FLIR ADK
Getting Sta rt e d
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6 Intrinsic Camera Calibration
Similar to a visible camera, a black and white chessboard pattern can be used with OpenCV
to do intrinsic calibration to correct for effects to the lens. Because thermal cameras sees
heat, more than just a chessboard is needed.
6.1 Building a Calibration Target
Print a checkboard pattern such as:
http://martinperis.blogspot.com/2011/01/opencv-stereo-camera-calibration.html
Mount the checkboard on a stiff material (such as cardboard) to keep the checkerboard flat.
Then illuminate with the sun or a lamp that emits IR. The light should get hot. (LED or
fluorescent lights will not work). For example:
https://www.amazon.com/HDX-250-Watt-Halogen-Portable-
Light/dp/B06XH49LZB/
Figure 5: Thermal and RGB images taken by illuminating the checkerboard with the sun
When planning the size of your target there are a few things to keep in mind:
1) ADK cameras have their focus set at infinity. This means the target needs to be several feet
from the camera to be in focus.
2) The target will need to be large enough in the FOV to clearly see the chessboard
3) The higher the contrast, the easier it is for the algorithm to find the chessboard. Keeping
extra hot and cold objects out of the picture will help.
4) You may want to print a black box around you checkerboard.
5) During the calibration procedure, the orientation of the chessboard will need to move in
relation to the camera.
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