JPH0795427A - Method and device for picture processing - Google Patents

Abstract

PURPOSE:To improve the color reproducibility of a transmission picture by storing expressable color areas different by apparatus and converting the picture signal, which is interpolated based on them, through a three-dimensional color space coordinate colorimetric system independent of apparatus. CONSTITUTION:A picture processor 51 receives an RGB colorimetric system picture signal dependent upon the characteristic of a color monitor 52 and temporarily converts it to the three-dimensiozaal color space coordinate colorimetric system which is independent of a specific device and has three axes of lightness (L), hue (H), and chroma (C). It is converted to a YMC (K) signal dependent upon the characteristic of a color printer 53 and is sent to this printer 53. The color printer 53 generates an output picture by the inputted YMC(K) signal. The picture processor 51 stores the color area, which can be expressed by the color monitor 52 and the color printer 53, on the L-C plane by polygonal approximation with respect to each II and interpolates L and C components of the picture signal by them to convert these components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a color display,
The present invention relates to a color image processing method and apparatus for inputting / outputting a color image signal between image input / output devices having different reproduction areas such as a color scanner and a color printer.

[0002]

2. Description of the Related Art An image processing system using a plurality of image input / output devices will be described. FIG. 17 shows a personal computer 11 with a color monitor 12 and a color scanner 13.
And an image processing system to which image input / output devices such as the color printer 14 are connected. The operator activates an image processing application on the computer 11, confirms the image on the color monitor 12, and lays out, edits, and processes characters and sentences by a keyboard input and a color image input from the color scanner 13, The final image is output from the color printer 14. FIG. 18 shows an image processing environment in which a color workstation 22 for image processing, a color scan server 23, a color print server 24, etc. are installed on the network 21. Here, the image input by the scan server 23 is sent to the image processing workstation 22 through the network 21. The operator edits the original color image while looking at the color monitor here.
The image editing process is performed by performing processing and inputting character data from the keyboard. The generated color image data is sent to the print server 24 through the network, where a color image output is obtained.

In these image processing systems, color matching between different image input / output devices has become a problem. In recent years, color correction / color space conversion is performed via a color space that does not depend on a specific image input / output device. An image processing system that copes with this has also been proposed. For example, FIG. 19 shows the CIE197 in the system of FIG.
This is an image processing system that measures color matching based on 6XYZ. Here, the BGR image input from the color scanner 33 in the computer main body 31 → CIE
1976XYZ CIE 1976XYZ → B output to color monitor 32
GR image CIE1976XYZ → YMC (K) image output to the color printer 34 is color-converted to achieve color matching between image input / output devices. Similarly, FIG. 20 shows an image processing system in which color matching is measured based on CIE1976L ^* a ^* b ^* in the system of FIG. Here, the color conversion necessary for each server is input in the scan server 43 BGR image → CIE197
6L ^* a ^* b ^* workstation 42 CIE1976L ^* a ^* b ^*
→ Monitor output BGR image CIE1976L ^* a ^* b ^{* on} print server 44 →
A YMC (K) image for printer output is performed, and only color signals that are not affected by the characteristics of each image input / output device are sent to the network to realize color matching between the image input / output devices.

However, in each image input / output device, for example, a color area that can be read by the characteristics of a sensor in the case of a scanner is limited, the characteristics of a light emitter in a color display, and the ink / toner in a color printer. The color regions that can be displayed and expressed are limited by the characteristics of the color materials such as (hereinafter, these color regions will be simply referred to as the color regions or color reproduction regions that can be expressed by the device). Therefore, even in the system as shown in FIGS. 19 and 20, if the color space conversion is performed without considering the difference in the color reproduction range between the devices, good color reproduction cannot be obtained. For example, the color reproduction range of a color display is generally wider than that of a color printer, and it is impossible for the printer to accurately output all the colors represented by the color display. Here, if a simple process such as assigning the closest color to the color of the area that cannot be represented by the printer is performed,
Collapse of the color occurs, which makes it impossible to distinguish between the colors expressed as different colors on the display, or the gradation is significantly impaired. Several methods have been proposed to deal with these problems by transforming (compressing) the three-dimensional space itself that expresses colors. JP-A-2-126774 and JP-A-2-12677
In No. 5, when converting the BGR signal read by the color scanner into the YMC signal to be output to the color printer, the tone curve / masking coefficient for BGR → YMC conversion is set to the lightness and color without changing the hue in the uniform color space. By determining that the degree is compressed, good gradation reproduction is performed. In this method, the difference between the expressible color areas of the scanner and the printer is absorbed during the color correction of BGR → YMC.

In Japanese Patent Laid-Open No. 4-115691, when an image displayed on a color monitor is output by a color printer,
A method has been proposed in which linear compression is performed for saturation in a uniform color space and only gradation reproduction is performed for lightness. In this method as well, since it is necessary to predict the brightness processing from the characteristics of the printer, the color correction from the uniform color space to YMC (K) and the processing related to the saturation and the brightness are performed at the same time. In the above two prior arts, the effect of the correction processing on different expressible color areas remarkably depends on the accuracy of the color correction method, and the parameters of the color correction are also fixed to a specific scanner / monitor, so that the system is expandable. There is a problem such as being poor. Japanese Patent Laid-Open No. 4-101566 proposes to provide a color compression unit before color correction for generating a color printer output signal from a signal read by a color scanner. The color compression means determines whether or not the input signal is within a color area that can be expressed by the color printer, and according to the result, a process of compressing only lightness and saturation is performed without changing the hue. However, there is a problem in that this color compression processing, particularly the processing of determining for each pixel whether or not it is within the color reproduction range of the color printer becomes very complicated. Japanese Patent Laid-Open No. 4-113773 discloses a method in which a color image signal is once converted into a uniform color space, the color space is reduced toward the center of gravity of a color area that can be represented by the color printer, and then converted into a recording color of the color printer. Proposed. In this case as well, the color space reduction ratio is set in advance for a specific image input / output device, and therefore the expandability of the system is poor.

[0006]

The prior art described above is conceptual in that the color correction (mainly compression) is dealt with by optimizing the color correction parameters, and a concrete configuration is not proposed. Absent. It assumes a specific image signal path such as monitor → printer or scanner → printer, and lacks system expandability / flexibility. There were two major problems. The present invention has been made in view of the above-described conventional art, and in an image processing system to which a plurality of image input / output devices are connected, color reproduction that occurs when color signals are transmitted / received (input / output) and the color reproduction ranges of those devices are different. / It is an object of the present invention to provide an image processing method and apparatus that eliminate defective gradation.

[0007]

According to a first aspect of the present invention, in a method in which a plurality of image input / output devices are connected and a color image signal is transmitted and received between the devices, the method depends on the characteristics of the first device. The color image signal represented by the first color system is converted into the color image signal represented by the second color system that does not depend on the characteristics of the device, and the first color space is converted into the color image signal of the second color system. Of the color image signal represented by the second color system on the basis of the color area information that can be represented by the second device and the second device that outputs the color image signal from the first device and the third device, respectively. Coordinate conversion is performed, and the color image signal subjected to the coordinate conversion is converted into a color image signal represented by a third color system depending on the characteristics of the second device. According to a second aspect of the invention, in a device in which a plurality of image input / output devices are connected and a color image signal is transmitted / received between the devices, the first color system depending on the characteristics of the first device is used. First color space conversion means for converting the generated color image signal into a color image signal represented by a second color system that does not depend on the characteristics of the device,
The second color system based on color region information that can be respectively expressed by the first device and the second device that outputs the color image signal from the first device in the color space of the second color system. And a three-dimensional color space conversion means for coordinate-converting the color image signal represented by the above in a three-dimensional color space, and the color image signal subjected to the coordinate conversion in a third color system depending on the characteristics of the second device. Second color space conversion means for converting the color image signal into a color image signal. According to a third aspect of the present invention, the three-dimensional color space conversion means approximates a color region that can be expressed by the first and second devices into a polygon by a lightness / saturation plane for each hue,
It is characterized in that each coordinate point on the color region of the first device is converted into each coordinate point on the color region of the second device so that each point in each color region corresponds to each other. According to a fourth aspect of the present invention, the three-dimensional color space means obtains at least one of the first and second expressible color regions by interpolating a hue luminosity and a saturation plane polygon stored in advance. The coordinate points on the color area of the first device are converted into the coordinate points on the color area of the second device so that each point in each color area corresponds to each other. It is characterized by According to a fifth aspect of the invention, the three-dimensional color space conversion means is required for coordinate conversion based on the storage means for storing color area information that can be expressed by the first and second devices and the stored color area information. Coefficient determining means for determining a specific coefficient, a coefficient table in which the determined coefficient is set, and coordinate points on the color area of the first device based on the coefficient set in the coefficient table. It is characterized by comprising an arithmetic means for converting into coordinate points on the area.

[0008]

According to the present invention, when a color signal is transmitted and received between image input / output devices, a color image is temporarily converted into a color system that does not depend on a specific image input / output device, and color area information that can be expressed by both devices is displayed. By appropriately performing coordinate conversion in the three-dimensional color space based on the above, the problem of color reproduction caused by the difference in the color reproduction range of each image input / output device is solved. In the inventions of claims 1 and 2, the color image signal represented by the first color system that depends on the characteristics of the first device is the color that is represented by the second color system that does not depend on the characteristics of the device. The image signal is converted into a second color space based on color gamut information that can be represented by the first device and the second device that outputs the color image signal from the first device in the color space of the second color system. Color image represented by the third color system in which the color image signal represented by the third color system is subjected to three-dimensional color space coordinate conversion and the color image signal subjected to the coordinate conversion depends on the characteristics of the second device. By converting the signal into a signal, it is possible to eliminate the problem of color reproduction caused by the difference in the color reproduction range of the first and second devices. According to a third aspect of the present invention, the color regions that can be expressed by the first and second devices that transmit and receive color signals are polygonally approximated by a lightness / saturation plane for each hue, and each point in each color region is Coordinates are converted by linear calculation so as to correspond to each other. In the inventions of claims 4 and 5, the coefficient necessary for the coordinate conversion is stored, and the coefficient is read and the coordinate conversion is performed. According to a sixth aspect of the present invention, a coefficient necessary for converting a color image signal represented by the first color system into a color image signal represented by the second color system is stored, and the coefficient is stored. Read and convert.
According to a seventh aspect of the present invention, the coefficient necessary for converting the color image signal subjected to the coordinate conversion into the color image signal represented by the third color system depending on the characteristics of the second device is stored. Then, this can be read and converted, and a black plate can be generated from the converted color image signal.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. (Embodiment 1) FIG. 1 is a diagram showing an embodiment of the present invention.
In the figure, 51 is an image processing apparatus as described in the present invention, 52 is a color monitor for displaying a color image, 53 is a color printer for outputting a color hard copy, and in this system, a color monitor 52 is provided. A hard copy of the displayed color image is a color printer 5.
Obtained from 3. First, the color monitor 5 with the BGR color system
The color image signal represented by 2 is the image processing device 51.
Sent to. Here, the YMC (K) signal is generated for absorbing the difference between the expressible color regions of the color monitor 52 and the color printer 53 and outputting the color printer 53. The color printer 53 generates an output image according to the YMC (K) signal input from the image processing device 51. FIG. 2 shows an outline of processing of the image processing apparatus 51. A color image signal input in the BGR color system that depends on the characteristics of the color monitor 52 does not depend on a specific image input / output device by the color space conversion means 61. The color system is converted into L ^* H ^* C ^* (L ^* : lightness, H ^* : hue (Hue-angle), C ^* : saturation (metric-Chroma)). Three
The dimensional color space conversion means 62 holds the hue based on the information of the expressible color areas of the color monitor 52 and the color printer 53 in the device-independent color space, and performs the three-dimensional coordinate conversion, and L ^{* '} H ^*. C ^{* '} is generated. The converted color signal is sent to the color printer 5 by the color space conversion means 63.
It is converted into a YMC (K) signal (depending on the characteristics of the color printer 53) for outputting to the No. 3, and is output to the color printer.

The details of the color space conversion means 61, 63 and the three-dimensional color space conversion means 62 will be described below. The color space conversion means 61 performs conversion from BGR to L ^* H ^* C ^* , which is performed by the matrix calculation means 71 and the LU as shown in FIG.
It is realized by a T (Look Up Table) 72.
In the matrix calculation means 71, The matrix operation, L ^* a ^* b ^* signal from the BGR signal is generated, the L ^* a ^* b ^* (when 0 ≦ a ^* and b ^* = 0) signal is LUT72 H ^* = 0 (0 < a ^* and 0 ≦ b ^* ) H ^* = Tan ⁻¹ (| b ^* | / | a ^* |) (when a = 0 ^* and 0 <b ^* ) H ^* = π / 2 (a ^* < 0 and 0 <b ^* ) H ^* = π-Tan ⁻¹ (| b ^* | / | a ^* |) (when a ^* <0 and b ^* = 0) H ^* = π (a ^* <0 And when b ^* <0) H ^* = π + Tan ⁻¹ (| b ^* | / | a ^* |) (when a = 0 ^* and b ^* <0) H ^* = π × (3/2) (0 <A ^* and b ^* <0) = 2π-Tan ^-1 (| b ^* | / | a ^* |) (2) C ^* = (a ^{* 2} + b ^{* 2} ) ^1/2 ...... ( It is converted into L ^* H ^* C ^* by the conversion formula of 3).

FIG. 4 similarly shows the color space converting means 63. The LUT 81 generates L ^{* '} a ^*' b ^{* '} from L ^*' H ^* C ^{* '} input from the three-dimensional color space conversion means 62, and the conversion is a ^*' = C ^{* '} ×. cos (H ^* ) ... (4) b ^{* '} = C ^*' * sin (H ^* ) ... (5). In the matrix calculation means 82, The L ^{* '} a ^*' b ^{* '} signal is converted into a YMC signal by the matrix calculation of. In the black plate generation means 83, Y′M′C′K obtained by adding K from the YMC three-color signal output from the matrix calculation means 82.
It is a means for generating a four-color signal. How to add the K plate largely depends on the characteristics of the color printer 53, but for example, k = min (Y, M, C) K = f (k) Y ′ = Y−g (k) M ′ = M−g ( k) C ′ = C−g (k) f (x) = α × x−γ (α: 0.0 to 1.0, γ: inking start point) g (x) = β × x−γ ( (β: 0.0 to 1.0, γ: Inking start point) ... (7) It is known to be realized by the calculation.

The three-dimensional color space conversion means 62 is shown in FIGS.
The outline of the processing performed in 1 is shown.

L ^* H ^* C ^{* The} hue is not changed by the coordinate conversion in the three-dimensional color space, and the expressible lightness in each hue is
Coordinate conversion on a (L ^* , C ^* ) two-dimensional plane is performed based on the saturation area information.

[0014] In the hue H _i is a 5 lightness and saturation region can be expressed by the color monitor _{52 (l Mi1, 0) -} (l Mi2, c Mi2) - (l Mi3, 0) , the Likewise Brightness that can be expressed by the color printer 53
_{Let the} saturation region be approximated by the triangle defined by (l _Pi1,0 )-(l _Pi2 , c _Pi2 )-(l _Pi3,0 ). At this time, a triangle defined by (l _Mi1 , 0)-(l _Mi2 , c _Mi2 )-(l _Mi2 , 0) is (l _Pi1 , 0)-(l _Pi2 , c _Pi2 )-(l _Pi2 , 0 ) modified to so as to match the triangle defined _{by, (l Mi2, 0) -} (l Mi2, c Mi2) - ( triangle defined by l _Mi3, 0) _{is, (l Pi2, 0) -} ( By transforming it so as to match the triangle defined by l _Pi2 , c _Pi2 )-(l _Pi3 , 0), coordinate conversion on the (L ^* , C ^* ) two-dimensional plane is performed.

In this embodiment, this modification is realized by a linear operation. As shown in Fig. 2, the input lightness / saturation is L
^* C ^* , where the converted lightness / saturation is L ^{* '} C ^*' , L ^{* '} = α × L ^* −α × l _Mi2 + l _Pi2 (when l _Mi1 ≦ L ^* ≦ l _Mi2 ) = β × _{^{L * -β × l Mi3 + l}} Pi3 ( when _{^{l Mi2 <L * ≦ l Mi3}} ) ...... (8) C * '= γ × C * ...... (9) here α = (l _Pi1 -l _{Pi2) / (l Mi1 -l Mi2) β} = represented by _{(l Pi2 -l Pi3) / (} l Mi2 -l Mi3). As a result, as shown in FIG. 6, the hue is preserved and the lightness and saturation are converted appropriately.

The structure of the three-dimensional color space conversion means 62 is shown in FIG. In FIG. 7, a storage unit 111 is a ROM that stores color reproduction information of an image input / output device that transmits / receives a color image signal. In this embodiment, as described above, the lightness / saturation (L) is set for each hue. ^* , C ^* ) A representable area on a two-dimensional plane is approximated by a triangle, and the vertex coordinate values are held. In the hue H _i given for color monitor 52 in FIG. 5, is stored _{(l Mi1, l Mi2, l} Mi3, c Mi2) is stored here, the same four data also for other hue here It Where L ^* H ^*
If each C ^* has 8 bits, the color gamut of the color monitor 52 is defined by the capacity of (8 bits × 4) × 256 = 8192 bits.

Further, here, for example, Yellow M
agenta, Cyan, Blue, Green, Re
It is also possible to store only data relating to representative hues such as d, and to generate lightness / saturation region data for all hues by correction between representative hues by the coefficient determining means 112 described later. The coefficient determining unit 112 reads the coordinate information from the storage unit 111 according to the image input / output device that transmits / receives the image, and based on the coordinate information, the calculating unit 11 described later.
This is a means for setting the coefficients necessary for the processings 4, 115 in the coefficient table 113 which will be described later. Hue H ^* is 8b
When have in it, the hue H _{i (i} = 0~255) about representable color space data such as shown in FIG. _{5 (l Mi1, l Mi2,} l Mi3, c Mi2) (l Pi1, l Pi2, l _Pi3 , c _Pi2 ) (i = 0 to 25
5) is read from the ROM 111 and the multiplication / addition coefficient α [= (l _Pi1 −l _Pi2 ) / (l _Mi1 −l _Mi2 )] β [= (l _{Pi2 -l Pi3) / (l Mi2 -l} Mi3)] γ [= (c Mi2 / c Pi2)] sought _{-α × l Mi2 + l Pi2 -β} × l Mi3 + l Pi3 (i = 0~255), coefficient table Set to 113. This coefficient table is obtained corresponding to the setting when the image input / output device for transmitting / receiving the color image data is set, and the real-time property is not required. Therefore, the coefficient is calculated by software. The calculation coefficient for each hue is set in the coefficient table 113, and the calculation coefficient corresponding to the input H _i is output to the calculation means 114 and 115. The calculation means 114 is a means for calculating L ^{* '} . Here, the multiplication coefficient from the coefficient table 112, "α", "β", addition coefficient "-α × l _Mi2 + l _Pi2" "-β × l _Mi3 + l
_{The values of} " _Pi3 " and "l _Mi2 " are loaded, and a new L ^{* '} signal is generated from the L ^* signal input by the calculation of the equation (8). Similarly, the calculation means 115 is a means for calculating C ^{* '} . Here, the value of the multiplication coefficient “γ” is loaded from the coefficient table 113, the operation of the equation (9) is performed on the input C ^* signal, and C ^{* ′} is output. Hue H ^*
With respect to, since the value is saved without performing the conversion process, L ^{* '} H ^* C ^*' is generated by the above process. In the present embodiment, the expressible color area data is stored for each hue, but only the representative hue is stored, and the expressible color area data of a desired hue is stored in two adjacent representative hues. The data may be obtained by linear interpolation.

(Embodiment 2) FIG. 8 shows another embodiment of this embodiment. In the figure, 121 is an image processing apparatus described in the present invention, 122 is a color scanner for inputting a color image, 123 is a host computer having a color monitor for displaying a color image, 12
A color printer 4 outputs a color hard copy. In this apparatus, a series of image processing is performed such that an image read by the scanner 122 is edited and processed by the host computer 123 while looking at the monitor, and the generated image is output from the printer 124. In this image processing device, the following three routes are conceivable as routes for the color image signal to travel.

Scanner → Color Printer Scan originals with a scanner and obtain color copies with a color printer as they are Scanner → Monitor (computer) Scan originals and obtain digital image data Monitor (computer) → color printer Create / Process / Edit on computer Or obtain a hard copy of a digital image obtained through a network or other medium. FIG. 9 is a diagram showing an outline of processing of the image processing apparatus 121. Color scanner 122, color monitor 123, etc.
The color image signal input including the characteristics of the device is converted into the color system L ^* a ^* b ^* independent of the specific image input / output device by the color space conversion means 131. The three-dimensional color space conversion unit 132 performs three-dimensional coordinate conversion based on the information of the expressible color area in the device-independent color space of both image input / output devices that transmit and receive images, and L ^{* '} a
^{* '} b ^*' is generated. The converted color signal is converted by the color space conversion unit 133 into a color image signal that matches the characteristics of the output destination device.

Hereinafter, the color space conversion means 131, 133, 3
The dimensional color space conversion means 132 will be described. FIG. 10 shows the color space conversion means 131. In the matrix calculation means 142, BGR → L ^* a ^{* is} calculated by the matrix calculation of the above equation (1) ^.
Conversion to b ^* is performed. In the storage means 141, BGR
→ L ^* a ^* b ^* multiplication coefficient set of a ₁₁ ~a _36, for example, BGR in this embodiment depends on the characteristics of the "scanner →
L ^* a ^* b ^* "" BGR → L ^* depending on monitor characteristics
Two coefficient sets “a ^* b ^* ” are prepared, and appropriate multiplication coefficients are read out to the matrix calculation means 142 based on a control signal sent from a control unit (not shown). Similarly, FIG. 11 shows the color space conversion means 133. In the matrix calculation means 152, L ^* a ^* b ^* → BGR or L ^* a ^* b is calculated by the same matrix calculation as the equation (6).
^* → YMC conversion is performed. The storage unit 151 stores 18 multiplication coefficient sets in the above calculation, for example, “L ^* a ^* b ^* → BG depending on monitor characteristics in this embodiment”.
“R” “L ^* a ^* b ^* → YM that depends on printer characteristics”
Two coefficient sets "C" are prepared, and appropriate multiplication coefficients are read out to the matrix calculation means 152 based on a control signal sent from a control unit (not shown). Black plate generation means 1
At 54, YMC3 output from the matrix calculation means 152
It is means for generating a four-color signal to which K is added from the color signal, for example, according to the expression (7). A signal switching unit 153 is an image processing apparatus that outputs a YMC three-color signal without performing black plate generation on the signal output from the matrix calculation unit 152 in accordance with a control signal input from a control unit (not shown). It goes without saying that these processes are greatly simplified.

FIG. 12 shows the three-dimensional color space conversion means 132. Here, in the L ^* H ^* C ^* space, the three-dimensional coordinate conversion performed using the equations (8) and (9) is performed in the L ^* a ^* b ^* space. Now, as in the first embodiment, FIG.
In, (l _Mi1, 0) a representable brightness and saturation region of the hue H _i with image input and output device that transmits a color image signal - in _{(l Mi3, 0) - (} l Mi2, c Mi2) Also, the brightness / saturation region that can be represented by the image input / output device that receives the color image signal is approximated by a triangle defined by (l _Pi1 , 0)-(l _Pi2 , c _Pi2 )-(l _Pi3 , 0). It shall be. (3),
From equations (8) and (9), coordinate conversion in the L ^* a ^* b ^* space is performed by the following equation.

[0022] ^{L * '= α × L *} -α × l Mi2 + l Pi2 (l Mi1 ≦ L * time of _{≦ l Mi2) = β × L} * -β × l Mi3 + l Pi3 (l Mi2 <L * <l _Mi3 ) ………… (8) a ^{* '} = γ × a ^* …… (10) b ^*' = γ × b ^* …… (11) where α = (l _Pi1 −l _Pi2 ) / (l _{mi1 -l Mi2) β = (l} Pi2 -l Pi3) / (l Mi2 -l Mi3) γ = (c Mi2 / c Pi2) However, usually a ^* b ^* of zero (a ^* = b ^* = 0 of the coordinate value) of a ^* and b ^*, for example, because 8bit Nari 7bit Nari displaced when it is quantized, it is necessary to linear operation to match it. For example, a ^* min to a ^* max, b ^*
It is assumed that min to b ^* max are each quantized into n bits. At this time, if the a ^* b ^* signal before quantization is A ^* B ^* and the a ^* b ^* signal after quantization is A ^{* '} B ^*' , then A ^{* '} = X * A ^* -X * a ^*. min …… (12) B ^{* '} = Y × B ^* −Y × b ^* min …… (13) A ^* = Z × A ^*' + a ^* min …… (14) B ^* = W × B ^{* '} + b ^* min (15) where X = ²ⁿ / (a ^* max-a ^* min) Y = ²ⁿ / (b ^* max-b ^* min) Z = ²ⁿ / (a ^* max-a ^* min) ) W = ²ⁿ / (b ^* max-b ^* min). Therefore, the three-dimensional color space conversion means 1
In 32, equations (14) and (15) → (8), (10),
Expression (11) → a ^{* ′} b by the calculation of Expressions (12) and (13)
^{* '} Is generated. However, since the above formula (7) is all linear operation, a ^{* '} = _Mai * a ^* + _Cai ... (16) b ^*' = _Mbi * b ^* + _Cbi ... (17) where _Mai : A ^{* '} calculation multiplication coefficient set for each hue _Cai : a ^*' calculation addition coefficient set for each hue M _bi : b ^{* '} calculation multiplication coefficient set for each hue C _bi : hue B ^{* ′} calculation addition coefficient set for each of the above, the same conversion as that in the first embodiment is performed in the L ^* a ^* b ^* space.

The storage means 161 is a ROM for storing color area information that can be expressed by an image input / output device for transmitting / receiving a color image signal. In the present embodiment, as described above, the lightness / saturation for each hue is ascertained. (L ^* C ^* ) A representable area on a two-dimensional plane is approximated by a triangle, and the vertex coordinate values are held. The color system of the data held here may be L ^* a ^* b ^* , but in the above-mentioned conversion formula, it is easier to carry out the calculation by holding the lightness / saturation, and therefore the same as in the first embodiment. To L
^It shall be stored as ^* C ^* . As in the case of the first embodiment, assuming that each L ^* H ^* C ^* is 8 bits, the capacity of (8 bits × 4) × 256 = 8192 bits defines the color gamut of one image input / output device. become. Also, here, for example, Yellow Ma
Genta / Cyan / Blue / Green / Red
Store only data related to typical hues such as
The coefficient determining unit 162, which will be described later, may generate the lightness / saturation region data of all the hues by correcting the representative hues. The coefficient determining means 162 reads the coordinate information from the storage means 161 according to the image input / output device that transmits and receives the image, and based on the coordinate information, the calculating means 165, 16 described later.
This is a means for setting the coefficients necessary for the processing of Nos. 6 and 167 in the coefficient table 163 which will be described later. Hue H ^* is 8b
When have in it, hue H _i representable color space gamut data such as shown in FIG. 5 _{(i = 0~255) (l Mi1} , l Mi2, l Mi3, c Mi2) (l Pi1, l Pi2, l _Pi3 , c _Pi2 ) (i = 0
To 255) are read from the storage means 161 (8), (16), (1
7) multiply-add coefficients required for the calculation of _{α [= (l Pi1 -l Pi2} ) / (l Mi1 -l Mi2)] β [= (l Pi2 -l Pi3) / (l Mi2 -l Mi3 _{)] γ [= (c Mi2} / c Pi2)] -α × l Mi2 + l Pi2 -β × l Mi3 + l Pi3 M ai, C ai M bi, C bi (i = 0~25
5) is calculated and set in the coefficient table 163. This coefficient table is obtained corresponding to the setting when the image input / output device for transmitting / receiving the color image data is set, and the real-time property is not required. Therefore, the coefficient is calculated by software. The LUT 164 is the LUT8 in FIG.
1 and a table for generating a hue signal H ^* from Similarly ^{a * b *, (2)} , can be expressed by the calculation of equation (3). The hue signal generated here is used for switching the multiplication / addition coefficient sent from the coefficient table 163 to the calculation means 165, 166, 167.

In the coefficient table 163, the calculation coefficient for each hue is set, and the calculation coefficient corresponding to the hue input from the LUT 164 is calculated by the calculating means 165, 166, 1.
Output to 67. The calculation means 165 is a means for calculating L ^{* '} . Here, from the coefficient table 163, multiplication coefficients “α” and “β” and addition coefficients “−α × l _Mi2 + l _Pi2 ” “−”
β × l _Mi3 + l _pi3 "and" the value of l _Mi2 "is loaded, (8) of L from L ^* a signal input by the operation ^{* '}
Generate a signal. The calculating means 166 is a means for calculating a ^{* '} . Here, the values of the multiplication coefficient “M _ai ” and the addition coefficient “C _ai ” are loaded from the coefficient table 163, and the operation of equation (16) is performed on the input a ^* signal to obtain a ^{* ′.}
Is output. Similarly, the calculation means 167 is a means for calculating b ^{* '} . Here, the values of the multiplication coefficient “M _bi ” and the addition coefficient “C _bi ” are loaded from the coefficient table 163, the input b ^* signal is calculated by the equation (17), and b ^{* ′} is output. To do. Through the above processing, the same lightness / saturation coordinate conversion as in the first embodiment is performed in the L ^* a ^* b ^* color system. In this embodiment, an image processing system in which one color scanner, one color monitor, and one color printer are connected has been described, but this system has the same effect even if more image input / output devices are connected. What you can get is clear.

(Embodiment 3) FIG. 13 shows still another embodiment of the present invention. FIG. 13 shows the three-dimensional color space conversion means 62 in FIG. 14 and 15 show the outline of the processing performed in this embodiment. In the present embodiment, the hue is not changed by the coordinate conversion in the L ^* H ^* C ^* three-dimensional color space, and the (L ^* , C ^* ) two-dimensional plane is calculated based on the color gamut information of the lightness / saturation in each hue. Coordinate conversion of. In Figure 14, in a certain hue H _i, lightness and saturation region can be expressed by the color monitor _{52 (l Mi1, 0) -} (l Mi2, c Mi2) - (l Mi3, 0) , the Likewise Color Brightness that can be expressed by the printer 53
_{Let the} saturation region be approximated by the triangle defined by (l _Pi1,0 )-(l _Pi2 , c _Pi2 )-(l _Pi3,0 ). At this _{time, (l Mi1 -l Mi3) :(} l Mi2 -l Mi3) = (l Pi1 -l Pi3) :( l Pi4 -l Pi3) l Pi4 = (l Mi2 -l Mi3) × (l Pi1 -l _{Pi3) / (l Mi1 -l Mi3} ) + l seek _{P i3} become _{l 14, (l Mi1, 0} ) - (l Mi3, c Mi2) - (l Mi2, 0) the triangle defined by (l _{Pi1 , 0) - (l Pi2,} c Pi2) - (l Pi4, 0) is deformed so as to match the triangle defined _{by, (l Mi2, 0) -} (l Mi2, c Mi2) - (l Mi3, The triangle defined by (0) is transformed so as to match the triangle defined by (l _Pi4 , 0)-(l _Pi2 , c _Pi2 )-(l _Pi3 , 0), and thus (L ^* C ^* ) Performs coordinate conversion on a two-dimensional plane.

In the present embodiment, this modification is realized by a linear operation. As shown in Fig. 2, input lightness / saturation is L ^*
If C ^{* is} the converted lightness / saturation L ^{* '} C ^*' , then L ^{* '} = α × L ^* + β × C ^* + γ (18) C ^*' = ε × C ^* ... (19) where _{α = (l Pi1 -l Pi3)} / (l Mi1 -l Mi3) represented by _{β = (l Pi2 -l Pi4)} / c Mi2 ε = (c Mi2 / c Pi2). As a result, as shown in FIG. 15, the hue is preserved and the lightness and saturation are converted appropriately.

Next, FIG. 13 will be described. In the figure, a storage unit 171 stores color area information that can be expressed by an image input / output device that transmits and receives color image signals.
OM, and in the present embodiment, as described above, the lightness for each hue
The color gamut is approximated by a triangle on a two-dimensional plane of saturation (L ^* C ^* ), and the vertex coordinate values are held. In the hue H _i given for color monitor 52 in FIG. 14, is stored _{(l Mi1, l Mi2, l} Mi3, c Mi2) is stored here, the same four data also for other hue here It Where L ^* H ^*
If each C ^* has 8 bits, the color gamut of the color monitor 52 is defined by the capacity of (8 bits × 4) × 256 = 8192 bits. In addition, here, for example, Yellow
The lightness / saturation region data of all hues may be generated by correction between representative hues such as nta, Cyan, Blue, Green, and Red. The coefficient determining unit 172 reads the coordinate information from the storage unit 171 according to the image input / output device that transmits / receives an image, and based on the coordinate information, the coefficient necessary for processing of the calculating units 174 and 175, which will be described later, is also described below. Means for setting in the coefficient table 173. Assuming that the hue H ^* is 8 bits, the hue H _i (i = 0
Representable color space gamut data such as shown in FIG. 14 of _{~255) (l Mi1, l Mi2} , l Mi3, c Mi2) (l Pi1, l Pi2, l Pi3, c Pi2) (i = 0~25
Read 5) from the storage unit 171 (14) - (15) multiply-add coefficients required for the calculation of the equation _{α [= (l Pi1 -l Pi3} ) / (l Mi1 -l Mi3)] β [= ( _{l Pi2 -l Pi4) / c Mi2} ] γ [= l Pi3 -l Mi3 × (l Pi1 -l Pi3) / (l
_{Mi1 -l Mi3)] ε [=} (c Mi2 / c Pi2)] (i = 0~
255) and set it in the coefficient table 173. This coefficient table is obtained corresponding to when the image input / output device for transmitting / receiving the color image data is determined, and real-time property is not required. Therefore, the above coefficient is calculated by software. The calculation coefficient for each hue is set in the coefficient table 173, and the calculation coefficient corresponding to the input H _i is output to the calculation means 174 and 175. The calculation means 174 is a means for calculating L ^{* '} . Here, from the coefficient cable 173, the multiplication coefficients “α”, “β”,
The value of the addition coefficient “γ” is loaded and input L ^*
Linear equation 18 is performed on the C ^* signal to output L ^{* '} . The calculation means 175 is a means for calculating C ^{* '} . Here, the multiplication coefficient “ε” is calculated from the coefficient table 173.
Is loaded and the input C ^* signal is subjected to the linear operation of equation (15) and C ^{* '} is output. Through the above processing, L ^{* '} C ^*' is generated.

In the above embodiment, L ^* a ^* b ^* and L ^* H ^* C ^* are used as the device-independent color space, but these are L ^* u ^* v ^* , YCrCb, etc. The same effect can be obtained if the color space is defined by lightness / chromaticity or lightness / hue / saturation. Similarly, in the above embodiment, the color gamut of each image input / output device is approximated by a triangle in the lightness / saturation plane for each hue.
Other polygons such as the quadrangle shown in (a) and the pentagon shown in FIG. 16 (b) may be used, or different polygons may be mixed and used. The same processing is performed by finding the corresponding points of each vertex of the polygon by linear operation, or in the case of different polygons, performing the linear operation by appropriately matching the vertices of the polygon with many vertices on other polygons. Obviously it is possible to do so.

[0029]

As described above, according to the present invention, a color image is transmitted / received (input / output) between a plurality of image input / output devices.
In doing so, it is possible to obtain a good image that is not affected by the difference in the color reproduction range. In the inventions of claims 1 and 2, the color image signal represented by the first color system that depends on the characteristics of the first device is the color that is represented by the second color system that does not depend on the characteristics of the device. The image signal is converted into a second color space based on color gamut information that can be represented by the first device and the second device that outputs the color image signal from the first device in the color space of the second color system. Color image represented by the third color system in which the color image signal represented by the third color system is subjected to three-dimensional color space coordinate conversion and the color image signal subjected to the coordinate conversion depends on the characteristics of the second device. Convert to signal. Therefore, according to the first and second aspects of the invention, an image that is not affected by the difference in the color gamut can be obtained,
Since it is not limited to a specific image input / output device, system expandability and flexibility can be achieved. According to the invention of claim 3, the expressible color areas of the first and second devices for transmitting and receiving color signals are polygon-approximated by a lightness / saturation plane for each hue, and each point in each color area is approximated. Coordinate conversion is performed by a linear operation so that each corresponds to. Therefore, according to the third aspect of the invention, the conversion process can be performed with a simple configuration. According to the invention of claim 4, the expressible color area of the desired hue is interpolated to obtain the expressible color area of the representative hue. Therefore, according to the invention of claim 4, it is sufficient to register only representative color regions that can be expressed, and the storage capacity can be small. According to the invention of claim 5, the coefficient necessary for the coordinate conversion is stored, and the coefficient is read and the coordinate is converted. Therefore, according to the invention of claim 5, it is possible to deal with any input / output device by changing the coefficient to be stored, and the system can be expanded.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an outline of processing of the image processing apparatus of FIG.

FIG. 3 is a diagram illustrating conversion from BGR to L ^* H ^* C ^* .

FIG. 4 is a diagram for explaining conversion from L ^{* '} H ^* C ^*' to Y'M'C'K.

FIG. 5 is a diagram in which a region of lightness / saturation that can be represented by a color monitor or a color printer in each hue is approximated to a triangle (L
^* , C ^* ) It is explanatory drawing at the time of coordinate-transforming on a two-dimensional plane.

FIG. 6 is an explanatory diagram in the case of saving hue and converting lightness / saturation by approximating a region of lightness / saturation that can be represented by a color monitor or a color printer into a triangle.

FIG. 7 is a diagram showing a configuration of a three-dimensional color space conversion unit.

FIG. 8 is a diagram showing another embodiment of the present invention.

9 is a diagram showing an outline of processing of the image processing apparatus of FIG.

10 is a diagram showing the color space conversion means 131 of FIG.

11 is a diagram showing the color space conversion unit 133 of FIG.

FIG. 12 is a diagram showing a three-dimensional color space conversion unit 132 in FIG.

FIG. 13 is a diagram illustrating a three-dimensional color space conversion means according to still another embodiment of the present invention.

FIG. 14 is an explanatory diagram of a case where lightness / saturation regions that can be represented by a color monitor and a color printer in each hue are approximated to a triangle and coordinate conversion is performed on a (L ^* , C ^* ) two-dimensional plane.

FIG. 15 is an explanatory diagram in the case of storing hue and converting lightness / saturation by approximating a region of lightness / saturation that can be expressed by a color monitor or a color printer into a triangle.

FIG. 16 is a diagram illustrating an example in which a color gamut of an image input / output device is approximated to a polygon.

FIG. 17 is a diagram illustrating an image processing system to which image input / output devices are connected.

FIG. 18 is a diagram showing an image processing environment in which a color workstation for image processing, a color scan server, a color print server, and the like are installed on a network.

FIG. 19 shows the system of FIG. 17 with CIE1976XY.
It is a figure which shows the image processing system which measured color matching on the basis of Z.

FIG. 20 shows the CIE1976L ^{* in} the system of FIG.
It is a figure which shows the image processing system which measured color matching on the basis of a ^* b ^* .

[Explanation of symbols]

51 ... Image processing device, 52 ... Color monitor, 53 ... Color printer, 61, 63 ... Color space conversion means, 62 ... Three-dimensional color space conversion means, 71, 82 ... Matrix calculation means, 72,
81 ... LUT, 83 ... Black plate generating means, 111 ... Storage means, 112 ... Coefficient determining means, 113 ... Coefficient table, 1
14, 115 ... Arithmetic means, 121 ... Image processing device, 12
2 ... color scanner, 123 ... host computer,
Reference numeral 124 ... Color printer, 131, 133 ... Color space conversion means, 132 ... Three-dimensional color space conversion means, 141 ... Storage means, 142 ... Matrix calculation means, 151 ... Storage means, 152
Matrix calculating means, 153 ... Signal switching section, 154 ... Black plate generating means, 161 ... Storage means, 162 ... Coefficient determining means, 163 ... Coefficient table, 164 ... LUT, 165,
166, 167 ... Calculation means, 171 ... Storage means, 172
... Coefficient determining means, 173 ... Coefficient table, 174, 1
75 ... Calculation means.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication H04N 1/46 4226-5C H04N 1/46 Z

Claims (5)

[Claims] 1. A method in which a plurality of image input / output devices are connected, and a color image signal is transmitted / received between the devices and output, the first color system depending on the characteristics of the first device is used. A color image signal is converted into a color image signal represented by a second color system that does not depend on the characteristics of the device, and the first device and the color image from the first device in the color space of the second color system. A color image subjected to coordinate conversion by three-dimensional color space coordinate conversion of the color image signal represented by the second color system based on color region information that can be respectively expressed by the second device that outputs the signal. An image processing method, characterized in that the signal is converted into a color image signal represented by a third color system that depends on the characteristics of the second device. 2. An apparatus in which a plurality of image input / output devices are connected and a color image signal is transmitted / received between the devices and is output by a first color system depending on the characteristics of the first device. A first color space conversion means for converting the color image signal into a color image signal represented by a second color system that does not depend on the characteristics of the device; a first device in the color space of the second color system; Coordinate conversion of a color image signal represented by the second color system in a three-dimensional color space based on color region information that can be expressed by the second device, from which a color image signal from the first device is output. And a second color space conversion means for converting the color image signal subjected to the coordinate conversion into a color image signal represented by a third color system depending on the characteristics of the second device. An image processing apparatus comprising: 3. The apparatus according to claim 2, wherein the three-dimensional color space conversion means approximates the expressible color areas of the first and second devices into polygons on a lightness / saturation plane for each hue. An image characterized by converting each coordinate point on the color region of the first device into each coordinate point on the color region of the second device so that each point in each color region corresponds to each other Processing equipment. 4. The apparatus according to claim 3, wherein the three-dimensional color space conversion means stores at least one of the color region information that can be expressed by the first and second devices in advance by storing the lightness / color of the hue. An image processing apparatus characterized by approximating a polygon obtained by interpolating a polygon of a plane of degrees. 5. The apparatus according to claim 2, wherein the three-dimensional color space conversion means stores the color area information that can be expressed by the first and second devices in the stored color area information. Coefficient determining means for determining a coefficient required for coordinate conversion based on the coefficient table, a coefficient table in which the determined coefficient is set, and coordinate points on the color region of the first device based on the coefficient set in the coefficient table. An image processing apparatus comprising: a calculation means for converting into coordinate points on a color area of a second device.