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Accessing Devices and Video Sources

This example shows how to access and connect to a video device.

Accessing an Image Acquisition Device

A video input object represents the connection between MATLAB® and an image acquisition device. To create a video input object, use the VIDEOINPUT function and indicate what device the object is to be associated with.

% Access an image acquisition device.
vidobj = videoinput('dt', 1, 'RS170')
Summary of Video Input Object Using 'Dt313xK'.

   Acquisition Source(s):  VID0, VID1, and VID2 are available.

  Acquisition Parameters:  'VID0' is the current selected source.
                           10 frames per trigger using the selected source.
                           'RS170' video data to be logged upon START.
                           Grabbing first of every 1 frame(s).
                           Log data to 'memory' on trigger.

      Trigger Parameters:  1 'immediate' trigger(s) on START.

                  Status:  Waiting for START.
                           0 frames acquired since starting.
                           0 frames available for GETDATA.

Identifying a Device's Video Source Object

A video source object represents a collection of one or more physical data sources that are treated as a single entity. For example, one video source object could represent the three physical connections of an RGB source (red, green, and blue).

The Source property of a video input object provides an array of the device's available video source objects.

% Access the device's video sources that can be used for acquisition.
sources = vidobj.Source
   Display Summary for Video Source Object Array:

      Index:   SourceName:   Selected:
      1        'VID0'        'on'     
      2        'VID1'        'off'    
      3        'VID2'        'off'  
whos sources
  Name          Size                   Bytes  Class

  sources       1x3                      872  videosource object

Grand total is 47 elements using 872 bytes	

Selecting a Video Source Object for Acquisition

A video source object can be selected for acquisition by specifying its name.

vidobj.SelectedSourceName = 'VID2')

% Notice that the corresponding video source has been selected.
sources
   Display Summary for Video Source Object Array:

      Index:   SourceName:   Selected:
      1        'VID0'        'off'    
      2        'VID1'        'off'    
      3        'VID2'        'on'

To obtain the video source object that is currently selected, use the GETSELECTEDSOURCE function.

selectedsrc = getselectedsource(vidobj)
   Display Summary for Video Source Object:

      Index:   SourceName:   Selected:
      1        'VID2'        'on'  

Accessing a Video Source Object's Properties

Each video source object provides a list of general and device specific properties.

% List the video source object's properties and their current values.
get(selectedsrc)
  General Settings:
    Parent = [1x1 videoinput]
    Selected = on
    SourceName = VID2
    Tag = 
    Type = videosource
    UserData = []

  Device Specific Properties:
    FirstActiveLine = 21
    FirstActivePixel = 140
    FrameType = interlacedEvenFieldFirst
    StrobeOutput = off
    StrobeOutputDuration = 3.3ms
    StrobeOutputPolarity = activeHigh
    StrobeOutputType = afterFrame
    SyncInput = composite
    TriggerTimeout = 0

Note: Each video source object maintains its own property configuration. Modifying the selected video source is equivalent to selecting a new video source configuration.

% Once the video input object is no longer needed, delete
% it and clear it from the workspace.
delete(vidobj)
clear vidobj

See also IMAQHWINFO, VIDEOINPUT, IMAQDEVICE/GETSELECTEDSOURCE, IMAQHELP, IMAQDEVICE/GET, IMAQDEVICE/PROPINFO.

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