Segmentation fault in VideoEmulation

[pflammertsma]

Firstly, I'd like to commend Bill and Noritsuna on the amazing job they've done in porting OpenCV to Android. Compiling the library was surprisingly simple and all-in-all it's a great achievement.

I have been running the VideoEmulation example (using the Java implementation of SocketCamera) on the emulator, and am encountering a segmentation fault at VideoEmulation.java:226:

data = mOpenCV.getSourceImage();

LogCat first warns me of a mismatch between JNI and Java:

WARN/dalvikvm(29093): JNI WARNING: method declared to return '[B' returned '[Z'
              failed in Lorg/siprop/opencv/OpenCV;.getSourceImage ('[B' not found)

I took a look at the C declaration and JNI declaration, and the former, [Z, is a boolean array while the latter, [B is a byte array.

A stack trace of org.siprop.opencv.OpenCV.getSourceImage(Native Method) is outputted and the VM instantly aborts.

What have I done wrong here? Is my library somehow not compiled correctly?

[pflammertsma]

After some debugging, I've confirmed that the native method getSourceImage() in cvjni.cpp:134 is actually called; the JNI WARNING above is raised immediately after the function returns, and has the following trace:

"Thread-8" prio=5 tid=15 RUNNABLE
  | group="main" sCount=0 dsCount=0 s=N obj=0x43d16548 self=0x119ff8
  | sysTid=16284 nice=0 sched=0/0 cgrp=default handle=1196176
  at org.siprop.opencv.OpenCV.getSourceImage(Native Method)
  at org.siprop.opencv.VideoEmulation$1.run(VideoEmulation.java:226)

[pflammertsma]

If I change the type declaration in OpenCV.java:38 from:

public native byte[] getSourceImage();

To:

public native boolean[] getSourceImage();

The application no longer crashes, but then of course I cannot decode the byte array in VideoEmulation.java:240.

[pflammertsma]

I resolved the problem, but needed to make changes to cvjni.h and cvjni.cpp:

1. The datatype of Java_org_siprop_opencv_OpenCV_getSourceImage() should be jbyteArray, not jbooleanArray.
2. With all subsequent modifications within that function (line 152, 154 and 157), the Android application works as expected.

I would also suggest changing the datatype of Java_org_siprop_opencv_OpenCV_findContours() to jbyteArray.

[ntbb]

The solution mentioned above was so useful, and therefore I've completed the porting of face detector from PC to android.

Thanks to pflammertsma and the author of this awesome project!

[bruciebruce]

Hello,

Thanks for all the good pointers (pardon the joke).

I took your advice and made changes to cvjni.h file. Here are the changes:

JNIEXPORT jbyteArray JNICALL Java_org_siprop_opencv_OpenCV_findContours(JNIEnv* env, jobject thiz, jint width, jint height);

and also this:

JNIEXPORT jbyteArray JNICALL Java_org_siprop_opencv_OpenCV_getSourceImage(JNIEnv* env, jobject thiz);

I then made chanes to the implementation file cvjni.cpp as such:

/ Generate and return a boolean array from the source image. // Return 0 if a failure occurs or if the source image is undefined. JNIEXPORT jbyteArray JNICALL Java_org_siprop_opencv_OpenCV_getSourceImage(JNIEnv* env, jobject thiz) {

...

jbyteArray res_array = env->NewByteArray(imageSize);
if (res_array == 0) {
    LOGE("Unable to allocate a new boolean array for the source image.");
    return 0;
}
env->SetByteArrayRegion(res_array, 0, imageSize, (jbyte*)strm->GetByte());

strm->Close();
SAFE_DELETE(strm);

return res_array;

}

and finally the 2nd file:

JNIEXPORT jbyteArray JNICALL Java_org_siprop_opencv_OpenCV_findContours(JNIEnv* env, jobject thiz, jint width, jint height) { ...

jbyteArray res_array = env->NewByteArray(imageSize);
LOGV("Load NewBooleanArray.");
if (res_array == 0) {
    return 0;
}
env->SetByteArrayRegion(res_array, 0, imageSize, (jbyte*)strm->GetByte());
LOGV("Load SetBooleanArrayRegion.");

LOGV("Release sourceImage");
if (m_sourceImage) {
    cvReleaseImage(&m_sourceImage);
    m_sourceImage = 0;
}
LOGV("Release binaryImage");
cvReleaseImage( &binaryImage );
LOGV("Release grayImage");
cvReleaseImage( &grayImage );
LOGV("Release contourImage");
cvReleaseImage( &contourImage );
LOGV("Release storage");
cvReleaseMemStorage( &storage );
LOGV("Delete strm");
strm->Close();
SAFE_DELETE(strm);

return res_array;

}

I still get the same seg fault alluded to by the previous writers on this thread.

I have not run the emulator program. I have an ADP2

Thanks!

-Bruce

[billmccord]

Yes, much thanks to pflammertsma. I have been rather disconnected from this project of late because of other priorities, but I am going to try to integrate this work back into the project.