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Figure 2
Effects of denoising on Fourier amplitudes. (a) Cryo-EM image of 20S proteasome recorded at a defocus of 0.4 µm. (b) The same cryo-EM image after denoising. (c) The same image after applying a low-pass filter in Fourier space to 1/20 Å. The image contrast in (a), (b) and (c) is manually scaled so that the histograms of pixel intensities are similar (small insert in each panel). (d) Fourier transforms calculated from the original (upper left) and denoised cryo-EM images (right). Thon-ring simulation for CTF determination is shown on the lower left. (e) Spectra signal-to-noise ratio (SSNR) profile calculated from cryo-EM images before (orange) and after (blue) denoising. SSNR = FRC/(1 − FRC), where FRC is calculated between sums of even and odd frames. (f) Scatter plot of defocus values determined from images before and after denoising. Defocus values were estimated using Gctf (Zhang, 2016BB39) and the major and minor defocus values were averaged. The small population of off-diagonal images (24 of 843) appear to be heavily contaminated with crystalline ice.

Volume 7| Part 6| November 2020| Pages 1142-1150
ISSN: 2052-2525