JP5293355B2 - Glossiness evaluation method, glossiness evaluation apparatus, image evaluation apparatus having the apparatus, image evaluation method, and program for executing the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gloss feeling evaluation method capable of achieving better correspondence with gloss feeling that humans feel, compared to conventional methods, by calculating gloss feeling by a single evaluation device using information of lightness components and chromaticity components of regularly reflected light and diffuse reflected light considering gloss variations and the like, a gloss feeling evaluation device, an image evaluation device provided with the device, an image evaluation method, and a program for performing the method. <P>SOLUTION: The gloss feeling evaluation method for determining a gloss feeling evaluation value of an object based on each of lightness components and chromaticity components of captured color images of regularly reflected light and diffuse reflected light from the object determines the gloss feeling evaluation value of the object by referring a gloss variation evaluation value based on the lightness components obtained from the regularly reflected light, a gloss reference value based on the lightness components of the regularly reflected light and the diffuse reflected light, and a chromaticity change amount indication value relating to the change amount of the color of the regularly reflected light and the diffuse reflected light. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for evaluating gloss of an image formed using color toner or color ink, such as a digital color copying machine, a laser color printer, an ink jet color printer, and offset printing, a gloss evaluation apparatus, and an image evaluation apparatus having the apparatus. The present invention relates to an image evaluation method and a program for executing the method.

  Conventionally, the glossiness of images and characters output by image forming apparatuses such as laser color printers and ink jet printers, or the paper that is the base material thereof, strongly affects the high-quality feeling of output images and the readability of characters. It is a factor of image quality and is used as one of the image quality control items.

  As a method for measuring the glossiness of the surface, a specular glossiness measurement method (JIS-Z8741) is known in which the surface is irradiated with light and the amount of reflected light is measured in the regular reflection direction to obtain the glossiness. Further, “JIS K 7105”, “JIS H 8686” and the like are used as the image clarity measurement method.

  The above specular gloss measurement method is an index indicating only the size of the reflected light beam in the specular reflection direction. The glossiness cannot be quantitatively determined from the specular gloss measurement method. For this reason, glossiness cannot be quantitatively managed, and a problem arises in managing quality.

  In the above-described image clarity measurement method, the intensity of specular reflection light is not measured, but only the reflected light intensity near specular reflection or only the component corresponding to the spread near specular reflection is measured. Therefore, the difference in glossiness due to the difference in the intensity of the regular reflection light cannot be detected, and there is a problem that the correlation with the subjective evaluation value is poor.

  In order to solve the above problems, Patent Document 1 proposes a gloss evaluation device having a higher correlation with subjective gloss than with the conventional method. However, the above-mentioned patent document 1 does not consider the color component of the image of regular reflection light, gloss fluctuation (noise, unevenness), and the gloss and color of the image when viewed under diffuse reflection conditions. It is difficult to evaluate the glossiness of color samples or samples with different gloss uniformity.

  Further, Patent Document 2 proposes a gloss evaluation device that takes into account surface gloss unevenness (gloss uniformity, gloss fluctuation). Gloss unevenness is an index caused by minute fluctuations in specularly reflected light from a measured object (in this case, an image formed) that can be visually judged by humans, and represents a so-called “glare sensation”. is there.

  In this glossiness evaluation apparatus, the sample is irradiated with incident light at a plurality of angles so that an evaluation value corresponding to the visual feeling can be easily obtained without complicating the configuration. The reflected light and the reflected light in the vicinity of the regular reflected light are received, and index values for image clarity and gloss unevenness are used. In the evaluation by the glossiness evaluation apparatus of Patent Document 2 described above, the influence of gloss unevenness is included, but the color of the image sample is not taken into consideration, and thus does not match the glossiness of human appearance.

  Further, Patent Document 3 discloses a method for evaluating the glossiness with reference to the saturation of the diffuse reflection light of the sample. However, the uniformity of the gloss of specularly reflected light cannot be evaluated with this apparatus, and the correlation between the glossiness of humans and samples may be poor in samples with different gloss uniformity. Furthermore, only information on the saturation of diffuse reflected light is used for color, and the chromaticity component of specular reflected light is not taken into account, and glossiness cannot be evaluated correctly.

  Patent Document 4 discloses an invention such as a quantitative evaluation apparatus for uneven gloss. In Patent Document 4, an image including a specularly reflected light component is captured, a deviation image from the average value is calculated, a spatial frequency characteristic of the deviation image is multiplied by a visual spatial frequency characteristic, and an integrated value is calculated. The gloss unevenness is evaluated by a value obtained by multiplying the value obtained by the above by a proportional coefficient, which is different from the invention for evaluating the gloss feeling felt by humans, such as the gloss evaluation apparatus of the present invention.

  As described above, various factors influence the gloss feeling felt by humans, and it is necessary to measure and analyze each factor in order to evaluate the gloss feeling.

  The present invention has been made in consideration of the above-described circumstances, and uses glossiness component and chromaticity component information of regular reflection light and diffuse reflection light to consider gloss variation and the like, and to evaluate glossiness as one evaluation device. Provides a gloss evaluation method, a gloss evaluation apparatus, an image evaluation apparatus having the apparatus, an image evaluation method, and a program for executing the method. The purpose is to do.

  The glossiness evaluation method of the present invention is a glossiness evaluation method for obtaining a glossiness evaluation value of an object based on each brightness component and each chromaticity component of a color image obtained by imaging regular reflection light and diffuse reflection light obtained from the object. The gloss fluctuation evaluation value based on the brightness component obtained from the regular reflection light, the gloss reference value based on the brightness components of the regular reflection light and the diffuse reflection light, the regular reflection light and the diffusion The glossiness evaluation value of the object is obtained by referring to a chromaticity change amount index value relating to the color change amount of reflected light.

  The glossiness evaluation method of the present invention is characterized in that, in the glossiness evaluation method, the gloss fluctuation evaluation value uses a standard deviation of the brightness component of the regular reflection light.

  The glossiness evaluation method of the present invention is the glossiness evaluation method according to any one of the above, wherein the chromaticity change amount index value is the brightness of the image obtained with the regular reflection light and the image obtained with the diffuse reflection light. The absolute value of the difference in average saturation of the color difference calculated using the average value of the component and each chromaticity component is used.

  The glossiness evaluation method of the present invention is the glossiness evaluation method according to any one of the above, wherein the chromaticity change amount index value is obtained by using the regular reflection light as a color change amount of the regular reflection light and the diffuse reflection light. The absolute value of the difference between the average saturation of the obtained image and the average saturation of the image obtained with the diffuse reflected light is used.

  A glossiness evaluation apparatus according to the present invention is a glossiness evaluation apparatus for obtaining a glossiness evaluation value of an object based on specular reflection light and diffuse reflection light obtained from the object, and is based on a lightness component of the regular reflection light. Gloss fluctuation evaluation value calculating means for calculating a gloss fluctuation evaluation value, Gloss reference value calculating means for calculating a gloss reference value based on each lightness component of the regular reflection light and the diffuse reflection light, the regular reflection light and the Gloss for calculating a glossiness evaluation value of the object with reference to the gloss variation evaluation value, the gloss reference value, and the color change amount, a color change amount calculation means for calculating a color change amount of diffusely reflected light And a feeling evaluation value calculation means.

  In the glossiness evaluation apparatus according to the present invention, in the glossiness evaluation apparatus, specular reflection light and diffuse reflection light obtained from the object are obtained using a color image by an imaging means, and the imaging means irradiates the object with light. The light source unit includes a light receiving unit that acquires the specularly reflected light and the diffusely reflected light from the object.

  The glossiness evaluation apparatus according to the present invention is characterized in that, in any one of the glossiness evaluation apparatuses described above, a plurality of the light receiving sections are received at different light reception opening angles with respect to incident light on the object.

  The glossiness evaluation apparatus according to the present invention is characterized in that in any one of the above glossiness evaluation apparatuses, a plurality of the light source units are provided.

  The image evaluation apparatus of the present invention is an image evaluation apparatus having the gloss evaluation apparatus, and the image evaluation apparatus includes a graininess evaluation unit that evaluates graininess based on an image captured with diffuse reflected light, and And display means for displaying the chromaticity, gloss fluctuation evaluation value, graininess evaluation value, and glossiness evaluation value of the regular reflection light image and the diffuse reflection light image.

  The image evaluation method of the present invention is characterized in that the chromaticity, gloss fluctuation evaluation value, granularity evaluation value, and glossiness evaluation value of a regular reflection light image and a diffuse reflection light image are obtained using the image evaluation apparatus. .

  A program for executing the glossiness evaluation method or the image evaluation method.

  According to the present invention, it is possible to obtain a glossy evaluation value having a better correlation with the glossiness perceived by humans than in a conventional glossiness evaluation apparatus, and such an evaluation value is much higher than in a conventional glossiness evaluation apparatus. It is possible to provide a gloss evaluation device that is close to the correlation between the gloss feeling perceived by humans.

It is a block diagram which shows the structural example of the glossiness evaluation apparatus which concerns on 1st Embodiment. It is a figure which shows the schematic structural example of the imaging part which concerns on 1st Embodiment. It is a flowchart which shows the example of a procedure of the glossiness evaluation apparatus process which concerns on 1st Embodiment. It is a figure which shows the schematic structural example of the imaging part which concerns on 2nd Embodiment. It is a figure which shows the schematic structural example of the imaging part which concerns on 3rd Embodiment. It is a flowchart which shows the example of a procedure of the glossiness evaluation apparatus process which concerns on 4th Embodiment. It is a figure which shows the example of the display part of the glossiness evaluation apparatus which concerns on 4th Embodiment.

  Hereinafter, the glossiness evaluation apparatus according to the present invention will be described in detail with reference to the drawings.

  First, from an ergonomic point of view, in the printed image, the human gloss feels not only the glossiness of the specular reflection condition where the gloss is the strongest, but also the glossiness of the object outside the specular reflection condition. It is considered that the glossy effect was obtained. When the sample is tilted at various angles with respect to the light source, the glossiness is the strongest to feel the glossiness. It can be said that it feels big and small. Furthermore, not only the size of the reflected light but also diffused light from the inside of the color material is felt. That is, it is known that the color component of the object in the diffuse reflection direction as well as the regular reflection direction affects the gloss.

  For example, since the gloss is mainly affected by the reflection of light from the light source, if the light source is white light such as a fluorescent lamp, the gloss will feel white. Therefore, if the image sample is black, the difference in color between the sample color and the diffuse reflected light under the specular reflection condition increases, and humans feel more glossy. The glossiness cannot be quantitatively evaluated without considering the color.

[First Embodiment]
<Configuration of glossiness evaluation device>
FIG. 1 shows a configuration example of the glossiness evaluation apparatus of the present embodiment. The glossiness evaluation apparatus includes an arithmetic device and an imaging unit. An imaging apparatus as an imaging unit includes a light source unit that irradiates an object (sample to be evaluated) with light, and a light receiving unit that acquires the regular reflection light and the diffuse reflection light from the object.

  First, the sample to be evaluated is set by the image fixing unit B1, and color images of the specular reflection light and the diffuse reflection light are acquired by the specular reflection light imaging unit B2 and the diffuse reflection light imaging unit B3. The configuration of the imaging apparatus will be described using the schematic configuration example of the imaging unit in FIG.

  In the conventional glossiness measurement method, the optical receiver is a sensor that can measure only the reflected light flux, so that the specular glossiness can be obtained, but information on factors such as gloss variation that affects color and glossiness is obtained. It is not possible. In addition, the spread of reflected light cannot be measured with only one value of specular reflection light. Therefore, the two-dimensional sensors 6 and 7 are used in the light receiver, and further, the sensor 6 and 7 can be used for photographing the specular reflection light (capturing direction of the specular reflection light) and the position capable of photographing the diffuse reflection light (the photographing direction of the diffuse reflection light) ).

  The light source 1 is disposed in the θ direction of the normal line of the sample 4 to be measured, the specular reflection light receiving unit 7 that receives specular reflection light in the −θ direction of the normal line is disposed, and the diffuse reflection light is received in the normal direction. A diffuse reflection light receiving unit 6 is disposed. Here, the normal direction is the direction directly above the measurement point of the object to be measured. In this configuration, the light source 1 is used both as a light source for detecting the specular reflection light and for detecting the diffuse reflection light. For detecting the specular reflection light, a θ-degree incident-θ-degree light receiving system (the light source 1 and the specular reflection light receiving unit 7 is used. Is used for the sample 4 to be measured, which is arranged in the θ-degree direction incidence-θ-degree direction regular reflection, and for detecting the diffuse reflection light, the θ-degree incidence-0 degree light receiving system (light source 1 and diffuse reflection light reception). The geometrical optical conditions of the part 6 are respectively arranged in the θ-degree direction incidence-0-degree normal direction reflection with respect to the sample 4 to be measured. That is, the configuration in the first embodiment is configured such that a common light source is used and specular reflection light and diffuse reflection light are detected by different light receiving units.

  In the glossiness evaluation apparatus of the present embodiment, regular reflection light and diffuse reflection light are received from one defined region of the sample 4 to be measured. The above-described configuration in the first embodiment has the advantage that the light source is a single optical system and can receive regular reflection light and diffuse reflection light simultaneously.

  The angle θ may be an arbitrary angle (excluding 0 degrees and 90 degrees or more). For example, θ can be set to 45 degrees. With respect to the sample 4 to be evaluated, for example, emitted light that has passed through the condenser lens 2 and the diffusing plate 3 from the halogen fiber light source in the imaging unit as the light source 1 is reflected from the sample 4 to be specularly reflected as specularly reflected light. The two-dimensional CCD camera which is the regular reflection light receiving unit 7 arranged is imaged, and the diffuse reflection light is imaged by the two-dimensional CCD camera which is the diffuse reflection light receiving unit 6 arranged in the diffuse reflection direction. Each CCD camera converts the received light into an image signal for each pixel for analysis. Here, a halogen fiber light source is used as the light source, but the present invention is not limited to this, and the light source 1 may be changed to a white LED light source or the like. Further, the regular reflection light imaging unit B2 and the diffuse reflection light imaging unit B3 are not limited to the CCD camera, and may each be a CMOS camera or the like.

  As shown in FIG. 1, the irradiation light emitted from the light source 1 to the sample 4 to be evaluated is received by the specular reflection light imaging unit B2 and the diffuse reflection light imaging unit B3, respectively (in each of the above imaging devices) (Acquired by the reflection direction imaging unit and the diffuse reflection direction imaging unit). The received color image is converted from RGB data into L * a * b * values by the color conversion unit B4 in FIG. 1, and the lightness component and the chromaticity component in each reflection direction are each a lightness component storage unit for regular reflection light. Are stored (saved) in the chromaticity component storage unit B5, the lightness component storage unit of diffuse reflected light, and the chromaticity component storage unit B6.

  Hereinafter, the calculation part in the glossiness evaluation apparatus of this embodiment is demonstrated.

  Next, in the gloss fluctuation evaluation value calculation unit B7, the gloss standard value calculation unit B8, and the color change amount calculation unit B9, reference values necessary for calculating the gloss evaluation value are calculated, and the gloss evaluation value calculation unit is calculated. The gloss evaluation value is calculated in B10, and finally the gloss evaluation value is displayed in the gloss evaluation value display section B11.

<Glossiness evaluation value calculation processing method>
Next, a specific calculation processing method will be described using the flowchart of FIG.

  When the glossiness evaluation is started (step S1), the user sets the sample 4 to be evaluated to the image fixing part B1 (step S2). Next, the sample 4 to be evaluated is irradiated with light from the light source 1 (step S3), and a two-dimensional color image is captured by each light receiving unit in the regular reflection direction and the diffuse reflection direction (step S4). Based on the captured image, the RGB value of each pixel is converted into a CIELab color value (L *, a *, b *) value (step S5).

  The color conversion calculation process (step S5) will be described in detail below.

[Color Conversion Calculation Process (S5)]
The color image signals obtained by imaging the sample 4 to be evaluated are R (x, y), G (x, y), and B (x, y). The R (x, y), G (x, y), and B (x, y) are converted into tristimulus values (X, Y, Z) in the sRGB color space using the following equation (1).

  The converted tristimulus values (X, Y, Z) are converted into CIELab color systems (L *, a *, b *) using the following formulas (2) to (4) from the X, Y and Z values. Convert. The CIELab color system is a color space recommended by the CIE (International Lighting Commission) in 1976, and the values of L *, a *, and b * are defined by the following equations (2) to (4).

  However, in the formulas (2) to (4), they are given as follows.

Here, Xn, Yn, and Zn are tristimulus values of the light source (n is a positive integer of 1 or more, and the same applies to the following equations). In the case of T / Tn ≦ 0.0008856, where T is X, Y, or Z (when T = X, T / Tn = X / _Xn , when T = Y, T / Tn = Y / Y _n, the case of T = Z, T / Tn = a Z / Z _n).), a portion of the cube root and 7.787 (T / Tn) +16/116.

  In the above-described equation (1), the sRGB space is used to convert the color image signal into tristimulus values, but other color spaces may be used. Further, although the CIELab colorimetric values are calculated from the tristimulus values XYZ, other color spaces may be used as long as they can be converted into lightness components and chromaticity components. For example, a CIELUV uniform color space can be used as another color space.

Using the above method, color values Ls ^* of the specular reflection light image (specular-image) (x, y), a s * (x, y), b * (x, y), diffuse reflected light image ( The color values L _D ^* (x, y), a _D ^* (x, y), and b _D ^* (x, y) of diffuse-image are acquired (step S6).

  Next, the process (step S7) for calculating the average value of each color value of the regular reflection light image and the diffuse reflection light image will be described.

[Average Color Value Calculation Processing (S7)]
When the number of pixels of the captured image is n × m (where n and m are positive integers of 1 or more, the same applies to the following formula), the average value of the color values of the image captured in the regular reflection direction Ls ^* ave, as ^* ave, bs ^* ave, and each average value is calculated using the following equations (5) to (7).

Similarly, average values L _D ^* ave, a _D ^* ave, and b _D ^* ave are obtained for diffusely reflected light (step S7). However the (5) - (7) ^{below, Ls * (x, y)} , a s * (x, y), instead of the value of ^{bs * (x, y),} L D * (x, y) , A _D ^* (x, y), b _D ^* (x, y) are used to obtain L _D ^* ave, a _D ^* ave, and b _D ^* ave.

  Next, a process (step S8) for calculating a gloss fluctuation evaluation value that serves as a reference value for evaluating glossiness will be described.

[Gloss fluctuation evaluation value calculation process (S8)]
The gloss fluctuation evaluation (index) value is calculated using the brightness component of the image captured by the light receiving unit positioned in the regular reflection direction. In the present embodiment, the gloss fluctuation evaluation value uses the standard deviation (8) expression of the lightness component L *.

  Note that the gloss fluctuation evaluation value is not limited to the equation (8), and an a * b * chromaticity component may be used, or an index value in consideration of the spatial frequency characteristics of fluctuation may be used.

  Next, similarly to the gloss fluctuation evaluation value, a process (step S9) for calculating a gloss standard value to be referred to when glossiness is evaluated will be described.

[Gloss Reference Value Calculation Processing (S9)]
The ratio (average (9) below) of the brightness average value of each image captured by the two light receiving parts of the regular reflection light and the diffuse reflection light is used as the gloss reference value.

[Calculation processing of chromaticity change amount (S10)]
The amount of chromaticity change is calculated using the lightness component and the chromaticity component of the image captured by the light receiving unit positioned in the regular reflection direction. Here, CIELab color difference (10) is used.

  ΔE is the amount of change in color between the regular reflection light image and the diffuse reflection light image.

[Glossiness Evaluation Value Calculation Processing (S11)]
The gloss evaluation value G is calculated by the following equation (11) using the reference values obtained from the above processing (steps S8 to S10) (step S11).

p _{1 to} p ₇ are coefficients. As the coefficient, a value obtained by calculating an evaluation point in advance from a subjective evaluation experiment result of glossiness for a sample and obtaining an optimum value is used.

  Since the glossiness depends on the color of the sample, this time, the color difference ΔE is used as the sample color information. For example, an absolute value of a difference in saturation values as shown in the following equation (12) may be used.

  Finally, the glossiness evaluation value is calculated, and the calculated value is displayed on the glossiness evaluation value display unit B11 in FIG. 1, and the series of glossiness evaluation value calculation processing ends (step S12).

[Second Embodiment]
In the example of the first embodiment described above, two different cameras are used as the regular reflection light imaging unit and the diffuse reflection light imaging unit for the glossiness evaluation value calculation process, but by using a plurality of light sources. The imaging unit may use a single light receiver.

  In the second embodiment shown in FIG. 4, a light source a1 for detecting regular reflection light is arranged in the θ direction of the normal line of the sample to be measured a4, and a light source a′1 for detecting diffuse reflection light is arranged in the normal direction. Then, a reflected light receiving part a6 that receives regular reflection light and diffuse reflection light in the −θ direction of the normal line is arranged.

  With such a configuration, the reflected light receiving part a6 can be used as both the light receiving part for detecting the regular reflected light and the diffuse reflected light, and the θ degree incident-θ degree light receiving system is used for detecting the regular reflected light. In order to detect diffuse reflected light, a 0 degree incident-.theta. Degree light receiving system is used. That is, in the configuration of the second embodiment, irradiation light emitted from different light sources becomes regular reflection light and diffuse reflection light reflected by the measurement object a4, and is detected by a common light receiving unit a6. In the configuration of the second embodiment, the light receiving unit is a single optical system and cannot receive regular reflection light and diffuse reflection light at the same time. Therefore, the two light sources a1 and a'1 are controlled and sequentially turned on at a predetermined timing. It is obtained by receiving regular reflection light and diffuse reflection light at different timings. As in the configuration of the second embodiment, by using a common light receiving unit, there is an advantage that measurement errors due to variations in sensitivity of light receiving sensors and variations in spectral sensitivity characteristics do not occur. Since the method for calculating the gloss evaluation value is the same as that in the first embodiment, description thereof is omitted.

[Third Embodiment]
FIG. 5 shows a schematic configuration example of the imaging unit of the third embodiment. As in the first embodiment, the light source b1 is provided with a halogen fiber, and a condenser lens b2 and a diffusion plate b3 are provided in front of the light source b1 in the irradiation direction. The difference between this embodiment and the first to second embodiments described above is that b1 to b3 which are optical systems of the light source are centered on the sample 4 to be measured so that a specular reflection light image and a diffuse reflection light image can be acquired. It is possible to move on the circumference. In other words, the light source and its optical system are combined into one and can be moved.

  In the present embodiment, the light receiving unit b6 is fixed in the −θ direction with respect to the normal direction, and when imaging regular reflection light, the light source b1 is controlled and moved in the θ direction with respect to the normal direction. Therefore, after the sample b4 to be measured is irradiated from the light source b1 and the regular reflection light is imaged by the light receiving unit b6, the captured image is stored in the regular reflection light imaging unit B2 of FIG. Next, when imaging diffuse reflected light, the light source b1 moves in the normal direction, that is, in the direction perpendicular to the sample b4 to be measured, irradiates the sample b4 to be measured, and the diffused reflected light is received by the light receiving unit b6. Is captured and stored (saved).

  The gloss evaluation value can be calculated by performing the same processing as in the first embodiment based on the color images picked up in the respective directions. According to this, since the light source b1 and the light receiving part b6 are each independent, there is no need to correct the difference between the light sources, and there is an advantage in that the cost can be reduced.

[Fourth Embodiment]
In this embodiment, a gloss evaluation apparatus will be described in which means for evaluating the graininess of an image from a diffuse reflected light image is provided in the gloss evaluation apparatus shown in the examples of the first to third embodiments. As the configuration of the imaging unit, the configurations of the first to third embodiments described above can be used as they are. In this embodiment, an image evaluation apparatus using the imaging unit shown in the first embodiment will be described as an example. Here, the graininess indicates noise or smoothness of an image, and is an important image quality item that determines image quality. The image from the regular reflection light is affected by the reflection light from the surface of the sample 4 to be measured, and the graininess cannot be correctly evaluated. Therefore, the granularity is evaluated together with the glossiness by using a color image of diffuse reflected light.

  FIG. 6 shows a flowchart of each process in the glossiness evaluation value calculation method according to this embodiment. This is obtained by adding a graininess calculation process (step S10 ′) to S8 to S10 in the flowchart of each process in the glossiness evaluation value calculation method of FIG.

  In step S10 ′, the graininess is evaluated using the chromaticity value (L * a * b *) of the diffusely reflected light image. There are multiple methods for evaluating graininess. For example, as an evaluation method for graininess, the deviation from the average value of the L * a * b * components of the read color image is converted into a spatial frequency component, and multiplied by the visual spatial frequency characteristic (VTF: Visual Transfer Function) for integration. There is a method to calculate based on the value. Here, the graininess evaluation method is not limited, and a graininess evaluation method suitable for the sample to be measured may be used. Such a graininess evaluation method is described below.

  Average values L * ave, a * ave, L * (x, y), a * (x, y), b * (x, y) represented by CIELAB color values L *, a *, b * b * ave is calculated using the same expression as the expressions (5) to (7), and the deviation images hL (x, y), ha (x, y), and hb shown in the following expression (13) Output (x, y).

hL (x, y) = (L * (x, y) −L * ave)
ha (x, y) = (a * (x, y) −a * ave) (13)
hb (x, y) = (b * (x, y) −b * ave)

  The deviation images hL (x, y), ha (x, y), and hb (x, y) obtained by the equation (13) are each subjected to two-dimensional Fourier transform to obtain a two-dimensional Wiener spectrum. At this time, a two-dimensional winner spectrum is displayed in polar coordinates. The Wiener spectrum displayed in polar coordinates is HL (λ, θ), Ha (λ, θ), and Hb (λ, θ) (λ is the spatial frequency (c / deg), and θ indicates the image direction).

  The Wiener spectrums HL (λ, θ), Ha (λ, θ), and Hb (λ, θ) can be integrated and made one-dimensional in the range of 0 to 2π.

  The two-dimensional to one-dimensional conversion shown in the above equation (14) is performed based on the knowledge that the visual spatial frequency characteristic does not depend greatly on the direction of the image to be observed, and simplifies subsequent calculations. Can do. However, whether or not to make it one-dimensional is not an essential part in the present embodiment, and the subsequent calculation may be performed with two dimensions.

  Next, after multiplying the one-dimensional winner spectrum Hg (λ) (where g is L, a, or b) by the human visual spatial frequency characteristic VTF (λ) (Visual Transfer Function), Integrate over the spatial frequency.

  Based on the integral values XL, Xa, and Xb calculated by the equation (15), the graininess evaluation value σ is calculated using the following equation (16).

  In the equation (16), q1 to q7 are parameters, and nonlinear regression analysis is performed from a subjective evaluation value of graininess, which is derived in advance to obtain a graininess evaluation value σ.

The reference value or evaluation value calculated in steps S7 to S11 is displayed on the display D1 in FIG. Average chromaticity of the specular reflection light image calculated in the step ^{(Ls * ave, as * ave} , bs * ave), the average chromaticity of diffuse reflected light image _{^{(L D * ave, a D}} * ave, b D * ave), the gloss reference value, the gloss fluctuation evaluation value, the graininess evaluation value, and the gloss evaluation value are displayed on the display units D2 to D7. Thereby, it is possible to present to the user an image quality evaluation result other than the glossiness evaluation.

  In the present embodiment, by evaluating the graininess from the color image of diffuse reflected light, it is possible to evaluate image quality other than the glossiness evaluation, and it is possible to perform comprehensive image quality evaluation. This makes it possible to perform comprehensive image quality evaluation in a single device, and thus it is possible to provide an image evaluation device that not only increases the speed of image quality evaluation but also has a merit for cost.

  Each block of the calculation part of the glossiness evaluation apparatus of the present invention shown in the block diagrams of FIGS. 1 and 6 described above stores, for example, a central processing unit (CPU) and a control program executed by the CPU. It can be realized by a device having a computer function including a read only memory (ROM), a random access memory (RAM) used by the CPU for calculation, an input / output device, and the like. Each block shown in FIG. 1 described above is a program that enables the computer to execute the above-described control program to calculate the glossiness evaluation value in the first embodiment or the flow shown in FIG. 3 in the fourth embodiment. It can correspond to each function implement | achieved by performing with the apparatus which has a computer function. The present invention includes the above-described program.

1, a1, a'1, b1 Light source unit 2, b2 Condensing lens 3, a3, b3 Diffuser plate 4, a4, b4 Sample 5, a5, b5 Image holding unit 6, 7, a6, b6 Light receiving unit

JP 2007-278949 A JP 2007-33099 A Japanese Patent No. 4111040 JP 2002-350355 A

Claims (11)

A gloss evaluation method for obtaining a gloss evaluation value of the object based on each lightness component and each chromaticity component of a color image obtained by imaging regular reflection light and diffuse reflection light obtained from an object,
The gloss fluctuation evaluation value based on the brightness component obtained from the regular reflection light, the gloss reference value based on the brightness components of the regular reflection light and the diffuse reflection light, and the colors of the regular reflection light and the diffuse reflection light A glossiness evaluation method for obtaining a glossiness evaluation value of the object with reference to a chromaticity change amount index value relating to a change amount of the object.   The gloss evaluation method according to claim 1, wherein the gloss fluctuation evaluation value uses a standard deviation of a brightness component of the regular reflection light.   The chromaticity change amount index value is an average saturation of color differences calculated by using each brightness component and an average value of each chromaticity component of the image obtained with the regular reflection light and the image obtained with the diffuse reflection light. The glossiness evaluation method according to claim 1 or 2, wherein an absolute value of the difference is used.   The chromaticity change amount index value is an average saturation of an image obtained with the specular reflection light and an average image of the image obtained with the diffuse reflection light. The glossiness evaluation method according to any one of claims 1 to 3, wherein an absolute value of a difference from saturation is used. A gloss evaluation device for obtaining a gloss evaluation value of the object based on regular reflection light and diffuse reflection light obtained from the object,
Gloss fluctuation evaluation value calculation means for calculating a gloss fluctuation evaluation value based on the lightness component of the regular reflection light, and a gloss reference value for calculating a gloss reference value based on the lightness components of the regular reflection light and the diffuse reflection light The calculation means, the color change amount calculation means for calculating the color change amount of the regular reflection light and the diffuse reflection light, the gloss variation evaluation value, the gloss reference value, and the color change amount A glossiness evaluation apparatus comprising: glossiness evaluation value calculation means for calculating a glossiness evaluation value of an object.   The specular reflection light and diffuse reflection light obtained from the object are obtained using a color image by the image pickup means, and the image pickup means emits light to the object, the specular reflection light from the object and the diffusion. The gloss evaluation apparatus according to claim 5, further comprising a light receiving unit that acquires reflected light.   The glossiness evaluation apparatus according to claim 6, wherein the light receiving section includes a plurality of light receiving portions that receive light with different light reception opening angles with respect to light incident on the object.   The glossiness evaluation apparatus according to claim 6 or 7, wherein a plurality of the light source units are provided.   An image evaluation apparatus comprising the glossiness evaluation apparatus according to any one of claims 6 to 8, wherein the image evaluation apparatus evaluates graininess based on an image captured with diffusely reflected light. An image evaluation apparatus comprising: evaluation means; and display means for displaying chromaticity, gloss fluctuation evaluation value, graininess evaluation value, and glossiness evaluation value of a regular reflection light image and a diffuse reflection light image.   An image evaluation method comprising: obtaining the chromaticity, gloss fluctuation evaluation value, graininess evaluation value, and gloss evaluation value of a regular reflection light image and a diffuse reflection light image using the image evaluation apparatus according to claim 9. .   A program for executing the glossiness evaluation method according to any one of claims 1 to 4 or the image evaluation method according to claim 10.

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