OpenCV Mat::operator= - does it support copy on write?

Question

From the OpenCV documentation, it appears that copying a matrix is done using a shallow copy, but when changing one of the copies, a copy is done.

The exact referenc

Answer 1

You can make a deep copy with Mat::copyTo(). E.g.

Mat a(5,5,CV_32C1),b;
a = 1;
a.copyTo(b);
a = 2;

But no, Mat does not support copy-on-write. When you need to make a change to a without affecting b, you need to make a deep copy of a to b, and then modify a.

Answer 2

It seems you misunderstood. "Before assigning new data, the old data is dereferenced via Mat::release" does not mean that when you write on a or b then a copy occurs. It means that when you type b=a, you lose the data that was in b.

Long story short : copy on write is not supported.