What is lens distortion?

This is a problem within the scope of optics, which has its own standard definition in optics. The image produced by taking a photo with the camera will be distorted. For example, we all have the experience of taking pictures with ordinary cameras at home. There is a kind of lens called a “wide-angle lens”, which is called a “fisheye lens” more ruthlessly. When you take a photo with this kind of lens, you will find that the image on the sides of the photo is curved. This phenomenon is caused by “lens distortion”. The example of “fisheye lens” is because the “fisheye lens” is a lens with large distortion.

The lens has distortion, the difference is that the distortion varies greatly. For a visual inspection system, it is of course hoped that the lens distortion used is as small as possible. This is because when the vision system performs detection, it is performed on the image imaged by the camera. If the camera’s imaging is “crooked”, the result of the system detection will not be “correct” — this means that the upper beam is not correct and the lower beam is crooked.

There are two ways for the vision system to correct lens distortion: that is, start from the hardware or start from the software. The way to start from the hardware is simple: just use a lens with little distortion. This kind of lens is called a telecentric imaging lens, which is expensive, more than 6 or 7 times the price of an ordinary lens. The distortion of this kind of lens is below 1%, and some can reach 0.1%. Most high-precision vision measurement systems use this type of lens: The second method is to start from the software. When doing “camera calibration”, use the dot matrix on the calibration standard module to calculate. The specific method is: after the completion of the “camera calibration”, the size of each point in the dot matrix is ​​obtained according to the known measurement, and the size of the dots on the periphery of the dot matrix is ​​analyzed. The point size is different. A ratio can be obtained by comparison, and this ratio is the distortion of the lens. With this ratio, the distortion can be corrected during actual measurement.

Post time: Oct-08-2021