How to “zero” everything within a masked part of an image in OpenCV

Question

If I have an image (IplImage 8-bit) and a binary mask (which is also an 8-bit IplImage of the same size, where every pixel has a value of either 0 or 255), how can I make every

Answer 1

You can simply use bitwise_and() function.

Check the documentation.

Answer 2

Simplest way, with 'Mat img' (image to be masked, input) and 'Mat masked' (masked image, output):

  img.copyTo(masked, mask)

where 'Mat mask' is a matrix not necessarily binary (copyTo considers elements with zero value). Masked can be of any size and type; it is reallocated if needed.

See the doc.

Answer 3

Multiply or bit-and the mask with the image. There are some OpenCV functions for that, but I do not know their names for the C interface.

in C++:

Mat image, mask;

image = image * mask;
// or 
image = image & mask;