c++ - Fastest way to extract individual pixel data?

Question

I have to get information about the scalar value of a lot of pixels on a gray-scale image using OpenCV. It will be traversing hundreds of thousands of pixels so I need the fastest possible method. Every other source I've found online has been very cryptic and hard to understand. Is there a simple line of code that should just hand a simple integer value representing the scalar value of the first channel (brightness) of the image?

Answer 1

for (int row=0;row<image.height;row++) {
    unsigned char *data = image.ptr(row);
    for (int col=0;col<image.width;col++) {
       // then use *data for the pixel value, assuming you know the order, RGB etc           
       // Note 'rgb' is actually stored B,G,R
       blue= *data++;
       green = *data++;
       red = *data++;
    }
}

You need to get the data pointer on each new row because opencv will pad the data to 32bit boundary at the start of each row