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Configuring Callback Properties

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This example explains how callback functions work and shows how to use them.

Callback functions are executed when an associated event occurs. To configure a callback to execute for a particular event, configure one of the video input object's callback properties:

  • ErrorFcn

  • FramesAcquiredFcn

  • StartFcn

  • StopFcn

  • TimerFcn

  • TriggerFcn

This tutorial uses a callback function, found in the

  • MATLABROOT\toolbox\imaq\imaqdemos\helper

directory, that displays the N'th frame, where N is provided as an input argument to the callback function.

Select a device to use for acquisition and configure it to acquire data upon executing a manual trigger.

% Access an image acquisition device.vidobj = videoinput('winvideo', 1);% Acquire an infinite number of frames when manually triggered.triggerconfig(vidobj,'manual'); vidobj.FramesPerTrigger = inf;

Configure the video input object to execute a callback function when the acquisition is stopped.

% Specify the N'th frame the callback function will display.frameNumber = 3;% Have the callback function executed when the acquisition ends.vidobj.StopFcn = {'util_showframe', frameNumber};% Initiate the acquisition.start(vidobj)

在触发图像采集设备,tennis ball is dropped within the camera's view.

% Trigger the object for logging and acquire data for a few seconds.trigger(vidobj) pause(5);

When the acquisition is stopped, it will cause the callback function to execute and display the N'th frame.

% Stop the acquisition.stop(vidobj)

Once the video input object is no longer needed, delete it and clear it from the workspace.

delete(vidobj) clearvidobj

Image Acquisition Toolbox Documentation

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