Fig. 7.

Equiphase average for better diagnosis. (a) Different spectra images of a typical cryoEM micrograph of HAV (Dataset-8) with ∼1800 Å astigmatism; left top: background-subtracted LAS; right top: circular average; left bottom: equiphase average; right bottom: simulated. (b) Enlarged region from 9 Å to 4 Å for detailed comparison of different diagnostic methods. Thong rings on the left sides in all the three images represent the simulated amplitude spectra; the right sides represent the observed spectra visualized in different methods. Obviously, Thong rings from the original spectra (i) are almost invisible at higher than 9 Å even after background reduction. After circular average (ii), the rings become clearer but significantly off the correct peak because of the large astigmatism. Some rings are almost in reverse contrast, indicating the circular average is meaningless at such resolution. The equiphase average (iii) makes all the rings clearly visible up to 4 Å.