JP6293466B2 - Image processing apparatus, image forming apparatus, image processing method, image processing program, and recording medium - Google Patents

Description

  The present invention relates to an image processing apparatus that converts color image data representing a color image into monochrome image data representing a monochrome image.

  Color image data (for example, RGB signals) obtained by reading a color document is converted into monochrome image data (a signal composed of gray gradation values), and a monochrome image is output (for example, printed) based on the monochrome image data ) Has traditionally been made. For example, in Patent Document 1, RGB color signals are converted into LCH color signals, color adjustment processing is performed on the LCH color signals, and then LCH color signals are inversely converted into RGB color signals. A printing apparatus that converts RGB color signals after inverse conversion into monochrome image data is shown.

JP 2001-16459 A

  When color image data is converted into monochrome image data by the above-described conventional technology, a color difference that is visually recognizable in the color image state becomes difficult to visually recognize in the monochrome image state. Depending on the situation, this phenomenon may be inconvenient. For example, in a document that uses different character colors (black characters, red characters, blue characters, etc.) depending on the importance of the text and the degree of attention, the difference in character colors must be clearly shown. When the color image data indicating is converted into monochrome image data, there is an inconvenience that the difference in character color is unclear.

  In the present invention, the color difference that can be visually recognized in a color image state is highly required to be visually recognizable in a monochrome image state even if the color image data is converted into monochrome image data. An object of the present invention is to provide an image processing apparatus capable of suppressing color recognition from becoming difficult to recognize.

  In order to solve the above-described problem, an image processing apparatus according to an aspect of the present invention provides a color space that includes, as coordinate values, a light / dark value correlated with lightness and a color value correlated with hue angle and / or saturation. An image conversion unit that performs a conversion process of converting the color image data into monochrome image data indicated by a gray gradation value, and the image conversion unit correlates at least the light and dark values in the conversion process. A first mode for outputting a gradation value and a second mode for outputting the gray gradation value having a stronger correlation with the color value than the first mode are switched.

  According to one aspect of the present invention, for an image that is highly required to be visually recognizable even in the state of a monochrome image, the color difference that can be visually recognized in the state of the color image is switched to the second mode. By performing the conversion process, it is possible to suppress the above-described color difference from becoming difficult to recognize.

1 is a block diagram showing a schematic configuration of a monochrome image printing apparatus according to Embodiment 1 of the present invention. It is explanatory drawing which shows the result at the time of converting the color image data read from the color document into monochrome image data in the image processing apparatus of a prior art. FIG. 6 is an explanatory diagram showing a result when color image data read from a color document is converted into monochrome image data in the monochrome image printing apparatus according to the first embodiment of the present invention. 3 is a flowchart showing a processing order in the monochrome image printing apparatus according to the first embodiment of the present invention.

Embodiment 1
(Outline of Embodiment 1)
First, an outline of the first embodiment will be described. The monochrome image printing apparatus of the present embodiment (hereinafter simply referred to as “printing apparatus”) converts color image data in the LCH color space into monochrome image data composed of K signals (gradation signals indicating gray gradation values). Conversion processing is performed, and monochrome images are printed.

  In particular, the printing apparatus according to the present embodiment includes (1) a brightness enhancement mode that outputs a K signal from only the L value without using the C value and the H value in the LCH color space, and (2) H A weighted average value of the L value, the C value, and the H value is determined with the highest value weight, and the color difference enhancement mode for outputting the weighted average value as a K signal is switched. In particular, the printing apparatus according to the present embodiment performs the conversion process in the light / dark enhancement mode (first mode) for pixels belonging to the print photograph area or the photographic paper photograph area, and the color difference enhancement mode (for the pixels belonging to the character area). The conversion process is performed in the second mode).

  As a result, for images (characters) that are highly required to be visually recognizable even in the state of a monochrome image, the color difference that can be recognized visually in the state of a color image, even after conversion from color to monochrome, It can suppress that a difference becomes difficult to recognize.

(Details of Embodiment 1)
Next, the first embodiment will be described in detail. FIG. 1 is a block diagram illustrating a configuration of a printing apparatus (image forming apparatus) according to the present embodiment.

  As shown in FIG. 1, the printing apparatus 1 of this embodiment includes an image input device 10, an image processing device 11, and an image output device 12. The image input apparatus 10 reads color originals to generate color image data (that is, image data in an RGB color space) that is decomposed into RGB color information. R means red, G means green, and B means blue. The image processing device 11 is a device that inputs image data from the image input device 10 and performs predetermined image processing on the image data. Details of the image processing apparatus 11 will be described later. The image output device 12 is a device that inputs image data after image processing is performed by the image processing device 11 and prints (outputs) an image of the image data on a sheet.

  Next, the configuration of the image processing apparatus 11 will be described in detail. As shown in FIG. 1, the image processing apparatus 11 includes a preprocessing unit 21, a region separation processing unit 22, a color conversion processing unit 23, a monochrome image output unit (image conversion unit) 24, and a halftone processing unit 25. With. The preprocessing unit 21 includes a memory processing unit 211, an RGB correction unit 222, and an interline adjustment unit 233.

  The memory processing unit 211 is a block that performs processing for temporarily storing RGB image data generated by the image input apparatus 10 in a first in first out (FIFO) memory. In addition, the memory processing unit 211 reads out image data stored in the FIFO memory for each original and transmits it to the RGB correction unit 222.

  The RGB correction unit 222 is a block that inputs RGB image data read from the FIFO memory and corrects the characteristics of the color scanner such as γ correction to the image data.

  The inter-line adjustment unit 233 is a block that develops the image data after the correction by the RGB correction unit 222 in the inter-line adjustment RAM and performs a pixel value correction process between the lines.

  The region separation processing unit 22 is a block that inputs RGB image data after the series of processing in the preprocessing unit 21 is completed, and performs region separation processing with reference to the image data. Specifically, the region separation processing unit 22 determines, for each pixel (or each block composed of a plurality of pixels), that the pixel (or block) is any image region such as a character image region, a halftone dot image region, or a photographic image region. And an area discrimination signal indicating which image area it is. The RGB image data input to the region separation processing unit 22 is sent to the color conversion processing unit 23 after the region separation processing.

  The color conversion processing unit 23 is a block that converts RGB image data, which is a color image signal in the RGB color space, into LCH image data, which is a color image signal in an LCH color space that is close to a human color sense. Here, L is a lightness value, C is a saturation value, and H is a hue angle.

  Specifically, as shown in FIG. 1, the color conversion processing unit 23 includes an L conversion unit 23a, a C conversion unit 23b, and an H conversion unit 23c. The L conversion unit 23a is a block that converts RGB image data into L values. The C conversion unit 23b is a block that converts RGB image data into C data. The H conversion unit 23c is a block that converts RGB image data into H data.

  Although a detailed description of the conversion method in the L conversion unit 23a is omitted, for example, an RGB signal may be converted into an L signal for each pixel, and can be converted by a known conversion formula. Similarly to the L conversion unit 23a, the C conversion unit 23b and the H conversion unit 23c may perform conversion processing for each pixel, for example, and can be converted by a known conversion formula.

  In this embodiment, the RGB values are each 8 bits (0 to 255), while the numerical value range of the L value converted from the RGB values is 0 (dark) to 99 (bright). The numerical value range of C (saturation value) converted from RGB values is 0 (dull) to 99 (bright), and both L and C are expressed in 100 levels. The numerical range of H (hue angle) converted from RGB values is 0 to 359 degrees, and is expressed in 360 steps (for example, 0 to 59: red to yellow, 60 to 119: yellow to green, 120 to 179: green to light blue, 180 to 239: light blue to blue, 240 to 299: blue to purple, 300 to 359: purple to red).

  On the other hand, in the present embodiment, the monochrome image output unit 24 subsequent to the color conversion processing unit 23 outputs an 8-bit (0 to 255) gray gradation value from the 8-bit LCH value. Yes. Therefore, in the color conversion processing unit 23 of the present embodiment, after converting the L value, the C value, and the H value from the R value, the G value, and the B value, each of the L value, the C value, and the H value is further converted into 8 bits. After normalizing to the above data, color image data of L value, C value, and H value is output to the monochrome image output unit 24.

  That is, the L conversion unit 23a normalizes the L value from 0 to 99 to the L value from 0 to 255, and the C conversion unit 23b normalizes the C value from 0 to 99 to the C value from 0 to 255, and performs the H conversion. The unit 23c normalizes the H value from 0 to 359 to the H value from 0 to 255. Then, the normalized color image data of L value, C value, and H value is transmitted from the color conversion processing unit 23 to the monochrome image output unit 24.

  The monochrome image output unit 24 is a block that performs conversion processing for converting the color image data sent from the color conversion processing unit 23 into monochrome image data indicated by a K signal (gray gradation value). Details of the processing of the monochrome image output unit 24 will be described later.

  The halftone processing unit 25 receives the monochrome image data converted by the monochrome image output unit 24 and performs halftone processing on the monochrome image data by a pseudo gradation method (error diffusion, dithering, etc.). At this time, the halftone processing unit 25 receives the region determination signal from the region separation processing unit 22 and refers to the region determination signal to thereby display each image region of the character region, the printed photograph (halftone dot photograph), and the photographic paper photograph. On the other hand, halftone processing suitable for each region is performed.

  The monochrome image data that has been subjected to the halftone processing by the halftone processing unit 25 is transmitted from the halftone processing unit 25 to the image output device 12. Then, the image output device 12 prints a monochrome image on the sheet based on the monochrome image data transmitted from the halftone processing unit 25.

  The flow of processing after the preprocessing by the preprocessing unit 21 is as shown in FIG. That is, a region separation process is performed for each pixel (S11), and after S11, a process of converting RGB image data into LCH image data is performed (S12a to 12c). Thereafter, a gray gradation value is generated using the L value, the C value, and the H value (S13), and halftone processing is performed on the monochrome image data including the gray gradation value (S14).

(About monochrome image output part)
Next, the monochrome image output unit 24 will be described in detail. As described above, the monochrome image output unit 24 of the present embodiment is a block that performs a conversion process for converting color image data into monochrome image data, but the conversion process is performed according to the determination result of the region separation processing unit 22. The contents are switched.

  Specifically, the monochrome image output unit 24 executes the contrast enhancement mode for the pixels belonging to the print photograph area or the photographic paper photograph area, and the color difference enhancement mode for the pixels belonging to the character image area. Yes.

  The brightness enhancement mode (first mode) is a mode for outputting a K value having a stronger correlation with the L value than the C value and the H value. In this embodiment, the L value is expressed as shown in the following equation 1. The K value is output as it is.

  On the other hand, the color difference enhancement mode (second mode) is a mode for outputting a K value having a stronger correlation with the H value than in the light and dark enhancement mode. In this embodiment, the weight given to the H value is made the heaviest. A weighted average of the L value, the C value, and the H value is obtained, and this weighted average is output as a K value. Specifically, the K value is output by the above equation 2.

  Thereby, when the image to be processed is a printed photograph or photographic paper photograph, a gray-scale monochrome image having a strong correlation with the lightness is output, and when the image to be processed is a character image (such as a document), the hue angle Thus, a gray-scale monochrome image having a strong correlation with respect to is output.

  In other words, (1) For printed photographs or photographic paper photographs, since they are converted into gray-scale monochrome images having a strong correlation with lightness as in the prior art, a monochrome image can be output without impairing the natural feeling. (2) For a character image that is highly required to be visually recognizable even in a monochrome image state, the color difference that can be visually recognized in the color image state is a gray-tone monochrome image that has a strong correlation with the hue angle. Since the data is output, it is possible to suppress the above-described color difference from becoming difficult to recognize.

  Next, advantages of this embodiment compared to the prior art will be described. FIG. 2A shows a black character of (R, G, B) = (0, 0, 0), a red character of (R, G, B) = (255, 0, 0), and (R, G, B). = Description showing results when processing of generating monochrome image data from color image data read from a color document indicated with blue characters of (0,0,255) is performed by a conventional image processing apparatus FIG. FIG. 2B is an explanatory diagram showing a result when the image processing apparatus 11 of the present embodiment performs processing for generating monochrome image data from color image data read from the color document.

  In the conventional image processing apparatus, the weighted average of the R value, the G value, and the B value is set as the K value by the conversion formula shown in FIG. 2A regardless of the type of the image region. Therefore, according to the prior art, as shown in FIG. 2A, the average of the gray gradation value differences generated between black characters, red characters, and blue characters is 51, and the minimum difference is 28.05.

  On the other hand, in the image processing apparatus 11 of the present embodiment, for the character image area, the color difference enhancement mode is selected, and thus the K value is obtained by the above equation 2. Therefore, according to the image processing apparatus 11 of the present embodiment, as shown in FIG. 2B, the average of the gray gradation value differences generated between black characters, red characters, and blue characters is 136, and the minimum difference is 102. It becomes.

  That is, according to the color difference enhancement mode of the image processing apparatus 11 of the present embodiment, in a monochrome image converted from a color image including black characters, red characters, and blue characters, the gray gradation value of the pixel corresponding to the black characters and the The difference between the gray gradation value of the pixel corresponding to the red character and the gray gradation value of the pixel corresponding to the blue character can be made larger than that of the conventional image processing apparatus. Therefore, according to the present embodiment, when a color character image is converted to a monochrome image, the color difference when the color is monochrome in the monochrome image becomes unclear compared to the image processing apparatus of the prior art. Can be suppressed.

  In the above embodiment, the contrast enhancement mode is selected for the pixels belonging to the printed photograph image or the photographic paper photograph. In the contrast enhancement mode, the monochrome image output unit 24 sets the C value and the H value. The K value is output only from the L value without using it. Therefore, as shown in FIG. 1, the region separation signal is also input to the color conversion processing unit 23, and in the case of a pixel belonging to a printed photograph or photographic paper photograph, the processing of the C conversion unit 23b and the H conversion unit 23c is stopped. Only the L conversion unit 23a performs the process, and in the case of a pixel belonging to a character image, all of the L conversion unit 23a, the C conversion unit 23b, and the H conversion unit 23c may perform the process. Thereby, useless processing can be omitted.

(Modification)
In the above color difference emphasis mode, the weight given to the H value is set to be the heaviest and the K value is output according to Equation 2. However, the present invention is not limited to this configuration. In short, a color space including at least a coordinate value (brightness value) correlated with lightness and a coordinate value (color value) having a weaker correlation with lightness than the lightness value and a strong correlation with hue angle and / or saturation. In the case of converting the image data into monochrome image data, it is only necessary to output gray-scale monochrome image data having a stronger correlation with the color value than in the contrast enhancement mode.

  For example, in the light / dark emphasis mode, when the K value is output by Equation 1, in the color difference emphasis mode, the weight given to the color value (C value or H value) is made the heaviest and each color space is It is only necessary to obtain a weighted average of coordinate values and output the weighted average as a K value (that is, b or c is maximized in Equation 2). In the color difference enhancement mode, the weight given to any one of the color values (C value or H value) is set to 1, the weight given to the other coordinate values is set to zero, the weighted average is obtained, and this weighted average is set as the K value. It may be designed to output. That is, in this case, in the color difference enhancement mode, the C value is output as it is as the K value, or the H value is output as it is as the K value.

  Further, in the above-described contrast enhancement mode, the L value is output as it is as the K value as shown in Equation 1, but the present invention is not limited to this configuration. In short, it is only necessary that the output gray gradation value has a stronger correlation with the L value (brightness value) than the C value (color value) and the H value (color value). For example, the weight of the L value (brightness / darkness value) is set to the highest weight, the weighted average of the L value, the C value (color value), and the H value (color value) is obtained, and this weighted average is output as the K value. It may be.

  The monochrome image data output from the monochrome image output unit 24 is not limited to the image data used for the printing process, but is used for a filing process for generating a PDF file or a TIFF file, or a transmission process using an Internet fax. May be.

[Embodiment 2]
In the first embodiment, the monochrome image output unit 24 switches between the light / dark enhancement mode and the color difference enhancement mode according to the result of the region separation processing. The result of the region separation processing is used as a trigger for mode switching. It is not restricted to a form, It is good also considering a user's instruction | indication as a trigger of mode switching.

  For example, on the operation panel of the monochrome image printing apparatus 1, a button indicating the normal document processing mode and a button indicating the color difference enhancement mode are displayed, and when the user selects the normal mode, the monochrome image output unit 24 displays the brightness enhancement mode. If the user selects the color difference enhancement mode, the monochrome image output unit 24 may perform the process in the color difference enhancement mode.

[Embodiment 3]
In the first embodiment, an example in which color image data read from an original document is converted into monochrome image data and printed by the image input apparatus 10 has been described. Of course, the monochrome image printing apparatus 1 is connected via a network or the like. The color image data transmitted from the terminal device may be converted into monochrome image data and printed. In this case, the image processing apparatus 11 includes an area determination unit that determines an image area to which each pixel belongs with reference to tag information added to color image data transmitted from the terminal apparatus. The image area determined here is a character image, a graph, a photographic image, or the like. Then, the color conversion processing unit 23 outputs an LCH value from the color image data, and the monochrome image output unit 24 performs processing in a light / dark emphasis mode for photographs, and for character images or graphs. Processing is performed in the color difference enhancement mode.

[Embodiment 4]
In the first embodiment, image data in the RGB color space is converted into image data in the LCH color space, and image data in the LCH color space is converted into monochrome image data. Color image data may be converted into monochrome image data. Specifically, the color space is limited to the LCH color space as long as the color space includes at least a coordinate value (brightness value) correlated with lightness and a coordinate value (color value) correlated with at least one of saturation and hue angle. Is not to be done.

For example, an L ^* a ^* b ^* color space may be used instead of the LCH color space (L ^* corresponds to the brightness value, and the a ^* value and b ^* value correspond to the color value). The following structure is mentioned as an example of embodiment in this case. For example, the color conversion processing unit 23 converts RGB image data into L ^* a ^* b ^* image data. Then, the monochrome image output unit 24 outputs the L ^* value as it is as the K value in the brightness enhancement mode, and in the color difference enhancement mode, the weight of one of the a ^* value and the b ^* value is set to be the heaviest. A weighted average of the ^* value, a ^* value, and b ^* value is obtained, and this weighted average is output as a K value.

Further, an L ^* u ^* v ^* color space may be used instead of the LCH color space (L ^* corresponds to the brightness value, and the u ^* value and v ^* value correspond to the color value). The following structure is mentioned as an example of embodiment in this case. The color conversion processing unit 23 converts RGB image data into L ^* u ^* v ^* image data. Then, the monochrome image output unit 24 outputs the L ^* value as it is as the K value in the brightness enhancement mode, and in the color difference enhancement mode, the weight of one of the u ^* value and the v ^* value is set to be the heaviest. A weighted average of the ^* value, u ^* value, and v ^* value is obtained, and this weighted average is output as a K value.

  Alternatively, an XYZ color space may be used instead of the LCH color space (Y value corresponds to the brightness value, and X value and Z value correspond to the color value). The following structure is mentioned as an example of embodiment in this case. The color conversion processing unit 23 converts RGB image data into XYZ image data. Then, the monochrome image output unit 24 outputs the Y value as it is as the K value in the brightness enhancement mode, and in the color difference enhancement mode, the weight of one of the X value and the Z value is set to be the heaviest, and the X value and the Y value are output. A weighted average of the value and the Z value is obtained, and this weighted average is output as a K value.

[Example of software implementation]
The control blocks (the area separation processing unit 22, the color conversion processing unit 23, and the monochrome image output unit 24) of the image processing apparatus 11 according to the present embodiment are configured by a logic circuit (hardware) formed on an integrated circuit (IC chip) or the like. It may be realized or may be realized by software using a CPU (Central Processing Unit).

  In the latter case, the image processing apparatus 11 includes a CPU that executes instructions of a program that is software that realizes each function, and a ROM (Read Only Memory) in which the program and various data are recorded so as to be readable by a computer (or CPU). Alternatively, a storage device (these are referred to as “recording media”), a RAM (Random Access Memory) that expands the program, and the like are provided. And the objective of this invention is achieved when a computer (or CPU) reads the said program from the said recording medium and runs it. As the recording medium, a “non-temporary tangible medium” such as a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, or the like can be used. The program may be supplied to the computer via an arbitrary transmission medium (such as a communication network or a broadcast wave) that can transmit the program. The present invention can also be realized in the form of a data signal embedded in a carrier wave in which the program is embodied by electronic transmission.

[Summary]
An image processing apparatus according to aspect 1 of the present invention provides color image data in a color space that includes, as coordinate values, a light / dark value correlated with lightness and a color value correlated with hue angle and / or saturation. A first mode for outputting the gray gradation value correlated with at least the brightness value in the conversion process, the image converting unit performing a conversion process for converting into monochrome image data indicated by the value; And a second mode that outputs the gray gradation value having a stronger correlation with the color value than the first mode.

  According to the configuration of the aspect 1, for an image that is highly required to be visually recognizable even in a monochrome image state, the color difference that can be recognized visually in the state of the color image is switched to the second mode. By performing the conversion process, it is possible to suppress the above-described color difference from becoming difficult to recognize.

  In the image processing device according to aspect 2 of the present invention, in addition to the configuration of aspect 1, the image conversion unit outputs the brightness value as the gray gradation value in the first mode, and the second mode In the mode, a weighted average of each coordinate value in the color space is obtained after the weight given to the color value is made heaviest, and the weighted average is output as the gray gradation value. .

  According to the configuration of the aspect 2, in the first mode, the gray gradation value correlated with the brightness value can be output, and in the second mode, the correlation with the color value is stronger than in the first mode. Gray tone value can be output.

In addition to the configuration of aspect 1 or aspect 2, the image processing apparatus according to aspect 3 of the present invention includes an LCH color space, an XYZ color space, an L ^* a ^* b ^* color space, and an L ^* u ^*. v ^* is any one of the color spaces; (a) when the color space is the LCH color space, the brightness value is an L value, and the color value is a C value or an H value. (B) When the color space is the XYZ color space, the brightness value is a Y value, and the color value is one of an X value and a Z value, c) When the color space is data of L ^* a ^* b ^* color space, the brightness value is an L ^* value, and the color value is one of an a ^* value and a b ^* value, (d) if the color space is ^L * ^u * ^{v *} color space, the brightness values are ^{L *} value, before Color value may be equal to either one of the u ^* values and v ^* values.

  An image processing apparatus according to aspect 4 of the present invention includes an area separation processing unit that performs area separation processing based on the color image data, in addition to the configuration of any one of aspects 1 to 3. The image conversion The image processing unit performs the conversion process in the first mode for an image area determined to be a printed photograph or a photographic paper photograph in the area separation process, and the second for an image area determined to be a character in the area separation process. The conversion process is performed according to a mode.

  As a result, for the image (character) that is highly required to be visually recognizable even in the monochrome image state, the color difference that can be visually recognized in the color image state is processed in the second mode. A low image (photo) is processed in the first mode, but switching between the first mode and the second mode can be performed automatically.

  In addition, when color image data is converted into monochrome image data for an image in which a photograph and a character are mixed, the pixel belonging to the photograph area is processed in the first mode, and the pixel belonging to the character area is changed to the first mode. It is possible to perform processing in two modes.

  An image forming apparatus according to an aspect 5 of the invention includes the image processing apparatus according to any one of the aspects 1 to 4.

  In addition, the image processing method according to aspect 6 of the present invention provides color image data in a color space that includes at least coordinate values including a light-dark value correlated with lightness and a color value correlated with hue angle and / or saturation. A conversion step of converting into monochrome image data indicated by a gradation value, and in the conversion step, a first mode for outputting the gray gradation value correlated with at least the brightness value, and the first mode more than the first mode. The second mode for outputting the gray gradation value having a strong correlation with the color value is switched.

  The image processing apparatus according to each aspect of the present invention may be realized by a computer. In this case, the image processing apparatus is realized by a computer by causing the computer to operate as each unit included in the image processing apparatus. An image processing program to be executed and a computer-readable recording medium on which the image processing program is recorded also fall within the scope of the present invention.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

  The present invention can be used in an image processing apparatus that processes digital image data.

1 Monochrome image printing device (printing device, image forming device)
11 Image Processing Device 22 Region Separation Processing Unit 24 Monochrome Image Output Unit (Image Conversion Unit)

Claims (7)

A conversion process that converts color image data in a color space that includes at least coordinate values of brightness values that correlate with brightness and hue values that represent hue angles and / or saturation , to monochrome image data that is indicated by gray gradation values. Having an image conversion unit to perform,
Wherein the image conversion section, in the conversion process, the outputs a first mode for outputting the brightness value as the gray level value, the gray level value is a strong correlation with respect to the color value than the first mode To switch between two modes ,
In the second mode, a weighted average of each coordinate value in the color space is obtained with the highest weight given to the color value, and the weighted average is output as the gray gradation value. A featured image processing apparatus. The color space is any one of an LCH color space, an XYZ color space, an L * a * b * color space, and an L * u * v * color space,
(A) When the color space is the LCH color space, the brightness value is an L value, and the color value is one of a C value and an H value,
(B) When the color space is the XYZ color space, the brightness value is a Y value, and the color value is one of an X value and a Z value,
(C) When the color space is data in the L * a * b * color space, the brightness value is an L * value, and the color value is one of an a * value and a b * value. ,
(D) When the color space is an L * u * v * color space, the brightness value is an L * value, and the color value is one of a u * value and a v * value. The image processing apparatus according to claim 1, wherein: A region separation processing unit that performs region separation processing based on the color image data;
The image conversion unit performs the conversion process in the first mode for an image area determined as a printed photograph or a photographic paper photograph in the area separation process, and for an image area determined as a character in the area separation process. the image processing apparatus according to claim 1 or 2, characterized in that said conversion processing by the second mode. An image forming apparatus comprising the image processing apparatus according to any one of claims 1 to 3. A conversion step of converting color image data in a color space including at least coordinate values including a light-dark value correlated with lightness and a hue value representing hue angle and / or saturation into monochrome image data indicated by a gray gradation value; Have
In the conversion step, a first mode in which the light / dark value is output as the gray gradation value and a second mode in which the gray gradation value having a stronger correlation with the color value than in the first mode is switched are switched. It has become,
In the second mode, a weighted average of each coordinate value in the color space is obtained with the highest weight given to the color value, and the weighted average is output as the gray gradation value. A featured image processing method. An image processing program for causing a computer to function as the image processing apparatus according to any one of claims 1 to 3, an image processing program for causing a computer to function as the above sections. A computer-readable recording medium on which the image processing program according to claim 6 is recorded.

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