A good operating platform should be able to handle images in the shortest time, and good machine vision software should be easily applied in a series of cases, good cameras and lenses should be with minimal distortion and sufficient resolution. However, what is the characteristic of good machine visual lighting? What is the role of the light source in the analysis processing of the image?
Judging the goodness of the lighting of the machine, you must first understand what is the light source needs! Obviously the light source should not only enable the detecting component to be "see" by the camera. Sometimes, a complete machine vision system cannot support work, but only optimizes the light source to work properly.
Contrast: Contrast is very important to machine vision. The most important task of the lighting of the machine's visual application is to make the characteristics that need to be observed with the most contrast between the image features that need to be ignored, so that it is easy to distinguish. Contrast is defined as a sufficient gray measurement between the regions around the feature and its surrounding. Good lighting should be able to ensure that the features that need to be detected are highlighted in other backgrounds. Brightness: When choosing two light sources, the best choice is to select the brighter. When the light source is not lit, there may be three bad situations. First, the signal-to-noise ratio of the camera is not enough; since the brightness of the light source is insufficient, the contrast of the image is inevitable, and the possibility of noise on the image is also increased. Second, the brightness of the light source is not enough, inevitably increase the aperture, thereby reducing the depth of field. In addition, when the brightness of the light source is insufficient, the effect of random light such as natural light is the largest. Robust: Another method of testing a good light source is to see if the light source is minimally sensitive to the position of the component. When the light source is placed in different regions or different angles of the camera, the resulting image should not change. The direction of directionality is high, increasing the possibility of specimens of the highlighting region, which is not conducive to the end of the features. In many cases, good light sources need to have the same effects in the laboratory in the actual work. A good light source needs to make the features you need to find very clearly. In addition to being outside the camera, a good light source should be capable of producing the maximum contrast, brightness is sufficient and is not sensitive to the location of the components. The light source is selected, and the remaining work is too much! The machine visual application is concerned about reflected light (unless you use backlight). The geometry, gloss and color of the object surface determine how light reflects the surface of the object. The light source control of the machine's visual application is attributed to how to control the light source reflection. How can I control the reflection of the light source, then the image obtained can be controlled. Therefore, in the machine visual application, when the light source is incident on the surface of the given object, it is to control the light source and its reflection. The light source can predict that the reflection of the light source is predicted when the light source is incident on the surface of the object. The light source may be absorbed or reflected. Light may be completely absorbed (black metal material, difficult to illuminate) or partially absorbed (resulting in different changes in color and brightness). Lights that are not absorbed will be reflected, the angle of incident light is equal to the angle of reflected light, greatly simplifies the machine visual light source, as the ideal desired effect can be achieved by controlling the light source. Object surface: If the light source propagates in a predictable manner, then what is the reason for the light source of the machine to be so tricky? It is caused by complicating machine visual illumination that is caused by changes in object surface. If the surface of all objects is the same, it is not necessary to use different light source technology when solving practical applications. However, due to the difference in the surface of the object, it is necessary to observe the surface of the object in the field of view, and the reflection of the light source incident. Control reflection: The above mentioned above, if the reflected light can be controlled, the image can be controlled. This is no longer over. Therefore, when designing the light source design involving the machine visual application, the most important principle is to control where the light source is reflected to the lens and reflection. The light source design of the machine's visual is the study of reflection. In the visual application, when an object is observed to determine what kind of light source, you must first ask yourself: "How can I make the object appear?" "How can I apply the light source to reflect the light to the lens To obtain an object appearance? "The factors affecting the reflection effect are: the position of the light source, the texture of the object surface, the geometric shape of the object, and the uniformity of the light source. Location of the light source: Since the light source is reflected in the incident angle, the position of the light source is important to obtain high contrast. The target of the light source is to achieve the reflection of the light source to the background of the characteristics of interest to the light source. The predicted light source can determine the position of the light source on the surface of the object.
Surface texture: The surface of the object may be highly reflected (specular reflection) or high diffuse reflection. The main factor determined that the object is a mirror reflection or a diffuse reflection is the smoothness of the surface of the object. A diffuse surface, such as a uncoiled paper, has a complex surface angle, which is very bright when viewed with a microscope, which is due to changes in the surface angle of the object, which caused the light source to illuminate the object surface and is dispersed. And a smooth paper has a smooth surface and reduces the angle of the surface of the object. The light source is irradiated on the surface of the light source and reflected in an incident angle. Surface shape: A spherical surface reflected light source is not close to the plane object. The more complex the shape of the surface of the object, and the change in the surface of the surface is complicated. Corresponding to a polished mirror surface, the light source needs to be irradiated at different angles. Lights can be reduced from different angles. Light source uniformity: uneven light will cause uneven reflection. Uniformity is related to three aspects. First, for the field of view, the visual portion of the camera should be uniform. Simply put, the dark area in the image is lacking reflected light, and the highlight is too strong here. The uneven light will make the light in part in the field of view more than other regions. Thereby, the surface reflection of the object is not uniform (assuming that the reflection of the surface of the object is the same). The uniform light source compensates the angular change in the surface of the object, even if the geometry of the object is different, the reflection of the light source is also uniform. Application of Light Source Technology: Light source technology is the geometric and position of the design of the light source to make the image have contrast. Light sources will make those areas of interest and require machine visual analysis more prominent. By selecting light source technology, you should care about how objects are reflected and scattered. Here are six lighting techniques: universal lighting, backlight, coaxial (coaxial), continuous reflection, dark domain, and structural light. General purpose illumination: General Lighting is generally carried out with annular or point-like illumination. The ring lamp is a common general purpose lighting method, which is easy to mount on the lens, which provides sufficient illumination to the diffuse surface. Backlight illumination: Backlighting is the back of the object in the object relative to the camera. This illumination method is very different from other illumination methods because image analysis is not a waterflower but incident light. Backlighting has a strong contrast. The surface characteristics of the object may be lost during the backlight technology. For example, a backlight technique can be applied to measure the diameter of the coin, but it is not possible to determine the front and negative surface of the coin. Coaxial illumination: Coaxial lighting is a surface that is irradiated with the axial direction of the camera in the same direction to the surface of the object. Coaxial lighting uses a special semi-reflective mirror reflecting the light source to the lens axis direction of the camera. The semi-reflective mirror is only passed by the light source from the surface of the object perpendicular to the lens. Coaxial lighting technology is useful for achieving uniform illumination of the flat object and the surface of the mirror feature. Furthermore, the technique can also achieve the surface angular change portion highlight because light reflected by the surface of the camera lens does not enter the lens, resulting in a dark surface. Continuously reflection illumination: continuous diffuse reflection illumination is applied to the reflective or complex angle of the surface of the object. Continuously diffuse reflection lighting applies a uniform illumination of hemispherical to reduce shadow and mirror reflection. This illumination is very useful for completely assembled circuit board lighting. This source can reach a uniform illumination of the 170 stereoscopic range. Dark domain lighting: dark domain lighting provides low angle lighting relative to the surface of the object. Using the camera to shoot the mirror to make it in its field of view, if you can see the light source in the field of view, it is considered to make the bright domain lighting, and the opposite can not see the light source in the field of view is dark domain lighting. Therefore, the light source is a bright domain lighting or a dark domain lighting is related to the position of the light source. Typically, dark domain illumination is applied to illumination of illumination or surface texture of the surface partial portion. Structural light: Structural light is light (eg, linear, circular, square) projected on the surface of the object. Typical structural lights relate to laser or optical fibers. Structural light can be used to measure the distance from the camera to the light source. Multi-axis lighting: In many applications, multiple lighting techniques are required in order to make different characteristics of different characteristics. Select the light source: Once the lighting technology is selected, the next step is to choose the problem.
