Matthias's profile - activity

I am using the java wrapper of OpenCV. I tried to write an Iterator over frames of a film. My problem is that the iterator is a huge memory leak. It fills a GByte within seconds. Here is a very simplified version of the iterator, which has this leak:

public final class SimpleIt implements Iterator<Mat> {

    private final VideoCapture capture;
    boolean hasNext;

    public SimpleIt(final VideoCapture capture) {
        this.capture = capture;
        hasNext = capture.grab();
    }

    @Override
    public boolean hasNext() {
        return hasNext;
    }

    @Override
    public Mat next() {
        final Mat mat = new Mat();
        capture.retrieve(mat);
        hasNext = capture.grab();
        return mat;
    }
}

When I Iterate over this code using e.g. this loop:

    final VideoCapture vc = new VideoCapture("/path/to/file");
    final SimpleIt it = new SimpleIt(vc);
    while (it.hasNext) {
        it.next();
    }

memory consumption will increase linear. I see that the problem is the first line in the next()-Method. It always creates a new Mat. But speaking of java alone, this Mat will run out of scope as soon as the it.next() statement is over.

I could overcome the problem, by not using a new Mat every time, but overwriting always the same Mat-Object, like this:

    private final VideoCapture capture;
    private final Mat mat = new Mat();
    boolean hasNext;

    @Override
    public Mat next() {
        capture.retrieve(mat);
        hasNext = capture.grab();
        return mat;
    }

But now the last frame which was given by the iterator will always be overwritten by the current frame. Thus, I cannot hold it outside for later use, if I am interested in this single frame. I could copy it, of course, but that would also be expensive.

To illustrate the problem with the last approach, imagin this code using the iterator:

    final VideoCapture vc = new VideoCapture("/path/to/file");
    final SimpleIt it = new SimpleIt(vc);
    int i = 0;
    Mat save = null;
    while (it.hasNext) {
        final Mat next = it.next();
        if (i == 10) {
            save = next;
            Highgui.imwrite("/path/to/10.png", save);
        } else if (i == 30) {
            Highgui.imwrite("/path/to/30.png", save);
        }
        i++;
    }

With the second version of the iterator, 10.png, and 30.png will be different images. But that's obviously not what was intended.

I assume that the problem is that the garbage collector will not destroy the Mat objects, because it does not recognize the memory consumption, since it is not java heap space. Calling mat.release() in the loop will help, but of course in real code this means I will have no garbage collection for my Mat objects.

Anybody has an idea how to do it?

Edit: I expermiented now a while with it, and came to the following solution:

    int count = 0;

    @Override
    public Mat next() {
        final Mat result = mat;
        mat = new Mat();
        capture.retrieve(mat);
        hasNext = capture.grab();
        if (++count % 200 == 0) {
            System.gc();
        }
        return result;

If I call the garbage collector on a regular basis, it will delete all the unreferenced Mat objects, and together with them the RAM allocated from C. Well, that's probably a problem you have to face when mixing ... (more)

Hi all,

I try to configure CMake to build OpenCV with java support. Everything is fine, but it will not build java. The configure output even says so:

Checking for Windows Platform SDK
Checking for Visual Studio 2012
Could NOT find PythonInterp (missing:  PYTHON_EXECUTABLE) (Required is at least version "2.7")
Could NOT find PythonInterp (missing:  PYTHON_EXECUTABLE) (Required is at least version "2.6")
Found apache ant 1.9.3: E:/bin/apache-ant-1.9.3/bin/ant.bat
Could NOT find Matlab (missing:  MATLAB_MEX_SCRIPT MATLAB_INCLUDE_DIRS MATLAB_ROOT_DIR MATLAB_LIBRARIES MATLAB_LIBRARY_DIRS MATLAB_MEXEXT MATLAB_ARCH MATLAB_BIN) 

General configuration for OpenCV 3.0.0-dev =====================================
  Version control:               2.4.7.2-2644-g80816f6

  Platform:
    Host:                        Windows 6.1 AMD64
    CMake:                       2.8.12.1
    CMake generator:             Visual Studio 12 Win64
    CMake build tool:            C:/PROGRA~2/MSBuild/12.0/Bin/MSBuild.exe
    MSVC:                        1800

  C/C++:
    Built as dynamic libs?:      NO
    C++ Compiler:                E:/visualStudio/VC/bin/x86_amd64/cl.exe  (ver 18.0.21005.1)
    C++ flags (Release):         /DWIN32 /D_WINDOWS /W4 /GR /EHa  /D _CRT_SECURE_NO_DEPRECATE /D _CRT_NONSTDC_NO_DEPRECATE /D _SCL_SECURE_NO_WARNINGS /Gy /bigobj /Oi  /wd4251 /MT /O2 /Ob2 /D NDEBUG  /Zi
    C++ flags (Debug):           /DWIN32 /D_WINDOWS /W4 /GR /EHa  /D _CRT_SECURE_NO_DEPRECATE /D _CRT_NONSTDC_NO_DEPRECATE /D _SCL_SECURE_NO_WARNINGS /Gy /bigobj /Oi  /wd4251 /D_DEBUG /MTd /Zi /Ob0 /Od /RTC1 
    C Compiler:                  E:/visualStudio/VC/bin/x86_amd64/cl.exe
    C flags (Release):           /DWIN32 /D_WINDOWS /W3  /D _CRT_SECURE_NO_DEPRECATE /D _CRT_NONSTDC_NO_DEPRECATE /D _SCL_SECURE_NO_WARNINGS /Gy /bigobj /Oi  /MT /O2 /Ob2 /D NDEBUG  /Zi
    C flags (Debug):             /DWIN32 /D_WINDOWS /W3  /D _CRT_SECURE_NO_DEPRECATE /D _CRT_NONSTDC_NO_DEPRECATE /D _SCL_SECURE_NO_WARNINGS /Gy /bigobj /Oi  /D_DEBUG /MTd /Zi /Ob0 /Od /RTC1 
    Linker flags (Release):      /machine:x64   /NODEFAULTLIB:atlthunk.lib /NODEFAULTLIB:msvcrt.lib /NODEFAULTLIB:msvcrtd.lib /INCREMENTAL:NO  /debug /NODEFAULTLIB:libcmtd.lib
    Linker flags (Debug):        /machine:x64   /NODEFAULTLIB:atlthunk.lib /NODEFAULTLIB:msvcrt.lib /NODEFAULTLIB:msvcrtd.lib /debug /INCREMENTAL  /NODEFAULTLIB:libcmt.lib
    Precompiled headers:         YES

  OpenCV modules:
    To be built:                 core flann imgproc highgui features2d calib3d ml objdetect video ocl bioinspired cudaarithm nonfree contrib cudawarping cuda cudafilters cudaimgproc legacy cudabgsegm cudacodec cudafeatures2d cudaoptflow cudastereo optim photo shape softcascade stitching superres ts videostab
    Disabled:                    world
    Disabled by dependency:      -
    Unavailable:                 androidcamera cudalegacy cudev java matlab python viz

  Windows RT support:            NO

  GUI: 
    QT:                          NO
    Win32 UI:                    YES
    OpenGL support:              NO
    VTK support:                 NO

  Media I/O: 
    ZLib:                        build (ver 1.2.8)
    JPEG:                        build (ver 90)
    WEBP:                        build (ver 0.3.1)
    PNG:                         build (ver 1.5.12)
    TIFF:                        build (ver 42 - 4.0.2)
    JPEG 2000:                   build (ver 1.900.1)
    OpenEXR:                     build (ver 1.7.1)

  Video I/O:
    Video for Windows:           YES
    DC1394 1.x:                  NO
    DC1394 2.x:                  NO
    FFMPEG:                      YES (prebuilt binaries)
      codec:                     YES (ver 55.18.102)
      format:                    YES (ver 55.12.100)
      util:                      YES (ver 52.38.100)
      swscale:                   YES (ver 2.3.100)
      gentoo-style:              YES
    OpenNI:                      NO
    OpenNI PrimeSensor Modules:  NO
    PvAPI:                       NO
    GigEVisionSDK:               NO
    DirectShow:                  YES
    Media Foundation:            NO
    XIMEA:                       NO
    Intel PerC:                  NO

  Other third-party libraries:
    Use IPP:                     NO
    Use Eigen:                   NO
    Use TBB:                     NO
    Use OpenMP:                  NO
    Use GCD                      NO
    Use Concurrency              YES
    Use C=:                      NO
    Use Cuda:                    NO ...