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Technically, there is not a big difference between passing cv::Mat or cv::Mat& just because this specific class uses smart pointers internally.

Input / Output Arguments: If the argument is an input argument I pass it as const reference const cv::Mat&. If it is an output or an input-output argument then I pass it as cv::Mat&. Using references avoids copying the matrix header (the data is never copied unless clone() is a called) and const marks my arguments as input arguments.

Function return values: If a function returns a single matrix I usually return it as cv::Mat as it does involve copying the data and allows to mark the instance as const directly in the calling code: const cv::Mat m = f(...); This short notation also implicitly marks m as read-only which is quite usefuly when using OpenMP in your programs.

Technically, there is not a big difference between passing cv::Mat or cv::Mat& just because this specific class uses smart pointers internally.

Input / Output Arguments: If the argument is an input argument I pass it as const reference const cv::Mat&. If it is an output or an input-output argument then I pass it as cv::Mat&. Using references avoids copying the matrix header (the data is never copied unless clone() is a called) and const marks my arguments as input arguments.

Function return values: If a function returns a single matrix I usually return it as cv::Mat as it does not involve copying the data (just the matrix header) and it further allows to mark the instance as const directly in the calling code: const cv::Mat m = f(...); This short notation also implicitly marks m as read-only which is quite usefuly when using OpenMP in your programs.

Technically, there is not a big difference between passing cv::Mat or cv::Mat& just because this specific class uses smart pointers internally.internally. (This does not apply to arbitrary C++ objects.)

Input / Output Arguments: If the argument is an input argument I pass it as const reference const cv::Mat&. If it is an output or an input-output argument then I pass it as cv::Mat&. Using references avoids copying the matrix header (the data is never copied unless clone() is a called) and const marks my arguments as input arguments.

Function return values: If a function returns a single matrix I usually return it as cv::Mat as it does not involve copying the data (just the matrix header) and it further allows to mark the instance as const directly in the calling code: const cv::Mat m mat = f(...); This short notation also implicitly marks mmat as read-only which is quite usefuly when using OpenMP in your programs.programs as you do not need to clare it shared or firstprivate.