Android: open camera and get raw data in C level

Question

I want to open android tablet's camera and get the data from camera in C level. After that I will modify the data, and C level will be efficient.

Now I'm thinking using the V4L2 C code. But I find the open function of V4L2 need the parameter of the camera's name, such as '/dev/video0'. However I can't find something like that in my tablet's dev folder. Besides, I am not sure whether using the V4L2 will be the right solution.

Does anyone know anything about this?

What version of Android? Android 4.4 provides the new ImageReader class (developer.android.com/reference/android/media/ImageReader.html), which speeds access to YUV buffers from the camera. — fadden
– fadden, Commented Nov 18, 2013 at 15:39
Thank you. Any version would be fine. But I need to get them in C level so I will modify the data in C level directly, which is more efficient than Java. — Brendon Tsai
– Brendon Tsai, Commented Nov 19, 2013 at 1:56

Serge · Accepted Answer · 2014-02-11 14:39:30Z

1

on my device "OpenCV for Android" does not provide required performance neither in 'native' mode nor in 'java' mode. it gives FPS=2 in 1920x1080, in same time when java MediaRecorder can record 1920x1080 with FPS=15

I'm trying to solve it using the code from Android Open Source Project used by native Camera application:

static void android_hardware_Camera_native_setup(JNIEnv *env, jobject thiz,
    jobject weak_this, jint cameraId)
{
    sp<Camera> camera = Camera::connect(cameraId);

    if (camera == NULL) {
        jniThrowRuntimeException(env, "Fail to connect to camera service");
        return;
    }

    // make sure camera hardware is alive
    if (camera->getStatus() != NO_ERROR) {
        jniThrowRuntimeException(env, "Camera initialization failed");
        return;
    }

    jclass clazz = env->GetObjectClass(thiz);
    if (clazz == NULL) {
        jniThrowRuntimeException(env, "Can't find android/hardware/Camera");
        return;
    }

    // We use a weak reference so the Camera object can be garbage collected.
    // The reference is only used as a proxy for callbacks.
    sp<JNICameraContext> context = new JNICameraContext(env, weak_this, clazz, camera);
    context->incStrong(thiz);
    camera->setListener(context);

    // save context in opaque field
    env->SetIntField(thiz, fields.context, (int)context.get());
}

answered Feb 11, 2014 at 14:39

Serge

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1 Comment

Senthil Mg Over a year ago

If you are good in ndk code for image processing ,help me to complete the ndk snippit of the receiver end from the below attached pdf. google.co.in/…

pettersson · Accepted Answer · 2013-11-19 09:43:49Z

0

You can always build a JNI method for the Java classes to get access from C. Another way could be using OpenCV for Android: OpenCV4Android

This gives you a interface to the camera, but as far as I remember, there is currently no support for Android 4.3+.

answered Nov 19, 2013 at 9:43

pettersson

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