Tuesday, June 23, 2015

Multi-View Stereo

Taking stereo pictures without a stereo camera is usually done with the cha-cha method (you shift the camera horizontally as best as possible after taking the first picture) or with a slide bar (enables you to slide camera along a straight line, hopefully horizontal). In any case, a little bit of alignment in Stereo PhotoMaker and you're in business. If you are planning to make a lenticular or wigglegram, then you are gonna need a depth map. For that, you need a depth map generator whose input is a pair of aligned or rectified images.

Now, what if you don't want to deal with all this stuff (being careful not to go out of alignment when you do the cha-cha) and want to use more than two images to get a depth map? Well, you are in luck because there is something called multi-view stereo. Usually, multi-view stereo is used in the context of 3d scene reconstruction. For instance, one can take hundreds of photographs of an object from as many viewpoints as possible and obtain a 3d version of the object (in the form of a point cloud which can then be post-processed to get a true 3d model). This is the poor man's 3d scanner. Here, I am only interested in getting the depth map, which makes it much easier although you still have to get the camera parameters for each image, in other words, the sparse reconstruction of the 3d scene (as opposed to dense). So, with multi-view stereo, you take a minimum of two images of an object from different view points (with different cameras even) and you can get a depth map, hopefully accurate. This of course assumes that the object as well the surroundings don't move. That's the downside of using a single-lens camera to do 3d.

If you are interested in multi-view stereo in the context of automatic depth map generation, you are invited to read this little article I wrote: Multi-View Stereo. This is the basis for Depth Map Automatic Generator 8 (DMAG8).


  1. Hi Ugo!
    Very interesting article Multi-View Stereo. Some time ago I experimented with VisualFM. I look forward to the new DMAG8

    1. thanks Pepe. I have to admit that I am bit puzzled by VisualSFM because I don't understand what is needed to get a good 3d sparse reconstruction. It's like a crap shoot every time.