JP2004007274A - Gradation conversion device and color conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gradation conversion device and a color conversion device capable of storing correction data with small memory capacity by reducing color conversion characteristic data for performing color matching of a plurality of printer heads and correction data for color correction of a projector, and more reducing correction data for gradation conversion processing such as γ correction especially. <P>SOLUTION: By performing compression of the gradation conversion characteristics or the color conversion characteristics of respective areas or respective pixels of an image output device such as a projector and a printer by a principal component analysis method, correction data for gradation conversion or color conversion can be stored with small memory capacity and gradation conversion or color conversion can be performed almost equivalently to the case of no compression. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gradation conversion device and a color conversion device for converting a gradation or color signal in a digital color copying machine, a color printer, a projector, and the like.
[0002]
[Prior art]
In recent years, media handling color images have been developed in various forms. For example, a system is known in which characters and images are read by a color scanner, edited and processed on a computer display, and the result is printed out by a color printer or the like.
[0003]
However, in this case, the color reproduced on the display and the color printed out may differ from each other due to differences in color reproduction methods, color mixing systems (RGB, CMY), and inconsistencies in the color reproduction range (gamut). Is also well known.
[0004]
In particular, in an output device such as a printer, a method of driving a plurality of heads in parallel in order to increase the printing speed is employed. In consideration of the output characteristics of the plurality of heads, a plurality of color conversion characteristics (color profile ), A method of taking the color matching with all the heads is considered.
[0005]
On the other hand, a display system using a plurality of projectors has also been developed. In this system, as in Japanese Patent Application Laid-Open No. 2000-253263, the projected images of the projectors are overlapped with each other, and color correction is performed so that images of a plurality of projectors are connected.
[0006]
[Problems to be solved by the invention]
However, when the number of the plurality of heads is increased in the case of a printer, the throughput (efficiency) of the printer is improved, but a large amount of data of color conversion characteristics (color profile) is provided so that all of the heads are used. I had to do color matching. For this reason, there is a problem that a large amount of memory must be mounted.
[0007]
In particular, in a system aimed at high-speed printing, a plurality of printer heads are arranged in the sub-scanning direction (paper transport direction) as shown in FIG. 17 and printing is performed. It causes unevenness.
[0008]
For example, the example of FIG. 17 shows that the arrangement of the heads of the four colors CMYK (cyan, magenta, yellow, and black) is different only for the C (cyan) head. In this case, as shown in FIG. 18, the printing result of the KMY head is printed at the same position, but only the C head is printed at a different position. That is, FIG. 18 shows that the left side of the head coincides with the left side, but the color becomes larger as it goes to the right side of the head, and color unevenness occurs in the head.
[0009]
Normally, a color profile is used for color processing in a color printer system. This is based on the premise that the head is properly positioned and all dots to be printed are printed at the same position. The color profile contains information on what colors are output from the respective color printers. The color profile can be set by a function of a color management system (CMS) of an operating system (OS). It has become.
[0010]
In the case as shown in FIG. 18, the overlap of the print dots of each color is different within the print width of the head, and since the characteristics of the print colors are different between the print dots within the print width of one head, the color profile is switched within the head. Such processing is required. For example, if the color profile is switched for each dot or minute area, good printing is expected without color unevenness, but the data amount of the color profile becomes enormous.
[0011]
In order to realize a processing function using a color profile, a CMYK conversion matrix and a γ correction unit may be used as shown in FIG. 19, or a CMYK conversion table may be used only as shown in FIG.
[0012]
In FIG. 19, the RGB input data corresponding to each dot is converted into C, M, Y, and K of the printing color by a color profile corresponding to each dot, that is, a CMYK conversion matrix, and then is converted to each dot. Γ correction is performed and output to the corresponding print head for printing. When the density characteristics are different in addition to the difference in the color characteristics of each dot, the γ correction of FIG. 19 is necessary. However, when there is no difference in the density characteristics of each dot, the RGB input data is changed as shown in FIG. This is a processing procedure in which only CMYK data is converted by the CMYK conversion table.
[0013]
On the other hand, in a display system using a projector, as shown in FIG. 21, color correction of RGB data by a single projector is performed by matrix correction and γ correction for each color of RGB. The gamma characteristic of the projector is almost uniform in the screen in a DLP projector (DLP is an abbreviation for Digital Light Processing), but the variation in the screen is 10% in an LCD projector (LCD is an abbreviation for Liquid Crystal Display). Must be adaptively performed in the image, in which case the gamma correction unit becomes enormous.
[0014]
Japanese Unexamined Patent Application Publication No. 2001-215542 discloses a technique for performing high-definition display using a plurality of projectors 10r and 10s as shown in FIG. In order to suppress the light amount, a light shielding plate is used as the light amount limiting unit 30. Since the light-shielding plate blocks the light beam, in the case of an LCD projector, the γ characteristic changes abruptly in the light-shielded portion (region A in FIG. 22). In order to cope with this change, it is necessary to change the γ characteristic to be corrected for each pixel or for each minute area, and the γ correction calculation is also enormous.
[0015]
In view of the above situation, the present invention reduces data of color conversion characteristics for performing color matching of a plurality of printer heads and correction data at the time of color correction of a projector. It is an object of the present invention to provide a gradation conversion device and a color conversion device which can reduce the amount of correction data and store the correction data with a small memory capacity.
[0016]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a gradation conversion device for converting a gradation of an input image signal in accordance with a gradation conversion characteristic of an output device for displaying or printing an image signal. For the gradation conversion characteristics, an average characteristic of the gradation conversion characteristics in a plurality of regions or pixels, and a principal component signal of an appropriate order for the difference characteristic between the average characteristics and the gradation conversion characteristics in each region or pixel are stored. Means for storing the coefficients of the principal components corresponding to the respective regions or pixels, and performing a linear combination of the principal component signals and the coefficients of the principal components on the image input signals of the respective regions or pixels. Means for expressing tone conversion characteristics.
[0017]
In the gradation conversion apparatus according to the first aspect of the present invention, there is provided a means for changing the quantization bit width according to the contribution ratio of each signal when the average characteristic and the main component signal are quantized and stored. , Is preferably stored.
[0018]
According to a second aspect of the present invention, a multi-band input color image signal is converted into a device independent color space such as CIE-XYZ or L * a * b *, and then a plurality of regions or pixels of an output device are converted. In a color conversion device that converts a color profile in accordance with the color output characteristics of an image, an average characteristic of color profile conversion characteristics of a plurality of regions or pixels, and a difference between the average characteristic and a color profile conversion characteristic of each region or pixel. Means for storing a principal component signal of an order suitable for the characteristic, means for storing the coefficients of the principal components corresponding to each region or pixel, and device-dependent color signals to be output in each region or pixel. Means for expressing a color profile conversion characteristic by a linear combination of the principal component signal and the coefficient of the principal component. It is characterized in.
[0019]
In the color conversion device according to the second invention, when the above-described average characteristic and the main component signal are quantized and stored, the color conversion device includes means for changing a quantization bit width according to a contribution ratio of each signal. Preferably, it is stored.
[0020]
According to a third aspect of the present invention, there is provided a tone conversion device for converting a tone of an input image signal in accordance with a tone conversion characteristic of an output device for displaying or printing an image signal. With respect to the gradation conversion characteristics, an average characteristic of the gradation conversion characteristics in a plurality of regions or pixels, a principal component signal of an appropriate order with respect to the average characteristic and a difference characteristic of the gradation conversion characteristics in each region or pixel, Means for calculating the coefficient of the principal component signal in each region or pixel, further performing clustering based on the distribution of the coefficient in the coefficient space of the principal component, and calculating a sample coefficient or coefficient vector; Means for calculating a curve of a sample gradation conversion characteristic from a principal component of a difference characteristic and a coefficient or a coefficient vector to be a sample; Means for associating the set of samples with the coefficients to be sampled, and means for creating a look-up table for linking the coefficients of the principal components in the region or pixel to the gradation conversion characteristics to be sampled. The gradation conversion is performed by storing a tone conversion characteristic curve and a look-up table corresponding to each area or pixel.
[0021]
According to a fourth aspect of the present invention, a multiband input color image signal is converted into a device independent color space such as CIE-XYZ or L * a * b *, and then a plurality of regions or pixels of an output device are converted. In accordance with the color output characteristics, in a color conversion device that performs color profile conversion, based on the color output characteristics of a plurality of regions or a plurality of pixels of the output device, extract only the overlapping regions of the created gamut mapping, Means for calculating a principal component signal of an appropriate order with respect to the average characteristic and the difference characteristic of the color profile conversion characteristic in each region with respect to the color profile conversion characteristics of the plurality of regions, Means for storing coefficients of main components corresponding to regions or pixels, and a color profile conversion function corresponding to each region or pixel of the output device. Characterized in that it includes a means of expressing the principal component coefficients of the differential characteristic.
[0022]
In the fourth aspect, based on the color output characteristics of the plurality of regions or the plurality of pixels of the output device, the created gamut mapping overlapping region and the non-overlapping region are divided into overlapping regions. On the other hand, the coefficients are stored as the principal components, and for the non-overlapping area, the conversion characteristics of the individual color profiles are stored, and the color profile conversion characteristics corresponding to a plurality of regions or a plurality of pixels of the output device, It is preferable that the apparatus further comprises means for generating by combining the coefficient of the main component of the overlapping area and the color profile conversion characteristic of the non-overlapping area.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
FIGS. 1 to 5 relate to a gradation conversion apparatus according to a first embodiment of the present invention. FIG. 1 shows the configuration of the gradation conversion device. This embodiment shows an application to a projector as an example.
[0024]
The projector has different gradation conversion characteristics (generally called γ characteristics) at each position in the screen. Here, each position specifically means a plurality of regions or pixels constituting a screen. Since the γ characteristics are different at each position in the screen, increasing the luminance causes color unevenness in the plane. In order to eliminate the color unevenness, tone conversion (inverse γ correction calculation) is performed on the input signal at each position in the screen of the projector so as to cancel the γ characteristic of the projector itself. In the present embodiment, the inverse γ correction calculation is performed with a small memory capacity.
[0025]
The input image signal 101 generated by the image signal generation unit 101 is subjected to level conversion of the average characteristic of inverse γ in a plurality of regions or pixels by the first level conversion unit 102, while the second level conversion is performed. The means 103-1, 103-2,... 103-N perform level conversion based on the main components of the above average characteristic and the inverse γ difference characteristic in each area or pixel. Note that 256 Byte * N in FIG. 1 represents the data capacity. When the main component is represented by 256 1-byte integers, it is necessary to record N data of 256 bytes in total up to the Nth component. Is shown.
[0026]
On the other hand, the memory means stores a table 105 in which the addresses of the respective regions or pixels generated by the address generation unit 104 are provided with coefficients a1, a2,... AN of the main components of the respective regions or pixels. deep.
[0027]
.. 103-N in the second level conversion means 103-1, 103-2,..., 103-N. , 106-N are multiplied by the main component coefficients a1, a2,... AN for each area or pixel stored in the table 105. Note that N is the number of main components.
[0028]
The multiplication results by the multipliers 106-1, 106-2,..., 106-N are added to the sum of the principal components in an adder 107, and the sum of the sum is compared with the average characteristic from the first level conversion means 102. The sum is taken by the adder 108 and output as a signal value S subjected to gradation conversion.
[0029]
Next, a method of calculating the main components of the average characteristic of inverse γ in the first level converting means and the difference characteristic of inverse γ in the second level converting means in the first embodiment will be described. In other words, for the gradation conversion characteristics of a plurality of regions or pixels, the average characteristic of the gradation conversion characteristics of the plurality of regions or pixels and the difference between this average characteristic and the gradation conversion characteristics of each region or pixel. An appropriate order principal component signal for the characteristic is obtained.
[0030]
As shown in FIG. 2, the gradation conversion characteristics (γ characteristics) previously measured and obtained for each region or pixel are defined as γa, γb,. Conventionally, the γ characteristic is discretely determined, and the intermediate point is complementarily determined by a method such as bilinear interpolation. Even if this method is used, curves as many as the number of grid points must be stored. On the other hand, in the first embodiment, first, the average characteristics of the γ characteristics of all the regions or pixels are calculated (see FIG. 3A), and the γ characteristics of each region a, b,. Principal component analysis of the difference characteristic between the characteristic and the average characteristic is performed (see FIG. 3B).
[0031]
Regarding the difference characteristics, each region or pixel is regarded as the number of trials, a covariance matrix is obtained, and orthonormal transform is performed on the matrix. The principal component and the respective difference characteristics obtained in this way are regarded as coefficient vectors, and their inner products are defined as the principal component coefficients a1, a2,... AN in each region or pixel.
[0032]
Performing principal component analysis on the difference signal has two effects. One is that each γ characteristic can be divided into a contribution of an average characteristic and a contribution of a main component, and therefore the bit width of quantization can be changed according to their contribution ratio. Therefore, when the average characteristic and the main component signal are quantized and stored, means for changing the bit width of quantization is provided according to the contribution ratio of each signal, and the storage capacity can be reduced by storing in the memory. For example, when the luminance signal is represented by 256 gradations, when the contribution ratio of the first principal component to the original signal is about 10% with respect to the average characteristic, the average characteristic is represented by 8 bits. The first principal component may be 5 bits, and the contribution rate of a higher-order principal component decreases, so that the bit width of the register as the storage means may be changed accordingly. Another reason is that, when calculating the eigenvector from the covariance matrix, an error can be eliminated even if a rank drop occurs, by devising an orthogonal transformation calculation.
[0033]
In this way, the principal components of the average characteristic of inverse γ and the differential characteristic of inverse γ are calculated and stored, and the γ characteristic of each region or pixel is represented by a linear combination of them as shown in FIG. What is necessary is just to calculate | require the coefficient of each principal component about each area | region or a pixel. The order of the main component to be stored is evaluated based on the error between the γ characteristic that can be restored and the actual characteristic, and the order until an error that does not cause a problem in practice is adopted.
[0034]
In the first embodiment, in order to perform the gradation conversion for canceling the γ characteristic of each area or pixel in the input image signal, what is actually stored in the memory means is the inverse conversion characteristic of the average γ characteristic, This is the inverse conversion characteristic of the main component of the difference signal. As a result, there is an advantage that the memory capacity required for the correction can be reduced.
[0035]
FIG. 5 is a modified example of the embodiment of FIG. In FIG. 5, a signal obtained by multiplying the image signal by the average characteristic of inverse γ by the first level converting means 102 in FIG. 1 is input to the adder 108, while the second level converting means 103-1 ', 103- .. 103-N ', and the main components constituting the second level converting means 103-1', 103-2 ',... 103-N' are stored accordingly. Each register stores a value obtained by level-converting the main component of the inverse γ difference characteristic with the average γ characteristic. With such a configuration, the same operation and effect as those in FIG. 1 can be obtained. Note that (principal component of inverse γ difference characteristic) * (average γ characteristic) in FIG. 5 represents a product when each characteristic curve can be represented by a vector (array of numbers). This product indicates the product for each element of the vector. That is, the product of the k-th component of the inverse γ characteristic and the k-th value of the average γ characteristic is used as the k-th value of the output characteristic.
[0036]
[Second embodiment]
6 to 11 relate to a color conversion device according to a second embodiment of the present invention. This embodiment shows an application to a color printer as an example.
[0037]
In an output device such as a conventional color printer, it is necessary to cancel a difference in color conversion characteristics of each printer head when a multi-head using a plurality of printer heads is used. As shown in FIG. 6A, for the colors Xi, Yi, Zi indicating a certain value in the device-independent XYZ color space, signals for controlling the first printer head (1) are represented by C, M. , Y, K. In the second separate head (2), it is assumed that the control signals must be C ', M', Y ', and K' for Xi, Yi, and Zi as shown in FIG. 6B. In order to unify these colors, it is necessary to have a color management table for performing color conversion for each head. Therefore, in the color printer, as shown in FIG. 7, the color signal generated by the color signal generating means 121 is decomposed into a plurality of signals by the distributor 122, and the conversion table (1, 2,... .., N), the number of conversion tables increases as the number of heads increases, and a large amount of memory is required. In the case of color profile conversion, the table is such that four variables (CMYK) are given to a three-dimensional argument (RGB).
[0038]
Therefore, in the second embodiment, the average characteristics of the color profiles of all the heads are obtained in the same manner as in the principal component analysis method described in the first embodiment with reference to FIGS. In the second embodiment, the color conversion characteristics of each print head are adjusted instead of the γ characteristics. For example, first, an average characteristic for each printer head area or pixel is obtained for each of the CMYK ink colors using arithmetic averaging. Next, an average color profile difference characteristic is obtained for each head. Principal component analysis is performed on the difference characteristics of each head. Next, the coefficient of the principal component is calculated from the difference characteristic of each head and the inner product of the principal component.
[0039]
The average color profile obtained in this way and the main components of the difference characteristics are stored. Regarding the order of the principal components to be adopted, the error is evaluated and performed in the same manner as described above.
[0040]
8 and 9 show the configuration of the color conversion device according to the second embodiment.
FIG. 8 is a configuration showing one output characteristic of CMYK. FIG. 9 shows a configuration in which these characteristics are assigned to each color of CMYK. In FIG. 9, a color conversion device that receives a color signal (XYZ) from the color signal generation unit 201 and converts a color profile is configured by four bands of CMYK (indicated by reference numerals 200-1 to 200-4). ) And four CMYK ink heads (indicated by reference numerals 203-1 to 203-4) of the printer head.
[0041]
In FIG. 8, the coefficients a1, a2,... AN of the principal components obtained by the above-described method are stored in the memory means as the table 204 for each head (for example, the head 203-1). In this case, there is a table for only the order of the necessary principal components for each of the CMYK signals. .., 202-N having first, second,..., N-th principal components relating to the difference characteristics, the difference color component is obtained. Multiplied by the coefficients a1, a2,... AN of the assigned main components of the corresponding colors in the multipliers 205-1, 205-2,. Then, the sum of signals obtained by multiplying the main components of the difference characteristics by the coefficients a1, a2,... AN from the output characteristic signals of the individual heads is obtained by an adder 206. A signal value S subjected to color conversion by adding to the color profile is obtained. In general, a printer head uses CMYK as an ink color, and additive / subtractive color mixing is not established. Therefore, all combinations of color signals must have characteristics of each color of the head.
[0042]
In a multi-head printer, data compression of a plurality of gamut mappings is performed based on the result of colorimetry according to the procedure shown in FIGS. This will be described with reference to FIGS.
[0043]
In FIG. 10, for example, ink ejection is controlled for each printer head by a predetermined control signal as shown in FIG. 10A, and the ejection result is measured by a colorimeter as XYZ as shown in FIG. Measure by color. An inverse conversion of this relationship is performed, and a table is created as shown in FIG. 10 (c) that allows the ink ejection amount to be obtained from the XYZ color space. If this operation is performed for a plurality of heads, a problem arises in that the gamut boundaries do not match. As a result, colors that cannot be expressed appear as the saturation or luminance approaches the periphery of the gamut mapping. Therefore, as shown in FIG. 11, only the area where the gamut mapping overlaps is extracted, and the color profile conversion characteristic of a plurality of areas is compared with the average characteristic and the color profile in each area. By calculating a principal component signal of an appropriate order with respect to the difference characteristic of the conversion characteristic, the color profile corresponding to each region or each pixel of the output device is stored as a coefficient of the main component. That is, for the overlapped area, compression by the principal component is performed. Further, with respect to a region having no overlap, the conversion characteristic of the color profile for each region or pixel is stored in a non-compressed state. The coefficients of the main components and the uncompressed color conversion characteristics obtained in this way are combined and stored, and are used as color profile conversion characteristics corresponding to a plurality of regions or pixels of the output device.
[0044]
In the second embodiment, the description has been made on the assumption that the colors are different between the heads. However, in the case shown in FIG. 17, the colors may be different even in the head. Of course, this embodiment can be applied.
[0045]
The first and second embodiments described above have the advantage of reducing the amount of data to be stored, but have the disadvantage of requiring a multiplier and having a heavy computational load. Therefore, in the following third embodiment, a method for making the calculation extremely light will be described.
[0046]
[Third Embodiment]
FIGS. 12 and 13 relate to a tone conversion device according to a third embodiment of the present invention.
[0047]
As a method for making the calculation lighter, a γ characteristic to be corrected is calculated in advance, and a method of simply selecting the γ characteristic is used. However, “samples that fall within a predetermined error can be obtained by dividing the level of 0 to 255 into N pieces with respect to the 8-bit input signal of the γ characteristic curve, and expanding the level into an N-dimensional coefficient space to perform clustering. 12, a method of performing principal component analysis in advance and expanding the characteristic curve of each sample in the coefficient space of the principal component as shown in FIG. Is good. At this time, the principal component analysis may be performed after separating into the average characteristic and the difference characteristic in consideration of the calculation accuracy as described above.
[0048]
First, as shown in FIG. 12, clustering is performed in the principal component coefficient space to obtain a sample value of the principal component coefficient, and a γ characteristic curve to be a sample is obtained from the sample value. At this time, the error is evaluated from the size of the cluster, and clustering is performed so as to be within an error that does not cause a problem in practical use.
[0049]
In the ellipse shown in FIG. 12, each point * contained therein is an N-dimensional value having the values of the coefficients (1 to N) of the principal components, and each point is classified into a cluster (ellipse). The value represents the characteristic of each point included in the cluster. That is, when such clustering is not performed, the characteristics of each point * must be stored. However, by performing clustering, only the cluster to which each point * belongs is stored. Good, saves memory space. The representative value of each cluster is called a “sample”.
[0050]
Since a set of coefficients constituting each cluster is associated with a sample coefficient, it is possible to create a look-up table that associates a coefficient of a main component in a certain region or pixel with a gradation conversion characteristic as a sample.
[0051]
Then, the above-mentioned sample gradation conversion characteristic curve and the look-up table corresponding to each region or pixel are stored in the memory unit, and gradation conversion is performed.
[0052]
FIG. 13 shows the configuration of the gradation conversion device of the third embodiment described above. .., 4013-N storing N γ characteristics, and a block-corresponding γ table number memory 4003 storing a table linking the coefficients of the principal components in the region or pixel and the γ characteristics to be sampled. , And the selection circuit 402, and does not require the arithmetic circuit as in the first and second embodiments. The γ characteristics stored in the first to Nth γ conversion units 401-1 to 4013-N are the γ characteristics of the sample obtained by the above-described clustering. The table stored in the block correspondence γ table number memory 4003 is a look-up table in which the coefficients of the principal components of a certain specified region or pixel correspond to the γ characteristics of a sample that is a cluster. The selection circuit 402 selects which γ characteristic curve to use based on the look-up table, and the selection circuit 402 outputs the signal value S as a gradation-converted signal value.
[0053]
[Fourth Embodiment]
FIGS. 14 to 16 relate to a color conversion apparatus according to a fourth embodiment of the present invention.
[0054]
In the fourth embodiment, creation of a color profile when the present invention is applied to a printer will be described. As shown in FIG. 18, when the CMYK head is misaligned, the color profile should be measured optimally for each nozzle of the head. However, since the number of processing steps becomes enormous, the profile is measured for each predetermined area. It is realistic to measure.
[0055]
As shown in FIG. 14, for example, it is effective in terms of processing man-hours to measure a color profile corresponding to an area of about 1/5 to 1/10 of the print width of the head. Then, a color patch is printed corresponding to each area as shown in FIG. The number of patches depends on the profile creation method, but if CMYK is divided into eight stages, then 8 * 8 * 8 * 8 = 4096 patches. The hatched portion in FIG. 14 indicates that there are 4096 patches. The printed patch is photographed by a camera, a chromaticity meter, or the like, and a gradation method for correcting each color is calculated using a conventional method.
[0056]
Further, as a modified example, a case where the system is used in a system in which a plurality of monochromatic heads are arranged as shown in FIG. This system has the advantage that high-speed printing is possible because it can print an area larger than a single head. However, since the color changes sharply near the joint of the head, the color patch for color profile measurement proposed in FIG. 14 is made finer near the joint of the head as shown in FIG. By making the color profile measurement patch fine near the joint of the head, it is possible to measure the color profile with high accuracy without increasing the number of patches. In the case where three or more heads are connected, the fineness of the overlap portion may be changed according to the magnitude of the positional shift of the head.
[0057]
Note that a multi-spectral scanner as disclosed in Japanese Patent Application Laid-Open No. 2000-168109 may be used for capturing the printed patch.
[0058]
In the embodiment described above, the CIE-XYZ color system has been described as a device-independent color space. However, in the present invention, a CIE-L * a * b * table is used as a device-independent color space. It may be a color system.
[0059]
【The invention's effect】
As described above, according to the present invention, tone conversion characteristics and color conversion characteristics of a plurality of regions or pixels of an output device such as a projector or a printer are approximated by a linear combination of a main component of an average characteristic and a difference characteristic. With such a representation, a large amount of conversion characteristic data can be compressed, and the luminance and color can be corrected over the entire output range of the output device with a small storage capacity. This also leads to cost reduction and downsizing of the output device.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a gradation conversion device according to a first embodiment of the present invention.
FIG. 2 is a diagram for describing a method of calculating principal components of an average characteristic of inverse γ in a first level conversion unit and a difference characteristic of inverse γ in a second level conversion unit in the first embodiment. .
FIG. 3 is a diagram illustrating a method of calculating principal components of an average characteristic of inverse γ in a first level conversion unit and a difference characteristic of inverse γ in a second level conversion unit according to the first embodiment; .
FIG. 4 is a diagram for expressing a γ characteristic of each region or pixel by a linear combination of these.
FIG. 5 is a block diagram showing a configuration of a gradation conversion device according to a modification of the first embodiment of the present invention.
FIG. 6 is a view for explaining a problem of color conversion in a conventional color printer having a plurality of printer heads.
FIG. 7 is a block diagram showing a configuration of a conventional color printer having a plurality of printer heads.
FIG. 8 is a block diagram showing a configuration of a color conversion apparatus according to a second embodiment of the present invention (a configuration showing one output characteristic of CMYK).
FIG. 9 is a block diagram illustrating a configuration of a color conversion apparatus according to a second embodiment of the present invention (a configuration in which FIG. 8 is assigned to each of CMYK colors).
FIG. 10 is a view for explaining a procedure for performing gamut mapping (color gamut compression) from colorimetric results in a multi-head color printer.
FIG. 11 is a view for explaining a procedure for performing gamut mapping (color gamut compression) from a result of color measurement in a multi-head color printer.
FIG. 12 is a view for explaining a method of performing a principal component analysis in advance and expanding a characteristic curve of each sample in a coefficient space of a principal component according to the tone conversion device of the third embodiment of the present invention.
FIG. 13 is a block diagram showing a configuration of a tone conversion device according to a third embodiment of the present invention.
FIG. 14 is a diagram illustrating a color profile measurement patch when a color profile is created in a color printer.
FIG. 15 is a diagram showing a system in which a plurality of monochromatic heads are arranged.
FIG. 16 is a diagram showing color patches for measuring a color profile when a color profile is created in a color printer having the system of FIG. 15;
FIG. 17 is a diagram showing a state in which a C head among multiheads used in a color printer is mounted with a positional shift;
FIG. 18 is a view showing a printing result of FIG. 17;
FIG. 19 is a block diagram showing a color conversion device in a conventional color printer.
FIG. 20 is a block diagram showing another conventional conversion device.
FIG. 21 is a block diagram showing a color conversion device in a conventional display system using a single projector.
FIG. 22 is a view for explaining a problem when performing gradation correction in a conventional display system using a plurality of projectors.
[Explanation of symbols]
102 first level conversion means (level conversion of average characteristics of γ)
103-1, 103-2,... 103-N Second level conversion means (level conversion based on the main component of the average characteristic and the inverse γ difference characteristic in each region or pixel)
104 table (table with coefficients a1, a2,... AN of main components of each region or pixel)
106-1, 106-2,... 106-N multiplier

Claims (7)

In a gradation conversion device that performs gradation conversion on an input image signal in accordance with the gradation conversion characteristics of an output device that displays or prints an image signal,
For the gradation conversion characteristics of a plurality of regions or pixels, an average characteristic of the gradation conversion characteristics in a plurality of regions or pixels and an appropriate characteristic for the difference characteristic between the average characteristic and the gradation conversion characteristics in each region or pixel. Means for storing a principal component signal of order;
Means for storing a coefficient of a principal component corresponding to each region or pixel;
Means for expressing a tone conversion characteristic by linear combination of the principal component signal and the coefficient of the principal component with respect to the input image signal of each area or pixel. . 2. The apparatus according to claim 1, further comprising means for changing a quantization bit width according to a contribution ratio of each signal when the average characteristic and the main component signal are quantized and stored. Tone converter. After converting a multiband input color image signal into a device-independent color space such as CIE-XYZ or L * a * b *, a plurality of output devices for displaying or printing the color image signal are provided. In a color conversion device that converts a color profile according to the color output characteristics of an area or a pixel,
Means for storing an average characteristic of the color profile conversion characteristics of a plurality of regions or pixels, and a main component signal of an appropriate order with respect to the average characteristic and a difference characteristic of the color profile conversion characteristics in each region or pixel;
Means for storing the principal component coefficients corresponding to each region or pixel;
Means for expressing a color profile conversion characteristic by a linear combination of the principal component signal and the coefficient of the principal component for a device independent color signal to be output in each region or pixel. Characteristic color conversion device. 4. The method according to claim 3, further comprising, when quantizing and storing the average characteristic and the principal component signal, means for changing a bit width of quantization according to a contribution ratio of each signal, and storing the result. Color conversion device. In a gradation conversion device that performs gradation conversion on an input image signal in accordance with the gradation conversion characteristics of an output device that displays or prints an image signal,
For the gradation conversion characteristics of a plurality of regions or pixels, an average characteristic of the gradation conversion characteristics in a plurality of regions or pixels and an appropriate characteristic for the difference characteristic between the average characteristic and the gradation conversion characteristics in each region or pixel. Means for calculating the order principal component signal and the coefficients of the principal component signal in each region or pixel, and further performing clustering based on the distribution of the coefficients in the coefficient space of the principal component to calculate a sample coefficient or coefficient vector When,
Means for calculating a curve of a gradation conversion characteristic to be a sample from the average characteristic and the principal component of the difference characteristic and a coefficient or a coefficient vector to be a sample;
Means for associating a set of coefficients constituting each cluster with a sample coefficient by the aforementioned clustering;
Means for creating a look-up table that links the coefficient of the main component in the region or pixel with the gradation conversion characteristic as a sample,
A gradation conversion apparatus which stores a gradation conversion characteristic curve as a sample and a look-up table corresponding to each region or pixel and performs gradation conversion. After converting a multiband input color image signal into a device-independent color space such as CIE-XYZ or L * a * b *, a plurality of output devices for displaying or printing the color image signal are provided. In a color conversion device that converts a color profile according to the color output characteristics of an area or a pixel,
Based on the color output characteristics of a plurality of regions or pixels of the output device, only the overlapping region of the created gamut mapping is extracted, and the average of the overlapping region and the color profile conversion characteristics of the plurality of regions is extracted. Means for calculating a principal component signal of an appropriate order for the characteristic and the difference characteristic of the color profile conversion characteristic in each region,
Means for storing a coefficient of a principal component corresponding to each region or pixel;
Means for expressing a color profile conversion characteristic corresponding to each area or pixel of the output device by a principal component coefficient of the difference characteristic. Based on the color output characteristics of a plurality of regions or pixels of the output device, the created gamut mapping overlapping region and the non-overlapping region are divided, and the overlapping region is stored as a main component coefficient. Then, for the non-overlapping region, the conversion characteristics of the individual color profiles are stored, and the color profile conversion characteristics corresponding to a plurality of regions or pixels of the output device are calculated as the main component coefficients of the overlapping region, 7. The color conversion apparatus according to claim 6, further comprising: means for generating a color profile conversion characteristic of the non-overlapping area by combining them.

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