Setting Camera Parameters in OpenCV Python

Question

I am using OpenCV  2 4  and Python  2 7 3  with a USB camera from Thorlabs  DC1545M    I am doing some image analysis on a video stream and I would like to be able to change some of the camera parameters from my video stream   The confusing thing is that I am able to change some of the camera properties but not all of them  and I am unsure of what I am doing wrong   Here is the code  using the cv2 bindings in Python  and I can confirm that it runs   import cv2    capture from camera at location 0 cap   cv2 VideoCapture 0   set the width and height  and UNSUCCESSFULLY set the exposure time cap set 3 1280  cap set 4 1024  cap set 15  0 1   while True      ret  img   cap read       cv2 imshow  input   img       cv2 imshow  thresholded   imgray thresh2       key   cv2 waitKey 10      if key    27          break   cv2 destroyAllWindows    cv2 VideoCapture 0  release     For reference  the first argument in the cap set   command refers to the enumeration of the camera properties  listed below     0  CV CAP PROP POS MSEC Current position of the video file in milliseconds  1  CV CAP PROP POS FRAMES 0-based index of the frame to be decoded captured next  2  CV CAP PROP POS AVI RATIO Relative position of the video file 3  CV CAP PROP FRAME WIDTH Width of the frames in the video stream  4  CV CAP PROP FRAME HEIGHT Height of the frames in the video stream  5  CV CAP PROP FPS Frame rate  6  CV CAP PROP FOURCC 4-character code of codec  7  CV CAP PROP FRAME COUNT Number of frames in the video file  8  CV CAP PROP FORMAT Format of the Mat objects returned by retrieve     9  CV CAP PROP MODE Backend-specific value indicating the current capture mode  10  CV CAP PROP BRIGHTNESS Brightness of the image  only for cameras   11  CV CAP PROP CONTRAST Contrast of the image  only for cameras   12  CV CAP PROP SATURATION Saturation of the image  only for cameras   13  CV CAP PROP HUE Hue of the image  only for cameras   14  CV CAP PROP GAIN Gain of the image  only for cameras   15  CV CAP PROP EXPOSURE Exposure  only for cameras   16  CV CAP PROP CONVERT RGB Boolean flags indicating whether images should be converted to RGB  17  CV CAP PROP WHITE BALANCE Currently unsupported 18  CV CAP PROP RECTIFICATION Rectification flag for stereo cameras  note  only supported by DC1394 v 2 x backend currently    My questions are   Is it possible to set camera exposure time  or the other camera parameters  through python opencv   If not  how would I go about setting these parameters     Note  There is C   code provided by the camera manufacturer showing how to do this  but I m not an expert  by a long shot  in C   and would appreciate any python-based solution   Thanks in advance

User · Answer

To avoid using integer values to identify the VideoCapture properties, one can use, e.g., cv2.cv.CV_CAP_PROP_FPS in OpenCV 2.4 and cv2.CAP_PROP_FPS in OpenCV 3.0. (See also Stefan's comment below.)

Here a utility function that works for both OpenCV 2.4 and 3.0:

# returns OpenCV VideoCapture property id given, e.g., "FPS"
def capPropId(prop):
  return getattr(cv2 if OPCV3 else cv2.cv,
    ("" if OPCV3 else "CV_") + "CAP_PROP_" + prop)

OPCV3 is set earlier in my utilities code like this:

from pkg_resources import parse_version
OPCV3 = parse_version(cv2.__version__) >= parse_version('3')

User · Answer

I had the same problem with openCV on Raspberry Pi    don t know if this can solve your problem  but what worked for me was  import time import cv2   cap   cv2 VideoCapture 0   cap set 3 1280   cap set 4 1024   time sleep 2   cap set 15  -8 0    the time you have to use  can be different

User · Answer

I wasn t able to fix the problem OpenCV either  but a video4linux  V4L2  workaround does work with OpenCV when using Linux  At least  it does on my Raspberry Pi with Rasbian and my cheap webcam  This is not as solid  light and portable as you d like it to be  but for some situations it might be very useful nevertheless   Make sure you have the v4l2-ctl application installed  e g  from the Debian v4l-utils package  Than run  before running the python application  or from within  the command   v4l2-ctl -d  dev video1 -c exposure auto 1 -c exposure auto priority 0 -c exposure absolute 10   It overwrites your camera shutter time to manual settings and changes the shutter time  in ms   with the last parameter to  in this example  10  The lower this value  the darker the image

User · Answer

If anyone is still wondering what the value in CV CAP PROP EXPOSURE might be   Depends  For my cheap webcam I have to enter the desired value directly  e g  0 1 for 1 10s  For my expensive industrial camera I have to enter -5 to get an exposure time of 2 -5s   1 32s

User · Answer

Not all parameters are supported by all cameras - actually  they are one of the most troublesome part of the OpenCV library  Each camera type - from android cameras to USB cameras to professional ones offer a different interface to modify its parameters  There are many branches in OpenCV code to support as many of them  but of course not all possibilities are covered   What you can do is to investigate your camera driver  write a patch for OpenCV and send it to code opencv org  This way others will enjoy your work  the same way you enjoy others    There is also a possibility that your camera does not support your request - most USB cams are cheap and simple  Maybe that parameter is just not available for modifications   If you are sure the camera supports a given param  you say the camera manufacturer provides some code  and do not want to mess with OpenCV  you can wrap that sample code in C   with boost  python  to make it available in Python  Then  enjoy using it

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