How hard is it to only extract specific class and functions?

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OpenCV have many modules in which I only need a few classes and functions. I know I can only build libs like core, highgui, imageproc by turning on these Macro and off all other Macro when build libs using the opencv official github.

However it may be still too much, I only need like cv::Mat, videocapture, colorconversion, encoder/decoder, gui. Can I just extract these functions from opencv, and directly use source code of these extracted opencv functions in my project. Even I only need these functions, but these functions may also depend on other libs/functions. So I am evaluating how hard it is to extract these specific functions/classes from opencv source code.

Thanks in advance for your answers and comments.