Question

I’m having the same problem issued in these two links: one, two. I need to calculate pixel intensity average on a small ROI in an image.

I selected the ROI and copied the image in it, so now I need to calculate pixel average intensity, avoiding a loop on all of the pixels.

The answers provided in the links suggest to use CvScalar c = cvAvg(img); but I can’t find the equivalent, using the C++ interface.

Can you please point it out to me? I couldn’t find it in the documentation!

Answer 1

I provide the code snippet solving the problem:

//defines roi
cv::Rect roi( roiVertexXCoordinate, roiVertexYCoordinate, roiWidth, roiHeight );

//copies input image in roi
cv::Mat image_roi = inputImage( roi );

//computes mean over roi
cv::Scalar avgPixelIntensity = cv::mean( image_roi );

//prints out only .val[0] since image was grayscale
cout << "Pixel intensity over ROI = " << avgPixelIntensity.val[0] << endl;