MexVision (Obsolete)

Using MexVision to capture images:

• In a terminal type:
  $pvm
  pvm>quit
  $matlab
  
• In matlab initialize MexVision:
  >>MexVision('init','S4R1'); %For "new" point-grey cameras at 640X480 resolution
  OR
  >>MexVision('init','S0R1'); %For webcams at 640X480 resolution
  (For initization at other resolutions see the description of the 'init' command below.)
  
• Capture images with MexVision (and show them):
  >>im=MexVision('frame');
  >>figure
  >>imshow(im);
  
• Quit MexVision:
  >>MexVision('quit');
  
• type halt in the pvm window before you log out:
  $pvm
  pvm>halt
  Also make sure that all the mexv2 processes are killed before logging out:
  $ps -A|grep mexv2
  $killall mexv2
• Another way to get MexVision started quickly is via the command:
  >>xvui
  This will start pvm, MexVision and bring up a window to initialize trackers. From this point you can grab images with the MexVision('frame') command.
• Another useful command is MexVision('get') which returns a vector of tracked image coordinates positions when any trackers are running.

• SSD1 tracker works well, and is mathematically sililar to the one you will implement in the labs. Trying SSD1 gives you an intution for what targets and how fast motions can be tracked.
• SSD2 does not currently work. For ssd2 think the call has to be modified to account for the 4DOF state.
• Color works acceptably, but perhaps some tuning of parameters could make it work better.
• Edge is to be used in combination with other trackers. By its nature it is not stable alone.

More MexVision Commands

• 'init': initialize using a ieee1394 camera as the video source
  preconditions: video has not already been created
  parameters (specifies the video mode):
  
  • For webcams:
    • 'S0R1': RGB 640X480 resolution
    • 'S0R0': YUV 640X480 resolution
    • 'S1R0': YUV 320X240 resolution
  • For "new" point-grey cameras:
    • 'S4R1': RGB 640X480 resolution
    • 'S2R0': YUV 1024X768 resolution
    • 'S3R0': YUV 800X600 resolution
    • 'S4R0': YUV 640X480 resolution
    • 'S5R0': YUV 320X240 resolution
  other options the can be appended to the above string (where X and Y are 0-255) are:
  
  • 'gX': set gain to X
    
  • 'uXvY': set white balance components to X,Y
    
  • 'sX': set saturation to X
    
  
  
• 'window': create a window to display the video, and use for interactive tracker initialization
  preconditions: video has been created
  parameters: window title (optional)
  
  
• 'edge': create an edge tracker and have the user initialize it
  preconditions: window has been created
  returns: id of the tracker
  
  
• 'ssd1': create a translation only ssd Tracker
  preconditions: window has been created
  parameters: with no parameters, the tracker will be initialized by the user.
  Optionally, a vector [Width Height X Y] specifying the initial state of the the tracker may be given as a parameter.
  returns: id of the tracker
  
  
• 'ssd2': create a translating/rotating/scaling ssd tracker and have the user initialize it
  preconditions: window has been created
  returns: id of the tracker
  
  
• 'blob': create a color blob tracker and have the user initialize it
  preconditions: window has been created
  returns: id of the tracker
  
  
• 'frame': grab a frame from the video
  returns: matrix containing the image (format depends on the 'init' string)
  
• 'framerate': get the current tracking framerate
  preconditions: video has been created
  returns: the tracking framerate
  
  
• 'image': get the transformed image associated with a tracker
  preconditions: the tracker exists and is of type ssd2
  parameters: the id of the tracker returns: grayscale image for the tracker
  
  
• 'get': get the state of a tracker
  preconditions: the tracker exists
  parameters: the id of the tracker or none to return all tracker states returns: vector containing the state of the tracker
  
  
• 'set': set the state of a tracker
  preconditions: the tracker exists
  parameters: the id of the tracker, and the new state returns: vector containing the state of the tracker
  
  
• 'delete': remove a tracker
  preconditions: the tracker exists
  parameters: the id of the tracker
  
  
• 'quit': End MexVision
  

When something doesn't work

• Quit programs using the camera and potentially hogging the interface.
  
• If you have used MexVision in matlab and it crashed, there may also be additional processses running. These are managed by pvm. In a terminal type:
  $pvm
  pvm>halt
  Also, check and kill stray pvm and mexv2 processes if any:
  $ps -A|grep pvmd3
  $killall pvmd3
  $ps -A|grep mexv2
  $killall mexv2
  
• If the problem still persists, try reloading camera drivers:
  
  • For webcams - first try resetting using coriander, if this does not work try plugging out and then plugging back in the camera.
  • For "new" point-grey cameras - ALWAYS use coriander to reset these cameras. NEVER plug out these cameras, they are very expensive and get ruined when the screw lock connectors are repeatedly connected and disconnected.
    
  • As a final resort log out of your account and then log back in (this will almost always fix the problem), but NEVER reboot the computers (TST does NOT like this).

How does MexVision interface with XVision?