将 RGB 转换为灰度

Question

output result I´m trying to convert from bgr to grayscale using opencv in android , when the application starts the screen displays the image as shown below and crashes. I tried all possible ways but couldn't get the grayscale. Please let me know the error in this code. It would be very helpful. Thanks.

JNIEXPORT void JNICALL
Java_com_preksh_cornerdetection_CameraClass_SendCamImageToNative(JNIEnv *env,
                                                                          jobject instance,
                                                                          jbyteArray data_,
                                                                          jint mPreview_height,
                                                                          jint mPreview_width,
                                                                          jintArray Keypoints_java_) {
if(gCornerObject == NULL) {
    return;
}

jbyte *data = env->GetByteArrayElements(data_, NULL);
jint *Keypoints_java = env->GetIntArrayElements(Keypoints_java_, NULL);

// Android returns data in NV21 format, convert it to RGB
cv::Mat cameraNV21Image(mPreview_height * 1.5, mPreview_width, CV_8UC1, data);
cv::Mat cameraRGBImage(mPreview_height * 1.5, mPreview_width, CV_8UC1);


cv::cvtColor(cameraNV21Image, cameraRGBImage, CV_YUV2RGB_NV21, 3);

cv::cvtColor(cameraRGBImage, cameraRGBImage, CV_BGR2GRAY);


gCornerObject->ProcessCameraImage(cameraRGBImage, mPreview_width, mPreview_height, Keypoints_java);

Answer 1

I think this problem is related with declaration cameraRGBImage . You defined this matrix as 1 channel matrix. To determine RGB matrix you should:

cv::Mat cameraRGBImage(mPreview_height * 1.5, mPreview_width, CV_8UC3);

If you convert RGB to Gray is recommended to declare a new matrix:

cv::Mat cameraGrayImagae;
cv::cvtColor(cameraRGBImage,cameraGrayImagae,CV_BGR2GRAY);

Check it.