Essay: RGB image color separation (with code)

I originally wanted to write several grayscale functions , The gray image is boring , So I wrote this ;

take BGR Separation of three primary colors ： The code is as follows
Method 1：

	uchar* pImgB = new uchar[col*row*3]; 
	uchar* pImgG = new uchar[col * row * 3];
	uchar* pImgR = new uchar[col * row * 3];

	for (int i = 0; i < row * col * 3; i+=3)
	{
    
		pImgB[i] = pImg[i];              // Separate blue 
		pImgB[i + 1] = 0;
		pImgB[i + 2] =0;

		pImgG[i] = 0;                    // Separate out green 
		pImgG[i + 1] = pImg[i + 1];
		pImgG[i + 2] = 0;

		pImgR[i] = 0;                    // Separate out red 
		pImgR[i + 1] = 0;
		pImgR[i + 2] = pImg[i + 2];
		
	}
	delete[] pImgB;
	delete[] pImgG;
	delete[] pImgR;

Use opencv The pointer to （ Comparison method 1 slow 30 times ）
Method 2：

for (int i = 0; i < img.rows; i ++)
	{
    
		for (int j = 0; j < img.cols; j++)
		{
    
			*imgB.ptr(i, j) = *img.ptr(i, j);                    // Separate blue 
			*(imgB.ptr(i, j) + 1) = 0;
			*(imgB.ptr(i, j) + 2) = 0;

			*imgG.ptr(i, j) = 0;								 // Separate blue 
			*(imgG.ptr(i, j) + 1) = *(img.ptr(i, j) + 1);
			*(imgG.ptr(i, j) + 2) = 0;

			*imgR.ptr(i, j) = 0;								 // Separate blue 
			*(imgR.ptr(i, j) + 1) = 0;
			*(imgR.ptr(i, j) + 2) = *(img.ptr(i, j) + 2);
		}	
	}