GPIO strobe signal continues after isochronous image transfer stops

Last Revision Date: 5/27/2014

This article explains why users may see the strobe output signal continue to fire even after stopping the isochronous transfer of images. 

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 of our IEEE-1394 cameras continually expose and read image data off of the sensor under the following conditions:

1. The camera is powered up. Some cameras provide the user with the ability to power down or power up the camera using the CAMERA_POWER register 610h. Refer to the the Digital Camera Register Reference

AND

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

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 even before a call to flycaptureStart() or after a call to flycaptureStop(). Use one of the following methods to stop a strobe from firing:

    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.
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