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Brightness and contrast in Detector control app

Detector control app gives access to manual and automatic brightness and contrast in the Amplification toolbar, see screenshot below

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Channel selection

As a first step. please select channels for which to control brightness and contrast. At the hardware level each channels has independent brightness and contrast, however the software can assist with control of multiple channels by grouping them into a logical groups, such as all quadrants of a signal, or by selecting all channels in the detector.

  • Single selection will only control brightness and contrast for the channel corresponding to the selected segment in the detector diagram. Click on the detector diagram to select desired segment.
  • Grouped selection will control brightness and contrast of multiple channels, corresponding to the selected group of segment in the detector diagram. Click on the detector diagram to select desired group.
  • All selection will control brightness and contrast for all channels in the detector.

If no group is configured for your detector, then the option Grouped will not appear in the user interface.

Manual control

For manual control, please always monitor signal in the acquisition system - either in a live Line Profile tool or live Histogram tool.

Avoid 100% of the imaging range, as there may drifts in the signal intensity over time, originating from drifts in the sample, contamination or charging!

For general purpose acquisition where dark (zero) level is not important and each channel can have different brightness and contrast

  • If minimum and maximum signals are clipped, then reduce contrast until both minimum and maximum signals are acquired well within the range of the acquisition system
  • Adjust brightness and contrast iteratively until minimum and maximum is using approximatively 75% of the imaging range. 

For a balanced acquisition where dark (zero) level is important and all channels selected must have the same contrast

  • Blank the beam to set dark conditions where no signal is produced by the sample
  • Set brightness to zero and confirm that the live signal is at the minimum input range of the acquisition system.
  • If signals are not at the minimum input range, then follow instructions for automatic Zero-ing in the Adjustments toolbar
  • Un-blank the beam to receive signal from the sample
  • Adjust contrast to use approximatively 75% of the imaging range.

If brightness and contrast of individual channels in a group are not well balanced, then use Single selection to control each channel individually.

Automatic control

Automatic control of brightness and contrast from the detector is inherently limited, as the detector is not aware of scanning or acquisition, therefore not aware of dwell time per pixel, start and end of frame, or flyback durations without signal acquisition. Because the microscope user is aware of scanning, the recommended approach is to use manual control of detector brightness and contrast, as described in the previous section on this page, with automatic image brightness and contrast, as described in the next page in this book.

Only use automatic control where sample signal is suitable for automation!

Because detector lacks information about frame start and end, automation of brightness and contrast is set to a fixed time period that may take place during several frames (for fast scanning) or only during a small part of the frame (for slow scanning). If automation period takes place during a small section of a slow scan, and if the sample presents different levels of signal outside this automation period, then automation results will be incorrect. Further, because the detector lacks information about the scan flyback period, including pre- and post-scanning outside the acquisition area, it will attempt to optimize brightness and contrast for features adjacent to the image, outside to the field of view of the operators. Therefore automatic control is useful only for cases where signal level is relatively uniform over the entire image.

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Two automation tools are provided for the cases described in the manual control section above, depending if channels needed to be balanced. These automatic procedure are initiated by the software, but run in the detector firmware for realtime monitoring and control. Automatic control procedures are run only once for each channel, then control of brightness and contrast is returned to manual. An automatic procedure can be stopped by clicking again on the automatic button.

Automatic brightness and contrast (ABC)

ABC is intended for general purpose control where channels don't have to be balanced and they may have different brightness and contrast. It may be user for individual channels, as selected in the detector diagram, or may be run sequentially for all channels in a selected group.

For each selected channel, ABC will monitor the live signal over a Measure Time (second) to find the minimum and maximum values (Volts). These will be compared to a -Peak...+Peak range (Volts), from which a new Brightness (Volts) and Contrast will be computed. The process is iterative and will continue until measured minimum and maximum are within a given Tolerance band (Volts) from required values. 

Automatic contrast (AC)

AC is intended for automatic control where channels have to be balanced to the same contrast and dark (zero) value is important. It is therefore specifically designed for channels in a logical group.

For the selected group, AC will monitor the live signal over a Measure Time (second) to find the minimum and maximum values (Volts). These will be compared to a 0...Peak range (Volts), from which a new Contrast will be computed. The process is iterative and will continue until measured minimum and maximum are within a given Tolerance band (Volts) from required values. 

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