Focal Stack Compositing for Depth of Field Control
Manipulating depth of field using a focal stack. (a) A single slice from a focal stack of 32 photographs, captured with a Canon 7D and a 28mm lens at f/4.5. The slice shown is focused 64cm away. (b) A simulated f/2.0 composite, focused at the same depth. To simulate the additional blur, objects closer to the camera are rendered from a slice focused afar, and objects far from the camera are rendered from a slice focused near. (c) An extended depth of field composite that blurs the foreground flower and is sharp for all depths beyond it. (d) A depth map for the scene, representing depth as image intensity (dark means close.) (e) A pair of defocus maps that encapsulate the requested amount of per-pixel defocus blur used to generate the composites above. Its magnitude is encoded with saturation.
Many cameras provide insufficient control over depth of field. Some have a fixed aperture; others have a variable aperture that is either too small or too large to produce the desired amount of blur. To overcome this limitation, one can capture a focal stack, which is a collection of images each focused at a different depth, then combine these slices to form a single composite that exhibits the desired depth of field. In this paper, we present a theory of focal stack compositing, and algorithms for computing images with extended depth of field, shallower depth of field than the lens aperture naturally provides, or even freeform (non-physical) depth of field. We show that while these composites are subject to halo artifacts, there is a principled methodology for avoiding these artifacts---by feathering a slice selection map according to certain rules before computing the composite image.
Paper: focalstack.pdf (4.8MB)
Video: focalstack.mov (285MB)
David E. Jacobs, Jongmin Baek, Marc Levoy. Focal Stack Compositing for Depth of Field Control. Stanford Computer Graphics Laboratory Technical Report 2012-1. October, 2012.