Auto-Brightness

Auto-Brightness is designed to maintain consistent brightness (or image intensity) in situations where lighting varies. The features benefit from being optimized for each application's lighting conditions.

The information below describes making these adjustments and the feature interdependencies. All feature example settings and acquisitions examples below are made using Using CamExpert with GigE Cameras .

IMPORTANT

Setup is critical. The Auto-Brightness algorithm cannot converge unless control features are set properly (as required by the imaging situation). The following cases describe simple setups and the control feature considerations required to make them work.

Auto-brightness features can be found in the Sensor Controls category.

Using Auto-Brightness

Three Auto-Brightness examples settings are described below.

Note that the Auto-Brightness function is not available if “Cycling Mode” is active.

Be sure to go through the general preparation steps.

General Preparation

  • Before using any controls, a simple setup for experimentation is to have a reasonable free running acquisition of n frames per second (AcquisitionFrameRate) and an exposure time (ExposureTime) that provides a viewable image.

  • Take note of the frame rate and exposure time. If the frame rate is very slow due to a long exposure, add analog gain (GainSelector and Gain) and adjust the exposure time again.

  • Enable all Auto-Brightness features by setting autoBrightnessMode to active (live acquisition must be off). This master feature only activates the auto-brightness, auto-exposure, and auto-gain controls but doesn’t enable the processing.

  • The features autoBrightnessSequence, autoBrightnessTargetSource, autoBrightnessTarget, autoBrightnessTargetRangeVariation, and autoBrightnessAlgorithm can remain at their default settings for this demo. 

Example: Auto-Brightness Using Auto-Exposure

After the preparations described above, the Auto-Exposure function is tested as follows. These setup steps are made before doing a live acquisition.

  • Set the autoBrightnessAlgoConvergenceTime to a larger value than the default 2 seconds if more time is required to ensure adequate time for convergence.

  • Set ExposureAuto to Continuous to activate all Auto-exposure features.

  • Referring to the ExposureTime value used to get a viewable image during the free-running preparation stage, set exposureAutoMaxValue to a maximum exposure time longer than was needed. This maximum exposure limit feature may be required in imaging situations where the frame rate must not be forced below some minimum value. Also check that exposureAutoMinValue is low enough to allow the auto exposure a wide range to function in (but not too low else the algorithm will undershoot).

  • Enable live acquisition (Grab button in CamExpert). The image exposure will adjust itself until the autoBrightnessTarget value is achieved. During live acquisition, the autoBrightnessTarget value can be changed to observe the algorithm converge to the new luminance value.

  • Stop live acquisition (Freeze button in CamExpert). The feature ExposureTime is updated with the last exposure time used by the auto exposure algorithm. Adjust frame rate and analog gain settings as required to test again. Adjust other features mentioned as required.

Example: Auto-Brightness Using Auto-Gain

An alternative method of automating exposure control is by varying the Nano-10G Digital Gain. The user needs to note that the digital gain stage is limited to a small positive multiplier and will have the side effect of increasing digital noise.

  • Setup will be similar to using auto exposure alone.

  • Enable automatic digital gain by setting the feature GainAuto to Continuous.

  • Limit the total digital gain range by adjusting the values for gainAutoMaxValue and gainAutoMinValue.

Example: Auto-Brightness Using Auto-Exposure and Auto-Gain

  • Use both ExposureAuto and GainAuto together to maximize the range of the Auto-Brightness range.

  • Use autoBrightnessSequence to select the order of automation. 

  • Caution: Even with both automatic functions enabled, exposure convergence to a target value requires proper setup.