Brightness and contrast
Each of the three main detectors on the FlexSEM have their own independent Brightness and Contrast settings. These control the range of pixel intensities displayed in your captured image, and thoughtful control over their setting will ensure you can see the desired detail in your SEM image.
Important Note!
Each detector has its own set of values, so if you intend to capture from two detectors simultaneously you must ensure you have correctly set the Brightness and Contrast for each detector.
Dynamic Range
The goal of setting the Brightness and Contrast values is to maximise the dynamic range of the captured image. This is the separation between the darkest pixels and the brightest pixels. At the same time, you don't want to have regions of your image that are absolute black or white, as details may be lost in these areas. It is a fine balance to achieve the most appealing image.
Most SEM instruments, including the FlexSEM, can display a histogram of your live image to allow you to visualise the distribution of pixel intensities in the image. Ideally you want the histogram to look like a "mountain range" and not a "valley". You also want the histogram to spread across as much of the pixel range as possible, not appear as a very narrow peak.
Below are three examples of images with varying B/C settings. Pay attention to the image histograms that are inset, and how the setting of the B/C values has resulted in these histograms. Which do you think looks the best?
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In this image the B/C is poorly set, resulting in lack of range of pixel intensities and thus lack of detail -
Here the B/C values have been optimised to maximise the spread of pixel intensities from dark to light, with saturating either, given the most detail from the image -
In this image the B/C settings are saturating the bright areas to try to visualise the dark areas. This is sacrificing detail in the bright areas leading to an unappealing image.
Auto Brightness Contrast function
More often than not, the Auto Brightness/Contrast adjustment in the FlexSEM software will do a good job of adjusting the image pixel intensities to give you an appropriate looking image for capture. Some adjustments may still be desired after this process to really optimise the histogram, but it is a good starting point.