Should I initialize a cv::Mat

Question

I have this code:

mapx.create(image.size(), CV_32FC1);
mapy.create(image.size(), CV_32FC1);

what is the values in the mapx and mapy after this? Are all data is zero?

what about this type of initialization:

  cv::Mat  mapx(image.size(), CV_32FC1);

Do I need explicitly set the value of each element to zero?

How can I set the value of each element to say -1?

Answer 1

Data after create should be undefined. In fact, your are just allocating memory.

cv::Mat  mapx(image.size(), CV_32FC1);

is exactly as

cv::Mat1f mapx(image.size());

and

cv::Mat mapy;
mapy.create(image.size(), CV_32FC1);

You can assign an initial value (e.g. -1) like this:

cv::Mat1f(images.size(), -1.f);

Regarding you main question Should I initialize a cv::Mat, the answer is that in general you don't need to. From OpenCV doc:

Instead of writing:

Mat color;
...
Mat gray(color.rows, color.cols, color.depth());
cvtColor(color, gray, CV_BGR2GRAY);

you can simply write:

Mat color;
...
Mat gray;
cvtColor(color, gray, CV_BGR2GRAY);