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Old 01-24-2008, 03:51 PM
v-clizzin v-clizzin is offline
Join Date: Sep 2006
Posts: 15
problems with webcam plug-in

Hi, I am experiencing problems with a Vizard script that makes use of some plug-ins that a previous member of the lab wrote a while ago to connect to a webcam. That person is now out of contact, so I'm hoping to get some help here.

The webcam connection relies on a DLL file called 'capture.dll' which was used to get information from the connected webcam. Right now, we've determined that the script chokes on a line that invokes a Webcam class from the capture module. The relevant code looks like this:
import facetrack
facetracker = facetrack.WebcamTrack()
import capture
import neven
import math
import threading
import Queue
import chunk
import datetime
import re

class WebcamTrack:
	def __init__(self,
					width = 320, height = 240, fps = 30, id = 0,
					minEyeDist = 20, maxEyeDist = 100, threshhold = 0.4,
					fdInit  = "V_FD_prec_100.bsk",
					ffdInit = "VFFD_22n_101.bsk",
					fftInit = "VFFT_22n_103.bsk"):    = capture.Webcam(width, height, fps, id,
										self._webcamCallback, 0)   # CHOKES ON THIS LINE
		self.fft       = neven.Fft(,,
									minEyeDist, maxEyeDist,
									fdInit, ffdInit, fftInit)
		self.threshhold = threshhold
		self.face      = None             # Current face.  May be None.
		self.validFace = GENERIC_FACE     # Most recent non-None face.
		self.image     = "\0" * ( *
		self.dataLock  = threading.Lock()
		self.queue     = Queue.Queue(-1)
		self.thread    = threading.Thread(name = "WebcamTrack" + str(id),
											target = _webcamTrackThread,
											args = (self,))
# and so on...
The code chokes on the line " = capture.Webcam(width, height, fps, id, self._webcamCallback, 0)". The error I get is:

ERROR in Webcam: Device has no acceptable format
Traceback (most recent call last):
  File "", line 326, in mytimer
    facetracker = facetrack.WebcamTrack()
  File ".\", line 957, in __init__
    self._webcamCallback, 0)
SystemError: NULL result without error in PyObject_Call
As far as I can tell based on the Python sys.path set up on this machine, 'import capture' refers to a 'capture.dll' file. I then presume that this DLL file was compiled based on some C/C++ code in a Visual Studio project. After rooting around a bit, I've found what I think is the C/C++ code that the DLL was compiled from, but the Capture.h and Capture.cpp files I found don't include any sort of class or method named 'Webcam'.

I don't have much experience with DLL's (I barely know what they are or how they work), much less compiling C/C++ projects into DLL's and then linking them to Python, so if someone could provide a link that explains how that works, that would be helpful.

I apologize if all this boils down to 'Please debug some code for me', but at this point I'm rather lost and would appreciate any help I can get. If someone is willing to take a look at the code, I'd be glad to email it to you and would be very appreciative of the help.

One other thing that may be useful: This program was working until just a couple weeks ago. I can think of a couple changes made that might have affected this:

1. I changed the Windows environment path used to look up Python so that I could use Python from the Windows command line. This was formerly "C:\Python", which was a nonexistent directory; I changed it to "C:\Python23" (we are using Python 2.3 because the plug-ins were written for Vizard 2.5, which uses Python 2.3). After the problem with the program started, I tried changing the environment path variable back, but this made no difference.

2. I installed a new device on the machine that required a PCI card which I also added. In doing so, I unplugged everything from the machine to make it easier to open up, and then re-plugged everything in afterwards, including the webcam. I don't know if this would affect the DLL's ability to locate the webcam, but some testing seems to suggest no because a getWebcamNames() method in the capture library still correctly lists the webcam attached to the computer.

Hope someone can help out, thanks very much in advance!

christopher lin
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