JP2008236045A - Image processor, image forming apparatus, image processing method, image processing program and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor which interpolates an interpolation image in the gap of a multichip line sensor while keeping the hue of an original image when reading an RGB full-color image, an image forming apparatus, an image processing method, an image processing program and a recording medium. <P>SOLUTION: A gap correction processing part 80 comprising a first signal conversion part for converting RGB signals to luminance / color difference signals or lightness / chrominance signals, an interpolation operation part for performing image interpolation of a gap region in a converted color space and a first signal inverse conversion part for inversely converting the luminance / color difference signals or the lightness / chrominance signals to the RGB signals is used. Since interpolation is performed not to RGB images but after converting signals to an LCaCb space, the interpolation is performed keeping the hue of an input image. Especially, while the change of colors tends to be conspicuous when colored even a little when the input image is an achromatic image, such a phenomenon does not easily occur when the interpolation is performed after performing conversion to the luminance / color different signals in this case. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image processing apparatus, an image forming apparatus, an image processing method, an image processing program, and a recording medium, and in particular, an image processing apparatus that corrects an image read by a multichip line sensor including a plurality of light receiving chips, The present invention relates to an image forming apparatus, an image processing method, an image processing program, and a recording medium.

  2. Description of the Related Art Conventionally, an image reading device that reads image information of a document is used as a reading device such as a copying machine or a facsimile, or an image scanner for computer input. In this type of image reading apparatus, a light source extending in a direction orthogonal to the document conveyance path is used to irradiate the document with light, and reflected light reflected from the irradiated document is received by an image sensor. Reading the image on the manuscript.

  As a conventional document reading method, for example, a method of irradiating a document with light using a xenon lamp as a light source and reading a reflected light from the document with an optical sensor through a reduction optical system has been generally used. For the purpose of downsizing and cost reduction of the device, what is called CIS (Contact Image Sensor) that uses an LED (Light Emitting Diode) as a light source and reads an image with a sensor through a lens, for example, is practical. It has become.

  As a sensor in such a CIS, for example, a so-called multi-chip type image sensor array in which a plurality of sensor chips (light receiving chips) in which a large number of photoelectric conversion sensors are arranged in a straight line is arranged in the sub-scanning direction is widely used. ing. However, in the multi-chip type image sensor array, since there is a gap between adjacent sensor chips, it becomes impossible to read an image of a document in the gap, and image information in this gap is lost. was there.

  In order to solve this problem, an image signal in the gap is obtained by using gap information between adjacent sensor chips and an image signal detected by the photoelectric conversion sensor at the gap side end of two adjacent sensor chips. A technique for interpolation has been proposed (see, for example, Patent Document 1).

  In addition, a technique for correcting the density of image data corresponding to a joint portion of a multi-chip line sensor using a plurality of multi-chip image sensors arranged in a staggered manner has been proposed (for example, Patent Document 2). reference). At the time of interpolation, the correction method is switched depending on whether the corresponding image area is a halftone image.

In addition, as color image processing in a color printer that has become widespread in recent years, RGB signals corresponding to color images are converted into CMY signals having the same attributes as YMCK signals used in the printer unit. After converting the signal into a YUV signal and performing spatial filtering on the YUV signal, the YUV signal is converted into a CMY signal, thereby increasing the accuracy of the color difference signal without increasing costs or reducing the processing speed. An image processing apparatus has been proposed that can realize high-accuracy luminance / color-difference spatial filter processing and improve image quality (see, for example, Patent Document 3).
JP 2000-196835 A JP 2006-67031 A JP 2004-112535 A

  However, among the above-described techniques, the technique of interpolating the image signal in the gap using gap information between adjacent sensor chips mainly assumes monochrome image reading. Alternatively, a signal corresponding to a signal component) is detected. That is, in the interpolation at this time, a signal corresponding to the luminance (or brightness) of the image signal in the gap is predicted from the image signals at both ends of the gap and is interpolated.

  In color image reading consisting of a plurality of line sensors, each of three types of signals, R (red), G (green), and B (blue), is read by a total of three line sensors. The three image data are interpolated independently. However, since the image obtained as a result of interpolation is not interpolation that preserves the color of the document, there is a problem that the color of the document and the color of the interpolated image are greatly different.

  The present invention has been made in view of such circumstances, and when reading RGB full-color images, luminance / color difference (or brightness / chromaticity) signals while taking into account the correlation of R, G, B reading values. It is an object to interpolate an interpolated image in a gap of a multi-chip line sensor while preserving the color of an original image by performing interpolation after dividing the image into two.

  According to the first aspect of the present invention, a plurality of multi-chip line sensors in which a plurality of image reading sensor chips are arranged in a straight line, and the plurality of multi-chip line sensors, at least R (red), G (green), RGB full-color image reading means for reading B (blue) color information; first signal conversion means for converting image data read by the RGB full-color image reading means into luminance / color difference signals or brightness / chromaticity signals; An image processing apparatus comprising: image interpolation means for interpolating image data between the image reading sensor chips constituting the multi-chip line sensor based on a conversion result of the first signal conversion means. .

  According to a second aspect of the present invention, at least R (red), G (green), a plurality of multi-chip line sensors in which a plurality of image reading sensor chips are arranged in a straight line, and the plurality of multi-chip line sensors, RGB full color image reading means for reading B (blue) color information, ink color information conversion means for converting image data read by the RGB full color image reading means into color information of ink used for printing, and the ink color information An image processing apparatus comprising: image interpolating means for interpolating image data between the image reading sensor chips constituting the multi-chip line sensor based on a conversion result of the converting means.

  According to a third aspect of the present invention, in the apparatus according to the second aspect, the ink color information converting means converts the RGB full-color image data input by the RGB full-color image reading means into C (cyan), M (magenta), and Y It is characterized by being converted into a color space represented by three colors (yellow).

  According to a fourth aspect of the present invention, a plurality of multi-chip line sensors in which a plurality of image reading sensor chips are arranged in a straight line, and the plurality of multi-chip line sensors, at least R (red), G (green), RGB full color image reading means for reading B (blue) color information, ink color information conversion means for converting image data read by the RGB full color image reading means into color information of ink used for printing, and the ink color information A second signal converting means for converting the image data output from the converting means into a luminance / color difference signal or a lightness / chromaticity signal, and the multi-chip line sensor based on the conversion result of the second signal converting means. Image interpolating means for interpolating image data between the image reading sensor chips constituting the image processing sensor chip. It is a device.

  Invention of Claim 5 is an image forming apparatus provided with the image processing apparatus of any one of Claim 1 to 4, Comprising: Image formation is performed based on the image data output from the said image processing apparatus, An image forming apparatus comprising image forming means for forming an image by transferring an image formed on a sheet.

  The invention according to claim 6 is an image forming apparatus having the image processing apparatus according to any one of claims 2 to 4, wherein the image forming apparatus performs image formation based on the image data output from the image processing apparatus, An image forming unit that forms an image by transferring the formed image onto a sheet, and a color that converts the image read by the RGB image reading unit into a color space of a transfer material used for transfer of the image forming apparatus An image forming apparatus, wherein the color conversion unit performs color conversion different from that of the ink color information conversion device.

  According to the seventh aspect of the present invention, at least R (red), G (green), and B (blue) color information is read by a plurality of multi-chip line sensors in which a plurality of image reading sensor chips are arranged on a straight line. An image input step by the RGB full-color image reading means, a signal conversion step for converting the RGB full-color image data input in the image input step into a luminance / color difference signal or a brightness / chromaticity signal, and a conversion result of the signal conversion step And an image interpolation step of interpolating image data between the image reading sensor chips constituting the multi-chip line sensor.

  According to the eighth aspect of the present invention, at least R (red), G (green), and B (blue) color information is read by a plurality of multi-chip line sensors in which a plurality of image reading sensor chips are arranged on a straight line. Based on the image input step by the RGB full-color image reading means, the ink color information conversion step for converting the RGB full-color image data input in the image input step into ink color information, and the conversion result of the color information conversion step, An image interpolation step of interpolating image data between the image reading sensor chips constituting the multi-chip line sensor.

  According to the ninth aspect of the invention, in the ink color information conversion step, the RGB full-color image data input in the image input step is expressed in three colors of C (cyan), M (magenta), and Y (yellow). 9. The image processing method according to claim 8, wherein the image processing method is converted into image data.

  According to a tenth aspect of the present invention, at least R (red), G (green), and B (blue) color information is read by a plurality of multi-chip line sensors in which a plurality of image reading sensor chips are arranged on a straight line. An image input step by the RGB full color image reading means, an ink color information conversion step for converting the RGB full color image data input in the image input step into ink color information, and the image data output in the ink color information conversion step. A second signal conversion step for converting to a luminance / color difference signal or a lightness / chromaticity signal, and between the image reading sensor chips constituting the multi-chip line sensor based on a conversion result of the second signal conversion step. And an image interpolation step for interpolating image data. .

  An eleventh aspect of the invention is an image processing program that causes a computer to execute the steps in the image processing method according to any one of the seventh to tenth aspects.

  A twelfth aspect of the present invention is a computer-readable recording medium on which the image processing program according to the eleventh aspect is recorded.

  According to the present invention, by interpolating an RGB full-color image after dividing it into a luminance signal and a chromaticity signal, the interpolated image in the gap of the multichip line sensor is interpolated while preserving the color of the original image. Can do.

  Embodiments according to the present invention will be described below in detail with reference to the drawings. The embodiments described below are preferred embodiments of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention is particularly limited in the following description. As long as there is no description which limits, it is not restricted to these aspects.

  FIG. 1 is a schematic block diagram of a digital full-color image processing apparatus according to this embodiment. With reference to FIG. 1, the flow of processing from reading a document to a copy image will be described below.

  When operating as a full-color copying machine, the image reading unit 1 reads image data that has been color-separated into R (red), G (green), and B (blue) from the document X, and converts the image data (analog signal) into digital data. Convert and output.

  The gap correction processing unit 80 interpolates image data between image reading sensor chips that constitute a multi-chip line sensor that constitutes a part of the image reading unit 1.

  As will be described later, the scanner correction unit 3 performs scanner γ correction processing on the RGB image data (digital data) read by the scanner and classifies the image area into characters, line drawings, patterns, etc. (image area separation). In addition, image processing such as emphasizing the character portion of the image and smoothing the pattern portion is performed to correct the characteristics of the scanner.

  The compression processing unit 4 compresses the multivalued image data after scanner correction, and sends the data to the general-purpose bus 5. The compressed image data is sent to the controller 6 through the general-purpose bus 5.

  The controller 6 has a semiconductor memory (not shown) and accumulates sent data. The accumulated data is written to a hard disk drive (HDD 7) which is a large-capacity storage device as needed. This is because paper is jammed at the time of printout, so that it is possible to avoid re-reading the original even if the output does not end normally, to perform electronic sorting to rearrange multiple original image data, and to store the read original This is to re-output when necessary.

  Although the image data is compressed here, if the bandwidth of the general-purpose bus 5 is sufficiently wide and the capacity of the HDD 7 to be stored is large, the data may be handled in an uncompressed state.

  Next, the controller 6 sends the image data of the HDD 7 to the decompression processing unit 9 via the general-purpose bus 5. The decompression processing unit 9 decompresses the compressed image data to the original multi-value data and sends it to the printer correction unit 81.

  In the printer correction unit 81, printer γ correction processing and gradation processing are performed, and the image by the light diffusion characteristic correction processing or the dithering processing according to the gradation characteristics of the plotter 82 and the gradation characteristics of the plotter 82 and the image area separation result is performed. Data quantization is performed.

  The plotter 82 is a transfer paper printing unit using a laser beam writing process. The plotter 82 draws image data as a latent image on a photoconductor, and forms a copy image on the transfer paper after image formation / transfer processing with toner.

  When operating as a distribution scanner that distributes image data to a PC via a network, a manuscript image is read from the scanner in the same way as when operating as a copier, and from the scanner correction unit 3 through the compression processing unit 4, the controller The image is sent to 6.

  The controller 6 performs format processing. In the format processing, general-purpose image format conversion into JPEG, TIFF, and BMP formats is performed. Thereafter, the image data is distributed to the external PC terminal 83 via the NIC (network interface controller) 8.

  FIG. 2 is a diagram illustrating an example of the image reading unit 1 configuring the image processing apparatus to which the present embodiment is applied. The image reading unit 1 is roughly divided into a document feeding unit 10 that sequentially conveys documents from a stacked document bundle, and a scanner 70 that reads images by scanning.

  The document feeder 10 includes a document tray 11 on which a bundle of documents composed of a plurality of documents is stacked, and a tray lifter 12 that raises and lowers the document tray 11. Further, a nudger roll 13 that conveys the original on the original tray 11 raised by the tray lifter 12, a feed roll 14 that conveys the original conveyed by the nudger roll 13 further downstream, and an original supplied by the nudger roll 13. Are provided with a retard roll 15.

  In the first conveyance path 31 where the original is first conveyed, a take-away roll 16 that conveys the originals that are being fed one by one to the downstream roll, and further conveys the original to the further downstream roll and creates a loop. The pre-registration roll 17 to be performed, the rotation is resumed at the timing after stopping once, the registration roll 18 for supplying the original while adjusting the registration to the original reading unit, the platen roll 19 for assisting the conveyance of the original being read, An out-roll 20 is provided for conveying the read original further downstream. Each of these rolls constitutes a document feeder.

  The first conveyance path 31 as a conveyance path is provided with a baffle 41 that rotates around a fulcrum according to the loop state of the conveyed document. Further, a CIS (Contact Image Sensor) 50 is provided between the platen roll 19 and the out-roll 20. A second transport path 32 and a third transport path 33 are provided on the downstream side of the out-roll 20, a transport path switching gate 42 for switching between these transport paths, a discharge tray 40 for stacking documents that have been read, and a discharge tray A first discharge roll 21 that discharges the original document 40 is provided.

  In addition, an inverter roll 22 and an inverter pinch roll 23 that are provided in the fourth transport path 34 and the fourth transport path 34 for switching back the document that has passed through the third transport path 33 and actually switch back the document, The document switched back by the fourth transport path 34 is guided again to the first transport path 31 including the pre-registration roll 17 and the like, and the document switched back by the fourth transport path 34 is discharged to the discharge tray 40. The transport paths of the second discharge roll 24, the fifth transport path 35, and the sixth transport path 36 that are provided in the sixth transport path 36 and the sixth transport path 36 and transport the reversely discharged document to the first discharge roll 21. An exit switching gate 43 for switching is provided. These third transport path 33, fourth transport path 34, and fifth transport path 35 constitute a reverse transport path.

  The nudger roll 13 is lifted up and held at the retracted position during standby, and descends to the nip position (original conveyance position) during conveyance of the document to convey the uppermost document on the document tray 11. The nudger roll 13 and the feed roll 14 convey a document by connecting a feed clutch (not shown). The pre-registration roll 17 makes a loop by abutting the leading end of the document against the stopped registration roll 18. In the registration roll 18, when the loop is created, the leading edge of the document bitten by the registration roll 18 is returned to the nip position. When this loop is formed, the baffle 41 opens around the fulcrum and functions so as not to disturb the document loop.

  Further, the take away roll 16 and the pre-registration roll 17 hold a loop during reading. By this loop formation, the read timing can be adjusted, and the skew associated with the document conveyance at the time of reading can be suppressed, and the alignment adjustment function can be enhanced. The stopped registration roll 18 starts rotating in accordance with the start timing of reading, and is pressed against the second platen glass 72B (described later) by the platen roll 19 to read the image data from the lower surface direction.

  The conveyance path switching gate 42 switches so that the document passing through the out-roll 20 is guided to the second conveyance path 32 and discharged to the discharge tray 40 at the end of reading one-sided document and at the same time when reading both-side documents simultaneously. It is done. On the other hand, the transport path switching gate 42 is switched so as to guide the document to the third transport path 33 in order to invert the document when the double-sided document is sequentially read.

  The inverter pinch roll 23 is retracted with the feed clutch (not shown) turned off during sequential reading of the double-sided document to open the nip, and guides the document to the inverter path (fourth conveyance path 34). Thereafter, the inverter pinch roll 23 is nipped, the original to be inverted by the inverter roll 22 is guided to the pre-registration roll 17, and the original to be reversed is conveyed to the second discharge roll 24 in the sixth conveyance path 36.

  The scanner 70 can include the above-described document feeding unit 10, supports the document feeding unit 10 with an apparatus frame 71, and reads an image of the document conveyed by the document feeding unit 10. In the scanner 70, a first platen glass 72A for placing a document on which an image is to be read in a stationary state on the apparatus frame 71, and a light opening for reading the document being conveyed by the document feeder 10 are formed. A second platen glass 72B is provided.

  In the present embodiment, the document feeder 10 is attached to the scanner 70 so as to be swingable with the back side as a fulcrum, and when the document is set on the first platen glass 72A, the document feeder 10 is lifted to place a document, and then the document feeder 10 is lowered to the scanner 70 side and pressed.

  The scanner 70 is stationary under the second platen glass 72B, and scans the entire first platen glass 72A to read an image, and the light obtained from the full rate carriage 73 is an image coupling unit. A half-rate carriage 75 is provided.

  The full-rate carriage 73 includes an illumination lamp 74 that irradiates light on the original and a first mirror 76A that receives reflected light obtained from the original. Further, the half-rate carriage 75 is provided with a second mirror 76B and a third mirror 76C that provide the light obtained from the first mirror 76A to the imaging unit. Further, the scanner 70 is an imaging lens 77 that optically reduces the optical image obtained from the third mirror 76C, and a CCD (Charge Coupled Device) that photoelectrically converts the optical image formed by the imaging lens 77. An image sensor 78 and a drive substrate 79 including a CCD image sensor 78 are provided, and an image signal obtained by the CCD image sensor 78 is sent to the gap correction processing unit 80 via the drive substrate 79.

  Here, first, when reading an image of a document placed on the first platen glass 72A, the full rate carriage 73 and the half rate carriage 75 move in the scanning direction (arrow direction) at a ratio of 2: 1. . At this time, the light of the illumination lamp 74 of the full rate carriage 73 is irradiated on the surface to be read of the document, and the reflected light from the document is reflected in the order of the first mirror 76A, the second mirror 76B, and the third mirror 76C. Then, it is guided to the imaging lens 77. The light guided to the imaging lens 77 forms an image on the light receiving surface of the CCD image sensor 78. The CCD image sensor 78 is a one-dimensional sensor and processes one line at the same time. When reading of one line in this line direction (main scanning direction of scanning) is completed, the full-rate carriage 73 is moved in a direction (sub-scanning direction) orthogonal to the main scanning direction to read the next line of the document.

  There are three line sensors, one each of which is assigned to read R (red), G (green), and B (blue) signals. By executing this over the entire document size, full-color image reading is completed for one page of the document.

  On the other hand, the second platen glass 72B is constituted by a transparent glass plate having a long plate-like structure, for example. The document conveyed by the document feeder 10 passes over the second platen glass 72B. At this time, the full-rate carriage 73 and the half-rate carriage 75 are stopped at the position indicated by the solid line shown in FIG.

  First, the reflected light of the first line of the document that has passed through the platen roll 19 of the document feeder 10 is imaged by the imaging lens 77 via the first mirror 76A, the second mirror 76B, and the third mirror 76C. An image is read by the CCD image sensor 78 which is the first sensor in the present embodiment.

  That is, the CCD image sensor 78 which is a three-dimensional RGB one-dimensional sensor simultaneously processes data for one line in the main scanning direction, and then one line in the next main scanning direction of the document conveyed by the document feeder 10. Is read. After the leading edge of the document reaches the reading position of the second platen glass 72B, the document passes through the reading position of the second platen glass 72B, whereby reading of one page is completed in the sub-scanning direction.

  In this embodiment, the full-rate carriage 73 and the half-rate carriage 75 are stopped, and the first platen glass 72B is used to read the first surface of the document by the CCD image sensor 78. It is possible to read the second side of the document by the CIS 50 (rather than the meaning when the same document is conveyed). That is, by using the CCD image sensor 78 and the CIS 50, it is possible to read the images on both the front and back sides of the original by one conveyance of the original to the conveyance path.

  FIG. 3 is a diagram for explaining a reading structure using the CIS 50 as a reading unit according to the present embodiment. As shown in FIG. 3, the CIS 50 is provided between the platen roll 19 and the out roll 20. One side (first side) of the original is pressed against the second platen glass 72B, and the image on the first side is read by the CCD image sensor 78.

  On the other hand, in the CIS 50, an image on one side (second side) is read from the other side facing through a conveyance path for conveying a document. The CIS 50 includes a glass 51, an LED (Light Emitting Diode) 52 that irradiates light onto the second surface of the document through the glass 51, and a SELFOC lens that is a lens array that collects reflected light from the LED 52. 53, and a line sensor unit 54 for reading the light collected by the Selfoc lens 53.

  As the line sensor unit 54, a CCD, a CMOS sensor, a contact sensor, or the like can be used, and an image having an actual width (for example, A4 longitudinal width 297 mm) can be read. Details of the line sensor unit 54 will be described later. In the CIS 50, since the image is captured using the SELFOC lens 53 and the line sensor unit 54 without using the reduction optical system, the structure can be simplified, the housing can be downsized, and the power consumption can be reduced. Can be reduced.

  In this embodiment, in order to read a full-color image, the LED 52 is combined with three LED light sources of R (red), G (green), and B (blue) or a white LED light source, and the line sensor unit 54 has three columns for RGB three colors. A set of sensors is used.

  When the image is read by the CIS 50, a control member 55 extending from the casing of the CIS 50 and an abutting member 60 for abutting the original pressed by the control member 55 are provided on the conveyance path constituting the reading unit. However, while the control member 55 is attached to the document feeder 10 (see FIG. 2) via the CIS 50, the butting member 60 is attached to the scanner 70 (see FIG. 2). Further, a guide member 61 is provided on the downstream side of the abutting member 60, and an opening 63 is formed between the guide member 61 and the abutting member 60. In a portion continuous with the opening 63, a dust storage portion 62 is provided as a collection portion for collecting dust and dirt adhering to the surface of the document. The control member 55 and the abutting member 60 correspond to the position of the conveyance path from the front surface to the rear surface of the document feeder 10 in a direction orthogonal to the document conveyance path (that is, from the front surface to the rear surface of the document feeder). Is provided.

  Here, the control member 55 is configured by a plate spring made of a U-shaped sheet metal wound around a shaft 50a provided in the CIS 50, and is conveyed by making the control member 55 flexible. The thickness of the original can be absorbed, and even a folded original can be stably conveyed.

  Further, the front end side of the control member 55 extends to the vicinity of the reading position by the CIS 50, and a folded portion 55a that is hemmed and bent is provided at a portion that comes into contact with the document, so that it smoothly contacts the document and generates paper dust or the like. Can be prevented. The distance between the folding portion 55a of the control member 55 and the abutting member 60 (gap for passing the document) is set to about 0.1 to 1.0 mm.

  On the other hand, the abutting member 60 is provided on the upstream side in the document conveyance direction, and a conveyance surface 60a for guiding the document to be conveyed, and one level lower than the conveyance surface 60a on the downstream side in the document conveyance direction from the conveyance surface 60a. And a step surface 60b formed. Further, the step surface 60b is formed so as to face an extension line of the light focus point by the Selfoc lens 53. On the step surface 60b, a white reference member made of a biaxially stretched polyester film is used. A reference tape 64 is affixed. Therefore, the white reference tape 64 is attached to the scanner 70 via the abutting member 60. In the present embodiment, the upper surface of the white reference tape 64 is arranged in a state of being exposed to the conveyance path.

  In the present embodiment, since the CIS 50 employs the SELFOC lens 53 as an optical imaging lens, the depth of focus (field of view) is as shallow as ± 0.3 mm, which is about 1/13 compared to the scanner 70 side. It is as follows. For this reason, when reading by the CIS 50, it is required to set the reading position of the document within a predetermined narrow range. Therefore, in the present embodiment, the above-described control member 55 is provided, and the document is conveyed while being pressed against the abutting member 60 by the control member 55, so that the posture of the document between the platen roll 19 and the out-roll 20 is stabilized. It was configured to be able to control automatically.

  A one-dot chain line arrow in FIG. 3 indicates the movement of the document when the control member 55 is provided. It is understood that the document is conveyed while being abutted against the abutting member 60 by the control member 55. In this way, the height of the original at the reading position can be made substantially constant, and the sweetness of the focus when using the CIS 50 with a shallow focal depth can be improved. By enabling reading with such a small optical unit, a low-cost optical unit can be provided.

  Next, the line sensor unit 54 will be described in detail. FIG. 6 is an overall view of the line sensor unit 54 according to the present embodiment. FIG. 7 is an enlarged view of the vicinity of the dotted line portion in FIG. As shown in FIG. 6, the line sensor unit is composed of three line sensors, and each has a sensitivity peak in the R, G, and B wavelength regions. FIG. 8 is a graph showing an example of sensitivity characteristics (wavelength dependence) of each sensor.

  In the present embodiment, the line sensor unit 54 includes three multichip line sensors arranged in parallel in a direction (main scanning direction) perpendicular to the document transport direction (sub-scanning direction), and a substrate on which the line sensor unit 54 is mounted. And have. Focusing on one multi-chip line sensor, it has a plurality of sensor chips arranged in the main operation direction.

  In the example shown in FIG. 6, a diagram in which four chips are arranged is shown, but in reality, several tens or more chips may be arranged. Further, as shown in FIG. 7 in which this is enlarged, each chip has small image reading sensors (for example, photoelectric converters such as photodiodes) arranged in a straight line in the main scanning direction. Here, it is assumed that n (n is an integer) image reading sensors are arranged on one chip, but this number is not limited to a certain value.

  Further, as can be seen from FIG. 7, there is a gap region (length d) where no image reading sensor exists on the multi-chip line sensor. This occurs when each sensor chip is die-bonded on the substrate. However, since there is no image reading sensor in this region, image information in that portion is lost. The present invention is made to solve the above-described problems. The gap between the sensor chips is interpolated from a plurality of pixels in the vicinity of the gap, and the accuracy of the interpolation is improved.

  Next, the gap correction processing unit 80 shown in FIG. 2 will be described. FIG. 9 is a diagram for explaining details of the gap correction processing unit 80 in the present embodiment. The gap correction processing unit 80 includes a first signal conversion unit that converts an RGB signal into a luminance / color difference signal or a lightness / chromaticity signal, an interpolation calculation unit that performs image interpolation of a gap region in the converted color space, and luminance / color difference. A first signal reverse conversion unit that performs reverse conversion from a signal or lightness / chromaticity signal to an RGB signal.

An example of the RGB-LCaCb conversion formula is shown below as the conversion performed by the first signal conversion unit.
L = (R + 2G + B) / 4
Ca = (R−G) / 2
Cb = (R + G-2B) / 4

  This calculation can be realized by addition / subtraction and division by power of 2 (realizable by bit shift). In this embodiment, an example of RGB-LCaCb conversion is given. However, it is possible to convert signals into so-called device-independent signals such as JPEG YCbCr signals used in compression methods and CIEL * a * b * signals called uniform color spaces. There is a way to do the conversion. When performing such signal attribute conversion, the RGB signal output from the scanner is first converted to a standard signal (color space) such as sRGB or XYZ, and then a masking operation is performed for YCbCr, and a nonlinear operation is performed for CIEL * a * b *. And a process of converting to a desired signal is required. Alternatively, direct conversion from RGB to a desired signal is performed using a three-dimensional LUT and an interpolation operation.

  The interpolation calculation unit performs the interpolation calculation using a known technique for interpolating the gap region image independently for each of the L, Ca, and Cb planes. In recent years, there is a multi-chip image sensor in which the length of the gap region is limited to a range corresponding to one pixel at 600 dpi reading. In this case, the length of the gap region can always be regarded as equivalent to one pixel at 600 dpi reading. .

  Here, since the interpolation is performed after converting the signal into the LCaCb space instead of the RGB image, it is possible to perform the interpolation while maintaining the color of the input image. In particular, when the input image is an achromatic image, the color change tends to be noticeable if even a little color is applied, but such a phenomenon occurs when interpolation is performed after conversion to a luminance / color difference signal. Hateful.

The first signal reverse conversion unit may perform reverse conversion of the first signal conversion unit. In the case of the present embodiment, the following equation is obtained.
R = L + (5Ca + 2Cb) / 4
G = L + (-3Ca + 2Cb) / 4
B = L + (Ca-3Cb) / 4
The output of the first signal inverse conversion unit is input to the scanner correction unit 3.

  The configuration of the scanner correction unit 3 will be described with reference to FIG. FIG. 4 is a diagram for explaining details of the scanner correction unit 3 according to the present embodiment. As shown in FIG. 4, the scanner correction unit 3 determines whether an image area (image area) of a document is a character area, a picture area, a chromatic area, or the like based on RGB image data input from the scanner. A region separation unit, a scanner γ correction unit that converts digital values of RGB image data based on the characteristics of the scanner into digital values proportional to lightness, and a sharpening process on image data based on the result of image region separation, A filter processing unit that applies a smoothing process and image data separated into RGB colors are recorded in C (cyan), M (magenta), Y (yellow), and K (black), which are different color spaces. It comprises a color correction unit that converts color image data including color information, and a scaling processing unit that outputs the input image with the size in the main scanning direction enlarged or reduced.

  The image area separation unit outputs a 1-bit signal C / P representing characters / non-characters and a 1-bit signal B / C representing chromatic / achromatic. If C / P = 1, it represents a character area, if C / P = 0, it represents a non-character area, B / C = 1 represents a chromatic area, and B / C = 0 represents an achromatic area.

  The filter processing unit applies the sharpening process to the character area and the smoothing process to the picture area with reference to the image area separation data.

  The color correction unit refers to the image area separation data and determines that the corresponding area is a black character area when it is a character area and an achromatic area, and generates Bk single color data as image data for plotter 82 output. . This processing is called black character processing. Compared to the case where the three CMY versions are mixed and the black character is output to the plotter 82, the black character can be greatly improved when the black character is processed and the plotter 82 is output.

  The configuration of the printer correction unit 81 will be described with reference to FIG. FIG. 5 is a diagram for explaining details of the printer correction unit 81 according to the present embodiment. As shown in FIG. 5, the printer correction unit 81 includes a printer γ correction unit that performs γ correction on CMYK image data that has passed through the expansion processing unit 9 according to the frequency characteristics of the plotter 82, and dither processing / error diffusion. A gradation processing unit that performs quantization such as processing, and outputs image data CMYK. This data is sent to the plotter 82. The plotter 82 creates an image based on the sent image data, and forms the image by transferring the created image onto a sheet.

  The printer γ correction unit refers to the image area separation data, the γ curve of the character area is set to have a steep slope so as to give contrast, and the γ of the pattern area is a γ that faithfully reproduces the gradation. Set the curve. The gradation processing unit performs processing that emphasizes resolving power in the character area, and performs processing that emphasizes gradation in the pattern area.

  According to the above embodiment, the RGB full-color image is divided into the luminance signal and the chromaticity signal, and then the interpolation is performed. Therefore, the interpolation image in the gap of the multichip line sensor can be interpolated while preserving the color of the original image. .

  Subsequently, another embodiment of the present invention will be described. Since the configuration other than the gap correction processing unit 80 is exactly the same as the above embodiment, only the gap correction processing unit (hereinafter referred to as “gap correction processing unit 80a”) is described here.

  There is also a problem that shading corresponding to luminance (or brightness) cannot be accurately interpolated with a halftone image. A halftone dot image is a system in which ink is regularly printed on paper or the like, and the pattern portion halftone of the printed image is realized by the density of the applied ink. When interpolating a gap image of a multi-chip line sensor, when interpolating a halftone image taking into account the regularity of shading seen in surrounding pixels, the regularity of the image becomes important, so the regularity is lost. A halftone dot image cannot be interpolated well.

  In the case of a full-color print image, the achromatic region of the image is printed with K (black) single color, but the chromatic region of the image, particularly the pattern portion with many halftone images, is C (cyan), M (magenta), Y ( Yellow) is often drawn with three colors of ink. Even if each of the three versions of C, M, and Y is a periodic halftone dot image, if the reading device that reads the color information of the three colors R, G, and B reads The ink color cannot be separated. For this reason, the full color halftone image read by the multi-chip line sensor cannot be accurately interpolated, and a streak image may be generated in the gap portion.

  The present embodiment described below is intended to solve the above-described problem. By converting an RGB full-color image into a CMY signal and then interpolating, the full-color halftone image in the gap of the multi-chip line sensor can be accurately obtained. Interpolate well.

  FIG. 10 is a diagram for explaining details of the gap correction processing unit 80a according to the present embodiment. The gap correction processing unit 80a includes an ink color information conversion unit that converts an RGB signal into an ink color space used for printing, an interpolation calculation unit that performs image interpolation of the gap region in the converted color space, and an ink color space. The ink color information reverse conversion unit performs reverse conversion to RGB signals.

In the ink color information conversion unit, for example, RGB-CMY conversion can be performed using the following equation (1).
C = α11 × R + α12 × G + α13 × B + β1
M = α21 × R + α22 × G + α23 × B + β2
Y = α31 × R + α32 × G + α33 × B + β3 (1)
However, for α11 to α33 and β1 to β3, a predetermined color correction coefficient CMY is a signal of 8 bits (0 to 255).

  In this conversion formula, coefficients α11 to α33 and β1 to β3 that determine the most color separation are determined for the three colors of ink used in the read document.

  For example, it is preferable to determine a coefficient such that only C reacts as much as possible and MY does not react when a printed original printed with C single color ink is read.

  When a signal with good color separation in this way is input to the interpolation calculation unit and interpolation is performed, the interpolation accuracy is higher than when interpolation is performed with the RGB signal. The interpolation calculation unit may perform interpolation calculation using a known technique independently for each plane, as in the above embodiment.

The ink color information inverse conversion unit inversely converts the CMY signal into an RGB signal. In this embodiment, since linear transformation is performed,
R = α11 ⁻¹ × (C−β1) + α12 ⁻¹ × (M−β2) + α13 ⁻¹ × (Y−β3)
G = α21 ⁻¹ × (C−β1) + α22 ⁻¹ × (M−β2) + α23 ⁻¹ × (Y−β3)
B = α31 ⁻¹ × (C−β1) + α32 ⁻¹ × (M−β2) + α33 ⁻¹ × (Y−β3)
... (2)
And calculate. However, α11 ^{−1 to} α33 ⁻¹ are components of an inverse matrix of a 3 × 3 matrix having α11 to α33 as components.

  The RGB signal that is the output of the ink color information inverse conversion unit is input to the scanner correction unit 3. In this embodiment, as the ink color information conversion, an example in which color conversion is performed on the three most common CMY colors has been described. However, any one color is independent of the other two colors. If a set of three colors (which cannot be expressed by mixing), linear conversion can be performed from the RGB color space.

  Some printed materials basically use colors other than CMY. In that case, the printed material may be optimized for colors other than CMY.

  By performing the interpolation after converting the RGB full-color image into the CMY signal according to the above embodiment, the full-color halftone image in the gap of the multi-chip line sensor can be accurately interpolated, and the color is also stored with high accuracy. Interpolation is possible as it is.

  Subsequently, another embodiment of the present invention will be described. Since this embodiment is also the same as the above embodiment except for the gap correction processing unit 80, only the gap correction processing unit (hereinafter referred to as “gap correction processing unit 80b”) that is a feature of the present embodiment is described. To do.

  FIG. 11 is a diagram for explaining details of the gap correction processing unit 80b according to the present embodiment. The gap correction processing unit 80b is an ink color information conversion unit that converts an RGB signal into an ink color space used for printing, and a second signal that converts the CMY-converted color space into a luminance / color difference signal or a brightness / chromaticity signal. A conversion unit, an interpolation calculation unit that performs image interpolation of a gap region in the converted color space, a second signal reverse conversion unit that performs reverse conversion from a luminance / color difference signal or lightness / chromaticity signal to a CMY signal, and ink color The ink color information reverse conversion unit performs reverse conversion from space to RGB signals.

  Here, the ink color information conversion unit is exactly the same as that described in the embodiment described with reference to FIG. The second signal conversion unit converts the CMY signal into a luminance / color difference signal or a brightness / chromaticity signal.

For example, it is converted into an LUV signal (L: luminance signal, UV: color difference signal) which is a luminance / color difference signal using the following equation (3).
L = floor {(C + 2 * M + Y) / 4}
U = CM
V = Y−M (3)
However, floor {} represents a floor function.

  The above formula (3) is adopted in JPEG2000, which is a standard compression method succeeding JPEG, and can be realized only by bit shift and addition / subtraction, and converted to a luminance / color difference signal that can be reversibly converted by integer arithmetic. It is a formula.

The interpolation calculation unit performs the interpolation calculation independently for each of the LUV signals as in the embodiment described with reference to FIG. The second signal inverse conversion unit inversely converts the luminance / color difference signal or the brightness / chromaticity signal into a CMY signal. In this embodiment, the following equation may be converted.
M = L-floor {(U + V) / 4}
C = U + M
Y = V + M (4)
Here, floor {} represents a floor function.

  This output is input to the ink color information inverse conversion unit. Here, the CMY signals are inversely converted into RGB signals in the same manner as the ink color information inverse conversion unit according to the embodiment described with reference to FIG. The RGB signal that is the output of the ink color information inverse conversion unit is input to the scanner correction unit 3.

  Here, the effect of performing the interpolation operation after conversion to the luminance / color difference system color space (the luminance / color difference signal or the color space based on the brightness / chromaticity signal) after conversion to the CMY signal will be described.

  As shown in FIG. 8, since spectral sensitivities of two to three colors overlap at a specific wavelength, responses of a plurality of colors are output with respect to light of the overlapping wavelengths. For example, when a green original having a spectral characteristic of 480 to 600 [nm] is read by a scanner, it is desirable that the output signal from the scanner has a response corresponding to the G signal. Will output a response that cannot be ignored.

  When this output signal is displayed on a CRT or the like, the color appears cloudy. A color difference (chromaticity) signal obtained by converting such a turbid signal by the above conversion formula cannot be said to be a signal with high color separation accuracy. In this case, even if the gap region interpolation calculation is performed after conversion to the luminance / color difference color space, the accuracy of maintaining the color tone is inferior.

  FIG. 12 is a diagram showing a saturation histogram calculated from RGB signals and CMY signals of a color image converted to color difference signals (U, V), respectively. In FIG. 12, the horizontal axis represents the pseudo saturation calculated by √ (U2 + V2), and “0” is achromatic, and a larger value indicates higher saturation. The vertical axis represents the frequency and indicates the number of pixels for each saturation.

  As shown in FIG. 12, in the case of the UV signal calculated from the RGB signal (broken line in the figure), the concentration of data on the low saturation side is high, whereas the UV signal calculated from the CMY signal is high. In the case of (a solid line in the figure), it can be seen that the distribution is also on the high saturation side. This is because in the case of a UV signal calculated from an RGB signal, the dynamic range is narrower than that of a UV signal calculated from a CMY signal, and thus the S / N ratio is lowered. As described above, the cause is that the UV signal calculated from the RGB signal has a turbid component.

  Therefore, the UV signal converted from the RGB signal has an S / N ratio lower than that of the UV signal converted from the CMY signal, so that an error is large and interpolation calculation is not performed with high accuracy. Therefore, accurate gap correction can be performed by converting the RGB signal into the CMY signal and further performing the interpolation calculation after the conversion into the luminance / color difference color space. However, this method requires a larger number of computations and consumes a larger amount of hardware and computation time than the embodiments described with reference to FIGS. Therefore, the embodiment may be changed according to the required accuracy and application of gap correction.

  Finally, details of the color correction unit 90 of the scanner correction unit 3 will be described. FIG. 13 is a diagram for explaining the details of the color correction unit 90 according to the present embodiment. As shown in FIG. 13, the color correction unit 90 includes a color space conversion unit and a BG / UCR processing unit. The BG / UCR processing unit generates a Bk signal that is a black component based on the CMY signal input from the color space conversion unit (BG), and performs undercolor removal (UCR) on the CMY signal. When the image area separation signal C / P = 1 (character area) and B / C = 0 (achromatic area), the C, M, and Y data are erased. This is because black characters are expressed only by the black component.

  The color space conversion unit and the BG / UCR processing unit output the input image area separation signals C / P and B / C without performing any conversion process. However, as described above, the signal is referred to.

Here, the generation of the Bk signal and the removal of the under color from the CMY signal can be performed by the following equation, for example.
Bk = Min (C, M, Y) × β4
C ′ = C−K × β5
M ′ = M−K × β5
Y ′ = Y−K × β5
However, Min (C, M, Y) represents the minimum of the CMY signals.
β4 and β5 are predetermined coefficients and are 8-bit signals.

  The color correction unit 90 needs to convert the signal attribute (color space) to be output to the plotter 82. Since the general plotter 82 uses CMY or CMYBk toner and ink, it is converted into their signal attributes, color correction processing, so-called color matching is performed, and the original color read by the scanner and the output from the printer. It is corrected so that the color of the copied material matches.

  The color correction unit 90 may perform color conversion processing by the same means as the ink color information conversion unit included in the gap correction processing unit 80 of the present embodiment (such as RGB-CMY conversion by linear masking processing). The purpose of color information conversion is to accurately perform gap correction of a multi-chip line sensor.

  On the other hand, the main purpose of the color space conversion unit of the color correction unit 90 is to optimize color matching via the plotter 82. This strongly depends on the characteristics of the toner and ink used when the image forming apparatus shown in this embodiment transfers.

  Therefore, it is generally necessary to perform different color conversions in the ink color information conversion unit and the color space conversion unit of the color correction unit 90. This includes, of course, the case where the RGB-CMY conversion method is different between masking and look-up table, but includes the case where both perform masking and color conversion, the masking coefficients are different, and the like. By performing different color conversions here, the ink color information conversion unit and the color space conversion unit 90 of the color correction unit 90 can be optimized according to the respective purposes.

  According to the above embodiment, the color reproduction (color matching) of the output image of the image forming apparatus is performed by performing color conversion different from the ink color information conversion unit that performs color conversion optimized for color separation of the ink color used for the document. ) Can be optimized.

  However, when the document read by the image reading unit 1 is mainly a copy document output by the image forming apparatus of this embodiment, the color space of the ink color information conversion unit and the color correction unit 90 of the present invention is used. It may be optimal to perform the same color conversion in the conversion unit. In that case, of course, it is not necessary to use different color conversions.

  As another embodiment according to the present invention, a storage medium (or recording medium) in which a program code of software having the functions of the above-described embodiments is recorded is supplied to a system or apparatus, and a computer of the system or apparatus is provided. An embodiment in which the program code stored in the storage medium is read and executed is also conceivable.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read out by the computer, not only the functions of the above-described embodiments are realized, but also an operating system running on the computer based on the instruction of the program code performs actual processing. In some cases, the functions of the above-described embodiments are realized by performing part or all of the above.

  Furthermore, after the program code read from the storage medium is written into a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function is determined based on the instruction of the program code. The case where the CPU of the expansion card or the function expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing is also included.

  Although the present invention has been specifically described above based on the preferred embodiments, it is needless to say that the present invention is not limited to the above-described ones and can be variously modified without departing from the gist thereof.

1 is a block diagram of a schematic configuration of a digital full-color image processing apparatus according to an embodiment of the present invention. 1 is a diagram illustrating an example of an image reading unit 1 configuring an image processing apparatus to which an embodiment of the present invention is applied. It is a figure for demonstrating the reading structure using CIS50 as a reading part which concerns on embodiment of this invention. It is a figure for demonstrating the detail of the scanner correction | amendment part 3 which concerns on embodiment of this invention. It is a figure for demonstrating the detail of the printer correction | amendment part 81 which concerns on embodiment of this invention. It is a general view of the line sensor unit 54 which concerns on embodiment of this invention. FIG. 7 is an enlarged view of the vicinity of the dotted line portion of FIG. 6. It is a graph which shows the example of the sensitivity characteristic (wavelength dependence) which each sensor which concerns on embodiment of this invention has. It is a figure for demonstrating the detail of the gap correction process part 80 in embodiment of this invention. It is a figure for demonstrating the detail of the gap correction process part 80a which concerns on embodiment of this invention. It is a figure for demonstrating the detail of the gap correction process part 80b which concerns on embodiment of this invention. It is the figure which showed an example of the histogram of the saturation calculated by converting the RGB signal and CMY signal of a color image into a color difference signal (U, V), respectively, and these color difference signals. It is a figure for demonstrating the detail of the color correction | amendment part 90 which concerns on embodiment of this invention.

Explanation of symbols

X document Y copy image 1 image reading unit 3 scanner correction unit 4 compression processing unit 5 general-purpose bus 6 controller 7 HDD
8 NIC
9 Decompression processing unit 80, 80a, 80b Gap correction processing unit 81 Printer correction unit 82 Plotter 83 External PC terminal 90 Color correction unit

Claims (12)

A plurality of multi-chip line sensors in which a plurality of image reading sensor chips are arranged in a straight line;
RGB full-color image reading means for reading color information of at least R (red), G (green), and B (blue) by the plurality of multichip line sensors;
First signal conversion means for converting image data read by the RGB full-color image reading means into luminance / color difference signals or brightness / chromaticity signals;
An image processing apparatus comprising: image interpolating means for interpolating image data between the image reading sensor chips constituting the multi-chip line sensor based on a conversion result of the first signal converting means. A plurality of multi-chip line sensors in which a plurality of image reading sensor chips are arranged in a straight line;
RGB full-color image reading means for reading color information of at least R (red), G (green), and B (blue) by the plurality of multichip line sensors;
Ink color information conversion means for converting image data read by the RGB full-color image reading means into color information of ink used for printing;
An image processing apparatus comprising: image interpolating means for interpolating image data between the image reading sensor chips constituting the multi-chip line sensor based on a conversion result of the ink color information converting means.   The ink color information converting means converts the RGB full color image data input by the RGB full color image reading means into a color space expressed by three colors of C (cyan), M (magenta), and Y (yellow). The image processing apparatus according to claim 2. A plurality of multi-chip line sensors in which a plurality of image reading sensor chips are arranged in a straight line;
RGB full-color image reading means for reading color information of at least R (red), G (green), and B (blue) by the plurality of multichip line sensors;
Ink color information conversion means for converting image data read by the RGB full-color image reading means into color information of ink used for printing;
Second signal conversion means for converting the image data output from the ink color information conversion means into luminance / color difference signals or brightness / chromaticity signals;
An image processing apparatus comprising: image interpolation means for interpolating image data between the image reading sensor chips constituting the multi-chip line sensor based on a conversion result of the second signal conversion means. An image forming apparatus comprising the image processing apparatus according to claim 1,
An image forming apparatus comprising: an image forming unit that forms an image based on image data output from the image processing apparatus, and forms the image by transferring the formed image onto a sheet. An image forming apparatus comprising the image processing apparatus according to claim 2,
An image forming unit that forms an image based on image data output from the image processing apparatus, and that forms an image by transferring the formed image onto paper;
Color conversion means for converting an image read by the RGB image reading means into a color space of a transfer material used for transfer of the image forming apparatus,
The image forming apparatus, wherein the color conversion unit performs color conversion different from that of the ink color information conversion apparatus. Image input by RGB full-color image reading means for reading color information of at least R (red), G (green), and B (blue) by a plurality of multi-chip line sensors in which a plurality of image reading sensor chips are arranged on a straight line Steps,
A signal conversion step of converting the RGB full-color image data input in the image input step into a luminance / color difference signal or a brightness / chromaticity signal;
An image processing method comprising: an image interpolation step of interpolating image data between the image reading sensor chips constituting the multi-chip line sensor based on a conversion result of the signal conversion step. Image input by RGB full-color image reading means for reading color information of at least R (red), G (green), and B (blue) by a plurality of multi-chip line sensors in which a plurality of image reading sensor chips are arranged on a straight line Steps,
An ink color information conversion step for converting RGB full-color image data input in the image input step into ink color information;
An image interpolation method comprising: an image interpolation step of interpolating image data between the image reading sensor chips constituting the multi-chip line sensor based on a conversion result of the color information conversion step.   In the ink color information conversion step, the RGB full-color image data input in the image input step is converted into image data expressed in three colors of C (cyan), M (magenta), and Y (yellow). The image processing method according to claim 8. Image input by RGB full-color image reading means for reading color information of at least R (red), G (green), and B (blue) by a plurality of multi-chip line sensors in which a plurality of image reading sensor chips are arranged on a straight line Steps,
An ink color information conversion step for converting RGB full-color image data input in the image input step into ink color information;
A second signal conversion step of converting the image data output in the ink color information conversion step into a luminance / color difference signal or a brightness / chromaticity signal;
An image processing method comprising: an image interpolation step of interpolating image data between the image reading sensor chips constituting the multi-chip line sensor based on a conversion result of the second signal conversion step.   11. An image processing program that causes a computer to execute the steps in the image processing method according to claim 7.   A computer-readable recording medium on which the image processing program according to claim 11 is recorded.

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