Documentation

This is machine translation

Translated by Microsoft
Mouse over text to see original. Click the button below to return to the English verison of the page.

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
Was this topic helpful?