UIImage nonlinear resizing

Question

I have unicolor image and i need to resize some parts from it, with different scale. Desired result is showed at image. I've looked at applying grid mesh in opengles but i could not find some sample code or more detailed tutorial. I've also looked at imgwrap but as far i can see this library requires qt framework. Any ideas, sample code or links for further read will be appreciated, thanks.

Answer 1

The problem you are facing is called "image warping" in computer graphics. First you have to define some control points in the original image and corresponding points in a sample destination image. Then you have to calculate a dense displacement field (in this application called also wrapping grid) and simple apply this field to the original image.

More practically: your best bet on iOS will be to create a 2D grid of vertices in OpenGL. Map your original image as a texture over this grid and deform the original grid by displacing some of its points. Then you simple take a screenshot of the resulting image with glReadPixels.

I do not know any CIFilter that would implement displacement field mapping of this kind.

UPDATE: I found also an example code that uses 8 control points to morph images with OpenCV. http://engineeering.blogspot.it/2008/07/image-morphing-with-opencv.html

OpenCV has working ports to iOS, so you could simple experiment with the code on the link above also on a target device.