Blurring non-rectangular region of an image, then downsample whole image - OpenCV
<p>I am using OpenCV3 to blur and downsample an image, I just want to blur the region inside the area defined by a binary mask like:</p>

<p><a href="https://i.stack.imgur.com/NkeCW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NkeCW.png" alt="enter image description here"></a></p>

<p>After that region is blurred, I would like to downsample the image without blurring the whole image again, so <code>pyrDown</code> is not useful for me.</p>

<p>Any idea?</p>