JP3723043B2 - Image processing apparatus, image reading apparatus, and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is applied to a system that reads an image divided into a plurality of pixels, generates image data for each read pixel, and outputs the image data. The image processing device performs gamma correction processing on image data before output. The present invention relates to an image reading apparatus and an image forming apparatus, and more particularly, to an image processing apparatus, an image reading apparatus, and an image forming apparatus that reduce and output noise in image data in a dark portion.
[0002]
[Prior art]
In recent years, an image is divided into a plurality of pixels and read, and an area CCD (charge coupled device) or a line CCD as an image sensor that generates and outputs image data for each read pixel is used in digital lab systems, facsimile machines, Widely used in many devices such as digital copiers, scanners, video cameras and digital cameras. In a conventional image reading apparatus using such an image sensor, an image projected on the image sensor is divided into pixels corresponding to a plurality of photoelectric conversion elements of the image sensor, and charges generated in proportion to the amount of incident light are generated. , And image data for each pixel is sequentially output.
[0003]
Japanese Patent Application Laid-Open No. 11-284880 discloses that an imaging apparatus performs gamma correction even when the S / N ratio of an input signal is low, suppresses an undesired level increase of a noise component in a low luminance portion, and has an excellent level. A technique for obtaining tonal reproducibility is disclosed. Specifically, the imaging apparatus includes a contour correction signal generation circuit that generates a contour correction signal, a distribution unit that distributes the generated contour correction signal into two systems with a variable ratio, a distribution ratio setting unit that sets a distribution ratio, and a CRT. A gamma correction circuit that compensates the voltage and light emission characteristics of the signal, a first adder that adds an input signal to the gamma correction circuit and the distributed first contour correction signal, and an output signal from the gamma correction circuit. A second adder for adding the second contour correction signal is included, and a luminance signal subjected to gamma correction is output.
[0004]
Japanese Patent Laid-Open No. 10-276348 discloses a standard gamma correction circuit having a gamma ROM that generates standard gamma curve characteristic data for an input Y signal to be corrected. A correction data generation unit that generates correction data that corrects the characteristics of the area near black in the gamma curve characteristics and a subtractor that subtracts the correction data from the standard gamma curve characteristics data are provided. A technique for realizing both functions of emphasizing S / N by the same signal processing is disclosed.
[0005]
[Problems to be solved by the invention]
  The image reading apparatus as described above has a gamma characteristic. The gamma characteristic is represented by a gamma curve as shown in FIG. 3, and when the image reading apparatus performs gamma correction according to this gamma curve, the input signal levelXIn the dark part where the signal is small, an output signal is obtained with a high gain, and the noise component is remarkably amplified. In other words, if there is a slight shift in the input signal, the shift is the output signal.Level YIs significantly amplified. Therefore, in the case of reading an image such as a photograph that requires smooth gradation, the output image becomes rough due to the influence of noise components, and smooth gradation cannot be reproduced. In addition, it is conceivable to suppress the increase of the noise component by changing the gamma characteristic so that the gain of the dark part becomes low. In this case, although the noise component can be suppressed, the dark part is crushed and smooth. The gradation cannot be reproduced.
[0006]
An object of the present invention is to provide an image processing apparatus, an image reading apparatus, and an image forming apparatus capable of performing gamma correction and reducing image roughness due to a noise component in a dark part.
[0007]
[Means for Solving the Problems]
  The present invention is constituted by matrix-like pixels.Respectively obtained by separating the red, green and blue color components of the imageGamma correction processing for image dataRespectivelyGamma correction processing means to be applied;
  Output means for outputting image data subjected to gamma correction processing;
  Gamma correction processing was appliedFor each color componentOf the image data, the gamma curve indicating the gamma characteristic of the output meansOutput level Y relative to input level XTilt, Predetermined in common for each color componentGreater than thresholdDark partPixelFor each color componentNoise reduction processing that reduces noise on image dataGive them to the output meansAn image processing apparatus comprising: a noise reduction processing unit.
[0008]
  According to the present invention, a gamma correction process has been performed.For each color component of red R, green G and blue BOf the image data, the gamma curve indicating the gamma characteristic of the output meansOutput level Y relative to input level XTilt, Predetermined in common for each color componentGreater than thresholdDark partPixelFor each color componentNoise reduction processing is applied to image dataRespectivelyThe image data is output from the output means, and the other image data is output as it is. Therefore, the slope of the gamma curve is a predetermined threshold, for exampleInclinationIt is possible to perform image processing that reduces noise in areas that exceed 1, and noise can be reduced even in the dark part of an image where noise amplification is likely to occur due to gamma correction, preventing smoothness of the image due to noise. It is possible to reproduce a good image having a good gradation.
[0009]
Further, the present invention is characterized in that the noise reduction processing means determines the pixel value of the target pixel by averaging the image data of the target pixel subjected to the noise reduction processing and its surrounding pixels.
[0010]
  The present invention is characterized in that the image data of the target pixel and the peripheral pixels are weighted, and the weighted image data is averaged.
  According to the present invention, the noise reduction processing is performed on image data of a target pixel on which noise reduction processing is performed and its surrounding pixels., Without weighting or with weightingAn averaging process is performed, and this average value is determined as the pixel value of the target pixel. By such noise reduction processing, the pixel value of the target pixel is determined to be an average value in the data including the peripheral pixels, so that smooth gradation can be reproduced by preventing the occurrence of roughness due to noise. it can.
[0011]
According to the present invention, the noise reduction processing means performs a filtering process using a median filter on the image data of the target pixel to be subjected to the noise reduction process and its surrounding pixels, and obtains the pixel value of the target pixel. It is characterized by determining.
[0012]
According to the present invention, the noise reduction process is obtained by applying a filter process using a median filter to image data of a target pixel to be subjected to the noise reduction process and its surrounding pixels. The intermediate value is determined as the pixel value of the target pixel. By such noise reduction processing, the pixel value of the target pixel is determined to be an intermediate value in the data including the peripheral pixels, so that smooth gradation can be reproduced by preventing the occurrence of roughness due to noise. it can.
[0013]
According to the present invention, the image data includes image data of a character area and a photograph area,
The image processing apparatus includes a region separation unit that separates image data of a character region and a photographic region,
The noise reduction processing means performs noise reduction processing only on image data in a photographic area.
[0014]
According to the present invention, the noise reduction process is performed only on the photographic area and the noise reduction process is not performed on the character area, so that blurring of the edge of the character can be avoided.
[0015]
  The present invention also providesThe predetermined threshold is an inclination of 1.
  The present invention also reads a document and displays a matrix image.NaturallyComposed ofRespectively obtained by separating the red, green and blue color components of the imageImage reading means for outputting image data;
  From image reading meansFor each color componentGamma correction processing for image dataRespectivelyGamma correction processing means to be applied;
  Output means for outputting image data subjected to gamma correction processing;
  Gamma correction processing was appliedFor each color componentOf the image data, the gamma curve indicating the gamma characteristic of the output meansOutput level Y relative to input level XTilt, Predetermined in common for each color componentGreater than thresholdDark partPixelFor each color componentNoise reduction processing that reduces noise on image dataGive them to the output meansAn image reading apparatus comprising: a noise reduction processing unit.
[0016]
  According to the present invention, the image is read and output by the image reading means.For each color componentGamma correction processing for image dataRespectivelyApplied. Gamma correction processing was appliedFor each color componentOf the image data, the gamma curve indicating the gamma characteristic of the output meansOutput level Y relative to input level XTilt, Predetermined in common for each color componentGreater than thresholdDark partPixelFor each color componentThe image data is subjected to noise reduction processing and output from the output means, and other image data is output as it is. Therefore, it is possible to perform image processing for reducing noise after the image data from the image reading unit is subjected to the gamma correction process and before being applied to the output unit. Therefore, image data with reduced noise can be given to an image forming apparatus provided outside the image reading apparatus. An image forming apparatus to which such image data is given can form a good image having smooth gradation even if it does not have a noise reduction processing function.
[0017]
In addition, the present invention includes a noise reduction processing setting unit that sets whether or not the noise reduction processing unit performs the noise reduction processing.
[0018]
According to the present invention, it is possible to select whether or not to perform noise reduction processing in the image reading apparatus. As a result, the noise reduction processing can be executed in accordance with the presence or absence of image processing including a noise reduction processing function of an image forming apparatus or the like to which image data is given. Therefore, normal image data can be output to the image forming apparatus without affecting image processing such as a noise reduction processing function provided in the image forming apparatus to which the image data is given. .
[0019]
In the present invention, the image data includes image data of a character area and a photographic area, and the image reading device includes an area separating unit that separates image data of the character area and the photographic area,
The noise reduction processing means performs noise reduction processing only on image data in a photographic area.
[0020]
According to the present invention, the noise reduction process is performed only on the photographic area and the noise reduction process is not performed on the character area, so that blurring of the edge of the character can be avoided.
[0021]
  The present invention also reads a document., MaTricksNaturallyComposed ofRespectively obtained by separating the red, green and blue color components of the imageImage reading means for outputting image data;
  From image reading meansFor each color componentGamma correction processing for image dataRespectivelyGamma correction processing means to be applied;
  Image forming means for printing out black, yellow, magenta, and cyan images on a recording medium, and printing image data for each of black, yellow, magenta, and cyan is provided on each of these image forming means. GivenPrint output means;
  Gamma correction processing was appliedFor each color componentOf the image data, the gamma curve indicating the gamma characteristic of the print output meansOutput level Y relative to input level XTilt, Predetermined in common for each color componentGreater than thresholdDark partPixelFor each color componentNoise reduction processing that reduces noise on image dataRespectivelyNoise reduction processing means to be applied,
  In response to the output of the noise reduction processing means, print image data for each of black, yellow, magenta and cyan is derived from the image data of each color component on which the noise reduction processing has been performed. Image data deriving means for printing given to the image forming means;An image forming apparatus comprising:
[0022]
  According to the present invention, the image is read and output by the image reading means.For each color component of red R, green G and blue BGamma correction processing is performed on the image data. Of the image data that has undergone gamma correction processing, the gamma curve indicating the gamma characteristic of the print output meansOutput level Y relative to input level XTilt, Predetermined in common for each color componentGreater than thresholdDark partPixelFor each color componentFor image dataTenoNoise reduction processingRespectivelyGivenThen, the image data for each of black, yellow Y, magenta M, and cyan C is obtained from the image data of each color component thus subjected to noise reduction processing by the print image data deriving means 41b and 41d, respectively. Given to the image forming means Pa to Pd of the print output means, thusPrint output from the print output means, other than thatFor each color componentImage data isWithout being subjected to noise reduction processing, the image data deriving means 41b, 41d for printing is given to the image forming means Pa to Pd of the printing output means,Printed out as is. Therefore, from the image reading meansFor each color componentImage processing for reducing noise can be performed after the image data is subjected to gamma correction processing and before being supplied to the print output means. For this reason, the image forming apparatus can form a good image having smooth gradation.
[0023]
According to the present invention, the image data includes image data of a character area and a photograph area,
The image forming apparatus includes a region separating unit that separates image data of a character region and a photographic region,
The noise reduction processing means performs noise reduction processing only on image data in a photographic area.
[0024]
According to the present invention, the noise reduction process is performed only on the photographic area, and the noise reduction process is not performed on the character area.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram of a color digital copying machine (hereinafter also simply referred to as “copying machine”) 1 which is an image forming apparatus according to an embodiment of the present invention. Here, an example in which the image processing apparatus of the present invention is applied to an image forming apparatus that prints out image data read by the document reading unit 40 of the copying machine 1 will be described.
[0026]
The copying machine 1 includes an image reading unit 40 that is an image data input unit, an image processing unit 41, an image memory 43 including a hard disk device and a RAM (random access memory), an image data output unit 42, a CPU (central processing unit). 44), an image editing unit 45, and external interface units 46 and 47.
[0027]
The document reading unit 40 includes a plurality of lines, for example, a three-line color CCD sensor 40a, a shading correction circuit 40b, a line correction unit 40c, a region separation unit 40d, a gamma inclination detection unit 40e, a gamma correction unit 40f, and a filter processing unit 40g. Consists of.
[0028]
  The CCD sensor 40a reads an image from a black-and-white or color document and outputs R (red), G (green) and B (blue).eachColor component(Hereinafter, each color component may be abbreviated as each color.)The line image data decomposed into is output. The shading correction circuit 40b corrects the signal level of the read image data, and the line correction unit 40c corrects the deviation of the read image data. The area separation unit 40d determines whether the read image data is image data of a character area or image data of a photographic area. The gamma tilt detection unit 40e is provided for each color.componentGamma curve for each image dataAs shown in FIG. 3, the output level Y with respect to the input level XTiltA predetermined threshold common to each color component andCompare. The gamma correction unit 40f is for each colorcomponentVisuality correction is performed by correcting the brightness for each image data. The filter processing unit 40g performs a filter process on the read image data of the photographic area.
[0029]
The image processing unit 41 includes a monochrome data generation unit 41a, an input processing unit 41b, a region separation unit 41c, a black generation unit 41d, a color correction circuit 41e for each of Y (yellow), M (magenta) and C (cyan), black and It includes a zoom processing circuit 41f for each YMC, a spatial filter 41g for each black and YMC, a print data input unit 41i for each black and YMC, a halftone processing unit 41h for each black and YMC, and a tracking pattern output unit 41j. The
[0030]
  The monochrome data generation unit 41 a generates monochrome data (monochrome document) from the RGB image data from the document reading unit 40. The input processing unit 41 b converts the RGB image data from the document reading unit 40 into a YMC line corresponding to the image forming station for each color of the copying machine 1.For printingConvert to image data and clock. The area separation unit 41c separates the image data of the character area, the halftone photographic area, and the photographic paper photographic area from the image data from the monochrome data generation unit 41a and the input processing unit 41b. The black generation unit 41d performs undercolor removal processing based on the line image data from the input processing unit 41b, and performs black color removal processing.For line printingGenerate image data. The YMC color correction circuit 41e corrects each YMC image data from the black generation unit 41d based on a predetermined conversion table for each color.
[0031]
The zoom processing circuit 41f for each black and YMC converts the image data of each color from the area separation unit 41c, the black generation unit 41d, and the color correction circuit 41e based on a preset magnification. The spatial filter 41g for each color performs spatial filter processing on the image data of each color from the zoom processing circuit 41f. Each color image data from the spatial filter 41g and each color image data from the document reading unit 40 are input to the print data input unit 41i for each color. The halftone processing unit 41h for each color performs halftone processing for expressing gradation properties such as multilevel error diffusion and multilevel design on the image data of each color from the print data input unit 41i. The tracking pattern output unit 41j outputs a tracking pattern for the Y image data from the Y halftone processing unit 41h. The black and CM image data from the black and CM halftone processing unit 41 h and the Y image data from the tracking pattern output unit 41 j are temporarily stored in the image memory 43.
[0032]
The image memory 43 sequentially receives 8-bit 4-color, that is, 32-bit image data serially output from the image processing unit 41, and stores 32-bit image data into 8-bit 4-color image data while temporarily storing the image data in a buffer. It includes four hard disks 43a to 43d that are converted and stored as image data for each color, that is, rotating storage media.
[0033]
Further, the image memory 43 includes a delay buffer memory 43e realized by a semiconductor memory or the like. In the copying machine 1, the image data of each color is temporarily stored in the delay buffer memory 43e, and the respective laser scanners are timed at the same timing. By sending image data to the unit, color misregistration caused by different positions of the image forming stations is prevented. Further, the image memory 43 includes an image composition memory 43f used at the time of image editing described later.
[0034]
The image data output unit 42 is a laser control unit for each color that performs pulse width modulation based on black and CM image data from the black and CM halftone processing unit 41h and Y image data from the tracking pattern output unit 41j. 42a, and laser scanner units 42b to 42e for each color that perform laser recording based on a pulse width modulation signal corresponding to the image data of each color output from the laser control unit 42a.
[0035]
The CPU 44 controls the document reading unit 40, the image processing unit 41, the image memory 43, the image data output unit 42, an image editing unit 45 and interface units 46 and 47, which will be described later, based on a predetermined sequence.
[0036]
The image editing unit 45 performs predetermined image editing on the image data temporarily stored in the image memory 43 via the document reading unit 40, the image processing unit 41, or interface units 46 and 47 described later. The image data editing work is performed using the image composition memory 43f.
[0037]
The interface unit 46 is a communication interface unit for receiving image data from a communication portable terminal device, a digital camera, a digital video camera, or the like, which is an external image input processing device provided separately from the copying machine 1. Note that image data input from the interface unit 46 is also converted to a data level that can be handled by the image forming unit of the copier 1 by performing color space correction or the like in the image processing unit 41, and the image memory 43. Are stored and managed in the hard disks 43a to 43d.
[0038]
The interface section 47 is a printer interface means for inputting image data created by an external device such as a personal computer, and is a monochrome or color facsimile interface means for receiving image data received by facsimile. The image data input from the interface unit 47 is already a CMYK signal and is subjected to halftone processing by the halftone processing unit 41h and stored and managed in the hard disks 43a to 43d of the image memory 43.
[0039]
FIG. 2 is a diagram showing a configuration of the copying machine 1. An original table 111 and an operation panel are provided on the upper surface of the copying machine 1, and an image reading unit 110, an image forming unit 210, and a paper feeding mechanism 211 are provided inside the copying machine 1. A double-sided automatic document feeder (RADF) 112 is mounted on the upper surface of the document table 111 of the copying machine 1 so as to be openable and closable with respect to the document table 111.
[0040]
First, the double-sided automatic document feeder 112 conveys a document so that one surface of the document faces the image reading unit 110 at a predetermined position on the document table 111, and when the image reading on one surface of the document is completed. The document is reversed and conveyed so that the other side of the document faces the image reading unit 110 at a predetermined position on the document table 111. When the image reading on the other side of the document is completed, the document is discharged. Transport the next document. Such document conveyance and front / back reversal operations are controlled in relation to the overall operation of the copying machine 1.
[0041]
The image reading unit 110 is disposed below the document table 111 in order to read an image of the document conveyed on the document table 111 by the double-sided automatic document feeder 112. The image reading unit 110 includes first and second document scanning units 113, 114, an optical lens 115, and a CCD sensor 116 that reciprocate in parallel along the lower surface of the document table 111.
[0042]
The first document scanning unit 113 includes an exposure lamp that exposes the surface of the document image and a first mirror that deflects the reflected light image from the document in a predetermined direction, and is constant with respect to the lower surface of the document table 111. While reciprocally moving in parallel at a predetermined scanning speed. The second document scanning unit 114 has second and third mirrors that deflect the reflected light image from the document deflected by the first mirror of the first document scanning unit 113 further in a predetermined direction. The first document scanning unit 113 reciprocates in parallel while maintaining a constant speed relationship. The optical lens 115 reduces the reflected light image from the original deflected by the third mirror of the second original scanning unit 114 and forms the reduced optical image at a predetermined position on the CCD sensor 116. The CCD sensor 116 sequentially photoelectrically converts the formed light image and outputs it as an electrical signal.
[0043]
The image data from the CCD sensor 116 is processed by the shading correction circuit 40b, the line correction unit 40c, the region separation unit 40d, the gamma inclination detection unit 40e, the gamma correction unit 40f, and the filter processing unit 40g of the document reading unit 40. The image is transferred to the image processing unit 41 and subjected to predetermined image processing.
[0044]
The paper feed mechanism 211 is provided below the image forming unit 210, and separates the sheets (recording media) P stacked and stored in the paper tray one by one and supplies them to the image forming unit 210. The sheets P separated and supplied one by one are transported to the image forming unit 210 with timing controlled by a pair of registration rollers 212 arranged in front of the image forming unit 210. The sheet P on which an image is formed on one side is re-supplied and conveyed to the image forming unit 210 at the image forming timing of the image forming unit 210.
[0045]
A transfer conveyance belt mechanism 213 is disposed below the image forming unit 210. According to the transfer / conveying belt mechanism 213, the paper P is electrostatically adsorbed and conveyed by the transfer / conveying belt 216 stretched between the driving roller 214 and the driven roller 215 so as to extend substantially in parallel.
[0046]
A fixing device 217 for fixing the toner image transferred and formed on the paper P on the paper P is disposed on the downstream side of the transfer and transport belt mechanism 213 in the paper transport path. The sheet P that has passed through the nip portion between the pair of fixing rollers of the fixing device 217 passes through the conveyance direction switching gate 218 and is discharged onto the discharge tray 220 attached to the outer wall of the copying machine 1 by the discharge roller 219. .
[0047]
The switching gate 218 selectively selects a conveyance path of the fixed sheet P between a path for discharging the sheet P to the outside of the copying machine 1 and a path for resupplying the sheet P toward the image forming unit 210. Switch. The sheet P whose transport direction has been switched again toward the image forming unit 210 by the switching gate 218 is turned upside down via the switchback transport path 221 and then supplied again to the image forming unit 210.
[0048]
Above the transfer / conveying belt 216 in the image forming unit 210, the first image forming station Pa, the second image forming station Pb, the third image forming station Pc, and the fourth image forming station 210 are close to the transfer / conveying belt 216. Image forming stations Pd are arranged in this order from the upstream side of the sheet conveyance path.
[0049]
The transfer / conveying belt 216 is frictionally driven in the direction indicated by the arrow Z in FIG. 2 by the driving roller 214, holds the paper P fed through the paper feeding mechanism 211 as described above, and feeds the paper P to the image forming stations Pa to Pd. Sequentially.
[0050]
Each of the image forming stations Pa to Pd has substantially the same configuration, and includes photosensitive drums 222a, 222b, 222c, and 222d that are rotationally driven in the direction of arrow F shown in FIG.
[0051]
Around the photosensitive drums 222a to 222d, chargers 223a, 223b, 223c, and 223d for uniformly charging the photosensitive drums 222a to 222d, and electrostatic formed on the photosensitive drums 222a to 222d, respectively. Developing devices 224a, 224b, 224c, and 224d that respectively develop the latent images; transfer dischargers 225a, 225b, 225c, and 225d that transfer the developed toner images on the photosensitive drums 222a to 222d onto the paper P; Cleaning devices 226a, 226b, 226c, and 226d for removing toner remaining on the photosensitive drums 222a to 222d are sequentially arranged along the rotation direction of the photosensitive drums 222a to 222d. Laser beam scanner units 227a, 227b, 227c, and 227d are provided above the respective photosensitive drums 222a to 222d.
[0052]
The laser beam scanner units 227a to 227d include a semiconductor laser element (not shown) that emits dot light modulated according to image data, and a polygon mirror (for deflecting the laser beam from the semiconductor laser element in the main scanning direction). Deflectors) 240a, 240b, 240c, 240d and fθ lenses 241a, 241b, 241c, 241d and mirror 242a for imaging the laser beams deflected by the polygon mirrors 240a-240d on the surfaces of the photosensitive drums 222a-222d. , 242b, 242c, 242d, 243a, 243b, 243c, 243d.
[0053]
The laser beam scanner unit 227a has a pixel signal corresponding to the black component image of the color document image, the laser beam scanner unit 227b has a pixel signal corresponding to the cyan component image of the color document image, and the laser beam scanner unit 227c has the pixel signal. The pixel signal corresponding to the magenta color component image of the color original image is input to the laser beam scanner unit 227d, and the pixel signal corresponding to the yellow color component image of the color original image is input thereto.
[0054]
As a result, electrostatic latent images corresponding to the color-converted document image information are formed on the photosensitive drums 222a to 222d. The developing device 224a contains black toner, the developing device 224b contains cyan toner, the developing device 224c contains magenta toner, and the developing device 224d contains yellow toner. The electrostatic latent images on the photosensitive drums 222a to 222d are developed with the toners of these colors. As a result, the document image information color-converted by the image forming unit 210 is reproduced as a toner image of each color.
[0055]
A sheet suction (brush) charger 228 is provided between the first image forming station Pa and the paper feed mechanism 211, and the suction charger 228 charges the surface of the transfer conveyance belt 216 to supply the sheet. The paper P supplied from the paper mechanism 211 is transported without shifting between the first to fourth image forming stations Pa to Pd in a state where the paper P is reliably adsorbed onto the transfer transport belt 216.
[0056]
A static eliminator 229 is provided between the fourth image forming station Pd and the fixing device 217 and almost directly above the drive roller 214. The static eliminator 229 is electrostatically attracted to the conveyance belt 216. An alternating current for separating the sheet P being transferred from the transfer conveyance belt 216 is applied.
[0057]
In the copying machine 1 configured as described above, cut sheet-like paper is used as the paper P. When the paper P is fed out from the paper feed cassette and supplied into the guide of the paper feed conveyance path of the paper feed mechanism 211, the leading end portion of the paper P is detected by a sensor (not shown). Is temporarily stopped by the pair of registration rollers 212 on the basis of the detection signal output from. Then, the sheet P is sent to the transfer conveyance belt 216 rotating in the direction of the arrow Z in FIG. 2 in time with the image forming stations Pa to Pd. At this time, the transfer conveyance belt 216 is charged by the adsorption charger 228 as described above, so that the sheet P is stably conveyed and supplied while passing through the image forming stations Pa to Pd. .
[0058]
In each of the image forming stations Pa to Pd, a toner image of each color is formed and superimposed on the support surface of the paper P that is electrostatically attracted and transported by the transfer transport belt 216. When the transfer of the image by the fourth image forming station Pd is completed, the paper P is sequentially peeled off from the top of the transfer conveyance belt 216 by the charge eliminator 229 from the leading end portion thereof and guided to the fixing device 217. Finally, the paper P on which the toner image is fixed is discharged onto a paper discharge tray 220 from a paper discharge port (not shown).
[0059]
In the above description, the laser beam scanner units 227a to 227d scan and expose the laser beam to perform optical writing on the photosensitive drums 222a to 222d, but instead of the laser beam scanner units 227a to 227d. A writing optical system (LED head) including a light emitting diode array and an imaging lens array may be used. The LED (light emitting diode) head is smaller in size than the laser beam scanner unit, and is silent because there are no moving parts. Therefore, it can be suitably used in an image forming apparatus such as a tandem digital color copying machine that requires a plurality of optical writing units.
[0060]
The document reading unit 40 is included in the image reading unit 110 in FIG. 2, and the CCD sensor 40 a corresponds to the CCD sensor 116. The image processing unit 41, the image data output unit 42, the image memory 43, the CPU 44, the image editing unit 45, and the interface units 46 and 47 are included in the image forming unit 210 in FIG. Each means constituting the image processing apparatus of the present invention is an area separation unit 40d, a gamma inclination detection unit 40e, a gamma correction unit 40f, and a filter processing unit 40g. Therefore, in the configuration of FIGS. 1 and 2, the document reading unit 40 or the image reading unit 110 corresponds to the image processing apparatus of the present invention. However, the present invention is not limited to this, and each unit of the image processing apparatus of the present invention may be included in the image forming unit 210 including the image processing unit 41 and the like.
[0061]
Next, gamma correction processing and noise reduction processing in the image processing apparatus configured by the above-described units of the copying machine 1 will be described. FIG. 3 is a diagram showing a gamma curve representing a gamma characteristic which is a relationship between an input signal level and an output signal level of image data of the image processing apparatus of the copying machine 1. FIG. 4 is a diagram showing a series of document reading processing operations of the document reading unit 40 of the copying machine 1. The copying machine 1 performs gamma correction in accordance with the gamma characteristics shown in FIG. 3. At this time, simply performing gamma correction amplifies a noise component particularly in a dark portion, thereby lowering the quality of an output image. Therefore, the copying machine 1 performs noise reduction processing after gamma correction so as to obtain a high-quality image having smooth gradation.
[0062]
Note that the noise reduction processing is executed only for the dark part and not for the bright part. This is because the noise reduction process is a process for smoothing the image, and noise amplification due to gamma correction does not occur in the bright part as in the dark part. Therefore, if the noise reduction process is performed in the bright part, excessive smoothing is performed. This is because the processing is performed, and this causes an adverse effect that the image is blurred.
[0063]
In order to perform the noise reduction processing only on the dark part, first, a certain threshold value, for example, 1 is determined with respect to the tangent slope of the gamma curve shown in FIG. When the slope of the tangent line of the gamma curve is large, it indicates a dark part where the gain of the output signal level with respect to the input signal level is large, and conversely, the part where the slope is small indicates a bright part. Then, noise reduction processing is performed only for a region where the slope of the tangent line of the gamma curve is larger than the determined threshold. As a result, noise can be reduced only for dark areas where noise amplification is caused by gamma correction, and noise reduction processing is not performed for bright areas, so image blur due to excessive smoothing does not occur.
[0064]
The noise reduction process can be performed by the following first or second method. The first method is a method of determining the pixel value of the target pixel by averaging the image data of the target pixel and its peripheral pixels. For example, for the pixel data a to i of a 3 × 3 matrix shown in FIG. 5, the image data Pe of the pixel of interest e is obtained from the following equation (1).
Pe = (a + b + c +... + H + i) / 9 (1)
[0065]
In addition, you may average, after giving predetermined weighting X1-X9 to each pixel data ai in a matrix using the following formula | equation (2).
P = (X1 · a + X2 · b +… + X8 · h + X9 · i) / (X1 + X2 + ... + X8 + X9) (2)
[0066]
In addition, the averaging is not limited to pixel data of a 3 × 3 matrix. For example, pixel data of a 5 × 5 matrix may be averaged to obtain image data P of the pixel of interest. . In this case, however, the resolution is lowered. Therefore, it is preferable to average the pixel data of the 3 × 3 matrix to obtain the image data P of the target pixel.
[0067]
The second method is a method of determining the pixel value of a target pixel by processing image data of the target pixel and its surrounding pixels using a median filter. For example, the pixel data a to i of the 3 × 3 matrix shown in FIG. That is, among the image data a to i, when the image data g is an intermediate value and the image data P of the target pixel is used, the pixel of the image data g is the target pixel.
[0068]
7 to 9 are graphs showing the results of noise reduction processing in the copying machine 1. Specifically, a gray patch of a commercially available IT-8 chart, that is, 24 patches (patch 0 to patch 23) from achromatic black to white shown in FIG. The standard deviation of the image data of each patch when the noise reduction process is performed by the first or second method and when the noise reduction process is not performed is obtained. FIG. 7 shows the result of the red component, FIG. 8 shows the result of the green component, and FIG. 9 shows the result of the blue component. ORG indicates the standard deviation of the image data when the noise reduction processing is not performed, AVE indicates the standard deviation of the image data when the noise reduction processing is performed by averaging, which is the first method, MID indicates a standard deviation of image data when noise reduction processing is performed by a method using a median filter, which is the second method. In addition, in AVE and MID in FIGS. 7 to 9, noise reduction processing is performed on the input of all toner patches, and noise reduction processing is not performed only on dark portions.
[0069]
In FIGS. 7 to 9, the large value of the standard deviation indicates that the variation of the output value is large with respect to the same input value, and the influence of noise is large. From the ORG, it can be seen that the output variation is large in the toner patch having a small number, that is, the toner patch corresponding to the dark portion. On the other hand, in AVE and MID, the standard deviation value is lowered in all toner patches, and it can be seen that the output variation, that is, the influence of noise is reduced. However, a toner patch having a large number, that is, a toner patch corresponding to a bright portion, has a smaller influence of noise (standard deviation is smaller) than that of a dark portion from the beginning, and therefore has a small noise reduction effect. For this reason, it can be said that it is not preferable to perform the noise reduction processing because the adverse effect of the image blur due to the smoothing becomes larger than the noise reduction effect.
[0070]
When the noise reduction processing range is a range where the tangent slope of the gamma curve exceeds 1 as in this embodiment, for example, in FIG. 3, the noise reduction processing range is that the input signal level is 57 or less and the output The signal level is in the range of 157 or less, and the noise reduction filter processing is performed on the image data in this range. 7 to 9, the range in which the tangent slope of the gamma curve exceeds 1 corresponds to the patch 18 or more.
[0071]
Note that noise reduction processing is effective because it requires a somewhat smooth gradation expression in a photographic region, but it is not preferable because it causes blurring of an edge in a character region including many edges. Accordingly, the copying machine 1 is configured to perform a noise reduction process only on the photographic area after performing an area separation process on the input image data into a photographic area (halftone area) and a character area. It is preferable. The determination of whether the image data of the document is a photographic region or a character region is automatically performed by the region separation unit 40d in FIG. 1, but before reading the document using a device such as a digitizer that can specify the region, An area may be designated.
[0072]
As described above, in the present embodiment, the image data read by the image reading unit 40 such as a scanner is subjected to the image processing according to the present invention and is output by the copying machine 1. The present invention is not limited to this configuration, and means for acquiring image data to be subjected to gamma processing and means for outputting image data to which gamma processing has been performed are not limited to the present embodiment. The present invention can also be applied to a system that displays and outputs image data captured by a digital camera on a display.
[0073]
【The invention's effect】
  As described above, according to the present invention, the gamma correction processing is performed.Each obtained by decomposing into red R, green G and blue B color componentsOf the image data, the gamma curve indicating the gamma characteristic of the output meansOutput level Y relative to input level XTilt, Predetermined in common for each color componentThresholdFor example, tilt 1Larger thanDark partPixelFor each color componentNoise reduction processing for image dataRespectivelySince it is output from the application output means, noise can be reduced even in the dark part of an image where noise amplification is likely to occur due to gamma correction, and it has smooth gradation characteristics by preventing image roughness due to noise. It is possible to reproduce a good image.
[0074]
According to the present invention, since the noise reduction processing for determining the pixel value of the target pixel by averaging the image data of the target pixel to be subjected to the noise reduction processing and its surrounding pixels is performed. This pixel value is determined as an average value in the data including the peripheral pixels, and it is possible to prevent the occurrence of roughness due to noise and reproduce smooth gradation.
[0075]
Further, according to the present invention, the noise reduction processing for determining the pixel value of the target pixel by applying the filter processing using the median filter to the image data of the target pixel subjected to the noise reduction processing and the surrounding pixels. Therefore, the pixel value of the target pixel is determined to be an intermediate value in the data including the peripheral pixels, and the smooth gradation can be reproduced by preventing the occurrence of roughness due to noise.
[0076]
Further, according to the present invention, for image data including a character area and a photographic area, noise reduction processing is performed only on image data in the photographic area, and noise reduction processing is not performed on image data in the character area. Therefore, blurring of the edge of the character can be avoided.
[0077]
  According to the invention, the image is read and output by the image reading means.Each obtained by decomposing the image into red R, green G and blue B color componentsAfter performing gamma correction processing on the image data, before applying it to the output means, perform noise reduction processing.RespectivelySince it is implemented, image data with reduced noise can be provided to an image forming apparatus provided outside the image reading apparatus. An image forming apparatus to which such image data is given can form a good image having smooth gradation even if it does not have a noise reduction processing function.
[0078]
Further, according to the present invention, since it is possible to select whether or not to perform noise reduction processing in the image reading apparatus, an image can be selected according to the presence or absence of a noise reduction processing function of an image forming apparatus or the like to which image data is given. Noise reduction processing can be executed in the reading device, and normal image data can be processed so as not to affect image processing such as a noise reduction processing function provided in an image forming apparatus to which image data is given. This can be applied to the image forming apparatus.
[0079]
In addition, according to the present invention, noise reduction processing is performed only on image data in a photographic area, and noise reduction processing is not performed on image data in a character area, so that blurring of character edges can be avoided. it can.
[0080]
  According to the invention, the image is read and output by the image reading means.Each obtained by decomposing the image into red R, green G and blue B color componentsPrint output means after performing gamma correction on image dataImage forming means Pa to Pd respectivelyBefore givingFrom the image data of the respective color components of red R, green G, and blue B subjected to the above-described noise reduction processing by the printing image data deriving means 41d, black, yellow Y, Printing image data for each of magenta M and cyan C is obtained and given to the image forming means Pa to Pd of the printing output means, and color printing is performed on the recording medium.Since the image is output from the print output means, it is possible to print out an image with reduced noise.
[0081]
In addition, according to the present invention, noise reduction processing is performed only on image data in a photographic area, and noise reduction processing is not performed on image data in a character area, so that blurring of character edges can be avoided. it can.
[Brief description of the drawings]
FIG. 1 is a block diagram of a color digital copying machine 1 which is an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of the copying machine 1;
FIG. 3 is a diagram illustrating a gamma curve of the image processing apparatus of the copying machine 1;
4 is a diagram showing a series of document reading processing operations of the document reading unit 40 of the copying machine 1. FIG.
FIG. 5 is a diagram illustrating matrix pixel data a to i subjected to noise reduction processing;
FIG. 6 is a diagram showing a gray patch of a commercially available IT-8 chart.
7 is a graph showing a result of noise reduction processing of a red component in the copying machine 1. FIG.
FIG. 8 is a graph showing the results of green component noise reduction processing in the copier 1;
FIG. 9 is a graph showing the result of blue component noise reduction processing in the copier 1;
[Explanation of symbols]
1 color digital copier
40 Document reading unit (image data input unit)
40a, 116 CCD sensor
40b Shading correction circuit
40c line correction unit
40d region separation part
40e Gamma tilt detector
40f Gamma correction unit
40g filter processing unit
41 Image processing unit
42 Image data output unit
43 Image memory
44 CPU (Central Processing Unit)
45 Image Editing Department
46, 47 interface
110 Image reading unit
112 Double-sided automatic document feeder
113 First document scanning unit
114 Second document scanning unit
115 Optical lens
210 Image forming unit
211 Paper feed mechanism

Claims (13)

A gamma correction processing unit that performs gamma correction processing each respective image data obtained by decomposing red composed image, the color components of green and blue by a matrix of pixels,
Output means for outputting image data subjected to gamma correction processing;
Among the image data of each color component the gamma correction process, the slope of the output level Y with respect to the input level X of the gamma curve indicating the gamma characteristic of the output means, wherein not greater than the common pre-determined threshold value to each color component An image processing apparatus comprising: noise reduction processing means for performing noise reduction processing for reducing noise on the image data of each color component of a pixel in a dark part and giving the output data to the output means .   2. The image processing according to claim 1, wherein the noise reduction processing means averages image data of a target pixel to be subjected to the noise reduction processing and its peripheral pixels to determine a pixel value of the target pixel. apparatus. The image processing apparatus according to claim 2, wherein the image data of the target pixel and the peripheral pixels are weighted, and the weighted image data is averaged.   The noise reduction processing means determines a pixel value of a target pixel by performing a filter process using a median filter on image data of the target pixel subjected to the noise reduction process and its surrounding pixels. The image processing apparatus according to claim 1. The image data includes image data of a character area and a photo area,
The image processing apparatus includes a region separation unit that separates image data of a character region and a photographic region,
The noise reduction processing means, the image processing apparatus according to one of claims 1-4, characterized in that performing the noise reduction process on image data of only photograph region. The image processing apparatus according to claim 1, wherein the predetermined threshold is an inclination of 1. Reading a document, an image reading unit to output red Thus configured image in a matrix of picture element, each image data obtained by decomposing the color components of green and blue,
A gamma correction processing unit that performs gamma correction processing each the image data of each color component from the image reading means,
Output means for outputting image data subjected to gamma correction processing;
Of the image data of each color component subjected to the gamma correction process, the slope of the output level Y with respect to the input level X of the gamma curve indicating the gamma characteristic of the output means is larger than a predetermined threshold common to the color components. An image reading apparatus comprising: noise reduction processing means for performing noise reduction processing for reducing noise on the image data of each color component of a dark pixel, and applying the noise reduction processing means to the output means . The image reading apparatus according to claim 7 , further comprising a noise reduction processing setting unit configured to set whether or not the noise reduction processing unit performs the noise reduction processing. The image data includes image data of a character area and a photo area,
The image reading apparatus includes a region separating unit that separates image data of a character region and a photographic region,
Wherein the noise reduction processing means includes an image reading apparatus according to claim 7 or 8, characterized by applying noise reduction processing to the image data of only photograph region. The image reading apparatus according to claim 7, wherein the predetermined threshold is an inclination of 1. Reading a document, an image reading unit to output red Matrix-like image containing the thus configured image, each image data obtained by decomposing the color components of green and blue,
A gamma correction processing unit that performs gamma correction processing each the image data of each color component from the image reading means,
Image forming means for printing out black, yellow, magenta, and cyan images on a recording medium , and printing image data for each of black, yellow, magenta, and cyan is provided on each of these image forming means. A print output means,
Of the image data of each color component subjected to the gamma correction processing, the slope of the output level Y with respect to the input level X of the gamma curve indicating the gamma characteristic of the print output means is greater than a predetermined threshold common to the color components. the image data of each color component of a pixel of the dark area has the size, and the noise reduction processing means for performing each of the noise reduction processing to reduce noise,
In response to the output of the noise reduction processing means, print image data for each of black, yellow, magenta and cyan is derived from the image data of each color component subjected to the noise reduction processing, and the print output means An image forming apparatus comprising: image data deriving means for printing to be provided to the image forming means. The image data includes image data of a character area and a photo area,
The image forming apparatus includes a region separation unit that separates image data of a character region and a photographic region,
The image forming apparatus according to claim 11 , wherein the noise reduction processing unit performs noise reduction processing only on image data in a photographic region. The image forming apparatus according to claim 11, wherein the predetermined threshold is an inclination of 1.

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