Tag Archives: camera
Building OpenCV Stereo Vision - Calibration
Once the hardware is set up, entire rig must be calibrated. Cheap cameras have a lot of distortion. Two major distortions are radial and tangential. Radial is usually noticed on the edge of the screen where image is slightly curved. Edges that should be perfectly straight are suddenly slightly bended. With tangential distortion the problem is somewhat similar, only that certain points on the image appear closer than their neighbors, even though they are not.
In order to overcome this problems cameras must be calibrated. Therefore, a series of images is taken with a well know pattern. OpenCV uses chessboard as shown below.
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Building OpenCV Stereo Vision - Setup
For my most recent project I decided to build Stereo Vision for depth detection. The idea is simple. Two cameras working together similar to human eyes and detecting depth in the image. There are a few nice practical usages such as 3D pictures or point clouds, measuring distance to a point on an image and many more.
I used two Logitech's S7500 cameras. Pretty old cameras supporting resolution of 640x480px for video capture, but were enough to build a basic setup. It is not completely necessary, that cameras are of the same model, but it is highly recommended for better results. Different lens distortion, quality etc. can affect calibration, resulting in larger errors.
I duct taped both cameras on a piece of wood so that they were completely stable. The distance between camera lenses was approximately 7 cm, similar to the distance between human eyes. I additionally aligned camera heads so they were as parallel as possible.
At this point everything is ready for the last step before making depth maps - calibration.
