MATLAB: Does Image Acquisition Toolbox not always honor the TriggerFrameDelay setting when using manual triggering

Image Acquisition Toolbox

I am trying to use the Image Acquisition Toolbox's TriggerFrameDelay property with manual triggering. Most of the time this works correctly and the first acquired frame occurrs the specified number of frames after the trigger. However, sometimes the first acquired frame is captured immediately after the trigger and it is the second frame that delays the specified number of frames

Best Answer

This is caused by a limitation in how the toolbox handles manual triggering. Occasionally the first frame is acquired immediately after the manual trigger is issued. In these cases, it is actually the second frame that is delayed by the amount specified in TriggerFrameDelay. It is possible to detect this by examining the timestamps of the returned frames:

vid = videoinput('winvideo', 1);

triggerconfig(vid, 'manual');

set(vid, 'TriggerFrameDelay', 100);

start(vid);

trigger(vid);

wait(vid);

[data time] = getdata(vid);

In this case time(1) will be very close to zero, but time(2) will correspond to a time 100 frames after the trigger.

Related Solutions

MATLAB: Am I not able to use an external trigger for the DT frame grabber with the Image Acquisition Toolbox 1.7 (R14SP1)

This bug has been fixed in Release 14 Service Pack 2 (R14SP2). For previous releases, please read below for any possible workarounds:

We have verified that there is a bug in the Image Acquisition Toolbox 1.7 (R14SP1) in the way the DT frame grabber handles external triggers.

Currently, there are two ways to work around this issue:

The first way is to set the FramesPerTrigger property to a value greater than 1. This should prevent MATLAB from crashing. However, you must capture more than one frame per trigger.

The other way is to call the ADDFRAME function directly, in a callback, rather than using the Image Acquisition Toolbox’s built-in file logging capability. Below is an example. ADDFRAME is a MATLAB function.

vid = videoinput('dt',1,'NTSC');
vid.FramesPerTrigger = 1;
triggerconfig(vid, 'hardware', 'risingEdge', 'triggerinput');
vid.DiskLogger = aviobj;
vid.TriggerRepeat = (300*1)-1;
vid.FramesAcquiredFcn = @loggingCallback
vid.FramesAcquiredFcnCount = 1;
aviobj = avifile(my_log, 'Compression', 'none', 'Quality', 20);
vid.UserData = aviobj;

Create a file logging callback function, naming it Callback.m

Function loggingCallback(obj, event)
frame = getdata(obj, 1);
aviobj = obj.UserData;
aviobj = addframe(aviobj, frame);
obj.UserData = aviobj;

MATLAB: FramesperTrigger vs. Trigger repeat

1. Since you have to record continuously, it is better to set "FramesPerTrigger" to Inf instead of setting "TriggerRepeat" to Inf. This is because, when "TriggerRepeat" is Inf it will capture specified number of frames only when the trigger condition is met. Thus, setting "FramesPerTrigger" to Inf is more reliable in capturing all the frames.

2. There is no direct command in MATLAB that I know of is able to do that.

Best Answer

Related Solutions

MATLAB: Am I not able to use an external trigger for the DT frame grabber with the Image Acquisition Toolbox 1.7 (R14SP1)

MATLAB: FramesperTrigger vs. Trigger repeat

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