Fig 1. Illustration of warped stretch transform in imaging.

(a) The field of view consists of a cell against the background such as a flow channel or a microscope slide. Illumination by an optical pulse that is diffracted into a one-dimensional rainbow maps one dimension of the space into the optical spectrum. The other dimension is scanned by the cell flow through the rainbow. In the conventional time stretch imaging (STEAM), the spectrum is linearly mapped into time using a dispersive optical fiber with a linear group delay. The temporal waveform is then sampled by a digitizer with fixed sampling rate resulting in uniform spatial sampling. But uniform spatial sampling generates superfluous data by oversampling the sparse peripheral sections of the field of view. (b) The human vision is a form of warped imaging system where high sampling resolution is needed in the central vision while coarse resolution can be tolerated in the peripheral vision. (c) Similar functionality can be achieved in STEAM by using a nonlinear group delay profile in the spectrum-to-time mapping process resulting in a nonuniform sampling of the line image, assigning more pixels to the information-rich central part of the field of view and less to the low-entropy peripherals. (d) The reconstruction is similar to anamorphic art where the drawn shape is a stretched and warped version of the true object yet the viewer sees the true object upon reflection from a curved mirror. In our system, this unwarping operation is a nonlinear mapping using the inverse space-to-frequency-to-time mapping transfer function.