Image processing device, image processing method, and program

Abstract

To provide an image processing device etc. that can appropriately output a monochrome image from a color image.SOLUTION: An image processing device includes an extraction unit that extracts information about the character color of characters included in a character area of a color image and the background color of the characters, a calculation unit that calculates a frequency indicating the conspicuousness of the character on the basis of the difference between the character color and the background color, and a conversion unit that converts the colored characters included in the character area to black characters and converts the black characters included in the character area to gray characters when the frequency is equal to or greater than a predetermined threshold.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This disclosure relates to an image processing device, etc. [Background technology]

[0002] Conventionally, when using image processing devices such as multifunction printers to output a color original (color document) in monochrome mode, the output may be a monochrome version of the original. In such cases, colored text and other elements contained in the color original are output in monochrome.

[0003] Furthermore, techniques have been proposed to reproduce the intended color scheme in a color original even when the original is converted to monochrome output, by correcting the image of the color original. For example, a technique has been proposed in which each color extracted from color data is determined to be a base color and an accent color, and the gray applied to the accent color is made to be a higher density gray than the gray applied to the base color (see, for example, Patent Document 1). In addition, a technique has been proposed in which the colored text portion of a color original is recognized, and the shape of the colored text is changed to italics or bold, or the font type and size are changed according to the recognition result (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-138359 [Patent Document 2] Japanese Patent Publication No. 2007-028181 [Overview of the project] [Problems that the invention aims to solve]

[0005] In conventional technologies such as those described in Patent Documents 1 and 2, when converting colored text to monochrome, processes such as bolding the text, enlarging the text, outlining the text, or adding a background color were employed to mitigate the reduction in the text's appeal. However, these methods sometimes worsened the text's visibility and readability, making them difficult to use. For example, bolding the text made it even bolder and harder to read. Outlining the text did not improve readability. Enlarging the text disrupted the original balance of the document. Adding a background color, in monochrome, reduced the brightness difference between the text color and the background color, making it harder to read.

[0006] In view of the above-mentioned issues, this disclosure aims to provide an image processing device, etc., that can appropriately output a monochrome image from a color image. [Means for solving the problem]

[0007] To solve the above-mentioned problems, the image processing apparatus of the present disclosure is characterized by comprising: an extraction unit that extracts information on the color of characters contained in a character area of ​​a color image and the background color of the characters; a calculation unit that calculates a degree indicating the visibility of the characters based on the difference between the character color and the background color; and a conversion unit that, if the degree is greater than or equal to a predetermined threshold, converts the colored characters contained in the character area to black characters and converts the black characters contained in the character area to gray characters.

[0008] The image processing method disclosed herein is characterized by extracting information on the color of characters contained in a character area of ​​a color image and the background color of those characters, calculating a degree indicating the visibility of the characters based on the difference between the character color and the background color, and, if the degree is greater than or equal to a predetermined threshold, converting the colored characters contained in the character area to black characters and converting the black characters contained in the character area to gray characters.

[0009] The program of this disclosure is characterized by providing a computer with an extraction function that extracts information on the color of characters contained in a character area of ​​a color image and the background color of those characters; a calculation function that calculates a degree indicating the visibility of the characters based on the difference between the character color and the background color; and a conversion function that, if the degree is greater than or equal to a predetermined threshold, converts the colored characters contained in the character area to black characters and converts the black characters contained in the character area to gray characters. [Effects of the Invention]

[0010] According to this disclosure, it will be possible to provide an image processing device, etc., that can appropriately output a monochrome image from a color image. [Brief explanation of the drawing]

[0011] [Figure 1] This is a perspective view of the multifunction device in the first embodiment. [Figure 2] This is a functional configuration diagram of the multifunction device in the first embodiment. [Figure 3] This figure shows an example of the data structure of character area information in the first embodiment. [Figure 4] This figure shows an example of the data structure of color value information in the first embodiment. [Figure 5] This figure shows an overview of the process in the first embodiment. [Figure 6] This is a flowchart of the main processing in the first embodiment. [Figure 7] This is a flowchart of the achromatic correction process in the first embodiment. [Figure 8] This figure shows an example where the first embodiment is not applied. [Figure 9] This figure shows an example of operation in the first embodiment. [Figure 10] This figure shows an example of operation in the first embodiment. [Figure 11] This is a flowchart of the achromatic correction process in the second embodiment. [Figure 12]This is a flowchart of a modified example of the achromatic correction process in the second embodiment. [Figure 13] This figure shows an example of operation in the second embodiment. [Figure 14] This is a flowchart of the main processing in the third embodiment. [Figure 15] This figure shows an example of operation in the third embodiment. [Figure 16] This is a functional configuration diagram of the multifunction printer in the fourth embodiment. [Figure 17] This figure shows an example of the data structure of color combination information and color value information in the fourth embodiment. [Figure 18] This figure shows an example of the data structure of color value information in the fourth embodiment. [Figure 19] This is a flowchart of the main processing in the fourth embodiment. [Figure 20] This is a flowchart of the main processing in the fifth embodiment. [Figure 21] This figure shows an example of operation in the fifth embodiment. [Figure 22] This is a flowchart of the achromatic correction process in the sixth embodiment. [Figure 23] This is a flowchart of the achromatic correction process in the sixth embodiment. [Figure 24] This is a flowchart of the achromatic correction process in the sixth embodiment. [Figure 25] This figure shows an example of operation in the sixth embodiment. [Figure 26] This figure shows an example of operation in the sixth embodiment. [Figure 27] This is a flowchart of the achromatic correction process in the seventh embodiment. [Figure 28] This figure shows an example of operation in the seventh embodiment. [Modes for carrying out the invention]

[0012] An embodiment for implementing this disclosure will be described below with reference to the drawings. Note that the following embodiment is merely an example for illustrating this disclosure, and the technical scope of the invention as described in the claims is not limited to the following description.

[0013] [1. First Embodiment] The first embodiment is an embodiment in which the image processing device of the present disclosure is applied to a multifunction printer 10. The multifunction printer 10 is a device to which the image processing device of the present disclosure is applied. The multifunction printer 10 is an image processing device having copy function, scan function, print function, fax function, etc., and is also called an MFP (Multi-Function Printer / Peripheral).

[0014] [1.1 Functional Configuration] The functional configuration of the multifunction printer 10 of this embodiment will be described with reference to Figures 1 and 2. Figure 1 is an external perspective view of the multifunction printer 10, and Figure 2 is a block diagram showing the functional configuration of the multifunction printer 10.

[0015] As shown in Figure 2, the multifunction device 10 comprises a control unit 100, an image input unit 120, an image forming unit 130, a display unit 140, an operation unit 150, a storage unit 160, and a communication unit 190.

[0016] The control unit 100 is a functional unit for controlling the entire multifunction device 10. The control unit 100 realizes various functions by reading and executing various programs stored in the memory unit 160, and is composed of, for example, one or more arithmetic units (CPU (Central Processing Unit)). The control unit 100 may also be configured as a SoC (System on a Chip) having multiple functions among those described below.

[0017] The control unit 100 functions as an image processing unit 102, a character area extraction unit 104, a color information extraction unit 106, a frequency calculation unit 108, and a color conversion unit 110 by executing a program stored in the memory unit 160.

[0018] The image processing unit 102 performs various image-related processing. For example, the image processing unit 102 performs sharpening and grayscale conversion processing on images input via the image input unit 120 and the communication unit 190.

[0019] The character region extraction unit 104 extracts regions containing text (character regions) from an image. For example, the character region extraction unit 104 switches the method of extracting character regions depending on whether the image is command-based data such as PDL (Page Description Language) data or vector data, or raster data.

[0020] If the image is command-based data, the character area extraction unit 104 searches for a command to output characters from the data, analyzes the searched command to identify the area where characters are output, and designates the identified area as the character area.

[0021] On the other hand, if the image is raster data, the character region extraction unit 104 extracts character regions using, for example, a known OCR (Optical Character Recognition) technique. In this case, the character region extraction unit 104 determines whether each pixel in the image is a pixel that constitutes a character (character pixel), and extracts the region containing the character pixel (for example, a rectangular region circumscribing consecutively existing character pixels) as the character region. Since character pixels are generally edge pixels with a large difference in brightness (luminance difference) from adjacent pixels, the character region extraction unit 104 may also determine a pixel to be a character pixel if the difference in brightness of the pixels adjacent to the pixel of interest is greater than or equal to a predetermined value.

[0022] The character area extraction unit 104 may extract character areas as areas for each character, or it may extract them as areas containing multiple characters whose character color and the background color adjacent to the character (around the character) are the same.

[0023] The color information extraction unit 106 extracts color information for the text color and color information for the background color. Color information is information used to identify a color, for example, L * a * b * Color values ​​in the color space (L * a * b * It is the value.

[0024] If the image is command-based data, the color information extraction unit 106 analyzes the command that outputs the character to identify the character's color and extracts the character information for that character. The color information extraction unit 106 also identifies the background color by identifying the background color set in the command for that character or by identifying the color of the object placed below the character, and extracts the color information for that identified background color.

[0025] On the other hand, when the image is raster data, the color information extraction unit 106 can extract color information for character colors by, for example, calculating the average value of the pixel values ​​using the color values ​​of the pixels (character pixels) that constitute the characters contained within the character area for each character area. Note that the color information extraction unit 106 may also use pixels that become black when the average value of the pixel values ​​of all pixels contained in the character area is used as a threshold for simple binarization as character pixels. Furthermore, when the color information extraction unit 106 extracts color information for the background color, it can also use the average value of the pixel values ​​using the pixel values ​​of the pixels (background pixels) adjacent to the character pixels contained within the character area for each character area. Note that the color information extraction unit 106 may also use pixels adjacent to character pixels as background pixels, as well as pixels adjacent to background pixels that are approximately the same color as the background pixels. In this case, the color information extraction unit 106 may calculate the background color using the pixel values ​​of the pixels designated as background pixels. Furthermore, the color information extraction unit 106 may use the color indicated by the average value of the pixel values ​​of pixels other than character pixels included in the character area as the background color.

[0026] The frequency calculation unit 108 calculates a numerical value (frequency) indicating the level of visibility (ease of standing out) of each character in the color manuscript, based on the character color and background color. The frequency indicating visibility is also called the degree of visibility. Here, characters with high visibility in the color manuscript are characters that are easily noticed even if the user is not paying particular attention to the contents of the color manuscript. Generally, characters with high visibility are colored or have a background such as a yellow marker in the color manuscript. Therefore, the frequency calculation unit 108 calculates the frequency indicating the visibility of the characters included in the color manuscript based on information such as what the character color and background color are, and information on the difference (color difference) between the character color and the background color. In this embodiment, the frequency is described as a numerical value indicating the level of visibility, but the frequency may also be a value indicating the level of readability (ease of finding the characters) or a value indicating the level of distinguishability (ease of distinguishing from other characters). The processing of the frequency calculation unit 108 will be described later.

[0027] The color conversion unit 110 converts the colors used in the image. The processing of the color conversion unit 110 will be described later.

[0028] The image input unit 120 inputs images to the multifunction printer 10. The image input unit 120 is composed of, for example, a scanner device that reads a document placed on the document glass. The scanner device is a device that converts an image into an electrical signal using an image sensor such as a CCD (Charge Coupled Device) or CIS (Contact Image Sensor), and then quantizes and encodes the electrical signal. The image input unit 120 is also composed of an interface (terminal) for reading images stored in a USB (Universal Serial Bus) memory, and images may be input by reading from the USB memory. Alternatively, the image input unit 120 may also input images by receiving them from other devices via the communication unit 190.

[0029] The image forming unit 130 forms (prints) an image on a recording medium such as recording paper. The image forming unit 130 is composed of a printing device such as a laser printer using an electrophotographic method. For example, the image forming unit 130 feeds recording paper from a paper feed tray 132 provided in the multifunction printer 10, forms an image on the surface of the recording paper, and ejects the recording paper from an output tray 134 provided in the multifunction printer 10.

[0030] The display unit 140 displays various information. The display unit 140 is composed of a display device such as an LCD (Liquid Crystal Display), an OLED (Electro-Luminescence) display, or a microLED (Light Emitting Diode) display.

[0031] The operation unit 150 receives operation instructions from the user of the multifunction printer 10. The operation unit 150 is composed of input devices such as key switches (hard keys) and touch sensors. The method for detecting input by contact (touch) in the touch sensor can be any common detection method, such as resistive, infrared, electromagnetic induction, or capacitive touch. The multifunction printer 10 may also be equipped with a touch panel in which the display unit 140 and the operation unit 150 are integrally formed.

[0032] The storage unit 160 stores various programs and data necessary for the operation of the multifunction printer 10. The storage unit 160 is composed of storage devices such as a semiconductor memory SSD (Solid State Drive) or an HDD (Hard Disk Drive).

[0033] The memory unit 160 reserves a character area information storage area 162 and a color value information storage area 164 as storage areas, and stores the judgment threshold 166.

[0034] The character area information storage area 162 stores information regarding the character area (character area information). As shown in FIG. 3, the character area information includes, for example, an ID (e.g., "1") for distinguishing the character area information, an upper left coordinate (e.g., "(100, 100)") indicating the upper left coordinate of the character area, a lower right coordinate (e.g., "(200, 124)") indicating the lower right coordinate of the character area, the character color (e.g., "L * =53, a * =80, b * =67") of the characters included in the character area, and the background color (e.g., "L * =99, a * =-10, b * =32") of the characters included in the character area, and the color difference (e.g., "107") between the character color and the background color.

[0035] The color value information storage area 164 stores information in which a color name and a color value corresponding to the color name are associated. As shown in FIG. 4, the color value information includes, for example, a color name (e.g., "black"), the minimum value of the L * value (e.g., "0"), the maximum value of the L * value (e.g., "30"), the minimum value of the a * value (e.g., "-5"), the maximum value of the a * value (e.g., "5"), the minimum value of the b * value (e.g., "-5"), the maximum value of the b * value (e.g., "5"). Note that the L * value, the a * value, and the b * values are different when converted to L * a * b * values by an RGB color space (e.g., sRGB or AdobeRGB). In the present embodiment, the range of the L * value is 0 or more and 100 or less, the range of the a * value is -128 or more and 127 or less, and the range of the b * value is -128 or more and 127 or less.

[0036] The judgment threshold 166 is a threshold value for frequency. For example, the judgment threshold 166 might be a value such as "120". The judgment threshold 166 may be pre-set or it may be configurable by the user.

[0037] The communication unit 190 communicates with other devices and equipment such as terminal devices 20 via a network such as a LAN (Local Area Network) or WAN (Wide Area Network). The communication unit 190 is composed of communication devices or communication modules such as a NIC (Network Interface Card) used in wired / wireless LANs. The communication unit 190 may also have an interface (network I / F) that can connect to a network. Furthermore, the communication unit 190 may be connected to a communication network such as a public telephone network, LAN, or the Internet, and may be capable of transmitting data to the outside via the communication network using communication methods such as facsimile or email.

[0038] [1.2 Summary of this Disclosure] Referring to Figure 5, the color conversion flow in the multifunction printer 10 will be explained. P100 in Figure 5 shows the image input to the multifunction printer 10. The image input to the multifunction printer 10 is also called the original image. The original image's color space can be either RGB or CMYK. The multifunction printer 10 performs a color conversion to convert the original image's color image to the CMYK color space (A1 in Figure 5), and as shown in P102 in Figure 5, the original image becomes CMYK color space data. This CMYK color space data represents the reproduced colors when printing the input color original. The multifunction printer 10 forms an image based on the CMYK color space data (A2 in Figure 5). As a result, normal printing is performed, as shown in P104 in Figure 5.

[0039] In the data shown on page 102, the color of each pixel in the image is represented by the color value in the intrinsic color space of the multifunction printer 10. Therefore, the data shown on page 102 represents the image using the output device's intrinsic color (output device color).

[0040] On the other hand, by converting the color space of the data shown on P102 using the input table of the output profile (e.g., ICC profile), the CMYK color space can be converted to the XYZ color space or L * a * b * It can be converted to a color space.

[0041] The XYZ color space is a color system that uses the tristimulus values ​​X, Y, and Z. Color values ​​expressed in the XYZ color space are device-independent. Therefore, the XYZ color space is an absolute color system and is often used as an intermediate color space between input and output devices during various color conversions.

[0042] Also, L * a * b * A color space is a color system that has a perceptually nearly uniform rate (uniform color space) and is often used to represent color difference (the difference between two colors).

[0043] The RGB color space is generally used for documents created on computers and other devices. However, even if the color values ​​(RGB values) in the RGB color space are the same, they will appear differently on different devices; therefore, RGB is a device-dependent color space.

[0044] When the multifunction printer 10 converts RGB values ​​in sRGB, a type of RGB color space standard, to color values ​​(XYZ values) in the XYZ color space, it performs the conversion using the following method.

[0045] (1) The multifunction printer 10 converts sRGB back to linear RGB. Since the RGB values ​​of sRGB are corrected to appear as natural brightness on the display (=screen RGB), the multifunction printer 10 converts the RGB color values ​​back to linear RGB color values. Specifically, it calculates R' from the R value (the value range is between 0 and 255) using the following formula. When R / 255 ≤ 0.040450 R' = R / 255 / 12.92 When R / 255 > 0.040450 R'=[(R / 255+0.055) / 1.055] 2.4 Similarly, G' and B' are determined from the G and B values.

[0046] (2) The multifunction printer 10 calculates the XYZ values. The multifunction printer 10 calculates the values ​​of X, Y, and Z using the following formula. X=0.4124×R'+0.3576×G'+0.1805×B' Y=0.2126×R'+0.7152×G'+0.0722×B' Z=0.0193×R'+0.1192×G'+0.9505×B'

[0047] Furthermore, the multifunction printer 10 sets the XYZ values ​​to L * a * b * Color values ​​in the color space (L * a * b * To convert to a value, use the following formula. The color temperature is assumed to be 6500K.

[0048] (3) The multifunction printer 10 calculates the values ​​of fX, fY, and fZ. Assuming Xn=0.9504, Yn=1, and Zn=1.0889, fX, fY, and fZ are calculated using the following formula. X / Xn>(6 / 29) 3 at that time fX = (X / Xn) 1 / 3 X / Xn ≤ (6 / 29) 3 at that time fX = (1 / 3) × (29 / 6) 2 ×(X / Xn)+4 / 29 = 7.787 × (X / Xn) + 0.1379 Y / Yn>(6 / 29) 3 at that time fY=(Y / Yn) 1 / 3 Y / Yn ≤ (6 / 29) 3 at that time fY = (1 / 3) × (29 / 6)2 ×(Y / Yn)+4 / 29 = 7.787 × (Y / Yn) + 0.1379 Z / Zn>(6 / 29) 3 at that time fZ=(Z / Zn) 1 / 3 Z / Zn ≤ (6 / 29) 3 at that time fZ = (1 / 3) × (29 / 6) 2 ×(Z / Zn)+4 / 29 = 7.787 × (Z / Zn) + 0.1379

[0049] (4) Multifunction printer 10 is L * a * b value * To seek The multifunction printer 10 is calculated by the following formula: L * value, a * value, b * Find the value. L * = 116 × fY - 16 a * = 500 × (fX - fY) b * = 200 × (fY - fZ)

[0050] Note that the method described above involves L * a * b * We have shown how to convert to values, but for CMYK values ​​as well, by using the input table of the output profile (the so-called A2B table), L * a * b * It can be converted to an L value. In this embodiment, as shown on P106 in Figure 5, the multifunction printer 10 converts RGB values ​​and CMYK values ​​to L * a * b * Convert to a value (A3 in Figure 5), L * a * b * The value is used to calculate the frequency. This allows the multifunction printer 10 to calculate the frequency based on the reproduced colors when printing a color original.

[0051] [1.3 Processing Flow] The processing flow performed by the multifunction printer 10 will be explained with reference to Figures 6 and 7. The processing shown in Figures 6 and 7 is performed when the control unit 100 reads a program stored in the storage unit 160. The processing shown in Figures 6 and 7 is performed when the user performs an operation to output a monochrome image using the print function or copy function.

[0052] [1.3.1 Main Processing] Referring to Figure 6, the main processing performed by the multifunction printer 10 will be explained. First, the control unit 100 acquires an image of the document via the image input unit 120 (step S100). At this time, for example, the image input unit 120 reads the document placed on the document glass and inputs the image data of the document to the multifunction printer 10.

[0053] The control unit 100 determines whether the image acquired in step S100 is a color original image (a color image) (step S102). For example, the control unit 100 can use a technique generally called ACS (Auto Color Selection). In this case, the control unit 100 determines that the image acquired in step S100 is a color original image (a color image) if the image contains a predetermined amount of chromatic pixels or regions.

[0054] The control unit 100 (character area extraction unit 104) extracts character areas from the image if the image is a color original (color image) (step S102; Yes → step S104). At this time, the character area extraction unit 104 generates an ID for each extracted character area and stores the character area information, which associates the ID with the top-left and bottom-right coordinates of the character area, in the character area information storage area 162.

[0055] Next, the control unit 100 (color information extraction unit 106) selects one character region from the image based on the character region information (step S106). For example, the color information extraction unit 106 selects an unselected character region from the character region information stored in step S104.

[0056] Next, the control unit 100 (color information extraction unit 106) extracts the color information of the character color of the character contained in the character area and the color information of the background color of the character from the character area indicated by the character area information selected in step S106 (step S108). For example, the color information extraction unit extracts the L of the character color based on the processing flow shown in Figure 5. * a * b * Value and background color L * a * b * The values ​​are extracted. The color information extraction unit 106 may store the color information in the storage unit 160 in association with the character area information selected in step S106.

[0057] Next, the control unit 100 (frequency calculation unit 108) calculates the color difference between the character color and the background color based on the color information of the character color and the background color (step S110). For example, the method for calculating the color difference can use the distance between two colors in the CIE-LAB color space (CIE76, ΔE76). In CIE-LAB1976, the L of a certain color * a * b * Let the values ​​be {L1, a1, b1}, and let the other color L * a * b * When the values ​​are {L2, a2, b2}, the color difference ΔE, which is the difference in color between the two colors, is calculated using the following formula. (Math 1) TIFF0007884396000001.tif15133

[0058] Furthermore, methods other than CIE76 may be used to calculate the color difference. For example, ΔE00 (CIEDE2000), an improved version of CIE-LAB1976, or CIE94 (ΔE94) may be used as the color difference calculation method.

[0059] Next, the control unit 100 (frequency calculation unit 108) calculates the frequency based on the color difference between the text color and the background color (step S112). For example, the frequency calculation unit 108 calculates the frequency by using the color difference value calculated in step S110 as the frequency itself.

[0060] Next, the control unit 100 determines whether the frequency is equal to or greater than the threshold (a value stored as the judgment threshold 166) (step S114). If the frequency is equal to or greater than the value stored as the judgment threshold 166, the control unit 100 performs achromatic (gray) correction processing (step S114; Yes → step S116).

[0061] Achromatic correction is a process that corrects the color of characters in an image to achromatic (gray) by converting (correcting) the pixels of characters in the image to achromatic pixels with the corresponding gray value. The gray value is a value (percentage) that indicates the density of the color, for example, from 0 to 100. The gray value may also be a value that indicates the amount of black output, and the unit of the gray value may be %. In this case, a gray value of 0 (%) indicates that no black will be output at all (white pixels will be output), and a gray value of 100 (%) indicates that black will be output (black pixels will be output). If the gray value is any value from 0 to 100, it indicates that the gray of the density indicated by the gray value will be output. By outputting a color based on the gray value, a color image is output as a monochrome (grayscale) image. Achromatic correction will be explained later.

[0062] On the other hand, if the frequency is not greater than or equal to the value stored as the determination threshold 166, the control unit 100 determines whether or not all characters have been judged (step S114; No → step S118).

[0063] The control unit 100 (image processing unit 102) performs monochrome conversion of the image if it has determined that all characters are present (step S118; Yes → step S120). For example, it converts a color image to a monochrome image by performing grayscale processing, posterization processing, or binarization processing using error diffusion. If the image has been corrected by achromatic correction processing, the image processing unit 102 performs monochrome conversion on the corrected image.

[0064] Furthermore, the control unit 100 outputs the monochrome image in step S120 (step S122). For example, the control unit 100 may output the monochrome image by forming it on recording paper via the image forming unit 130. Alternatively, the control unit 100 may output the monochrome image by displaying it on the display unit 140, or by transmitting or storing it in another device via the communication unit 190.

[0065] If the control unit 100 has not yet determined all characters, it returns to step S106 (step S118; No → step S106). In other words, the control unit 100 executes the processes from step S106 to step S118 on the unselected character regions. As a result, the frequency and threshold are compared in the character regions included in the image, and if even one character region has a frequency greater than or equal to the threshold, the achromatic correction process is executed.

[0066] Furthermore, if the image acquired in step S100 is not a color original image (color image), the control unit 100 omits the processing from steps S104 to S118 and performs monochrome conversion of the image (step S102; No → step S120).

[0067] [1.3.2 Achromatic Correction Processing] Referring to Figure 7, the flow of the achromatic correction process will be explained. First, the control unit 100 (color conversion unit 110) extracts black characters from the image (step S150). Black characters are characters that are drawn in black or a color close to black when a color original is output in color. For example, the color conversion unit 110 identifies character areas in the image by reading character area information stored in the character area information storage area 162. Furthermore, the color conversion unit 110 extracts characters from the character pixels included in the character area whose color values ​​fall within the range of "black" defined in the color value information.

[0068] Next, the control unit 100 (color conversion unit 110) converts the black text to gray text (step S152). Gray text is achromatic text that is lighter than black (gray value K=100%). Gray text is, for example, L * The value is set to the gray value corresponding to the character being highlighted, a * Value and b * This text uses a color represented by a color value that is set to 0 (a color value corresponding to the gray value).

[0069] For example, if the image is command-based data, the color conversion unit 110 extracts black text by extracting commands corresponding to text areas. Furthermore, the color conversion unit 110 converts the black text to gray text by including a setting to set the text color to gray for the extracted commands. On the other hand, if the image is raster data, the color conversion unit 110 extracts black text by extracting text pixels contained in text areas. Furthermore, the color conversion unit 110 converts the black text to gray text by setting the color value of the extracted text pixels to the color value corresponding to the gray value.

[0070] Next, the control unit 100 (color conversion unit 110) extracts colored characters from the image (step S154) and converts the colored characters to black characters (step S156). Colored characters are characters that are drawn in chromatic colors when a color original is output in color. The process in step S154 is the same as the process in step S150, but the difference is that the color conversion unit 110 extracts colored characters instead of black characters. Note that the colored characters may be characters of a color other than black, or color value information such as red or blue may be stored in the color value information storage area 164 in advance, so that the character color is any color other than black. Also, the process in step S156 is the same as the process in step S152, but the difference is that the color conversion unit 110 converts the colored characters to black characters by setting the gray value K of the colored characters to 100%.

[0071] Furthermore, even if the explanation is not as described above, the order of the steps may be changed or some steps omitted, as long as it is not inconsistent. For example, the control unit 100 may calculate the frequency for all character areas and then determine whether or not there are any character areas whose frequency is equal to or greater than a threshold.

[0072] [1.4 Example of Operation] Next, we will explain the difference in operation between cases where this embodiment is not applied and cases where it is applied. Figure 8 shows the case where a color document is output in monochrome when this embodiment is not applied. Figure 9 is a table showing the color difference between the text color and the background color. Figure 10 shows an example of output when a color document is output in monochrome when this embodiment is applied.

[0073] Figures 8(a) and 8(b) show the gray values ​​for each color when a color original is converted to monochrome and output using the NTSC weighted average method, resulting in gray (intermediate black) output. The NTSC weighted average method is a method of obtaining the gray value corresponding to a color by multiplying the R, G, and B values, respectively, by different coefficients when the color value is expressed in RGB. The specific conversion formula is as follows. Gray value K = 100 - (0.299 × R + 0.587 × G + 0.114 × B) However, R, G, and B in the above formula are values ​​that express the magnitude of the R value, G value, and B value as percentages, respectively.

[0074] For example, the gray values ​​K for each of the colors black, red, yellow, and white are as follows: Black (RGB=0%,0%,0%) → K=100% • Red (RGB=100%,0%,0%) → K=70.1% ·Yellow (RGB=100%,100%,0%) → K=11.7% ·White (RGB=100%,100%,100%) → K=0%

[0075] Figure 8(a) shows the change in gray values ​​when saturation and brightness are set to 100% and the hue is changed to red, yellow, green, light blue, blue, purple, and red. C100, C102, and C104 in Figure 8(a) correspond to red, yellow, and blue, respectively. Comparing C100 and C102, yellow is converted to a brighter color (lower density) than red when converted to monochrome. On the other hand, comparing C100 and C104, blue is converted to a darker color (higher density) than blue when converted to monochrome. Thus, chromatic colors have different gray values ​​depending on the color.

[0076] On the other hand, for achromatic colors, the density remains unchanged even after conversion to monochrome. For example, black before monochrome conversion remains black (gray value K=100%) after conversion. As a result, if a color document primarily uses black text, but some important information is highlighted in red, the black text will be output as solid black (gray value K=100%) and the red text as gray (gray value K=70%) after monochrome conversion. Consequently, text that was highlighted in red as important information in the color document will become lighter and less noticeable in the monochrome output.

[0077] Furthermore, to further emphasize colored text, some of the most important items may be displayed in red text on a yellow background. In this case, while black text on a white background is output as solid black (gray value K=100%), red text on a yellow background is output as light gray (gray value K=11.7%) or gray (gray value K=70%). As a result, the contrast of the text in red text on a yellow background is reduced due to the monochrome effect.

[0078] Thus, in typical image processing, black text is output as solid black, and colored text is output as gray (a medium shade of black). Therefore, in cases where text is made red for emphasis, or where a yellow marker is added to the red text for further emphasis, the colored text will appear faint when the image is converted to monochrome.

[0079] Figure 8(c) shows an example output P110 when a color original is converted to monochrome using the NTSC weighted average method. In Figure 8(c), text area E110 is the area that contained red text on a yellow background. In Figure 8(c), text area E112 is the area that contained red text on a white background. In Figure 8(c), text area E114 is the area that contained black text on a white background.

[0080] Here, in the case of red text on a yellow background, the difference between the gray value of the text color and the gray value of the background color is 58.4 (=70.1-11.7). In the case of red text on a white background, the difference between the gray value of the text color and the gray value of the background color is 70.1 (=70.1-0). On the other hand, in the case of black text on a white background, the difference between the gray value of the text color and the gray value of the background color is 100 (=100-0). As a result, even if the text in text areas E110 and E112 is colored by the user for emphasis, the colored text will be output with a lighter shade and lower contrast. Consequently, text that was colored in the color original will have lower contrast than black text on a white background when output in monochrome, resulting in lower visibility and eye-catchingness.

[0081] Figure 9 is a table showing the color difference calculated by the color conversion unit 110 in this embodiment. Figure 9 shows the color difference ΔE for combinations of background color and text color, and the difference in gray values ​​calculated by the NTSC weighted average method.

[0082] Figure 9, D120, shows that the color difference ΔE between the text color and the background color in red text on a yellow background is 114. Figure 9, D122, shows that the color difference ΔE between the text color and the background color in black text on a white background is 100. Comparing D120 and D122, the color difference between red text on a yellow background is greater than that between black text on a white background. In this embodiment, since the color difference is used as a frequency, red text on a yellow background can be treated as more conspicuous than black text on a white background. Furthermore, in this embodiment, if the frequency calculated based on the color difference between the text color and the background color exceeds a threshold, the multifunction printer 10 outputs colored text in solid black and black text in light gray.

[0083] Figure 10 shows an example of output when the multifunction printer 10 of this embodiment converts a color document to monochrome. Text areas E130, E132, and E134 in Figure 10 correspond to text areas E110, E112, and E114 in Figure 8(c), respectively.

[0084] Here, if the frequency of the character area corresponding to a character that has been colored by the user for emphasis exceeds a threshold, achromatic correction processing is performed, and the colored character is output as solid black. As a result, as shown in character areas E130 and E132 of Figure 10, the colored character becomes solid black. On the other hand, black text on a white background is output as light gray, as shown in character area E134 of Figure 10. Comparing output example P130 shown in Figure 10 with output example P110 shown in Figure 8(c), in output example P130, the gray value of the colored character is higher than that of black text on a white background, and the contrast between the character color and the background color is greater. Therefore, compared to output example P110, in output example P130 of this embodiment, the colored character is output in a manner that is more eye-catching and has good visibility.

[0085] Thus, with the multifunction printer of this embodiment, when outputting a color document in monochrome, if the frequency of colored characters exceeds a threshold, the colored characters are output in solid black, and the black characters are output in gray. As a result, the multifunction printer of this embodiment can highlight the colored characters that were intended to be emphasized when the document was created by outputting them in solid black, while the other black characters are output in gray without emphasis. Consequently, when a user converts a color document to monochrome, they can obtain a monochrome output that matches their intended purpose.

[0086] [2. Second Embodiment] The second embodiment is an embodiment in which the color of the text is converted using a frequency in the achromatic correction process of the first embodiment. In this embodiment, Figure 7 of the first embodiment is replaced with Figure 11. The same reference numerals are used for the same processes, and their descriptions are omitted.

[0087] [2.1 Processing Flow] Figure 11 shows the flow of the achromatic correction process in this embodiment. In this embodiment, the control unit 100 (color conversion unit 110) calculates the frequency for all color characters (step S200). The process in step S200 is the same as the process in step S112 in Figure 6, but differs in that it calculates the frequency for all character regions extracted from the image acquired in step S100. The color conversion unit 110 may store the character regions and the frequencies in those character regions in the storage unit 160 in association with each other.

[0088] Next, the control unit 100 (color conversion unit 110) extracts characters whose frequency is equal to or greater than the threshold (a value stored as the judgment threshold 166) (step S202). The control unit 100 (color conversion unit 110) also extracts characters whose frequency is less than the threshold (step S204).

[0089] Next, the control unit 100 (color conversion unit 110) converts the characters extracted in step S202, whose frequency is greater than or equal to a threshold, into black characters (step S206). Also, the control unit 100 (color conversion unit 110) converts the characters extracted in step S204, whose frequency is less than a threshold, into gray characters (step S208). The color conversion unit 110 may convert the characters whose frequency is less than a threshold into gray characters of a specific gray value (for example, gray value K=70%), or into gray characters of a gray value corresponding to the frequency.

[0090] In this way, the color conversion unit 110 can convert characters whose frequency is above a threshold into black characters, and characters whose frequency is below the threshold into gray characters. At this time, by setting the judgment threshold 116 to a value greater than the color difference of black characters on a white background, colored characters such as red characters on a yellow background become black characters, and black characters on a white background become gray characters. As a result, when the multifunction printer 10 converts a color original to monochrome and outputs, characters that are colored for emphasis become black characters, and black characters that are not emphasized become gray characters. As a result, the multifunction printer 10 can output characters that were emphasized in the color original in the same emphasized manner in the monochrome image.

[0091] Next, a modified example of this embodiment will be described. In the modified example, the color conversion unit 110 converts colored text to gray text using a frequency in the achromatic correction process. The processing flow in this case is shown in Figure 12. Note that Figure 12 is a replacement for Figure 7, and the same reference numerals are used for the same processes, and their explanations are omitted.

[0092] The control unit 100 (color conversion unit 110) performs the process of extracting colored characters and then calculates the frequency for all colored characters (step S154 → step S250).

[0093] Next, the control unit 100 (color conversion unit 110) identifies the maximum value of the frequency calculated in step S200 (step S252). The control unit 100 (color conversion unit 110) also calculates the gray value of each colored character based on the frequency for that colored character and the maximum value of the frequency identified in step S252 (step S254). For example, the color conversion unit 110 takes the value obtained by dividing the frequency of the character area of ​​interest by the maximum value of the frequency as the gray value for the colored character in that character area.

[0094] Next, the control unit 100 (color conversion unit 110) converts the color of the colored text to a color based on a gray value (step S256). As a result, the color of the colored text is output based on a gray value corresponding to the color difference between the text color and the background color.

[0095] [2.2 Example of Operation] Figure 13 shows an example of the operation when the processing shown in Figure 12 is performed. Figure 13 is a table showing the relationship between the color difference ΔE between the text color and the background color, and the gray value calculated based on the maximum frequency. In Figure 13, the maximum value of the color difference ΔE is 235.15 (background color is yellow, text color is blue) (D200 in Figure 13).

[0096] Furthermore, for each combination of text color and background color, the gray value can be calculated by dividing the color difference ΔE based on the combination by the maximum value of the color difference ΔE, which is 235.15. Here, the gray value for text with a yellow background and black text is 58.3 (=137.2 / 235.15) (D202 in Figure 13), the gray value for text with a white background and blue text is 63.8 (=149.96 / 235.15) (D204 in Figure 13), and the gray value for text with a yellow background and blue text is 100 (D206 in Figure 13).

[0097] Note that the control unit 100 (color conversion unit 110) may also calculate a gray value based on the color difference for black characters, convert them into the color of the color value corresponding to the gray value, and then output them. In this case, in the example of FIG. 13, the gray value of the black characters on the white background is 42.5 (= 100 / 235.15) (D208 in FIG. 13). Thereby, the control unit 100 can output, for example, blue characters on a yellow background with the largest color difference between the characters and the background in solid black, blue characters on a white background and black characters on a yellow background with the next largest color difference in dark gray, and black characters on a white background in light gray.

[0098] Note that when the maximum value of the color difference ΔE is a large value, the gray value for combinations other than the combination of the background color and character color with the largest color difference ΔE may be relatively small. In this case, the gray value may be determined so that the minimum value of the gray value becomes a predetermined value (for example, 70). For example, let the maximum value of the color difference ΔE in the image to be processed be ΔE MAX and the minimum value of the color difference ΔE be ΔE MIN and let the color difference ΔE for which the gray value is to be calculated be ΔE T Then, the gray value may be calculated by the following formula. Gray value = 100 - { (ΔE MAX - ΔE T ) / (ΔE MAX - ΔE MIN )} × 30 When the gray value is calculated by the above formula, if ΔE T = ΔE MAX , the gray value is 100, and if ΔE T = ΔE MIN , the gray value is 70.

[0099] Furthermore, while the above explanation described the case where CIE76 (ΔE76) is used as the method for calculating the color difference ΔE, ΔE00 or ΔE94 may also be used as methods for calculating the color difference. Also, when using ΔE00, the color difference of color combinations that include chromatic colors (for example, red / white or red / yellow) may be smaller than the color difference when the color combination is black / white. In such cases, the control unit 100 (color conversion unit 110) may use ΔE00 to determine the gray value for each color combination for those where ΔE76 exceeds 100, which is the color difference ΔE for black / white.

[0100] Alternatively, the difference from the paper white (the background color of the original document) can be used by averaging the color of the text and the background color surrounding the text. This method calculates the gray value by focusing on the visual appeal of the string, including not only the text but also the background adjacent to the text. For example, L for each color white, yellow, red, and black. * a * b * Assume the value is as follows: White: L * =100, a * =0, b * =0 Yellow:L * =97.14, a * = -21.56, b * =94.48 Red: L * = 53.24, a * =80.09, b * =67.2 Black: L * =0, a * =0, b * =0 Furthermore, the average color values ​​of the text color and background color are as follows. Note that, below, the color names are listed as text color / background color. Average of black / white: L * =50, a * =0, b * =0 Average of red / white: L * =76.62, a * =40.05, b * =33.6 Average of red / yellow: L * =75.19, a * =29.27, b * =80.84 For these average values, the paper white (L of the paper white) * a * b * The value is L * =100, a * =0, b * The color difference ΔE (assuming = 0) is 50 for black / white, 57.3 for red / white, and 89.5 for red / yellow. By calculating the gray value based on this color difference ΔE, the gray values ​​increase in the order of black / white (=50) < red / white (=57.3) < red / yellow (=89.5). As a result, the color of red text on a white background and red text on a yellow background will be output as darker colors when converted to monochrome compared to black text on a white background.

[0101] Thus, the multifunction printer of this embodiment can convert character colors using frequency. Specifically, characters with a frequency above a threshold, or characters with higher frequencies, can be converted to colors with higher gray values. As a result, when the multifunction printer of this embodiment converts a color document to monochrome output, characters that should stand out can be printed in a darker (emphasized) color.

[0102] [3. Third Embodiment] The third embodiment differs from the first embodiment in that the frequency is calculated based on the difference in brightness between the text color and the background color. This embodiment replaces Figure 6 of the first embodiment with Figure 14. The same reference numerals are used for the same processes, and their descriptions are omitted.

[0103] [3.1 Processing Flow] Figure 14 shows the flow of the main processing in this embodiment. In this embodiment, the control unit 100 (frequency calculation unit 108) calculates the brightness difference between the text color and the background color following the processing in step S108 (step S108 → step S300). Furthermore, the control unit 100 (frequency calculation unit 108) calculates the frequency from the brightness difference calculated in step S300 (step S302).

[0104] For example, in step S300, the frequency calculation unit 108 calculates the brightness (L) of the character color. * a * b * L in value * The value of the background color (L) * a * b * L in value * The absolute value of the difference between the value of and is calculated as the brightness difference. Furthermore, in step S302, the frequency calculation unit 108 calculates the frequency by using the brightness difference between the background color and the text color as the frequency.

[0105] It is self-evident that the difference in brightness is greatest when the text color is black and the background color is white. Therefore, in the comparison process between the frequency and the threshold in step S114, the control unit 100 may process only colored text, or it may exclude (exception to) black text on a white background from the comparison.

[0106] [3.2 Example of Operation] Figure 15 is a diagram showing an example of operation in this embodiment. Figure 15(a) shows L for black, blue, yellow, and white. * a * b * This figure shows the values ​​and the color difference ΔE from black. For example, the color difference between blue and black is 137.7 (D300 in Figure 15(a)), and the color difference between yellow and black is 137.2 (D302 in Figure 15(a)).

[0107] Here, CIE-LAB is designed as a perceptually uniform color space, and the color difference ΔE, which represents the distance between two points in that color space, can generally approximate the difference in perceived colors. However, in practical use, there are cases where this does not match perception. For example, when comparing black text on a blue background with black text on a yellow background, the black text on the yellow background is clearly more noticeable, yet the color difference ΔE between the text color and the background color is almost the same value. Strictly speaking, the difference for black text on a blue background is slightly larger, which does not match how it looks in practical use.

[0108] On the other hand, Figure 15(b) shows the NTSC difference value (ΔNTSC), color difference (ΔE), and brightness difference (ΔL) for combinations of text color and background color. Here, according to the brightness difference ΔL, the brightness difference ΔL for black on a blue background is 32.3 (D310 in Figure 15(b)), while the brightness difference ΔL for black on a yellow background is 97.1 (D312 in Figure 15(b)). This can be said to represent the difference in perception well.

[0109] Therefore, by using the brightness difference in the calculation of the frequency, the control unit 100 can determine whether or not to perform achromatic correction processing based on a value that accurately represents the perceptual difference.

[0110] Furthermore, this embodiment may be combined with the second embodiment. In this case, the gray value for colored characters is determined based on the difference in brightness. As a result, the control unit 100 calculates a frequency based on the difference in brightness (ΔL) between the colored characters and the background color, and determines the gray value, which is the density when graying, based on the calculated frequency, so that characters that stand out in the color original are output darker (emphasized) to stand out when outputting in monochrome.

[0111] Thus, when the multifunction printer of this embodiment converts a color document to monochrome and outputs it, it calculates the degree using the difference in brightness, and in a manner that conforms to perceptual differences, it can output characters that should stand out in a darker (emphasized) manner.

[0112] [4. Fourth Embodiment] The fourth embodiment differs from the first embodiment in that the frequency is calculated based on the difference between the text color and background color of the colored text. In this embodiment, when the text color and background color of the colored text are a specific color combination, the frequency for that colored text is the frequency associated with the color combination. This embodiment replaces Figure 2 of the first embodiment with Figure 16, and Figure 6 of the first embodiment with Figure 19. The same reference numerals are used for the same functional parts and processes, and their descriptions are omitted.

[0113] [4.1 Functional Configuration] Figure 16 shows the functional configuration of the multifunction printer 12 in this embodiment. Compared to the multifunction printer 10 shown in Figure 2, the multifunction printer 12 differs in that the storage unit 160 has an additional color combination information storage area 168.

[0114] The color combination information storage area 168 stores information (color combination information) that associates color combinations with the frequency of those color combinations. As shown in Figure 17, the color combination information includes, for example, the first color, color 1 (e.g., "red"), the second color, color 2 (e.g., "white"), and the frequency of the combination of color 1 and color 2 (e.g., "130").

[0115] Furthermore, the frequency included in the color combination information will be set to a value greater than the value stored as the judgment threshold of 166. As a result, if the text color and background color are a specific color combination, achromatic correction processing will be performed.

[0116] In this embodiment, the color value information storage area 164 also contains color value information for colors included in color 1 or color 2 of the color combination information. For example, as shown in Figure 18, the color value information storage area 164 stores color value information for black, white, red, blue, yellow, green, and purple.

[0117] [4.2 Processing Flow] Figure 19 is a diagram showing the flow of the main processing in this embodiment. In this embodiment, following the processing in step S108, the control unit 100 (frequency calculation unit 108) determines whether the combination of background color and text color is a predetermined specific combination (step S108 → step S400). For example, the frequency calculation unit 108 searches the color combination information storage area 168 for color combination information where the text color is color 1 and the background color is color 2, or color combination information where the text color is color 2 and the background color is color 1. If the frequency calculation unit 108 can find the color combination information, it determines that the combination of background color and text color is a specific combination. On the other hand, if the frequency calculation unit 108 cannot find the color combination information, it determines that the combination of background color and text color is not a specific combination.

[0118] The control unit 100 (frequency calculation unit 108) obtains the frequency corresponding to the background color and text color combination if the combination of background color and text color is a specific combination predetermined (step S400; Yes → step S402). For example, the frequency calculation unit 108 only needs to obtain the frequency included in the color combination information searched in step S400.

[0119] Furthermore, if the combination of background color and text color is not one of the predetermined specific combinations, the control unit 100 (frequency calculation unit 108) executes the process in step S110 (step S400; No → step S110).

[0120] By performing the above-described process, the control unit 100 performs achromatic correction processing if the color original contains color text and background colors in specific combinations such as red-white, blue-white, yellow-black, green-white, or yellow-red-purple. As a result, the control unit 100 can convert text with specific color combinations to black text and black text to gray text.

[0121] This embodiment may be combined with the second embodiment. This allows for the calculation of a gray value based on the frequency corresponding to a specific color combination for colored text.

[0122] Here, given the diversity of human color vision, JIS safety colors are used in various places, including road signs, evacuation guidance signs, and product warning labels, with consideration for visibility. JIS safety colors are colors defined in JIS Z 9103 (Graphical symbols - Safety colors and safety signs - Range of chromaticity coordinates and measurement methods for safety colors).

[0123] JIS safety colors specify six additional safety colors besides the two contrasting colors of white and black: red, yellow-red, yellow, green, blue, and magenta. Furthermore, the latter six colors have corresponding contrasting colors or colors associated with graphic symbols, and the color combinations are designed to be easily identifiable.

[0124] Therefore, the multifunction printer of this embodiment sets a high frequency for combinations of colored text and background colors in a color document, such as red-white, blue-white, yellow-black, green-white, and yellow-red-violet. As a result, the multifunction printer of this embodiment can output color schemes that are easily distinguishable by people with diverse color vision, and make them stand out (emphasize) even when outputting in monochrome.

[0125] [5. Fifth Embodiment] The fifth embodiment differs from the first embodiment in that the frequency is calculated based on the difference between the colored text and the background color, and the difference between the background color adjacent to the text and the background color. This embodiment is a replacement of Figure 6 of the first embodiment with Figure 20. The same reference numerals are used for the same processes, and their descriptions are omitted.

[0126] [5.1 Processing Flow] Figure 20 is a diagram showing the flow of the main processing in this embodiment. In this embodiment, the control unit 100 (color information extraction unit 106) extracts background color information from the image if the image acquired in step S100 is a color original image (color image) (step S102; Yes → step S500). The background is the part of the original where no objects such as text, figures, or photographs are placed. The color information extraction unit 106 may fix the background color to white, or it may set it to a color selected by the user, or, if the original is to be copied in monochrome, it may read the color of the background part of the original to be copied and use the read color as the background color.

[0127] The control unit 100 (frequency calculation unit 108) calculates the color difference between the character color and the background color based on the color information of the character color and the background color (step S502). The control unit 100 (frequency calculation unit 108) also calculates the color difference between the background color and the background color based on the color information of the background color and the background color (step S504).

[0128] The control unit 100 (frequency calculation unit 108) calculates the frequency based on two color differences: the color difference between the character color and the background color, and the color difference between the background color and the background color (step S506). For example, the frequency calculation unit 108 calculates the frequency based on the two color differences by adding the color difference value calculated in step S502 and the color difference value calculated in step S504. Alternatively, the frequency calculation unit 108 may compare the color difference value calculated in step S502 and the color difference calculated in step S504 and calculate the maximum value as the frequency.

[0129] [5.2 Example of Operation] Referring to Figure 21, the cases in which this embodiment is not applied and the cases in which this embodiment is applied will be described. Figure 21(a) shows an example output P500 in which this embodiment is not applied. Example output P500 is the same as example output P110 shown in Figure 8(c). The colored characters in character area E500 and character area E502 in Figure 21(a) are both colored characters intended for emphasis, but they appear faint due to monochrome output.

[0130] Figure 21(b) shows an example output P510 of the multifunction printer 10 to which the second embodiment is applied. The colored text in text area E512 is colored for emphasis. The colored text in text area E512 can be made darker when outputting in monochrome. On the other hand, the colored text in text area E510 has a color marker of the same color as the text color added for further emphasis compared to the colored text in text area E512. However, because the difference between the text color and the background color is calculated to be small, it is not emphasized when outputting in monochrome.

[0131] Figure 21(c) shows an example output P520 of the multifunction printer 10 to which this embodiment is applied. In this embodiment, the frequency is calculated based on two color differences: the color difference between the character color and the background color, and the color difference between the background color and the background color. As a result, even if the colored character and the background color of that character are similar colors, the colored character is highlighted and output as shown in character area E520. Furthermore, as shown in character area E522, the color difference between the character color and the background color is taken into consideration when calculating the frequency, so the multifunction printer 10 to which this embodiment is applied can highlight and output colored characters even if they do not have a background color.

[0132] In this context, some text within a document may be highlighted with colored text, and further highlighted with a colored marker (colored background). It is generally believed that using both colored text and a colored marker provides a higher degree of emphasis than using only one of them.

[0133] However, due to design constraints or if the original plan was for two-color printing rather than multi-color printing, the text color and the color marker may be similar in color. In this case, if the frequency is calculated based on the difference between the text color and the background color, the calculated frequency will be low, which contradicts the intended emphasis in the color original. Therefore, the multifunction printer 10 of this embodiment calculates the frequency of the text color based on the difference between the text color and the background color, and the frequency of the background color based on the difference between the background color adjacent to the text and the background color, and then calculates the frequency of the string of characters including the background adjacent to the text based on the sum or maximum value of the calculated values. As a result, even when outputting a color original that was intended for two-color printing in monochrome, the multifunction printer 10 of this embodiment can appropriately output the text that should stand out in a darker (emphasized) color.

[0134] Whether a color document input to the multifunction printer is intended for two-color printing can be specified by the user, included as additional information in the image data of the input color document, or automatically determined by the multifunction printer. When the multifunction printer determines whether a color document intended for two-color printing has been input, for example, the multifunction printer can calculate a histogram of the chromatic pixels in the image of the color document and determine that a color document intended for two-color printing has been input if the frequency of use of a particular hue is above a predetermined threshold (for example, 90% or more).

[0135] As a result, in the case of a color original intended for two-color printing, the multifunction printer 10 of this embodiment can increase the gray value and output the text in the following order: black text on a white background, red text on a white background, and red text with a background marked with a red color marker (red text on a red background).

[0136] In the explanation above, the frequency is calculated based on the color difference between the text color and the background color, and the color difference between the background color (text background color) and the background color. However, the frequency may also be calculated based on the color difference between the text color and the background color (text background color), and the color difference between the background color (text background color) and the background color. By calculating the frequency based on the color difference between the text color and the background color (text background color), and the color difference between the background color (text background color) and the background color, the frequency can be increased when the text color is close to the background color, which is white (paper white).

[0137] For example, gray (50% black, L * =50, a * =0, b * When a background color is applied to the text (=0) with a black marker, the color difference between the text and the background (calculated using ΔE76) is 50, the color difference between the text background and the background is 100, and the color difference between the text and the text background is 50. In this case, the frequency calculated based on the color difference between the text color and the background color, and the color difference between the text background color and the background color is 150, and the frequency calculated based on the color difference between the text color and the text background color, and the color difference between the text background color and the background color is also 150.

[0138] On the other hand, pale yellow (20% yellow, L * =98.88, a * = -8.052, b * When the text (=24,45) is given a background color using a black marker, the color difference between the text and the background is 25.7, the color difference between the text background and the background is 100, and the color difference between the text and the text background is 102.2. In this case, the frequency calculated based on the color difference between the text color and the background color, and the color difference between the text background color and the background color is 125.7, and the frequency calculated based on the color difference between the text color and the text background color, and the color difference between the text background color and the background color is 202.2.

[0139] Thus, when the frequency is calculated based on the color difference between the text color and the background color, and the color difference between the background color (text background color) and the background color, light yellow text will have a lower frequency than gray text. On the other hand, when the frequency is calculated based on the color difference between the text color and the background color (text background color), and the color difference between the background color (text background color) and the background color, light yellow text will have a higher frequency than gray text. Therefore, if a color original contains text highlighted with colored text on a black background, the frequency may be calculated based on the color difference between the text color and the background color (text background color), and the color difference between the background color (text background color) and the background color. This will result in a higher frequency for light yellow text with a black marker background. Note that if the background color density is high, such as with a black marker, increasing the density of the text in the achromatic correction process will make the text difficult to see in the monochrome image. Therefore, in the achromatic correction process, for text with a high frequency and a black background, the gray value of the text may be set to 0 or a value close to 0. As a result, text highlighted with a black marker is output as white text, increasing the contrast between the background color and the text color, and improving visibility. The method for calculating the frequency may be determined by the control unit 100 (frequency calculation unit 108) based on the combination of text color and background color used in the color original, or it may be set by the user.

[0140] Thus, the multifunction printer of this embodiment can output color documents in monochrome, based on the character color, the background color of the characters, and the background color of the original document, by darkening (emphasizing) the characters that should stand out.

[0141] [6. Sixth Embodiment] The sixth embodiment is an embodiment in which, in addition to the processing in the first embodiment, a process is performed to convert the background color adjacent to the string to a different color. In this embodiment, Figure 7 of the first embodiment is replaced with one of Figures 22, 23, or 24. The same reference numerals are used for the same processes, and their descriptions are omitted.

[0142] In this embodiment, one of the following three methods will be used to convert the background color adjacent to the text to a different color. (Method 1) How to lighten the background color (Method 2) A method of leaving the background color uncolored and preserving the edges of the background color area. (Method 3) Invert the text color and background color or make the text white. Of the methods described above, the method used by the multifunction printer 10 may be predetermined or it may be configurable by the user. The following describes the processing when each method is used.

[0143] [6.1 Processing of Method 1] Figure 22 shows the flow of the achromatic correction process when Method 1 is used among the methods for converting the background color. In this case, the control unit 100 (color conversion unit 110) extracts the background of the colored characters from the character area of ​​the colored characters, following the process of extracting the colored characters (step S154 → step S600). For example, if the image is command-based data, the color conversion unit 110 may extract the command (text command) that draws text as the background if a background color is set for that command. Alternatively, if the text command does not have a background color set, the color conversion unit 110 may extract an object placed below the text and filled with a predetermined background color as the background. Furthermore, if the image is raster data, the color conversion unit 110 may extract the background pixels within the character area as the background.

[0144] Furthermore, the control unit 100 (color conversion unit 110) performs a process to lighten the background extracted in step S600 (step S602). For example, if the image is command-based data, the color conversion unit 110 changes the background color to a lighter color (a color with higher brightness) than the set color. The color conversion unit 110 may also place a white-filled object with a predetermined transparency below the text. This makes the color of the object placed below the text a whitish color, resulting in a lighter background for the colored text. If the image is raster data, the color conversion unit 110 only needs to change the color of the background pixels to a lighter color (for example, a color with higher brightness) than the color before conversion.

[0145] [6.2 Processing Method 2] Figure 23 shows the flow of the achromatic correction process when Method 2 is used among the methods for converting the background color. In this case, the control unit 100 (color conversion unit 110) extracts the background of the colored characters from the character area of ​​the colored characters, following the process of extracting the colored characters (step S154 → step S610). The process in step S610 is the same as the process in step S600 in Figure 22.

[0146] The control unit 100 (color conversion unit 110) performs a process to remove color from the background extracted in step S610 (step S612). For example, the color conversion unit 110 may delete or change the background color setting of a text command to white, delete or change the background color setting of an object placed below the text to white, or change the color of a background pixel to white.

[0147] Furthermore, the control unit 100 (color conversion unit 110) performs a process to add a border to the background boundary extracted in step S600 (a process to leave a border) (step S614). For example, if the image is command-based data, the color conversion unit 110 may add a setting to add a border to the boundary of the text command corresponding to the text area of ​​interest, or it may add a rectangular object with the top-left and bottom-right coordinates of the text area as diagonals. If the image is raster data, the color conversion unit 110 may change the pixels at the positions of the sides of the rectangle with the top-left and bottom-right coordinates of the text area as diagonals to black pixels.

[0148] [6.3 Processing of Method 3] Figure 24 shows the flow of the achromatic correction process when Method 3 is used among the methods for converting the background color. In this case, the control unit 100 (color conversion unit 110) extracts the background of the colored characters from the character area of ​​the colored characters, following the process of extracting the colored characters (step S154 → step S620). The process in step S620 is the same as the process in step S600 in Figure 22.

[0149] Next, the control unit 100 (color conversion unit 110) determines whether or not to invert the text color and background color (step S622). Whether or not to invert the text color and background color may be set by the user or may be set in advance.

[0150] When the control unit 100 (color conversion unit 110) reverses the text color and background color, it sets the text color of the extracted colored text in step S154 as the background color of the colored text, and sets the background color of the colored text as the text color of the colored text (step S622; Yes → step S624). For example, if the image is command-based data, the color conversion unit 110 sets the current background color as the text color of the text command and the current text color as the background color. If the image is raster data, the color conversion unit 110 may set the color of the character pixels in the character area containing the colored text as the current background color, and set the color of the background pixels in the character area as the text color of the colored text.

[0151] On the other hand, if the control unit 100 (color conversion unit 110) does not invert the character color and background color (step S622; No), it sets the background color of the character color to black (step S626) and the character color to white (step S628). For example, if the image is command-based data, the color conversion unit 110 sets the character color of the text command that draws colored characters to white and the background color of the text command to black. If the image is raster data, the color conversion unit 110 may set the color of the character pixels in the character area containing the colored characters to white and the color of the background pixels in the character area to black.

[0152] Furthermore, in the processes described in methods 1 to 3 above, the color conversion unit 110 may decide whether or not to convert the background color based on the relationship between the character color and the background color, rather than converting the background color for all colored characters. For example, the color conversion unit 110 may perform a process to convert the background color of a character area only for character areas where the color difference between the character color and the background color falls within a predetermined range (for example, a character area where the color difference ΔE is greater than 100 and less than 120). Furthermore, the color conversion unit 110 may perform a process to convert the background color of a character area only for character areas where the contrast value between the character color and the background color is less than a predetermined threshold.

[0153] [6.4 Example of Operation] Referring to Figure 25, this figure shows an example of operation when this embodiment is applied to the fifth embodiment. Figure 25(a) shows an example output P600 when an image containing a text area E600, in which the text color and background color are similar, is converted to monochrome. When the text color and background color are similar, the contrast between the text and the background is low, as shown in the text area E600.

[0154] Figure 25(b) shows an example output P602 when the background color adjacent to the colored text is lightened by the processing of Method 1. Compared to the text area E600 in Figure 25(a), the text area E602, where the text color and background color are similar in color, has higher contrast and improved readability of the text.

[0155] Figure 25(c) shows an example output P604 when the processing of Method 2 is performed, resulting in colored text (text in text area E604) with similar text and background colors being converted to black text on a white background. Figure 25(d) shows an example output P606 when the processing of Method 3 is performed, resulting in colored text (text in text area E606) with similar text and background colors being converted to white text. In both the text in text area E604 in Figure 25(c) and the text in text area E606 in Figure 25(d), the contrast is greatly increased, improving the legibility of the text.

[0156] Furthermore, this embodiment may also be applied to a third embodiment. Figure 26 shows an example of operation when this embodiment is applied to the third embodiment. Figure 26(a) shows the image P610 before monochrome conversion. Image P610 includes a region E610 with black text on a blue background, a region E612 with black text on a yellow background, and a region E614 with black text on a white background.

[0157] Figure 26(b) shows image P620, an example of the output when image P610 is converted to monochrome using the normal method. Here, as the density of the black text is reduced based on the frequency, the area where the area with black text on a blue background is converted to monochrome (area E620 in Figure 26(b)) has a smaller density difference between the background color and the text color, resulting in reduced visibility. In addition, as the density of the black text is reduced based on the frequency, the density of the background color and the text color may be reversed, and in such cases, visibility is also reduced.

[0158] Figure 26(c) shows image P630, which is an example of the output when image P610 is converted to monochrome by lightening the background color using Method 1 of this embodiment. In this case, for example, the background in region E610 of image P610 is lightened. As a result, region E610 of image P610 is converted to monochrome so that the gray value of the background color is lower, as shown in region E630 of Figure 26(c). This increases the density difference between the background color (blue) and the text color (black), resulting in higher contrast. This ensures visibility.

[0159] Thus, with the multifunction printer of this embodiment, it is possible to improve the visibility of text by changing the background color in addition to the text color.

[0160] [7. Seventh Embodiment] The seventh embodiment differs from the first embodiment in that the greater the difference between the color of a character and the color of the character with the highest frequency of occurrence, the more emphasis the character is placed on the output. This embodiment is a replacement of Figure 7 of the first embodiment with Figure 27. The same reference numerals are used for the same processes, and their descriptions are omitted.

[0161] [7.1 Processing Flow] Figure 27 shows the flow of the achromatic correction process in this embodiment. In this embodiment, the control unit 100 determines whether or not to convert black text to a specific color (for example, 70% gray) (step S700). Whether or not to convert black text to a specific color may be predetermined or may be set by the user.

[0162] When the control unit 100 (color conversion unit 110) performs a process to convert black text to a specific color, that is, when it converts black text to a specific color and converts colored text to a color based on the difference from the most frequently occurring text color, it aggregates the text colors of the colored text (step S700; Yes → step S702). For example, the color conversion unit 110 identifies the text color for each character based on the color value stored as color value information and aggregates the number of characters for each text color. At this time, the color conversion unit 110 may aggregate the number of text areas or the number of characters. Also, the color conversion unit 110 excludes black text from the aggregation.

[0163] The color conversion unit 110 may cluster the character colors included in the image into a predetermined number (for example, 20), and then aggregate the number of regions or characters included in each cluster. In this case, the color conversion unit 110 excludes black characters from the clustering.

[0164] Furthermore, if the control unit 100 (color conversion unit 110) does not perform the process of converting black characters to a specific color, that is, if it converts the color of all characters to a color based on the difference from the character color with the highest frequency of occurrence, it aggregates the character colors of all characters, including black characters (step S700; No → step S704).

[0165] The control unit 100 (color conversion unit 110) identifies the most frequently occurring character color from the aggregate of the processing in step S702 or step S704 (step S706). The most frequently occurring character color is the color of the character that is used most often in the image.

[0166] The control unit 100 (color conversion unit 110) calculates the color difference for each character color from the character color with the highest occurrence frequency (step S708).

[0167] The control unit 100 (color conversion unit 110) calculates a gray value for each character color (step S710). Here, the color conversion unit 110 assigns a larger gray value the greater the color difference between the character color of the character of interest and the character color of the character of interest. For example, the color conversion unit 110 calculates the color difference between the character color of the character of interest and the character color of the character of interest as ΔE now In this case, the gray value is calculated using the following formula. ΔE now If <30 Gray value K = 70 + ΔE now ΔE now If ≥30 Gray value K=100 In this case, if the color of the character of interest and the color of the character with the highest frequency are approximately the same, then ΔE now The value of becomes close to 0, and the value of the gray value K becomes close to 70. On the other hand, if the color of the character of interest and the color of the character with the highest frequency of occurrence are significantly different, ΔE now The value of becomes 30 or greater, and the value of the gray value K becomes 100. As a result, for example, when converting black text to a specific color, the greater the color difference between the color of the text in question and the color of the most frequently used text in the image, the larger the gray value for that text in question will be. Consequently, the color of the text with a large color difference from the color of the most frequently used text in the image can be converted to a text with a high density.

[0168] The control unit 100 (color conversion unit 110) determines whether or not to perform a process to convert black text to a specific color (step S712). If the control unit 100 (color conversion unit 110) decides to perform a process to convert black text to a specific color, it converts the text color of the black text to a color indicated by the corresponding gray value (step S712; Yes → step S714). The gray value corresponding to the text color of the black text is, for example, a predetermined value (gray value K = 60%, etc.). Furthermore, the control unit 100 (color conversion unit 110) converts the colored text to the gray value calculated in step S710 (step S716).

[0169] On the other hand, if the control unit 100 (color conversion unit 110) does not perform the process of converting black text to a specific color, it converts the text color of all text to the color indicated by the corresponding gray value (step S712; No → step S718). If black text is not converted to a specific color, the number of black text characters is tallied in step S704, and the gray value corresponding to the black text is calculated in step S710. Therefore, the color conversion unit 110 can convert the text color of all text included in the color document, including black text, to the text color of the gray value corresponding to the text color of that text.

[0170] In this way, the control unit 100 (color conversion unit 110) can set the gray value of characters included in the color document to a larger value the greater the color difference from the most frequently occurring character color, and output them as dark black characters. As a result, the control unit 100 (color conversion unit 110) can emphasize characters of colors that are used less frequently among the characters included in the color document.

[0171] [7.2 Example of Operation] Figure 28 is a diagram illustrating an example of operation in this embodiment, and is a table that associates the number of character areas for each character color, the color difference with the most frequently occurring character color (blue), and the gray value. Figure 28 shows that the aggregated results of colored characters in a certain color document show that there are 106 character areas for blue characters, 50 character areas for green characters, and 30 character areas for red characters. From this, it can be seen that the most frequently used character color (the character color with the highest frequency of occurrence) in the color document is blue.

[0172] Furthermore, for each text color, the color difference from blue, the most frequently occurring text color, is calculated. Figure 28 shows that the color difference between green and blue is 10, and the color difference between red and blue is 30. A gray value is also calculated based on the color difference. As shown in Figure 28, the larger the color difference from blue, the higher the gray value. As a result, the gray value for red, which has the largest color difference from blue, is 100, the gray value for green, which has the next largest color difference from blue, is 80, and the gray value for blue is 70. Consequently, blue text, which is the most frequently used in color originals, becomes light gray, and red text, which has the largest color difference from blue in color originals, becomes black text. In this way, red text in color originals where blue text is frequently used will be emphasized when converted to monochrome.

[0173] As described above, when the multifunction printer of this embodiment converts a color document to monochrome and outputs it, the greater the difference between the color of the text and the most frequently occurring text color, the more the text color can be emphasized.

[0174] [8. Eighth Implementation] The eighth embodiment differs from the embodiments described above in that the frequency is calculated by a method other than the method that uses only the color difference between the text color and the background color or the method that uses only the brightness difference between the text color and the background color.

[0175] For example, the frequency may be calculated by combining multiple scales. For example, by combining the first and third embodiments, the frequency may be calculated by combining the color difference and brightness difference between the text color and the background color. In this case, in the main process, the frequency calculation unit 108 executes step S108, and then executes the processes of step S110 in Figure 6 and step S300 in Figure 14 to calculate the color difference and brightness difference between the text color and the background color. Furthermore, after calculating the color difference and brightness difference between the text color and the background color, the frequency calculation unit 108 calculates the sum of the color difference and brightness difference as the frequency in the process of calculating the frequency (for example, step S112 in Figure 6). At this time, the frequency calculation unit 108 may change the weighting of the color difference and brightness difference and use the sum of the weighted values ​​as the frequency.

[0176] Furthermore, the frequency may be calculated by focusing on a scale such as hue. For example, suppose it is known in advance that in a color original, text is made to stand out by using red-based text or red-based markers. In this case, the frequency calculation unit 108 multiplies the color difference or brightness difference by 1 or more for text areas using red-based text or background colors to obtain the frequency. On the other hand, for text areas using text or background colors other than red, the color difference or brightness difference is used as the frequency. By doing so, the multifunction printer 10 can more easily perform achromatic correction processing on color originals using red-based colors, and can increase the gray value of red-based text.

[0177] Thus, according to this embodiment, the frequency can be calculated using various scales, and color originals can be converted to monochrome and output more appropriately.

[0178] [9. Variant] This disclosure is not limited to the embodiments described above, and various modifications are possible. That is, embodiments obtained by combining technical means that are appropriately modified without departing from the gist of this disclosure are also included in the technical scope of this disclosure.

[0179] Furthermore, although the embodiments described above describe the application of the image processing device of this disclosure to a multifunction printer and the printing of a color document onto paper, the image processing device of this disclosure may be applied to devices other than multifunction printers. For example, this disclosure can be applied to displaying color documents on electronic paper terminals, most of which are currently monochrome, and also to fax machines. That is, in an electronic paper terminal that can transfer and display documents on terminal devices such as PCs, an image after performing achromatic correction processing on the document may be displayed. This makes it possible to display colored text more prominently (emphasized) when a color document is displayed in monochrome. Also, when applied to a fax machine, it is possible to transmit and output an image in which the colored text in the color document has been corrected to stand out. That is, the embodiments described above may be implemented as a program or application, or they may be incorporated as a function in a device that displays color documents in monochrome, such as an electronic paper terminal. Furthermore, the embodiments described above may be applied to a server on a network such as the Internet and provided as a service. In this case, the service only needs to receive an image from a device (image processing device) that uses the service and send a monochrome version of the image to the device that sent the original image. Devices using the service (image processing devices, etc.) can obtain monochrome images by sending color original images to a service that performs monochrome conversion.

[0180] Furthermore, although the embodiments described above are explained separately for the sake of explanation, it goes without saying that they may be combined and implemented to the extent that is technically possible.

[0181] Furthermore, in the embodiments, the programs that run in each device are programs that control the CPU and the like (programs that make the computer function) in order to realize the functions of the embodiments described above. The information handled by these devices is temporarily stored in a temporary storage device (for example, RAM) during processing, and then stored in storage devices such as various ROMs (Read Only Memory) and HDDs, and read, modified, and written by the CPU as needed.

[0182] Here, the recording medium for storing the program may be any of the following: semiconductor media (e.g., ROM, non-volatile memory card, etc.), optical recording media / magneto-optical recording media (e.g., DVD (Digital Versatile Disc), MO (Magneto Optical Disc), MD (Mini Disc), CD (Compact Disc), BD (Blu-ray® Disc), etc.), magnetic recording media (e.g., magnetic tape, flexible disk, etc.). Furthermore, in addition to realizing the functions of the embodiments described above by executing the loaded program, the functions of this disclosure may also be realized by processing in cooperation with the operating system or other application programs based on the instructions of the program.

[0183] Furthermore, when distributing the program to the market, it can be stored on a portable storage medium and distributed, or transferred to a server computer connected via a network such as the Internet. In this case, the storage device of the server computer is, of course, also included in this disclosure.

[0184] Furthermore, each functional block or feature of the apparatus used in the embodiments described above may be implemented or executed by an electrical circuit, such as an integrated circuit or a combination of integrated circuits. An electrical circuit designed to perform the functions described herein may include a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or a combination thereof. The general-purpose processor may be a microprocessor, a conventional processor, controller, microcontroller, or state machine. The aforementioned electrical circuit may consist of digital circuits or analog circuits. Also, if advances in semiconductor technology lead to the emergence of integrated circuit technologies that replace current integrated circuits, one or more aspects of this disclosure may use new integrated circuits based on such technologies. [Explanation of Symbols]

[0185] 10, 12 Multifunction device 100 Control Unit 102 Image Processing Unit 104 Character area extraction part 106 Color information extraction section 108 Frequency Calculation Unit 110 Color conversion unit 120 Image Input Section 130 Image forming unit 140 Display section 150 Operation section 160 Storage section 162 Character area information storage area 164 Color value information storage area 166 Judgment threshold 168 Color combination information storage area 190 Communications Department

Claims

1. An extraction unit that extracts information about the color of characters contained in the text area of ​​a color image and the background color of those characters, A calculation unit that calculates a degree indicating the visibility of the characters based on the difference between the character color and the background color, If the aforementioned frequency is greater than or equal to a predetermined threshold, a conversion unit converts the colored characters contained in the character area to black characters, and converts the black characters contained in the character area to gray characters. Equipped with, The image processing apparatus is characterized in that the aforementioned frequency is a value associated with the color combination of the character color and the background color.

2. An extraction unit that extracts information on the color of characters and the background color of characters included in the character area of ​​a color image, A calculation unit that calculates a degree indicating the visibility of the characters based on the difference between the character color and the background color, If the aforementioned frequency is greater than or equal to a predetermined threshold, a conversion unit converts the colored characters contained in the character area to black characters, and converts the black characters contained in the character area to gray characters. Equipped with, The image processing apparatus is characterized in that the aforementioned frequency is a value calculated using the color difference between the text color and the background color, and the color difference between the background color and the background color of the image.

3. The image processing apparatus according to claim 1 or 2, characterized in that the conversion unit converts the background color of the colored characters to another color.

4. The image processing apparatus according to claim 3, characterized in that the conversion unit performs a conversion to make the background color of the colored characters uncolored and leave the edges of the background colored area, or a conversion to make the colored characters white.

5. The image processing apparatus according to any one of claims 1 to 3, characterized in that the conversion unit converts the color of the colored character of interest into a high-density black character as the color difference between the colored character of interest and the colored character most frequently used in the image increases.

6. An extraction unit that extracts information on the color of characters and the background color of characters included in the character area of ​​a color image, A calculation unit that calculates a degree indicating the visibility of the characters based on the difference between the character color and the background color, If the aforementioned frequency is greater than or equal to a predetermined threshold, a conversion unit converts the colored characters contained in the character area to black characters, and converts the black characters contained in the character area to gray characters. Equipped with, The conversion unit is characterized in that the greater the color difference between the color of the colored character of interest and the color of the most frequently used colored character in the image, the more the color of the colored character of interest is converted into a high-density black character.

7. The image processing apparatus according to claim 1 or 2, characterized in that the aforementioned frequency is calculated based on the reproduced color during color printing.

8. Extract information about the text color of characters within the text area of ​​a color image and the background color of those characters. Based on the difference between the aforementioned text color and the aforementioned background color, a degree indicating the visibility of the text is calculated. If the aforementioned frequency is greater than or equal to a predetermined threshold, the colored characters contained in the character area are converted to black characters, and the black characters contained in the character area are converted to gray characters. The image processing method is characterized in that the frequency is a value associated with a color combination of the text color and the background color, or a value calculated using the color difference between the text color and the background color and the color difference between the background color and the background color of the image.

9. On the computer, An extraction function that extracts information about the text color of characters contained within the text area of ​​a color image, and the background color of those characters. A calculation function that calculates a degree indicating the visibility of the text based on the difference between the text color and the background color, If the aforementioned frequency is above a predetermined threshold, a conversion function is provided that converts the colored characters contained in the character area to black characters and converts the black characters contained in the character area to gray characters. To make it happen, The program is characterized in that the aforementioned frequency is a value associated with the color combination of the text color and the background color, or a value calculated using the color difference between the text color and the background color and the color difference between the background color and the background color of the image.

Images