Blackfly - CYLOD

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Point Grey <strong>Blackfly</strong> Technical Reference 7 Image Acquisition Control GenICam—Acquisition Control Exposure Mode Timed Exposure Time Integration Time Exposure Auto Off 7.2 External Trigger Timing The time from the external trigger firing to the start of shutter is shown below: 1. Trigger Pulse 2. Propagation Delay 3. Exposure Time 4. Sensor Readout 5. Data Transfer Figure 7.3: External trigger timing characteristics It is possible for users to measure this themselves by configuring one of the camera’s GPIO pins to output a strobe pulse (see Programmable Strobe Output on page 29) and connecting an oscilliscope up to the input trigger pin and the output strobe pin. The camera will strobe each time an image acquisition is triggered; the start of the strobe pulse represents the start of exposure. 7.3 Maximum Frame Rate in External Trigger Mode This section only applies to Rolling Shutter models. When image capture on a rolling shutter camera is triggered by an external source, achievable frame rate is half the rate achievable in free-running mode, regardless of the rate that is specified. This difference is caused by a change in the way rolling shutter cameras operate between free-running and trigger modes. In free-running mode, integration can occur as quickly as the camera's pixel clock allows, because by the time the bottom row of the image sensor has integrated, the top row is already read out, and is free to integrate the next image without delay. In trigger mode, however, rolling shutter cameras begin read-out only after the entire image is integrated. The camera is not ready to receive another trigger until read-out is complete. Essentially, one frame is required for reset, and one frame for read-out. As a result, the frame rate achieved in trigger mode will be half the rate specified for free-running mode. Revised 12/13/2012 Copyright ©2012 Point Grey Research Inc. 38
Point Grey <strong>Blackfly</strong> Technical Reference 7 Image Acquisition Control 7.4 Camera Behavior Between Triggers When operating in external trigger mode, the camera clears charges from the sensor at the horizontal pixel clock rate determined by the current frame rate. For example, if the camera is set to 10 FPS, charges are cleared off the sensor at a horizontal pixel clock rate of 15 KHz. This action takes place following shutter integration, until the next trigger is received. At that point, the horizontal clearing operation is aborted, and a final clearing of the entire sensor is performed prior to shutter integration and transmission. 7.5 Changing Video Modes While Triggering You can change the video format and mode of the camera while operating in trigger mode. Whether the new mode that is requested takes effect in the next triggered image depends on the timing of the request and the trigger mode in effect. The diagram below illustrates the relationship between triggering and changing video modes. Figure 7.4: Relationship Between External Triggering and Video Mode Change Request When operating in trigger mode 0 (page 36), video mode change requests made before point A on the diagram are honored in the next triggered image. The camera will attempt to honor a request made after point A in the next triggered image, but this attempt may or may not succeed, in which case the request is honored one triggered image later. In trigger mode 15 (page 37), change requests made after point A for any given image readout are honored only after a delay of one image. 7.6 Asynchronous Software Triggering Shutter integration can be initiated by setting the Trigger Source to Software in the GenICam features. The time from a software trigger initiation to the start of shutter is shown below: Revised 12/13/2012 Copyright ©2012 Point Grey Research Inc. 39
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