JPH11265450A - Color difference identification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To globally analyze the color state of a processed object such as a piece of dyed or colored cloth, and to identify the delicate color differences with high accuracy and high reproducibility by showing plural check objects in two-dimensional lattice array and comparing the feature values obtained from the lattice arrays with each other for identification of colors of those check objects. SOLUTION: Plural check objects are represented as two-dimensional lattice arrays of the multi-valued color information respectively, and the feature values obtained from the lattice arrays are compared with each other for identification of the check objects. When the check objects are represented as such lattice arrays, the color distribution is decided in a three-dimensional color space based on the coordinate color information on every inputted check object. Then the color distribution is extracted for a two-dimensional plane consisting of two optional elements which are obtained from three elements forming the three- dimensional color space. A one-dimensional color number showing a position in the two-dimensional plane is given to each of lattice forming the two-dimensional plane, and a color number corresponding to the coordinate color information is assigned to each of coordinates of the check objects.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for discriminating a color difference occurring in an object to be treated which has been colored through steps such as dyeing, coloring and printing.

[0002]

2. Description of the Related Art Industries that apply coloring materials, such as dyeing and printing, or painting and plastic coloring, have shown extremely widespread development, and the colors represented by the coloring materials are overflowing in all fields. Particularly in textiles, higher quality is required for color and pattern than users, but even for fabrics dyed using the same prescription dye, a color difference occurs between the center and the end of the fabric. And so on.

However, in order to solve the above-mentioned problem, evaluation of “color”, particularly, identification of a color having a subtle difference, requires
Since knowledge and technology on the material science aspects of color materials and information and technology on the sensory aspects of color materials are required, two knowledge and technologies that are essentially completely different from each other are required, so that extremely automation is required. It is a difficult process, and in dyeing factories etc., to detect such subtle color differences,
A method in which a skilled worker visually inspects the cloth traveling on the inspection table is mainly used, and a color difference measuring device such as a spectrophotometer is used as a supplement to the visual inspection. Was the actual situation.

[0004] However, the visual inspection by an operator is 1).
Because it depends on human perception, skills, fatigue,
Errors may occur due to individual differences in the work environment and situations,
2) it cannot cope with a test object exceeding the color difference discrimination ability of human vision; 3) it has problems such as an increase in cost due to low productivity and high labor cost, and also has a problem such as a spectrophotometer. The color difference measuring device is 1) difficult to distinguish subtle color differences.
2) The reproducibility of the measured value is low, and 3) the running of the cloth supplied to the inspection table must be stopped for the inspection, so that the productivity is further reduced.

A color difference measuring device such as the above-mentioned spectrophotometer generally measures three numerical values of L ^* (brightness), a ^* , and b ^* (chromaticity and saturation), and determines the values according to JIS. Z / 8729
Since the color difference ΔE ^* _ab is calculated by the following equation (i) defined in the following equation, in the case of two cloths having extremely small differences in L ^* , a ^* , and b ^* , depending on the threshold value of the pass / fail judgment. However, one has no color difference, and the other has a color difference, which results in a different result, which has a problem that the reliability of the measurement result is impaired. Although an online type color difference measuring device for measuring has been developed, a color difference ΔE ^* _ab calculated by the above-described method is generally used, and has the same problem.

[0006]

(Equation 1)

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made to analyze the state of the color of an object to be treated such as a dyed or colored cloth, and to delicately analyze the state. It is an object of the present invention to provide a method capable of accurately distinguishing a color difference with high reproducibility.

[0008]

To achieve the above object, the present invention has the following arrangement. First, in the first invention, a plurality of inspection objects are represented by a two-dimensional grid array of multivalued color information, and at least one or more feature amounts obtained from the two-dimensional grid array are compared. This is a color difference identification method characterized in that the color of the inspection target is identified by the following.

In particular, when the inspection object is represented by a two-dimensional lattice-like array of multi-valued color information, the input color information of each coordinate (A) of the inspection object is used as in the second invention. The color distribution in the three-dimensional color space (B) is obtained based on the two-dimensional plane (C). A color distribution is extracted, and a one-dimensional color number (D) representing a position in the two-dimensional plane (C) is assigned to each grid constituting the two-dimensional plane (C), and the grid to be inspected is given. A method of substituting the color number (D) corresponding to the color information of the coordinates into each coordinate (A) to represent the inspection target with a two-dimensional lattice-like array of multivalued color information is optimal.

Here, the above-mentioned “three-dimensional color space (B) is composed.
Consists of any two elements obtained based on the three elements
The two-dimensional plane (C) is a three-dimensional color space (B).
Not only the combination of two of the three elements that
In addition, from the operation result of any one element and the remaining two elements,
Elements, for example, "element 1 and (element 2^Two+ Element 3^Two)
^0.5And the like.

More specifically, when there are two types of dyed cloths having subtle color differences as inspection objects, these images are converted into gray-scale images of each of the three primary colors (R, G, B) using a CCD camera or the like. The RGB color system including the R, G, and B image values is converted into another three-dimensional color system that can be converted.

For example, the RGB grayscale image value of each coordinate of the cloth image is calculated by using the RGB-XYZ conversion formula of the NTSC color television system shown in the following formula (ii).
After conversion into tristimulus values X, Y, and Z in the XYZ color system, the tristimulus values X, Y, and Z are converted into CIE1976 (L ^* , L ^* , a ^* , b ^* )
A method of converting into three values L ^* , a ^* , b ^* in a three-dimensional space (1) called a space is exemplified.

In the following equation, X, Y, and Z are tristimulus values in the XYZ color system to be inspected, and X _n ,
Y _n, Z _n are tristimulus values of a perfectly diffuse surface.

[0014]

(Equation 2)

[0015]

(Equation 3)

However, when X / X _n , Y / Y _n and Z / Z _{n have} a value of 0.008856 or less, (iii)
) The terms represented by the cubic roots in the expression are replaced by the following expression (iv).

[0017]

(Equation 4)

CIE as a three-dimensional space (1)
Three elements constituting a 1976 (L ^* , a ^* , b ^* ) space,
A two-dimensional plane (2) composed of any two elements of L ^* , a ^* , b ^* , for example, a two-dimensional a ^* b composed of a ^* , b ^*
* Extract only the color distribution in the plane.

Further, a one-dimensional color number representing a position in the plane (2) is assigned to each lattice constituting the a ^* and b ^* plane (2). As shown in FIG. 2, (a ^* maximum value, b ^* maximum value), (a ^* maximum value, b ^* minimum value), (a ^* minimum value, b
^An area (3) consisting of four points of ^* maximum value) and (a ^* minimum value, b ^* minimum value) is divided into a desired resolution, and as shown in FIG. A color number (4) representing the position in 3) is assigned. That is, the area (3) is defined as a
^{In the case} of x-division in the ^* -axis direction and b-division in the ^* -axis direction, color numbers from 0 to xy-1 are given (in the example of FIG. 3, x = 16, y = 16 Because there is
Numbers from 0 to 255 are given. )

In this way, a color system capable of expressing a color in one dimension is obtained. Therefore, the color at each coordinate of the cloth is replaced with a color number (4) to represent the color information of the cloth. That is, by substituting the color number (4) corresponding to the color information of the coordinates into each coordinate of the inspection object, the color information of the continuous cloth surface is converted into the multi-valued discrete color information. It can be represented by a two-dimensional grid array. Hereinafter, in the present specification, the color number (4) selected as described above is referred to as “density value”.

Subsequently, based on the two-dimensional grid-like array of the multivalued density values, a feature amount required for color identification is calculated. like,
First, the two-dimensional lattice array is converted into a simultaneous density occurrence matrix, and thereafter, a feature amount is obtained using the simultaneous density occurrence matrix.

At this time, in converting the two-dimensional lattice array into a simultaneous density occurrence matrix, a pixel (m, n) in an image and a pixel ((Δm, Δ
n), including (−Δm, −Δn) ≡−δ, which will be represented by δ) ((m, n), (m + Δm,
n + Δn)), the image density value: f, g pair (f
A simultaneous concentration occurrence matrix M (f, g) ≡M (g, f) of (m, n), f (m + Δm, n + Δn)) is obtained.

Specifically, as shown in FIG.
In the case of an image consisting of × 5 pixels, δ = (1, 0) and M
When (f, g) is obtained, it is obtained as shown in FIG. For example, the value of M (1,2) is adjacent to the m-axis direction in FIG. 4A where the density value pair (f, g) is (1,2) (that is, Δm = 1). ) The number of pixel pairs. In this example, there are four (1,2) and (2,1),
As shown in FIG. 4B, M (1, 2) and M
(2,1) becomes 4.

Further, as shown in the following equation (v), a matrix M (f,
A value obtained by normalizing each element of g) by the sum of all elements is defined as a simultaneous density occurrence probability P (f, g).

[0025]

(Equation 5)

Then, based on the simultaneous density occurrence matrix M (f, g) and the simultaneous density occurrence probability P (f, g) obtained as described above, the contrast, The energy and entropy are calculated, and a subtle color difference of the inspection object is identified using at least one of them. The contrast: C, energy: E, and entropy: ENT are as follows (vi) to
It is calculated based on (viii).

[0027]

(Equation 6)

[0028]

(Equation 7)

[0029]

(Equation 8)

Further, in addition to the method using a simultaneous density occurrence matrix as a method for calculating a characteristic amount required for color identification based on the two-dimensional lattice-like array of the multivalued density values, First, the two-dimensional lattice array is converted into a density-run-length matrix, and then the density-
A method of obtaining a feature using a run-length matrix is used. Note that the density-run length matrix is a two-dimensional array represented by density values and run lengths. It means a pixel column.

For example, when a run is determined for a two-dimensional array of original images represented by density values shown in FIG. Looks like In this way, the number of runs having the density value f and the length 1 is counted, and the density-run length matrix M (f, l) shown in FIG.

Then, based on the density-run length matrix M (f, l) obtained as described above, as described in the sixth aspect, the strength of a short run, the strength of a long run, The uniformity of the run density and the uniformity of the run length are calculated, and at least one of them is used to identify a subtle color difference of the inspection object. Note that short run strength:
S ₁ , long run strength: S ₂ , run concentration uniformity:
S ₃ and run length uniformity: S ₄ are calculated based on the following equations (ix) to (xii).

[0033]

(Equation 9)

[0034]

(Equation 10)

[0035]

[Equation 11]

[0036]

(Equation 12)

Thus, for a plurality of inspection objects,
Each feature amount is obtained, the feature amount is normalized based on the following equation (xiii), and comparison is performed to identify the color difference of the inspection target (in the case of the present invention, C = 655).
35).

[0038]

(Equation 13)

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

First, the color difference between the two types of wool / polyester mixed cloth, cloth (a), and cloth (b) to be inspected is measured using a handy type spectrophotometer that identifies the color difference by the above equation (i). As a result of measurement, ΔE ^* _ab = 0.72. Hereinafter, the color difference between these two types of fabrics is measured based on the present invention.

In obtaining the color information of these cloths,
Inspection surface illuminance is 95 using 5W inverter fluorescent lamp
Irradiate so as to be 0 Lux, and place the interline transfer system CC at a position where the distance from the inspection target surface is 100 cm.
D, a 3CCD camera having a three-plate type imaging element was installed, and images of the same size were taken with respect to the cloth (a) and the cloth (b) at an aperture f = 2.6. Then, the image data output from the 3CCD camera is output to a personal computer, and all the RGB grayscale images are captured in 256 gradation colors, and an image of 128 × 128 pixels out of 640 × 400 pixels (hereinafter referred to as an original image). Was used for analysis.

Next, based on the RGB grayscale image of 128 × 128 pixels of each of the cloth (a) and the cloth (b),
The tristimulus values of the XYZ color system are obtained by using the equation (ii), and based on these, the CIE1976 is obtained by using the equation (iii).
Each value of L ^* , a ^* , and b ^{* in} the (L ^* , a ^* , b ^* ) space was determined.

Then, the three elements constituting the above three-dimensional space
L^*, A^*, B^*Of which a^*And b^*On a plane consisting of
After extracting only the information of (a)^*Maximum value, b^*maximum
Value), (a^*Maximum value, b^*(Minimum value), (a^*Minimum value, b
^*Maximum value), (a^*Minimum value, b ^*Minimum value)
Region was extracted.

Next, these areas are set in the a ^* direction by 16,
And divided into 16 in the b ^* direction to form a two-dimensional grid array consisting of a total of 256 grids. Then, color numbers from 0 to 255, that is, “density values” of 256 gradations are assigned to each grid. A density value corresponding to each color of the coordinates was substituted for each of the 128 × 128 coordinates of the image. In this way, 1
An original image of 28 × 128 pixels was represented by density values of 256 gradations from 0 to 255.

Thereafter, based on the above-described method, a simultaneous density occurrence matrix and a density-run length matrix were obtained for each of the cloth (a) and the cloth (b).
Based on the equations (vi) to (xii), the feature amounts (contrast: C, energy: E, entropy: ENT, short run intensity: S ₁ , long run intensity: S ₂ , uniform run concentration Sex: S ₂ , run-length uniformity: S ₄ ) were calculated and compared. FIG. 6 shows the result.

[0046]

As described in detail above, when the color difference discrimination method of the present invention is used, it is possible to make a remarkable difference in a specific feature value and evaluate it. Can be accurately identified, and furthermore, since the method of the present invention uses a statistical method, it is possible to identify with high reproducibility.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a three-dimensional color system.

FIG. 2 is an explanatory diagram showing a two-dimensional plane including arbitrary two elements among three elements constituting a three-dimensional color space.

FIG. 3 is an explanatory diagram showing a state in which a region consisting of four points surrounded by maximum values and minimum values of a ^* and b ^* is divided, and density values are given to all grids.

FIG. 4 is an explanatory diagram showing an original image and a simultaneous density occurrence matrix.

FIG. 5 is an explanatory diagram showing an original image, a run, and a density-run length matrix.

FIG. 6 is a radar chart for comparing characteristic amounts of two types of cloths.

[Explanation of symbols]

1 3D space 2 2D plane 3 4 surrounded by maximum and minimum values of a ^* and b ^*
Area consisting of dots 4 Color number (density value)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazuhiro Ishikawa 2-171-1, Tsudanuma, Narashino-shi, Chiba Chiba Institute of Technology (72) Inventor Masahiro Sawamura 4-1-1, Shonohayama, Suzuka-shi, Mie Nebo Textile Co., Ltd. Suzuka Factory

Claims (6)

[Claims] A plurality of inspection objects are represented by a two-dimensional lattice array of multivalued color information, and an inspection is performed by comparing at least one or more feature amounts obtained from the two-dimensional lattice array. A color difference identification method characterized by identifying a target color difference. 2. A color distribution in a three-dimensional color space (B) is determined based on the input color information of each coordinate (A) of the inspection object, and then the three-dimensional color space (B) is configured. Two-dimensional plane (C) consisting of arbitrary two elements obtained based on three elements
, And assigning a one-dimensional color number (D) representing a position in the two-dimensional plane (C) to each grid constituting the two-dimensional plane (C), By substituting the color number (D) corresponding to the color information of the coordinates into each coordinate (A), the inspection object is represented by a two-dimensional grid-like array of multivalued color information. The color difference identification method according to claim 1. 3. The method according to claim 1, wherein the two-dimensional lattice-like array of the multivalued color information is converted into a simultaneous density occurrence matrix, and a feature amount is obtained using the simultaneous density occurrence matrix. Alternatively, the color difference identification method according to claim 2. 4. The color difference identification method according to claim 3, wherein the feature amount selected by using the simultaneous density occurrence matrix is at least one of contrast, energy, and entropy. 5. The method according to claim 1, wherein the two-dimensional grid-like array of the multivalued color information is converted into a density-run-length matrix, and a feature amount is obtained using the density-run-length matrix. The color difference identification method according to claim 1 or 2. 6. The feature quantity selected using the density-run length matrix is a short run strength, a long run strength,
6. The color difference discriminating method according to claim 5, wherein the color difference is at least one of uniformity of run density and uniformity of run length.