A fisheye camera captures the surrounding environment (360°) through a wide-angle lens. The camera not only sees what is in front, behind, left, and right of the camera, but also what is below it. With just one camera, you can capture an entire environment. How does this camera work and when is it beneficial to use this type of camera?
A fisheye lens is not new. A well-known example is the door viewer in the front door of senior citizens’ homes. Via a wide-angle lens in a tube, you can not only see who is at the door, but you also have a view of the hallway, including the ceiling and the floor. The person directly in front of the door is clearly visible, but beyond that, the image becomes increasingly distorted (‘warped’).
Action
The same type of lens as in the door viewer has also been used in security cameras for some time. The camera is then called a fisheye or 360° camera. The camera itself is a more or less flat disc with the fisheye lens in the middle. Behind it is the (single) CMOS chip that converts the visible light (including the people or objects that reflect the light) into an electronic signal. That signal is then visualized on a screen or can be recorded, just like with a regular security camera.
With a fisheye camera, you can identify people, but the angle is also large enough to see where people are coming from and where they are going. In certain situations, you can opt for just one multifunctional fisheye camera instead of a separate camera for identification with an additional camera for overview.
Positioning
A fisheye camera can be positioned in various ways. Hanging from the ceiling, the camera visualizes the entire space from that point, and, for example, the stairwell, elevator, porch, and/or hallway are fully captured. Public transport benefits greatly from the use of this camera. If the camera is mounted on the wall, it gives the same effect, but from the side. If the camera is mounted upside down in a conference table, all persons at and around the table are captured.
Eliminate Image Distortion
However, the image from a 360° camera is fundamentally distorted. Fortunately, in addition to all the technology for, among other things, image enhancement, the camera also has an application that can correct the image, or ‘dewarp’ it. This function is especially useful if you are going to zoom in digitally and want to have people in the distorted part clearly in view. Because you are now only recording part of the total image, it is wiser to have the image corrected by the recorder. The camera then sends the complete 360° image to the recorder, which also records it as such. Live and afterwards, you can zoom in or move through the image (via a joystick or the pan-and-tilt buttons), and the software in the recorder straightens the image if necessary. Just like with a controllable PTZ camera, but without all the mechanics to rotate the camera. And also much more compact and therefore more aesthetically pleasing.
Points
Unfortunately, there are also limitations to this type of camera. When zooming in far, for example, the image becomes blocky, and it is difficult to recognize people. This is due to the large amount of detailed information, brought together by the fisheye lens, that the megapixel CMOS chip must convert into a signal. The complete image that the lens creates is divided over the number of megapixels on the chip. Even with 6 or 8 megapixel chips, the image becomes blocky when we zoom in far. The rule of thumb is currently that with a 6 megapixel fisheye camera, a person is still recognizable at 5 meters distance in all directions from the camera. This applies if the camera is mounted at approximately 2.5 meters height. If the objective is to be able to recognize people, then a fisheye camera is only suitable if the space is no larger than 10×10 meters. Applying a fisheye camera in larger spaces is possible, but then there is only an overview image after 5 meters. You can then see if a person is walking, but not who it is. In the future, more megapixels will provide a better image and recognition at greater distances.
Furthermore, a fisheye camera is less suitable for extremely dark situations. A fisheye lens is a thick piece of glass that blocks more light than ordinary lenses and also gives more lens errors. A larger lens would be better, but that is not realistic due to the price and the limited size of the camera. Due to the development of more light-sensitive chips and higher quality lenses, this will certainly improve in the future. More luxurious fisheye cameras are often already equipped with infrared light to support the quality of the image in dark conditions.
Conclusion
A fisheye camera is a practical solution in many cases. With one camera, a situation can be captured that would normally require multiple cameras. However, keep the limitations in mind. Therefore, always seek good advice about the right camera for your situation.