JPH11261831A - Method for removing density fluctuation of three-dimensional lookup table for color signal conversion and image output apparatus for performing the method - Google Patents

Abstract

(57) [Abstract] [Problem] Image output device (image recording device and development processing device)
A method for removing a density fluctuation of a three-dimensional look-up table for color signal conversion of an image output device capable of removing a steady density fluctuation caused by the above-mentioned factors and improving the production accuracy, and a density non-uniformity due to a steady fluctuation. Provided is an image output device that does not generate any image. An image output device outputs a first color chart having a plurality of color patches of a combination in which output values of three colors are changed and a second color chart having an image of a uniform output value over the entire surface. The color density of the plurality of color patches and the uniform output value image is measured, and the density fluctuation value is obtained from the colorimetric values of the uniform output value image. The above problem is solved by removing the density fluctuation and removing the density fluctuation of the three-dimensional lookup table created from the plurality of color patches.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing a variation in density of a three-dimensional lookup table for color signal conversion and an image output apparatus for performing the same, and more particularly, to a three-dimensional lookup table for color signal conversion of an image output apparatus. The present invention relates to a method for removing a density variation inherent in an image output device from an image output device and an image output device having the function.

[0002]

2. Description of the Related Art At present, with the progress of digital technology, multimedia which transmits color image information among a large number of media such as photographs, prints, copies (hard copies), televisions, monitors (soft copies), etc., has attracted attention. Have been.
In such a multimedia system, color image information is performed by digital color image data.
In such a multimedia system, input / output devices that handle various input / output media have their own color spaces. Therefore, color image data input by the input device, for example, R (red), G ( Green), B
In order to accurately reproduce (blue), C (cyan), M (magenta), Y (yellow), and the like on an output device, the color spaces of the input and output devices appropriately correspond to each other, for example, each other without excess or shortage. Must be converted as follows:

[0003] However, such color conversion is often not linear. For example, when input image data input from an input medium by an input device is r, g, b, and output image data to be output to an output medium by an output device is R, G, B, input image data (r , G, b) to output image data (R, G, B)
Is generally not in a linear mapping relationship, but is a complex non-linear function f _R , as shown in the following equation (1).
It is expressed as a mapping relationship using f _G and f _B. In some cases, such functions f _R , f _G , and f _B themselves cannot be determined. R = f _R (r, g, b) G = f _G (r, g, b) (1) B = f _B (r, g, b) Therefore, output image data (R, G, B) with good color reproducibility cannot be easily obtained from the input image data (r, g, b). For this reason, in a real image output system, 3 × 3,
Color conversion using a color conversion matrix such as 3 × 4, 3 × 9, or 3 × 10 is often performed.

On the other hand, in recent years, as a technique for accurately reproducing digitized color image data and for mutually converting color information between different devices, three techniques have been proposed.
A conversion method using a dimensional lookup table (hereinafter referred to as 3DLUT) is also often used. Here, as shown in FIG. 6, in a system for actually outputting a color image, the 3DLUT converts input signal values (r, g, b) input from an input medium by an input device to an output medium by an output device. The output signal value (R,
6 is a search table representing a correspondence relationship between input and output signal values for conversion into G, B). However, such 3DL
The UT is given as a mapping of the input / output signal values for N × N × N grid points because the UT is given with a fixed (finite) number of stages, for example, N stages, for each of the input / output signal values. For this reason, in a real conversion, it is extremely rare that a point to be converted hits a grid point, so that a three-dimensional (volume)
The output signal value is obtained from the input signal value by interpolation such as interpolation.

When creating such a 3DLUT,
The target image output system outputs a plurality of specific color patches to an output medium, measures the density of the output color patches, and maps the obtained density values to output values for outputting the color patches. The method of seeking a relationship is taken. This color patch consists of three primary independent colors (RGB,
CMY) is composed of N × N × N color patch image data, which is a combination of N stages of signal values representing each signal value of CMY), ie, input / output grid point data. The total number of color patches is determined from the viewpoint of interpolation accuracy. Is desirable, but on the other hand, it is desirable to reduce it from the viewpoint of practical color patch output and simplicity of measurement.

Incidentally, even in a commercially available image output device, in order to reproduce a desired color, an output signal for outputting a color image and a color of the obtained color image as described above are used. A method is used in which a 3DLUT is created and an output value is determined from a desired color by inverse conversion. However, a commercially available image output device is not suitable for image output for outputting a hard copy image such as a color reflection print or a color transparent positive image, for example, fluctuations in the light amount of the light beam light source and variations in the main and sub scanning speeds of the light beam. In the apparatus, a light amount variation of a light beam of a light source such as an LD, an optical deflector such as a polygon mirror for deflecting the light beam in a main scanning direction, a rotation speed variation of a motor thereof, and a pair of rollers for conveying a photosensitive material in a sub-scanning direction are provided. Since it is not possible to completely eliminate fluctuations in the rotational speed of the motor, etc., it is difficult to reproduce uniform density over the entire solid image output for a uniform output value, and an error occurs between the target value and the solid image. There is a problem that uneven density occurs in the solid image. In other words, when creating a three-dimensional look-up table for color signal conversion of an image output device, a color patch with a different output level for each color is created. There is a problem in that an error occurs between the desired density value and the output value, and desired accuracy cannot be obtained in the created 3DLUT.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide an output value for obtaining an output reproduced image output from an image output device and a density of the obtained output reproduced image. Of the errors between the image processing apparatus and the image output apparatus (image recording apparatus or development processing apparatus) and the steady density fluctuations caused by the processing and the like are removed, and the accuracy of creating a three-dimensional lookup table is improved. A method of removing a density fluctuation of a three-dimensional lookup table for color signal conversion of an image output device, and a method of processing a solid image having a uniform density over the entire surface due to the device itself and its processing. An object of the present invention is to provide an image output device that does not cause density unevenness due to fluctuation.

[0008]

In order to achieve the above object, a first aspect of the present invention is a first aspect of the present invention, in which an image output device has a first color patch having a plurality of color patches each having a different output value of each of three colors. Is output, and the densities of the plurality of color patches in the first color chart are measured to form a three-dimensional lookup table for color signal conversion of an image output device. An output device outputs a second color chart having an image of uniform output values over the entire surface, determines a density variation value from the uniform output value image of the output second color chart, and based on the obtained density variation value. A density variation inherent in the image output device included in the first color chart and a density variation of a created three-dimensional lookup table are removed. There is provided a concentration rejection method No. converting three-dimensional lookup table.

Here, the density fluctuation value is a fluctuation amount of a density value at a position corresponding to each position of the plurality of color patches of the first color chart from the uniform output value image of the second color chart. The removal of the density variation inherent in the image output apparatus is performed by removing the variation of the density value of each color patch of the first color chart using the determined variation value of the density value at the position corresponding to each color patch. It is preferable to carry out. In addition, the change of the density value of the color patch is removed by calculating the change amount of the density value corresponding to each position of the plurality of color patches of the second color chart via the one-dimensional lookup table. Preferably, the conversion is performed by converting the output values of the three colors into variations, and removing the conversion variation from the output values of the color patches.

The one-dimensional look-up table converts the output value of the image output device into a characteristic value close to a linear relationship with the density, and then creates the one-dimensional lookup table for density correction.
Preferably it is a dimensional lookup table. Also,
The one-dimensional lookup table outputs a multi-step pattern in which the same output values of three colors are assigned from the image output device. The output value given to each step of the pattern and the density of the corresponding step of the output pattern are output. It is preferably created from the relationship with Preferably, the multi-step pattern is created on the first color chart together with the plurality of color patches.

According to a second aspect of the present invention, an input image signal is converted into an output image signal by a color signal conversion three-dimensional look-up table, and a visual reproduction is performed on a recording medium based on the obtained output image signal. An image output apparatus for outputting an image, comprising: means for storing a combination of output values of three colors of a plurality of color patches of a first color chart and a uniform output value of an image of a second color chart; Means for outputting the color chart and the second color chart as a visible reproduced image to the recording medium; and a plurality of color patches of the output first color chart and the second color chart.
Density measuring means for measuring the density with the image of the color chart, means for obtaining a density variation value from the measured density value of the image of the entire color uniform output value of the second color chart, based on this density variation value, Means for removing density fluctuations from the measured density values of the plurality of patches of the first color chart;
The three-dimensional look-up table is obtained from a combination of output values of three colors of the plurality of color patches of the first color chart and a measured density value from which the density fluctuation of the plurality of color patches of the first color chart is removed. And a means for creating the image output device.

Here, it is preferable that the density fluctuation removing means removes the fluctuation of the density values of the plurality of color patches of the first color chart. The density fluctuation removing unit converts a density fluctuation value of the second color chart at a position corresponding to the color patch of the first color chart into a fluctuation amount of the output values of the three colors of the color patch. Preferably, it has a one-dimensional lookup table. Further, in the image output device of the present invention, the storage means further stores an output value of a multi-step pattern in which the same output values of three colors for creating the one-dimensional lookup table are allocated. It is preferable that the apparatus further comprises means for creating the one-dimensional look-up table from the measured density values of the multi-step pattern output to the recording medium based on the allocation output values of the step patterns and the allocation output values.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a color signal conversion three-dimensional lookup table according to the present invention; I do.

FIG. 1 is a block diagram showing an embodiment of an image output apparatus according to a second aspect of the present invention which implements the method for removing the density fluctuation of the three-dimensional lookup table for color signal conversion according to the first aspect of the present invention. FIG. As shown in the figure, the image output device 10 according to the second embodiment of the present invention converts a input image data D1 into an output image data D2 using a three-dimensional lookup table for color signal conversion (hereinafter referred to as 3DLUT). The image processing unit 12 that performs the conversion and performs the density fluctuation removal processing in the 3DLUT density fluctuation removal method according to the first aspect of the present invention, and the output image data D2 output from the image processing unit 12 and the first aspect. Based on the color patch output data D3, the step pattern output data D4, the solid image output data D5 that is a uniform output value, and the like, the output image P1 and a plurality of colors are output based on the color patch output data D3 for performing the density fluctuation removal method of the 3DLUT. A first color chart P2 having a patch P2a and a step pattern P2b and a second color chart P3 having a solid image P3a And the color density (RGB) of the plurality of color patches P2a and step patterns P2b of the first color chart P2 and the solid image P3a of the second color chart P3 are measured. Color patch data D
6, a density measuring unit 16 for obtaining step pattern data D7, solid image data D8, and the like.

First, as described above, the image processing unit 12 shown in FIG. 1 converts the input image data D1 (r, g, b) into a color signal using a built-in 3DLUT and outputs the output image data D2.
(R, G, B) is output to the image output unit 14. In the present invention, in order to create a 3DLUT for color signal conversion with no or extremely reduced density variation,
This is to implement a 3DLUT density variation removing method for removing a unique density variation caused by the image output device 10 from the color patch data D6 of the plurality of color patches P2a of the first color chart P2.

The image processing section 12 is provided with a color conversion means 18 for performing color signal conversion of input / output image data D1 and D2 by a built-in 3DLUT, and color patch output data D3, step pattern output data D4 and uniform output values. Memory 20 for storing certain solid image output data D5 and the like
And the step pattern output data D4 read from the memory 20 and the step pattern data D7 of the first color chart P2 output by the image recording unit 14 and measured by the density measurement unit 16 based on the data D4. 1DLUT creating means 22 for creating a one-dimensional look-up table (hereinafter referred to as 1DLUT) of density conversion density-output data using
6, the image density values at the positions corresponding to the plurality of color patches P2a of the first color chart P2 and the average which is the average value of these image density values from the solid image data D8 of the second color chart P3 measured at 6. The image density values are calculated, and the density fluctuation value calculation unit 24 calculates the density fluctuation value D9 of the position corresponding to the color patch using the 1DLUT for density conversion created by the 1DLUT creation unit 22 from these values.
And the density fluctuation value D9 at the position corresponding to the color patch in the solid image P3a of the second color chart P3 is
Using the 1DLUT for density conversion created by the T creating means 22, it is converted into a density variation value of the color patch data D6 of the first color chart P2, and the converted density variation value is removed from the color patch data D6 to remove the density. Density fluctuation removing means 26 for obtaining color patch data D10 from which fluctuation has been removed
And density variation elimination color patch data D10 for the plurality of color patches P2a of the first color chart P2 obtained by the density variation elimination means 26, and the first color chart P2 having the plurality of color patches P2a.
Color output data D3 used to output 2
3D to create 3DLUT by associating
LUT creation means 28.

Although not shown, the image processing section 12 is provided with a control section for controlling the image processing section 12 itself, the image recording section 14, and the entire image output apparatus 10, and a CPU.
Etc. Therefore, the memory 20 stores the color patch output data D3, the step pattern output data D4, and the solid image output data D which is a uniform output value.
In addition to 5 and the like, information necessary for controlling the image output device 10, the image processing unit 12, the image recording unit 14, and the like by the control unit is also stored. In addition, the memory 20 may store a 3DLUT, that is, grid point data of the 3DLUT. In this case, the color conversion means 18
May be configured by software of the CPU of the control unit, and the 3DLUT may be read from the memory 20 to perform color conversion. Further, the density fluctuation value calculating means 24, the density fluctuation removing means 26, and the 3DLUT which constitute the image processing section 12
A part or all of the creation unit 28 may be configured by software executed by the CPU. The operation of each of the above-described means of the image processing unit 12 will be described in detail.

As shown in FIG. 1, the image recording unit 14 includes digital output image data D2 for image output, color patch output data D3 used in the method of the present invention, and a step pattern output from the image processing unit 12. Output data D4
The image is exposed to a dedicated or unique recording medium such as a photosensitive material or a photoreceptor based on the solid image output data D5 which is a uniform output value or the like, and the exposed recording material is subjected to a developing process to obtain an output image P1, a plurality of images. For outputting as a visible reproduction image such as a first color chart P2 having a color patch P2a or a step pattern P2b, and a second color chart P3 having a solid image P3a. And the like. In the present invention, the exposure system of the image exposure apparatus and the development system of the developing device are not particularly limited, and for example, a conventionally known system such as a laser exposure system or a wet or dry development system can be applied.

The density measuring section 16 measures the color densities of the plurality of color patches P2a and step patterns P2b of the output first color chart P2 and the solid image P3a of the second color chart P3 and outputs a plurality of colors. This is for obtaining patch data D6, step pattern data D7, solid image data D8, and the like. In the present invention, the density measuring unit 16 may be configured by any device that can measure color density and obtain color density data, such as a densitometer, a colorimeter, a scanner ( Image reading device).

The image output device according to the second embodiment of the present invention is basically constructed as described above. The operation thereof and the three-dimensional color signal conversion three-dimensional look according to the first embodiment of the present invention will be described below. A method of removing the density fluctuation of the up-table will be described. FIG. 2 is a flowchart illustrating an example of the method for removing the density fluctuation of the three-dimensional lookup table for color signal conversion according to the first embodiment of the present invention.

As shown in FIG. 2, the color patch output data D3, the step pattern output data D4, and the solid image output data D5 are read from the memory 20 of the image processing unit 12, and are read out from the image recording unit 14 such as a laser printer. Output to In the image recording unit 14, based on the output data D3, D4, and D5, a unique photosensitive material, for example, a reversal film or color photographic paper (paper) is exposed (printed), developed, and developed into a plurality of colors. First having a patch P2a and a step pattern P2b
And a second color chart P3 having a solid image P3a. Here, FIG.
As shown in FIG. 5, the first color chart P2 has a plurality of color patches P2a and step patterns P2b, but the output characteristics of the image output unit 14 to the recording medium are known, and Output data (input signal value to the image output unit 14) and density (gray density reproduced on the output recording medium) of each color of RGB for gray
Information about (eg, calibration characteristics, etc.)
Is known, it is only necessary to have at least a plurality of color patches P2a. On the other hand, as shown in FIG. 3B, the second color chart P3 includes at least a plurality of color patches P2a of the first color chart P2.
May be any as long as it has the solid image P3a at the position corresponding to.

In this manner, as shown in FIGS. 2 and 3A, the first color chart P2 includes primary independent hues, such as R (red), G (green), and B, as 3DLUT color patches P2a. for (Blue), N (a plurality N is 3 (in a) 3) for each hue input signal values (r _i to a color patch output data D3 of the stage, that is, the image recording unit 14, g _j, b _k , i = 1 to N, j = 1 to
N, k = 1 to N), and N × N × N color patch images, that is, N × N × N color patches P2a can be created. In the first color chart P2, at the same time, as a density conversion gray (achromatic color) pattern P2b, step pattern output data D4 of L (25 in FIG. 3A) (steps) for each color of RGB, that is, image recording Input signal values (r _di , g _dj , b
_dk , i = 1 to L, j = 1 to L, k = 1 to L), a gray (achromatic) image pattern P2b of L steps from white to black, that is, L gray patterns (patches) P2b can be created. Further, as shown in FIGS. 2 and 3B, the second color chart P
3 is a solid image output data D5 in which uniform or substantially the same output value for each of the RGB colors, that is, the same or substantially the same level value for each of the RGB colors, is assigned as a one-color solid image P3a for density fluctuation removal (correction). That uniform input signal value to the image recording section 14 of the _{(r c, g c, b} c),
Solid image of all color gray (achromatic color) one color (gray patch)
P3a can be created.

Subsequently, the first color image thus output
N × N × N color patches P2a of the chart P2 and
L step pattern (L gray patches) P2b
The measurement is performed by the density measuring unit 16. And the first color char
From P2, the darkness of N × N × N color patches P2a is obtained.
Multiple (N x N x N) color patches
The data D6, that is, the output signal value (R
_i, G_j, B_k, I, j, k = 1 to N), and L
Density measurement of L gray patches P2b in a Tep pattern
Thereby, the L step pattern data D7, ie, the image
The output signal value (R_di, G_dj, B_dk, I,
j, k = 1 to L). Thus, the first color
Color patch data D6 obtained from the chart P2
(R_i, G_j, B _k, I, j, k = 1 to N)
And sent to the density fluctuation removing means 26 in the subsequent stage.
Can be Further, the L step pattern data D7 (R_di,
G_dj, B_dk, I, j, k = 1 to L) also correspond to the image processing unit 12
And sent to the next stage 1DLUT creation means 22
You.

On the other hand, the output second color chart P3
1-color solid image (beige gray patch with a single color of gray)
P3a is also measured by the concentration measuring unit 16. Then, from the second color chart P3, measurement of a one-color solid image (a full-color gray one-color beta ray patch) P3a at a position corresponding to the N × N × N color patches P2a of the first color chart P2 Thus, the solid image data D8, that is, the output signal values (R _ci , G _cj , B _ck ,
i, j, k = 1 to N). The solid image data D5 thus obtained from the second color chart P3
(R _ci , G _cj , B _ck , i, j, k = 1 to N) are input to the image processing unit 12 and sent to the density fluctuation value calculation unit 24 at the next stage.

Next, the 1DLUT creating means 22 sends the L step pattern data D7 (R _di , G _dj , B _dk , i, L) of the first color chart P2 sent from the density measuring section 16.
j, k = 1 to L) and this L step pattern P2b
Is output from the memory 20 to output the step pattern output data D4 (r _di ,
g _dj , b _dk , i = 1 to L, j = 1 to L, k = 1 to L) for the density conversion 1 between the output density and the output data.
Create a dimension lookup table (1DLUT).
Here, although the 1DLUT for density conversion is created by actually measuring a plurality of step patterns output by the image recording unit 14, the present invention is not limited to this, and functions, particularly simple functions, for example, If it can be expressed or approximated by a linear function, the 1DLUT creating means 22 may not be provided, but means for generating such a function may be provided. In addition, if the output characteristics of the image recording unit 14 are particularly known and the factors and causes of the steady density fluctuation of the system including the image output device 10 and the characteristics of the recording medium such as a photosensitive material are known, the step together with the color patch P2a is performed. Pattern P2
It is not necessary to output b, a 1DLUT preset according to known information may be used, or a simple function such as a linear function may be used to represent or approximate.

Next, the density fluctuation value calculating means 24 outputs the solid image data D5 ( _Rci , _Gcj , _Bck , i, j, k = 1) of the second color chart P3 sent from the density measuring section 16. ~
N) is averaged for each color, and the average value (R _cAV ,
G _cAV , B _cAV ) are calculated. The second calculated in this way
Solid image data D5 (R _ci , G
_{cj, B ck, i, j} , k = 1~N) and its average value (R _cAV, G _cAV, from B _CAV), density conversion for density created by the 1DLUT creating unit 22 - Output data 1
Using the DLUT, reverse conversion is performed, and output data D5 of the solid image P3a of the second color chart P3 at the position corresponding to the color patch P2a of the first color chart P2
(R _c , g _c , b _c ), the concentration fluctuation value D9 (d
Qr, dQg, dQb) are calculated. For example, when the density-output data 1DLUT for density conversion shown in FIG. 5 is used, the color patch P2a of the first color chart P2 is used.
When the B density value of the solid image data D8 of the second color chart P3 at the corresponding position is B1 and the average value thereof is B _AV , the inverse conversion is performed using a function representing a 1DLUT related to the B density. Output data difference dQ
(DQb) can be obtained. The converted density fluctuation value D9 (dQr, dQg, dQb) thus obtained is sent to the density fluctuation removing means 26.

Subsequently, the density fluctuation removing means 26 performs the 1DL
Density for density conversion created by UT creation means 22-
Using the output data 1DLUT, the color patch data D6 (R _i , G _j , B _k , i, j, k = 1 to N) of the first color chart P2 sent from the density measurement unit 16 is subjected to density fluctuation. The density fluctuation value D9 (d
Qr, dQg, dQb) and color patch data D6 (R _i , G _j , B _k , i, j, k = 1 to
N), the density variation is removed from the color patch data D10 from which the density variation of the color patch P2a has been removed.
(R ′ _i , G ′ _j , B ′ _k , i, j, k = 1 to N) are obtained. For example, when the density-output data 1DLUT for density conversion shown in FIG. 5 is used, the first color chart P
When the B density value of the color patch data D6 at the corresponding position of the second color patch P2a is A1, if inverse conversion is performed using a function representing a 1DLUT related to the B density, Q1 is obtained as the corresponding output data. With respect to this Q1, dQ (dQb) of the density fluctuation value D9 relating to the B density at this position calculated by the density fluctuation value calculation means 24,
B density value B1 from average value B _AV in solid image P3a
, The output data Q2 is obtained. By converting the output data Q2 using the 1DLUT, the B density value C1 of the color patch data D10 from which the density fluctuation has been removed can be obtained. In this way, the density fluctuation removal color patch data D10 of the N × N × N color patches P2a of the first color chart P2 thus obtained is obtained.
(R ′ _i , G ′ _j , B ′ _k , i, j, k = 1 to N)
The data is sent to the 3DLUT creating means 28.

Next, the 3DLUT creating means 28 outputs the output data (input signal value) D3 (r _i , r) used to output the previously input N × N × N color patch images.
g _j , b _k , i, j, k = 1 to N), and density patch elimination color patch data (output signal value) D10 (R ′ _i ) of the N × N × N color patch images P2 thus input. ,
G ′ _j , B ′ _k , i, j, k = 1 to N), that is, by associating the input and output signal values of each color patch,
An N × N × N-stage 3DLUT is created. Thus, an N × N × N-stage 3DLUT for color signal conversion, which is the object of the present invention, can be created. By the way, N × N × N-stage 3DLU
As long as T can exhibit sufficient accuracy in the color signal conversion targeted by the present invention, this N × N × N stage 3DL
The UT may be used as it is, but when the number N of stages is smaller than the required accuracy, it is preferable to increase the number of stages of the 3DLUT by interpolation.

In this case, the 3DLUT creating means 24
Is the N × N × N stage 3DLU thus created
T is interpolated by three-dimensional interpolation such as spline interpolation, and the number of division levels for each hue is changed from N to M (M> N).
For example, a high precision (M is increased to M = (N−1) × L + 1)
(× M × M stages) 3DLUT is created. Where 3DL
The method of interpolation of the UT may be linear interpolation, area interpolation, or volume interpolation, and is not particularly limited. If three-dimensional interpolation is possible, a conventionally known three-dimensional interpolation may be used. For example, spline interpolation, tetrahedral interpolation, Triangular prism (prism) interpolation, hexahedral (cube) interpolation, pyramid interpolation, volume interpolation, and the like can be given. From the viewpoint of color reproducibility, spline interpolation is particularly preferable. Thus, a highly accurate interpolation M × M × M-stage 3DLUT can be obtained. Note that, as described above, the N
Of course, if the number N of stages has sufficient accuracy for the target color conversion for the 3D LUT of × N × N stages, the 3D LUT need not be interpolated.

Thus, the 3D LU according to the first embodiment of the present invention
By performing the method of removing the density fluctuation of T, a corrected N × N × N-stage 3DLUT and a corrected M × M × M-stage 3DLUT can be obtained. The corrected N × N × N stage 3 thus obtained
The DLUT or the corrected M × M × M-stage 3DLUT is sent to the color conversion means 18, held or stored, and subjected to color signal conversion between the input / output image data D1 and D2.

It should be noted that the number N of steps of each hue of the 3DLUT which is created first and which is linearly independent is created to create an N × N × N-stage 3DLUT and the number N × N of color patches actually measured.
XN are determined, but if there are a plurality of them, there is no particular limitation, and they may be appropriately selected according to the required accuracy of color reproducibility. Further, the number M of stages of each independent hue of the corrected M × M × M stage 3DLUT created by interpolation is the original 3DL
If the number of stages of each hue of the UT is larger than N, it is not particularly limited, and may be appropriately selected according to required accuracy and continuity of color reproducibility. Of course, the number of steps N and M should be large in terms of color reproduction accuracy and continuity, but as described above, the number of actually measured color patches is N × N
X N, so that a smaller one is preferable as long as the required color reproduction accuracy and continuity are satisfied. For example, the number N of stages of the first 3DLUT is preferably 7 or more, more preferably 9 or more, and the number M of 3DLUTs after interpolation is preferably 12 or more. Preferably, the number is 17 or more. In addition,
It is not necessary to set the upper limits of the number of steps N and M, since the larger the better, from the point of color reproducibility. Note that the relationship between the number N of stages and the number M of stages is not particularly limited, but as one index, as described above, (L-1) points are set between lattice points of an N × N × N-stage 3DLUT. Considering the case of interpolation, M
= (N−1) × L + 1. here,
L is 2 or more, and the case where L is 2 is a case where the midpoint between the grid points of the 3DLUT is interpolated. The 3DLUT concentration variation removing method according to the first embodiment of the present invention is basically configured as described above.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for removing a density fluctuation of a three-dimensional look-up table according to a first aspect of the present invention will be specifically described below based on embodiments. (Embodiment 1) First, in this embodiment, it is assumed that the laser scanning type exposure apparatus has a light amount difference in the main scanning direction, and the effect of the 3DLUT density fluctuation removing method of the present invention is as follows.
The following simulation was performed and confirmed.

First, as a laser scanning type exposure apparatus, a laser color printer (Phisul2; manufactured by Fuji Photo Film Co., Ltd., 7th Color Engineering Conference Paper P11)
9-P126, see October 30 and 31, 1990)
Using a color reversal film Provia (PRO
VIA) (Fuji Photo Film Co., Ltd.) as exposure data for creating a first color chart P2 (hereinafter referred to as patch A) having a plurality of color patches P2a and step patterns P2b for one film. 9.times.9.times.9 3D exposures in which the exposure amount for each hue of RGB is allocated in 9 steps from the maximum value to the minimum value.
LUT creation color patch output data D3 (r _i , g
_j , b _k , i, j, k = 1 to 9) and 25-step (gray) step pattern output data D4 in which three color equivalents are assigned to the exposure amount for each hue of RGB.
Also, using the same laser color printer, exposure data for creating a second color chart P3 (hereinafter referred to as patch B) having a solid image P3a over the entire surface for the same type of film is used for each hue of RGB. A solid image output data D5 having a uniform output value with respect to the exposure amount was prepared.

In this embodiment, since a device having a light amount difference in the main scanning direction of the laser color printer is assumed, a color patch image as shown in FIG. It is assumed that the relationship between the size of the color patch image (the image area of the color chart) in the main scanning direction and the assumed light amount distribution of the laser color printer is as shown in FIG. That is, in the exposed portion as shown in FIG. 4B, it is assumed that only the change in the angle between the scanning light and the photosensitive material causes the light amount distribution, and the light amount difference between the central portion and the point C is: It was assumed to be represented by the following equation (2). d (log ₁₀ E) = − log ₁₀ (cos θ) ² (2) In this embodiment, the image data is represented by the above equation (2) which is generated by the relationship shown in FIGS. 4A and 4B. Assuming that there is such a light amount distribution in the main scanning direction, the logarithmic value of the light amount difference from the central part of the light amount distribution is represented by the color patch output data D3 of the patch A and the step pattern output data D4,
And superimposed on the solid image output data D5 of the patch B.

Based on the color patch output data D3 and the step pattern output data D4 thus obtained, one of the color reversal film vias (PROVIA) (manufactured by Fuji Photo Film Co., Ltd.) is produced using the laser color printer. The film was exposed to light and developed to form a first color chart P2 (patch A) having a step pattern P2b consisting of 9 × 9 × 9 color patches P2a and 25 gray patches.
Using the same laser color printer, the same type of another film is exposed on the entire surface based on the solid image output data D5 in which the light amount difference is superimposed, developed, and subjected to a second process having a solid image P3a. The color chart P3 (patch B) was prepared.

Images of patch A and patch B after development are input using a color scanner SG-1000 (manufactured by Dainippon Screen) and converted into density values of a three-color automatic densitometer (manufactured by Wakasa Optical Laboratory). did. Then, patch A 9 × 9 ×
The density (density A) of each point of the nine color patches P2a and 2
From the density of each point of the 5-step gray step pattern P2b, that is, the color patch data D6 and the step pattern data D7, and the solid image P3a of the patch B,
Density value (density B) at a position corresponding to 9 × 9 × 9 color patches P2a of patch A, ie, solid image data D
8 was read.

As described above, for the 25-step gray step pattern P2b under the read patch A (under the color patch P2a), the output data D4 of the 25-step pattern given to the laser color printer and the density (25 One-dimensional lookup table (1DL) shown in FIG.
UT). In the 1DLUT shown in FIG.
(Blue) The density value will be described as a representative example.
The average value (B _AV ) of the densities B at all the corresponding positions of the color patch P2a, and the density values (B
1) was inversely transformed using a 1DLUT, and the difference (dQ) between the output data D5 of these density values, that is, the density fluctuation value D9 was obtained. Subsequently, (dQ) corresponding to a steady variation is corrected (subtracted) from the color patch output data (Q1) obtained by inversely converting the density value (A1) of the point for obtaining the color patch of the patch A. B) Color patch output data (Q2) was obtained. Thereafter, the corrected density corresponding to the color patch output data Q2, that is, the density fluctuation elimination color patch data D10 (C1) was obtained using the 1DLUT. Similarly, correction was performed for each point of the color patch P2a having the density A, and the density fluctuation removal color patch data D10 (density C) was created for all the points.

The color patch output data D3 and the density C
A 9 × 9 × 9-stage three-dimensional look-up table (3DLUT) for color signal conversion is created between the three-dimensional look-up table (3DLUT) and the 9 × 9 × 9-stage three-dimensional look-up table (3DLUT). ) Is re-interpolated,
A 33 × 33 × 33 stage three-dimensional lookup table (3DLUT) for color signal conversion was created.

In order to evaluate the density reproduction accuracy, MacVesti
The original is a translucent positive image captured in 24 colors.
The three-dimensional conversion templates created by the conventional method and the method according to the present invention, respectively.
Output via cable (3DLUT) LUT1 and LUT2
CIEL for transparent printing ^*a^*b^*Defined in space
Image data of the original image and the reproduced image
The results are shown in Tables 1 and 2.

[0040]

[Table 1]

[0041]

[Table 2]

The average color difference and the maximum color difference obtained from the results obtained by the conventional method and the method according to the present invention shown in Tables 1 and 2 are shown below. Conventional method Method according to the invention Average color difference 1.41 Average color difference 1.16 Maximum color difference 2.91 Maximum color difference 2.17

As is clear from the above results, the density error between the original image and the reproduced image caused by the steady density fluctuation caused by the image output device is 1.41 in average color difference and 2 in maximum color difference in the conventional method. Was 1.91 and the average color difference was 2.16 and the maximum color difference was 2.1 in the method according to the present invention.
7 can be reduced.

The method for removing the density fluctuation of the three-dimensional lookup table and the image output apparatus for implementing the method according to the present invention are basically constructed as described above, but the present invention is not limited to this. Of course, various improvements and design changes can be made without departing from the spirit of the present invention.

[0045]

As described above in detail, according to the method for removing the density fluctuation of the three-dimensional look-up table according to the first aspect of the present invention, the output value for obtaining the output reproduced image output from the image output device is obtained. Of the error between the obtained density of the output reproduced image and the density of the obtained output reproduced image, the steady density fluctuation caused by the image output device (image recording device or development processing device) or its processing is removed, and the three-dimensional The accuracy of creating the look-up table can be improved. Further, according to the image output apparatus of the second aspect of the present invention, even if a solid image has a uniform density over the entire surface, the density unevenness due to a steady fluctuation caused by the apparatus itself and its processing is generated. Can be output without images. Therefore, by preliminarily including a pattern of occurrence of a regular unevenness, the exposure position and the correction amount (for example, the correction amount obtained from FIG. 5) can be stored in the memory, and a uniform solid image can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of an image output device according to a second aspect of the present invention.

FIG. 2 is a flowchart of an embodiment of a method for removing density fluctuation of a three-dimensional lookup table according to the first aspect of the present invention.

FIGS. 3A and 3B are explanatory diagrams showing examples of a first color chart (patch A) and a second color chart (patch B) used in the present invention, respectively.

FIGS. 4A and 4B show an example of the size of a first color chart (patch A) used in Embodiment 1 of the present invention, a photosensitive material of this size, and an exposure unit of a laser scanning exposure apparatus. It is explanatory drawing which shows an example of a relationship.

FIG. 5 is a graph showing an example of a one-dimensional look-up table for density conversion of data for density-output used in the method for removing a density fluctuation of a three-dimensional look-up table of the present invention.

FIG. 6 is an explanatory diagram illustrating an outline of a three-dimensional lookup table in a real image output system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image output device 12 Image processing part 14 Image recording part 16 Density measurement part 18 Color conversion means 20 Memory 22 One-dimensional lookup table creation means 24 Density variation value calculation means 26 Density variation removal means 28 Three-dimensional lookup table creation means D1 Input image data D2 Output image data D3 Color patch output data D4 Step pattern output data D5 Solid image output data D6 Color patch data D7 Step pattern data D8 Solid image data D9 Density fluctuation value D10 Density fluctuation removal color patch data P1 Output Image P2 First color chart P3 Second color chart

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Makoto Yamada 210 Nakanakanuma, Minamiashigara-shi, Kanagawa Fuji Photo Film Co., Ltd.

Claims (10)

[Claims] An image output device outputs a first color chart having a plurality of color patches in a combination in which output values of three colors are changed, and outputs a first color chart of the plurality of color patches of the first color chart. In preparing the three-dimensional look-up table for color signal conversion of the image output device by measuring the color density, the same image output device outputs a second color chart having an image of a uniform output value over the entire surface; A density variation value is obtained from the uniform output value image of the output second color chart, and a density variation specific to the image output device included in the first color chart is removed based on the obtained density variation value. A density fluctuation of a three-dimensional look-up table for color signal conversion, wherein a density fluctuation of a three-dimensional look-up table created is removed. 2. The method according to claim 1, wherein the density variation value is obtained from the uniform output value image of the second color chart as a variation amount of a density value at a position corresponding to each of the plurality of color patches of the first color chart. The removal of the density variation unique to the image output device is performed by removing the variation of the density value of each color patch of the first color chart using the obtained variation amount of the density value at the position corresponding to each color patch. 2. The method according to claim 1, wherein
3. A method for removing a density fluctuation of a three-dimensional lookup table for color signal conversion according to item 1. 3. The method according to claim 1, wherein the variation of the density value of the color patch is removed by changing a variation amount of the density value corresponding to each position of the plurality of color patches of the second color chart via a one-dimensional lookup table. 3. The color signal conversion device according to claim 2, wherein the conversion is performed by converting the output value of the three colors of the color patch into a variation and removing the conversion variation from the output value of the color patch. Density fluctuation removal method of dimensional lookup table. 4. The one-dimensional look-up table is a one-dimensional look-up table created for density correction after converting the output value of the image output device into a characteristic value close to a linear relationship with density. 4. The method according to claim 3, further comprising the steps of: 5. The one-dimensional lookup table outputs a multi-step pattern in which the same output values of three colors are assigned from the image output device, and outputs the output value given to each step of the pattern and the output pattern. 4. The method according to claim 3, wherein the information is created from the relationship with the density of the corresponding step.
Or the method for removing the density fluctuation of the three-dimensional look-up table for color signal conversion according to 4. 6. The color signal conversion 3 according to claim 5, wherein the multi-step pattern is created together with the plurality of color patches on the first color chart.
Density fluctuation removal method of dimensional lookup table. 7. An image output apparatus for converting an input image signal into an output image signal by a color signal conversion three-dimensional lookup table and outputting a visible reproduced image to a recording medium based on the obtained output image signal. Means for storing a combination of output values of three colors of a plurality of color patches of the first color chart and a uniform output value of an image of the second color chart; and the first color chart and the second color chart Means for outputting to the recording medium as a visible reproduction image, density measurement means for measuring the density of the output plurality of color patches of the first color chart and the image of the second color chart, Means for calculating a density variation value from a measured density value of an image having a uniform output value over the entire surface of the second color chart; and the first color chart based on the density variation value. Means for removing density fluctuations from the measured density values of the plurality of patches of the plurality of patches, combinations of output values of three colors of the plurality of color patches of the first color chart, and a plurality of color patches of the first color chart Means for creating the three-dimensional lookup table from the measured density value from which the density fluctuation has been removed. 8. The image output apparatus according to claim 7, wherein said density fluctuation removing means removes fluctuations in density values of a plurality of color patches of said first color chart. 9. The method according to claim 1, wherein the density fluctuation removing unit calculates a density fluctuation value of the second color chart at a position corresponding to the color patch of the first color chart by a variation amount of the output values of the three colors of the color patch. The image output device according to claim 7, further comprising a one-dimensional lookup table for converting the image data into an image. 10. An image output apparatus according to claim 9, wherein said storage means further assigns output values of a multi-step pattern to which the same output values of three colors for creating said one-dimensional lookup table are assigned. And means for creating the one-dimensional look-up table from the measured density values of the multi-step pattern output to the recording medium and the allocation output values based on the allocation output values of the multi-step pattern. An image output device characterized by the above-mentioned.