JP2001352456A - Image-processing method and image-processing unit, and image-forming device provided with them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing unit, that applies color correction processing more properly to each area by selecting an interpolation arithmetic method in color correction processing employing an LUT, depending on a type of a received image so as to properly select the accuracy and the processing speed of color correction. SOLUTION: A control section 50 provided to a color correction section 14 specifies the kind of image and selects an interpolation arithmetic processing corresponding to the kind of the image. A data separation section 2 separates RGB input image data into high-order N-bit data and low-order M-bit data, in response to the interpolation arithmetic processing selected by the control section 50. A color correction table access section 3 uses the LUT for the selected interpolation arithmetic processing to read a table value, corresponding to the high-order N-bit data. An interpolation arithmetic processing section 4 uses the table value read and the low-order M-bit data separated from the input image data by the data separation section 2, to conduct the selected interpolation arithmetic processing and to obtain CMY output image data consisting of CMY.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color correction process by a look-up table (Look Up Table, hereinafter referred to as LUT) method used in an image forming apparatus such as a digital color copying machine or a color management system. The present invention relates to an image processing method and an image processing apparatus for suitably performing image and color space conversion processing, and an image forming apparatus including the same.

[0002]

2. Description of the Related Art In recent years, digitalization of OA equipment has rapidly progressed, and demand for color image output has increased, so that digital color copying machines of an electrophotographic system and color printers of an ink jet system and a thermal transfer system have been developed. It has been widely spread. For example, image information input from an input device such as a digital camera or a scanner, or image information created on a computer is output using these output devices. In these input / output devices, it is necessary to always output an image with stable color reproduction for input image information, and color correction processing (color conversion processing) of digital image processing technology plays an important role. Plays.

A number of color correction methods have been proposed, including a color coordinate conversion method for converting input image data into uniform color space data. One such method is the Color Science Handbook, New Edition, No. 1137
1149 (edited by the Japan Society of Color Science, published by The University of Tokyo Press), and the LUT method described in the Journal of the Imaging Society of Japan, Vol. 37, No. 4, (1998), pp. 555-559. In this specification,
Processing to correct color signals that would otherwise be inappropriate as output, processing to convert color signals to change the color itself, and conversion of color signal coordinate system even if the color itself does not change Color correction (or color conversion)
Call.

In the direct conversion method, which is one of the LUT methods, color correction data is calculated in advance for all combinations of input image data, and the result is stored in a color correction table, which is an LUT. Look at the table values,
This is a method of outputting as output image data. This direct conversion method accesses a color correction table, has the advantage that the circuit configuration is simple, processing can be performed at relatively high speed, and any nonlinear characteristics can be applied.

However, this direct conversion method can obtain high conversion accuracy even when the relationship between the input image data and the output image data has an arbitrary non-linearity. Must be stored in the color correction table, and the size of the color correction table becomes very large. For example, 8
48 Mbytes for input image data of 3 bits, 1
In the case of 0-bit 4-color input image data, a table size of 4 Gbytes is required, which is problematic in terms of cost.

On the other hand, there is a three-dimensional interpolation method as another LUT method. In the three-dimensional interpolation method, a table value for a combination of a part of selected input image data is calculated in advance, stored in a color correction table, and a vicinity of the input image data whose table value is stored in the color correction table. The input image data is calculated by three-dimensional interpolation using table values stored in the color correction table.

As an example, FIG. 7 shows an example in which each axis of the color space of 8-bit RGB image data constituting the input image data is divided into 4 bits, that is, 2 ⁴ = 16.

In this case, the input color space is 4096 (16 × 16
It is divided into (x16) cubes, and the total number of grid points, that is, tables, is 4913 (17x17x17). Each grid point p _i
The coordinates of (i = 0, 1,..., 7) are represented by the upper 4 bits of the image data of each color, and the grid point p _i stores the color correction data corresponding to the input image data. For input image data that is a point other than the grid point p _i , the color conversion data is obtained by interpolation using the lower 4 bits of the image data of each color and the table values of eight neighboring grid points p _i. Desired.

[0009] Now, as shown in FIG. 7, respectively the relative ratio grid width in each grid of any of the input image data p, X-axis grid point p ₀ in the standard, Y-axis, the Z-axis direction a,
Assuming that b and c (0 ≦ a, b, c ≦ 1), the interpolation value f (p) in the eight-point interpolation (cubic interpolation) is expressed by the following table, where f (p _i ) is the table value at the grid point p _i . It can be determined by equation (1).

[0010]

(Equation 1)

This three-dimensional interpolation method can obtain color conversion values for all combinations of input image data even when the number of input image data for which table values are to be calculated in advance is limited. Can be reduced in size as compared with the direct conversion method described above.

The present applicant has proposed a two-dimensional interpolation method in Japanese Patent Application No. 11-260977 prior to the present invention. Although the above-described three-dimensional interpolation method has no problem with respect to the table size, the three-dimensional interpolation operation requires a large amount of calculation,
Further, since a complicated circuit for this processing is separately required, there is a problem that the processing speed is reduced.

On the other hand, according to the two-dimensional interpolation method,
Omitting the table value corresponding to the lower bit data,
Since the size of the LUT (look-up table) is much smaller than that used in the direct conversion method, and the two-dimensional interpolation operation is used, the time of the interpolation operation is shorter than that of the three-dimensional interpolation operation. That is, in the two-dimensional interpolation method, L
It is possible to perform high-speed color conversion processing from input image data of the first color system to output image data of the second color system while suppressing the size of the UT. In addition, 2
The details of the dimensional interpolation method will be described in an embodiment of the invention described later.

Table 1 shows the results of comparing the conversion accuracy, circuit configuration, table memory size, conversion speed, and cost in the direct conversion method, the three-dimensional correction method, and the two-dimensional interpolation method.

[0015]

[Table 1]

As described above, various color correction processes based on the LUT method have been invented. On the other hand, it has been considered that the color correction process is performed according to regions. For example, Japanese Patent Application Laid-Open
Japanese Patent No. 292307 discloses that a document is obtained by reading a document.
The color signal of each pixel in the input image is separated into any one of a photograph, a halftone dot, and a line drawing region, and a plurality of color correction processing units perform an optimum color correction process according to the region separation result. The configuration to be selected is described. According to this, it is possible to perform a color correction process corresponding to each area, so that
Each color of the halftone dot region and the line drawing region can be reproduced with higher accuracy than a configuration in which the same color correction processing is performed on all regions.

[0017]

However, the technique disclosed in Japanese Patent Application Laid-Open No. Hei 5-292307 has the following problems when trying to perform an optimal color correction process according to each area.

1) As a method of color correction processing, a method using a non-linear masking method is described, but this method does not have sufficient conversion accuracy. The order of the non-linear masking method is at most a second order, and is inadequate particularly in color correction processing for an input / output device having strong non-linearity or when converting a color signal in a uniform color space to an output device.

2) When using the non-linear masking method,
The problem of the algorithm cannot be solved. For example, when a tone gap (color skip) occurs, changing the coefficient for performing the matrix operation only changes the region where the matrix operation occurs, and cannot suppress the tone gap.

3) As a color correction method, a direct conversion method using an LUT is used instead of the nonlinear masking method.
If output image data corresponding to all image data that can be input to the LUT is stored, the conversion accuracy is improved, but in this case, the memory capacity of the LUT becomes very large, and the access speed to the LUT is reduced. I do.

The present invention has been made in view of the above problems, and the purpose of performing the optimum color correction processing for each area is the same as that of Japanese Patent Application Laid-Open No. 5-292307. By switching the interpolation calculation method in the color correction processing using the table reference method according to the type of image to be processed, the image processing apparatus can perform the color correction processing more suitable for each area by appropriately switching the color correction accuracy and processing speed. It is an object of the present invention to provide a processing method and apparatus, and an image forming apparatus.

[0022]

In order to solve the above-mentioned problems, an image processing method according to the present invention uses a first color system input image data in which image data of each coordinate is represented by predetermined bits. The color correction processing of obtaining image data of each coordinate of the second color system and setting it as output image data is performed by using a combination of image data of each coordinate in a selected part of input image data as address data. Using an LUT in which image data at predetermined coordinates of output image data corresponding to the above is stored as a table value, for input image data represented by the address data, a table value is read from the LUT, and for other input image data, , LU
In an image processing method implemented by performing an interpolation operation using a table value read from T, an LUT corresponding to a plurality of interpolation operation methods is used, and the interpolation operation method is switched according to the type of image. It is characterized in that a color correction process suitable for is performed.

Conventionally, input image data of a first color system has been converted to output image data of a second color system by using an LUT and an interpolation operation.
By using the LUT in combination with the interpolation operation, the LUT
The size can be reduced to reduce the cost. As an interpolation calculation method used, a three-dimensional interpolation method has been conventionally known, and in addition to this, the present applicant has proposed a two-dimensional interpolation method.

The applicant of the present invention has conducted various studies on such a plurality of interpolation calculation methods. As a result, each interpolation calculation method has a difference in processing speed, ripple error, interpolation error, and the like. Even when the method is used, it has been found that the image quality of the output image depends on the type of the original image.

Therefore, in the above-described image processing method of the present invention, the interpolation calculation method is appropriately switched according to the type of input image such as a character, a photographic paper photograph, or a print photograph.
An interpolation calculation method appropriate for the type of image is selectively performed. This makes it possible to perform color correction processing according to the characteristics of the input image by utilizing the characteristics of each of the interpolation calculation methods. By applying the image processing method of the present invention to an image forming apparatus, an output image with high image quality can be obtained. Can be obtained.

Further, the applicant of the present application has further studied and found that an LUT in which output image data is stored only for a part of input image data is used, and a table value is not stored in the LUT. It has been found that, even if a table value of address data close to the input image data is used as it is as the output image data corresponding to the input image data without interpolation, the image quality is not particularly deteriorated depending on the type of the image.

Therefore, in the above-described image processing method of the present invention, it is preferable that the interpolation calculation method includes a method of outputting the table value read from the LUT as it is and performing no interpolation calculation. For an image in which the image quality does not matter even if the calculation is not performed, there is an advantage that the processing can be performed at higher speed.

More specifically, the relationship between the type of image and the interpolation calculation method uses a three-dimensional interpolation method when the image is a photographic paper photograph, and uses a two-dimensional interpolation method when the image is a print photograph. When the image is a character or a line drawing, it is preferable to use a method that does not perform an interpolation operation that outputs a table value as it is.

Since the three-dimensional interpolation method has a feature of being superior in gradation, the interpolation calculation method is used when a photographic paper photograph in which gradation is particularly important is an original, so that the image quality faithful to the original image is obtained. Output image can be obtained. In addition, the two-dimensional interpolation method is characterized in that the interpolation error is small and accurate, and the conversion speed and gradation are good. Therefore, a printed photograph (halftone photograph) that is printed in area gradation and in which ripples are inconspicuous can be obtained. By using the interpolation calculation method in a certain case, it is possible to obtain a high-quality output image at a good processing speed. The method that does not perform the interpolation operation does not require gradation because of the coarse conversion.However, since the interpolation operation is not performed, the processing speed is very fast. By using the interpolation calculation method for a character document (document including characters and line drawings) which is hardly affected by a ripple error, an interpolation error, and the like, an output image with no problem can be obtained at a very high speed.

An image processing apparatus for realizing the image processing method of the present invention has the following configuration.

An image processing apparatus according to the present invention obtains image data of each coordinate of a second color system from input image data of a first color system in which image data of each coordinate is represented by predetermined bits. In an image processing apparatus having a color correction unit that sets output image data, the color correction unit converts input image data of the first color system into address data and interpolation data.
Data separation means for separating according to each of the plurality of interpolation calculation processes; and a combination of image data of each coordinate in a selected part of the input image data is set as the address data, and the output image data corresponding to the address data is output. LUT in which image data of each coordinate is stored as a table value
A color correction table access means for reading a table value corresponding to the address data separated by the data separation means using one LUT among the LUTs, and a color correction table access means Based on the table value read from the LUT and the interpolation data separated by the data separation means, the type of the image and the interpolation calculation processing means for performing any one of a plurality of interpolation calculation processings are determined. In order to perform interpolation calculation processing suitable for the type of image, the image processing apparatus is provided with a control unit that controls the data separation unit, the color correction table access unit, and the interpolation calculation processing unit.

According to the above arrangement, the control means discriminates the type of the image, and performs the interpolation calculation processing suitable for the type of the image, the data separation means, the color correction table access means, and the interpolation calculation processing means. Control. The data separating means separates the input image data of the first color system into address data and interpolation data in accordance with an interpolation calculation process appropriate for the type of image selected by the control means. The address data indicates an address for reading a table value stored in the LUT of the color correction table access unit provided at the subsequent stage of the data separation unit.
In T, the combination of the image data of each coordinate in the selected part of the input image data is stored as the address data, and the image data of each coordinate of the output image data corresponding to the address data is stored as a table value. . Such an LUT is provided for each interpolation calculation process.

The color correction table access means selects one of the LUTs for the interpolation calculation process corresponding to the type of the image selected by the control means from the plurality of LUTs, and uses the LUT to convert the address data into address data. The corresponding table value is read and output to a subsequent interpolation calculation processing means. In the interpolation calculation processing means, the interpolation calculation suitable for the type of image selected by the control means is performed by using the table value read by the color correction table access means and the interpolation data separated by the data separation means. Perform processing.

As a result, the color correction processing according to the characteristics of the input image is performed. As a result, in an image forming apparatus having such an image processing apparatus, a high image quality utilizing the characteristics of the image is obtained. An output image can be provided. The image forming apparatus is realized by, for example, a digital color copying machine using an inkjet system or an electrophotographic system.

Further, in the above-described image processing apparatus of the present invention, in the interpolation calculation processing performed by the interpolation calculation processing means, there is no interpolation calculation for directly outputting the table value read from the LUT without performing the interpolation calculation. It is preferable to adopt a configuration that includes a process. With this configuration, it is possible to process an image at a higher speed with respect to an image in which image quality does not matter even in a rough color conversion in which an interpolation operation is not performed.

In the above-described image processing apparatus of the present invention, the interpolation calculation processing means performs no interpolation calculation processing for directly outputting the table value and performs three-dimensional interpolation using the table value and the interpolation data. It is possible to perform two-dimensional interpolation processing for performing two-dimensional interpolation using table values and interpolation data, and the control means selects the three-dimensional interpolation processing when the image is a photographic paper photograph. It is more preferable that the two-dimensional interpolation processing is selected when the image is a printed photograph, and the processing without interpolation calculation is selected when the image is a character or a line drawing.

By providing this image processing apparatus in an image forming apparatus, a high-quality output image with excellent gradation can be obtained for a photographic paper original, and a high-quality output image with excellent gradation can be obtained for a printed photographic original. It is possible to obtain an output image having no problem in image quality at a very high speed from a character document (document including characters and line drawings) at a good processing speed.

Further, in the above-described image processing apparatus of the present invention, a simple mode regardless of the image quality is provided, and when the simple mode is set, the control means performs the processing without interpolation calculation regardless of the type of the image. It is also possible to adopt a configuration for selection. According to this, regardless of the image quality, it is possible to respond to a user's request to obtain an output image anyway quickly.

In the above-described image processing apparatus of the present invention, the color correction means converts the input image data of the first color system into output image data of the second color system including black. It is also possible to adopt a configuration in which
Since the black generation processing can be performed according to the type of the input image, the image quality of the output image is further improved as compared with a configuration in which the black generation processing is performed by the same processing regardless of the type of the image. Becomes possible.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] An embodiment of the present invention will be described below with reference to FIGS.

FIG. 2 is a block diagram showing the configuration of a digital color copying machine (image forming apparatus) according to an embodiment including a color image processing apparatus 1 to which the image processing method and the image processing apparatus according to the present invention are applied. Shown in the figure.

As shown in FIG. 2, the color image processing apparatus 1
Are an A / D conversion unit 10, a shading correction unit 11, an input gradation correction unit 12, an area separation processing unit 13, a color correction unit (color correction unit) 14, a black generation / under color removal unit 15, a spatial filter processing unit 16, an output tone correction unit 17, and a tone reproduction processing unit 18, to which a color image input device 20 and a color image forming unit 30 are connected. Constructs a color copier.

Color image input device (image reading means) 20
Is constituted by, for example, a scanner unit having a CCD (Charge Coupled Device), and converts a reflected light image from a document into an RG image.
B (R: red, G: green, B: blue) analog signal C
The image is read by a CD and input to the color image processing apparatus 1.

The analog signal read by the color image input unit 20 is supplied to the A / D conversion unit 10, the shading correction unit 11, and the input gradation correction unit 1 in the color image processing apparatus 1.
2. The area separation processing unit 13, the color correction unit 14, the black generation / under color removal unit 15, the spatial filter processing unit 16, the output gradation correction unit 17, and the gradation reproduction processing unit 18 are sent in this order.
Is output to the color image forming unit 30 as a digital color signal of

A / D (analog / digital) converter 10
Are the input image data RGB (R: red, G: green,
B: blue) analog signal is converted into a digital signal, and the shading correction unit 11 applies the illumination system of the color image input unit 20 to the digital RGB signal sent from the A / D conversion unit 10. This is a process for removing various distortions generated in the imaging system and the imaging system.

The input tone correction unit 12 outputs an RGB signal (R signal) from which various distortions have been removed by the shading correction unit 11.
In addition to adjusting the color balance with respect to the GB reflectance signal), the signal is converted into a signal such as a density signal which can be easily handled by the image processing system employed in the image processing unit 1.

The segmentation processing unit 13 converts the RGB signals into
Each pixel in the input image is separated into a character area, a halftone dot area, and a photograph area. The area separation processing unit 13
Based on the result of the separation, an area identification signal indicating which area the pixel belongs to is output to the black generation / under color removal section 15, the spatial filter processing section 16, and the tone reproduction processing section 18, and the input floor is processed. The signal output from the tone correction unit 12 is directly output to the color correction unit 14 at the subsequent stage.

As an area separation processing method performed by the area separation processing unit 13, for example, “Analysis of the Institute of Image Electronics Engineers of Japan 9
0-06-04 ". This method will be described below.

Here, M × N (
The following determination is performed in a block of pixels (M and N are natural numbers), and this is used as the region identification signal of the pixel of interest.

The average value (Dave) of the signal level is obtained for the central nine pixels in the block, and each pixel in the block is binarized using the average value. Also, the maximum pixel signal level (Dmax) and the minimum pixel signal level (Dmin) are determined at the same time.

In the halftone dot region, the halftone dot region is identified by utilizing the fact that the image signal in a small region has a large fluctuation and that the density is higher than the background. For the binarized data, the number of transition points from 0 to 1 and the number of transition points from 1 to 0 are obtained in the main scanning and sub-scanning directions, respectively, and K _H and K are respectively obtained.
_V, which is compared with the threshold values T _H and T _V, and when both of them exceed the threshold value, are regarded as halftone dot regions. Also, Dmax, Dmin, and Dave are compared with thresholds B ₁ and B ₂ to prevent erroneous determination of the background.

[0052]

(Equation 2)

In the character area, since the difference between the maximum signal level and the minimum signal level is large and the density is considered to be high, the character area is identified as follows. The maximum and minimum signal levels previously determined in the non-dot area and the difference (Dsub) between them are compared with thresholds P _A , P _B , and P _C. If any one exceeds, the character area is all below the threshold. Then, it is set as a photograph area.

[0054]

(Equation 3)

The color correction section 14 converts the input image data of the first color system represented by RGB coordinates into CMY (C: cyan,
(M: magenta, Y: yellow) is converted into output image data of a second color system represented by coordinates. In addition, in order to realize faithful color reproduction, CMY containing unnecessary absorption components is used.
This is a process for removing color turbidity based on the spectral characteristics of the color material. Although details of the color correction unit 14 will be described later, the color correction unit 1 in the digital copying machine of the present embodiment is described.
No. 4 performs color correction processing using the LUT method. At this time, the interpolation calculation processing method is switched according to the type of image so that the optimum color correction processing is performed on the image. ing.

The black generation / under color removal unit 15 outputs the color-corrected C
A process for generating a black (K) signal from three color signals of MY and a process of subtracting the K signal obtained by the black generation from the original CMY signal to generate a new CMY signal is performed.
The three color signals of Y are converted into four color signals of CMYK.

As an example of the black generation processing, there is a method (general method) of generating black using skeleton black.
In this method, the input / output characteristics of the skeleton curve are represented by y = f
(X), input data is C, M, Y, output data is C ', M', Y ', K', UCR (Under Color Remova
l) If the rate is α (0 <α <1), the black generation / undercolor removal processing is represented by the following equation (2).

[0058]

(Equation 4)

The spatial filter processing unit 16 performs a spatial filter process by a digital filter on the image data of the CMYK signal input from the black generation / under color removal unit 15 based on the region identification signal, and removes the spatial frequency characteristics. The output gradation correction unit 17 and the gradation reproduction processing unit 18 perform the CMY correction in the same manner as the spatial filter processing unit 16.
A predetermined process is performed on the image data of the K signal based on the region identification signal.

For example, the region separated into characters by the region separation processing section 13 is subjected to sharp emphasis processing in the spatial filter processing by the spatial filter processing section 16 in order to enhance the reproducibility of black characters or color characters. The emphasis amount is increased. At the same time, the tone reproduction processing section 18 selects binarization or multi-value processing on a high-resolution screen suitable for reproduction of a high frequency.

Further, for the area separated into halftone dots by the area separation processing section 13, the spatial filter processing section 16 performs a low-pass filter processing for removing an input halftone dot component. Then, the output tone correction unit 17 performs an output tone correction process of converting a signal such as a density signal into a dot area ratio which is a characteristic value of the color image forming unit 30.
The tone reproduction processing section 18 performs a tone reproduction process (halftone generation) for finally separating an image into pixels and performing processing so that each tone can be reproduced. For the regions separated into photographs by the region separation processing unit 13, binarization or multi-value processing is performed on a screen that emphasizes tone reproducibility.

The image data subjected to each of the above-described processes is
The data is temporarily stored in the storage unit, read out at a predetermined timing, and input to the color image forming unit 30.

The color image forming section 30 outputs image data to a recording medium (for example, paper), and includes, for example, a color image forming apparatus using an electrophotographic system or an ink jet system. There is no particular limitation.

Hereinafter, the color correction section 14 will be described in detail.

Here, the input image data composed of the RGB image data represented by the first color system is represented by the CMY (CNYK) image data of the second color system. An example in which the image data is converted into output image data to be output will be described. However, the present invention can also be applied to a case where RGB is converted to R′G′B ′ (for example, a case where image data read from a scanner is output to a display). It is. Also,
The present invention is also applicable to a system in which an image input device such as a scanner, an image processing device, an image forming device such as a color printer, and an image display device such as a display are configured via a network.

FIG. 1 shows the configuration of the color correction section 14 in the color image processing apparatus 1. As shown in FIG. 1, the color correction unit 14 includes a data separation unit (data separation unit) 2, a color correction table access unit (color correction table access unit) 3,
It comprises an interpolation operation processing section (interpolation operation processing means) 4 and a control section (control means) 50 for controlling these operations.

As described above, this color correction unit 14
The color correction process using the UT method is performed, and the color correction process is switched to an interpolation calculation process that matches the type of the image according to the type of the image so that the optimal color correction process is performed on the image. Specifically, CPU (Central Processing Unit)
The control unit 50 configured as described above includes the data separation unit 2,
The color correction table access unit 3 and the interpolation calculation processing unit 4 are controlled to perform no interpolation calculation without any interpolation calculation.
The three-dimensional interpolation processing using the three-dimensional interpolation method and the two-dimensional interpolation processing using the two-dimensional interpolation method are selectively switched according to the type of the image from the three processings.

Table 2 shows the results of comparing the conversion speeds and gradations of these three interpolation calculation processes.

[0069]

[Table 2]

As shown in Table 2, the process without interpolation calculation does not perform the interpolation calculation, so that the gradation is not expected, but the conversion speed is extremely high and the speed is high. On the other hand, the three-dimensional interpolation processing is characterized in that although the conversion speed is low, the ripple error is small and the gradation is excellent. Ripple is light and dark stripes of density. If the ripple error is large, ripples appearing in the image such as ripples appear in the image. On the other hand, the two-dimensional interpolation processing using the two-dimensional interpolation method previously proposed by the present applicant has a small interpolation error, is accurate, has a higher conversion speed than the three-dimensional interpolation processing, and has a higher gradation. It has a characteristic point that the property is not as good as the three-dimensional interpolation processing but is good.

As described above, each interpolation processing has its own characteristic. By considering in advance the optimal interpolation calculation processing for the type of image in consideration of the difference in the characteristics, it is possible to perform the color correction processing optimal for the type of image.

The type of image in the control unit 50 is specified based on an image mode signal input to the control unit 50 or an area identification signal from the area separation processing unit 13.
The image mode signal is an image such as a character mode, a print photograph mode, or a photographic paper photograph mode, which is input by an operator from an image mode setting button provided on an operation panel 40 (see FIG. 2) of the digital color copying machine. This is a signal representing the type of. As described above, the area identification signal is a signal resulting from the separation of a certain pixel or pixel block into characters, halftone dots, and other areas (areas other than characters and halftone dots such as photographs).

Here, the area identification signal is set by default. Therefore, when the image mode setting button is operated and the image mode signal is input, the type of the image is specified based on the image mode signal and interpolation calculation processing is performed prior to the area identification signal. This method is not limited, and if one of the above-described plurality of image mode signals is set to a default and an image mode setting button is used to set a mode other than the default image mode, the area is set. Interpolation calculation processing using the identification signal may be performed.

Table 3 shows the relationship between the above-mentioned image mode signal and the area identification signal, which are stored in the memory (not shown) of the control unit 50 and indicate the type of image, and the interpolation calculation processing.

[0075]

[Table 3]

As shown in Table 3, a character document is hardly affected by a ripple error or an interpolation error as a feature of an image. Therefore, when the image mode signal is the character mode or the area identification signal is the character area, the interpolation processing is performed. This enables high-speed processing. In addition, prints often include printed photographs as well as characters.
Therefore, the interpolation calculation takes a little longer than the case where the process without interpolation calculation is selected, but the two-dimensional interpolation process is set as the interpolation method when the image mode signal is the character mode or the region identification signal is the character region. And this
It is possible to efficiently reproduce the color of the printed photo portion included in the text document.

On the other hand, in the case of a photographic paper photographic original, the gradation is particularly important. Therefore, when the image mode signal is a photographic paper photograph mode or the region identification signal is a photograph region (or another region that is neither a character region nor a halftone dot region), a three-dimensional interpolation process excellent in gradation expression is performed even if the conversion speed is low. I do.

The original of a printed photograph (also called a halftone dot photograph) is an image originally expressed in area gradation, and therefore does not include the gradation expression of a photographic paper photograph. Also, even if ripples occur, they are inconspicuous in printed photographs represented by halftone dots. Therefore, when the image mode signal is the print photograph mode or the area identification signal is a halftone area, the interpolation error is small and accurate, the conversion speed is faster than the three-dimensional interpolation processing, and the gradation is better than the processing without interpolation calculation. And a secondary interpolation process.

The digital color copying machine also has a simple (high-speed) mode as one of the image modes input by the image mode setting button. Simple mode is
This mode is selected when it is desired to quickly obtain an image without worrying about the image quality. When the simple mode is set, the control unit 50 selects the process without interpolation calculation as the interpolation method regardless of the area identification signal. As a result, it is possible to respond to a user's request to quickly obtain an image.

The operation of the control unit 50 is controlled by the data separation unit 2, the color correction table access unit 3, and the interpolation operation processing unit 4, which are the CMs constituting the output image data.
The data separation unit 2 includes a cyan data separation unit 2a, a magenta data separation unit 2b, and a yellow data separation unit 2c. The color correction table access unit 3 From the cyan table access unit 3a, the magenta table access unit 3b, and the yellow table access unit 3c, the interpolation calculation processing unit 4
Cyan interpolation calculation processing section 4a, magenta interpolation calculation processing section 4
b and a yellow interpolation operation processing unit 4c.

The cyan data separating unit 2a, cyan table access unit 3a, and cyan interpolation processing unit 4a convert the C image data of the output image data from the RGB image data constituting the input image data. The magenta data separation unit 2b, the magenta table access unit 3b, and the magenta interpolation calculation processing unit 4b convert the M image data from each of the RGB image data into the yellow data separation unit 2c, the yellow table access unit 3c, and the yellow The interpolation operation processing unit 4c obtains Y image data from each of the RGB image data.

The data separation unit 2 converts the RGB signals, which are input image data represented by predetermined bits, into upper N bits serving as address data of an LUT, which will be described later, and an interpolation signal used for an interpolation operation. The data separation process is performed to separate the data into lower-order M bits as the data for use. In accordance with the interpolation calculation process selected by the control unit 50, the separation mode, that is, the numerical values of N and M are switched. Has become.

More specifically, when the process without interpolation calculation is selected, among the RGB image data of the input image data, data of a color having a complementary color relationship with the output image data is compared with other colors. Are also separated so that the number of bits of the upper bit data is increased. That is, in the cyan data separation unit 2a in which the output image data to be obtained is C, the upper N bits of R are separated so that N is larger than that in GB, and similarly, the magenta data whose output image data is M is M In the separation unit 2b, N of the upper N bits of G
In the yellow data separation unit 2c whose output image data is Y, the upper N bits of B are separated so that N becomes larger than that of RG.

Here, the reason why the input image data having a complementary color relationship with the desired output image data is extracted so that N is greater than the N of the other colors is that the color having the complementary color relationship is given to the conversion accuracy. This is because the influence is larger than other colors. By extracting more data of complementary colors than other colors, the color conversion accuracy can be improved even in a process without interpolation.

On the other hand, when the two-dimensional interpolation processing is selected, of the RGB image data, data of a color having a complementary color relationship with the output image data is output as it is without separating the data, and the remaining data is output. Are separated into upper N-bit data and lower M-bit data. That is, the cyan data separation unit 2a outputs R as it is and separates GB into upper N-bit data and lower M-bit data. Similarly, the magenta data separation unit 2
In b, G is output as it is, RB is separated into upper N-bit data and lower M-bit data, and B is output as it is in the yellow data separation unit 2c, and RG is converted into upper N bits.
Bit data and lower M-bit data.

Also in this case, by handling input image data having a relationship of complementary colors, which have a greater effect on conversion accuracy than other colors, without separating them, errors due to interpolation calculations can be avoided as much as possible.

When the three-dimensional interpolation processing is selected,
Regardless of the color of the output image data, each of the cyan, magenta, and yellow data separation units 2a to 2c extracts the upper N bits of the input image data RGB together with the upper N bits of data and the lower M bits of data. To separate.

Table 4 shows an example of data separation in each interpolation operation in the cyan data separation unit 2a when the RGB signals are each 8 bits. Table 4 shows the bit number N of the upper N bits.

[0089]

[Table 4]

In this data separation example, in the case of the process without interpolation calculation, N = N
6, N = 5 for the other two colors. In the two-dimensional interpolation processing, color data having a complementary color relationship is not separated and N = 8, and the other two colors are separated into N = 4 and M = 4. In the three-dimensional interpolation processing, N = 5 and M = 3 are separated for each of yellow, magenta, and cyan.

The upper bit data separated by the data separator 2 is output to the corresponding color correction table access unit 3, and the lower bit data is output to the corresponding interpolation operation processing unit 4.

Here, each of the RGB image data constituting the input image data is 8 bits. However, the present invention is not limited to this, and other bits such as 10 bits may be used. The number M may be arbitrary as long as the above specific conditions are satisfied.

The color correction table access unit 3 stores cyan,
Magenta and yellow color correction table access units 3a to
For each 3c, a plurality of color correction tables corresponding to the type of interpolation processing, here, three types of LUTs for no interpolation processing, two-dimensional interpolation processing, and three-dimensional interpolation processing, One of the tables is selected from among the tables corresponding to the interpolation calculation process selected by the control unit 50.

Each color correction table contains predetermined coordinates (a certain color in CMY) of output image data corresponding to a combination of coordinates (each color of RGB) represented by data of the upper N bits in the input image data. Table values are calculated and stored in advance. The table value of the address corresponding to the data of the upper N bits of the input image data is read from the color correction table and input to the corresponding interpolation operation processing unit 4.

Each color correction table corresponding to the type of the interpolation calculation process is individually created. Among them, for example, a color correction table for two-dimensional interpolation is created corresponding to an input color space as shown in FIG. In the figure, the X-axis, Y-axis, and Z-axis coordinates each correspond to one of the RGB image data, and the coordinates (x, y, z) of one point in the input color space designated by a combination of these. ) Corresponds to one input image data. The input color space is divided into 2 ⁴ = 16 in the directions of the X axis and the Z axis, and the X coordinate and Z coordinate of each grid point correspond to the upper 4 bits of two types of image data. The input color space is divided into 2 ⁸ = 256 in the Y-axis direction, and the Y coordinate of the grid point corresponds to image data represented by 8 bits. Then, the coordinates (x,
y, z) correspond to the address data, and the color correction table stores a table value for each address data.

For example, the color correction table for two-dimensional interpolation provided in the cyan table access unit 3a is (x,
y, z) = (G ′, R, B ′) is created corresponding to the input color space with the coordinates of the grid points, and the image data of C corresponding to each grid point on a one-to-one basis is stored in the table value. Is stored as G 'and B' are the upper N bits of data of G and B separated by the cyan data separation unit 2a. When the coordinates (G ', R, B') of a certain grid point are designated, the cyan table access unit 3a reads out a table value corresponding to this grid point from the C color interpolation table. Here, R is a complementary color of C and, as described above, most affects the conversion accuracy of C to output image data.
Are prepared, and errors due to interpolation calculation described later are avoided as much as possible. As a result, color conversion processing can be performed accurately and efficiently without causing color shift.

The method of creating a color correction table is performed, for example, in the following procedure. 1) The color image forming unit outputs each color patch of CMY. 2) Each output color patch is read from the color image input device to obtain RGB image data. 3) The output CMY values are associated with the read RGB values, and the input / output characteristics of the image forming apparatus, that is, the coefficients between the CMY values and the RGB values are defined by a neural network or a masking operation coefficient determination method.

In the input color space, grid points are provided only for every 16 bits in the input image data in the X-axis direction and the Z-axis direction. The table value corresponding to the address to be specified by the lower 4-bit data is not stored. As described above, the color correction table according to the present embodiment omits the table values corresponding to the lower-order M-bit data for the two types of image data, so that the size is much smaller than the LUT used in the direct conversion method. Become smaller.

[0099] The interpolation operation processing unit 4 is adapted to store the table value input from the color correction table access unit 3 and the data separation unit 2
Based on the input lower-order M-bit data, any one of the interpolation-free processing, the two-dimensional interpolation processing, and the three-dimensional interpolation processing selected by the control unit 50 is performed.
Accordingly, each of the cyan, magenta, and yellow interpolation calculation processing units 4a to 4c stores a function for performing a two-dimensional interpolation calculation and a function for performing a three-dimensional interpolation calculation.

When the process without interpolation calculation is selected, the interpolation calculation processing unit 4
The table value corresponding to the extracted high-order bit data read from the color correction table for no interpolation operation provided in the above is output as it is to the subsequent black generation / under color removal unit 15 and is used for the low-order bit data. No interpolation operation is performed.

On the other hand, when the three-dimensional interpolation processing is selected, the table values read from the three-dimensional interpolation color correction table provided in the color correction table access unit 3 and the input from the data separation unit 2 The above-described three-dimensional interpolation calculation is performed using the three types of lower-order M-bit data.

When the two-dimensional interpolation processing is selected, the table values read from the two-dimensional interpolation color correction table provided in the color correction table access unit 3 and the input values from the data separation unit 2 A two-dimensional interpolation operation is performed using the two types of lower-order M-bit data thus obtained.

That is, in the two-dimensional interpolation operation, in order to obtain output image data corresponding to a point other than a grid point, as shown in FIG. 3, four grid points p _i (i =
Extract a unit square with the vertices of 0, 1, 2, 3)
A two-dimensional interpolation operation is performed using the table value g (p _i ) stored corresponding to each grid point p _i of the unit square.
The position coordinates of a point in the unit square of the arbitrary input image data p are the lower 4 bits of data extracted by the data separation unit 2,
For example, C is determined by the lower bit data of GB. Given the position coordinates, the relative ratio to the grid width in each grid is determined.

As shown in FIG. 3, this relative ratio is calculated by
_A , b (0 ≦
a, when b ≦ 1) that obtains interpolated value g (p) for any input image data p by 4-point interpolation, the table value at the lattice point p _i as g (p _i), the following equation (3) Can be

[0105]

(Equation 5)

The amount of calculation of equation (3) by four-point interpolation is only about one third of the amount of calculation of equation (1) by eight-point interpolation used in the three-dimensional interpolation method. In comparison, the speed of the color conversion processing can be increased.

Finally, the processing procedure of the color correction section 14 will be described with reference to the flowchart of FIG. In the color correction process, first, the control unit 50 selects an interpolation calculation process according to the image mode signal (S1). Next, the data separation unit 2
Is based on the selection result of the interpolation calculation processing in S1, based on the image data of the first color system, that is, here, RG
Each of the image data B is separated into upper N-bit data serving as address data in a form conforming to the interpolation calculation method and lower M-bit data serving as interpolation data (S2).

Next, the color correction table access unit 3
A color correction table corresponding to the selected interpolation calculation process is selected, and a table value is read from the color correction table using the data of the upper N bits as address data (S3).

The interpolation operation processing section 4 performs the interpolation operation selected at S1 using the table value read from the color correction table and the lower M bits of data (S4).
The value obtained by the interpolation operation is output as image data of the second color system (S5). However, if there is no interpolation operation, S1
If S is selected, S4 is omitted, and the table value read out in S3 is output directly as image data of the second color system in S5.

As described above, in the digital color copying machine according to the present embodiment, the control unit 50 specifies the type of the input image, and determines the type of the input image such as a character, a photographic paper photograph, or a print photograph. Since the configuration is such that the data separation unit 2, the color correction table access unit 3, and the interpolation calculation processing unit 4 are controlled to appropriately switch the interpolation calculation process, the interpolation calculation process appropriate for the type of image is selectively performed. Is done.

As a result, it is possible to perform color correction processing in accordance with the characteristics of the input image by utilizing the characteristics of each of the interpolation calculation methods. By applying the image processing method of the present invention to an image forming apparatus, the image quality can be improved. It is possible to obtain a high output image.

[Second Embodiment] The following will describe another embodiment of the present invention with reference to FIG. For convenience of explanation, components having the same functions as those shown in the drawings of Embodiment 1 are given the same reference numerals, and descriptions thereof are omitted.

In a digital color copying machine according to another embodiment of the present invention, black is simultaneously generated at the time of color correction processing, and the color correction unit 1 shown in FIG.
A color correction / black generation unit 55 is provided instead of the color generation unit 4 and the black generation / under color removal unit 15 as shown in FIG.

With such a configuration, black color generation /
Since it is not necessary to separately provide the under color removing unit 15, not only the circuit configuration of the color image processing apparatus 1 can be simplified, but also the black generation processing is performed according to the type of the image. It is possible to further improve the image quality of the output image as compared with a configuration in which the same processing is performed regardless of the type of the output image.

The color correction / black generation unit 55 sends the first color system RGB of the first color system constituting the input image data to the data separation unit 2, the color correction table access unit 3, and the interpolation operation processing unit 4. A black data separation unit 2d, a black table access unit 3d for obtaining black (K) image data among the CMYK image data of the second color system forming the output image data from each image data; And a black interpolation calculation unit 4d.

The control unit 50 also controls the black data separation unit 2d, the black table access unit 3d, and the black interpolation calculation processing unit 4d, which generate the black output image data, for the interpolation calculation processing selected according to the type of image. Is controlled to be performed.

When the process without interpolation calculation is selected, the black data separation unit 2d outputs, for each of the RGB image data as input image data, data of a color having a high contribution rate to a gray component (or a lightness component). Is extracted so that the number of bits of higher-order bit data is larger than that of data of other colors. When the two-dimensional interpolation processing is selected, data of a color having a high contribution to the gray component (or lightness component) is output as it is without being separated.

In general, the contribution rate to the gray component (or lightness component) in each of the RGB image data is represented by G ≧
R ≧ B. Therefore, here, the number of upper bits N to be extracted is increased for the G component in the case of the process without the interpolation operation, and the data is not separated in the case of the two-dimensional interpolation process.

In the case of the three-dimensional interpolation processing, as in the case of the data separation unit 2 for other colors, the same upper N bits are extracted for the input image data RGB, and the upper N bits data and the lower M bits data are extracted. To separate.

Table 5 shows an example of data separation in each interpolation calculation process in the black data separation unit 2d when the RGB signals are each 8 bits. In Table 5, the upper N
The number N of bits is shown.

[0121]

[Table 5]

In this data separation example, in the case of the processing without interpolation calculation, N = 6 for G and N = 5 for the other two colors.
And In the two-dimensional interpolation processing, G is not separated and N = 8, and the other two colors are N = 4 and M =
4 In the three-dimensional interpolation processing, both RGB are N
= 5, M = 3.

The black table access section 3d also includes cyan, magenta and yellow table access sections 3a to 3d.
Similar to 3c, three types of color correction tables are provided for processing without interpolation calculation, for two-dimensional interpolation processing, and for three-dimensional interpolation processing. Select one applicable table. In each color correction table, black image data corresponding to a combination of coordinates (each color of RGB) represented by the upper N bits of the input image data is calculated in advance and stored as a table value.

In the present embodiment, unlike the first embodiment in which the black generation processing for generating black data is performed separately from the color correction processing, the black data is simultaneously generated during the color correction processing. Because it is a generation,
Cyan, magenta, and yellow table access units 3
As the table values of the respective types of color correction tables provided in a to 3c, the values after the undercolor removal is performed (the values obtained by subtracting the black data already) are stored.

The operation of the black interpolation calculation processing section 4d is as follows: each of the cyan, yellow, and magenta interpolation calculation processing sections 4d.
Same as a to 4c.

[Embodiment 3] The following will describe another embodiment of the present invention with reference to FIG. For convenience of explanation, components having the same functions as those shown in the drawings of Embodiment 1 are given the same reference numerals, and descriptions thereof are omitted.

In a digital color copying machine according to another embodiment of the present invention, the color correction section 14 in the color image processing apparatus 1 has a configuration of a color correction section 14 'shown in FIG.

As shown in FIG. 6, the color correction section 14 'provided in the color image processing apparatus 1 of the digital color copying machine according to the present embodiment comprises a color coordinate conversion section 60, a color conversion / data processing section 70. , A data separation unit 2 ', a color correction table access unit 3', and an interpolation processing unit 4 '.

The color coordinate conversion section 60 includes the input gradation correction section 12
The input image data of the RGB signals input from the CIE (Commission Internationale de l'Eclai)
rage: C, a uniform color space defined by the International Commission on Illumination)
IE 1976 L ^* a ^* b ^* color space (CIELAB color space)
It is to be converted to data. In the above L ^* a ^* b ^* , L ^* represents lightness, and a ^* b ^* represents chromaticity.

The color coordinate conversion method is performed according to the following procedure. 1) Measure each color patch of a color chart original with a colorimeter to obtain L ^* a ^* b ^* values. 2) The color chart original used for color measurement is read from a color image input device to obtain RGB values. 3) In order to associate the measured L ^* a ^* b ^* value with the read RGB value, a coefficient between the L ^* a ^* b ^* value and the RGB value is obtained by a neural network or a masking operation coefficient determination method. 4) Perform color coordinate conversion using the coefficients obtained by the above method.
At this time, the circuit configuration may be a masking operation using a matrix, may be an LUT method using a three-dimensional interpolation operation, or may be an LUT method using a two-dimensional interpolation operation. .

The color conversion / data processing unit 70 converts the uniform color space data L ^* a ^* b converted by the color coordinate conversion unit 60.
^* Data processing such as color conversion processing by image editing and brightness / saturation compression by color reproduction area interpolation is performed on ^* .

Each of the cyan, magenta, and yellow data separation units 2a 'to 2c' constituting the data separation unit 2 '
This is to separate the uniform color space data L ^* a ^* b ^* , which is the input image data of the first color system, into upper N bits data and lower M bits data. In the case of the uniform color space data L ^* a ^* b ^* , the brightness data L ^* has a greater effect on the conversion accuracy than the chromaticity data a ^* b ^* . Therefore, if the process without interpolation calculation is selected,
The lightness data L ^* is extracted such that the number N of high-order bits increases. If two-dimensional interpolation processing is selected,
The brightness data L ^{* is} output as it is without performing data separation, and the data a ^* b ^* is separated into upper N-bit data and lower M-bit data.

Table 6 shows an example of data separation in each interpolation operation in the data separation section 2 'when the RGB signals are each 8 bits. Table 6 shows the number N of upper N bits.

[0134]

[Table 6]

In this example of data separation, in the case of the processing without interpolation calculation, N = 6 for the brightness data L ^* and N = 5 for the other two data. In the two-dimensional interpolation processing, the brightness data L ^* is not separated and N = 8, and the other two data are separated into N = 4 and M = 4. In the three-dimensional interpolation processing, N = 5 and M for both L ^* a ^* b ^*
= 3.

Each of the cyan, magenta and yellow table access units 3a 'constituting the table access unit 3'
To 3c ′, for processing without interpolation calculation,
Each of the color correction tables for the two-dimensional interpolation processing and the three-dimensional interpolation processing includes a combination of coordinates represented by upper N bits of input image data represented by uniform color space data L ^* a ^* b ^*. Is stored in a table value of the coordinates of the output image data corresponding to.

Note that the color correction section 14 'is configured to perform black generation / undercolor removal processing after color correction processing. However, similar to the second embodiment, the color correction section 14' is used to obtain black (K) image data. , A black data separation unit 2d, a black table access unit 3d, and a black interpolation calculation unit 4d ′ may be further provided inside the color correction unit 14 ′, thereby achieving the same effect as in the second embodiment. To play.

[0138]

As described above, according to the image processing method of the present invention, the first image data of each coordinate is represented by a predetermined bit.
A color correction process that obtains image data of each coordinate of the second color system from the input image data of the color system and sets the image data as output image data. Is used as address data, using an LUT in which image data at predetermined coordinates of output image data corresponding to the address data is stored as a table value,
For an input image data represented by the address data, a table value is read from the LUT, and for other input image data, an interpolation operation is performed by using the table value read from the LUT. Using an LUT corresponding to a plurality of interpolation calculation methods, the interpolation calculation method is switched according to the type of image, and color correction processing suitable for the type of image is performed.

According to this, an appropriate interpolation operation method can be selectively executed depending on the type of input image such as a character, a photographic paper photograph, or a print photograph. A color correction process according to the characteristics of an image can be performed, and by applying the image processing method of the present invention to an image forming apparatus, an effect of providing an output image with high image quality can be obtained.

In the image processing method of the present invention, it is preferable that the interpolation calculation method includes a method in which the table value read from the LUT is output as it is and the interpolation calculation is not performed. For an image in which the image quality does not matter even without performing the above, it is possible to process at a higher speed.

In the image processing method of the present invention, a three-dimensional interpolation method is used when the image is a photographic paper photograph, and a two-dimensional interpolation method is used when the image is a printed photograph. In some cases, it is preferable to use a method that does not perform an interpolation operation that outputs a table value as it is. By applying the image processing method of the present invention to an image forming apparatus, a photographic paper photo document has excellent gradation. It is possible to obtain high-quality output images at high processing speed for high-quality output images with good gradation characteristics in printed photo originals, and extremely high-speed output images for character originals with no problem in image quality. This has the effect of being possible.

As described above, the image processing apparatus according to the present invention converts the input image data of each coordinate in the second color system from the input image data of the first color system in which the image data of each coordinate is represented by predetermined bits. In an image processing apparatus having a color correction means for obtaining image data of a first color system and using the same as output image data, the color correction means converts the input image data of the first color system into a plurality of forms in the form of address data and interpolation data. And a data separating unit that separates according to each of the interpolation calculation processes, and a combination of the image data of each coordinate in the selected part of the input image data is set as the address data, and each of the output image data corresponding to the address data is output. An LUT in which image data of coordinates is stored as a table value is provided for each interpolation calculation process, and an address separated by the data separation unit is used by using one of the LUTs. A plurality of color correction table access means for reading table values corresponding to data, and a plurality of table values read from the LUT by the color correction table access means and interpolation data separated by the data separation means. An interpolation calculation unit for performing any one of the interpolation calculation processes; and a data separation unit, a color correction table access unit, and an interpolation unit for determining an image type and performing an interpolation calculation process suitable for the image type. And control means for controlling the arithmetic processing means.

As a result, the color correction processing according to the characteristics of the input image is performed. As a result, by providing such an image processing apparatus in the image forming apparatus, an output image with high image quality utilizing the characteristics of the image can be obtained. Can be provided.

Further, in the above-described image processing apparatus of the present invention, the interpolation calculation processing performed by the interpolation calculation processing means does not include the interpolation calculation for directly outputting the table value read from the LUT without performing the interpolation calculation. It is preferable to adopt a configuration that includes a process, which also has the effect of enabling a higher-speed processing of an image output that does not cause degradation in image quality without performing an interpolation operation.

Further, in the above-described image processing apparatus of the present invention, the interpolation calculation processing means performs no interpolation calculation processing for directly outputting the table value, and performs three-dimensional interpolation using the table value and the interpolation data. It is possible to perform two-dimensional interpolation processing for performing two-dimensional interpolation using table values and interpolation data, and the control means selects the three-dimensional interpolation processing when the image is a photographic paper photograph. It is more preferable that the two-dimensional interpolation processing is selected when the image is a printed photograph, and the processing without interpolation calculation is selected when the image is a character or a line drawing.

By applying this image processing apparatus to an image forming apparatus, a high-quality output image with excellent gradation can be obtained for a photographic paper photographic original, and a high-quality output image can be obtained for a print photographic original. In addition, it is possible to obtain an output image having no problem in image quality at a very high speed, and an output image having no problem in image quality can be obtained at a very high speed.

Further, in the above-described image processing apparatus of the present invention, a simple mode regardless of the image quality is provided. When the simple mode is set, the control means selects the processing without interpolation calculation regardless of the type of the image. Can be configured to
According to this, by providing the image processing apparatus in the image forming apparatus, it is possible to respond to a user's request to quickly obtain an output image regardless of the image quality.

In the above-described image processing apparatus of the present invention, the color correction means converts the input image data of the first color system into output image data of the second color system including black. It is also possible to adopt a configuration in which
Since the black generation processing can be performed according to the type of the input image, the image quality of the output image is further improved as compared with a configuration in which the black generation processing is performed by the same processing regardless of the type of the image. It also has the effect that can be done.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a color correction unit in a color image processing apparatus provided in a digital color copying machine according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of the color image processing apparatus.

FIG. 3 is an explanatory diagram showing a two-dimensional interpolation calculation method performed by the color correction unit.

FIG. 4 is a flowchart illustrating a color correction processing procedure performed by the color correction unit.

FIG. 5 is a block diagram illustrating a configuration of a color correction unit in a color image processing apparatus provided in a digital color copying machine according to another embodiment of the present invention.

FIG. 6 is a block diagram illustrating a configuration of a color correction unit in a color image processing apparatus provided in a digital color copying machine according to another embodiment of the present invention.

FIG. 7 is an explanatory diagram illustrating a conventional three-dimensional interpolation calculation method performed by a color correction unit.

[Explanation of symbols]

Reference Signs List 1 color image processing device (image processing device) 2 data separation unit (data separation unit) 2 'data separation unit (data separation unit) 3 color correction table access unit (color correction table access unit) 3' color correction table access unit ( Color correction table access means) 4 Interpolation processing unit (Interpolation processing unit) 14 Color correction unit (Color correction unit) 14 'Color correction unit (Color correction unit) 50 Control unit (Control unit) 55 Color correction / black generation unit (Color correction means)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C262 AA24 AA26 AC02 AC04 BA02 BC01 BC15 BC19 EA04 EA06 FA13 5B021 AA02 BB01 BB04 BB10 CC05 LG07 5B057 AA11 CA01 CB01 CE17 5C077 LL18 LL19 MP08 PP27 PP28 PP32 PP33 P36 PQ23 RR19 SS06 5C079 HB03 LA28 LA31 LB02 MA04 MA11 NA03 NA11 PA02

Claims (9)

[Claims] An image data of each coordinate of a second color system is obtained from input image data of a first color system in which image data of each coordinate is represented by predetermined bits, and a color as output image data is obtained. Correction processing is performed by using a combination of image data of each coordinate in the selected partial input image data as address data, and an LUT in which image data of predetermined coordinates of output image data corresponding to the address data is stored as a table value.
Image processing is performed by reading a table value from the LUT for input image data represented by the address data and performing an interpolation operation using the table values read from the LUT for other input image data. An image processing method, comprising: using an LUT corresponding to a plurality of interpolation calculation methods, switching an interpolation calculation method according to the type of image, and performing color correction processing suitable for the type of image. 2. The image processing method according to claim 1, wherein said interpolation calculation method includes a method of directly outputting a table value read from an LUT and performing no interpolation calculation. 3. As the interpolation operation method, a three-dimensional interpolation method is used when the image is a photographic paper photograph, a two-dimensional interpolation method is used when the image is a print photograph, and when the image is a character or a line drawing. 3. An image processing method according to claim 2, wherein a method of performing no interpolation operation for directly outputting a table value is used. 4. A color used as output image data by obtaining image data of each coordinate of a second color system from input image data of a first color system in which image data of each coordinate is represented by predetermined bits. In the image processing apparatus having a correction unit, the color correction unit converts input image data of a first color system into
In the form of address data and interpolation data, a data separating means for separating according to each of a plurality of interpolation arithmetic processes, and a combination of image data of each coordinate in selected selected input image data is set as the address data. A LUT in which the image data of each coordinate of the output image data corresponding to the address data is stored as a table value for each of the interpolation calculation processes, and one of the LUTs is used for separation by the data separation means. A color correction table access means for reading a table value corresponding to the address data obtained, and a table value read from the LUT by the color correction table access means and interpolation data separated by the data separation means, An interpolation operation processing means for performing any one of a plurality of interpolation operation processes; In order to implement the interpolation calculation processing suitable to the class, the image processing apparatus, characterized in that it comprises the data separation means, color correction table access means, and a control means for controlling the interpolation arithmetic processing means. 5. An interpolation calculation process performed by said interpolation calculation processing means includes a process without interpolation calculation for directly outputting a table value read from an LUT without performing an interpolation calculation. The image processing device according to claim 4. 6. An interpolation operation processing means comprising: an interpolation operation-free process for directly outputting a table value; a three-dimensional interpolation process for performing three-dimensional interpolation using a table value and interpolation data; And two-dimensional interpolation processing for performing two-dimensional interpolation using data. The control means selects the three-dimensional interpolation processing when the image is a photographic paper photograph, and selects the three-dimensional interpolation processing when the image is a print photograph. 6. The image processing apparatus according to claim 5, wherein a two-dimensional interpolation process is selected, and a process without interpolation calculation is selected when the image is a character or a line drawing. 7. A simple mode irrespective of image quality is provided, and said control means, when said simple mode is set, selects processing without interpolation calculation irrespective of the type of image. Item 7. The image processing device according to item 5 or 6. 8. The image processing apparatus according to claim 4, wherein said color correction means converts input image data having a first color system into output image data having a second color system including black. 7
The image processing apparatus according to claim 1. 9. An image forming apparatus comprising the image processing apparatus according to claim 4. Description: