JP2019075702A - Image reading device, image reading method, and image reading program - Google Patents

Abstract

To reduce dots sporadically remaining after removal of a specified color.SOLUTION: An image reading device 1 removes a removal color that is a color specified in advance. The image reading device 1 comprises: an image reading unit 100 that reads an image to create RGB image data including an R gradation value, a G gradation value, and a B gradation value; a mask processing unit 151 that converts a pixel having the removal color into a white pixel that is a pixel in white color having the highest brightness; and an isolated point processing unit 152 that takes, as a target pixel, a non-white adjacent pixel adjacent to the white pixel, having a brightness higher than a first threshold set in advance, and being a non-white pixel that is a pixel not converted into the white pixel, and when all peripheral pixels that are pixels on the periphery of the target pixel are the white pixel, converts the target pixel into the white pixel.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image reading apparatus, an image reading method, and an image reading program, and more particularly to image processing for removing a specific color.

  The image forming apparatus typically reads an original image in an additive RGB color space to generate image data, and reproduces an image in a colorant in a subtractive CMY color space (or CMYK color space). . In the case of an original image, for example, when the print medium itself has a specific color or when show-through occurs, it may be difficult to read characters. Furthermore, the user may wish to remove handwritten characters and the like after writing the characters and the like by handwriting in a predetermined color on a monochrome document. Given such a case, a designated color removal function has been proposed for removing a specific color.

  Specifically, for example, in Patent Document 1, it is determined whether the removal unit that removes the removal color (designated color) from the read image, and whether the read image from which the removal color is removed by the removal unit is a black and white image or a color image. A technique is proposed which comprises: According to this technology, it is possible to create an image from which color components designated by the user have been removed, and to perform color / monochrome determination accurately. In Patent Document 1, the color is determined to be the designated color when the saturation value is equal to or greater than a predetermined threshold and the lightness is within the predetermined range within a predetermined threshold range from the hue value designated by the user. .

JP, 2009-100026, A

  However, the inventor of the present application has found that the designated color removal function is a sporadic occurrence (remaining) of dots caused by noise during reading, particularly in the low density portion. Such sporadic dots are particularly visible on white print media after removal of specified colors, leading to image quality degradation.

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a technique for suppressing dots that remain sporadically after removal of a designated color.

  The present invention provides an image reader that removes a removal color that is a pre-specified color. The image reading apparatus reads an image and generates an RGB image data including R gradation value, G gradation value, and B gradation value, and a pixel having the removed color. A mask processing unit that converts a white pixel that is the highest in brightness to a white pixel, and a non-white pixel that is a pixel that is not converted to the white pixel and has a brightness higher than a preset first threshold If the non-white adjacent pixel adjacent to the white pixel is a pixel of interest and all surrounding pixels around the pixel of interest are the white pixels, an isolated point for converting the pixel of interest to a white pixel And a processing unit.

  The present invention provides an image reading method for removing a removal color that is a predesignated color. The image reading method includes an image reading step of reading an image to generate RGB image data including a tone value of R, a tone value of G, and a tone value of B, and a pixel having the removed color. There is a mask processing step of converting into a white pixel which is a white pixel having the highest lightness, and a non-white pixel which is an unconverted pixel of the white pixel and has a brightness higher than a preset first threshold. If the non-white adjacent pixel adjacent to the white pixel is a pixel of interest and all surrounding pixels around the pixel of interest are the white pixels, an isolated point for converting the pixel of interest to a white pixel And a processing step.

  The present invention provides an image reading program for controlling an image reading apparatus that removes a removal color that is a predetermined color. The image reading program reads an image and generates an RGB image data including an R gradation value, a G gradation value, and a B gradation value, and an image reading unit for lightening pixels having the removed color. Mask processing unit that converts a white pixel that is the highest white pixel, and a non-white pixel that is a pixel that is not converted to the white pixel and has a brightness higher than a preset first threshold An isolated point process that converts a target pixel into a white pixel when a non-white adjacent pixel adjacent to the white pixel is a target pixel and all peripheral pixels around the target pixel are the white pixel. The image reading apparatus functions as a part.

  According to the present invention, it is possible to suppress sporadically remaining dots after removal of a designated color.

FIG. 1 is a schematic configuration view showing an entire configuration of an image forming apparatus 1 according to a first embodiment of the present invention. 1 is a block diagram showing an entire configuration of an image forming apparatus 1 according to a first embodiment. It is a flowchart which shows the content of the image data generation process which concerns on 1st Embodiment. It is explanatory drawing which shows the residual dot after the mask process which concerns on 1st Embodiment, and a mask process. It is a flowchart which shows the content of the adjacent isolated point removal process which concerns on 1st Embodiment. It is explanatory drawing which shows the content of the adjacent isolated point removal process which concerns on 1st Embodiment. It is a flow chart which shows the contents of the image data generation processing concerning a 2nd embodiment. It is an explanatory view showing the contents of the mask processing concerning a 2nd embodiment. It is a flowchart which shows the content of the adjacent isolated point removal process which concerns on 2nd Embodiment. It is explanatory drawing which shows the content of the adjacent isolated point removal process which concerns on 2nd Embodiment.

Hereinafter, modes for carrying out the present invention (hereinafter, referred to as “embodiments”) will be described in the following order with reference to the drawings.
A. First embodiment:
B. Second embodiment:
C. Modification:

A. First embodiment:
FIG. 1 is a schematic configuration view showing an entire configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a block diagram showing the overall configuration of the image forming apparatus 1 according to an embodiment. The image forming apparatus 1 includes a control unit 10, an image reading unit 100, an image forming unit 20, an automatic document feeder (ADF) 30, and a storage unit 40. The image reading unit 100 reads an image from a document and generates an image data ID which is digital data.

  The control unit 10 includes a main storage unit such as a RAM and a ROM, and a control unit such as an MPU (Micro Processing Unit) and a CPU (Central Processing Unit). The control unit 10 also has a controller function related to interfaces such as various I / O, USB (Universal Serial Bus), bus, and other hardware, and controls the entire image forming apparatus 1.

  The image forming unit 20 forms and discharges an image on a print medium based on the image data ID. The image forming unit 20 includes a color conversion processing unit 21 and a halftone processing unit 22. The color conversion processing unit 21 color converts image data, which is RGB data, into CMYK data. The halftone processing unit 22 performs halftone processing on the CMYK data to generate CMYK halftone data.

  The storage unit 40 is a storage device such as a hard disk drive or a flash memory, which is a non-temporary recording medium, and stores control programs (including an image reading program) and data of processing executed by the control unit 10.

  The image reading unit 100 includes a light source driver 111 and a light source 112. The light source 112 has a plurality of LEDs (not shown) for irradiating the document P with light. The light source driver 111 is an LED driver that drives a plurality of LEDs arranged in the main scanning direction, and performs on / off driving control of the light source 112. Thus, the light source 112 can irradiate the document P with pulse width modulation (PWM) of variable drive duty.

  The image reading unit 100 further includes a first reflecting mirror 113, a first carriage 114, a second reflecting mirror 115, a third reflecting mirror 116, a second carriage 117, a condenser lens 118, and an image sensor 121. And have. The first reflecting mirror 113 reflects the reflected light L from the document P in the direction of the second reflecting mirror 115. The second reflecting mirror 115 reflects the reflected light L in the direction of the third reflecting mirror 116. The third reflecting mirror 116 reflects the reflected light L in the direction of the condensing lens 118. The condensing lens 118 focuses the reflected light L on the light receiving surface of the light receiving element 122 included in the image sensor 121.

  The image sensor 121 has three types of color filters (not shown) of R, G, and B, and a plurality of light receiving elements 122 arranged in the main scanning direction. The plurality of light receiving elements 122 generate charges photoelectrically converted according to the intensity of each incident light, and accumulate the charges in each potential well (well of charges) formed by the CCD element corresponding to each pixel. The charges accumulated in each potential well are simultaneously transferred to a shift register not shown. Each charge transferred to the shift register is converted by the charge-to-voltage conversion amplifier into an analog electrical signal which is a voltage signal. Thus, the image sensor 121 can output an analog electrical signal for each pixel in the main scanning direction.

  The first carriage 114 mounts the light source 112 and the first reflecting mirror 113, and reciprocates in the sub-scanning direction. The second carriage 117 mounts the second reflecting mirror 115 and the third reflecting mirror 116, and reciprocates in the sub scanning direction. The first carriage 114 and the second carriage 117 are controlled by the control unit 10. Thus, the light source 112 can scan the document in the sub-scanning direction, so the image sensor 121 can output an analog electrical signal according to the two-dimensional image on the document.

  When the automatic document feeder (ADF) 30 is used, the first carriage 114 and the second carriage 117 are fixed at a preset sub-scanning position, and the document P is automatically fed to the sub-scanning direction. Scan is performed. The scanning speed at this time is different depending on the scanning speed of scanning due to the reciprocating motion of the first carriage 114 and the second carriage 117 and the mechanism.

  The image reading unit 100 further includes a signal amplifier 123, an A / D conversion unit 124, an AGC processing unit 130, a white reference plate 132 (see FIG. 1), and an image processing unit 150. The signal amplifier 123 is a variable gain amplifier. The signal amplifier 123 amplifies the analog electrical signal with the gain set by the AGC processing unit 130 and stored in the storage unit 40. The A / D converter 124 A / D converts the amplified analog electrical signal to generate original image data RID which is digital data. The original image data RID is data having a range width of the minimum value “0” and the maximum value “255”. The image forming unit 20 forms and discharges an image on a print medium based on the image data ID after the image processing unit 150 performs image processing on the original image data RID.

  In the present embodiment, the AGC processing unit 130 is a gain adjustment unit that sets optimum gains and offset values for each of the plurality of light receiving elements 122 using a black reference signal and a white reference signal. The black reference signal is an analog electrical signal of the light receiving element 122 when the light source 112 is off. The white reference signal is an analog electric signal of the light receiving element 122 when the white reference plate 132 is illuminated instead of the document P. The AGC processing unit 130 sets an offset value such that the value of the original image data RID when the black reference signal is A / D converted by the A / D conversion unit 124 becomes the minimum value “0”. The AGC processing unit 130 uses a gain such that the value of the original image data RID when the white reference signal is A / D converted by the A / D conversion unit 124 using this offset value becomes the maximum value “255”. Set

  Thereby, the fluctuation of the analog electrical signal caused by the increase or decrease of the reflected light between the black reference signal and the white reference signal is effectively used from the minimum value "0" to the maximum value "255" of the original image data RID. It will be possible. However, the original image data RID includes noise due to individual differences among a plurality of CCD elements inside the image sensor 121 and deviation due to the characteristics of the color filter (not shown) and the color material. It will be. Although the image processing unit 150 includes the mask processing unit 151 and the isolated point processing unit 152, these functions will be described later.

  FIG. 3 is a flowchart showing the contents of image data generation processing according to an embodiment. In step S100, the image forming apparatus 1 receives from the user an operation input for setting the operation mode to the removal color designation processing mode. In the removal color designation processing mode, the image forming apparatus 1 receives an operation input for designating a removal color. In this example, it is assumed that red is selected.

  In step S200, the image reading unit 100 scans a document. Thus, the image reading unit 100 generates original image data RID having each gradation value of RGB for each pixel (step S300). The original image data RID is input to the image processing unit 150 (see FIG. 2).

  FIG. 4 is an explanatory view showing a mask process according to an embodiment and a remaining dot after the mask process. FIG. 4A shows the image P1 represented by the original image data RID and the image P2 after the mask processing. The image P1 indicates red, which is the color of the background of the document, and indicates a state in which the image is not displayed. FIG. 4B shows the contents of the mask process.

  In step S400, the mask processing unit 151 of the image processing unit 150 executes mask processing based on hue. The mask processing unit 151 generates a mask divided by hue in accordance with the designated removal color. The mask is configured to select pixels within the range of red to the threshold of the hue angle Th0 (also referred to as within the first hue range) (see FIG. 4 (b)).

  The mask processing unit 151 masks the original image data RID in pixel units, stores the pixel selected by the mask, removes the color, and converts it into a white pixel. The white pixel is a white pixel having the highest lightness in which all of the gradation values of R, G, and B are converted into 255. Thereby, the mask processing unit 151 can generate image data representing the image P2.

  In the image P2 after mask processing, dots are sporadically generated (remaining) after removal of the designated color (red). The inventor of the present application has found that such sporadic dots are generated (remaining) due to noise at the time of reading, particularly in the low density portion. Such sporadic dots are particularly visible on white print media after removal of specified colors, leading to image quality degradation.

  In step S500, the isolated point processing unit 152 of the image processing unit 150 executes an adjacent isolated point removal process. In the adjacent isolated point removal process, the isolated point processing unit 152 determines that the pixel in which the sporadic dots adjacent to the white pixel stored in step S400 are formed is surrounded by the pixels converted to other white pixels. Identify. As a result, the isolated point processing unit 152 determines that the density of the main pixel adjacent to the white pixel is not the density representing the image on the document P but the density due to noise at the time of reading, Convert.

  FIG. 5 is a flowchart showing the contents of the adjacent isolated point removal process (step S500) according to one embodiment. FIG. 6 is an explanatory view showing the contents of the adjacent isolated point removal process according to the embodiment. FIG. 6A shows the white pixel stored in step S400 with an * mark, and shows that the pixel 1 adjacent in the main scanning direction is selected as the target pixel.

  In step S510, the isolated point processing unit 152 determines whether there is a non-white adjacent pixel. The non-white adjacent pixel means a non-white pixel which is a pixel adjacent to a white pixel and which has not been converted to a white pixel. If the non-white adjacent pixel is not present, the isolated point processing unit 152 proceeds the process to step S600 (see FIG. 3), and if the non-white adjacent pixel is present, the process proceeds to step S520.

  In step S520, the isolated point processing unit 152 determines whether the density of the pixel of interest is smaller than a predetermined threshold. The target pixel is selected one by one as a pixel adjacent in a direction (in this example, the main scanning direction) set in advance with respect to the white pixel among the non-white adjacent pixels. In this example, it is assumed that the pixel 1 (see FIG. 6A) is selected as the target pixel. If the density of the pixel of interest is greater than or equal to the predetermined threshold (corresponding to the first threshold), the isolated point processing unit 152 proceeds to step S600 and the density of the pixel of interest is less than the predetermined threshold If so (ie, if the lightness is higher than the first threshold), the process proceeds to step S530.

  The density means the density of the color material on the assumption that the color of the pixel of interest is reproduced by the subtractive color mixture, and corresponds to the lightness when each gradation value of RGB is converted to the HSV color space, for example. Since “low density” corresponds to “high lightness”, it can be determined based on lightness.

  In step S530, the isolated point processing unit 152 determines whether all the peripheral pixels (pixels A to G in FIG. 6A) of the pixel of interest 1 are white pixels (pixels converted to white pixels). . That is, the isolated point processing unit 152 determines whether or not the pixel of interest 1 is a pixel in which sporadic dots surrounded by white pixels are formed. If all the peripheral pixels are white pixels, the isolated point processing unit 152 proceeds to step S590. If there is at least one non-white pixel in the peripheral pixels, the isolated point processing unit 152 proceeds to step S540.

  In the example of FIG. 6A, it is assumed that the isolated point processing unit 152 is a pixel in which a single dot in which the pixel 1 (see FIG. 6A) is surrounded by white pixels is formed. As a result, the isolated point processing unit 152 determines that the density of the pixel of interest 1 is not the density representing the image on the document P but the density due to noise at the time of reading and converts it into white pixels (step S 590).

  On the other hand, in the example of FIG. 6B, it is assumed that the pixel 2 which is one of the peripheral pixels of the pixel 1 exists as a non-white pixel. In this case, the isolated point processing unit 152 causes the process to proceed to step S540 because there is at least one non-white pixel in the peripheral pixels.

  In step S540, the isolated point processing unit 152 determines whether or not the peripheral pixels include two or more non-white pixels. The isolated point processing unit 152 proceeds the process to step S600 when the peripheral pixels include two or more non-white pixels, and when the peripheral pixels do not include two or more non-white pixels. That is, if a single non-white pixel is included, the process proceeds to step S550.

  In the example of FIG. 6B, since the single pixel 2 adjacent in the main scanning direction of the pixel 1 exists as a non-white pixel, the isolated point processing unit 152 proceeds with the process to step S550. On the other hand, in the example of FIG. 6D, since the pixels 2 and 3 exist as non-white pixels around the pixel 1, the isolated point processing unit 152 can be configured such that the pixels 1 to 3 constitute an image. It is determined that there is a sex, and the process proceeds to step S600.

  In step S550, the isolated point processing unit 152 executes a pixel of interest change process. In the example of FIG. 6 (b), the isolated point processing unit 152 selects a single non-white pixel (FIG. 6 (b)) adjacent to the pixel of interest (pixel 1 of FIG. 6 (b), ie, the pixel of interest before changing). Pixel 2) is selected as a new target pixel (target pixel after change).

  In step S560, the isolated point processing unit 152 determines whether the density of the newly selected focused pixel (pixel 2 in FIG. 6B) is smaller than a predetermined threshold. If the density of the pixel of interest 2 is equal to or greater than the predetermined threshold, the isolated point processing unit 152 proceeds to step S570. If the density of the pixel of interest 2 is less than the predetermined threshold, the isolated point processor 152 proceeds to step S530. Back to.

  In step S570, the isolated point processing unit 152 does not convert the newly selected focused pixel (pixel 2 in FIG. 6B) into a white pixel, and thus the pixel 1 that is the original focused pixel (see FIG. )) Is returned to the target pixel. As a result, the isolated point processing unit 152 determines that the pixel 1 which is the pixel of interest is not the density representing the image on the document P but the density due to noise at the time of reading, and converts it into white pixels ( Step S590).

  In the example of FIG. 6B, the density of the pixel of interest 2 is less than the predetermined threshold, and the isolated point processing unit 152 returns the process to step S530. In the example of FIG. 6B, all the peripheral pixels (pixels A to G in FIG. 6B) of the target pixel 2 are white pixels (pixels converted to white pixels).

  In step S530 (second time), the isolated point processing unit 152 determines whether all the peripheral pixels of the pixel of interest 2 are white pixels. In the example of FIG. 6B, the isolated point processing unit 152 is a single non-white adjacent pixel (pixel in which a dot is formed) surrounded by white pixels in the pixel 2 (see FIG. 6B). As a result, it can be specified that two pixels of the pixel 1 and the pixel 2 are isolated pixel groups (pixel groups in which dots are formed) surrounded by white pixels.

  Thus, the isolated point processing unit 152 determines that the density of the two pixels of the pixel 1 and the pixel 2 is not the density representing the image on the document P but the density resulting from the noise at the time of reading. Convert to pixels (step S590).

  On the other hand, in the example of FIG. 6C, it is further assumed that the pixel 3 which is one of the peripheral pixels of the pixel 2 exists as a non-white pixel. In this case, the isolated point processing unit 152 causes the process to proceed to step S540 because there is at least one non-white pixel in the peripheral pixels. In steps S540 to S560, the isolated point processing unit 152 returns the process to S530 with the pixel 3 as a new target pixel. In the example of FIG. 6C, it is assumed that all the peripheral pixels (pixels A to G in FIG. 6C) of the pixel of interest 3 are white pixels.

  In step S530 (third time), the isolated point processing unit 152 determines whether all the peripheral pixels (pixels A to G in FIG. 6C) of the pixel of interest (pixel 3 in FIG. 6C) are white pixels. To judge. In the example of FIG. 6B, the isolated point processing unit 152 is a pixel in which a single dot in which the pixel 3 (see FIG. 6C) is surrounded by white pixels is formed, and thus the pixels 1 to 3 It can be specified that the pixel in which the three dots are formed is an isolated pixel group surrounded by white pixels.

  Thus, the isolated point processing unit 152 determines that the density of the three pixels of the pixels 1 to 3 is not the density representing the image on the document P but the density due to the noise at the time of reading. Convert to pixels (step S590).

  The isolated point processing unit 152 converts a pixel group configured by a preset number (three) of pixels into white pixels, while configured by pixels (four or more) exceeding the preset number. It is configured to end the processing (steps S530 to S560) of generating a pixel group without performing conversion to a white pixel as there is a possibility that the density is attributed to the image for the pixel group being processed. Do. The number of pixels of the pixel group to be converted into white pixels can be appropriately adjusted in accordance with the resolution of the image, the noise level at the time of reading, and the like.

  In step S600, the color conversion processing unit 21 color converts image data, which is RGB data, into CMYK data. In step S700, the halftone processing unit 22 performs halftone processing on the CMYK data to generate CMYK halftone data. Thereby, the image forming apparatus 1 can form an image on the print medium based on the halftone data.

  As described above, in the image forming apparatus 1 according to the first embodiment, a linear pixel group or a single pixel consisting of pixels in which a sporadic number of three or less dots adjacent to a white pixel is formed is white. It can be specified that it is surrounded by pixels. Thereby, the image forming apparatus 1 determines that the density of the pixel group or the like is not the density representing the image on the document P but the density caused by the noise at the time of reading, converts it into white pixels and converts the image quality. It can be improved.

  It should be noted that the hue angle Th0 as a threshold value is not only the removal color that the user wants to remove if it is large, but the possibility of erroneously removing the image is large, while the color is sufficiently removed. Is set in consideration of the trade-off problem of not being able to

B. Second embodiment:
FIG. 7 is a flowchart showing the contents of the image data generation process according to the second embodiment. In the image data generation process according to the second embodiment, the mask process (step S400) and the adjacent isolated point removal process (step S500) are respectively replaced with the mask process (step S400a) and the adjacent isolated point removal process (step S500a). This is different from the image data generation process according to the first embodiment in that it is present.

  FIG. 8 is an explanatory view showing the contents of the mask process (step S400a) according to the second embodiment. In step S410, the mask processing unit 151 performs mask processing using the first mask. The first mask is configured to select pixels in the range from red to the threshold of the hue angle Th1 (also referred to as the first hue range) (see FIG. 8B). The hue angle Th1 as the threshold may be the same as the hue angle Th0 of the mask used in the mask processing according to the first embodiment, or may be smaller than the hue angle Th0.

  In step S420, the mask processing unit 151 masks the original image data RID in pixel units, stores the pixel selected by the mask, removes the color, and converts it into a white pixel. This point is common to the mask processing according to the first embodiment.

  In step S430, the mask processing unit 151 performs mask processing using the second mask. The second mask has a threshold of the hue angle Th2 larger than the hue angle Th1 (see FIG. 8B). The second mask selects pixels in a range from red to a threshold value of the hue angle Th2 (also referred to as a second hue range), that is, a range including a first hue range wider than the first hue range. It is configured as shown in FIG. 8 (b).

  In step S440, the mask processing unit 151 determines whether the non-white pixel selected by the second mask is adjacent to the white pixel selected by the first mask. If the non-white pixels selected in the second mask are not adjacent to the white pixels selected in the first mask, the mask processing unit 151 proceeds to step S600 to select the second mask. If the determined non-white pixel is adjacent to the white pixel selected by the first mask, the process proceeds to step S450.

  In step S450, the mask processing unit 151 is adjacent to the white pixel selected by the first mask, and converts the non-white pixel selected by the second mask into a white pixel. In this method, there is a high possibility that the image is not formed in the area converted into the white pixel and the image adjacent to the pixel forming the area in which the image is not formed is formed. Focusing on

  Thereby, the mask processing unit 151 removes the removal color that the user wants to remove using the first mask having the relatively small threshold (the hue angle Th1), and the relatively large threshold (the hue angle Th1). The above-mentioned trade-off problem is solved by making a determination based on the color of the pixel and the positional relationship between the white pixel and the second mask using the hue angle Th2).

  FIG. 9 is a flowchart showing the contents of the adjacent isolated point removal process (step S500a) according to the second embodiment. FIG. 10 is an explanatory view showing the contents of the adjacent isolated point removal process according to the second embodiment. The adjacent isolated point removal process according to the second embodiment is different from the adjacent isolated point removal process (step S500) according to the first embodiment (FIG. 5 and FIG. 5) in that the processes of step S580 and step S585 are added. 10 (e)).

  The adjacent isolated point removal process (step S500a) according to the second embodiment can execute the same process as that of the first embodiment for the other processes (see FIGS. 10A to 10D). In the example of DP1 in FIG. 10E, it is assumed that three pixels with high density are included in the peripheral pixels of the pixel of interest 2.

  Step S 580 is processing to be performed when two or more non-white pixels are included in the peripheral pixels of the pixel of interest whose density is equal to or less than the threshold. In step S580, the isolated point processing unit 152 determines whether the density of two or more non-white pixels is equal to or greater than a threshold (corresponding to a second threshold). If the densities of the two or more non-white pixels are all equal to or greater than the threshold (ie, if the lightness is lower than the second threshold), the isolated point processing unit 152 proceeds to step S585 to perform at least one. If the density of one non-white pixel is less than the threshold, the process proceeds to step S600. In the example of DP1 of FIG. 10E, the process proceeds to step S585.

  In step S585, the isolated point processing unit 152 determines whether all the other peripheral pixels of the pixel of interest 2 except for the three non-white pixels 3 are white pixels. If all the other peripheral pixels are white pixels, the isolated point processing unit 152 proceeds to step S590. If the other peripheral pixels include non-white pixels, the process proceeds to step S600. Advance.

  In steps S580 and S585, it is assumed that the isolated point processing unit 152 detects the contour of the image. In the example of DP1 of FIG. 10 (e), the image is composed of pixels including three pixels 3 and black circles. The three pixels 3 constitute the contour of the image. Thereby, the isolated point processing unit 152 makes the non-white pixels of the pixel 1 and the pixel 2 as white pixels while maintaining the color of the three pixels 3, thereby clarifying the outline formed by the three pixels 3 be able to.

  On the other hand, in the example of DP2 in FIG. 10E, it is assumed that three pixels 3 including at least one pixel with low density are included in the peripheral pixels of the pixel of interest 2. In step S580, the isolated point processing unit 152 determines that the pixel 3 may have an image configuration with the pixel 1 and the pixel 2, and advances the process to step S600.

  This processing assumes that the isolated dots are sufficiently removed in the mask processing (step S400a) according to the second embodiment, and it is assumed that the contour of the image is detected to clarify the contour. . This is because the inventor of the present application has found that the mask processing (step S400a) according to the second embodiment and the adjacent isolated point removal processing (step S500a) have a synergistic effect.

  As described above, the image forming apparatus 1 according to the second embodiment converts a pixel or pixel group adjacent to a white pixel in which a sporadic dot or dot group is formed into a white pixel to obtain a vivid read image with little noise. While the image outline can be clarified to improve the image quality.

C. Modifications: The present invention can be implemented not only in the above embodiment but also in the following modifications.

  Variation 1: In the above embodiment, the removal color is specified by hue, but may be specified by an amount that quantitatively represents a color such as saturation, for example.

  Modified Example 2 In the above embodiment, the present invention is applied to an image forming apparatus, but the present invention may be applied to various electronic devices including an image reading unit such as an image reading device, a smartphone, or a camera. it can.

Reference Signs List 1 image forming apparatus 10 control unit 20 image forming unit 21 color conversion processing unit 22 halftone processing unit 30 automatic document feeder (ADF)
40 storage unit 100 image reading unit 111 light source driver 112 light source 113 first reflecting mirror 114 first carriage 115 second reflecting mirror 116 third reflecting mirror 117 second carriage 118 condensing lens 121 image sensor 122 light receiving element 123 signal amplifier 124 A / D converter 130 AGC processor 132 white reference plate 150 image processor 151 mask processor 152 isolated point processor L reflected light

Claims (9)

An image reading apparatus for removing a removal color which is a color designated in advance, which is
An image reading unit which reads an image and generates RGB image data including a gradation value of R, a gradation value of G, and a gradation value of B;
A mask processing unit configured to convert the pixel having the removed color into a white pixel which is a white pixel having the highest lightness;
A non-white pixel which is a non-white pixel which has not been converted to the white pixel and which has a lightness higher than a preset first threshold value and which is adjacent to the white pixel is a target pixel An isolated point processing unit configured to convert the target pixel into a white pixel when all the peripheral pixels that are peripheral pixels of the pixel are the white pixel;
An image reading apparatus comprising: The image reading apparatus according to claim 1,
When the single non-white pixel exists in the peripheral pixels, the isolated point processing unit changes the single non-white pixel to a target pixel, and the lightness of the target pixel after the change is the second light When it is higher than the threshold of 1, a pixel group including the focused pixel before the change and the focused pixel after the change is generated, and when all the peripheral pixels of the focused pixel after the change are the white pixels, the pixel An image reader that converts a group into white pixels. The image reading apparatus according to claim 2,
The isolated point processing unit changes the single non-white pixel to a target pixel when a single non-white pixel is present in the peripheral pixels of the target pixel after the change, and the target after the change When the lightness of the pixel is higher than the first threshold value, the changed target pixel is added to the pixel group, and the number of pixels included in the pixel group exceeds a preset number. An image reading apparatus that ends the process of generating the pixel group. The image reading apparatus according to claim 2 or 3, wherein
When the plurality of non-white pixels exist in the peripheral pixel, the isolated point processing unit has a lightness lower than a second threshold set in advance in the plurality of non-white pixels, and the peripheral pixel An image reading device for converting the focused pixel into a white pixel while maintaining the color of the plurality of non-white pixels when all the pixels except the plurality of non-white pixels are the white pixels; The image reading apparatus according to any one of claims 1 to 4, wherein
The image processing apparatus according to claim 1, wherein the mask processing unit selects a pixel having a color within a first hue range preset for the removed color as the pixel having the removed color. The image reading apparatus according to any one of claims 1 to 4, wherein
The mask processing unit selects a pixel having a color within a first hue range preset for the removal color as a pixel having the removal color, and a pixel having a color within the first hue range A pixel adjacent to the selected pixel as a pixel within the second hue range including the first hue range and wider than the first hue range is further selected as a pixel having the removal color Image reader. The image reading apparatus according to claim 6, wherein
When the plurality of non-white pixels exist in the peripheral pixel, the isolated point processing unit has a lightness lower than a second threshold set in advance in the plurality of non-white pixels, and the peripheral pixel The image reading apparatus further converts the non-white adjacent pixel into a white pixel when all the pixels except the plurality of non-white pixels are the white pixels. An image reading method for removing a removal color which is a color designated in advance, which is
An image reading step of reading an image and generating RGB image data including a tone value of R, a tone value of G, and a tone value of B;
A mask processing step of converting the pixel having the removed color into a white pixel which is a white pixel having the highest lightness;
A non-white pixel which is a non-white pixel which has not been converted to the white pixel and which has a lightness higher than a preset first threshold value and which is adjacent to the white pixel is a target pixel An isolated point processing step of converting the focused pixel into a white pixel when all the peripheral pixels that are peripheral pixels of the pixel are the white pixel;
An image reading method comprising: An image reading program for controlling an image reading apparatus for removing a removal color which is a color designated in advance,
An image reading unit which reads an image and generates RGB image data including a gradation value of R, a gradation value of G, and a gradation value of B;
A mask processing unit that converts a pixel having the removed color into a white pixel that is a white pixel having the highest lightness, and a first non-white pixel that is a pixel that is not converted to the white pixel. When the non-white adjacent pixel adjacent to the white pixel has a lightness higher than the threshold value as the pixel of interest, and all peripheral pixels around the pixel of interest are the white pixels, the pixel of interest is selected. An image reading program that causes the image reading apparatus to function as an isolated point processing unit that converts white pixels.

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