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Specifying the Trigger Type

Comparison of Trigger Types

To specify the type of trigger you want to execute, set the value of the TriggerType property of the video input object. You must use the triggerconfig function to set the value of this property. The following table lists all the trigger types supported by the toolbox, with information about when to use each type of trigger.

Comparison of Trigger Types

TriggerType Value

TriggerSource and TriggerCondition Values

Description

'immediate'

Always 'none'

The trigger occurs automatically, immediately after the start function is issued. This is the default trigger type. For more information, see Using an Immediate Trigger.

'manual'

Always 'none'

The trigger occurs when you issue the trigger function. A manual trigger can provide more control over image acquisition. For example, you can monitor the video stream being acquired, using the preview function, and manually execute the trigger when you observe a particular condition in the scene. For more information, see Using a Manual Trigger.

'hardware'

Device-specific

Hardware triggers are external signals that are processed directly by the hardware. This type of trigger is used when synchronization with another device is part of the image acquisition setup or when speed is required. A hardware device can process an input signal much faster than software. For more information, see Using a Hardware Trigger.

    Note:   Only a subset of image acquisition devices supports hardware triggers. To determine the trigger types supported by your device, see Determining Valid Configurations.

    Note:   To get a list of options you can use on a function, press the Tab key after entering a function on the MATLAB® command line. The list expands, and you can scroll to choose a property or value. For information about using this advanced tab completion feature, see Using Tab Completion for Functions.

Using an Immediate Trigger

To use an immediate trigger, simply create a video input object. Immediate triggering is the default trigger type for all video input objects. With an immediate trigger, the object executes the trigger immediately after you start the object running with the start command. The following figure illustrates an immediate trigger.

Immediate Trigger

The following example illustrates how to use an immediate trigger:

  1. 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);

    Verify that the object has not acquired any frames.

    vid.FramesAcquired
    ans =
    
    	0
  2. Configure properties — To use an immediate trigger, you do not have to configure the TriggerType property because 'immediate' is the default trigger type. You can verify this by using the triggerconfig function to view the current trigger configuration or by viewing the video input object's properties.

    triggerconfig(vid)
    ans =
    
             TriggerType: 'immediate'
        TriggerCondition: 'none'
           TriggerSource: 'none'

    This example sets the value of the FramesPerTrigger property to 5. (The default is 10 frames per trigger.)

    vid.FramesPerTrigger = 5
  3. Start the image acquisition object — Call the start function to start the image acquisition object. By default, the object executes an immediate trigger and acquires five frames of data, logging the data to a memory buffer. After logging the specified number of frames, the object stops running.

    start(vid)

    To verify that the object acquired data, view the value of the FramesAcquired property. The object updates the value of this property as it acquires data.

    vid.FramesAcquired
    ans =
    
       5

    To execute another immediate trigger, you must restart the object. Note, however, that this deletes the data acquired by the first trigger. To execute multiple immediate triggers, specify a value for the TriggerRepeat property. See Specifying Multiple Triggers for more information.

  4. Clean up — Always remove image acquisition objects from memory, and the variables that reference them, when you no longer need them.

    delete(vid)
    clear vid

Using a Manual Trigger

To use a manual trigger, create a video input object and set the value of the TriggerType property to 'manual'. A video input object executes a manual trigger after you issue the trigger function. The following figure illustrates a manual trigger.

Manual Trigger

The following example illustrates how to use a manual trigger:

  1. Create an image acquisition object — This example creates a video input object for a webcam 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('winvideo',1);
    

    Verify that the object has not acquired any frames.

    vid.FramesAcquired
    ans =
    	0
  2. Configure properties — Set the video input object's TriggerType property to 'Manual'. To set the values of certain trigger properties, including the TriggerType property, you must use the triggerconfig function. See Setting the Values of Trigger Properties for more information.

    triggerconfig(vid, 'Manual')

    This example also sets the value of the FramesPerTrigger property to 5. (The default is 10 frames per trigger.)

    vid.FramesPerTrigger = 5
  3. Start the image acquisition object — Call the start function to start the image acquisition object.

    start(vid);

    The video object is now running but not logging. With manual triggers, the video stream begins when the object starts but no frames are acquired until the trigger executes.

    isrunning(vid)
    
    ans =
    
         1
    
    islogging(vid)
    
    ans =
    
         0

    Verify that the object has still not acquired any frames.

    vid.FramesAcquired
    ans = 
    	0
  4. Execute the manual trigger — Call the trigger function to execute the manual trigger.

    trigger(vid)

    The object initiates the acquisition of five frames. Check the FramesAcquired property again to verify that five frames have been acquired.

    vid.FramesAcquired
    ans = 
    	5

    After it acquires the specified number of frames, the video input object stops running.

    isrunning(vid)
    
    ans =
    
         0

    To execute another manual trigger, you must first restart the video input object. Note that this deletes the frames acquired by the first trigger. To execute multiple manual triggers, specify a value for the TriggerRepeat property. See Specifying Multiple Triggers for more information.

  5. Clean up — Always remove image acquisition objects from memory, and the variables that reference them, when you no longer need them.

    delete(vid)
    clear vid

Using a Hardware Trigger

To use a hardware trigger, create a video input object and set the value of the TriggerType property to 'hardware'. You must also specify the source of the hardware trigger and the condition type. The hardware monitors the source you specify for the condition you specify. The following figure illustrates a hardware trigger. For hardware triggers, the video stream does not start until the trigger occurs.

    Note   Trigger sources and the conditions that control hardware triggers are device specific. Use the triggerinfo function to determine whether your image acquisition device supports hardware triggers and, if it does, which conditions you can configure. Refer to the documentation that came with your device for more detailed information about its hardware triggering capabilities.

Hardware Trigger

The following example illustrates how to use a hardware trigger:

  1. 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. The device must support hardware triggers.

    vid = videoinput('matrox',1);
    
  2. Determine valid trigger property configurations — Use the triggerinfo function to determine if your image acquisition device supports hardware triggers, and if it does, to find out valid configurations of the TriggerSource and TriggerCondition properties. See Determining Valid Configurations for more information.

    In this example, triggerinfo returns the following valid trigger configurations.

    triggerinfo(vid)
    Valid Trigger Configurations:
    
          TriggerType:   TriggerCondition:   TriggerSource:
          'immediate'    'none'              'none'        
          'manual'       'none'              'none' 
    	    'hardware'     'risingEdge'        'TTL' 
    	    'hardware'     'fallingEdge'       'TTL' 
  3. Configure properties — Configure the video input object trigger properties to one of the valid combinations returned by triggerinfo. You can specify each property value as an argument to the triggerconfig function

    triggerconfig(vid, 'hardware','risingEdge','TTL')

    Alternatively, you can set these values by passing one of the structures returned by the triggerinfo function to the triggerconfig function.

    configs = triggerinfo(vid);
    triggerconfig(vid,configs(3));

    This example also sets the value of the FramesPerTrigger property to 5. (The default is 10 frames per trigger.)

    vid.FramesPerTrigger = 5
  4. Start the image acquisition object — Call the start function to start the image acquisition object.

    start(vid)

    The object is running but not logging any data.

    isrunning(vid)
    
    ans =
    
         1
    
    islogging(vid)
    
    ans =
    
         0

    The hardware begins monitoring the trigger source for the specified condition. When the condition is met, the hardware executes a trigger and begins providing image frames to the object. The object acquires the number of frames specified by the FramesPerTrigger property. View the value of the FramesAcquired property to see how much data was acquired. The object updates the value of this property as it acquires data.

    vid.FramesAcquired
    ans =
    
        5

    After it executes the trigger and acquires the specified number of frames, the video input object stops running.

    isrunning(vid)
    
    ans =
    
         0

    To execute another hardware trigger, you must first restart the video input object. Note that this deletes the frames acquired by the first trigger. To execute multiple triggers, specify a value for the TriggerRepeat property. See Specifying Multiple Triggers for more information.

  5. Clean up — Always remove image acquisition objects from memory, and the variables that reference them, when you no longer need them.

    delete(vid)
    clear vid

Setting DCAM-Specific Trigger Modes

You can now use all trigger modes and all trigger inputs that DCAM cameras support. Previous toolbox releases supported only trigger mode 0. Support for additional trigger modes and inputs do not affect any existing code you use.

Control trigger functionality using the triggerinfo and triggerconfig functions and the triggersource property. Before R2010a, one triggersource was available, externalTrigger. Selecting externalTrigger configures the camera to use trigger mode 0 with trigger source 0.

The triggersource property is now composed of the trigger type (internal or external), the trigger source (0, 1, 2, etc.), and the mode number (0 through 5, 14 and 15). The following table summarizes the options.

Trigger ModeParameterExternal SourceMultiple Frames Per Trigger
0noneyesyes
1noneyesno
2(N >= 2)yesno
3(N >= 1)noyes
4(N >= 1)yesno
5(N >= 1)yesno
14unknownunknownunknown
15unknownunknownunknown

For example, the second triggersource for trigger mode 1 is called externalTrigger1-mode1. To use mode 3, the triggersource is internalTrigger-mode3.

    Note:   Toolbox versions before R2010a supported DCAM trigger mode 0 with the first available triggersource as externalTrigger. The existing externalTrigger property will be maintained so to prevent backward compatibility issues. In addition, in order to preserve symmetry with the new functionality, triggersource externalTrigger0-mode0, which is synonymous, will also be supported. The new trigger modes do not work before R2010a.

Usage Notes

If a trigger mode has multiple trigger sources (modes 0, 1, 2, 4, and 5), then triggersource has a digit indicating the corresponding camera source, even if only one camera source is available. For example, if the camera has only a single triggersource available, the toolbox reports the triggersource name as externalTrigger0-modeX. If the trigger mode does not have multiple sources (mode 3), then no source digit appears in the name (i.e, internalTriggerMode3 instead of internalTriggerMode3-Source0).

The DCAM adaptor includes a TriggerParameter property that is passed to the camera when you set trigger configurations. The TriggerParameter property is validated when you call START after selecting a hardware trigger mode.

If the selected trigger mode prohibits multiple frames per trigger, then an error appears when you call START without setting FramesPerTrigger to 1.

If the camera supports only trigger mode 0 with source 0, then the original functionality of having only the externalTrigger triggersource is supported.

Trigger modes 14 and 15 are vendor-specific and are assumed to be external triggers and have no restrictions on any settings. You must validate any settings you use.

The following sections detail the trigger modes.

Trigger Mode 0

This is the only trigger mode supported before R2010a. When a trigger is received, a frame is acquired. You can acquire multiple frames per trigger by switching the camera for hardware triggered mode to free running mode when a triggered frame is acquired.

No parameter is required.

The camera starts the integration of the incoming light from the external trigger input falling edge.

Trigger Mode 1

In this mode, the duration of the trigger signal is used to control the integration time of the incoming light. This mode is used to synchronize the exposure time of the camera to an external event.

No parameter is required.

The camera starts the integration of the incoming light from the external trigger input falling edge. Integration time is equal to the low state time of the external trigger input if triggersource is fallingEdge, otherwise it is equal to the high state time.

Trigger Mode 2

This mode is similar to mode 1, except the duration of the trigger signal does govern integration time. Instead the number of trigger signals received does. Integration commences upon the start of the first trigger signal and continues until the start of the Nth trigger signal.

Parameter N is required and describes the number of trigger signals in an integration.

The camera starts the integration of the incoming light from the first external trigger input falling edge. At the Nth external trigger input falling edge, integration stops. Parameter N is required and must be 2 or greater. (N >= 2).

Trigger Mode 3

Use this internal trigger mode to achieve a lower frame rate. When the trigger generates internally, a frame is acquired and returned. A new frame is not acquired for N x Tf when N is the parameter and Tf is the cycle time of the fastest frame rate supported by the camera.

A parameter is required, as described above.

This is an internal trigger mode. The camera issues the trigger internally and cycle time is N times of the cycle time of the fastest frame rate. Integration time of incoming light is described in the shutter register. Parameter N is required and must be 1 or greater (N >= 1).

Trigger Mode 4

This mode is the "multiple shutter preset mode." It is similar to mode 1, but the exposure time is governed by the shutter property. On each trigger, shutter property defines the exposure duration. When N triggers are received, a frame is acquired.

Parameter N is required and describes the number of triggers.

The camera starts integration of incoming light from the first external trigger input falling edge and exposes incoming light at shutter time. Repeat this sequence until the Nth external trigger input falling edge, then finish integration. Parameter N is required and must be 1 or greater (N >= 1).

Trigger Mode 5

This mode is the "multiple shutter pulse width mode." It is a combination of modes 1 and 2. The exposure time is governed by the duration of the trigger signal and a number of trigger signals can be integrated into a single readout. If the trigger parameter is 1, this mode is degenerate with mode 1.

A parameter is required. The parameter describes the number of triggers.

The camera starts integration of incoming light from first the external trigger input falling edge and exposes incoming light until the trigger is inactive. Repeat this sequence until the Nth external trigger input falling edge, then finish integration. Parameter N is required and must be 1 or greater (N >= 1).

Trigger Mode 14

This is a vendor-specific mode and no information is available. Consult the documentation for your camera.

Trigger Mode 15

This is a vendor-specific mode and no information is available. Consult the documentation for your camera.

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