focusdefocus

FocusDefocus is a term used in optics and image processing to describe the deliberate combination or alternation of focused and defocused regions within a single image. It encompasses both physical focusing techniques and computational methods that manage depth-of-field effects to control visual emphasis and perception.

In physical optics, focus-defocus is achieved by adjusting the lens focal plane, aperture, and depth of field. Wider apertures create shallower depth of field and more pronounced defocus in background or foreground. In computational imaging, focus-defocus is simulated or edited after capture using depth maps, point spread functions, and blur kernels to render selective focus or refocus effects.

Techniques include selective focus in photography, tilt-shift and graded blur, and post-processing defocus using depth-aware blur, synthetic focal stacks, or refocusing algorithms. In rendering and computer graphics, defocus is modeled by approximating the PSF as a function of depth to produce realistic or stylized depth of field and bokeh effects.

Applications span photography, cinematography, microscopy, and visualization in VR/AR, where controlling focus-defocus directs attention and improves comprehension. Challenges include accurately estimating depth, avoiding artifacts at depth boundaries, and balancing computing cost with visual fidelity.

See also: depth of field, bokeh, defocus, refocus, tilt-shift, focal stack, point spread function, depth map.