Deleting N rows (or columns) from cv::Mat.

opencv_helpers.hpp

void MatRemoveRows(cv::Mat& matIn, int row, int rowCount=1)
{
	cv::Size size = matIn.size();
	cv::Mat matOut(size.height - rowCount, size.width, matIn.type());
	if (!(matIn.isContinuous() && matOut.isContinuous())) throw "both should be continous"; //fix later if required, maybe use the rect solution if not continious https://gist.github.com/enpe/369a7a17fd9b3856b544 OR use as https://kezunlin.me/post/61d55ab4/

	int rowSizeInBytes = size.width * sizeof(matIn.elemSize());

	if (row > 0)
	{
		int numRows = row;
		int numBytes = rowSizeInBytes * numRows;
		// copy to before row, from 0
		std::memcpy(matOut.data, matIn.data, numBytes);
	}

	if (row < size.height - 1)
	{
		// copy rest after rows
		int matOutOffset = rowSizeInBytes * row; // start copy to position 
		int matInOffset = matOutOffset + (rowSizeInBytes* rowCount); // start copy from position

		int numRows = size.height - (row + rowCount); //cout of rest rows
		int numBytes = rowSizeInBytes * numRows;
		std::memcpy(matOut.data + matOutOffset, matIn.data + matInOffset, numBytes);
	}
	matIn = matOut;

}


void MatRemoveCols(cv::Mat& matIn, int col, int colCount = 1)
{
	cv::Size size = matIn.size();
	cv::Mat matOut(size.height, size.width - colCount, (int)matIn.elemSize());
		
	if (!(matIn.isContinuous() && matOut.isContinuous())) throw "both should be continous";  //fix later if required, maybe use the rect solution if not continious https://gist.github.com/enpe/369a7a17fd9b3856b544 OR use as https://kezunlin.me/post/61d55ab4/

	int rowInInBytes = size.width * ((int)matIn.elemSize());
	int rowOutInBytes = (size.width - colCount) * ((int)matIn.elemSize());

	if (col > 0)
	{
		int matInOffset = 0;
		int matOutOffset = 0;
		int numCols = col;
		int numBytes = numCols * ((int)matIn.elemSize());

		for (int y = 0; y < size.height; ++y)
		{
			std::memcpy(matOut.data + matOutOffset, matIn.data + matInOffset, numBytes);

			matInOffset += rowInInBytes;
			matOutOffset += rowOutInBytes;
		}
	}

	if (col < size.width - 1)
	{
		int matInOffset = (col + colCount) * ((int)matIn.elemSize());
		int matOutOffset = col * ((int)matIn.elemSize());
		int numCols = size.width - (col + colCount);
		int numBytes = numCols * ((int)matIn.elemSize());

		for (int y = 0; y < size.height; ++y)
		{
			std::memcpy(matOut.data + matOutOffset, matIn.data + matInOffset, numBytes);

			matInOffset += rowInInBytes;
			matOutOffset += rowOutInBytes;
		}
	}

	matIn = matOut;

}

code not well tested yet, it compiles.