JPS6117281B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention detects the surface direction of a highly glossy or mirror-like surface (hereinafter simply referred to as a glossy surface) in the form of a normal direction. This invention relates to a method for detecting the normal direction of a glossy surface, which is used in applications such as the following.

In general, it is extremely difficult to recognize the undulations and three-dimensional shapes created by a glossy surface using conventional methods based on brightness distribution patterns, since the brightness distribution pattern includes images of the surroundings and light source.

One solution is to use silhouettes. However, as a matter of course, we cannot know what is happening inside the contour line.

The present invention was made in view of the above, and it focuses on the fact that the direction of each constituent surface is a powerful clue in understanding the shape and undulation of an object, and it is based on the method of glossy surfaces with various orientations. The main purpose of this invention is to provide a method that can easily detect the line direction (ultimately, the direction of the glossy surface) in a systematic manner, and to enable shape-recognizing weaving of such objects.

First, the principle of the present invention will be explained.

We see surfaces through reflected light. The reflected light consists of a regular reflection component and a diffuse reflection component.
Of these, the reflection component has distinct properties.
That is, (1) It follows the law of reflection.

(2) It has polarization characteristics that can be derived theoretically. This is known as Fresnel's formula.

Since the diffuse reflection component is large on ordinary surfaces with low glossiness, the above-mentioned properties do not appear clearly, and the brightness appears in relation to the inclination of the surface with respect to the direction of the light source. As a result, the brightness distribution pattern is useful for understanding the shape.

On the other hand, on a glossy surface, since the specular reflection component is significant, the brightness of the light source in the direction according to the law of reflection makes a large contribution. Therefore, the content expressed by the brightness distribution pattern is significantly different from that of the non-glossy surface.
very different.

From this, it is appropriate to use the properties of specularly reflected light to determine the direction of the glossy surface.

Among the properties of specularly reflected light, the law of reflection is the first to be considered for its use, but if the reflecting surface is not close to a mirror surface, the image will be blurry, and therefore accuracy cannot be expected, and even if the position of the light source is known, The direction of a surface cannot be determined from reflected light alone. On the other hand, when polarized light is incident, the polarized component included in the specularly reflected light (if the surface is not a perfect mirror, part of the reflected light changes to diffused light and some non-polarized components also occur) changes depending on the angle of incidence. Appears with. Therefore, by illuminating with a light source whose polarization state is known, it should be possible to determine the direction of the reflecting surface from the polarization state of the observed specularly reflected light.

However, there has been no attempt to utilize the properties of reflected polarized light for such purposes, and there are several problems in concretely realizing this. First, since the direction of the target surface is unknown in the first place, it is necessary to arrange a large number of light sources around the target surface. Next, it is necessary to identify which light source is responsible for the observed reflected light. Furthermore, if linearly polarized light such as that used in normal polarization measurements is used as a polarized light source, the processing becomes extremely complicated because the orientation of the plane of polarization must be considered for each light source. Furthermore, in cases such as shape recognition of glossy objects, it is also important to be able to efficiently detect a large number of surfaces.

The present invention solves these problems at once by using circularly polarized light as a light source and measuring and analyzing the Stokes vector of reflected light. That is, if it is known that the light source is circularly polarized light, even if a large number of light sources are used, there is no need to identify the position of the light source, and there is no need to consider the polarization plane of the light source itself. Furthermore, the observed Stokes vector has a simple form, and this Stokes vector can be obtained by counting each part of an image where specularly reflected light is observed, for example in an image input from a television camera. processing becomes possible.

Here, how to represent the surface direction or normal direction to be determined will be explained in advance with reference to FIG.

The observation surface 3 is perpendicular to the specularly reflected light 6 of the incident light 4 at the incident point 5 on the reflection tangent plane (simply referred to as "reflection surface") 1.

A reference orientation ξ is taken within the observation plane 3.

Since the entrance plane 2 is perpendicular to the observation plane 3, the inclination can be expressed by the angle ξ formed by the intersection line between the two.
Here, as shown in the figure, an angle α shifted by 90° is adopted.

The angle formed by the observation direction ζ and the surface normal 7 is the reflection angle, which is equal to the incidence angle.

The direction of the normal at the point of incidence 5 is this α(-90
It can be expressed as (゜≦α≦90°) and (0≦≦90°).

Next, assuming that the amplitude reflectance of the reflecting surface is ρ⊥, ρ‖, the phase difference is δ, and the complex refractive index is m^=n−iK, the following relational expression can be derived from Fresnel's formula.

Here, the subscripts ‖ and ⊥ are parallel to the plane of incidence, respectively,
It represents a vertical component, and sin,
Cos is written as S and C to make it easier to see. This notation will also be used below.

On the other hand, the Mueller matrix representing the polarization change characteristics of a reflective surface whose incident surface is tilted by α can be expressed as follows.

〓〓〓
However, r^ ^* is the conjugate complex number P, U, and V of r^ are P ²
There is a relationship of +U ² +V ² =1, and the change in the relationship is shown in FIG. 2. U is a monovalent function of .

Now, if the incident light is circularly polarized, the Stokes
The vector is Since it can be expressed as

Since some kind of depolarization is involved in an actual reflective surface, the observed Stokes vector is expressed in the following form with the natural light component added.

〓〓〓
Here, in order to remove the influence of the absolute value of the light source brightness and amplitude reflectance, normalization is performed as follows.

Using this relationship, the angle representing the plane direction and α can be determined by the following procedure.

(1) Measure L′, X′, and O′.

(2) Calculate Ip′ as √′ ² +′ ² +′ ² .

(3) Calculate l, x, and o.

(4) Find a condition that satisfies U=o.

Find P and V for (5).

(6) Calculate α from the following relational expression.

signα=sign(-Vl+Px) Next, an example of the configuration of an apparatus for implementing the present invention is shown in FIG. Here, 10 is a group of light sources that generate circularly polarized light 4, for example, right-handed circularly polarized light, from multiple directions, and is designed to project light from around a shiny object 12 with a shiny surface whose direction is unknown. multiple circularly polarized light sources. 1/4 of the reflected light 6 from this object 12 as polarization detection means
The light is guided to an imaging device 17 such as a television camera via a wavelength plate 13 and a linear polarizing plate 14. This reflected light 6
is imaged by the light-receiving lens 15 of the imaging device 17 onto a photoelectric element 16 as a light-receiving element arranged on the observation surface 3 (FIG. 1), thereby identifying the glossy surface of the glossy object 2 as the part to be measured. Here, it is preferable to rotate the 1/4 wavelength plate 13 and the linear polarizing plate 14 using a pulse motor or the like so that changes in the intensity of the reflected light guided to the light receiving element 16 can be automatically sampled. In the present invention, an image taken while rotating the 1/4 wavelength plate 13 is sent to a computer (not shown).
send to The computer analyzes a plurality of sampled images and calculates the normal direction of the object surface, that is, the angle and α, for the portion where specularly reflected light can be observed, using the procedure described above.

The light source 10 may be a point light source such as a light bulb, a line light source such as a fluorescent lamp, or a finite surface light source.Although there may be some difference in brightness, the light source 10 may be a circularly polarizing plate (Fig. (not shown), and arranged so that the circularly polarized light 4 can enter the glossy object 2 from sufficiently many directions, or so that the circularly polarized light 4 can enter the glossy object 2 from many directions. scan. This is to enable specularly reflected light from a glossy surface whose direction is unknown to be observed using any one of circularly polarized lights out of multiple directions of circularly polarized light.
However, it is not necessary to know the direction or brightness of the light source.

The reference orientation taken on the observation plane can be chosen arbitrarily, but
Generally, the horizontal direction is taken.

Various methods of measuring Stokes vectors are known, and one can choose one that is easy to use depending on the purpose and situation, such as accuracy and equipment. If precision is not required, the following method is simple. That is, if the received light intensity measured with the directions of the 1/4 wavelength plate 13 and the linear polarizing plate 14 as β and γ is expressed as I〓 and 〓, for example, I ₀゜, ₀゜, I ₉₀゜, ₉₀゜, I ₄₅
Using four types of measurement values: ゜, ₄₅゜, I ₀゜, ₄₅゜,
It can be obtained as follows.

〓〓〓
The values of P, U, and V can be calculated in advance from the complex refractive index of the reflecting surface or measured separately, and can be appropriately interpolated and stored to shorten the calculation process. can be achieved.

When simultaneously detecting multiple or continuous surfaces, replace the part including the lens 15, observation surface 3, and light receiving element 16 with an imaging device 17, such as a TV camera, indicated by phantom lines in the figure, and detect each image surface. All you have to do is process the points. However, it is assumed that the distance to the object is sufficiently large compared to the aperture and focal length of the lens, and lateral correction is performed for general points that are off the optical axis.

As is clear from the above, according to the present invention, when the glossy surfaces form not only a single plane but also undulations or three-dimensional shapes, the normal direction of each surface, and even the surface direction, can be systematically detected. Furthermore, since a device for this purpose can be provided with a simple configuration, it becomes possible to recognize the shape of objects with glossy surfaces, which has been difficult with conventional methods, and the degree of contribution to this type of shape recognition technology is extremely high.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of how to represent the surface direction or normal direction of a glossy surface, and Figure 2 is a schematic diagram of changes in relational values P, U, and V with respect to the angle of incidence and reflection necessary to define the surface direction. FIG. 3 is a schematic diagram of an example of an apparatus for carrying out this method. In the figure, 1 is a reflective tangent plane, 2 is an incident plane, 3 is an observation plane, 4 is incident light, 5 is an incident point, 6 is reflected light, 7 is a normal to the reflective tangent plane, 10 is a group of circularly polarized light sources, 12 is a glossy object as a measurement target having a glossy surface; 13
14 is a 1/4 wavelength plate, 14 is a linear polarizing plate, 15 is an imaging lens, 16 is a light receiving element, and 17 is the entire imaging device. 〓〓〓

Claims (1)

[Claims] 1. Arranging a plurality of circularly polarized light sources that generate circularly polarized light around a glossy surface whose direction is unknown, and disposing a light receiving means via a polarization detection means in a fixed observation direction with respect to the glossy surface, Each circularly polarized light from a circularly polarized light source is made incident on the glossy surface, the reflected light from the glossy surface reaching the observation direction is guided to the polarization detection means, the output light is received by the light receiving means, and the light is received by the light receiving means. Based on the output of the means, the polarization state of the reflected light is obtained in the form of a Stokes vector, and the normal to the glossy surface is calculated by calculating the Stokes vector and the Mueller matrix representing the polarization change characteristics for the glossy surface. A glossy surface direction detection method characterized by detecting direction.