User`s guide

8 Using Events and Callbacks

8-16

Too many input arguments.

Warning: The FramesAcquiredFcn callback is being disabled.

To enable a callback that has been disabled, set the value of the property associated with

the callback or restart the object.

Viewing a Sample Frame

This example creates a video input object and sets the frames acquired event callback

function property to the display_frame function, created in “Writing a Callback

Function” on page 8-13.

The example sets the TriggerRepeat property of the object to 4 so that 50 frames are

acquired. When run, the example displays a sample frame from the acquired data every

time five frames have been acquired.

Create an image acquisition object — This example creates a video input object

for a Matrox image acquisition device. To run this example on your system, use the

imaqhwinfo function to get the object constructor for your image acquisition device

and substitute that syntax for the following code.

vid = videoinput('matrox', 1);

Configure property values — This example sets the FramesPerTrigger value

to 30 and the TriggerRepeat property to 4. The example also specifies as the value

of the FramesAcquiredFcn callback the event callback function display_frame,

created in “Writing a Callback Function” on page 8-13. The object will execute

the FramesAcquiredFcn every five frames, as specified by the value of the

FramesAcquiredFcnCount property.

vid.FramesPerTrigger = 30;

vid.TriggerRepeat = 4;

vid.FramesAcquiredFcnCount = 5;

vid.FramesAcquiredFcn = {'display_frame'};

Acquire data — Start the video input object. Every time five frames are acquired,

the object executes the display_frame callback function. This callback function

displays the most recently acquired frame logged to the memory buffer.

start(vid)

Clean up — Always remove image acquisition objects from memory, and the

variables that reference them, when you no longer need them.