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Figure 1
The EER file format. (a) Direct detector device (DDD) cameras operating in counting mode record the impact positions of electrons on the sensor at the frame rate of the camera. (b) Conventionally, groups of successive movie frames are summed to fractionate the exposure, reducing the size of movie files from DDD cameras. This exposure fractionation requires decisions to be made by the experimentalist about the temporal resolution to be preserved in order to avoid loss of information from specimen movement during imaging. (c) The electron-event representation (EER) file format uses efficient data encoding, marking the position and time (in raw frame number) for each electron. (d) Example data sizes under typical conditions. All reported data sizes assume a total exposure on the specimen of 50 e− Å−2, a pixel size of 1 Å, a frame size of 4096 × 4096 pixels and neglect any loss of electrons between specimen exposure and detection with the camera. Green curve: data size for uncompressed exposure fractions with 16 bits per pixel or (equivalently) four bits per pixel with 2 × 2 super-resolution. Blue and orange curves: EER file sizes with 4 × 4 super-resolution at exposure rates of 0.0125 and 0.025 e− Å−2 per frame, respectively. The EER file size depends only on the total electron exposure and the exposure rate of the camera, while the file size for conventional movies depends on the number of fractions recorded. EER thus preserves the full temporal resolution of the electron-detection events and requires a smaller file size for many practical fractionation conditions. More camera frames are required to reach the same total exposure when a lower exposure rate is used, and consequently EER files with 0.0125 e− Å−2 per frame are larger than those with 0.025 e− Å−2 per frame, as described in (5)[link].

IUCrJ
Volume 7| Part 5| September 2020| Pages 860-869
ISSN: 2052-2525
https://doi.org/10.1107/S205225252000929X