JP3815465B2 - Color image processing device - Google Patents

Description

  The present invention relates to a color image processing apparatus such as a copying machine, a facsimile machine, a multi-function machine having multiple functions such as a copying function and a facsimile function.

In general, a color space (for example, RGB) of an image obtained by scanning is converted into an intermediate color space (for example, CIELAB or CIELV) including a brightness component or an intermediate color space (for example, YCC or YIQ) including a luminance color difference component, and the intermediate color space Each component of the color is subjected to correction processing (color correction) for adjusting the user's preference as necessary, and then converted into an output color space (for example, CMYK) to form an image. An image processing apparatus is known. In this type of color image processing apparatus, in order to reduce wasteful consumption of toner (toner), color system data representing hue, brightness, and saturation is generated from RGB data, and at most two types of CMYK. A technique is disclosed in which approximate hue data that can be expressed using toner is generated, at most three types of density data of CMYK are generated, and an electrophotographic process is executed using the maximum of three types of density data ( For example, see Patent Document 1).
JP-A-9-163169

  In the technique described in Patent Document 1 described above, color system data including brightness, hue, and saturation is generated from RGB data, and approximate hue data that can be expressed using at least two types of toners of CMYK is generated. Since it is generated, there is a risk that the color reproducibility may be lowered, and at most three types of density data of CMYK are generated, and the electrophotographic process is executed using the maximum of three types of density data in order, so that the processing is complicated. There is a problem of becoming.

  The present invention has been made paying attention to the above problems, and an object thereof is to provide a color image processing apparatus capable of realizing toner saving with a simple configuration and minimizing a decrease in color reproducibility. It is said.

The color image processing apparatus according to claim 1 of the present invention converts the color space of the input image into an intermediate color space represented by a brightness component , a hue component and a saturation component, or an intermediate color space represented by a luminance component and a color difference component. It converted, after performing correction processing on each component of the intermediate color space, a color image processing apparatus for converting a color space of the output, when the mode to reduce the amount of recording material is designated The control means for executing the correction process so as to lower the saturation is provided.

  The control means of the color image processing apparatus of the present invention is preferably one that controls so as to lower the saturation without substantially changing the hue. The fact that the hue is not substantially changed means that a change in hue is not easily noticed when a person compares the images before and after the correction. Further, to control so as to decrease the saturation is to reduce the saturation relatively easily when a person compares the images before and after the correction. However, in this regard, the amount of reduction may be smaller than the degree of noticing the change in saturation depending on the implementation situation.

  The control means of the color image processing apparatus of the present invention divides the interval from the minimum value to the maximum value of the input value in the saturation input / output characteristics into at least a low saturation interval, a medium saturation interval, and a high saturation interval, In the low saturation section, the output value is suppressed to a constant value (zero) regardless of the change in the input value. In the middle saturation section, the output value has a predetermined relationship with the input value (straight line or a downwardly convex curve). ), And in the high saturation section, an upper limit value of the output value can be set to limit the output value so as not to exceed the upper limit value.

  In the present invention, the amount of recording material used can be reduced while minimizing the effect of appearance.

  Further, the control means of the color image processing apparatus of the present invention is a color correction means (second image processing section 5) that performs color correction (brightness, saturation, hue correction) according to the user's preference on the components of the intermediate color space. The control means can change the parameter set in the color correction means from the normal mode when the mode for reducing the usage amount of the recording material is designated.

  According to the present invention, a recording material can be saved without using a special block for reducing the amount of recording material used by simply using a color correction block performed according to the user's preference and changing its parameters.

  Further, the control means of the color image processing apparatus of the present invention provides a ground color correction means (second image processing) for performing ground color correction for removing the ground color (background color) of the input image and outputting it to the components of the intermediate color space. The control means can change the parameter set in the ground color correction means from the normal mode when the mode for reducing the usage amount of the recording material is designated.

  Further, the control means of the color image processing apparatus of the present invention may comprise means for controlling so as to change the amount of decreasing the saturation according to the lightness component. For example, when the lightness is high, the amount of decrease in saturation is reduced, and when the lightness is low, the amount of decrease in saturation is increased (compared to when the lightness is high). In this way, in general, when the lightness is high, it is easy for the human eye to recognize when the saturation is small, but when the lightness is low, the human being can be recognized even if the saturation is slightly small. It is known that it is difficult to recognize with the eyes, so even if the saturation is lowered, the amount can be reduced according to the lightness, and a recording-saving material can be realized without causing a decrease in saturation.

According to the present invention, when a mode for reducing the amount of recording material used is specified , correction processing is performed so as to lower the saturation, so that a special circuit can be used while minimizing a decrease in color reproducibility. Therefore, a recording material can be realized by a relatively simple process.

  Hereinafter, the present invention will be described in more detail with reference to embodiments.

  FIG. 1 is a block diagram showing a configuration of a color multifunction peripheral according to an embodiment of the present invention. The color multifunction machine according to this embodiment includes a printer (image recording unit) 8, an image reading unit 9, a main control unit (CPU) 10, a display unit 11, an operation unit 12, a ROM 13, a RAM 14, and an image memory. 15, CODEC 16, NCU 17, MODEM 18, and LAN I / F 19.

  The printer 8 is an electrophotographic color printer, and color-records a read image and image data transferred from a PC or the like through the LAN I / F 17 on a recording sheet. This printer 8 uses CMYK four-color recording agents (toners), and in addition to monochrome printing using only K (black) component recording agents, color printing using all CMYK four-color recording agents is also possible. Is possible.

  The image reading unit 9 optically scans a document and reads image data when copying. A color image can also be read. Details will be described later. A main control unit (CPU) 10 is connected to each unit through a bus 20 and executes reading processing, printing processing, and other various controls according to a program stored in the ROM 13. The display unit 11 displays icons, key buttons, message contents necessary for operation, and the like. As the display unit 11, an LCD (Liquid Crystal Display) is mainly used, but a CRT or other display may be used.

  The operation unit 12 includes a numeric keypad, a clear key, a stop key, and the like in addition to the mode switching key 12a and the start key 12b. The mode switching key 12a can switch between the normal mode and the toner saving mode. The toner saving mode is selected when it is desired to reduce and save the color toner (recording material) consumed compared to the normal mode. The ROM 13 stores a program for controlling the operation of the entire apparatus. The RAM 14 stores data necessary for control by the main control unit 10 and data that needs to be temporarily stored during the control operation. The image memory 15 stores the image data read by the image reading unit 9 in a compressed state. Further, the image memory 15 is a binary memory and stores binary image data (CMYK or K) in a compressed state.

  The CODEC 16 encodes (encodes) and decodes (decodes) binary data using the MH, MR, MMR method, or the like. The NCU 17 is controlled by the CPU 10 to control connection with a telephone line network (PSTN) 21 that is a communication line. Further, the NCU 17 has a function of sending a dial pulse corresponding to a telephone number (including a FAX number) of a communication partner and a function of detecting an incoming call. MODEM 18 is an ITU (International Telecommunication Union) -T recommendation T.30. 30, T.M. 4 according to the facsimile transmission control procedure (facsimile communication procedure) according to FIG. 17, V. 27ter, V.I. The transmission data is modulated and the received data is demodulated in accordance with 29. MODEM 18 is a V. 8, V. 34 using V. It is also applicable to 34 FAX. Specifically, the MODEM 18 has a function of modulating transmission data, which is a digital signal, into an analog audio signal so as to be transmitted to the telephone line network 21 via the NCU 17. The MODEM 18 has a function of demodulating an analog voice signal received from the telephone line network 21 via the NCU 17 into a digital signal. The LAN I / F 19 is used to exchange data with an external device via a LAN (local area network). From the external PC (personal computer) via the LAN I / F 19, a network print and a network scanner are provided. Receive requests such as.

As shown in FIG. 2, the image reading unit (color image processing circuit) 9 includes a CCD 1 as a color image data input unit for inputting color image data, and an A / D conversion unit 2 including an analog front end (AFE) circuit. , A first image processing unit 3, a first color space conversion unit 4, a second image processing unit 5, a second color space conversion unit 6, and a binarization unit 7. Each unit of the image reading unit 9 is controlled by the CPU 10. The processed image data is printed by the printer 8. The normal mode / toner saving mode can be set by inputting an instruction from the operation unit 12.

  The CCD 1 is a line sensor that reads an image of a document separately into R, G, and B, and sequentially reads scanning line images at a predetermined interval. The A / D converter 2 analog-amplifies the output of the CCD 1 with an AFE circuit. This analog value is converted into digital data and output in multi-value. The first image processing unit 3 performs processing such as shading correction and gamma correction on RGB multi-value data.

  The first color space conversion unit 4 is an image of L, a, b (intermediate color space) that can represent RGB image data (multi-valued data) output from the first image processing unit 3 by separating lightness components. Convert to data. As will be described later with reference to FIG. 3, the Lab color space can represent saturation and hue with two parameters a (RG axis) and b (YB axis). The second image processing unit 5 receives image data (multi-valued data) in the Lab color space, and performs color correction such as ground color correction, brightness, saturation, and hue. In the color correction, the lightness, saturation, and hue that are input are adjusted with the user's preference and output. The color correction can be performed by conversion using a table or by calculation using a predetermined function.

  The second color space conversion unit 6 receives image data (multi-valued data) in the Lab color space, and converts the Lab image data into CMYK (output color space) image data (multi-valued data) by interpolation using the 3D-LUT 6a. Data). The binarization unit 7 binarizes the input CMYK multilevel data and outputs it.

In the apparatus according to this embodiment, the operation unit 12 includes a mode switching key 12a that can selectively set a normal mode (a mode that is not a toner saving mode) and a toner saving mode, and the toner saving mode is set. If so, the second image processing unit 5 has a function of correcting the brightness component (L) to be brighter than in the normal mode. In addition, in addition to correcting the brightness component brightly or in addition to correcting the brightness component brightly, in the toner saving mode, a function is provided to correct the saturation to be lower than in the normal mode. May be.

  Next, processing operations at the time of image formation in the color multifunction peripheral according to this embodiment will be described. When the start key 12b of the operation unit 12 is pressed, the RGB scan of the document is executed by the CCD 1. The RGB image data read by this processing is A / D converted by the A / D converter 2 and converted into multi-value digital data. Next, the multi-value data of the A / D conversion unit 2 is input to the first image processing unit 3. The first image processing unit 3 performs shading correction and gamma correction on the RGB image data, and the corrected RGB image data is input to the first color conversion unit 4.

In the first color space conversion unit 3, the RGB image data is converted into image data in the Lab color space, and the image data in the Lab color space is input to the second image processing unit 5. The second image processing unit 5 refers to the setting state by the mode switching key 12a in the operation unit 12 to determine whether or not the toner saving mode is set. In the normal mode instead of the toner saving mode, the second image processing unit 5 performs image processing such as ground color correction and color correction on the input Lab image data as necessary, and after correction. Are input to the second color space conversion unit 6. The ground color correction and the color correction are corrections for adjusting to a user's favorite color, and are set by a user operation input. On the other hand, when the toner saving mode is set, image processing such as ground color correction is performed on the Lab image data input in the second image processing unit 5 in order to reduce the amount of toner to be used. For example, in the toner saving mode, the lightness component L is corrected to be brighter by ground color correction or color correction. In the correction to make the brightness component L brighter, it is preferable to shift the value of the brightness component L to the brighter side for the entire image. In addition to correcting the lightness component L in the brightening direction, or instead of correcting the lightness component L to brighten, the a component and the b component may be corrected to correct the saturation. In this case, the hue value is not changed. Here, the amount of decreasing the saturation is a ratio according to the saturation value. Further, the amount of reduction in saturation may be changed based on the L component. For example, the saturation reduction ratio can be a ratio obtained by multiplying the ratio based on the L component.

In the Lab coordinate system, as shown in FIG. 3, when the a-axis value a ₁ and the b-axis value b ₁ are used, the saturation is saturation C = √ ( a ₁ ² + b ₁ ² ). In this case, θ = tan ⁻¹ b / a = H is the hue. Therefore, lowering the saturation C and not changing the hue θ can be realized by multiplying a and b by the same negative coefficient. When the relationship of the output with respect to the saturation input is shown, the characteristic shown in A of FIG. When toner is not saved, toner is used based on this characteristic A (input value = output value). In the case of toner save, for example, as shown in B1 and B2, the characteristic is downwardly convex. In the examples of B1 and B2, the amount of decrease is in accordance with the saturation value. From the characteristic A toward the characteristics B1 and B2, an amount of toner corresponding to the area protruding downward is reduced. A characteristic B1 in FIG. 4 shows a case where brightness and luminance are larger than those of the characteristic B2. That is, when the lightness and saturation are large, the amount of reduction in saturation is smaller than when the lightness and saturation are small.

  As another example of lowering the saturation for toner saving, as shown in FIG. 5, the saturation is 0 in the low input range from 0 to i1 (low saturation interval), and the input is from i2 to i3 in the high input range ( In the high saturation interval), the saturation is limited to the upper limit value, and between the input intermediate values i1 to i2 (intermediate saturation interval) may be a characteristic B2 connecting the i2 point of the characteristic A and the 0 point of i1 with a straight line. Further, instead of the linear portion between i1 and i2 of the characteristic B2, a characteristic B3 having a downward convex curve characteristic may be used. In FIG. 5, i3 is the maximum value of input, j2 is the maximum value of output, and j1 is the upper limit value of output. The output upper limit j1 can be adjusted by a user command. A characteristic A (input value = output value) is an input / output characteristic in a normal mode (a mode in which saturation correction is not performed).

  The second color conversion unit 6 converts the input Lab image data into image data in the CMYK color space by interpolation using the 3D-LUT 6a. The CMYK image data is input to the binarization unit 7. The binarization unit 7 binarizes the multi-value CMYK data and outputs it to the printer 8. The printer 8 executes print processing based on the input binarized data.

In the above embodiment, a case where ground color removal correction is performed will be described. When performing ground color removal correction, the peak value P of the immediately preceding line or lines is obtained. This peak value P is a maximum value or an average maximum value of a plurality of pixels. For the L component of Lab, conversion processing is performed according to the following equation.

Vout = Vin · 255 / (α · P + β)
In the toner saving mode and when ground color removal correction is performed, the parameter α is set to α <1 or the parameter β is set to a negative value. In this case, the denominator of the above equation becomes small and the corrected value Vout becomes large. As a result, the L component is corrected brightly as a whole.

  Note that α = 1 and β = 0 when performing ground color removal correction instead of the toner saving mode (normal mode). When the background color removal correction is not performed in the toner saving mode, P = fixed value (for example, 255) and α <1 or the parameter β is negative. When the toner-saving mode is not used and the ground color removal correction is not performed, P = fixed value (for example, 255), α = 1, and β = 0.

  In the above-described embodiment, the case where the color document image is read by the image reading unit 9 provided therein and the color image data in the RGB color space is input is described. However, the method of inputting the color image data is not limited to this. For example, color image data in an RGB color space is input from an external data processing device such as a PC via an external I / F such as a LAN I / F 19 and converted into color image data in an intermediate color space such as Lab or YCC. It can also be applied to cases. Further, the present invention can be applied to a case where a portable storage medium is mounted on the apparatus and data is read from the storage medium.

  In the above embodiment, the toner saving mode is set by the operation unit 12, but may be automatically set by detecting the remaining amount of toner.

  In the above-described embodiment, one of the normal mode and the toner saving mode is selected. The toner saving mode is selected from the first toner saving mode, the second toner saving mode, the third toner saving mode, and the third toner saving mode. The toner saving mode and a plurality of stages may be provided. In this case, in each toner saving mode, the brightness level of the brightness component is changed, or the degree of lowering the saturation is changed.

  In the above embodiment, the case where the lightness component of the Lab color space is raised and the saturation is lowered to save toner has been described. However, instead of the Lab color space, a YCC color space comprising a luminance component and a color difference component is described. May be used. When the YCC color space is used, the brightness can be changed by changing the value of the luminance component Y.

1 is a block diagram illustrating a configuration of a color multifunction peripheral according to an embodiment of the present invention. 2 is a block diagram illustrating a configuration of an image reading unit of the color multifunction peripheral according to the first embodiment. FIG. It is a figure explaining the saturation and hue in a Lab color space. FIG. 5 is a diagram for explaining how to decrease the saturation when toner is saved by reducing the saturation in the color multifunction peripheral according to the embodiment. FIG. 10 is a diagram for explaining another example of how to decrease the saturation when the toner is saved by decreasing the saturation.

Explanation of symbols

1 CCD
2 A / D converter 3 First image processing unit 4 First color space conversion unit 5 Second image processing unit 6 Second color space conversion unit 6a 3D-LUT
7 Binarizing unit 8 Printer 9 Image reading unit 10 CPU
11 Display Unit 12 Operation Unit 12a Mode Switch Key 12b Start Key 13 ROM
14 RAM
15 Image memory 16 CODEC
17 NCU
18 MODEM
19 LAN I / F
20 buses

Claims (6)

Converts the color space of the input image to an intermediate color space represented by a brightness component, a hue component, and a saturation component, or an intermediate color space represented by a luminance component and a color difference component, and corrects each component of the intermediate color space. A color image processing device that converts the output color space into an output color space and outputs the converted color space;
A color image processing apparatus comprising control means for executing correction processing so as to lower saturation when a mode for reducing the amount of recording material used is designated. It said control means, a color image processing apparatus according to claim 1, characterized in that the control to lower the chroma without substantially changing the hue. The control means divides the interval from the minimum value to the maximum value of the input value into at least a low saturation interval, a medium saturation interval, and a high saturation interval in the input / output characteristics of the saturation, and the input in the low saturation interval Regardless of the change in value, the output value is suppressed to a constant value, so that the output value becomes smaller with a predetermined relationship with the input value in the middle saturation interval, and the upper limit of the output value is increased in the high saturation interval. 3. The color image processing apparatus according to claim 1 , wherein the color image processing device is set and is limited so that the output value does not exceed the upper limit value. The control means includes color correction means for performing color correction according to the user's preference on the components of the intermediate color space, and when the mode for reducing the amount of recording material used is designated, the control means 4. The color image processing apparatus according to claim 1, wherein the parameter to be set is changed from that in the normal mode. The control means includes ground color correction means for applying a ground color correction to an intermediate color space component to be output after removing the ground color of the input image, and the control means designates a mode for reducing the amount of recording material used. 4. The color image processing apparatus according to claim 1, wherein the parameter set in the ground color correction means is changed from that in the normal mode. The said control means contains a means to control to change the amount which reduces the said saturation according to a lightness component , The claim 2, Claim 3, Claim 4, or Claim characterized by the above-mentioned. 5. A color image processing apparatus according to 5 .

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