JP2008103987A - Image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor capable of emphasizing a place written in a specified color when a color image read out of a document is monochromatically printed. <P>SOLUTION: The image processor, which processes the color image comprising luminance data and chromaticity data by pixels read out of the document and outputs a monochromatic image, is composed of: a color hue specifying unit 21 which generates color hue specification information specifying a color hue to be converted according to user's operation; a conversion table storage unit 24 which stores a conversion table for decreasing an upper-limit value of luminance and making a monotonous increase in correspondence of luminance within a predetermined range including the upper-limit value; a pixel extracting unit 2 which extracts pixels of the color hue specified with the color hue specification information from the color image based upon a color hue obtained from chromaticity data; and a luminance data converter 4 which converts the luminance data of the pixels extracted by the pixel extracting unit 2 according to the conversion table to generate the monochromatic image from the color image. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, and more particularly to an improvement in an image processing apparatus that performs image processing on a color image read from an original by an imaging device such as a scanner and outputs a monochrome image.

  In recent years, a technique has been proposed for generating a monochrome image (monochrome image) by converting a specific color into a white level for a color image read from an original (for example, Patent Document 1). The image processing apparatus described in Patent Document 1 includes an image reading unit that reads an image from a document, a color designation unit that designates a color, and an image processing unit that converts the designated color into a white level to generate a monochrome image. Consists of. In this image processing apparatus, a pixel within a range of hue, saturation, and brightness specified in advance is extracted, and a process of converting the luminance component into a white level is performed on the pixel. As a result, a black and white image in which pixels of a specific color are whitened from a color image is obtained, and objects such as entry frames printed with the specific color, for example, red ink, in the document are deleted from the image data. Can do.

On the other hand, there has been proposed a color printing apparatus that prints a color image by increasing the saturation of a pixel whose hue is within a predetermined range and emphasizing a specific hue (for example, Patent Document 2). In this color printing apparatus, the hue range for increasing the saturation is designated in advance, and the saturation of the pixels whose hue is within this range is increased, thereby improving the print quality of the color image.
Japanese Patent Laid-Open No. 2005-303584 JP 2003-118168 A

  If a color image read from an original by an imaging device such as a color scanner is printed in black and white on a print sheet, it is extremely possible to print with emphasis on specific parts such as characters written with a red pen on an original printed in black. Convenient. In particular, if a specific part such as a character written in red is darkened and emphasized, and other parts printed in black can be thinned and printed, even if it is a monochrome image, the part written in red And a portion printed in black is convenient.

  The present invention has been made in view of the above circumstances, and provides an image processing apparatus capable of highlighting a portion written in a specific color when a color image read from an original is printed in monochrome. It is an object. In particular, an object of the present invention is to provide an image processing apparatus that can emphasize pixels of a hue specified by a user when obtaining a monochrome image from a color image made up of luminance data and chromaticity data for each pixel. It is another object of the present invention to provide an image processing apparatus capable of suppressing the conspicuous boundary between a hue specified by a user and a hue close to the hue in a color space.

  An image processing apparatus according to a first aspect of the present invention is an image processing apparatus that performs image processing on a color image composed of luminance data and chromaticity data for each pixel read from a document and outputs a monochrome image, based on a user operation. The hue designation means for generating hue designation information for designating the hue to be converted and the pixel of the hue designated by the hue designation information are extracted from the color image based on the hue obtained from the chromaticity data. And a luminance value using a function that decreases the upper limit value of the luminance and monotonously increases within a predetermined range including the upper limit value with respect to the luminance data of the pixel extracted by the pixel extracting unit. And luminance data conversion means for generating the monochrome image from the color image.

  In this image processing apparatus, hue designation information is generated based on a user operation, and pixels having a hue designated by the hue designation information are extracted from a color image read from a document. And the process which converts the luminance data of the extracted pixel is performed, and a monochrome image is produced | generated from a color image. The luminance data conversion process is performed using a function that decreases the upper limit value of luminance and monotonously increases within a predetermined range including the upper limit value. With such a configuration, the luminance value in the vicinity of the upper limit value of the pixel of the hue specified by the user is reduced, so that it is darkly printed when the monochrome image is printed, and the portion can be emphasized.

  In addition to the above configuration, the image processing apparatus according to the second aspect of the present invention is configured such that the luminance data conversion means associates a luminance value with a value obtained by multiplying the luminance value by a certain number.

  In the image processing apparatus according to a third aspect of the present invention, in addition to the above configuration, the luminance data conversion unit associates a luminance value existing in a range from a lower limit value to a first threshold value with the lower limit value, and The luminance value existing within the range from the threshold value to the upper limit value is associated with a value obtained by subtracting a certain number from the luminance value.

  In addition to the above configuration, the image processing apparatus according to the fourth aspect of the present invention, when the pixel extraction unit extracts pixels from a color image based on a hue obtained from the chromaticity data, is more saturated than the second threshold value. Are extracted, and pixels having a saturation smaller than the second threshold value are not extracted. According to such a configuration, the extraction process is performed only for pixels having a saturation greater than the second threshold value, and thus pixels having a small saturation different from the hue specified by the user are erroneously extracted. Can be prevented.

  In addition to the above configuration, the image processing apparatus according to the fifth aspect of the present invention compares the luminance value of the luminance data after the conversion processing by the luminance data conversion means with a third threshold value, and binaries based on the comparison result A binarization processing unit for generating data is provided, and the monochrome image including the binary data for each pixel is output.

  In addition to the above configuration, an image processing apparatus according to a sixth aspect of the present invention uses the luminance value existing in the first range including the lower limit value for the luminance data after the conversion processing by the luminance data conversion means as the lower limit value. Or a luminance correction unit that performs a process of converting a luminance value existing in a second range including the upper limit value into the upper limit value, and the binarization processing unit converts the luminance value by the luminance correction unit. The binary data is generated based on the luminance data after processing.

  In addition to the above configuration, the image processing apparatus according to the seventh aspect of the present invention is configured such that the luminance data conversion means increases the luminance value for pixels other than the hue specified by the hue specifying information. .

  In addition to the above configuration, an image processing apparatus according to an eighth aspect of the present invention generates a peripheral area specifying information for specifying a peripheral area in a color space of a hue specified by the hue specifying information based on the hue specifying information. Comprising: designation means, wherein the luminance data conversion means converts the luminance data with respect to the pixels in the peripheral area designated by the peripheral area designation information at a lower rate of increasing the luminance value than the conversion process, The monochrome image is generated from the color image. According to such a configuration, luminance data is also appropriately converted for pixels in the peripheral region of the hue specified by the user, so that the boundary between the hue specified by the user and a hue close to the hue in the color space is present. Conspicuousness can be suppressed when printing a monochrome image.

  According to the image processing apparatus of the present invention, the brightness value of the pixel of the hue specified by the user is lowered, so that the specific hue is printed darkly when the monochrome image is printed, and the portion can be emphasized. Since the luminance data is also appropriately converted for pixels in the peripheral area of the hue specified by the user, the boundary between the hue specified by the user and a hue close to this hue in the color space is noticeable when printing a monochrome image. Can be suppressed. Therefore, when a color image read from a document is printed in monochrome, a portion written in a specific color can be emphasized.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing an example of a schematic configuration of an image processing apparatus according to Embodiment 1 of the present invention, and includes a color scanner unit 10, an image processing unit 20, and a printer unit 30 as an example of the image processing apparatus. A digital multi-function peripheral 100 is shown. The color scanner unit 10 is an imaging device that generates image data by irradiating a document to be read with light and receiving reflected light from the document. Here, it is assumed that the handwritten characters and the print pattern on the document are read by scanning the irradiation light in the paper feed direction of the document (paper). In addition, color image data including luminance data for at least three different colors is generated.

  The image processing unit 20 performs processing for changing the luminance value of the luminance data for the color image data read from the original by the color scanner unit 10 to generate monochrome image data, and outputs the generated monochrome image data to the printer unit 30. It is operating. The process of changing the luminance value is performed based on the hue specified by the user. In the image processing unit 20, an input screen for designating a hue is displayed on the display unit 42, and a hue is designated based on an input signal from the operation input unit 41.

  The printer unit 30 is a monochrome image data output device, and includes an LED print head 31, a drive control unit 32, a photosensitive drum 33, a charger 34, a developing unit 35, a transfer unit 36, and a fixing unit 37. The LED print head 31 includes an LED array in which a plurality of LEDs (Light Emitting Diodes) are arranged on a straight line, and emits light to the photosensitive drum 33 based on monochrome image data input from the image processing unit 20. The operation to irradiate is performed.

  The drive control unit 32 controls a printer mechanism including the photosensitive drum 33, the charger 34, the developing unit 35, the transfer unit 36, and the fixing unit 37. The photosensitive drum 33 is a cylindrical rotating body having a photosensitive layer formed on the surface, and the surface is uniformly charged by the charger 34 during printing. An electrostatic latent image is formed by irradiating light on the surface of the photosensitive drum 33 thus charged.

  The developing unit 35 performs an operation of forming a toner image by attaching toner to the surface of the photosensitive drum 33 on which the electrostatic latent image is formed. The transfer unit 36 performs an operation of transferring the toner image formed on the surface of the photosensitive drum 33 onto the printing paper. The fixing unit 37 performs an operation of fixing the monochrome image on the surface of the printing paper by subjecting the printing paper on which the toner image has been transferred to heat treatment and pressure treatment.

  FIG. 2 is a block diagram illustrating a configuration example of the color scanner unit 10 in the digital multifunction peripheral 100 of FIG. The color scanner unit 10 includes a line sensor 11, an AFE circuit 12, an A / D converter 13, a shading correction circuit 14, a γ correction circuit 15, and a color space conversion circuit 16. The line sensor 11 includes a light receiving element array in which a plurality of light receiving elements such as a CCD (Charge Coupled Device) is arranged on a straight line L, and receives an analog signal indicating the amount of received light (luminance), for example, a voltage signal. An operation for generating each color of R (red), G (green), and B (blue) is performed.

  An AFE (Analog Front End) circuit 12 is an amplifier that adjusts the voltage level of an analog signal input from the line sensor 11 and outputs the analog signal to the A / D converter 13. The A / D converter 13 is a conversion element that samples the analog signal input from the AFE circuit 12 at a predetermined sampling rate and generates digital data. Here, it is assumed that luminance data composed of 8-bit (256 gradations) bit data is generated for each color of R, G, and B.

  The shading correction circuit 14 is a digital processing circuit that performs luminance data correction processing in order to align the reference of received light amount for each pixel in the line sensor 11. Specifically, a plurality of objects, which are prepared in advance for shading correction and are arranged in the line direction (straight line L direction) and having a known reflectance of light, so-called “white reference” or “black reference” are applied to the line sensor 11. Let me read. Based on the luminance data obtained at this time and the reflectance information of the object, the luminance data newly read from the document is corrected. As a result, the variation in the line direction (straight line L direction) in the brightness of the light source for reading the document, the influence of the decrease in the peripheral light amount in the irradiation condenser lens, or the variation in the line direction in the light receiving sensitivity of the line sensor 11 is corrected. can do.

  The γ (gamma) correction circuit 15 is a digital processing circuit that performs γ correction processing for color adjustment of the R, G, and B luminance data input from the shading correction circuit 14. For example, color adjustment of luminance data is performed in accordance with an international standard color system “sRGB (standard RGB) color system” for an RGB color space that depends on a device. The RGB color space is a color space used to represent an additive color mixture using the three primary colors (R, G, B) of light, and approaches white as the value increases. The sRGB color system is used in various image input / output devices such as scanners, digital cameras, printers, monitors, and the like. By adjusting the color according to the sRGB color system, the color of the input and output colors can be adjusted. Differences can be reduced.

  The color space conversion circuit 16 is a digital processing circuit that converts the color space of the R, G, and B luminance data input from the γ correction circuit 15 and outputs color image data. Specifically, processing for converting the RGB color space into a color space composed of luminance and hue, for example, a YCbCr color system is performed. The YCbCr color system is a color system used for JPEG format image data, etc., where Y indicates luminance data and CbCr indicates chromaticity data. In the chromaticity data CbCr, Cb indicates a blue difference (hue component) and Cr indicates a red difference (hue component). The color space conversion circuit 16 generates color image data including luminance data and chromaticity data for each pixel.

  Instead of converting to the YCbCr color system, it may be converted to the Lab color system which is one of the uniform color spaces. In the Lab color system, L indicates luminance data, and ab indicates chromaticity data. In the chromaticity data ab, a and b each indicate a hue component. Note that the L component in the Lab color system is usually called lightness. The luminance data in this specification includes Lab color system L component data, that is, lightness data.

  FIG. 3 is a block diagram illustrating a configuration example of a main part of the digital multifunction peripheral 100 of FIG. 1, and illustrates an example of a functional configuration of the image processing unit 20. The image processing unit 20 includes a hue specifying unit 21, a peripheral region specifying unit 22, a monochrome image generating unit 23, a conversion table storage unit 24, a peripheral region conversion table storage unit 25, a luminance correction unit 26, and a binarization processing unit 27. Become. The hue designation unit 21 performs an operation for generating hue designation information for designating a hue to be converted into luminance values based on a user operation.

  In this hue designation, different hue components Cb and Cr in the YCbCr color system can be designated independently. Here, it is assumed that the color space is divided into a plurality of hue regions in advance, and one of these hue regions is selected by the user.

  Based on the hue designation information from the hue designation unit 21, the peripheral area designation unit 22 performs an operation of generating peripheral area designation information that designates a peripheral area in the color space of the hue designated by the hue designation information. The peripheral area specified by the peripheral area specifying information is an area that does not overlap with the hue area specified by the user.

  The conversion table storage unit 24 is a memory that stores a conversion table that saturates luminance values higher than the first threshold and increases luminance values lower than the first threshold. This conversion table is association information that defines the association of luminance values. Here, the input value of luminance before conversion processing existing in the range from the lower limit value to the first threshold value is multiplied by a certain number. It is assumed that a conversion table in which values are output as luminance output values after conversion processing is stored in advance.

  The peripheral area conversion table storage unit 25 is a memory that stores a peripheral area conversion table having a smaller ratio of increasing the luminance value than the conversion table.

  The monochrome image generation unit 23 extracts pixels from the color image data based on the hue designation information and the surrounding area designation information, and converts the luminance data of the extracted pixels based on the conversion table and the surrounding area conversion table to obtain monochrome image data. Processing to generate.

  The luminance correction unit 26 performs a process of correcting the luminance of the monochrome image data from the monochrome image generation unit 23 in order to remove noise. Specifically, with respect to the luminance data, the luminance value existing in the first range including the lower limit value is converted into the lower limit value, and the luminance value existing in the second range including the upper limit value is converted to the upper limit value. Processing to convert to a value is performed.

  By extracting pixels from the color image and converting the luminance data to generate a monochrome image before the luminance correction processing, hue determination, that is, the hue region to which the hue indicated by the chromaticity data belongs Judgment can be made accurately.

  The binarization processing unit 27 performs a process of binarizing the luminance data after the conversion processing by the luminance correction unit 26 by reducing the number of gradations. Specifically, the luminance value of the luminance data is compared with a predetermined threshold (fourth threshold), and binary data is generated based on the comparison result. Monochrome image data generated by the binarization processing unit 27 and including binary data for each pixel is output to the LED print head 31.

  Here, when the luminance component is binarized, pseudo gradation display processing (halftone display processing) such as a dither method is performed in order to reproduce black and white multi-value gradation changes in binary. . The pseudo gradation display process is an image process for obtaining monochrome image data by setting a threshold for binarization for each block composed of a plurality of pixels.

  FIG. 4 is a block diagram illustrating a configuration example of the monochrome image generation unit 23 in the image processing unit 20 of FIG. The monochrome image generation unit 23 includes a chromaticity data extraction unit 1, a pixel extraction unit 2, a luminance data extraction unit 3, and a luminance data conversion unit 4. The chromaticity data extraction unit 1 performs an operation of extracting chromaticity data from color image data. Specifically, the chromaticity data CbCr is extracted from the color image data (here, YCbCr) generated by the color space conversion circuit 16 and output to the pixel extraction unit 2.

  Based on the chromaticity data CbCr from the chromaticity data extraction unit 1, the pixel extraction unit 2 performs an operation of extracting pixels having a hue designated by the hue designation information and the surrounding area designation information.

  Specifically, the hue area in the color space to which the pixel belongs is determined based on the hue component included in the chromaticity data CbCr, and the pixel that matches the hue area specified by the user is extracted. Also, pixels that match the hue area specified by the peripheral area specifying information are extracted.

  The luminance data extraction unit 3 performs an operation of extracting luminance data from the color image data. Specifically, the luminance data Y is extracted from the color image data YCbCr generated by the color space conversion circuit 16 and output to the luminance data conversion unit 4.

  The luminance data conversion unit 4 includes an enhancement processing unit 5 and a luminance selection unit 6. The luminance data conversion unit 4 converts the luminance data of the pixels extracted by the pixel extraction unit 2 based on the conversion table, and generates monochrome image data from the color image data. It is operating.

  The enhancement processing unit 5 converts the luminance data Y based on the conversion table read from the conversion table storage unit 24 and the peripheral region conversion table read from the peripheral region conversion table storage unit 25, and increases the luminance value. Processing for generating luminance data and second luminance data is performed. Specifically, the first luminance data is generated by converting the luminance value according to the conversion table. Further, the second luminance data is generated by converting the luminance value according to the peripheral area conversion table.

  The luminance selection unit 6 performs an operation of selecting luminance data based on the pixel extraction information from the pixel extraction unit 2 and outputting it as monochrome image data. Specifically, the first luminance data is selected for the pixels extracted based on the hue designation information, and the second luminance data is selected for the pixels extracted based on the surrounding area designation information. Also, the luminance data Y is selected for the pixels that have not been extracted by the pixel extraction unit 2.

  In the present embodiment, when conversion processing is performed on the luminance data of the pixels extracted by the pixel extraction unit 2, a conversion table in which association of luminance values is defined is used. However, instead of such software processing, In addition, hardware processing may be performed using an arithmetic circuit.

  FIG. 5 is a diagram showing an example of the operation in the image processing unit 20 of FIG. 3, and shows a color space used when the user specifies a hue. This color space is a color space of the YCbCr color system, in which the Cb axis is arranged on the vertical axis and the Cr axis is arranged on the horizontal axis. When the Cb component is increased, the bluish color is increased, and when the Cb component is decreased, the yellow color is increased. Moreover, if Cr component becomes large, redness will become strong, and if it becomes small, greenness will become strong.

  Here, it is assumed that the color space is divided into 16 hue regions by the six straight lines 51 to 56 passing through the origin, the Cb axis, and the Cr axis. Also, it is assumed that the input range of the Cb component and the input range of the Cr component are the same.

  A straight line 51 represents a straight line Cb = 2Cr having a slope 2, a straight line 52 represents a straight line Cb = Cr having a slant 1, and a straight line 53 represents a straight line Cb = (1/2) Cr having a slant 1/2. The straight line 54 is a straight line (−2) Cb = Cr with an inclination (−1) / 2, the straight line 55 is a straight line Cb = −Cr with an inclination (−1), and the straight line 56 is a straight line with an inclination (−2). Cb = (− 2) Cr is shown. The hue regions divided by the straight lines 51 to 56 are regions having the same area.

  A region near the origin of the color space is an achromatic region 57 in which the absolute value of the hue component is small. The achromatic color (monotone) region 57 is a region showing a hue with low saturation, and is defined by a predetermined relational expression established between the hue components Cb and Cr. In this example, an achromatic region 57 is shown as the inside of a circle centered on the origin.

  Such an achromatic color region 57 is excluded from hues to be converted into luminance values. That is, when pixels are extracted from a color image based on chromaticity data, only pixels having a saturation greater than a predetermined threshold (third threshold) are extracted, and pixels having a saturation less than the threshold are extracted. Will not be extracted.

  For such a color space, a hue area and a peripheral area to be whitened from a monochrome image by changing the luminance value are designated.

  FIG. 6 is a diagram illustrating an example of the operation in the image processing unit 20 of FIG. 3, in which a hue area A1 and a peripheral area A2 designated by the user are shown. In this example, the hue area A1 between the straight line 52 and the straight line 53 in the first quadrant is designated by the user, and two hue areas adjacent to the hue area A1 are designated as the peripheral area A2. That is, if one hue area A1 is designated by the user, the peripheral area A2 is automatically designated based on the position or division of the hue area A1 in the color space.

  The monochrome image generation unit 23 converts luminance data of pixels whose hue belongs to the hue area A1 based on the conversion table, and converts luminance data of pixels whose hue belongs to the peripheral area A2 based on the peripheral area conversion table. Is done.

  FIG. 7 is a diagram illustrating an example of the operation in the image processing unit 20 of FIG. 3, and graphs B <b> 2 and B <b> 3 representing conversion tables used when changing the luminance value and whitening a specific hue are illustrated. . The graph B1 is a straight line with a slope of 1, and is a graph representing the association in which the input luminance value is associated with the output value of the same luminance.

  The graph B2 is a polygonal line representing a conversion table of pixels belonging to the hue area designated by the user, and the input value of the luminance within the range from the first threshold value a1 to the upper limit value (saturation value) 255 of the luminance is the output value 255. It is associated with. Further, the graph B2 correlates with the output value obtained by increasing the input value of the luminance within the range from the lower limit value 0 of the luminance to the first threshold value a1 in proportion to the luminance.

  In this example, the proportionality coefficient (straight line) of the graph B2 in the range from the lower limit value 0 to the first threshold value a1 is 4, and 1/4 of the upper limit value 255 is the first threshold value a1. Yes.

  The graph B3 is a line representing a peripheral area conversion table used when converting the luminance data of pixels belonging to the peripheral area, and the rate of increasing the luminance value is smaller than that of the graph B2. Specifically, the input value of the luminance within the range from the threshold value a2 to the upper limit value 255 is associated with the output value 255, and the input value of the luminance within the range from the lower limit value 0 to the threshold value a2 (> a1) is set as the luminance. The output value is proportionally increased. The proportional coefficient of the graph B3 in the range from the lower limit value 0 to the threshold value a2 is larger than 1 and smaller than the proportional coefficient of the graph B2.

  In this example, the proportional coefficient of the graph B3 in the range from the lower limit value 0 to the threshold value a2 is 2, and 1/2 of the upper limit value 255 is the threshold value a2.

  In the monochrome image generation unit 23, processing for converting the luminance data is performed based on the conversion tables represented by such graphs B2 and B3, and the luminance data after the conversion processing is output as monochrome image data.

  FIG. 8 is a diagram showing an example of the operation in the image processing unit 20 of FIG. 3, and shows a graph C1 representing a conversion table used for luminance correction for noise removal. This graph C1 associates the luminance value existing in the first range including the lower limit value 0 of the luminance, that is, in the range of 0 to b1 with the lower limit value 0, and is in the second range including the upper limit value 255. That is, the luminance value existing in the range of b2 to 255 is associated with the upper limit value 255. Further, the graph C1 associates luminance values in the range from b1 to b2 with luminance values obtained by multiplying the difference from b1 by a certain number.

  In the brightness correction unit 26, the monochrome image data generated by the monochrome image generation unit 23 is subjected to conversion processing based on such a conversion table represented by the graph C1. By correcting the luminance based on such a conversion table, the luminance value close to the upper limit value is saturated, and the luminance value close to the lower limit value is converted to the lower limit value. It is possible to suppress black noise from being scattered or white noise from being scattered in a black region.

  Steps S101 to S108 in FIG. 9 are flowcharts showing an example of the operation in the image processing unit 20 in FIG. First, the hue designation unit 21 generates hue designation information when the user designates a hue area to be converted in luminance value (step S101). When the hue designation information is input from the hue designation section 21, the peripheral area designation section 22 generates the peripheral area designation information based on the hue designation information.

  Next, when the hue designation information and the peripheral area designation information are input, the monochrome image generation unit 23 reads the color image data from the color scanner unit 10, and the pixels belonging to the designation area based on the hue component of the chromaticity data. It is determined whether or not there is a pixel, and pixels belonging to the hue area designated by the hue designation information and pixels belonging to the peripheral area designated by the peripheral area designation information are extracted (steps S102 to S104).

  At this time, the monochrome image generation unit 23 performs luminance conversion processing based on the conversion table for the extracted pixel luminance data to generate monochrome image data (step S105).

  Next, when the monochrome image data is input from the monochrome image generation unit 23, the brightness correction unit 26 performs brightness correction processing for noise removal on the monochrome image data (step S106). Then, the binarization processing unit 27 performs a process of reducing the number of gradations for the monochrome image data after the correction process, and outputs it as binary data (steps S107 and S108).

  FIG. 10 is a diagram showing an example of the operation in the image processing unit 20 of FIG. 3, and a graph B4 showing another example of the conversion table used when changing the luminance value and whitening a specific hue is shown. ing. This graph B4 is a polygonal line representing a conversion table of pixels belonging to the hue area designated by the user. In the graph B4, the input value of the luminance within the range from the first threshold value a4 to the upper limit value 255 is associated with the output value 255, and is smaller than the second threshold value a3 (for example, 128) that is smaller than the first threshold value a4. The input value of the brightness higher than the first threshold value a4 is increased, and the input values of the brightness within the range from the lower limit value 0 to the second threshold value a3 are associated with the same brightness.

  Here, the luminance input value within the range from the second threshold value a3 to the first threshold value a4 is associated with an output value obtained by multiplying the difference from the threshold value a3 by a certain number. That is, in the graph B4, the slope of the straight line is changed in two steps between the lower limit value 0 and the first threshold value a4.

  Luminance data may be converted using a conversion table represented by such a graph B4 in which the slope is changed in multiple steps between the lower limit of luminance and the first threshold. In this way, when changing the luminance data for the pixel of the hue specified by the user, the luminance value within the range from the lower limit value to the first threshold value is changed in multiple stages. It is possible to more effectively suppress the boundary of

  FIG. 11 is a diagram illustrating an example of the operation in the image processing unit 20 in FIG. 3, and a graph B <b> 5 representing another example of the conversion table used when changing the luminance value and whitening a specific hue is shown. ing. This graph B5 is a polygonal line representing a conversion table of pixels belonging to the hue area designated by the user. In the graph B5, the luminance input value in the range from the first threshold value a6 to the upper limit value 255 is associated with the output value 255, and the luminance input value x in the range from the lower limit value 0 to the first threshold value a6 is represented. The output value (x + a5) is increased by a certain amount a5.

  In the graph B5, the first threshold value a6 satisfies the relationship of a6 + a5 = 255. Luminance data may be converted using a conversion table represented by such a graph B5.

  According to the present embodiment, for pixels belonging to the hue region specified by the user, the luminance data is changed according to the luminance value, and the luminance value higher than the first threshold is changed to the upper limit value of luminance. Therefore, it is possible to whiten a specific hue while suppressing the black-and-white boundary from being noticeable when printing a monochrome image.

  Specifically, when text or the like is written on a manuscript paper printed in light color, for example, red with high brightness (brightness) with a pen of the same color as the text frame, etc. It is assumed that a monochrome image is printed by whitening only an entry frame and a template without whitening a character written with a pen or an object printed in black. In the digital multi-function peripheral 100 according to the present embodiment, using the fact that characters written with a pen on manuscript paper have lower brightness (darker) than an entry frame or the like, an entry frame and a template are appropriately used while leaving handwritten characters. Can be whitened.

  In addition, according to the present embodiment, since extraction processing is performed on pixels whose saturation is greater than the third threshold value, pixels with small saturation different from the hue region specified by the user are erroneously extracted. Can be prevented.

  Also, luminance data is converted according to the peripheral area conversion table for pixels in the peripheral area of the hue area specified by the user, so the boundary between the hue specified by the user and the hue close to this hue in the color space is a monochrome image. Can be suppressed from being noticeable during printing.

  In this embodiment, an example in which the present invention is applied to a digital multi-function peripheral having a scanner function for reading a color image from a document and a printer function for printing a monochrome image obtained from the read color image on printing paper. However, the present invention is not limited to this. For example, the present invention can be applied to an image reading apparatus having only a scanner function or a printing apparatus having only a printer function. The present invention also relates to a facsimile apparatus that converts a color image read from a document into monochrome image data and transmits it to a communication destination, converts the color image data received from the communication destination into monochrome image data, and prints it on printing paper. Can be applied.

  Further, in the present embodiment, any of the graph B2 in FIG. 7, the graph B4 in FIG. 10, or the graph B5 in FIG. 11 is used as a conversion table used when changing the luminance value to whiten a specific hue. Although an example of the case has been described, a configuration in which a conversion table used for whitening can be switched to any of the conversion tables represented by these graphs as necessary may be employed. In addition, when a user specifies a hue area by holding a plurality of conversion tables with different brightness values according to the hue area, the brightness value conversion process is performed using the conversion table corresponding to the hue area. May be performed.

  In the present embodiment, an example in which the luminance data Y is selected for pixels that are not extracted by the pixel extraction unit 2 has been described, but the present invention is not limited to this. For example, the luminance data Y extracted by the luminance data extraction unit 3 is converted to generate third luminance data with a reduced luminance value. Then, the third luminance data may be selected for pixels that are not extracted by the pixel extraction unit 2.

  In the present embodiment, an example in which pixel extraction and luminance data conversion processing is performed based on the color image data YCbCr generated in the color space conversion circuit 16 has been described. However, the present invention is not limited to this. It is not something that can be done. For example, the present invention can be applied to the case where color data in RGB color space is input as color image data. When RGB data is input as color image data, the chromaticity data extraction unit 1 calculates color component differences (GR) and (GB) based on the RGB data, and as chromaticity data. Is output. Further, the luminance data extraction unit 3 extracts the G component from the RGB data and outputs it as luminance data.

Embodiment 2. FIG.
In the first embodiment, the example has been described in which the luminance value is increased for the pixel of the hue specified by the user and whitened when the monochrome image is printed. On the other hand, in the present embodiment, a case will be described in which the luminance value is lowered with respect to the pixel of the hue specified by the user in order to emphasize the portion written in a specific color.

  FIG. 12 is a diagram illustrating an example of an operation in the image processing apparatus according to the second embodiment of the present invention. Graphs D1 and D2 representing conversion tables used when changing a luminance value to emphasize a specific hue are shown. It is shown. The image processing apparatus according to the present embodiment is different from the digital multifunction peripheral 100 according to the first embodiment only in the conversion table used when changing the luminance value of a pixel whose hue belongs to a specific hue area. Other configurations are the same as those in the first embodiment.

  The graph D1 is a straight line representing a conversion table used when changing the luminance value for pixels belonging to the hue region designated by the user. This graph D1 is associated with an output value obtained by lowering the luminance input value in the range from the lower limit value 0 to the upper limit value (saturation value) 255 in proportion to the luminance. That is, the graph D1 represents the association in which the luminance value is associated with a value obtained by multiplying the luminance value by a certain number. In this example, the proportional coefficient (straight line) of the graph D1 is ¼, and for example, the input value 255 is associated with an integer 63 or 64 close to 255/4 as an output value. Here, it is assumed that both the input value and the output value are integers, and when the output value on the graph D1 corresponding to the input value is a decimal, the decimal part is rounded up, rounded down, or rounded off. Shall.

  The graph D2 is a straight line representing a peripheral area conversion table used when changing the luminance value for pixels whose hue belongs to the peripheral area. In the graph D2, the ratio of decreasing the luminance value is smaller than that in the graph D1. Specifically, the proportional coefficient of the graph D2 is smaller than 1 and larger than the proportional coefficient of the graph D1. In this example, the proportional coefficient of the graph D2 is ½, and for example, the input value 255 is associated with the output value 255/2.

  In the monochrome image generation unit 23, processing for converting the luminance data is performed based on the conversion table represented by such graphs D1 and D2, and the luminance data after the conversion processing is output as monochrome image data. The conversion table used for such luminance data conversion processing only needs to be such that the function that defines the association of luminance values becomes a monotonically increasing function within a predetermined range including the upper limit value 255.

  FIG. 13 is a diagram showing an example of the operation in the image processing apparatus according to the second embodiment of the present invention, and is a graph showing another example of the conversion table used when emphasizing a specific hue by changing the luminance value D3 is shown. This graph D3 is a polygonal line representing a conversion table of pixels belonging to the hue area designated by the user.

  In the graph D3, the input value of the luminance within the range from the lower limit value 0 of the luminance to the first threshold value d2 is associated with the output value 0, and the input value of the luminance within the range from the first threshold value d2 to the upper limit value 255. This is associated with an output value (x−d1) in which x is reduced by a certain number d1. That is, the graph D3 associates the brightness value existing in the range from the lower limit value 0 to the first threshold value d2 with the lower limit value 0, and the brightness value existing in the range from the first threshold value d2 to the upper limit value 255. Is associated with a value obtained by subtracting a certain number d1 from the luminance value.

  In the graph D3, the first threshold value d2 satisfies the relationship d2-d1 = 0. Luminance data may be converted using a conversion table represented by such a graph D3.

  According to the present embodiment, since the luminance value of the pixel in the hue area specified by the user is reduced, the specific hue is printed darkly when printing a monochrome image, and the portion can be emphasized.

  Specifically, a specific portion such as a character written with a red pen can be emphasized and printed on an original in which an entry frame or a template is printed in black. In particular, it is possible to darken and emphasize a specific portion such as a character written in red and to lighten other portions printed in black.

Embodiment 3 FIG.
In the second embodiment, the example in which the luminance value is decreased with respect to the pixels in the hue region designated by the user has been described. On the other hand, in the present embodiment, a case will be described in which the luminance value is decreased for a pixel belonging to the hue area designated by the user and the luminance value is increased for a pixel not belonging to the hue area.

  In the image processing apparatus according to the present embodiment, the luminance value is changed based on the conversion table for the pixels belonging to the hue area designated by the hue designation information. That is, a process for reducing the luminance value is performed for the pixel. On the other hand, for pixels that do not belong to the hue area designated by the hue designation information, processing for increasing the luminance value is performed.

  With this configuration, the luminance value is decreased for the pixels in the hue area specified by the user, and the luminance value is increased for the other pixels. Therefore, when a monochrome image is printed, the specific hue portion is emphasized and printed. can do.

1 is a block diagram illustrating an example of a schematic configuration of an image processing apparatus according to Embodiment 1 of the present invention, in which a digital multifunction peripheral 100 is illustrated as an example of an image processing apparatus. FIG. 2 is a block diagram illustrating a configuration example of a color scanner unit 10 in the digital multifunction peripheral 100 of FIG. 1. FIG. 2 is a block diagram illustrating a configuration example of a main part of the digital multifunction peripheral 100 of FIG. 1, and illustrates an example of a functional configuration of the image processing unit 20. FIG. 4 is a block diagram illustrating a configuration example of a monochrome image generation unit 23 in the image processing unit 20 of FIG. 3. FIG. 4 is a diagram illustrating an example of an operation in the image processing unit 20 in FIG. 3, and illustrates a color space used when a user specifies a hue. FIG. 4 is a diagram illustrating an example of an operation in the image processing unit 20 of FIG. 3, in which a hue area A1 and a peripheral area A2 designated by a user are illustrated. FIG. 4 is a diagram illustrating an example of an operation in the image processing unit 20 of FIG. 3, and graphs B <b> 2 and B <b> 3 representing conversion tables used for whitening are illustrated. FIG. 4 is a diagram illustrating an example of an operation in the image processing unit 20 of FIG. 3, and shows a graph C <b> 1 representing a conversion table used for luminance correction for noise removal. 4 is a flowchart illustrating an example of an operation in the image processing unit 20 of FIG. 3. FIG. 4 is a diagram illustrating an example of an operation in the image processing unit 20 of FIG. 3, and shows a graph B4 representing another example of a conversion table used for whitening. FIG. 4 is a diagram illustrating an example of an operation in the image processing unit 20 of FIG. 3, and shows a graph B5 representing another example of a conversion table used for whitening. It is a figure which showed an example of the operation | movement in the image processing apparatus by Embodiment 2 of this invention, and the graphs D1 and D2 showing the conversion table used in the case of hue emphasis are shown. It is a figure which showed an example of the operation | movement in the image processing apparatus by Embodiment 2 of this invention, and the graph D3 showing the other example of the conversion table used in the case of hue emphasis is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Chromaticity data extraction part 2 Pixel extraction part 3 Luminance data extraction part 4 Luminance data conversion part 5 Enhancement processing part 6 Brightness selection part 10 Color scanner part 11 Line sensor 12 AFE circuit 13 A / D converter 14 Shading correction circuit 15 γ correction Circuit 16 Color space conversion circuit 20 Image processing unit 21 Hue designation unit 22 Peripheral region designation unit 23 Monochrome image generation unit 24 Conversion table storage unit 25 Peripheral region conversion table storage unit 26 Luminance correction unit 27 Binary processing unit 30 Printer unit 31 LED print head 32 drive control unit 33 photoconductor drum 34 charger 35 developing unit 36 transfer unit 37 fixing unit 41 operation input unit 42 display unit 100 digital multifunction device

Claims (8)

In an image processing apparatus that performs image processing on a color image composed of luminance data and chromaticity data for each pixel read from a document and outputs a monochrome image,
Based on a user operation, hue designation means for generating hue designation information for designating a hue to be converted;
Pixel extraction means for extracting, from the color image, pixels of the hue designated by the hue designation information based on the hue obtained from the chromaticity data;
For the luminance data of the pixels extracted by the pixel extracting means, processing for converting the luminance value using a function that decreases the upper limit value of luminance and monotonously increases within a predetermined range including the upper limit value is performed. An image processing apparatus comprising: luminance data conversion means for generating the monochrome image from the color image.   The image processing apparatus according to claim 1, wherein the luminance data conversion unit associates the luminance value with a value obtained by multiplying the luminance value by a certain number.   The luminance data conversion means associates a luminance value existing within a range from the lower limit value to the first threshold value with the lower limit value, and determines a luminance value existing within the range from the first threshold value to the upper limit value. The image processing apparatus according to claim 1, wherein the image processing apparatus is associated with a value obtained by subtracting a certain number from the value.   When the pixel extracting means extracts pixels from the color image based on the hue obtained from the chromaticity data, the pixel extracting means extracts pixels having a saturation higher than the second threshold, and the saturation is higher than the second threshold. The image processing apparatus according to claim 1, wherein a small pixel is not extracted. Comparing the luminance value with the third threshold value for the luminance data after the conversion processing by the luminance data converting means, the binarization processing means for generating binary data based on the comparison result,
The image processing apparatus according to claim 1, wherein the monochrome image including the binary data for each pixel is output. With respect to the luminance data after the conversion processing by the luminance data converting means, the luminance value existing in the first range including the lower limit value is converted into the lower limit value, or the luminance data existing in the second range including the upper limit value. A luminance correction means for performing processing for converting the existing luminance value into the upper limit value;
6. The image processing apparatus according to claim 5, wherein the binarization processing unit generates the binary data based on the luminance data after the conversion processing by the luminance correction unit.   The image processing apparatus according to claim 1, wherein the luminance data conversion unit increases a luminance value for pixels other than the hue designated by the hue designation information. Peripheral area specifying means for generating peripheral area specifying information for specifying a peripheral area in the color space of the hue specified by the hue specifying information based on the hue specifying information,
The luminance data conversion means converts luminance data with respect to the pixels in the peripheral area specified by the peripheral area specification information at a lower rate of increasing the luminance value than the conversion process, and converts the luminance data from the color image. The image processing apparatus according to claim 1, wherein a monochrome image is generated.

Images