Description

  One embodiment according to the present invention relates to an image reading apparatus, a control method thereof, and an image forming apparatus. This apparatus is preferably applied to an image reading apparatus that optically reads a document with a scanner, and is also preferably applied to a digital copying machine that forms an image based on the read image data.

  Conventionally, a three-line CCD sensor composed of three lines of RED, GREEN, and BLUE has been employed for color image reading. In the 3-line CCD sensor, RED, GREEN, and BLUE color filters are arranged on the light receiving surfaces of the three line sensors. And it is the structure by which the three line sensors were arranged in parallel.

  In the 3-line CCD sensor, all the line sensors cannot simultaneously read the same portion of the document. For this reason, the positional deviation between the lines in the document scanning direction is compensated by a memory circuit constituted by a line memory or the like. That is, the time alignment of the image signals read by the respective line sensors is performed using the memory circuit.

  Recently, a 4-line CCD sensor has also been commercialized. The 4-line CCD sensor has a monochrome reading line sensor for reading monochrome images in addition to the 3-line CCD sensor. This monochrome reading line sensor has no color filter on the light receiving surface. There are Patent Documents 1 to 3 as documents showing technologies related to the CCD sensor.

  Also in this 4-line CCD sensor, it has been proposed to change the light receiving area of a pixel with a line sensor for monochrome reading and three line sensors for color reading, and read a monochrome original with high resolution and a color original with high sensitivity. .

  By the way, in the conventional image reading apparatus, it is necessary to read the entire document, store the image data in a storage portion such as a page memory, and determine the character area and the photographic area from the entire image. This is because it is necessary to set appropriate characteristics according to the character area and the photograph area when performing image processing.

  When the entire document is read and the image data is temporarily stored in the page memory, a large-capacity page memory is required and time is required. For example, when the paper A4 is set to a resolution of 600 dpi and a single original as the paper A4 is read, a capacity of about 35 Mbytes for monochrome and three times that of 105 Mbytes for color is required. Furthermore, a work area for determining whether an image is a character or a photograph based on the area is necessary.

As described above, a large-capacity memory is also required for reading one original and storing image data. Accordingly, Nto1 for printing a plurality of document images on one sheet, for example, when printing four images on one sheet, it is necessary to store a plurality of document images such as 4to1 (Nto1). There is a need for a memory with a larger capacity.
JP2004-272840 JP2004-180196 JP2003-274115

  An object of one embodiment of the present invention is to provide an image reading apparatus, a control method therefor, and an image forming apparatus capable of determining image characteristics in a read image during image reading on a document.

In the present embodiment, first, second, and third line sensors of red, green, and blue for reading a document image;
The first, the number of pixels is more than the second and third line sensor, wherein the original image first, and a fourth line sensor for monochrome reading before the second and third line sensors, the character portion processing A non-character portion processing unit, an image processing unit that processes and outputs an image signal obtained by synthesizing read signals from the first to fourth line sensors, and an output of the fourth line sensor. And determining a spatial frequency of the document image, and a processing characteristic control unit that controls processing characteristics of the edge enhancement processing of the character part processing unit and the filter processing of the non-character part processing unit according to the determination result, Have.

  By using the above-described apparatus, it is possible to detect in advance whether the information described in the document is a line drawing or a halftone image, so that processing corresponding to each image information can be easily performed. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an image input apparatus using a CCD line sensor.

  The scanner that is an image input device includes a first carriage 4, a second carriage 7, a condenser lens 8, a CCD sensor substrate 10, a control substrate 11, a white reference plate 13, a document glass 14, a document pressing cover 15, and a scanner housing. It has a body 16.

  The first carriage 4 includes a light source 1, a reflector 2 that corrects light distribution characteristics of the light source 1, and a first mirror 3. The second carriage 7 has a second mirror 5 and a third mirror 6. The CCD line sensor 9 is mounted on the CCD sensor substrate 10. A circuit for controlling the 4-line CCD sensor 9 and various processes is mounted on the control board 11. The white reference plate 13 is used as a white reference. A document org is placed on the document glass 14, and a document pressing cover 15 holds the document org so that it does not float.

  This apparatus focuses on the 4-line CCD sensor 9 and the control board 11. First, the schematic operation of the scanner will be described with reference to FIG.

  The light emitted from the light source 1 passes through the original glass 14 and is applied to the original org. In addition, the light distribution from the light source 1 is not uniform, and uneven light distribution occurs in the illuminance on the document org. Therefore, the document org is also irradiated with the reflected light from the reflector 2, so that the document The light distribution on org is uniform.

  Reflected light from the document org is reflected by the first mirror 3, the second mirror 5, and the third mirror 6, passes through the condenser lens 8, and forms an image on the light receiving surface of the CCD line sensor 9. The 4-line CCD sensor 9 is mounted on the CCD sensor substrate 10 and is controlled by a control signal input from the control substrate 11. The control board 11 and the CCD sensor board 10 are connected by a harness 12. Details of the control board 11 will be described later with reference to FIG.

  The document pressing cover 15 presses the document org placed on the document glass 14 so that the reading surface of the document org is in close contact with the document glass 14.

  Details of the configuration of the 4-line CCD sensor 9 will be described with reference to FIG. The analog signal output from the 4-line CCD sensor 9 has high frequency distortion due to variation in conversion efficiency of each photoelectric conversion unit and low frequency distortion composed of aberration caused by the reduction optical system using the condenser lens 8. Contains. For this reason, reference data is required for normalization correction of the analog signal. In FIG. 1, the reference data is image data when the white reference plate 13 is read.

  The configuration of the control board 11 will be described with reference to FIG. The control board 11 includes a processing IC 11A that performs various processes, a timing generation circuit 11B that generates various timings, an analog processing circuit 11C, an image processing circuit unit 11E, a line memory circuit 11D, a data bus, and an address bus.

  The timing generation circuit 11B generates various timings. The analog processing circuit 11C processes an analog signal from the CCD line sensor 9, and performs processing until the analog signal is converted into a digital signal. The image processing circuit unit 11E performs shading correction for correcting the above-described high-frequency and low-frequency distortion, and time correction processing for correcting line position deviation between a plurality of line sensors, with respect to the digital signal output from the analog processing circuit 11C. And so on. The line memory circuit 11D is a circuit for delaying image data in units of lines when the image processing circuit unit 11E performs the time correction process.

  Further, the processing IC 11A controls the CCD sensor control circuit 10A mounted on the CCD sensor substrate 10 and the light source control circuit 16 for controlling the light emission of the light source 1, and moves the first carriage 4 and the second carriage 7. The drive system control circuit 17 that controls the motor 18 is also controlled.

  The CCD sensor substrate 10 includes a CCD line sensor 9, a CCD sensor control circuit 10A, and a CCD driver 10B. The CCD driver 10B receives the output of the CCD sensor control circuit 10A and drives the 4-line CCD sensor 9.

  FIG. 3 shows a schematic configuration of the 4-line CCD sensor 9. Incident light is converted into an amount of charge corresponding to the amount of light by photoelectric conversion of a RED photodiode array 9R1 in which a RED color filter (not shown) is arranged on the light receiving surface, and the charge is accumulated in each photodiode. The accumulated charges are transferred to the analog shift register 9R3 through the shift gate 9R2 by the control signal SH1 applied to the shift gate 9R2. The charges transferred to the analog shift register 9R3 sequentially move toward the output AMP9R4 in the subsequent stage by the control signals φ1 and φ2, and are output to the outside from the output AMP9R4. The output signal at that time is OUT1.

  Similarly, the photoelectric conversion of the GREEN photodiode array 9G1 in which a GREEN color filter (not shown) is arranged on the light receiving surface converts the incident light into a charge amount corresponding to the light amount, and charges are accumulated in each photodiode. The accumulated charges are transferred to the analog shift register 9G3 through the shift gate 9G2 by the control signal SH2 applied to the shift gate 9G2. The charges transferred to the analog shift register 9G3 are sequentially moved to the subsequent output AMP9G4 by the control signals φ1 and φ2, and are output to the outside from the output AMP9G4. The output signal at that time is OUT2.

  Similarly, by photoelectric conversion of the BLUE photodiode array 9B1 in which a BLUE color filter (not shown) is arranged on the light receiving surface, incident light is converted into a charge amount corresponding to the light amount, and the charge is accumulated in each photodiode. The accumulated charges are transferred to the analog shift register 9B3 through the shift gate 9B2 by the control signal SH3 applied to the shift gate 9B2. The charges transferred to the analog shift register 9B3 are sequentially moved to the subsequent output AMP9B4 by the control signals φ1 and φ2, and are output to the outside from the output AMP9B4. The output signal at that time is OUT3.

  Similarly, the photoelectric conversion of the BLACK photodiode array 9K1 in which no color filter is arranged on the light receiving surface is converted into an amount of charge corresponding to the amount of incident light, and the charge is accumulated in each photodiode. The odd-numbered pixel of the accumulated charge passes through the shift gate 9K2_O to the analog shift register 9K3_O by the control signal SH4 applied to the shift gate 9K2_O, and the even-numbered pixel shifts by the control signal SH4 applied to the shift gate 9K2_E. It passes through 9K2_E and is transferred to the analog shift register 9K3_E.

  The charges transferred to the analog shift register 9K3_O are sequentially moved to the subsequent output AMP9K4_O by the control signals φ1 and φ2, and are output to the outside from the output AMP9K4_O. The charges transferred to the analog shift register 9K3_E are sequentially moved to the output AMP9K4_E in the subsequent stage by the control signals φ1 and φ2, and are output to the outside from the output AMP9K4_E. The output signals at that time are OUT4 and OUT5, respectively.

  FIG. 4 shows the mutual distances of the RED photodiode array 9R1, the GREEN photodiode array 9G1, the BLUE photodiode array 9B1, and the BLACK photodiode array 9K1.

  The RED photodiode array 9R1 and the GREEN photodiode array 9G1 are arranged at a distance of m times the pixel size (details will be described later). The GREEN photodiode array 9G1 and the BLUE photodiode array 9B1 are arranged at a distance of m times the pixel size.

  The BLUE photodiode array 9B1 and the BLACK photodiode array 9K1 are arranged at a distance of n times the pixel size.

Here, the pixel size of the BLACK photodiode array 9K1 will be described. When reading a 297 mm width which is the longitudinal direction of A4 size at a resolution of 600 dpi,
(600 dpi / 25.4 mm) × 297 mm = 7015.7, and at least 7016 or more pixels are required. Considering the mounting error of the CCD line sensor 9 and the deviation of the place where the document org is placed, the number of pixels of 7016 + α is necessary. Therefore, here, the number of pixels of the BLACK photodiode array 9K1 is 7500 pixels.

  When this pixel size is accommodated in a chip having a size of 35 mm, the pixel pitch is 4.7 μm (4.7 μm × 7500 pixels = 35.25 mm). Since this size varies depending on the optical magnification of the reduction optical system, if the pixel pitch is 7 μm, the chip size is 52.5 mm.

  In this embodiment, the description will be made assuming that the pixel pitch of the BLACK photodiode array 9K1 is 4.7 μm.

  The number of pixels of the RED photodiode array 9R1, the GREEN photodiode array 9G1, and the BLUE photodiode array 9B1 is 3750 pixels (half the number of 7500 pixels that is the number of pixels of the BLACK photodiode array 9K1).

  FIG. 5 is an explanatory diagram of the reading positions of the 4-line CCD sensor 9 and the document org.

  The inside of the CCD line sensor 9 is composed of four line sensors as shown in FIG. The scanner is a reduction optical system using a condenser lens 8. Therefore, as shown in FIG. 5, the CCD line sensor 9 is arranged so that the BLACK photodiode array 9K1 is close to the original platen glass 14 and comes upward in the explanatory view. With this arrangement, an image is read in the order of BLACK (BK), BLUE (BL), GREEN (GR), and RED (RE) line sensors on the document surface from the right. The interval between the reading positions is determined by the arrangement of the photodiode arrays shown in FIG. 4 and the optical magnification.

  The interval between the RED photodiode array 9R1 and the GREEN photodiode array 9G1 in FIG. 4 is m times the pixel size of the BLACK photodiode array 9K1. Therefore, in order to read a document with a resolution of 600 dpi with the BLACK photodiode array 9K1, the optical line size is adjusted to be 42.3 μm × 42.3 μm on the document surface. 42.3 μm, N line = n × 42.3 μm.

  FIG. 6 is an explanatory view of the image reading apparatus shown in FIG. 1 as viewed from above. The original org placed on the original platen glass 14 scans the original org by the first carriage 4 being moved in the reading direction by a drive system (not shown), and sequentially reads information on the original org. In this case, since the document org is placed face down, the image information is written on the back side as shown. The reflected light from the original org is imaged on the 4-line CCD sensor 9 through the condenser lens 8 as described with reference to FIG. 1 and converted into an electrical signal, and the control board 11 through the CCD board 10 and harness 12 (not shown). Processed above.

  The condensing lens 8, the 4-line CCD sensor 9, the CCD substrate 10, the control substrate 11, and the harness 12 are sealed with a dust-proof cover member 21 to prevent foreign matters such as dust from adhering.

  In the above-described apparatus, the BLACK photodiode array 9K1 having a large number of pixels of the 4-line CCD sensor 9 can read the document first as compared with the other line sensors. For this reason, the spatial frequency of the information described in the document org is detected from the read result, and it is detected whether the described information is information such as a character line or information with continuous density change such as a photograph. Thus, it is possible to switch the subsequent processing.

  A specific example will be shown and described with reference to FIG. FIG. 7 shows the profile of the image signal of the character portion at the top of the document as a result of reading with the configuration of FIG. The horizontal axis of the profile is document position information, and the vertical axis is luminance information. In this case, the vertical axis is 0 for black (dark part) and 255 for white (bright part). The horizontal axis indicates the position from the left to the right of the character portion 31 of the document org.

  As is apparent from the figure, in the case of a line drawing such as a character, the reflectance of the background and the line drawing information changes abruptly, resulting in a high frequency profile with a steep slope of the change point of the image signal as shown in the figure. When the background is not white, the vertical axis of the profile is smaller than 255, and when the line drawing part is not black, the line drawing part is larger than 0, but the profile change point is the boundary between the background and the line drawing part. Since the slope of is steep, it can be determined that the portion is composed of line drawings such as characters. When this determination is made, for the purpose of making the line drawing portion easy to see, edge enhancement processing for emphasizing the change point of the image, range correction for widening the density difference between the background and the character portion, and the like are performed.

  With reference to FIG. 8, an example in which the read image is not a line drawing but a halftone will be described. When the image data of the photographic part 32 at the bottom of the document is enlarged, it becomes like (partial enlargement) in the figure. In fact, since the image is read by the BLACK photodiode array 9K1 that does not have a filter that cuts off a specific wavelength on the light receiving surface, luminance information that is an electrical signal proportional to the amount of reflected light having a wavelength from about 400 nm to about 800 nm, and Become. In the profile, the vertical axis is luminance information. On the vertical axis, 0 is black (dark part) and 255 is white (bright part). The horizontal axis indicates the position from the left to the right of the character portion 31 of the document org.

  In the profile of the luminance information, as shown in FIG. 7, the change point is not steep, and continuously changes gently or has a shape with a small change amount. From such characteristics, it can be determined that the read image information is not a line drawing but a photographic part composed of halftones or continuous density changes. When this determination is made, averaging processing, low-pass filter processing for removing high-frequency components, and the like are performed for the purpose of reducing pseudo contours due to insufficient number of gradations and unnatural line images due to over-emphasis of edges.

  These processes are performed with the output read in advance by the BLACK photodiode array 9K1, and can be reflected in the outputs of the other photodiode arrays of RED, GREEN, and BLUE.

  The processing operation will be described with reference to FIG. The read image signal (image signal in) is a signal including K which is monochrome information and RGB which is a color signal. Each signal shown here is a signal after normalization by shading correction processing and correction between RGB lines. Further, in the output from the 4-line CCD sensor 9, the monochrome signal has a resolution of 600 dpi and the color signal has a resolution of 300 dpi. However, the color signal reading resolution may be converted from 300 dpi to 600 dpi using the monochrome signal. In this description, a color signal having a resolution of 600 dpi after resolution conversion is described.

  The image signal in is input to the processing characteristic control unit 46 and the image signal processing unit 47. In the processing characteristic control unit 46, the monochrome signal K of the image signal in is input to the spatial frequency determination unit 41, where the spatial frequency of the image information described in FIGS. 7 and 8 is detected, and the determination signal JUD is detected. Is output. The determination signal JUD is input to the character area calculation unit 42. The character area calculation unit 42 uses the determination signal JUD to calculate which part of the read image is a character area and which part of the read image is a non-character area composed of a photograph or the like. To do. This calculation result is used in the image processing unit 47 as a control signal for controlling the processing characteristics of the image signal read by at least the first line sensor.

  The area calculation unit 42 may convert the image area into coordinates. For example, in the case of an A4 size document, if the document is placed on the document table glass 14 as shown in FIG. 6, the document coordinates in the main scanning direction are 1250 to 6250 (A4: 210 mm = corresponding to 5000 pixels), and the sub-scanning direction The document coordinates are 0 to 7020 (A4: 297 mm = corresponding to 7020 pixels). If the main scanning direction is defined as X and the sub-scanning direction is defined as Y, the character area (X, Y) = (1500, 100), (6000, 100), (1500, 3000), (6000, 3000), non- For the character area (X, Y), the coordinates of the vertices of each area can be calculated as (1700, 3100), (5000, 3100), (1700, 6000), (5000, 6000).

  In this apparatus, since the difference in reading position between the BLACK photodiode array 9K1 and the BLUE photodiode 9B1 is N lines, the feature of the region can be determined in real time by setting the determination range in the sub-scanning direction to N at the maximum. it can.

  When the character area is determined, the CHA signal is input to the character processing unit 43 that performs edge enhancement processing and range correction processing, and the color signal RGB is processed. The PIC signal is input to the non-character part processing unit 44 that performs processing, and the color signals RGB are processed. The color image signals RGB from the character part processing unit 43 and the non-character part processing unit 44 are synthesized by the synthesis unit 45 in the subsequent stage. Is done.

  In addition, a region where there is no density change as in the background and becomes a uniform luminance signal is output via either the character part processing unit 43 or the non-character part processing unit 44 (which has no density change, It does not change even if the processing unit is performed).

  The above character part, non-character part, and background part are combined by the subsequent combining unit and output to the subsequent processing as image information.

  Further, information indicating the processing status of the processing characteristic control unit 46 may be input to the system control unit 13. The system control unit 13 may use the information indicating the processing status to display on the display unit 27a of the control panel 27 during processing of the character area, processing of the image area, and the like. For example, as the current setting state, the second line sensor may read a document image in advance, and the result may indicate a mode in which processing characteristics are controlled.

  With reference to FIG. 10A, FIG. 10B, and FIG. 10C, description will be made regarding the memory capacity necessary for adjusting the time between lines when an image is read in the above reading direction. For convenience of explanation, it is assumed that the interval between the photodiode arrays is m = 4 and n = 6.

  As is apparent from FIGS. 10A and 10B, when the BLACK photodiode array 9K1 is pre-read, a memory capacity of 160 kBytes is required to align all positions of the RED information, the GREEN information, the BLUE information, and the BLACK information. For reference, if the color signal is handled as it is at 300 dpi, it becomes 48 kBytes (see FIG. 10C) because alignment with BLACK becomes unnecessary. However, when a color image is handled as a copy, the resolution is insufficient at 300 dpi, leading to image quality degradation. there is a possibility.

  FIG. 11A is an explanatory diagram of the document transport mechanism, and FIG. 11B is a description of the document reading direction. In the previous embodiment, the image of the original org is read by moving the first carriage 4. However, a scanner that reads a document image by moving the document org may be used. As shown in FIG. 11A, the original org is conveyed between the rotating roller 51 and, for example, the original glass 52. At this time, the original image of the original org is guided to the 4-line CCD sensor 9 through the mirrors 3, 5, 6 and the condenser lens 8.

  In this case, since the BLACK photodiode array 9K1 prefetches the original, the same processing as in the previous embodiment can be performed.

  FIG. 12 is a schematic diagram of a digital copying machine using the image reading apparatus shown in FIG. The digital copying machine includes a scanner unit A, which is the image reading apparatus described with reference to FIG. 1, and a printer unit B that forms an image on paper.

  The normalized image signal output from the image processing circuit unit 11E shown in FIG. 1 in the scanner unit A is input to the image processing unit. In this part, the image signal is stored in a temporary recording unit such as a page memory (not shown), enlarged / reduced, or YELLOW, which is a format in which the image signal that is a BLUE, GREEN, RED component is in image formation. It is converted into four colors, MAGENTA, CYAN, and BLACK. The image signal converted into the four-color component image signal is converted into a semiconductor laser control signal in the subsequent laser optical system 15 and input to the laser optical system 15.

  The image forming unit 16 includes a photosensitive drum 17, a charger 18, a developing device 19, a transfer charger 20, a peeling charger 21, a cleaner 22, a paper transport mechanism 23, a fixing device 24, a paper discharge roller 25, and the like. Is transported by the paper transport mechanism 23 and discharged to the paper discharge tray 26 through each step. Since the configuration and method of the image forming apparatus 16 is a general electrophotographic method, detailed description thereof is omitted.

  Further, recently, since the transfer efficiency of the developer onto the paper P has been improved, there is a case where the cleaner 22 is not provided.

  FIG. 13 shows a schematic configuration of a digital copying machine viewed from an electrical configuration. The system control unit 13 is a part that totally controls the system, and controls the scanner unit A, the image processing unit 14, and the printer unit B, and includes an I / F that transmits and receives data to and from the outside via a network. .

  An image signal output from the scanner unit A is input to the image processing unit 14, performs various processes in the image processing unit 14, and is input to the printer unit B. When the original org is read for the purpose of copying, the process is performed as described above. When the original org is read for the purpose of filing, the image signal output from the scanner unit A is sent to the external client via the system control unit 13 via the network. The compressed image signal is transferred to the PC.

  Whether the copying process or the filing process is set by a user input through the control panel 27.

  When the image reading apparatus shown in FIG. 1 is used in a single color image forming apparatus, it is possible to convert a color signal into a monochrome signal after performing the processing described with reference to FIG. When the image reading apparatus of FIG. 1 is used as a color scanner connected to a network, the system control unit converts it into a desired file format, for example, JPEG, TIFF, PDF, etc. after the processing of FIG. A color image file can be transferred to an external client PC.

  In this explanation, the structure of single color copying as shown in FIG. 11 is described in the image forming apparatus section. However, the developing device 19 is a color (multiple color) copying having four colors of YELLOW, MAGENTA, CYAN, and BLACK. Needless to say, it is used. The present invention is basically an apparatus having a first line sensor and a second line sensor that has a higher resolution than the first line sensor and reads a document image in advance of the first line sensor. If applicable, it is applicable. In the above description, it has been described that there are m lines and n lines as the distance between the lines, but the distance between the lines may be the same.

  By using the above-described apparatus, it is possible to detect in advance whether the information described in the document is a line drawing or a halftone image, so that processing corresponding to each image information can be easily performed. be able to.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

FIG. 1 is a diagram showing a schematic configuration of an image reading apparatus using a CCD line sensor. FIG. 2 is a diagram illustrating a schematic configuration of a control system of the image reading apparatus. FIG. 3 is a diagram showing a schematic configuration of a 4-line CCD sensor. FIG. 4 is an explanatory diagram of the line-to-line distance of the 4-line CCD sensor. FIG. 5 is a diagram for explaining the positional relationship between the image reading position on the document surface and each line sensor. FIG. 6 is a diagram illustrating an outline when the image reading apparatus is viewed from above. FIG. 7 is a diagram for explaining an image data profile when a character portion of a document is read. FIG. 8 is a diagram for explaining an image data profile when a photographic part of a document is read. FIG. 9 is a diagram illustrating a configuration example of an image processing unit that performs processing for each area of a character part and a non-character part. It is explanatory drawing which shows the time between lines when a monochrome line sensor reads ahead. It is explanatory drawing of the capacity | capacitance of the line memory required in order to time-adjust the information previously read by the monochrome line sensor between lines. Similarly, it is an explanatory diagram of a capacity of a line memory necessary for time-adjusting information pre-read by a monochrome line sensor between lines. FIG. FIG. 11A is an explanatory diagram of the document transport mechanism. FIG. 11B is an explanatory diagram of a document transport direction by the document transport mechanism. FIG. 12 is a diagram illustrating a schematic configuration example of a mechanism unit of the image forming apparatus. FIG. 13 is a schematic configuration example of functional blocks of the image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source 3, 5, 6 ... Mirror, 8 ... Optical lens, 9 ... CCD line sensor, 10 ... CCD sensor board, 11 ... Control board, 12 ... Harness, 11A ... Processing IC, 11B ... Timing generation circuit, 11C ... Analog processing circuit, 11E ... Image processing circuit, 11D ... Line memory circuit, 10A ... CCD sensor control circuit, 10B ... CCD driver, 9R1 ... RED photodiode array, 9G1 ... GREEN photodiode array, 9B1 ... BLUE photodiode array, 9K1 ... BLACK photodiode array.

Claims (5)

First, second and third line sensors of red, green and blue for reading an original image;
A monochrome fourth line sensor that has a larger number of pixels than the first, second, and third line sensors and reads the original image before the first, second, and third line sensors;
An image processing unit having a character part processing unit and a non-character part processing unit, and processing and outputting an image signal obtained by synthesizing read signals from the first to fourth line sensors;
The output of the fourth line sensor is used to determine the spatial frequency of the document image, and processing characteristics of edge enhancement processing of the character part processing unit and filter processing of the non-character part processing unit according to the determination result A processing characteristic control unit for controlling
An image reading apparatus. The processing characteristic control unit
A spatial frequency discriminating unit for detecting a spatial frequency of information from the output of the fourth line sensor ;
The image reading apparatus according to claim 1, further comprising an area calculation unit that outputs the control signal that is different in an area having a different detected spatial frequency. First, second and third line sensors of red, green and blue for reading an original image;
A monochrome fourth line sensor having a larger number of pixels than the first, second, and third line sensors and reading the document image before the first, second, and third line sensors;
An image processing unit having a character part processing unit and a non-character part processing unit, and processing and outputting an image signal obtained by synthesizing read signals from the first to fourth line sensors;
The output of the fourth line sensor is used to determine the spatial frequency of the document image, and processing characteristics of edge enhancement processing of the character part processing unit and filter processing of the non-character part processing unit according to the determination result A processing characteristic control unit for controlling
A printer unit to which the output of the image processing unit is supplied;
An image forming apparatus. The first, second, and third line sensors of red, green, and blue that read an original image, and the first, second, and third line sensors have more pixels, and the original image is converted into the first, second, and second line sensors . And a monochrome fourth line sensor to be read before the third line sensor, a character part processing unit and a non-character part processing unit, and synthesizing read signals from the first to fourth line sensors. An image reading apparatus control method comprising: an image processing unit that processes and outputs an image signal; and a processing characteristic control unit that controls processing characteristics of the image processing unit using an output of the fourth line sensor. There,
The processing characteristic control unit determines the spatial frequency of the output of the fourth line sensor ,
According to the determination result of the spatial wave number by the area calculation unit, obtain a different control signal that identifies the character area and the non-character area of the document image,
A control method for an image reading apparatus, wherein processing characteristics of edge enhancement processing of the character part processing unit and filter processing of the non-character part processing unit of the image signal processing unit are controlled by the control signal. The method for controlling the image reading apparatus according to claim 4, wherein an output of the image processing unit is supplied to a printer unit of the image forming apparatus.

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