start

Obtain exclusive use of image acquisition device

Syntax

start(videoinput)

Description

start(videoinput) obtains exclusive use of the image acquisition device associated with the videoinput object and locks the configuration of the device. Using the start command to begin running the object is a necessary first step to acquire image data. To control data logging, use the TriggerType property. To configure the trigger settings of the object, use the triggerconfig function.

For more information about the video input acquisition, see Algorithm.

Examples

Configure Video Input Object

Construct a video input object.

vid = videoinput("winvideo",1);

Configure the trigger properties for the object by setting the trigger type to "manual". When you set the trigger type to "manual", data logging occurs when you call the trigger function..

triggerconfig(vid,"manual")

Start the videoinput object to acquire image data, pause for 5 seconds, and then display the number of acquired frames. Observe that no frames are acquired.

start(vid)
pause(5)
vid.FramesAcquired

ans = 
0

Trigger the acquisition, wait until the image acquisition stops, and then display the number of acquired frames. Observe that 10 frames are acquired.

trigger(vid)
wait(vid)
vid.FramesAcquired

ans = 
10

Remove the videoinput object from memory.

delete(vid)

Input Arguments

videoinput — Video input

videoinput object | array of videoinput objects

Video input, specified as a single videoinput object or an array of videoinput objects.

If an error occurs, the function restores any configured videoinput objects in the array to their original configurations.

Algorithms

Operational Workflow and Conditions for Video Input Acquisition and Termination

When an acquisition starts, the videoinput object performs these operations:

1. Transfers the configuration of the object to the associated hardware.

2. Executes the StartFcn callback of the object.

3. Sets the Running property of the object to "On".

If the StartFcn of the object errors, the hardware never starts and the Running property of the object remains "Off".

The EventLog of the object property records the start event.

An image acquisition object stops running under one of these conditions:

• Issuance of the stop function.

• Acquisition of the requested number of frames. Acquisition is complete when

  FramesAcquired = FramesPerTrigger * (TriggerRepeat + 1).

  FramesAcquired, FramesPerTrigger, and TriggerRepeat are properties of the videoinput object.

• Occurrence of a run-time error.

Version History

Introduced before R2006a