JP2007067908A - Image processor, image forming apparatus, image processing method, and image processing program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve visibility of a yellow character drawn on a white or nearly white background. <P>SOLUTION: After a pixel corresponding to an edge part is detected on the basis of a pixel value of Y component (S3), a pixel corresponding to a color character area is detected (S4). Next, pixel values of YCM components are detected for each pixel (step S5). Then, with respect to each pixel, it is judged whether the pixel value of Y component is extremely large in comparison with the pixel value of M component and C component (S6). In succession, with respect to each pixel, it is judged whether the pixel corresponds to the edge part and to the color character area (step S7). When the judgment at steps S6 and S7 are both positive, pixel values of the C component and M component are converted into higher pixel values (step S8); when any of the judgement is negative, the conversion is not performed. Next, an image signal is printed (S9). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing technique for converting an image signal and an image forming technique using the image processing technique.

In a color image forming apparatus, when an input image signal represents an achromatic character (referred to as a black character) drawn on a chromatic background (referred to as a colored background), the black character is detected, For black characters, there is known a technique for increasing the density of black (referred to as BK) and decreasing the density of yellow (referred to as Y), cyan (referred to as C), and magenta (referred to as M) (for example, patents). Reference 1, paragraph "0001"). That is, the related art reproduces black characters in a single black color, thereby improving the quality of an image printed on recording paper.
JP-A-8-186725

  However, when a character mainly composed of yellow (referred to as a yellow character) is drawn on a white or near-colored background, the character is visually unclear. Since the image forming apparatus according to the above prior art only supports black characters, the visibility of such yellow characters cannot be increased.

  The present invention has been made in view of the above problems, and provides an image processing technique for improving the visibility of yellow characters drawn on a white background or a background close thereto, and an image forming technique using the image processing technique. The purpose is to do.

  In order to solve the above-described problems and achieve the above-described object, according to a first aspect of the present invention, there is provided an image processing apparatus for detecting a character region that is a character region in an input image signal. An area detection unit; an edge detection unit that detects an edge portion of the input image signal; and the input image signal is received in a form expressed by a color component including yellow, cyan, and magenta, and the density of yellow is cyan and magenta. A yellow detection portion that detects a yellow portion that is higher than a predetermined standard in comparison with the density of the image, and the yellow character edge portion that is the character region and the edge portion and the yellow portion. An edge enhancement processing unit for converting the input image signal so as to increase the density of at least one of the color components excluding yellow. .

  According to this configuration, the character region is determined from the input image signal, the edge portion is detected, and the yellow portion is detected. A yellow character edge portion that is a character region, an edge portion, and a yellow portion is an edge portion of a character region mainly composed of yellow. When the background of the character is white or close to it, the outline of the character mainly composed of yellow becomes visually unclear when an image signal is printed on a recording material or displayed on a display. The edge enhancement processing unit converts the input image signal so as to increase the density of at least one color component excluding yellow for the yellow character edge portion. That is, a kind of edge enhancement processing is performed on the yellow character edge portion. Thereby, the outline of a character becomes clear visually and the visibility of a character improves.

  Note that the predetermined reference adopted by the yellow detection unit does not have to be a constant value, and does not have to be the same between cyan and magenta. For example, the yellow detection unit may detect a yellow portion by comparing a density difference between yellow, cyan, and magenta, or a density ratio with a predetermined value. Yellow, magenta , And some function having the density of cyan as a variable, for example, a sum may be calculated, and the value of the function may be compared with a predetermined value, and various forms may be employed.

  Further, the character region, the edge portion, and the yellow portion may be those in which the other one is detected within a range in which one of them is detected. For example, the edge detection unit may detect an edge portion in the character region detected by the character region detection unit, and the yellow detection unit may detect a portion corresponding to the detected character region and the edge portion. Among them, the yellow portion may be detected. The present configuration includes such a form.

  According to a second aspect of the present invention, there is provided the image processing device according to the first aspect, wherein the character region detection unit is a color character region that is a region of a chromatic character in the input image signal. Is detected as the character area.

  According to this configuration, the color character area is selected as the character area to be edge-enhanced. For this reason, unnecessary edge emphasis processing is performed on the achromatic character region, thereby coloring the edge portion of the achromatic character region or unnecessarily increasing the density of the edge portion of the achromatic character region. Avoided.

  According to a third aspect of the present invention, there is provided the image processing apparatus according to the first or second aspect, wherein the edge detection unit rapidly increases the density along the main scanning direction as the edge portion. A first edge portion that is one of the portions that increase or decrease, a second edge portion that is one of the portions where the density rapidly increases or decreases along the sub-scanning direction, the first edge portion, and Only one of the third edge portion including both of the second edge portions is detected.

  According to this configuration, since only one of the first to third edge portions is detected as the edge portion, it is as if the yellow-based characters are in the main scanning direction or the opposite direction, the sub-scanning direction. Alternatively, an image signal is obtained in which a character is accompanied by a shadow generated by light rays emitted from one or both of the opposite directions. For this reason, even a relatively thin character can be edge-enhanced while leaving the original color portion of the yellow-based character. In addition, a visually distinctive beauty is added to yellow-based characters.

  Note that the density at which the edge detection unit detects an edge portion as a portion where the density rapidly changes may be a density of a specific color component or a combination of a plurality of densities. For example, the density of the Y (luminance) component when Y (luminance), U (color difference), and V (color difference) are color components can be taken as the simplest and most reasonable form.

  According to a fourth aspect of the present invention, there is provided the image processing apparatus according to any one of the first to third aspects, wherein the yellow detector has a yellow density of the input image signal. A portion where the density of cyan is higher than the first predetermined value and the density of yellow is higher than the second predetermined value than the density of magenta is detected as the yellow portion.

  According to this configuration, the yellow detection unit detects a portion where the yellow density is higher than both of the cyan and yellow densities exceeding a predetermined value set for each as a yellow portion. Can be configured simply.

  According to a fifth aspect of the present invention, there is provided the image processing apparatus according to any one of the first to fourth aspects, wherein the yellow detecting section is expressed in a form expressed by a color component further including black. The input signal is received, and the edge emphasis processing unit performs the conversion by increasing at least the density of black for the yellow character edge portion.

  According to this configuration, since the edge enhancement processing unit performs edge enhancement by increasing at least the density of black, the visibility of yellow characters is effectively enhanced.

  According to a sixth aspect of the present invention, there is provided the image processing apparatus according to any one of the first to fifth aspects, wherein the edge enhancement processing unit applies the color to the yellow character edge part. The conversion is performed by adding a third predetermined value to at least one of the components excluding yellow.

  According to this configuration, since the edge enhancement processing unit performs edge enhancement by adding a predetermined value to the density of at least one color component excluding yellow, the edge enhancement processing unit can be configured simply.

  According to a seventh aspect of the present invention, there is provided the image processing apparatus according to any one of the first to fifth aspects, wherein the edge emphasis processing unit applies the color to the yellow character edge part. The conversion is performed by setting at least one of the components excluding yellow as a fourth predetermined value.

  According to this configuration, since the edge enhancement processing unit performs edge enhancement by setting the density of at least one color component excluding yellow to a predetermined value, the edge enhancement processing unit can be configured simply.

  According to an eighth aspect of the present invention, there is provided the image processing apparatus according to any one of the first to seventh aspects, wherein the edge emphasis processing unit is configured to perform yellow processing on the yellow character edge portion. The process of reducing the density is further performed as the conversion.

  According to this configuration, the edge enhancement processing unit further performs a process of lowering the density of yellow as the edge enhancement process, and therefore, when an image signal is printed, unnecessary yellow recording is suppressed, whereby ink, toner Etc. can be saved somewhat.

  According to a ninth aspect of the present invention, there is provided an image forming apparatus, wherein the image processing apparatus according to any one of the first to eighth aspects and an image signal are generated by reading a document image, and generated And a scanner unit for supplying the image signal as the input image signal to the image processing apparatus.

  According to this configuration, since the image processing apparatus of the present invention and the scanner unit that supplies the input image signal to the image processing apparatus are provided, the original image is read, and the yellow main component in the image signal obtained by reading the original image Can improve the visibility of the characters.

  According to a tenth aspect of the present invention, there is provided an image forming apparatus, wherein the image processing apparatus according to any one of the first to eighth aspects and an image signal output from the image processing apparatus are used as a recording material. And a printing unit for printing.

  According to this configuration, since the image processing apparatus according to the present invention and the printing unit that prints the image signal output from the image processing apparatus on the recording material are provided, the input image is improved in a form in which the visibility of mainly yellow characters is improved. The signal can be printed on the recording material.

  According to an eleventh aspect of the present invention, there is provided an image processing method comprising: a character region detecting step for detecting a character region which is a character region in an input image signal; and an edge in the input image signal. An edge detection step for detecting a portion and the input signal is received in a form expressed by color components including yellow, cyan, and magenta, and the density of yellow is a portion that is higher than a predetermined standard compared to the densities of cyan and magenta. A yellow detection step of detecting a yellow portion, and at least one density excluding yellow of the color component is increased with respect to the yellow character edge portion which is the character region and the edge portion and the yellow portion; And an edge enhancement processing step for converting the input image signal.

  According to this configuration, since each of the above steps is provided, the visibility of yellow-based characters drawn on white or a background close thereto is improved for the same reason as described for the image processing apparatus of the present invention.

  According to a twelfth aspect of the present invention, there is provided an image processing program, wherein the computer detects a character area that is a character area in the input image signal, and the input image signal The edge detection means for detecting the edge portion and the input signal are accepted in a form expressed by color components including yellow, cyan and magenta, and the density of yellow is higher than a predetermined standard compared to the densities of cyan and magenta. A yellow detection means for detecting a yellow portion that is a portion; and at least one of the color components excluding yellow for the yellow character edge portion that is the character region and the edge portion and the yellow portion. It functions as an edge enhancement processing means for converting the input image signal so as to increase the density.

  According to this configuration, since the computer functions as each of the above-described means, the visibility of yellow-based characters drawn on white or a background close thereto is improved for the same reason as described for the image processing apparatus of the present invention. To do.

  As described above, according to the present invention, the visibility of yellow characters drawn on white or a background close thereto is improved.

(Overall configuration of the device)
FIG. 1 is a block diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 100 includes a scanner unit 10, an image processing unit 20, a printing unit 30, and a control unit 40. The scanner unit 10 optically reads an image of a document to generate an image signal, and includes an exposure lamp 11, a CCD (charge coupled device) 12, and an AFE (Analog Front End) 13. Yes. The AFE 13 has an analog-digital converter (not shown).

  The scanner unit 10 irradiates the original with the exposure lamp 11 and receives the reflected light by the CCD 12 to read an image from the original, and converts an image signal corresponding to the read image from an analog format to a digital format by the AFE 13. After that, the data is output to the image processing unit 20. The scanner unit 10 is configured to be able to read not only monochrome originals but also color originals and photographic originals. In the example of FIG. 1, the scanner unit 10 outputs a color image signal having red (referred to as R), green (referred to as G), and blue (referred to as B) as color components. The image signal is expressed by, for example, 8 bits for each color component of each pixel so as to have 256 gradations for each color component. Since the configuration of the scanner unit 10 is conventionally known, a detailed description thereof will be omitted.

  The image processing unit 20 performs various image processing on the image signal input from the scanner unit 10, and includes an image memory 22, an input image processing unit 23, and a print image processing unit 24. The input image processing unit 23 corresponds to the embodiment of the image processing apparatus of the present invention. For the input image signal, predetermined correction processing such as level correction and γ correction, image signal compression or expansion processing, Various image processing (processing) such as enlargement or reduction processing is performed. It should be noted that, as will be described later, the image processing unit 23 has a function of performing edge enhancement on yellow characters. The image memory 22 stores the image signal processed by the input image processing unit 23. For this purpose, for example, an HDD (Hard Disc Drive), a RAM (Random Access Memory), and a flash ROM (Read Only) are used. Memory; ROM).

  The input image processing unit 23 and the print image processing unit 24 can also be realized by a computer that operates by software. However, in order to realize high-speed processing following the reading speed of the scanner unit 10, these are configured by ASIC (Application Specific Integrated Circuits) equipped only with hardware that does not require software. It is desirable to be done. In the present embodiment, these are ASICs and are configured on a single semiconductor chip.

  The print image processing unit 24 reads the image signal stored in the image memory 22 and converts it into an image signal for printing. The print image processing unit 24 includes a binarization unit 25 and converts an image signal having gradation stored in the image memory 22 into a binarization signal for printing as a main function. The binarization unit 25 binarizes an image signal having gradation, for example, based on a known error diffusion method.

  The printing unit 30 prints an image on a recording material such as a recording sheet or a recording sheet based on the image signal for printing output from the print image processing unit 24. Printing an image based on the image signal is referred to as “printing the image signal” or “printing the image signal”. The printing unit 30 is configured as a known electrophotographic printer using a laser beam, and includes an LSU (Laser Scanner Unit) 31, a developing unit 32, a transfer unit 33, a fixing unit 34, and paper conveyance. Part 35 is included.

  The LSU 31 modulates the laser beam based on the image signal output from the print image processing unit 24 and scans it on a charged photosensitive drum (not shown), thereby forming a latent image on the photosensitive drum. The developing unit 32 electrostatically attracts the developer including toner and carrier to the photosensitive drum on which the latent image is formed, thereby revealing the latent image. The transfer unit 33 transfers the developer from the photosensitive drum to the recording material. The fixing unit 34 fixes the developer on the recording material. The paper transport unit 35 transports the recording material from a recording paper tray (not shown) to the transfer unit 33, further transports the recording material to the fixing unit 34, and then discharges the recording material to a recorded paper tray (not shown).

  In addition to a CPU (Central Processing Unit) 41, the control unit 40 includes storage units such as a ROM 43 that stores a program that defines the operation of the CPU 41, and a RAM 42 that temporarily stores data. Yes. That is, the control unit 40 includes a computer. As a result, the control unit 40 performs the scanner unit 10 and image processing in accordance with user instruction information received by an operation panel (not shown) or the like, or detection signals from sensors provided in various parts of the image forming apparatus 100. A process of controlling the entire image forming apparatus 100 including the unit 20 and the printing unit 30 is executed.

  The above-described program for realizing these functions by being read by the computer as the control unit 40 is stored in a non-volatile, large-capacity external storage device such as an HDD (not shown), and the main memory using the RAM 42, for example. It can also be used for execution by the CPU 41 by appropriately transferring to the apparatus. The program can be supplied through a recording medium such as the ROM 43 or a CD-ROM (not shown), or can be supplied via a transmission medium such as a network connected to a network interface (not shown). The transmission medium is not limited to a wired transmission medium, and may be a wireless transmission medium. The transmission medium includes not only a communication line but also a relay device that relays the communication line, such as a router.

  When the program is supplied through the ROM 43, it can be used for execution by the CPU 41 by mounting the ROM in which the program is recorded in the control unit 40. When the program is supplied through a CD-ROM, the CD-ROM reader is connected to a parallel interface (not shown), for example, and the program is transferred to the RAM 42 or an HDD (not shown) for execution by the CPU 41. be able to. When the program is supplied through a transmission medium, the program received through the network interface can be transferred to the RAM 42 or the HDD (not shown) for execution by the CPU 41.

  Note that image forming apparatuses generally include apparatuses that input and output images or image signals, such as copiers, printers, facsimile machines, or multi-function machines having both. The image forming function is a concept that broadly includes a function of inputting and outputting an image or an image signal. Accordingly, in general, an image forming apparatus is provided with an image input unit that takes in an image signal, an image output unit that outputs an image or an image signal, and a control unit that controls them. The image input unit includes at least one of a scanner unit 10 that reads an image from a recording sheet on which an image is recorded and an image signal reception unit that receives an image signal. The image output unit uses the image as a recording material. At least one of the printing unit 30 for recording and the image signal transmission unit for transmitting the image signal is included. For example, in the case of a printer, an image signal receiving unit and a printing unit 30 are provided. If attention is paid only to a portion that performs the transmission function of the facsimile apparatus, a scanner unit 10 and an image signal transmitting unit are provided. . The general concept of the image forming apparatus is as described above. The image forming apparatus 100 according to the embodiment of the present invention includes the scanner unit 10 in the image input unit and the printing unit 30 in the image output unit. .

(Configuration of image processing unit)
FIG. 2 is a block diagram illustrating a configuration example of the input image processing unit 23. The input image processing unit 23 includes a shading correction unit 51, a γ (gamma) correction unit 52, a chromatic aberration correction unit 53, an MTF (Modulation Transfer Function) correction unit 54, a scanner color correction unit 55, and an RGB / YCM conversion unit 56. A character region detection / edge detection unit 57, an adaptive filter processing unit 58, and an edge color conversion processing unit 59. It should be noted that the image processing unit 23 includes an edge color conversion processing unit 59 that performs edge enhancement on yellow characters. Since the configuration and function of each unit from the shading correction unit 51 to the adaptive filter processing unit 58 are well known in the art, the following description will be simplified.

  The shading correction unit 51 receives an image signal having RGB as a color component output from the scanner unit 10 and performs shading correction on the input image signal. The shading correction is based on the white reference and black reference data, and the value of the image signal, that is, the pixel value (also expressed as density) due to the variation in the light amount of the exposure lamp 11 along the main scanning direction and the variation in sensitivity of the CCD 12. It is intended to correct the variation of. The γ correction unit 52 performs gamma correction for changing the gradation characteristics for each color component of each pixel on the image signal after shading correction.

  The chromatic aberration correction unit 53 performs chromatic aberration correction for each pixel on the image signal after γ correction. The chromatic aberration correction is to correct a color shift caused by a difference in wavelength of each RGB color and a characteristic of a lens (not shown) included in the scanner unit 10. The MTF correction unit 54 performs MTF correction on the image signal after chromatic aberration correction. The MTF correction is to convert the light incident on the CCD 12 into an image signal with a sharpening effect by correcting the “blur” in consideration of the occurrence of “blur” by a lens (not shown). is there. The scanner color correction unit 55 performs correction for removing the mixed color component included in the pixel values of the RGB colors for each pixel on the image signal after the MTF correction. The RGB / YCM conversion unit 56 converts an image signal having RGB as a color component into an image signal having YCM as a color component.

  The character region detection / edge detection unit 57 determines, for each pixel, which image region, such as a character region or a halftone dot region, corresponds to the image signal output from the scanner color correction unit 55, and It is detected whether it corresponds to the edge portion. The character area detection / edge detection unit 57 outputs an area determination signal ASIG and an edge detection signal EDGE expressing each determination result for each pixel. The adaptive filter processing unit 58 performs a filter process for improving the image quality on an image signal having YCM as a color component. The adaptive filter processing unit 58 refers to the region determination signal ASIG and the edge detection signal EDGE in order to perform filter processing suitable for the type of image. The characteristic edge color conversion processing unit 59 will be described in detail later.

  FIG. 3 is a block diagram showing a configuration of the character area detection / edge detection unit 57. Since each component of the character area detection / edge detection unit 57 is also well known, its description is only a brief description. The character region detection / edge detection unit 57 includes an RGB / YUV conversion processing unit 61, a saturation determination unit 62, a Y inversion unit 63, a character candidate / character surrounding detection unit 64, an edge detection unit 65, a dense thin line / photo region detection unit. 66, a character area signal generation unit 67, a black / color character signal generation unit 68, a character area signal expansion unit 69, a halftone signal generation unit 70, and an area signal synthesis unit 71.

  The RGB / YUV conversion processing unit 61 uses, as color components, Y (luminance), U (color difference), and V (color difference) as image components having RGB as color components input to the character region detection / edge detection unit 57. Convert to image signal. The saturation determination unit 62 determines whether each pixel is a chromatic color or an achromatic color based on the pixel values of the U component and the V component output from the RGB / YUV conversion processing unit 61. This determination is performed when, for example, the target pixel satisfies TL <U <TH and TL <V <TH using two predetermined threshold values TL and TH (0 <TL <TH <255). The determination is made by determining that the pixel is an achromatic color, and determining that the pixel is a chromatic color when the pixel is not satisfied. The determination result is used by the black / color character signal generation unit 68.

  The Y inversion unit 63 inverts the pixel value of the Y component. That is, the pixel value Y is converted to 255-Y. The detection processing by the character candidate / character surrounding detection unit 64, the edge detection unit 57, and the dense thin line / photo area detection unit 66 is executed using the pixel value of the Y component after inversion. The character candidate / character surrounding detection unit 64 detects whether the target pixel corresponds to a character candidate and whether it corresponds to a character periphery. For this purpose, the character candidate / character surrounding detection unit 64 sequentially performs gamma correction processing, integration filter processing, second-order differential filter processing, and threshold processing on the pixel value of the Y component after inversion, for example. The gamma correction processing performed here is processing for converting pixel values less than a predetermined value to zero. The integration filter process is, for example, an integration process that uses a 7 × 7 filter centered on the pixel of interest. The secondary differential filter processing is, for example, for performing secondary differential processing using a 7 × 7 filter centered on the target pixel. The threshold processing is performed by using, for example, two predetermined threshold values TC and TA (0 <TC <255; −128 <TA <127), and the pixel value D after the second order differential processing is TC <D. It is determined that the target pixel corresponds to the character candidate. If D <TA, it is determined that the target pixel corresponds to the character periphery.

  The edge detection unit 65 detects whether the target pixel corresponds to an edge portion. For this purpose, for example, the edge detection unit 65 sequentially performs gamma correction processing, secondary differential filter processing, background pixel count processing, and edge signal generation processing on the pixel value of the inverted Y component. The gamma correction processing performed here is the same processing as the gamma correction processing performed by the character candidate / character surrounding detection unit 64. The secondary differential filter processing is performed using, for example, a 7 × 7 secondary differential filter centered on the target pixel as shown in FIG. In general, the filtering process is executed by integrating the product of the value of each pixel and the value of the corresponding filter. In the background pixel counting process, for example, out of 7 × 7 pixels centered on the target pixel, the number of pixels having a pixel value less than a predetermined threshold is counted for a total of 8 pixels including the four corners and the center of the four sides. It is determined whether or not the count value is equal to or greater than another predetermined threshold value TN. In the edge signal generation process, when the value obtained by performing the second-order differential filter process exceeds another predetermined threshold value and the count value is equal to or greater than the threshold value TN, the target pixel is an edge portion. In other cases, it is determined not to correspond to the edge portion. As illustrated in FIG. 5, the determination result by the edge detection unit 65 is expressed by, for example, a 1-bit edge detection signal EDGE.

  Returning to FIG. 3, the dense fine line / photo area detection unit 66 determines whether or not the pixel of interest corresponds to the vertical dense fine line, whether it corresponds to the horizontal dense fine line, and whether it corresponds to the photo area. To do. This determination is made, for example, for a 9 × 9 pixel centered on the target pixel, by integrating the absolute value of the pixel value difference between adjacent pixels along the main scanning direction and the pixel value between adjacent pixels along the sub-scanning direction. This is done by calculating an integrated value of the absolute value of the difference between the two and comparing the magnitude of these integrated values with a predetermined threshold value.

  The character area signal generation unit 67 generates a character area signal indicating whether or not the target pixel corresponds to the character area. For example, the character region signal generation unit 67 determines that the target pixel corresponds to the character region when the pixel of interest corresponds to the edge portion and corresponds to either the character candidate or the dense thin line. The black / color character signal generation unit 68 determines whether the character region corresponds to a color character region that is a chromatic character region or a black character region that is an achromatic character region. If the target pixel corresponds to the character region and the determination unit 62 determines that the target pixel is a chromatic color again, the character region signal generation unit 67 determines that the target pixel corresponds to the color character region, and achromatic color. If it is determined that it corresponds to the black character area.

  The character area signal extension unit 69 performs processing for extending the character area to surrounding pixels. More specifically, for example, if there is one or more color character area pixels among 3 × 7 pixels centered on the target pixel, the character area signal extension unit 69 determines that the target pixel corresponds to the color character area, If there is at least one black character area, it is determined that it corresponds to the black character area.

  The halftone signal generator 70 determines whether or not the target pixel is a halftone area. For example, when the target pixel does not correspond to the periphery of the character and does not correspond to the photograph area, the halftone signal generation unit 70 determines that the pixel corresponds to the dot area.

  The area signal synthesis unit 71 generates and outputs an area determination signal ASIG indicating the image area to which the target pixel corresponds, based on whether the target pixel corresponds to the black character area, the color character area, or the halftone dot area. To do. Regarding the pixel of interest, the determination that it corresponds to the black character region, the determination that it corresponds to the color character region, and the determination that it corresponds to the halftone dot region are not necessarily exclusive. A certain pixel of interest may be determined to correspond to a black character region, at the same time, determined to correspond to a color character region, and further determined to correspond to a halftone dot region. The area signal combining unit 71 determines a priority order between the determinations in advance, adjusts the overlapping determinations according to the priority order, and generates an area determination signal ASIG. As illustrated in FIG. 6, the area determination signal ASIG represents an area to which the target pixel corresponds, for example, with 2 bits.

  Of the components of the character region detection / edge detection unit 57, the edge detection unit 65 corresponds to an embodiment of the edge detection unit of the present invention, and the edge detection unit 65 for generating the region determination signal ASIG is provided. A series of constituent elements including also corresponds to an embodiment of the character area detection unit of the present invention.

(Configuration of edge color conversion processor)
FIG. 7 is a circuit diagram illustrating a configuration example of the edge color conversion processing unit 59. As illustrated in FIG. 7, the edge color conversion processing unit 59 can be easily configured by combining known digital ICs (integrated circuits). This indicates that the edge color conversion processing unit 59 can be easily configured by the ASIC together with other components of the input image processing unit 23. In the example of FIG. 7, the edge color conversion processing unit 59 includes subtractors 75 and 76, comparators (comparators) 79 and 80, AND circuits 81 to 83, adders 84 and 85, registers 77, 78, 86, 87. , And multiplexers 88 and 89.

  The subtractor 75 calculates a difference ΔYC (= Y−C) between the pixel values of the Y component and the C component output from the adaptive filter processing unit 58. Similarly, the subtractor 76 calculates the difference ΔYM (= Y−M) between the Y component and M component pixel values output from the adaptive filter processing unit 58. The comparator 79 determines whether or not the difference ΔYC is larger than a predetermined value (first predetermined value) held in the register 77. Similarly, the comparator 80 determines whether or not the difference ΔYM is larger than a predetermined value (second predetermined value) held in the register 78.

  The registers 77 and 78 are configured in the same way as, for example, a RAM memory cell, and each hold an 8-bit signal. The values of the registers 77 and 78 are written by the CPU 41 of the control unit 40 in the initialization process performed immediately after the power of the image processing apparatus 100 is turned on, for example. The registers 77 and 78 may be replaced with eight resistor element rows individually connected to either a negative power supply line (not shown) or a positive power supply line of the edge color conversion processing unit 59. The same applies to the registers 86 and 87.

  The AND circuit 81 activates the output LL only when both of the two comparators 79 and 80 activate (ie, assert) the output. That is, the subtractors 75 and 76, the comparators 79 and 80, the registers 77 and 78, and the AND circuit 81 correspond to an embodiment of the yellow detector of the present invention.

  The AND circuit 82 is used only when the area signal synthesis unit 71 outputs “10” as the 2-bit area determination signal ASIG, that is, when it is determined that the target pixel to be processed is a color character area. Activate output CC. The AND circuit 83 activates the output only when both the output LL and the output CC are active and the 1-bit edge detection signal EDGE output from the edge detection unit 65 is “1”. That is, when the target pixel corresponds to the edge portion and the color character area, and the Y component is higher than the C component by a predetermined value and the Y component is higher than the M component by a predetermined value. In this case, the AND circuit 83 outputs an active signal.

  The adder 84 adds a predetermined value (third predetermined value) held in the register 86 to the C component pixel value output from the adaptive filter processing unit 58. Similarly, the adder 85 adds a predetermined value (third predetermined value) held in the register 87 to the pixel value of the M component output from the adaptive filter processing unit 58. The multiplexer 88 selects and outputs either the C component pixel value output from the adaptive filter processing unit 58 or the added value output from the adder 84 in accordance with the output from the AND circuit 83. Similarly, the multiplexer 89 selects and outputs either the M component pixel value output from the adaptive filter processing unit 58 or the addition value output from the adder 85 in accordance with the output from the AND circuit 83. Both multiplexers 88 and 89 select and output the addition value when the output of the AND circuit 83 is active.

  Therefore, the target pixel corresponds to the edge portion and the color character area, and the Y component is higher than the C component by a predetermined value and the Y component is higher than the M component by a predetermined value. The pixel values of the C component and the M component are raised, assuming that the target pixel corresponds to the edge portion of the yellow character area. As a result, edge emphasis is applied to the edge portion of the yellow character area. When the target pixel does not correspond to the edge portion of the yellow character area, the edge color conversion processing unit 59 outputs the pixel values of the Y, C, and M components output from the adaptive filter processing unit 58 as they are without conversion. To do. That is, the AND circuit 83, the adders 84 and 85, the registers 86 and 87, and the multiplexers 88 and 89 correspond to an embodiment of the edge enhancement processing unit of the present invention.

(Operation of image processing device)
FIG. 8 is a flowchart showing an example of a main flow of processing by the image processing unit 20 (FIG. 1). At the same time that the scanner unit 10 starts reading a document, the image processing unit 20 starts processing. When the process starts, first, various correction units (FIG. 2) from the shading correction unit 51 to the scanner color correction unit 55 perform various corrections on the input image signal having RGB as color components (step S1). ). Next, the RGB / YUV conversion processing unit 61 (FIG. 3) converts the corrected image signal from a format having RGB as a color component to a format having YUV as a color component (step S2).

  Next, the edge detection unit 65 detects a pixel corresponding to the edge portion based on the pixel value of the Y component (step S3). Next, the portion from the saturation determination unit 62 to the region signal synthesis unit 71 detects pixels corresponding to the color character region (step S4). Subsequently, the edge color conversion processing unit 59 (FIG. 7) detects the pixel value of each YCM component for each pixel (step S5).

  Next, the circuit (FIG. 7) from the subtracters 75 and 76 to the AND circuit 81 determines whether or not the pixel value of the Y component is extremely larger than the pixel values of the M and C components for each pixel. Determination is made (step S6). Subsequently, the logical product circuit 82 and the logical product circuit 83 determine, for each pixel, whether the pixel corresponds to the edge portion and the color character area (step S7). The circuits from the adders 84 and 85 to the multiplexers 88 and 89 convert the pixel values of the C component and the M component to higher values when the determinations at steps S6 and S7 are both positive (step S8). If any determination is negative, no conversion is performed.

  Next, the image signal output from the edge color conversion processing unit 59 is recorded in the image memory 22 and then converted into an image signal for printing by the print image processing unit 24 based on or simultaneously with the user's instruction. After conversion, the image is printed by the printing unit 30 (step S9). When the above processing is completed for all input image signals sent from the scanner unit 10, the processing ends.

  Since the image processing unit 20 is configured and operates as described above, yellow characters are converted as shown in FIG. 9, for example. In FIG. 9, it is assumed that a thick character “P” corresponds to a yellow character. FIG. 9A shows the YCM components of the yellow character “P” before conversion in an exploded manner, and FIG. 9B shows the YCM components after conversion in an overlapping manner. As shown in FIG. 9B, the density of the C component and the M component is increased at the edge portion of the yellow character “P”, thereby realizing edge enhancement. As a result, the outline of the yellow letter “P” drawn on the background of white or a color close to it can be clearly read visually.

  In the example of FIG. 9B, as the edge portion, a portion where the Y (luminance) component rapidly decreases along the main scanning direction and a portion where the Y (luminance) component rapidly decreases along the reverse direction of the sub-scanning direction are detected. ing. Therefore, edge emphasis is applied to the right side and the upper side of the yellow character. For this reason, even a relatively thin character can be edge-enhanced while leaving the original color portion of the yellow-based character. In addition, a visual effect is obtained as if shades were added to yellow-based characters, and a unique visual appearance is added. In such processing, the coefficients around the target pixel of the secondary differential filter for edge detection illustrated in FIG. 4 are set above (in the reverse direction of the sub-scanning direction) and right (in the main scanning direction) above the target pixel. It can be realized by arranging only. Various edge portions can be extracted by designing a second-order differential filter.

(Other embodiments)
(1) In the above embodiment, the edge color conversion processing unit 59 determines whether or not the target pixel corresponds to the yellow character region based on the difference in pixel value between the Y component and the C component. went. On the other hand, the edge color conversion processing unit 59 may perform the determination based on the ratio of pixel values between the Y component and the C component. For this purpose, the subtracters 75 and 76 (FIG. 7) may be replaced with dividers, and the values of the registers 76 and 77 may be given a numerical value far exceeding 1, for example, a numerical value in the range of 10 to 100. Further, regarding the pixel value, whether the Y component is larger than a predetermined value than the sum of the C component and the M component, or the Y component exceeds a predetermined ratio than the sum of the C component and the M component. The determination may be made on the basis of whether or not it is large.

  (2) In the above embodiment, the input image processing unit 23 determines whether or not each of the character region, the edge portion, and the yellow portion is applicable to all the pixels. On the other hand, the input image processing unit 23 may detect another one of the character region, the edge portion, and the yellow portion within a range where one of them is detected. For example, each of the subtracters 75 and 76 (FIG. 7) includes Y, C, and M components only when the area determination signal ASIG indicates a color character area, or when the edge detection signal EDGE indicates an edge portion. You may comprise so that it may be input.

  (3) In the above embodiment, the edge detection unit 65 detects the edge part based on the pixel value of the Y (luminance) component. On the other hand, the edge detection unit 65 may be configured to detect an edge part based on a combination of pixel values of another component or a plurality of components.

  (4) In the above embodiment, the edge color conversion processing unit 59 performs edge emphasis on the yellow character region under the condition that the region determination signal ASIG indicates a color character region. On the other hand, the edge color conversion processing unit 59 may be configured so as to perform edge enhancement on the yellow character region including the case where the region determination signal ASIG indicates a black character region. In this case, since the area determination signal ASIG does not need to distinguish between a color character and a black character, there is an advantage that the character area detection / edge detection unit 57 does not need to have the saturation determination unit 62. . However, in the form of performing edge enhancement by selecting only the color character region, unnecessary edge enhancement processing is performed on the black character region, whereby the edge portion of the black character region is colored or the density of the edge portion of the black character region is reduced. Inconveniences that are unnecessarily high are avoided.

  (5) In the above embodiment, the edge color conversion processing unit 59 performs processing for increasing the density of each component of C and M on the edge portion of the yellow character region, thereby performing edge enhancement of the yellow character region. . On the other hand, the edge color conversion processing unit 59 processes four components including the BK (black) component in the three components Y, C, and M, and applies black to the edge region of the yellow character region. Edge enhancement may be performed by increasing the density of the image. Thereby, the visibility of yellow characters can be effectively enhanced, and the edge color conversion processing unit 59 can be configured more simply. For this purpose, for example, in FIG. 7, a set of an adder 84, a register 86, and a multiplexer 88 is prepared for the BK component output from the adaptive filter processing unit 58, and a set for the Y and C components is used instead. It is good to delete.

  (6) In the above embodiment, the edge color conversion processing unit 59 adds the pixel values of the C and M components by a predetermined value (third predetermined value) for the edge portion of the yellow character area to enhance the edge. Went. On the other hand, the edge color conversion processing unit 59 may perform edge enhancement by raising the pixel values of the C and M components to a predetermined value (fourth predetermined value). In this case, the edge color conversion processing unit 59 (FIG. 7) does not need to include the adders 84 and 85, and the values held in the registers 86 and 87 can be directly input to the multiplexers 88 and 89. A simpler configuration can be obtained.

  (7) The edge color conversion processing unit 59 may be configured to reduce the density of the Y (yellow) component, which is no longer useful, or to zero for the pixel to be edge-enhanced. For this purpose, in FIG. 7, another multiplexer is inserted in the Y component signal line, and the Y component signal is passed according to the output of the AND circuit 83, or a low fixed value held in another register. The edge color conversion processing unit 59 is preferably configured so that Since the useless yellow component is lowered, unnecessary printing of yellow can be suppressed when the image signal is printed, and thereby recording agents such as ink and toner can be saved somewhat.

1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. It is a block diagram which shows the structural example of the input image process part of FIG. FIG. 3 is a block diagram illustrating a configuration of a character area detection / edge detection unit in FIG. 2. It is explanatory drawing which illustrates a secondary differential filter. It is explanatory drawing of the table format which illustrates the value of an edge detection signal. It is explanatory drawing of the table format which illustrates the value of an area | region discrimination signal. FIG. 3 is a circuit diagram illustrating a configuration example of an edge color conversion processing unit in FIG. 2. 3 is a flowchart illustrating an example of a main flow of processing by an image processing unit in FIG. 1. FIG. 3 is an operation explanatory diagram of an edge color conversion processing unit in FIG. 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Scanner part 20 Image processing part 23 Input image processing part (image processing apparatus)
30 Print section 57 Character area detection / edge detection section 59 Edge color conversion processing section 62 Saturation determination section 64 Character candidate / character surrounding detection section 65 Edge detection section 67 Character area signal generation section 68 Black / character signal generation section 69 Character area Signal expansion unit 71 Area signal synthesis unit 100 Image forming apparatus

Claims (12)

A character area detection unit that detects a character area that is a character area of the input image signal;
An edge detector for detecting an edge portion of the input image signal;
A yellow detection unit that accepts the input image signal in a form expressed by color components including yellow, cyan, and magenta, and detects a yellow portion in which the density of yellow exceeds a predetermined standard compared to the densities of cyan and magenta When,
An edge for converting the input image signal so as to increase at least one density excluding yellow among the color components with respect to the yellow character edge portion which is the character region and the edge portion and the yellow portion. An emphasis processing unit;
An image processing apparatus comprising:   The image processing apparatus according to claim 1, wherein the character region detection unit detects a color character region that is a region of a chromatic character in the input image signal as the character region.   The edge detection unit includes, as the edge portion, a first edge portion that is one of the portions where the density rapidly increases or decreases along the main scanning direction, and the density increases rapidly along the sub-scanning direction, or 3. Only one of a second edge portion that is one of the decreasing portions and a third edge portion that includes both the first edge portion and the second edge portion is detected. The image processing apparatus described.   In the input image signal, the yellow detection unit has a yellow density higher than a cyan density by a first predetermined value and a yellow density higher than a magenta density by a second predetermined value. The image processing apparatus according to claim 1, wherein a part is detected as the yellow part. The yellow detection unit accepts the input signal in a form expressed by a color component further including black,
The image processing apparatus according to claim 1, wherein the edge enhancement processing unit performs the conversion by increasing at least a density of black with respect to the yellow character edge portion.   6. The edge enhancement processing unit performs the conversion by adding a third predetermined value to at least one density excluding yellow among the color components for the yellow character edge portion. The image processing apparatus according to any one of the above.   The edge enhancement processing unit performs the conversion on the yellow character edge portion by setting at least one density excluding yellow among the color components as a fourth predetermined value. An image processing apparatus according to claim 1.   The image processing apparatus according to claim 1, wherein the edge enhancement processing unit further performs, as the conversion, a process of reducing a yellow density for the yellow character edge portion. An image processing apparatus according to any one of claims 1 to 8,
An image forming apparatus comprising: a scanner unit that generates an image signal by reading a document image, and supplies the generated image signal to the image processing apparatus as the input image signal. An image processing apparatus according to any one of claims 1 to 8,
An image forming apparatus comprising: a printing unit that prints an image signal output from the image processing apparatus on a recording material. A character region detection step of detecting a character region that is a character region of the input image signal;
An edge detection step of detecting an edge portion of the input image signal;
A yellow detection step of accepting the input signal in a form expressed by color components including yellow, cyan, and magenta, and detecting a yellow portion in which the density of yellow exceeds a predetermined standard compared to the densities of cyan and magenta; ,
An edge for converting the input image signal so as to increase at least one density excluding yellow among the color components with respect to the yellow character edge portion which is the character region and the edge portion and the yellow portion. Emphasis processing step;
An image processing method comprising: Computer
A character region detection means for detecting a character region which is a character region in the input image signal;
Edge detection means for detecting an edge portion of the input image signal;
Yellow detection means for accepting the input signal in a form expressed by color components including yellow, cyan, and magenta, and detecting a yellow portion in which the density of yellow exceeds a predetermined standard compared to the densities of cyan and magenta; ,
An edge for converting the input image signal so as to increase at least one density excluding yellow among the color components with respect to the yellow character edge portion which is the character region and the edge portion and the yellow portion. An image processing program that functions as enhancement processing means.

Images