OpenCV 2.2 + Webcam + Windows not working
Hey there…
it has been a while since my last post… but I’m here again, although I’ll not stay long =P. This will be a short post… another quick and dirty tip. I’ve been very busy and without the time to post something really substantial. However, I think this can be helpful, so…
These days I had a problem using my webcam with OpenCV 2.2 in Windows. Most of the time I use Linux and never had any problem like this, but last week I needed to use OpenCV 2.2 + Windows for a Computer Vision project and figured out that my webcam simply do not work in this configuration: when I try to create a capture object, a window opens requiring I select the device. However, it does not succeed, even if I select the device correctly.
Oddly, this does not occur with OpenCV 2.1 + Windows. Thus, I concluded it’s a bug in OpenCV 2.2, specifically in the highgui package. Apparently, this version of OpenCV is using a back-end for cameras different from DirectShow, despite OpenCV supports it and, as I know, this is the recommended way of accessing cameras in Windows.
A solution is to force OpenCV to use DirectShow, what can be done by defining the macros HAVE_VIDEOINPUT and HAVE_DSHOW during the building configuration. Just edit the flag CMAKE_C_COMPILER adding the proper options. For example, if you’re building OpenCV using Visual Studio, append “/DHAVE_DSHOW /DHAVE_VIDEOINPUT” to that flag.
Well, this worked for me… I hope it can be helpful to you =).
PS: As a matter of fact, this is a bug in the setup of the OpenCV building, not a bug in OpenCV itself.
Posted on June 5, 2011, in OpenCV and tagged not working, opencv, webcam, windows. Bookmark the permalink. 27 Comments.
Rafael Barreto 
so what can we do solve this problem?
Hi, sorry the delay in the answer. I think it’s clear in the text. You have to rebuild OpenCV with the macros
HAVE_VIDEOINPUTandHAVE_DSHOWdefined.Can u please tell me the way to edit these macros in step by step manner
Right now I don’t have access to a Windows machine, so I can’t show pictures. Anyway, it’s not difficult. Follow the OpenCV install guide (http://opencv.willowgarage.com/wiki/InstallGuide). When configuring the build through CMake options, you’ll see the flag CMAKE_C_COMPILER. This stores the options passed to the C compiler. So, you can define the macros HAVE_VIDEOINPUT and HAVE_DSHOW here. How do you do this? It depends on your compiler. For Visual Studio this can be done adding “/DHAVE_DSHOW /DHAVE_VIDEOINPUT” to CMAKE_C_COMPILER flag. For MinGW, you must add “-DHAVE_DSHOW -DHAVE_VIDEOINPUT”. For any other compiler, you must figure out the correct syntax.
I hope it helps…
i cant find the CMAKE_C_COMPILER flag in the CMake options, what do i do to fix this??? And how exactly do i add macros to it afterwards??
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