Splitting a color image into three channels using Open CV and C++?

src = imread("pic.png");
	// . read image file 'pic.png' and save data to variable 'src'
	// . at this time, 'src' will have all informations about
	// . 'pic.png' such as bit count, width, height, plane count,
	// . all pixel values
	// . pixel values will be stored as 3-dimensions array, i.e
	// . src[x][y][i] = i th channel pixel-value for coordinate (x,y)
	// . here 0 : R, 1 : G, 2 : B, or inversely
	// . 0 : B, 1 : G, 2 : R
	
vector spl(3);
	// . vector is array that has N columns and one row.
	// . above means spl is array that has N columns and 3 rows.
	
split(src,spl);
	// . split src into spl
	// . this resuls spl[0] = B space
	// . 			 spl[1] = G space
	// .			 spl[2] = R space

Mat empty_image = Mat::zeros(src.rows, src.cols, CV_8UC1);
	// . initialize empty_image as one channel image which size is
	// . [ src.rows * src.cols ]
	// . here CV_8UC1 is opencv definition value and means that
	// . empty_image will be created as 1 channel matrix.
	// . CV_8UC3 that can be found below line menas that
	// . result_blue will be created as 3 channel matrix.
	
Mat result_blue(src.rows, src.cols, CV_8UC3); // notice the 3 channels here!

// Create blue channel

Mat in1[] = { spl[0], empty_image, empty_image };
	// . in1[] is 3 channel image
	// . channel 1 - B space
	// . channel 2, 3 - zeros
	
int from_to1[] = { 0,0, 1,1, 2,2 };
	// . color-space convertion mapping
	
mixChannels( in1, 3, &result_blue, 1, from_to1, 3 );
	// . here from_to1 is mapping that means that there are no color-space
	// . convertion because from_to1[] is equal-value-mapping.
	// . result_blue[0] = in1[0] = spl[0] = B space
	// . result_blue[1] = in1[1] = zero
	// . result_blue[2] = in1[2] = zero

imshow("blue image", result_blue);
	// . show image on window named "blue image"