When a standard strobe output is enabled off one of the camera's GPIO pins, the strobe will fire every time an image is exposed (shutter opens and closes) and read off the sensor. All PGR IEEE-1394 cameras will continually expose and read image data off of the sensor under the following conditions:

1. The camera is powered up. Some PGR Imaging Products provide the user with the ability to power down or power up the camera using the CAMERA_POWER register 610h (refer to the PGR IEEE-1394 Digital Camera Register Reference).

AND

2. The camera is not in asynchronous trigger mode. When in async trigger mode, the camera simply clears the sensor and does not read the data off the sensor.

It is important to note that the camera will continue exposing images even when isochronous data transfer is disabled and images are not being streamed to the PC. The camera continues exposing images even when ISO is off in order to keep things such as the auto exposure algorithm (if enabled) running. This is done to ensure that when a user starts requesting images (ISO turned on), the first image they receive will be properly exposed. The alternative of clearing the sensor until ISO is enabled would lead to the first N images (where N is undefined) being improperly exposed as the auto exposure algorithm works to accommodate the lighting environment.

As a result of the above behaviour, customers can expect to see the strobe or strobe pattern fire (see Related Article 207 below) even before a call to flycaptureStart() or after a call to flycaptureStop(). To stop a strobe from firing, either:

1. Disable the strobe pulse by toggling the appropriate GPIO register ON/OFF bit.
2. Put the camera into an asynchronous external trigger mode.
3. Power the camera down via the CAMERA_POWER register 610h, where applicable.