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In machine vision systems and image processing lighting plays an important role. The biggest machine vision experts in the world say that the most sensitive and critical thing in doing a machine vision project is the choice of light source. Choosing the right light source in machine vision systems makes it easy to program image processing. On the other hand, the wrong choice in many cases causes the project to fail.
Due to the importance of the topic Bina Pardazesh Company, as the first Persian site, has provided specialized training on various types of light sources in machine vision. In the article lighting techniques in machine vision and image processing types of lighting methods and the application of each We taught them to you. In this article, we will introduce 5 of the most widely used light sources used in image processing systems.
Note: some concepts used in this article such as: lighting from the front, lighting in the dark field, light from the back (back light), direct light and diffuser in the article lighting techniques in machine vision and image processing systems are described.
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1- Screen light source (Array Light) used in machine vision
The figure below shows an example of screen light used in front light mode. It can be used as a dark field light source by adjusting the angle of the screen light obliquely. Screen lights are produced in different sizes and colors. Sometimes it is necessary to use a combination of several screen light sources to illuminate a large space.
In the figure below, you can see an example of a screen light in which a diffuse sheet or light spreader is not used. Of course, sometimes a light source with more diffusion is needed, in this case models are used whose screen spreads light (the screen is opaque).
Tips about page light
- The light source should be installed at a suitable distance from the object at a suitable angle.
- Light screen can be used in dimensional control of objects.
- Spreads light on smooth and uneven surfaces.
- It is used to identify product defects.
- It can be used as front lighting and dark field.
2- Ring Light
The picture shows how to place the light ring to see the object. According to the shape of the camera, it sees the object from the middle ring of the ring light. Ring lights are produced in various sizes and shapes, two examples of which are shown in the figure; Depending on the height of the ring light and the angle of the LEDs on it, these types of lights can be used in both front lighting and dark field lighting modes.
One of the important applications of ring light is in the examination of circular objects. For this, it is enough for the camera to see the bottle from a high angle. As shown in the picture, the use of ring light can clearly display this appendage.
Tips about ring lights
- They are cheap compared to other lights and have many uses.
- Their distance from the object and the angle of light radiation should be adjusted correctly.
- They create a good image contrast.
- Checking circular objects such as washers and bottle caps are suitable.
3- Light from behind (Back Light)
Back lights are produced in various sizes and colors; These lights have regular and professional models. The difference between normal and professional Back Light is that in the professional type, the Back Light beam is completely straight. In the figure, you can see an example of Back Light and how it is placed in the field of view of the camera; Depending on the need, Back Light can be used in various applications. As an example, pay attention to the image of an incandescent lamp taken with Back Light; In this image, it is easy to identify whether the lamp string is healthy.
Characteristics of the light from behind (Back Light)
- Maximum contrast is created between the object and the background.
- Back lightt’s are used in measuring objects, detecting holes in objects, etc. As an example, the presence (or absence) of holes on a metal piece can be checked using a backlight.
- In this type of imaging, the photo is simplified as a silhouette, thus simplifying the recognition of the relevant features in the image.
- This type of lighting can be used in product inspection at high speed.
- In semi-transparent objects, defects can be detected with the help of backlight.
- Details on the surface will be lost with Backlight.
- For objects that contain several bases or parts, the backlight is difficult to use or basically unusable!
4- Linear light sources (Bar Light) in machine vision
Linear light is the cheapest light used in image processing, which can be used in front lighting and dark field. You can see how to identify barcodes using linear light in the picture. Linear lights take up little space. These lights can be easily installed and by adjusting their distance and angle to objects, unwanted reflection in the image can be avoided. One of the applications of these lights can be reading the barcode as shown in the picture.
Features of linear light (Bar Light)
- Linear lights can be used to control the external dimensions of the object, inspect labels and inspect product defects.
- Light light is linear and direct.
- It is used to illuminate smooth and non-smooth surfaces.
Linear lights can be combined with each other in pairs and fours to illuminate objects from the sides. The image below shows a combination of four lights installed on a stand. In this case, the angle of individual lights can be changed using the adjustment screw on the base to reach the desired state. If we bring this quadruple light close to the object and reduce the angle of the lights to zero, we will see the dark field image of the object. (The concept of dark field is described in lighting techniques)
5- Dome light source in vision systems
Dome light is a fully diffused light. In this method, the light shines on the object in all directions and illuminates all the details of the image uniformly. The dome light with its uniform brightness makes dark and bright particles invisible in the image. Pay attention to the pictures taken of a metal piece with a dome light and a screen. The image of the metal piece with dome light does not have any reflection and is uniform.
These types of lights are made in two types of dome (Dome Light) and tunnel (Tunnel Dome Light). Tunnel lights can be used to illuminate objects whose length is greater than their width.
This light source will generally be located near the object and increasing the distance will cause the light to appear directly on them and the part of the object that has more curvature will be a little dark.
Features of light dome
- Due to the presence of a single light, the irregularities and scratches on the figure are illuminated uniformly and are less noticeable; In other words, these lights weaken the texture; Therefore, they are very suitable for detecting particles or contamination on surfaces.
- In this type of lighting, different colors in the photo can be clearly distinguished and distinguished from each other. For this reason, they are very suitable for color recognition.
- This type of lighting is excellent for identifying shiny and metallic materials, rounded and curved shapes, and suppresses reflections.
- One of the disadvantages of tunnel and dome lights is that they have a hole in the center, the camera sees the object through the middle of that hole; Because of this hole, the center of the photo is a bit dark.
In this article, we explained 5 widely used light sources in machine vision and image processing systems. If you need more information, please ask your questions below the article so that we can answer them as soon as possible.
If you need more specialized knowledge in this field, you can visit the lighting section on the main language site of vision-doctor refer to
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