Need help with multiplying mask and disparity map in C++ opencv

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I have a mask (mat) having pixel either 0 or 255 values obtained after background substraction. Same image has been used to create a disparity matrix. Now I want to multiply this mask with disparity matrix pixelwise, so that it makes all the values in the disparity map zero, where corresponding pixel value in mask is 0 and should retain disparity value same as original disparity, where corresponding pixel value in mask is 255.