iOS - 2d image turn into a 3d

问题:

I was checking out this cool app called Morfo. According to their product description -

Use Morfo to quickly turn a photo of your friend's face into a talking, dancing, crazy 3D character! Once captured, you can make your friend say anything you want in a silly voice, rock out, wear makeup, sport a pair of huge green cat eyes, suddenly gain 300lbs, and more.

So if you take a normal 2D image of steve jobs & feed it to this app it converts it into a 3D model of that image & the user can interact with it.

My questions are as following -

1. How are they doing this?
2. How is this possible in iPad?
3. Isn't it computationally intensive to render and convert 2D image into 3D?

Any pointers, links to websites or libraries in objectiveC which do this is very much appreciated.

UPDATE: this demo of this product here shows how morfo, uses a template mechanism to do the conversion. i.e. after a 2D image is fed, one needs to set the boundaries of the face, where the eyes are located, size & length of lips. then it goes off to convert it into a 3D model. How is this part done? What frameworks or libraries they might be using?

回答1:

This is a broad question but i can point you in the right direction of how 3D Rendering works, trust me this is a huge subject with decades of work behind it and to much to put here. Not sure how up to speed you are on 3D Rendering techniques so i will give you a basic idea of texturing and point you to a good set of tutorials.

1. How are they doing this?
   The idea is that in 3D Rendering, 3D models can be textured with a 2d image known as a texture map. You use a 2D image and wrap it around a 3d model, be that a simple primitive like a sphere of a cube or more advanced such as the classic teapot or the model of a human head e.t.c. A texture can be taken from anywhere, I have used the camera feed in the past to texture meshes with the video from the camera stream, I have used photos from the camera which s how there doing it. So this is how the face is rendered to the 3D Model.

2. Is this efficient?
   On iOS and most mobile devices 3D rendering uses hardware acceleration utilizing OpenGLES. In regards to your question this is really fast depending on how you implement your render code.

The way it uses the mapping (scale rotate template in the video) as mentioned by anticyclope allows you to make the texture fit a model and also place the eyes which are part of there render code.

So if you want to pick this up i recommend reading Jeff Lamarche Tutorial "from the ground up" as a primer:

http://iphonedevelopment.blogspot.com/2009/05/opengl-es-from-ground-up-table-of.html

Second to that i have read about 4 books on OpenGLES, for general design and for platforms specifics. I recommend this book:

http://www.amazon.co.uk/iPhone-Programming-Developing-Graphical-Applications/dp/0596804822/ref=sr_1_1?ie=UTF8&qid=1331114559&sr=8-1

回答2:

In my opinion, there is how they doing it. Just my thoughts, haven't saw the application in real-life.

They have a 3D model of human's head. When you click on certain points on 2D image, they are adjusting corresponding points in 3D model, so it is represents a specific face's features like distance between eyes, lips width and so on. Next, texture from 2D image is applied to 3D model using that control points, so we have a textured 3D model of human's head. Given the fact, that our perception is able to reconstruct a 3D shape from 2D images (say, we looking at 2D photo and still imagining a 3D person), there's no need to reconstruct 3D shape accurately, texture will do the work.

回答3:

There is an issue in the rendering of 3D images, called UV mapping, takes the 3D model and defines a set of edges, and this creates an image that is used to generate different textures to the model.

Now if you notice in Morfo, you define the edge of the head, eyes, mouth and nose. with this information the Morfo knows how to place it texture to the model that has defined.

the process of loading a texture on a model is not very complex and this can be done on any device that has support of some technology such as OpenGL

回答4:

Isn't it computationally intensive to render and convert 2D image into 3D?

Apple is sinking billions of dollars into developing custom chipsets, and recent models have impressive performance, considering the battery life and low operating temperature (no fans).