Android JNI：将cv：：mat转换为jbyteArray

Question

我有C/C++源代码（在Windows上运行良好）将输入帧转换为新帧。

>

将byte[]帧从Java转换为JNI jarrayByte

将jarrayByte转换为Jyte*

从JByte*创建新的cv：：mat原始代码*

extern "C" JNIEXPORT jbyteArray
JNICALL
Java_com_xyz_NativeUtil_convertFrame(JNIEnv *env, jobject obj,
                                                                  jbyteArray yuvFrame) {
// convert jByteArray to jbyte*
jbyte* yuvByte = env->GetByteArrayElements(yuvFrame, 0);
// convert jbyte* to cv::Mat
cv::Mat frame_original_yuv = cv::Mat(height + height/2, width, CV_8UC1, yuvByte);
// convert YUV cv::Mat to RGBA cv::Mat
cv::Mat frame_original_rgba = cv::Mat(height, width, CV_8UC4);
cv::cvtColor(frame_original_yuv, frame_original_rgba, CV_YUV2RGBA_NV21);
env->ReleaseByteArrayElements(yuvFrame, yuvByte, 0);
// convert frame
cv::Mat frame_converted = convert_frame(frame_original_rgba);
frame_original_yuv.release();

if (frame_converted .empty()) {
    frame_converted = frame_original_rgba;
}
frame_original_rgba.release();
// convert cv::Mat to jbyteArray
jbyteArray result = ???

return result;

}

我的Java代码：

mImageReader.setOnImageAvailableListener(new ImageReader.OnImageAvailableListener() {
            @Override
            public void onImageAvailable(ImageReader reader) {
                Image image = reader.acquireLatestImage();
                if (image == null)
                    return;

                Image.Plane Y = image.getPlanes()[0];
                Image.Plane U = image.getPlanes()[1];
                Image.Plane V = image.getPlanes()[2];

                int Yb = Y.getBuffer().remaining();
                int Ub = U.getBuffer().remaining();
                int Vb = V.getBuffer().remaining();

                byte[] yuvFrame = new byte[Yb + Ub + Vb];

                Y.getBuffer().get(yuvFrame, 0, Yb);
                U.getBuffer().get(yuvFrame, Yb, Ub);
                V.getBuffer().get(yuvFrame, Yb + Ub, Vb);

                image.close();
            }
        }, mBackgroundHandler);

Answer 1

假设您希望将本机cv::mat对象传递给Java并将其转换为bitmap。

在这种情况下，最好将其转换为JintArray，因此我将使用它编写一个示例，但您可以轻松地修改该代码以使用JByteArray

请注意，在该代码中，我假设cv::mat有4个通道(bgra)，请相应地更改它。如果您的垫子是灰色的-将R、g、B设置为相同的灰色，将A设置为255。如果您的mat是bgr-将A设置为255。

jintArray matToBitmapArray(JNIEnv *env, const cv::Mat &image) {
    jintArray resultImage = env->NewIntArray(image.total());
    jint *_data = new jint[image.total()];
    for (int i = 0; i < image.total(); i++) {
        char r = image.data[4 * i + 2];
        char g = image.data[4 * i + 1];
        char b = image.data[4 * i + 0];
        char a = image.data[4 * i + 3];
        _data[i] = (((jint) a << 24) & 0xFF000000) + (((jint) r << 16) & 0x00FF0000) +
                   (((jint) g << 8) & 0x0000FF00) + ((jint) b & 0x000000FF);
    }
    env->SetIntArrayRegion(resultImage, 0, image.total(), _data);
    delete[]_data;

    return resultImage;
}

jintArray matToBitmapArray(JNIEnv *env, const cv::Mat &image) {
    jintArray resultImage = env->NewIntArray(image.total());
    jint *_data = new jint[image.total()];
    for (int i = 0; i < image.total(); i++) {
        char r = image.data[3 * i + 2];
        char g = image.data[3 * i + 1];
        char b = image.data[3 * i + 0];
        char a = (char)255;
        _data[i] = (((jint) a << 24) & 0xFF000000) + (((jint) r << 16) & 0x00FF0000) +
                   (((jint) g << 8) & 0x0000FF00) + ((jint) b & 0x000000FF);
    }
    env->SetIntArrayRegion(resultImage, 0, image.total(), _data);
    delete[]_data;

    return resultImage;
}

jintArray matToBitmapArray(JNIEnv *env, const cv::Mat &image) {
    jintArray resultImage = env->NewIntArray(image.total());
    jint *_data = new jint[image.total()];
    for (int i = 0; i < image.total(); i++) {
        // Note that you can use better gray->rgba conversion
        char r = image.data[i];
        char g = image.data[i];
        char b = image.data[i];
        char a = (char)255;
        _data[i] = (((jint) a << 24) & 0xFF000000) + (((jint) r << 16) & 0x00FF0000) +
                   (((jint) g << 8) & 0x0000FF00) + ((jint) b & 0x000000FF);
    }
    env->SetIntArrayRegion(resultImage, 0, image.total(), _data);
    delete[]_data;

    return resultImage;
}

Bitmap bitmap = Bitmap.createBitmap(ourNativeArray, width, height, Bitmap.Config.ARGB_8888);

编辑

考虑到您有BGRA4通道映像，以下是如何将其转换为JByteArray

jbyteArray matToByteArray(JNIEnv *env, const cv::Mat &image) {
    jbyteArray resultImage = env->NewByteArray(image.total() * 4);
    jbyte *_data = new jbyte[image.total() * 4];
    for (int i = 0; i < image.total() * 4; i++) {
        _data[i] = image.data[i];
    }
    env->SetByteArrayRegion(resultImage, 0, image.total() * 4, _data);
    delete[]_data;

    return resultImage;
}