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Frame Averaging

Frame averaging is a technique to get better statistics, that is more image data or a better signal to noise ratio (SNR) in your images. Increasing the dwell time per pixel is the primary way to improve these qualities in an image, but can result in image artifacts such as charging. With frame averaging, and a relatively short dwell, the beam does not stay on any one spot as long, but rather revisits each spot for several scans, with each scan being averaged with the ones before it. In x-ray maps or SCA images, counts are integrated rather than averaged, as relatively few counts per pass are generally acquired.

Open the Scan Generate Preferences to reveal the Image Scan Options which include the Frame Average setting:

Scan Generate Preferences

Use the arrows or type directly into the Frame Average field to set the number of frames to average.

When Frame Averaging is activated by selecting a number greater than 1 in the Image Scan Options, a new field will appear beneath the Revolution toolbar representing the current frame number being scanned in preview or acquire mode.

Dwell Time versus Acquisition time

Using frame averaging rather than higher dwell times does incur a penalty of increased acquisition time due to the accumulation of delays inherent in each line-scan, including both the horizontal retrace interval and various processing and overhead delays in the acquisition hardware. Here is a chart comparing equivalent dwell times from 1µS to 1000µS using both single frame with increased dwell times, and 1uS dwell times with 1, 10, and 100 frame averages. The time for a 1000 frame average, equivalent to one frame with a 1000µS pixel dwell, is too large to fit on the graph.

In all cases, the frame averaging will be slower than longer dwell times, but the benefit is that the beam moves more quickly over the sample, avoiding artifacts that may occur with some samples when using larger dwell times.

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