Jun.28, 2013

One common method to create a 3D scan of an object is to use Microsoft Kinect to build DIY 3D scanning rigs. But Computer engineer Giancarlo Todone has found a new approach to 3D scanning: using focus stacking.

This concept is called depth from focus which is often used in microscopy. Todone simplified it and managed to build a super affordable system using only a Canon Powershot and some custom firmware.

In an image, you can fairly easily estimate how much a pixel is focused by subtracting the luminance component of a suitable neighborhood to each pixel and summing absolute values. Todone's process is to take a collection of photos and analyze the luminance of each pixel in relation to its neighbors. The result will tell how well in focus it is, assigning the pixel a "focus rank." He can then use that focus rank to create a depth map of the object. Finally Todone combines a depth map with RGB and creates the final point clouds in MeshLab.

The best part about this technique is that it doesn't alter any of the original pixels - they retain their original color. So the final result is a 3D scan in full color.

Several problem Todone discovered:

  • the camera has to be very close to the object, or the difference in focus would not be noticeable, and this exagerates the proportions of the object
  • illumination plays a central role: areas with deep shadows or visible reflections are detected like crap (must use a softener next time)
  • in the case of faces, the subject has to be perfectly still while taking pics

Todone's next step is to improve the technique, such as implementing .OBJ output with focus-fused stack as texture and correcting distorsion. This is a very cheap method of creating 3D images from a stack of multi-focused 2D images. Todone says DephtInition is an only $50 system so everyone can try it out. To learn more about this process you can find all the details on his blog here.



Posted in 3D Scanning



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