JP2012184933A - Method and device for measuring distribution of specular reflection light - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and device for measuring the distribution of specular reflection light, capable of measuring the distribution and evaluating unevenness in brightness on a sample surface.SOLUTION: A method for measuring the distribution of specular reflection light includes the steps of allowing illumination light to enter a sample, and measuring the sample surface through a tilted optical system. The angle of the optical axis of the incident illumination light on the sample and the angle of the optical axis for measuring the sample surface have a mirror reflection relation relative to the normal of the sample.

Description

  The present invention relates to a specular reflected light distribution measuring method and apparatus for evaluating the characteristics of specular reflected light of a sample that affects the image quality / texture of paper or plastic. The present invention also relates to a method and apparatus for measuring and analyzing specular reflection unevenness of a sample easily and in a short time.

  The sample here is a generic term for a support capable of forming a surface, such as paper, PET, RC paper (photographic support), wood, plastic, concrete, cloth, leather, metal, and the like. Further, the present invention can also be applied to a printed material in which ink is applied to the sample partially or on the entire surface. Furthermore, this technique can be applied to the measurement of human skin and mucous membranes. Here, an example will be described in which paper is used as a sample, and paper offset printed material is used as printed material.

  Light incident on the paper is reflected by the surface, scattered and reflected inside, and part of the incident light is absorbed. Such reflection and scattering of light is a physical phenomenon that occurs in paper. In particular, in glossy paper such as gloss coated paper and photographic inkjet paper, specular reflection that occurs on the surface of the paper has a strong influence on the appearance such as image quality and texture as gloss perceived by humans.

  The specular reflection here refers to the reflection of light that is incident and received at the same angle on the opposite side from the normal direction of the sample surface, and is also called regular reflection. Gloss is a visual perception attribute mainly determined by the intensity of reflected light.

  Attempts have been made to evaluate subjective glossiness with quantitative measurement values. The main measurement values and measurement methods related to the present invention are as follows. However, since these measuring methods measure part of the gloss phenomenon, many measuring methods have been proposed depending on the purpose.

  As methods for measuring specular gloss, JIS Z8741 specular gloss-measurement method, JIS P8142 paper and paperboard-75-degree specular gloss measurement method, and P8142 (parallel light system) are known (non-patent literature). 1, 2). The measured value is measured as the total amount of this incident light. The measurement result is calculated as one measurement value, here glossiness. In general, as the light receiver for the method of measuring the specular gloss, a photoelectric conversion device that changes the intensity of light such as a photocell or a phototube into an electric signal is used. However, these are methods for measuring the reflected light amount as a total amount, and it is impossible to measure the distribution and unevenness of the specular reflected light at minute positions.

  As a method for measuring image clarity (image definition), JIS K7374 plastic-image definition measurement method is known (Non-patent Document 3). Image definition is also called image clarity. This measurement method obtains characteristics close to the spatial frequency characteristics of the specular reflected light of the sample. This measurement method includes a step of passing an optical comb when measuring the image of the light source slit with a light receiver. Even in this case, similarly to the specular gloss, the value to be measured is the total amount of the specular reflected light that has passed through the comb as one measured value.

  A goniophotometer is known as an apparatus for measuring a goniophotometer. The variable angle luminous intensity is a measurement method that can measure the amount of reflected light by arbitrarily changing the incident angle and the light receiving angle. For example, when the light receiving angle is made equal to a certain incident angle, specular reflection occurs, and the amount of reflected light is measured by changing the angle several times, thereby obtaining a variable angle luminous intensity. Further, an angle when the sample surface is tilted left and right with respect to the incident direction of light is referred to as a declination here. Measurement of this declination luminous intensity is also known. The variable light intensity is also measured under each condition by measuring the reflected light quantity as a total amount, and the light quantity distribution under that condition cannot be measured.

  The gloss index that can be measured by the prior art includes the above-described glossiness, image clarity (image definition), and variable-angle light intensity. In addition, there is a composite evaluation value such as an index expressed by the ratio of specular reflection light and diffuse reflection light such as the contrast glossiness.

  The gloss of the paper is evaluated by the above measured value, for example. However, these evaluation methods measure and evaluate the total amount of reflected light in a somewhat large range (for example, several mmφ to several tens mmφ). On the other hand, the gloss on the paper surface is never completely uniform, and gloss unevenness exists. In particular, in glossy paper such as gloss coated paper and photographic inkjet paper, these gloss unevenness that occurs on the surface of the paper has a strong influence on the appearance such as image quality and texture as gloss unevenness felt by humans.

  The gloss unevenness is a distribution of the amount of reflected light in a minute area of the sample, and is an index based on the specular reflection light distribution.

  The specular reflection light distribution (gloss unevenness) measurement can be realized by measuring the reflection light distribution of the sample by specular reflection. The camera can measure the light distribution, and paper stains and uneven printing density can be measured and analyzed on the sample surface with an imaging device such as a CCD camera that can measure a two-dimensional light amount distribution. In general, however, they measure diffusely reflected light. For example, a method of illuminating from 45 degrees oblique to the sample normal direction and measuring with a camera from the normal direction (0 degrees) has been widely used.

  However, the specular reflection light distribution (gloss unevenness) measurement is a reflection light amount distribution measurement under a condition close to the specular reflection (regular reflection) angle or the specular reflection angle.

  For this reason, when the surface of the sample is measured with a general camera system composed of an image sensor and a lens, since the measurement is performed from an oblique angle, the focal point is blurred before and after being focused at the center. In addition, since the distance from the imaging surface to the sample surface differs before and after the sample and from the perspective of the camera system, the size of the image measured on the imaging surface varies depending on the perspective.

  As described above, it is difficult to measure the reflected light amount distribution of the sample as a surface under the condition of specular reflection.

JIS Z8741 Specular Glossiness-Measuring Method JIS P8142 paper and paperboard-75 degree specular gloss measurement method (parallel light method) JIS K7374 Plastic-Method for measuring image clarity

  An object of the present invention is to provide a measurement method and apparatus capable of measuring and evaluating a specular reflection light distribution that cannot be obtained by a conventional measurement method. The present invention provides a new measuring method and apparatus for uneven gloss and specular reflection light distribution.

  As a result of intensive studies in view of the above, the present inventors have invented the specular reflection light distribution measuring method and apparatus of the present invention.

  That is, (1) including a step of making the illumination light incident on the sample and a step of measuring the surface of the sample with a tilting optical system, the angle of the optical axis at which the illumination light is made incident on the sample, and the surface of the sample A method of measuring specular reflection light distribution of a sample, characterized in that the angle of the optical axis to be measured has a specular reflection relationship with respect to the normal of the sample.

  (2) It includes means for making the illumination light incident on the sample and means for measuring the surface of the sample with a tilting optical system, and measures the angle of the optical axis for making the illumination light incident on the sample and the surface of the sample. An apparatus for measuring a specular reflection light distribution of a sample, characterized in that the angle of the optical axis has a specular reflection relationship with respect to the normal of the sample.

  According to the present invention, even when measuring a specular reflection light distribution having an angle larger than 0 degrees with respect to a normal line of the sample, it is possible to focus on the sample surface widely, and the specular reflection light distribution measurement can be performed on the sample surface at a time. Can do.

  If the specular reflection light distribution can be measured, the gloss unevenness of the sample can be evaluated, and the subjective glossiness felt by humans can be evaluated.

  As described above, the specular reflection light distribution measuring method and apparatus of the present invention can measure the specular reflection light distribution and gloss unevenness of a large area of the sample in one measurement, thereby increasing the accuracy and efficiency of the measurement. it can.

  It is also possible to derive a new index for evaluating the subjective glossiness felt by humans from the specular reflection light distribution.

  The specular reflection light distribution measuring method and apparatus of the present invention can also measure specular reflection light distribution characteristics of human skin and mucous membranes, and can obtain useful information in medical and cosmetic development.

  In particular, the specular reflection light distribution measuring method and apparatus of the present invention can measure specular reflection light distribution of paper, that is, gloss unevenness, and can obtain useful information in paper development.

1 is an overall schematic view of a specular reflection light distribution measurement method and apparatus. The block diagram of an incident device. The block diagram of a light-receiving device. Measurement result of specular reflection light distribution.

  Hereinafter, a specular reflection light distribution measuring method and apparatus according to the present invention will be described with reference to the drawings. The specular reflection light distribution measuring method and apparatus of the present invention are configured as shown in FIG. 1, for example.

  In FIG. 1, the incident device 1 and the light receiving device 3 are installed so as to have a specular reflection relationship at the same angle on the opposite side with respect to the normal of the surface of the sample 2 to be measured. The normal direction of the sample 2 is defined as 0 degree, the angle formed by the optical axis of the incident device 1 with the sample normal line is defined as the incident angle, and the angle formed by the optical axis of the light receiving device 3 with the sample normal is defined as the light receiving angle.

  For example, the incident device 1 is set to an incident angle of 30 degrees, and the light receiving device 3 is set to a light receiving angle of 30 degrees on the opposite side of the normal line.

  In order to comply with the glossiness measurement of paper, the incident device 1 preferably has a positional relationship of 75 degrees and the light receiving device 3 has a positional relationship of 75 degrees. In order to comply with the measurement of plastic glossiness, the incident device 1 preferably has a positional relationship of 60 degrees and the light receiving device 3 has a positional relationship of 60 degrees.

  Although the incident angle and the light receiving angle have a specular reflection relationship with respect to the sample, it is known that the specular reflection light is distributed at the front and rear angles of a sample that is not a perfect mirror surface such as paper. For this reason, the incident angle or the light receiving angle may be set to be shifted by several degrees before and after the specular reflection angle. For example, the incident device 1 is set to 28 degrees, and the light receiving device 3 is set to 30 degrees on the opposite side of the normal line.

  In this way, the specular reflection relationship narrowly means that the incident angle and the light receiving angle are opposite to and equal to the normal, but in the present invention, the specular reflection relationship is the specular reflection angle and its front and rear. An angle. The incident angle or the light receiving angle may be arbitrarily set within the range of the specular reflection angle ± 10 degrees, preferably the specular reflection angle ± 5 degrees.

  The measurement in which the incident angle or the light receiving angle is shifted by several degrees before and after the specular reflection angle is important for evaluation of gloss unevenness.

  As shown in FIG. 2, for example, the incident device 1 can include a light source 11, a point image chart 12, and a collimator lens 13 that generates parallel light using the point image as a light source. The collimator lens 13 may be a single lens or a plurality of lenses.

  The point image chart 12 can be created, for example, by making a hole in a metal plate. A metal plate can be vapor-deposited on a glass plate so that only a point image can be transmitted.

  In the incident device 1 shown in FIG. 2, the set point image chart 12 is converted into parallel light by the collimator lens 13, and the parallel light is incident on the sample 2.

  Since the parallel light has the same incident light and is parallel to the optical axis, the illumination light is preferably parallel light.

  The sample 2 is set on the sample bed 21 as shown in FIG. The sample bed 21 is desirably processed so as not to reflect light when the sample is transparent or transparent because it is thin.

  For example, as shown in FIG. 3, the light receiving device 3 receives the specular reflection light of the illumination light incident on the sample 2 and forms an image with the lens group 31. The light quantity distribution of the formed image is formed on the light receiving sensor 33 and the light quantity distribution is measured. The light receiving sensor 33 takes in this light quantity distribution as two-dimensional (surface, image) data using an array type sensor such as a CCD sensor or an imaging tube. For example, a CCD camera can be used as the light receiving sensor 33 as a device.

  In the case of using a light amount measuring device that measures data of a small area using a photocell, a phototube, or the like, the light receiving sensor 33 changes the measurement position to measure the light amount distribution. For example, as a method of changing the measurement position, an XY stage that can be automatically moved by a program is used.

  The lens group 31 of the light receiving device 3 is a tilt optical system. Here, the surface of the light receiving sensor 33, the surface of the lens group 31, and the sample surface are characterized by being parallel. The optical axis connecting the light receiving sensor 33 of the light receiving device 3, the lens, and the sample is a specular reflection angle with respect to the normal of the sample.

  The tilt optical system is a special technology that has been used for photography. By making the surface of the object parallel to the film surface and moving these intermediate lenses parallel to the surface, the entire object surface is focused. In addition, the surface of the subject is recorded at the same perspective on the film surface. For example, it has been used to shoot a tall building with a focus entirely on the whole. In some cases, the tilt optical system refers to a technique of tilting the lens with respect to the optical axis. Here, the tilt optical system is defined as a technique for measuring a sample surface, a lens surface, and an imaging surface in parallel.

  The specular reflection light distribution measuring method and apparatus of the present invention can measure specular reflection light in a wide range of the sample surface, which has been difficult in the past, by introducing this tilting optical system technique to gloss measurement.

  In the measured two-dimensional (surface, image) light amount distribution data, each point of the data is a reflected light amount at each minute position on the sample surface. When measured under specular reflection conditions, each point of data is the amount of specular reflection light at each minute position on the sample surface, that is, gloss. It is possible to measure how the amount of specular reflection light, that is, gloss is uneven on the sample surface.

  A Wiener spectrum can be obtained from the measured reflected light amount distribution. The Wiener spectrum is a Fourier transform pair of autocorrelation functions, and has been used for analysis of noise (unevenness and variation) in image engineering. The specular reflection light distribution measuring method and apparatus according to the present invention can evaluate unevenness (noise, variation) of reflected light (gloss) on a sample surface.

  Although the embodiment of the invention has been described so far by taking paper as an example, the method of the present invention can be applied to measurement of printed matter, human skin, and mucous membrane. By measuring human skin and mucous membranes, it can be used for medical treatment, diagnosis and development of cosmetics.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this Example.

(Example)
The incident device 1, the sample bed 21, and the light receiving device 3 were manufactured by combining optical components. The sample bed 21 can move in the vertical direction. By this mechanism, the sample surface height can be adjusted in accordance with the thickness of the set paper sample and sample 2.

  A sample was set, illumination light was incident, specular reflection light was measured with a light receiving device of an optical system, and a specular reflection distribution of the sample was obtained.

  The configuration of the incident device 1 will be described with reference to FIG. The light source 11 is an LED lamp and is installed at a predetermined position of the incident device via an optical fiber. The collimator lens 13 was installed and produced so that the point image chart 12 became parallel light. The brightness of the light source 11 can be adjusted. Here, a thin metal plate having a hole having a diameter of 100 micrometers was used as a point image.

  The configuration of the light receiving device 3 will be described with reference to FIG. The camera used was a CCD camera DensitoCam manufactured by Mitsui Optronics. The received mirror-reflected light is imaged by a lens. This image was made so that it could be measured with a CCD camera. The CCD camera used has a 14-bit gradation, and the measured image (light quantity distribution) is transferred to a computer. The detection signal was converted into light quantity from the relationship between the detection signal and the reflection density using a chart having a known optical reflection density in advance, this time using a gray scale of KODAK. As a result, since the detection signal has a substantially linear proportional relationship with the light amount, the detection signal value is hereinafter expressed as the light amount. The minimum value is 0 and the maximum value is 65536 (gradation is 14 bits).

  The lens group of the light receiving device 3 is a tilt optical system. Here, the CCD camera and the lens are provided via a bellows, the imaging device (CCD camera) surface, the lens surface, and the sample surface are parallel, and the optical axis connecting the imaging device (CCD camera) of the light receiving device 3, the lens, and the sample is Specular reflection angle with respect to the normal of the sample.

(Measurement Example 1)
The measurement results are shown below. Moreover, the measurement result by the measuring method of a prior art is shown together, and the effect of this invention is shown.

  Graph paper was measured as a sample. Graph paper is drawn every 1 mm, and vertical and horizontal lines are orthogonal.

  An apparatus based on the specular light distribution measurement method described in the examples was manufactured. The lens group of the light receiving device is an optical system. The optical axis of the light receiving device is 30 degrees with respect to the sample normal. The incident device was also 30 degrees on the opposite side to the sample normal, but here the grid was measured by illuminating uniformly from the surroundings without applying light from the incident device. As a result, an image focused on the entire surface of the graph paper could be measured.

  Although the measured graph paper was measured from an oblique direction of 30 degrees, the grid size of the graph paper was equal on the measurement surface, and the vertical and horizontal lines were parallel and orthogonal. In addition, it was confirmed that the focus was on the entire measurement surface.

(Measurement Comparative Example 1)
The lens group of the light receiving device was prepared as a normal optical system. The optical axis of the light receiving device is 30 degrees with respect to the sample normal. The incident device was also 30 degrees on the opposite side to the sample normal, but here the grid was measured by illuminating uniformly from the surroundings without applying light from the incident device.

  Since the graph paper measured with this apparatus is measured from an oblique direction of 30 degrees, the grid size of the graph paper is different on the measurement surface. The near is big and the far is small. The horizontal line tends to converge toward the vanishing point. In addition, it was confirmed that the focal point is in the center on the measurement surface, but the focal point is blurred in the far and near parts. These are phenomena that occur in normal camera measurements.

(Measurement Example 2)
The measurement results of representative samples are shown below.

  The measurement results of three types of paper are shown as samples.

  Sample a is a glossy (glossy) type of photographic inkjet paper. This is an inkjet paper based on RC paper in which polyethylene is laminated on paper, and is a paper having the same glossiness as glossy photographic printing paper. Hereinafter, it is written as RC gloss IJ paper, identified by a, and the measurement result is shown in FIG. 4a.

  Sample b is a coated paper for printing and is a gloss (gloss) type. This is a printing paper that is calendered to increase its gloss by applying pigments, and is a glossy paper used for calendars and women's monthly magazine photo pages. Hereinafter, it is written as gloss coated paper, identified by b, and the measurement result is shown in FIG. 4b.

  Sample c is high-quality paper for printing. This is a non-glossy printing paper that is not coated with pigment, and is a low-gloss paper that is used for pages with many characters and photo pages with low gloss. Hereinafter, it is referred to as fine paper, identified by c, and the measurement result is shown in FIG. 4c.

  The sample was measured with a measuring machine manufactured based on the specular reflection light quantity distribution measuring method and apparatus of the present invention. The reflected light amount distribution of each material is shown in FIG.

  FIG. 4 is a diagram displayed in a three-dimensional graph. The x-axis (left and right in the figure) is 0 to 100 and is the left and right position in the light beam direction. The y-axis (depth in the figure) is 0 to 100 and is the position in the light beam direction. The z-axis (up and down in the figure) is a light quantity value (detection signal value of the sensor), which is 40000-80000.

  Each sample clearly differs in subjective glossiness. In order from a sample with a high subjective glossiness, RC gloss IJ paper> gloss coated paper> quality paper for printing. It can be seen that the reflected light amount distribution (FIG. 4) tends to correlate with the subjective glossiness of these samples.

  As mentioned above, although this invention was demonstrated based on the Example, this invention is not limited to this Example, Various deformation | transformation is possible.

  The present invention provides a simple and highly accurate measurement method for directly obtaining the specular reflection light distribution of a sample. By this measurement method, unevenness of specular reflection on the sample surface can be measured, and useful information can be obtained in the development of printing paper and a printing method.

DESCRIPTION OF SYMBOLS 1 Incident apparatus 2 Sample 3 Light receiving apparatus 11 Light source 12 Point image chart 13 Collimator lens 21 Sample bed 31 Lens group 33 Light receiving sensor

Claims (2)

  An optical axis for measuring the surface of the sample, and an angle of an optical axis at which the illumination light is incident on the sample. The specular reflection light distribution measuring method for a sample, wherein the angle of the mirror has a specular reflection relationship with respect to the normal of the sample.   Means for injecting illumination light into the sample; and means for measuring the surface of the sample by a tilting optical system; and an optical axis for measuring the surface of the sample, and an angle of an optical axis at which the illumination light is incident on the sample The specular reflection light distribution measuring apparatus for a sample is characterized in that the angle is a specular reflection relationship with respect to the normal of the sample.