background detection having font with same color as backgound

background detection having font with same color as backgound

Ok, here is question: I have image as following (so, this is white figure
on red background. This figure have two thin red lines inside it)

and I want to receive following image (remove red background but not two
red lines inside figure)

I was trying convexHull from OpenCV, but, obviously that approach works
only on convex figures. My feeling that convolution may help here, but
have no real idea yet...
Thanks for any suggestions!