JP2005094085A - Image processor and color conversion adjustment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor capable of properly carrying out color adjustment by evaluating granularity with a simple method in the presence of variations in a state of an output device or at an output to an unexpected recording medium and to provide a color conversion adjustment method for the image processor. <P>SOLUTION: An ordinary output processing of image data is shown in a flow (a). An evaluation image output processing is carried out in a flow (b) in addition. Adjustment of parameters is instructed automatically or by designation of a user. When the adjustment of the parameters is instructed, an evaluated image stored in an evaluation image storage means 6 is read in the flow (b). Since it is required to output the evaluation image by a plurality of UCR / UCA parameters, a flow of read, processing, and output is repeated for several times while a parameter adjustment means 7 varies the UCR / UCA parameters. The user selects an image with the best granularity and uses a user evaluation entry means 8 to enter the selected image. The adjustment of the parameters is shown in a flow (c). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus such as a color printer or a copying machine, and a color conversion adjustment method in the image processing apparatus.

  When a color image is printed by an electrophotographic or inkjet printer or copying machine, four color materials of cyan (C), magenta (M), yellow (Y), and black (K) are used. There are many cases. At this time, since an input image is a color image expressed in three colors of red (R), green (G), and blue (B), color conversion processing from an RGB image to a CMYK image is required. .

  In color conversion, the amount of K greatly affects the quality of the image. In particular, when K is added to the highlight portion, the graininess deteriorates and the image quality deteriorates. Therefore, appropriately adjusting the amount of K has a great influence on the image quality. As a method of adjusting K, there is a UCR / UCA method, which first converts an input RGB signal into a CMY signal and generates K based on the minimum value of CMY.

Assuming that the final output signal is C′M′Y′K ′, for example, K ′ is generated by the following equation (1), and CMY is adjusted accordingly. However, each signal is an 8-bit signal having a value of 0 to 255, and K ′ is 0 when the value is 0 or less in the equation (1).
K ′ = α × (min (C, M, Y) −γ) / (255−γ)
C ′ = C−β × K ′
M ′ = M−β × K ′
Y ′ = Y−β × K ′. . . . . . (1)

  The black amount can be adjusted by adjusting the parameters α, β, and γ in the equation (1). FIG. 7 is a graph showing the relationship between K ′ and min (C, M, Y) in Equation (1). As can be seen from FIG. 7, the parameter γ represents the black starting point, and this parameter particularly affects the graininess of the highlight portion. That is, if this value is increased, highlights can be reproduced only with CMY. However, since it is necessary to reproduce the shadow portion with an increased K amount, it is necessary to set the shadow portion at an appropriate position.

  In addition, in the ink jet recording apparatus, in addition to CMYK, ink having the same hue as C and M, such as light cyan (Lc) and light magenta (Lm), and a low density may be used. The main purpose is to improve the graininess by using Lc and Lm in the reproduction of C and M at the highlight. However, since the shadow portion needs to be reproduced with a dark CM, it is necessary to appropriately adjust the position where the dark ink starts to be added in order to improve the graininess.

  In image processing apparatuses such as color printers and copiers, these color conversion parameters are adjusted before shipment. In particular, in an inkjet recording apparatus, not only plain paper but rather several types of dedicated paper are often used as a recording medium, and a plurality of color conversion parameters are prepared corresponding to the type of paper. This is because the color development, graininess, and the like of the color material differ depending on the paper.

  However, the color conversion parameters are prepared only for several types of assumed recording media, and for other recording media, the color conversion parameters that have been optimally adjusted cannot be used, An image with poor graininess may be output.

In particular, in the electrophotographic system, the state of the machine may change little by little during use, so the tendency of graininess may also change. Therefore, even if the color conversion parameter is adjusted in the initial state, an image with poor graininess may be output at a certain point in time. As the prior art related to the present invention, there are the following patent documents.
JP 2001-47665 A Japanese Patent No. 27756040 JP 2000-78418 A

  In the prior art, for example, as described in Patent Document 1, when the color is different from the initial state, there is a method of performing color adjustment by simple density adjustment by the user, but this improves the graininess. You cannot make adjustments.

  Patent Document 2 describes a UCR / UCA parameter determination method by a user, but is a setting method based on gray balance, and does not consider graininess. Further, Patent Document 3 describes a method for generating K in consideration of graininess in a method different from the UCR / UCA method. However, since this generation method is very complicated, Therefore, it is not suitable as a method for performing color adjustment easily.

  The present invention has been made in view of the above problems, and by evaluating the graininess by a simple method when outputting to an unexpected recording medium or when the state of the output device varies. An object of the present invention is to provide an image processing apparatus capable of performing appropriate color adjustment and a color conversion adjustment method in the image processing apparatus.

  In order to achieve the above object, an invention according to claim 1 is an image processing apparatus that performs color conversion on an input color image and outputs the image, and evaluates the graininess of the recording medium. The image processing apparatus includes an output unit that outputs an evaluation image, an input unit that inputs an evaluation by the user for the evaluation image, and an adjustment unit that adjusts color conversion according to the input evaluation.

  The invention described in claim 2 is an image processing apparatus that performs color conversion on an input color image and outputs the image, and an output unit that outputs an evaluation image for evaluating the graininess of the recording medium. An image reading means for reading the evaluation image output by the output means, a calculation means for calculating an evaluation value capable of evaluating the graininess from the read evaluation image, and a color according to the calculated evaluation value. Adjusting means for adjusting the conversion.

  According to the third aspect of the invention, in the invention according to the first or second aspect, the image for image evaluation is output by the output means only when an image output to a recording medium not supported by the image processing apparatus is instructed. Is output to a recording medium.

  The invention according to claim 4 is the invention according to claim 2, wherein the evaluation value is granularity or texture.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the color conversion performs conversion into a signal of a plurality of colors including black, and the adjusting means includes a UCR / The parameter of the UCA process is changed.

  According to a sixth aspect of the present invention, in the first aspect of the present invention, the color conversion is performed by converting the signal into a plurality of colors including black, and the adjusting means is a color used for the color conversion. The conversion table is changed.

  The invention according to claim 7 is the invention according to any one of claims 1 to 4, wherein the image processing apparatus is capable of forming and outputting an image with color materials having the same hue and different densities, The adjusting means is characterized by changing the mixing ratio of the color materials having the same hue and different densities.

  According to an eighth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the image processing apparatus uses liquid ink as a color material, and changes the weight of the ink to have two or more sizes. It is possible to form an image using different ink dots, and the adjusting means changes the mixing ratio of the size of the ink dots to be used.

  The invention according to claim 9 is an image processing apparatus for performing color conversion on an input color image and outputting the image, an output means for outputting an evaluation image for the recording medium, and an evaluation by the user for the evaluation image Only when an image output to a recording medium that is not supported by the image processing apparatus is instructed, and an input unit that inputs color conversion according to the input evaluation. The output means outputs an image for image evaluation to a recording medium.

  A tenth aspect of the present invention is a method for performing color conversion on an input color image and adjusting the color conversion in an image processing apparatus that outputs the image, for evaluating the graininess of the recording medium. An output step of outputting an evaluation image, an input step of inputting an evaluation by the user for the evaluation image, and an adjustment step of adjusting color conversion according to the input evaluation are characterized.

  The invention described in claim 11 is a method for performing color conversion on an input color image and adjusting the color conversion in an image processing apparatus for outputting the image, for evaluating the graininess of the recording medium. An output step for outputting an evaluation image, a reading step for reading the evaluation image output by the output step, a calculation step for calculating an evaluation value capable of evaluating the graininess from the read evaluation image, and a calculation step An adjustment step of adjusting color conversion according to the evaluation value.

  In addition to normal image data output processing, user designation or automatic parameter adjustment is instructed. When parameter adjustment is instructed, the evaluation image stored in the evaluation image storage means is read out. The read evaluation image is processed in the same flow as the image data output process, and an image is output. Reading the evaluation image, processing the read image, and outputting the image are repeated a plurality of times while assigning the UCR / UCA parameters by the parameter adjusting means. The user selects the image with the best graininess and inputs it with the user evaluation input means. As a result, the UCR / UCA parameter adjustment is performed, and an appropriate color can be obtained by evaluating the graininess by a simple method when output to an unexpected recording medium or when the state of the output device changes. Adjustments can be made.

  Embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration and a data flow in the color conversion adjustment method of the image processing apparatus according to the first embodiment of the present invention. Normally, when outputting an image, the image data is output according to the flow indicated by (a) in the figure. The details will be described below.

  The image input means 1 is not limited as long as it can input a color image such as a scanner or a digital camera, and is usually captured as an RGB image defined as an 8-bit signal in which each signal takes a value of 0 to 255.

  The input RGB image is converted by the color conversion processing means 2 into CMY color signals in consideration of the color material characteristics of the printer. As the conversion method, there are known methods such as a hue division masking method and a method using linear interpolation using a color conversion lookup table, and any method may be used.

  The UCR / UCA processing means 3 calculates min (C, M, Y) from the input CMY signal, and calculates the K signal based on the value. Further, CMY is corrected according to the calculated K signal to generate a CMYK signal. The CMYK signal here is also an 8-bit signal in which each signal takes a value of 0 to 255.

  The halftone processing means 4 is a process for reducing the value of the CMYK 8-bit signal. Inkjet and electrophotographic output devices do not have the ability to directly reproduce 8-bit gradation, so by performing pseudo-halftone processing such as dithering or error diffusion, multi-valued representation is possible with small dots. It is carried out.

  The halftone processed CMYK signal is printed on a recording medium by image output means 5 such as an ink jet or an electrophotographic apparatus.

  The above is the flow for normal image output. Next, the flow of UCR / UCA parameter adjustment will be described.

  As for the parameters, appropriate parameter adjustments are made at the time of shipment of the apparatus, and normally there is no need for parameter adjustments. However, when outputting to a recording medium that is not assumed by the output device, or when the output characteristics of the output device have changed due to long-term use, by adjusting the parameters, High-quality output can be performed.

  As a specific determination method of the timing for performing parameter adjustment, the user may specify the timing, or the type of the recording medium set automatically is identified, and the process starts when an unexpected sheet is set. It is also effective. In addition, a change in output characteristics may be detected by a sensor or the like, and parameter adjustment may be performed when there is a large change. Further, when automatically determining the start timing, a mechanism that displays a message asking the user for permission and starts the processing when a permission instruction is input can be considered.

  When parameter adjustment is instructed, an evaluation image is first output. An evaluation image output flow is shown in FIG.

  First, an evaluation image stored in the evaluation image storage unit 6 is read out. As the evaluation image, for example, an achromatic gradation image of R = G = B is prepared, processed by a plurality of UCR / UCA parameters, and output, thereby outputting a UCR / UCA parameter having the best granularity. I understand. Assuming that the UCR / UCA parameters represented by the equation (1) and FIG. 7 are used, it is necessary to produce an image processed with a plurality of parameters γ, which is a black ink starting point that greatly affects graininess. Other parameters α and β may be fixed because the effect on the graininess is not so great.

  As a specific flow, the read evaluation image is processed in the same manner as the flow (a), and an image is output. However, since it is necessary to output with a plurality of UCR / UCA parameters, the flow of reading the evaluation image → processing → output is repeated a plurality of times while the UCR / UCA parameters are assigned by the parameter adjusting means 7.

  The output evaluation image is subjectively evaluated by the user, and the UCR / UCA parameters are adjusted according to the evaluation result. Specifically, the user selects an image with the best graininess and inputs it with the user evaluation input means 8. As the user evaluation input means 8, a method of preparing a touch panel or the like, displaying a number associated with the output evaluation image, and selecting from the number is conceivable. Next, the UCR / UCA parameters are adjusted by the parameter adjusting means 7 in accordance with the input evaluation result. That is, it is changed to the UCR / UCA parameter used when the image having the best graininess is output. The parameter adjustment flow is shown in FIG.

  An appropriate UCR / UCA parameter can be selected by the flow as described above.

  Next, a second embodiment of the present invention will be described. FIG. 2 is a block diagram showing a configuration and a data flow in the color conversion adjustment method of the image processing apparatus according to the second embodiment of the present invention.

  In the first embodiment, the evaluation image is stored as an RGB image, but this is not necessarily the case. In the second embodiment, the CMYK image after halftone processing is stored. That is, as shown in FIG. 2, the evaluation image storage means 6 stores the CMYK image after halftone processing and sends it directly to the image output means 5, so that the processing time is shortened. The image data output process is performed according to the flow shown in FIG. 2A as in the first embodiment. The evaluation image output flow is shown in FIG. The parameter adjustment flow is shown in FIG. However, it is necessary to store an image processed using at least several types of UCR / UCA parameters.

  Next, a third embodiment of the present invention will be described. FIG. 3 is a block diagram showing a configuration and a data flow in the color conversion adjustment method of the image processing apparatus according to the third embodiment of the present invention.

  In the first and second embodiments, the output evaluation image is evaluated by the user. In the third embodiment, the granularity is measured from the output image, and the UCR / UCA parameter is changed based on the granularity. . In FIG. 3, the evaluation image storage means 6 is the same as that of the second embodiment, but the evaluation image storage means 6 may be the same as that of the first embodiment.

  In the third embodiment, the image data output flow (a) and the evaluation image output flow (b) are the same as in the first and second embodiments, but the parameter adjustment flow (c) is different. Therefore, the operation after the evaluation image is output will be described.

  First, the output evaluation image is read by image reading means 9 such as a scanner. The granularity calculation means 10 calculates the granularity from the read image, and sets the UCR / UCA parameter when the image having the best granularity value is output.

  Details of the procedure for calculating the granularity will be described. FIG. 4 is a flowchart illustrating an example of the granularity calculation procedure. First, the RGB image read by the image reading means 9 is converted into an L * a * b * signal that is a CIELAB color system. Next, a spatial frequency component, that is, a spectrum is calculated from the L * signal. The obtained spectrum is corrected in consideration of human visual characteristics, and finally integrated over the entire frequency. This value is used as the granularity obtained by evaluating the granularity as an objective numerical value. Specifically, for example, JP-A-10-23191 describes a detailed calculation method of the graininess evaluation value. However, as a method for calculating the granularity, another calculation method may be used as long as a value capable of evaluating the granularity as a numerical value can be calculated.

  Next, a fourth embodiment of the present invention will be described. In the first, second, and third embodiments, the UCR / UCA parameters are adjusted at the time of parameter adjustment, but other parameter adjustments can also be performed. In the fourth embodiment, in addition to CMYK, it is assumed that there is an ink jet recording apparatus that outputs an image with six color inks using Lc and Lm as output means, and dark and light ink, that is, mixing of C and Lc, M and Lm Adjust the percentage.

  As a method for setting the mixing ratio of dark and light inks, there is a method of performing color conversion to CMYK and then converting the CM signal into a dark and light ink amount by performing conversion using a γ table. Hereinafter, the C signal will be described, but the same applies to the M signal.

  FIG. 5 is a graph showing a γ table for decomposition. Here, it is assumed that Lc has a density of 1/3 of the thick C. The low density region is reproduced only by Lc with respect to the inputted C before decomposition, and the dark C starts to enter from a certain density α. As the concentration C increases, Lc begins to decrease, and at a certain concentration β, Lc = 0. Higher density parts than β are reproduced only with concentrated C. By adjusting α and β, appropriate dark and light inks can be mixed to output a high-quality image.

  In FIG. 5, for the sake of simplicity, the function form is a polygonal line. However, this is not always necessary, and any function form can be used, and the parameters change accordingly.

  As for the actual parameter adjustment method, an evaluation image may be output in the same manner as in the above-described embodiment, and the parameters may be changed by user evaluation or granularity measurement.

  FIG. 6 is a block diagram showing a configuration and a data flow in the color conversion adjustment method of the image processing apparatus according to the fourth embodiment of the present invention. FIG. 6 shows a case where the parameter is changed by measuring the granularity. (A) is a normal image data output flow, (b) is an evaluation image output flow, and (c) is a parameter adjustment flow.

  Regarding the evaluation image, it is necessary to prepare an image different from that in the case of UCR / UCA parameter adjustment. For example, an image created by waving color separation parameters α and β with respect to C and M gradation images may be prepared.

  Also. The same adjustment can be made for an ink jet recording apparatus that can eject single-color ink with a plurality of dot sizes instead of dark and light inks. For example, when small dots and large dots can be divided, if small dots are considered Lc and large dots are dark C, large and small dots can be appropriately adjusted in exactly the same manner. In this case, it is possible to adjust not only for CM but also for all CMYK.

  Next, a fifth embodiment of the present invention will be described. In the above embodiment, color conversion to CMYK is performed by color conversion to CMY and UCR / UCA processing. However, such a configuration is not necessarily required. In the fifth embodiment, for example, there is a configuration that performs direct conversion from RGB signals to CMYK. As a method, there is a method of preparing a color conversion lookup table 3-4 and performing color conversion by interpolation calculation. In this case, it is conceivable to adjust K of the color conversion lookup table itself. However, in this case, it is preferable to adjust CMY in synchronization with K in accordance with, for example, a mathematical expression used in the UCR / UCA system. In addition, it is better to avoid a large change from the initial value. Thereby, it is possible to prevent the color reproducibility from deteriorating. Further, it is apparent that any other color conversion system can be applied to any color conversion system capable of adjusting K.

  Next, a sixth embodiment of the present invention will be described. In the said embodiment, it evaluated using the granularity. In order to evaluate the graininess, that is, the roughness of the image, it is also effective to adjust the parameters by evaluating the texture. In the sixth embodiment, parameter adjustment is performed by texture evaluation. Texture is a mainly periodic structure included in an image. If this is noticeable, it is perceived as image quality degradation such as roughness.

  Actually, in the case of subjective evaluation by the user, it is considered that the evaluation includes the degradation of the image due to the texture as a result. It is also possible to calculate a texture evaluation value from an image captured by a scanner, and to adjust UCR / UCA parameters and the like according to the value. For example, a texture feature amount described in Japanese Patent Laid-Open No. 2002-245465 or a granularity considering the texture feature amount can be used.

  Next, a seventh embodiment of the present invention will be described. In the first embodiment, the case where an unexpected recording medium is set is considered as the timing of parameter adjustment, that is, the evaluation image output. This is effective not only for the color adjustment based on the graininess evaluation but also for the timing for performing the general color adjustment. The present invention is characterized by this timing. In the seventh embodiment, the timing is the same as in the first embodiment, but a general method is used for color adjustment. As a general color adjustment method, for example, a density correction method described in JP-A-2001-47655 can be used.

  Although the embodiment of the present invention has been described in detail as described above, the above embodiment is an example of a preferred embodiment of the present invention, and is not limited thereto. Various modifications can be made without departing from the scope.

It is a block diagram which shows the structure and data flow in the color conversion adjustment method of the image processing apparatus of 1st Embodiment of this invention. It is a block diagram which shows the structure and data flow in the color conversion adjustment method of the image processing apparatus of 2nd Embodiment of this invention. It is a block diagram which shows the structure and data flow in the color conversion adjustment method of the image processing apparatus of 3rd Embodiment of this invention. It is a flowchart which shows an example of the granularity calculation procedure in 3rd Embodiment of this invention. It is a graph which shows the gamma table for decomposition | disassembly in 4th Embodiment of this invention. It is a block diagram which shows the structure and data flow in the color conversion adjustment method of the image processing apparatus of 4th Embodiment of this invention. It is a graph which shows the relationship between K 'in Formula (1), and min (C, M, Y).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image input means 2 Color conversion processing means 3 UCR / UCA processing means 4 Halftone processing means 5 Image output means 6 Evaluation image storage means 7 Parameter adjustment means 8 User evaluation input means 9 Image reading means 10 Granularity calculation means 11 Dark ink Disassembling means

Claims (11)

An image processing apparatus that performs color conversion on an input color image and outputs the image,
Output means for outputting an evaluation image for evaluating the graininess of the recording medium;
Input means for inputting an evaluation by the user for the evaluation image;
An image processing apparatus comprising: adjusting means for adjusting color conversion in accordance with the input evaluation. An image processing apparatus that performs color conversion on an input color image and outputs the image,
Output means for outputting an evaluation image for evaluating the graininess of the recording medium;
Image reading means for reading the evaluation image output by the output means;
A calculation means for calculating an evaluation value capable of evaluating the graininess from the read evaluation image;
An image processing apparatus comprising: adjusting means for adjusting color conversion in accordance with the calculated evaluation value.   The image output image is output to the recording medium by the output means only when an image output to a recording medium not supported by the image processing apparatus is instructed. An image processing apparatus according to 1.   The image processing apparatus according to claim 2, wherein the evaluation value is granularity or texture.   5. The color conversion according to claim 1, wherein the color conversion performs conversion into a signal of a plurality of colors including black, and the adjustment unit changes a parameter of UCR / UCA processing in the color conversion. An image processing apparatus according to 1.   5. The color conversion according to claim 1, wherein the color conversion performs conversion into a signal of a plurality of colors including black, and the adjustment unit changes a color conversion table used for color conversion. Image processing apparatus.   The image processing apparatus is capable of forming and outputting an image with color materials having the same hue and different densities, and the adjusting means changes a mixing ratio of the color materials having the same hue and different densities. The image processing apparatus according to any one of claims 1 to 4.   The image processing apparatus uses liquid ink as a color material and can form an image using two or more different ink dots by changing the weight of the ink. 5. The image processing apparatus according to claim 1, wherein a mixing ratio of the sizes is changed. An image processing apparatus that performs color conversion on an input color image and outputs the image,
Output means for outputting an evaluation image for the recording medium;
Input means for inputting an evaluation by the user for the evaluation image;
Adjusting means for adjusting color conversion according to the input evaluation, and only when the image output to a recording medium not supported by the image processing apparatus is instructed by the output means, An image processing apparatus that outputs an image for image evaluation to the recording medium. A method for performing color conversion on an input color image and adjusting color conversion in an image processing apparatus that outputs the image,
An output step of outputting an evaluation image for evaluating the graininess of the recording medium;
An input step of inputting an evaluation by the user for the evaluation image;
A color conversion adjustment method comprising: an adjustment step of adjusting color conversion in accordance with the input evaluation. A method for performing color conversion on an input color image and adjusting color conversion in an image processing apparatus that outputs the image,
An output step of outputting an evaluation image for evaluating the graininess of the recording medium;
A reading step of reading the evaluation image output by the output step;
From the read evaluation image, a calculation step of calculating an evaluation value capable of evaluating the graininess,
A color conversion adjustment method comprising: an adjustment step of adjusting color conversion according to the calculated evaluation value.

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