Mac PhotoBooth dent effect in iOS

Question

I'm trying to implement various distortion effects on UIImage. I found GPUImage framework which work like charm for Swirl, Bulge, Pinch, Stretch, Sphere, GlassSphere etc. But now I want to apply dent effect which we can see it in macbook Photo booth application. How we can achieve such effect any idea ?

Answer 1

The Photo Booth dent effect is merely a bulge distortion with a negative scale. Photo Booth:

GPUImageBulgeDistortionFilter with a negative scale:

I'm surprised that you wouldn't have seen this when trying out the various filters.