User`s guide

Retrieving Timing Information

7-25

To see an example, see “Determining the Frame Delay Duration” on page 7-25.

Getting the Absolute Acquisition Time

When you use the getdata function, you can optionally specify three return values.

The first contains the image data, the second contains a vector of relative acquisition

times, and the third is an array of structures where each structure contains metadata

associated with a particular frame.

[data time meta ] = getdata(vid);

Each structure in the array contains the following four fields. The AbsTime field contains

the absolute time the frame was acquired. You can also retrieve this metadata by

using event callbacks. See “Retrieving Event Information” on page 8-8 for more

information.

Frame Metadata

Field Name Description

AbsTime Absolute time the frame was acquired, returned in MATLAB clock

format

[year month day hour minute seconds]

FrameNumber Frame number relative to when the object was started

RelativeFrame Frame number relative to trigger execution

TriggerIndex Trigger the event is associated with. For example, when the object

starts, the associated trigger is 0. Upon stop, it is equivalent to the

TriggersExecuted property.

Determining the Frame Delay Duration

To illustrate, this example calculates the duration of the delay specified by the

TriggerFrameDelay property.

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

for a Data Translation image acquisition device using the default video format. 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.