Spherize part of a canvas HTML5

I am currently doing canvas manipulation and I would like to spherize a part of an image.

The situation: - I have a flat image - When a user clicks on a region, this region will spherize / grow up to highlight that part. - More clicks produce more spherization effect...

The looking effect is not like zooming because it has to preserve the continuity with the rest of the image, not just highlight a certain part.

The closer exemple I have found so far is http://ift.tt/1m1saYA but I don't know how to adapt it to my needs.

Thanks for your help !