Phasefree

Phasefree is a term used in signal processing, optics, and related areas to describe representations or analyses that do not require phase information. In this sense, a phasefree approach relies on magnitude or amplitude data alone, or on models in which phase is treated as unnecessary or indeterminate.

In optics and imaging, phasefree methods are employed when phase measurements are unavailable or impractical. This occurs in intensity-based imaging, holography with loss of phase, and remotely sensed data. The goal is to reconstruct a plausible signal or image from magnitude-only measurements by imposing additional constraints such as non-negativity, known support, sparsity, or prior information about the object.

Techniques often associated with phasefree include magnitude-only Fourier data reconstruction, magnitude spectrogram analysis in audio, and analytic-signal representations where instantaneous amplitude is emphasized over phase. Iterative algorithms for phasefree problems typically alternate between applying amplitude constraints and enforcing prior information, without attempting to recover the exact phase.

Applications span optical imaging, X-ray crystallography, electron microscopy, and audio signal processing, where phase information is incomplete or unreliable. The term phasefree is used mainly descriptively to highlight the reliance on magnitude information, rather than as a formal mathematical classification.

See also: Phase retrieval, magnitude-only measurements, non-negative matrix factorization, compressed sensing.