Standardization of the Optical Transfer Function

Optical Transfer Functions (OTF) are a standard tool for specifying the performance of an optical system. In the past they have often been normalized to one or, e.g. in the case of confocal microscopy, to the relative optical transmission of the system. Our proposal is to instead normalize optical transfer functions to a common signal-to-noise performance, yielding the concept of the noise-normalized optical transfer function (OTFnn), closely related to the spectral signal to noise ratio (SSNR) which can be experimentally determined. Many modern microscopy modes inherently need image processing to interpret the measured data. We therefore also include linear image processing techniques in our description by constraining them to white-noise behavior, which enables us to quantitatively compare noise-normalized OTFs for a large variety of systems. We here compare the OTFnn of widefield and confocal microscopy with those for image inversion interferometry, image scanning and optical photon reassignment. The validity of such curves also forPoisson noise is verified through forward simulations, which show that the result of reconstructions from simulated series of raw data are visibly identical to a single convolution with the calculated white-noise OTF scaled for the predicted overall efficiency. The noise-normalized OTFnn and the noise-normalized weighted averaging in Fourier-space are envisioned to have numerous future applications.