Industrial polarization camera whitepaper
Gaspar van Elmbt
Daheng Imaging is familiar in the industrial polarized camera segment by implementing the Sony-IMX250 monochrome image-sensor. Recently the IMX264 has also been added to the portfolio. The Industrial polarization camera systems are able to capture information which a normal line or area industrial camera is not able to obtain. A polarization camera conducts a two-dimensional analysis. It measures both the degree and direction of the polarization of the light. As a result, the final image has almost no reflections from external light sources. A polarized camera is ideal for applications like the inspection of glossy products and transparent products.
Standard Machine vision camera versus polarized camera
The following examples show on the left-hand side an image captured with a standard machine vision camera and on the right-hand side an image captured with our polarized camera.
Glass inspection (scratch and stain)
These examples show dents and dust on a homogenous glass plane. We can easily find scratches and stains (fingerprint and dust) due to differences in the degree of polarization.
Tablet filling inspection
Again, the left image is captured with a standard industrial camera. The right image is captured with our polarization camera. Thanks to the difference in the degree of polarization between the tablet and the aluminum package, it is easy to identify whether the tablets are filled in or not.
Distortion inspection
Left image = standard industrial camera. Right image = polarization camera. With the information of direction of polarization, we can identify both distortions and the direction of distortion of the plane.
Removal reflection
Left image = standard vision camera. Right image = polarized camera.
The information of polarization can be used to remove reflections. IMX250MZR / IMX264MZR has a four-directional polarizer which can simultaneously remove reflection in multiplanes.
Would you like to know if a polarization camera would be suitable for your application? Reach out below or read further.
How does a polarization camera work?
The image below explains how a polarization filter works. A light (yellow ray) sends out light beams (Black line). Every light beam consists of light waves with different angles (the orange and gray waves). A polarization filter (the light gray stripes) block light waves that have a certain angle (in the image the gray waves) and the light waves that have the right angle (orange waves) will pass. So, only the light wave with the right angle (orange waves) will hit the lens and sensor of the camera. When a polarized light wave (the remaining orange waves after the polarization filter) hits the surface of a non-metallic or transparent object the direct reflected wave stays polarized, while the rest of the polarized light gets unpolarized in all directions.
The polarized reflected light can cause undesirable glare from reflective surfaces, making it harder or impossible for your machine vision system to detect certain elements of an object. With the use of a polarizing filter this effect can be controlled. The polarized light will be blocked by the polarized filter of the camera while the unpolarized light will pass. As a result, the glare and reflections are reduced, making it easier for your vision system to detect defects.
Example 1: Application for polarization camera
The first example application where polarization cameras can be used is the capturing of single-colored objects, like tomatoes. With the use of a normal vision camera, it is hard in some applications to segment the different products (like tomatoes) of each other or detect surface defects. Polarized camera systems on the other hand make this process easier, where the additional dimension of analyses can detect difference in the surface of single-colored objects. Polarized cameras could for example be used on conveyor belts which scan single-colored objects, like tomatoes in a production line.
Example 2: Application for polarized camera
The second example of an application where a polarized camera could be utilized is capturing images of transparent objects. For normal vision camera systems, it is in some cases difficult to detect the characteristics of transparent objects from an image that was captured. Namely, because when light transits through a translucent object, its polarization changes. Present camera systems need their polarization parameters adjusted to detect the product properly. However, differentiation of light transmittance can be automatically captured by a polarization camera. A polarized camera system is well suited for conveyor belts in a production line which transport
transparent products, detecting the presence of foreign materials and detecting stamped marks.
Specification of the Sony IMX250MZR polarization camera
The MER2-502-79U3M-POL polarization camera with the Sony IMX250MZR image sensor uses a 3,45µm pixel size and has a total resolution of 5.07 Megapixel. The polarization camera has a polarizer filter which is a four-directional polarizer placed on the photodiode of the image sensor. This means that this polarized camera is able to capture a four directional image in one shot. And calculates the angle and direction of polarization based on the intensity of every direction of polarization. The filter incorporates a 2x2 pattern, where every pixel has a filter with a different angle. Whilst using polarized light the only portion of light perpendicular to the angle of the filter will pass.
Polarization filter angles
Summarized, the polarization filter characteristics are:
- When the filter blocks light at a 90º angle, it passes 0º through the filter.
- When it blocks light at a 45º angle it passes 135º through the filter.
- When it blocks light at an 135º angle it passes through 45º the filter.
- Finally, when it blocks lights at an 0º angle it passes light through a 90º angle.
The model of this polarization camera is MER2-502-79U3M-POL. It has a USB3 interface, a 2448(H)x2048(V) resolution, 79 fps, 2/3”, global-shutter, and a 3,45µm x 3,45µm cell size.
Specification of the Sony IMX264MZR polarization camera
Our MER2-503-36U3M-POL polarization camera with the Sony IMX264MZR image sensor uses a 3,45µm pixel size and has a total resolution of 5.03 Megapixel. The polarization camera has a polarizer filter which is a four-directional polarizer placed on the photodiode of the image sensor. This means that this polarized camera is able to capture a four directional image in one shot. And calculates the angle and direction of polarization based on the intensity of every direction of polarization. The filter incorporates a 2x2 pattern, where every pixel has a filter with a different angle. Whilst using polarized light the only portion of light perpendicular to the angle of the filter will pass.
Polarization filter angles
Summarized, the polarization filter characteristics are:
- When the filter blocks light at a 90º angle, it passes 0º through the filter.
- When it blocks light at a 45º angle it passes 135º through the filter.
- When it blocks light at an 135º angle it passes through 45º the filter.
- Finally, when it blocks lights at an 0º angle it passes light through a 90º angle.
The model of our polarization camera is MER2-503-36U3M POL. It has a USB3 interface, a 2448(H)x2048(V) resolution, 36 fps, 2/3”, global-shutter, and a 3,45µm x 3,45µm cell size.
Conventional polarization camera sensors compared to theIMX250MZR / IMX264MZR
When speaking of conventional polarization camera sensors, you see that the polarizer is placed on top of the chip lens layer. The Sony IMX250MZR / IMX264MZR sensor on the other hand is placed under the on-chip lens layer. As a result, the incident angle and extinction ratio improved because of the shorter distance between the photodiode and polarizer. Often vision integrators also tend to use a polarization filter mounted on the lens. This filter can only block polarized light in one angle, while our polarization camera with the Sony IMX250MZR / IMX264MZR can block and detect light in 4 angles simultaneously.
VA Imaging and Polarization Cameras?
Daheng Imaging has a polarization camera with the Sony IMX250MZR image sensor and recently released a polarization camera with the Sony IMX264MZR image sensor. If you think your application requires a polarized camera, please contact us. We are more than happy to help select the right polarization camera for you.
