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Figure 2
Reconstructed images of the cell phantom shown in Fig. 1[link](a) obtained for NFH, FFP and NFP at the photon fluences nph indicated. For a photon fluence higher than 350 photons per pixel, only results obtained using the LSQ cost function are shown; for fluences at or below that value, we show the reconstructions obtained using both the LSQ cost function [equation (7[link])] and the Poisson cost function [equation (9[link])]; these are placed side by side. At high photon fluence, both NFH and FFP yield high-quality images. However, their behaviors differ at low fluence. For NFH, the images gain a more salt-and-pepper appearance, as one would expect from low-photon statistics. The use of the Poisson noise model does not significantly improve the reconstruction quality. In FFP, the decrease in photons scattered beyond the illumination probe's numerical aperture at low fluence means the images tend more and more towards the probe's limit of spatial resolution. While the LSQ cost function gives blurry reconstructions at low photon dose, the results with the Poisson cost function preserve sharp features even at very low photon count, but instead show fringe-like artifacts. With NFP, using the Poisson cost function at low dose slightly improves the contrast in reconstructed images. However, both LSQ and Poisson results contain high-frequency artifacts that are eliminated only with noise-free diffraction data (see insets).

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